JPH06182993A - Driving method of ink jet head - Google Patents

Abstract

PURPOSE:To optionally set amplitude of a pulse voltage by a method wherein a rising time constant adjusting means, a rising time adjusting means and a falling time constant adjusting means for the pulse voltage applied to a piezoelectric element are provided and the rising time is optionally set. CONSTITUTION:In the case where a signal as indicated with Pc and a signal as indicated with Pd are applied to an input terminal IN1 and IN2, respectively, firstly when Pc signal becomes H level, a transistor Q6 is changed to an on- state. At that time, a transistor Q8 is changed to an on-state to charge a condenser C1 which is connected to a corrector of the transistor Q8. A corrector current of the transistor Q8 flows via a variable resistor VR1 connected to an emitter of the transistor Q8. The differential voltage between terminals of the variable resistor VR1 is equal to a base-emitter voltage of a transistor Q9. A current of charging condenser C1 via the variable resistor VR1 is rendered constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an inkjet head of an inkjet recording apparatus.

[0002]

2. Description of the Related Art The structure of an inkjet head using a piezoelectric element is shown in FIG. In the inkjet head shown in FIG. 5, the piezoelectric element 3 is expanded and contracted in the direction of arrow 6 by applying a pulse voltage, and the printing liquid 4 generated at this time is printed.
The recording liquid 5 is discharged from the nozzle 1 to the outside by the pressure wave of the recording medium 5 and is arranged in front of the outlet opening of the nozzle 1.
To record. As a conventional method of driving the ink jet head, for example, according to Japanese Patent Laid-Open No. 59-136266, a method using a circuit shown in FIG. 6 has been devised. The operation of the circuit shown in FIG. 6 will be described below.

The input terminal IN101 is connected to an inverter U101 having an open collector output, and the inverter U10
The output of 1 is pulled up to + 5V by R101. The output of the inverter U101 is connected to the base of a transistor Q101 whose emitter is grounded through R102. The collector of the transistor Q101 is pulled up to the high power supply voltage VH through R103. Further, the bases of the output stage transistors Q102 and Q103 are connected to the collector of the transistor Q101. The emitters of the output stage transistors Q102 and Q103 are connected to each other to form the output terminal OUT101. A feedback capacitor C101 is provided between the output terminal OUT101 and the base of the transistor Q101.
Has been inserted. A piezoelectric element P101, which is the load of this drive circuit, is connected to the output terminal OUT101.

FIG. 7 is a timing chart of input / output signals of this drive circuit. When an input signal such as IN is input to the input terminal IN101 of the drive circuit, the input signal IN becomes "
When H ", the transistor Q101 is turned off and the drive voltage rises to + VH, but the drive voltage waveform rises linearly because the Miller integrating circuit is constituted by the transistor Q101, the capacitor C101, and the resistor R102. The input signal IN Similarly, in the case of "L", the drive waveform linearly falls to 0V, and a trapezoidal drive voltage waveform like OUT is obtained.

[0005]

However, even if a pulse voltage having the same voltage waveform is applied to the piezoelectric element due to variations in the displacement amount of the piezoelectric element and variations in manufacturing, the amount of printing liquid ejected is different for each inkjet head. Different to Therefore, in order to eject an appropriate amount of printing liquid, it is necessary to appropriately adjust the voltage amplitude of the pulse voltage applied to the piezoelectric element for each inkjet head. At this time, in the method of driving the inkjet head having the driving circuit as described in the related art, the voltage amplitude of the pulse voltage rises to + VH of the power supply voltage. Therefore, if the power supply voltage is not changed for each inkjet head, an appropriate voltage amplitude is obtained. There is a problem that cannot be obtained. Further, the fall time of the pulse voltage affects the ejection speed of the printing liquid, and therefore needs to be appropriately adjusted.

[0006]

In order to solve the above problems, the present invention comprises a rise time constant adjusting means, a rise time adjusting means, and a fall time constant adjusting means of a pulse voltage applied to a piezoelectric element. The voltage amplitude of the pulse voltage is arbitrarily set by setting the rising time arbitrarily.

[0007]

The voltage amplitude of the pulse voltage applied to the piezoelectric element can be arbitrarily set by the rise time constant and rise time of the pulse voltage regardless of the power supply voltage, so that an appropriate amount of printing liquid can be ejected.

[0008]

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a circuit diagram of a pulse voltage generator of an ink jet head in an embodiment according to claim 1 of the present invention, and FIG. 2 is a timing chart of input / output signals used in this embodiment.

IN1 and IN2 are input terminals for input signals, and Q
6 is a transistor for level shift, transistor Q
8, Q9, variable resistor VR1 is a constant current circuit for charging waveform,
Transistors Q4, Q5, variable resistor VR2 are constant current circuits for discharge waveform, C1 is a capacitor for drive waveform formation, O
UT1 is an output terminal of a drive waveform, and P1 is a piezoelectric element that is a load.

The operation of this circuit will be described below.
When a signal such as Pc is input to the input terminal IN1 and a signal such as Pd is input to the input terminal IN2, the transistor Q6 is turned on when the Pc signal becomes "H". At this time, the transistor Q8 is turned on, and the capacitor C1 connected to the collector of the transistor Q8 is charged. The collector current of the transistor Q8 flows through the variable resistor VR1 connected to the emitter of the transistor Q8,
The potential difference across the variable resistor VR1 becomes the potential between the base and emitter of the transistor Q9. Since the potential between the base and the emitter is substantially constant when the transistor Q9 is in the ON state, the current for charging the capacitor C1 via the variable resistor VR1 becomes a constant current. Since the capacitor C1 is charged with a constant current, the waveform of the potential difference across the capacitor C1 rises linearly from 0 [V], as indicated by Po1 in FIG. Rising time constant τc, which is the slope of the waveform Po1
[V / sec] is the resistance value r1 [Ω] of the variable resistor VR1, the capacitance value c1 [F] of the capacitor C1 and the transistor Q9.
From the base-emitter voltage VBE9 [V] of τc = VBE9 ÷ (r1 × c1) <Equation 1>, and is adjusted by changing the resistance value r1 of the variable resistor VR1 or the capacitance value c1 of the capacitor C1. . If the Pc signal remains "H" as it is, the capacitor C1
The potential difference between both ends of the voltage rises to the power supply voltage VM, but Pc
When the Pc signal becomes "L" after tc [sec] after the signal becomes "H", the transistor Q6 is turned off and the transistor Q8 is turned off, so that the potential difference V1 [both ends of the capacitor C1 is V] rises to V1 = τc × tc, and the potential difference is held by the charges accumulated in the capacitor C1. After th [sec],
When the Pd signal becomes "H", the transistor Q4 is turned on, and the electric charge accumulated in the capacitor C1 is discharged through the variable resistor VR2. Since the potential difference across the variable resistor VR2 becomes the potential between the base and emitter of the transistor Q5, the capacitor C1 is discharged with a constant current as in the case of rising, and the waveform of the potential difference across the capacitor C1 falls linearly. . The falling time constant τd [V / sec], which is the slope of the waveform, is the resistance value r2 [Ω] of the variable resistor VR2, the capacitance value c1 [F] of the capacitor C1 and the base-emitter voltage VBE5 [V of the transistor Q5. ]
Τd = VBE5 ÷ (r2 × c1) <Equation 2>, and adjustment is performed by changing the resistance value r2 of the variable resistor VR2 or the capacitance value c1 of the capacitor C1. P
The potential difference between both ends of the capacitor C1 is set to 0 [by setting the time from the d signal being “H” to the Pc signal being “L” sufficiently longer than the fall time td [sec], td = V1 ÷ τd. V] and falls linearly. In this way, a pulse voltage having an arbitrary voltage amplitude, rise time, constant voltage holding time, and fall time is applied to the capacitor C.
It occurs at both ends of 1.

The transistors Q1, Q2, Q3 and Q7 form a current buffer, which outputs a waveform similar to the voltage waveform generated across the capacitor C1 to the output terminal OUT1 and connects the piezoelectric element of the load connected to OUT1. It supplies the necessary current to drive the device. At this time, the voltage amplitude V2 [V] of the voltage waveform output to the output terminal OUT1 is smaller than the voltage amplitude V1 of the voltage waveform across the capacitor C1 by the voltage between the base and emitter of the transistors Q1, Q2, Q3, and Q7. And V2 is V1 and the voltage V between the base and emitter of the transistors Q1, Q2, Q3 and Q7.
From BE1, VBE2, VBE3 and VBE7, V2 = V1- (| VBE1 | + | VBE3 | + | VBE2 | +
| VBE7 |). In this embodiment, the current buffer is composed of transistors Q1 and Q3 and transistors Q2 and Q7 in two stages of amplification by Darlington connection. However, depending on the current required to drive the piezoelectric element of the load, one stage or It is also possible to configure the transistors with three or more stages, and it is clear that the same effect can be obtained in that case as well. In this case, the voltage amplitude of the voltage waveform output to the output terminal OUT1 becomes smaller than the potential difference V1 across the capacitor C1 by the voltage between the base and emitter of the transistor forming the current buffer.

In the ink jet head having the pulse voltage generator for performing the above-described operation, the rising time tc of the pulse voltage is appropriately set in advance,
The rising time constant τc is set so that an appropriate voltage amplitude V2 of the pulse voltage of each inkjet head is obtained, and τc = (V2 + | VBE1 | + | VBE3 | + | VBE2 | +
By setting | VBE7 |) ÷ tc as a standard, it is possible to set an appropriate voltage amplitude of the pulse voltage without changing the power supply voltage for each inkjet head.

Τc and τd are obtained by <Equation 1> and <Equation 2>. VBE9 and VBE5 are unique values of the device, and c1 is common to τc and τd, so τc and τd are independent. In order to adjust by adjusting r1 and r2, τc and τd are adjusted. In FIG. 1, variable resistors VR1 and VR2 can arbitrarily set resistance values r1 and r2, which are parameters for determining τc and τd.

In the first embodiment, the rise time, fall time, and voltage amplitude of the pulse voltage applied to the piezoelectric element can be set arbitrarily, but the rise time constant τc for each head using each circuit board. And the fall time constant τd must be adjusted. Therefore, FIG. 3 is shown as a second embodiment of the present invention. In FIG. 3, the variable resistor VR1 of FIG. 1 is configured by connecting the variable resistor VR1 and a removable fixed resistor R1 in series, and similarly, the variable resistor VR2 of FIG. 1 is connected to the variable resistor VR2 and a removable fixed resistor R2. Are connected in series. In this configuration, the sum of the resistance values of the fixed resistor R1 and the variable resistor VR1 and the sum of the resistance values of the fixed resistor R2 and the variable resistor VR2 are obtained in advance for the voltage amplitudes of a plurality of pulse voltages required, and the resistances for the adjustments are adjusted. The resistance value minus the value is the fixed resistance R1 and R2.
Assign to. The voltage amplitude of the pulse voltage can be set by selecting the fixed resistors R1 and R2 having resistance values corresponding to the appropriate voltage amplitude of the pulse voltage of the inkjet head used and mounting them on the circuit board. In this case, the value of each element varies from circuit board to circuit board, and the accuracy of the voltage amplitude of the pulse voltage and the fall time of the pulse voltage decreases. Therefore, the resistance of the reference resistance value is previously set to the resistors R1 and R2 for each circuit board. Attach the variable resistors VR1 and V
By adjusting R2 so that the proper voltage amplitude and fall time of the pulse voltage can be obtained, the precision of the voltage amplitude of the pulse voltage and the fall time of the pulse voltage decreases due to the variation in the constants of each element on each circuit board. Is suppressed.

The third embodiment of claim 1 will be described below. In the second embodiment, the fixed resistors R1 and R
It is possible to obtain the same effect even if 2 is configured by the collective resistance RM1 as shown in FIG.
By replacing the, the voltage amplitude of the pulse voltage and the falling time of the pulse voltage suitable for it can be set at the same time.

[0016]

As described above, in the method of driving an ink jet head according to the present invention, a proper voltage amplitude of the pulse voltage for each ink jet head can be easily set without changing the power supply voltage. Is stable, and the effect of improving print quality is great. Further, since the power supply voltage of the power supply for driving the inkjet head may be higher than the voltage amplitude of the pulse voltage, the power supply voltage of another drive system such as a carriage drive or a paper feed which configures the printer does not drive the inkjet head. If the voltage amplitude is higher than that of the pulse voltage to be driven, these power sources can be shared and the printer can be simplified in structure.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a timing chart of input / output signals according to the embodiment of the present invention.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of the present invention.

FIG. 5 is a sectional view showing the structure of an inkjet head.

FIG. 6 is a circuit diagram of a prior art embodiment.

FIG. 7 is a timing chart of input / output signals according to the example of the related art.

[Explanation of symbols]

 IN1 Input signal input terminal IN2 Input signal input terminal Q6 Level shift transistor Q8 Charge waveform constant current transistor Q9 Charge waveform constant current transistor VR1 Charge waveform constant current variable resistor R1 Charge waveform Fixed resistance for constant current Q4 Transistor for constant current of discharge waveform Q5 Transistor for constant current of discharge waveform R2 Fixed resistor for constant current of discharge waveform C1 Capacitor for driving waveform formation OUT1 Driving waveform output terminal P1 Load Piezoelectric element

Claims (1)

[Claims] 1. A method for driving an ink jet head comprising a nozzle, a flow path for supplying a printing liquid to the nozzle, and a piezoelectric element arranged on the wall surface of the flow path to expand and contract, and which is applied to the piezoelectric element. A pulse voltage rise time constant adjusting means, a rise time adjusting means, and a fall time constant adjusting means, wherein the rise time constant is arbitrarily set to arbitrarily set the voltage amplitude of the pulse voltage. Method for driving an inkjet head.