JP3156393B2 - Driving method of inkjet head - Google Patents

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 ink jet head of an ink jet printer.

[0002]

2. Description of the Related Art FIG. 5 shows a structure of an ink jet head of an ink jet printer using a piezoelectric element. In the ink jet 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 is discharged from the nozzle 1 to the outside by the pressure wave of the printing liquid 4 generated at this time. Recording is performed on a recording medium 5 arranged before the outlet opening of the nozzle 1. As a conventional technique for driving the inkjet head, for example, according to Japanese Patent Application Laid-Open No. Sho 59-136266, a method using a circuit shown in FIG. 3 has been devised. The operation of the circuit of FIG. 3 will be described below.

[0003] An input terminal IN101 is connected to an inverter U101 having an open collector output.
The output of 1 is pulled up to + 5V by R101. The output of the inverter U101 is connected to the base of the transistor Q101 whose emitter is grounded through R102. The collector of the transistor Q101 is pulled up to a high power supply voltage through R103. Further, the collector of the transistor Q101 is connected to the bases of the transistors Q102 and Q103 in the output stage. The emitters of the transistors Q102 and Q103 in the output stage are connected to each other to form an output terminal OUT101. This output terminal OUT101 and the transistor Q
A feedback capacitor C101 is inserted between the base and the base 101. Further, a piezoelectric element P101, which is a load of the driving circuit, is connected to the output terminal OUT101.

FIG. 4 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 driving 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 transistor Q101, the capacitor C101, and the resistor R102 form a Miller integrating circuit. Similarly, in the case of "L", the drive waveform linearly falls to 0 V, and a trapezoidal drive voltage waveform such as OUT is obtained.

[0005]

However, even if a pulse voltage having the same voltage waveform is applied to the piezoelectric element due to a variation in the amount of displacement of the piezoelectric element or a manufacturing variation, the amount of the printing liquid to be discharged is different for each ink jet head. Different. Therefore, in order to discharge an appropriate amount of printing liquid, the voltage amplitude of the pulse voltage applied to the piezoelectric element must be appropriately adjusted for each inkjet head. At this time, in the method of driving an ink jet head having a driving circuit as described in the related art, the voltage amplitude of the pulse voltage rises to + VH of the power supply voltage. There is a problem that cannot be obtained.

[0006]

In order to solve the above-mentioned problems, according to the present invention, a plurality of nozzles and a plurality of nozzles are provided.
A flow path for supplying a printing liquid, and the nozzle on a wall of the flow path.
Piezoelectric element that is arranged in accordance with
And a method for driving an inkjet head comprising:
A first period defining a rising period of the pulse voltage.
Defines the input signal and the start of the fall of the pulse voltage
And a second input signal supplied to the pulse voltage generation circuit.
The pulse voltage generation circuit supplies the pulse voltage
Means for adjusting rising time constant indicating rising slope
The pallet appropriately determined by the adjusting means
Of the pulse voltage based on the rising time constant of the pulse voltage.
High state of the first input signal that defines a rising period
By setting the active period, an appropriate
The pulse voltage is supplied .

[0007]

The voltage amplitude of the pulse voltage applied to the piezoelectric element is
Set the rising period of the pulse voltage regardless of the power supply voltage
Thus, a proper amount of the printing liquid can be discharged.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on illustrated embodiments. FIG. 1 is a circuit diagram of a pulse voltage generator of an ink jet head according to an embodiment of the present invention.
9 shows a timing chart of input / output signals used in the present embodiment.

IN1 and IN2 are input terminals for input signals,
6 is a transistor for level shift, transistor Q
8, Q9 and a resistor R1 are constant current circuits for a charging waveform, transistors Q4, Q5 and a resistor R2 are constant current circuits for a discharging waveform, C1 is a capacitor for forming a driving waveform, and OUT1 is an output terminal for a driving waveform. P1 is a piezoelectric element as 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 Pd is input to the input terminal IN2, first, when the Pc signal becomes "H", the transistor Q6 is turned on. 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 resistor R1 connected to the emitter of the transistor Q8,
The potential difference between both ends of 1 becomes the potential between the base and the emitter of the transistor Q9. When the transistor Q9 is on, the potential between the base and the emitter is substantially constant, so that the resistance R
The current for charging the capacitor C1 via the constant 1 becomes a constant current. Since the capacitor C1 is charged with a constant current, the waveform of the potential difference between both ends of the capacitor C1 rises linearly from 0 [V] as shown by Po1 in FIG. The rising time constant τc [V / sec], which is the slope of the waveform, includes the resistance value r1 [Ω] of the resistor R1, the capacitance value c1 [F] of the capacitor C1, and the base-emitter voltage VBE9 of the transistor Q9.
From [V], τc = VBE9 ÷ (r1 × c1), which is adjusted by changing the resistance value r1 of the resistor R1 or the capacitance value c1 of the capacitor C1. If the state of the Pc signal remains “H” as it is, the potential difference between both ends of the capacitor C1 rises to the power supply voltage VM. However, the Pc signal becomes “tc” after tc [sec] after the Pc signal becomes “H”.
When it becomes "L", the transistor Q6 is turned off,
Since the transistor Q8 is turned off, the capacitor C
The potential difference V1 [V] between both ends of 1 rises up to V1 = τc × tc, and the potential difference is held by the electric charge accumulated in the capacitor C1. Further, the Pd signal is "H".
, The transistor Q4 is turned on and discharges the electric charge accumulated in the capacitor C1 via the resistor R2. Since the potential difference between both ends of the resistor R2 becomes the potential between the base and the emitter of the transistor Q5, the capacitor C1 is discharged with a constant current as in the case of the rise, and the waveform of the potential difference between both ends of the capacitor C1 falls linearly. Falling time constant τd [V / sec] which is the slope of the waveform
Is obtained from the resistance value r2 [Ω] of the resistor R2, the capacitance value c1 [F] of the capacitor C1, and the base-emitter voltage VBE5 [V] of the transistor Q5 as τd = VBE5 ÷ (r2 × c1). The adjustment is performed by changing the resistance value r2 of R2 or the capacitance value c1 of the capacitor C1. By making the time td [sec] from the time when the Pd signal becomes “H” to the time when the Pc signal becomes “L” sufficiently longer than td = V1 ÷ τd, the potential difference between both ends of the capacitor C1 becomes 0 [V]. Fall down linearly. In this way, a pulse voltage having an arbitrary voltage amplitude, a rise time, a time during which a constant voltage is maintained, and a fall time is transferred to the capacitor C.
1 occurs at both ends.

The transistors Q1, Q2, Q3, and Q7 form a current buffer, output a waveform similar to the voltage waveform generated at both ends of the capacitor C1 to an output terminal OUT1, and output a piezoelectric signal of a load connected to OUT1. It supplies the current necessary to drive the device. At this time, the voltage amplitude V2 of the voltage waveform Po2 output to the output terminal OUT1
[V] is the voltage amplitude V of the voltage waveform across the capacitor C1.
1 to bases of transistors Q1, Q2, Q3, Q7
V2 is reduced by the voltage between the emitters, and V2 is obtained from V1 and the voltages VBE1, VBE2, VBE3, and VBE7 between the bases and the emitters of the transistors Q1, Q2, Q3, and Q7 as V2 = V1- (VBE1 + VBE3) + (VBE2 + VBE7). Can be In this embodiment, the current buffer is constituted by transistors Q1 and Q3 and the transistors Q2 and Q7 by two-stage amplification by Darlington connection. However, depending on the current required to drive the piezoelectric element of the load, one stage or one stage is used. It is also possible to use three or more stages of transistors, and it is clear that a similar effect can be obtained in such a case. In this case, the voltage amplitude of the voltage waveform output to the output terminal OUT1 is smaller than the potential difference V1 across the capacitor C1 by the voltage between the base and the emitter of the transistor constituting the current buffer.

In the ink-jet head having the pulse voltage generating section for performing the above-described operation, the rising time constant τc and the falling time constant τd of the pulse voltage are appropriately set in advance, and the appropriate pulse voltage of each ink-jet head is set. The power supply voltage is changed for each ink jet head by setting the rise time tc of the input signal Pc as a guide so that the voltage amplitude V2 is obtained as follows. It can be set to an appropriate voltage amplitude of the pulse voltage.

[0013]

As described above, the method of driving an ink jet head according to the present invention can easily set the appropriate voltage amplitude of the pulse voltage for each ink jet head without changing the power supply voltage. And printing quality can be expected to be improved. Further, since the power supply voltage of the power supply for driving the ink-jet head only needs to be higher than the voltage amplitude of the pulse voltage, the power supply voltage of another driving system such as a carriage drive or a paper feed, which constitutes the printer, changes the power supply voltage of the ink-jet head. If the voltage amplitude is higher than the pulse amplitude to be driven, these power supplies can be shared with the power supplies, so that the configuration of the printer can be simplified.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an 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 conventional example.

FIG. 4 is a timing chart of input / output signals according to an embodiment of the prior art.

FIG. 5 is a structural diagram of a conventional inkjet head.

[Explanation of symbols]

 IN1 Input terminal of input signal IN2 Input terminal of input signal Q6 Transistor for level shift Q8 Transistor for constant current of charging waveform Q9 Transistor for constant current of charging waveform R1 Resistor for constant current of charging waveform Q4 Constant of discharge waveform Current transistor Q5 Discharge waveform constant current transistor R2 Discharge waveform constant current resistor C1 Drive waveform formation capacitor OUT1 Drive waveform output terminal P1 Load piezoelectric element Pc Input signal to input terminal IN1 Pd input Input signal to terminal IN2 Po1 Voltage waveform across capacitor C1 Po2 Output voltage waveform at output terminal OUT1

Claims (1)

(57) [Claims] A plurality of nozzles, a channel for supplying a printing liquid to the nozzles, and a wall corresponding to the nozzle on a wall surface of the channel.
And a piezoelectric element that is arranged and expanded and contracted by a pulse voltage.
A first input for defining a rising period of the pulse voltage.
Signal and a second signal defining the start of the fall of the pulse voltage.
And the second input signal to the pulse voltage generation circuit.
And the pulse voltage generation circuit generates a pulse
There is a means to adjust the rise time constant indicating the slope
And the pulse voltage appropriately determined by the adjusting means.
The rise of the pulse voltage is based on the rise time constant.
The high state period of the first input signal that defines the
By setting, the appropriate pulse for each piezoelectric element
A method of driving an ink jet head for supplying a source voltage .