JPH09323412A - Drive circuit of ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the effect to be produced by the driving of an adjacent channel, to prevent the distortion of a drive voltage waveform, to obtain proper rising and falling times of driving and to dispense with an increase of a switching circuit by lowering the impedance of a circuit when drive output is held to 'H' or 'L'. SOLUTION: This drive circuit is constituted so that two dual gate transistors Q1, Q2 are connected across a power supply and a ground in series and the connection point of them is connected to an electrode to control the application of voltage to the electrode. The first gate G1 of one transistor Q1 is a raising one for applying voltage to the electrode and the second gate G2 thereof is one for holding a high level while the first gate G1 of the other transistor Q2 is one for lowering applied voltage and the second gate G2 thereof is one for holding a low level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an ink jet head used in an ink jet recording apparatus that ejects ink from nozzles to perform printing.

[0002]

2. Description of the Related Art Conventionally, as an ink jet head, an actuator having an electrode for applying voltage corresponding to a channel having a plurality of nozzles for ejecting ink has been provided, and a voltage is applied to this electrode by a drive circuit. A method of ejecting ink from a nozzle is generally known. FIG. 1 is a sectional view of an inkjet head of this type. The inkjet head 1 includes a piezoelectric element substrate 2
A plurality of pressure chambers (hereinafter, referred to as channels) 3 serving as groove-shaped ink chambers are continuously formed side by side. A nozzle plate 5 having nozzle holes 4 corresponding to each channel 3 is provided at one end of the piezoelectric substrate 2, and a cover plate 6 is covered on the upper surface of the piezoelectric element substrate 2. An electrode 7 to which a voltage is applied is provided on the wall surface of the channel 3 and constitutes an actuator for driving the head. In addition, 8 is a manifold, 9 is an ink supply port,
Reference numeral 10 is an electrode lead terminal.

FIG. 2 is a sectional view taken along the line AA of FIG. 1. Adjacent channels 3 are indicated by 3a, 3b, 3c, 3d and 3e, and partition walls 13 between them are denoted by 13a, 13b, 13c and 13.
The electrodes 7 provided corresponding to the respective channels 3 are indicated by 7a, 7b, 7c, 7d, and 7e. FIG. 3 shows an equivalent circuit of the head having the above-mentioned configuration, in which each partition wall 13 sandwiched between adjacent electrodes 7 serves as a capacitance (capacitor) component connected in series.

FIG. 4 is a diagram showing the connection relationship between the equivalent circuit of such a head and the drive circuit. The output of the drive circuit 14 is connected to the electrode 13 corresponding to each channel 3, and each capacitance is loaded. Becomes The input terminal of the drive circuit 14 is a,
b, c and output terminals are indicated by d, e, f. FIG. 5 shows one configuration of the drive circuit 14. The drive circuit 14
MOS field effect transistor (FET) 1 as a switching element connected in series between a power supply and GND
5, 16 and diodes 17 and 18 for reverse bias protection connected in parallel to each of them, and a level converter 19
Consisting of

FIG. 6 shows a signal waveform when the load composed of electrostatic capacitances connected in series as described above is driven by the drive circuit. When three signals as shown in a, b, c of FIG. 6 are inputted to the input terminals a, b, c of the drive circuit 14, the output terminals d, e, f are d, e, f of FIG. The output voltage as shown appears. This is the case where the output impedance of the drive circuit 14 is 300Ω and the electrostatic capacitance is 1200 pF. The rise time (referred to as Tr) and the fall time (referred to as Tf) of the output voltages d, e, and f are about 2 μS (this value must be a predetermined value for proper ink ejection). There is).

[0006]

The problem with the conventional drive circuit as described above is that when one of the output voltages d, e, and f is turned on, that is, when it is in the "H" level state, , OFF, that is, in the "L" level state, the "H" or "L" level voltage is not stable under the influence of the moment when the adjacent channel is turned OFF or ON. That is, the drive voltage waveform of the drive circuit 14 is distorted. As a result, the partition walls of the head may be unintentionally deformed, which may adversely affect the ink ejection and hinder stable ejection. This is because the output impedance of the drive circuit 14 is large. For example, when the drive circuit 14 is in the off state, the output terminal d is connected to GND via the transistor 16 in the on state, but this is because the impedance (on resistance) of the transistor 16 in the on state is not zero.

The present invention has been made in order to solve the above-mentioned problems, and provides a drive circuit for driving an actuator which is provided corresponding to a plurality of channels and whose capacitances are equivalently connected in series. Therefore, when the drive output is held at “H” or “L”, by lowering the impedance of the circuit, the influence of the adjacent channel drive is lessened and the drive voltage waveform may be distorted. It is an object of the present invention to provide an inexpensive inkjet head drive circuit that does not require an appropriate drive rise time and fall time, and does not require an additional switching circuit.

[0008]

In order to achieve the above object, a drive circuit for an ink jet head according to a first aspect of the present invention has a channel having a plurality of nozzles for ejecting ink which are continuously formed, and a channel formed in the channel. An actuator composed of a corresponding electrode for voltage application is provided,
In a drive circuit of an inkjet head that ejects ink from a nozzle by applying a voltage to an electrode of this actuator, two switching elements having a plurality of control terminals are connected in series between a power supply side and a ground side,
The connection point is connected to an electrode to control the voltage application to the electrode, and the first control terminal of one switching element is for starting up for applying a voltage to the electrode,
The second control terminal is for holding a high level, the first control terminal of the other switching element is for lowering the applied voltage, and the second control terminal is for holding a low level.

In the above structure, an ON signal is applied to the first control terminal of one of the switching elements connected to the power supply side so that the switching element is semi-conducted and the voltage application to the electrodes is started up. A high level state of the applied voltage is held by applying an ON signal to the second control terminal of (1) to make it fully conductive. In addition, the ON signal is applied to the first control terminal of the other switching element connected to the ground side to make it semi-conductive to lower the voltage applied to the electrode, and then the second control terminal of this switching element. A low level state of the applied voltage is maintained by applying an ON signal to the switch and making it all conductive. In this way, the output impedance can be lowered in both the high level state in which the applied voltage is raised and the low level state in which the applied voltage is lowered, and it is possible to reduce the influence of the actuator drive of the adjacent channel. It is also easy to select the optimum time for raising and lowering the voltage.

According to a second aspect of the present invention, in the drive circuit for an ink jet head according to the first aspect, the channels of the actuator are continuously formed on the piezoelectric element substrate and the electrodes are formed on the channel walls. The piezoelectric element is provided and the piezoelectric element is deformed by applying a voltage to the electrode, and the volume of the channel is changed to eject ink. In this configuration, the piezoelectric element between the electrodes of the adjacent channels is equivalently connected in series with the capacitance, but the electrodes are connected to the power supply side,
Alternatively, since the output impedance of the drive circuit connected to the ground is low, the influence of driving the adjacent channel is reduced.

According to a third aspect of the present invention, there is provided a driving circuit for an ink jet head, wherein the switching element is a dual gate field effect transistor in the configuration according to the first or second aspect. With this configuration, it is possible to hold the high level after the applied voltage rises and hold the low level after the applied voltage rise without separately adding a switching element.

According to a fourth aspect of the present invention, there is provided a drive circuit for an ink jet head according to the first or second aspect, wherein the first control terminal of one of the switching elements is at the transition of rising of the applied voltage. Only the first control terminal of the other switching element is turned on during the transition of the fall of the applied voltage. In this configuration, in addition to the above operation, the optimum time for raising and lowering the applied voltage can be arbitrarily selected.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 7 is a diagram showing an equivalent circuit of the ink jet head and its drive circuit. The inkjet head itself has the same configuration as that of FIGS. 1 to 3 described above, and includes a channel having a plurality of nozzles for ejecting ink formed continuously and a voltage application provided corresponding to this channel. An actuator including an electrode is provided. As shown in FIG. 7, the partition walls 13a, 13b, 13c, 13d, and 13e formed of piezoelectric elements have equivalent capacitances, and these electrodes 7a, 7b, 7c, 7d, and
It is connected in series by 7e. Each of the drive circuits 24 has electrodes 7a, 7b, which are adjacent to the output terminals p, q, r ...
A voltage is applied to 7c. Each drive circuit 24 has two input terminals (j, m), (k, n), (l, o) .... For further continuous electrodes, the drive circuit 24 is configured in the same repeating mode as described above.

FIG. 8 shows the structure of one drive circuit 24.
The drive circuit 24 includes two MOS type dual gate field effect transistors (FETs, hereinafter referred to as transistors) Q as switching elements whose drains and sources are connected in series between the power supply side (+ B) and the ground side.
1 and Q2, and the connection point thereof is connected to the electrode as an output terminal p. The first gates (control terminals) G1 of the transistors Q1 and Q2 are control terminals for electrostatic charge / discharge control. The former is for raising voltage application to the electrodes, and the latter is for lowering. In addition, each second gate (control terminal) G
Reference numeral 2 is a control terminal for holding "H" level and "L" level of the output signal. Protective diodes D1 and D2 are connected in parallel with each of these transistors Q1 and Q2. Then, the gate G1 and the transistor Q2 of the transistor Q1 are inputted through the level converter 19 by the input terminal j
ON / OFF control is performed by applying a control voltage to the gate G1 of the above, and signals of "H" and "L" levels are produced at the output terminal p, that is, signals for raising and lowering the voltage application to the electrodes. Also, the signal m controls the gate G2 of the transistor Q1 and the gate G2 of the transistor Q2 via the level converter 19, and holds the "H" and "L" levels of the output terminal p. Although not shown, the other adjacent drive circuits have the same configuration, and the input terminal j is k (or l) and the other input terminal m is n (or o).
And q (or r) at the output terminal p.

Next, the operation of the drive circuit configured as described above will be described with reference to FIG. Input terminal j,
k and l are set to the “H” level and the “L” level at the timings shown, and the input terminals m, n, and o of the signals of the respective input terminals j, k, and 1 (hereinafter referred to as the j signal and the k signal) The H level is set only immediately after the rising and falling of the “H” level. First, when the signal j and the signal m are "H", an ON signal is given to the first gate G1 of the transistor Q1 to make it semi-conductive. As a result, the output terminal p becomes "L" as shown in A in the figure.
To “H” with a rising time (Tr). When the signal m becomes "L" after this transient time, the ON signal is also applied to the second gate G2 of the transistor Q1.
As a result, the transistor Q1 becomes fully conductive, and the power supply is connected to the output terminal p through this transistor Q1.
The state of "H" is held as shown in FIG. At this time,
A large drain current flows through the transistor Q1.

Incidentally, the dual gate transistor Q
Output voltage of 1 and Q2 is 20V, charge and discharge current is 50mA,
When the holding current is 200 mA, when the first gate G1 and the second gate G2 are ON and OFF, the first gate-
The characteristics of the drain current with respect to the voltage between the sources are as shown in FIG. As can be seen from the figure, compared to when the first gate G1 is in the ON state and the second gate is OFF,
When the second gate is turned on, there is a characteristic that the drain current greatly increases. According to this characteristic, as described above, "H"
A large drain current flows when the state is maintained. The output impedance of the rise time (Tr) is 400Ω,
The output impedance when the "H" state is maintained is 100Ω.

Next, the signal j changes from "H" to "L",
When the signal m becomes “H” again at that timing, the transistor Q1 is turned off from full conduction, and the transistor Q2 is turned off.
The first gate G1 of the above turns from OFF to ON, so that the output terminal p falls from "H" to "L" as shown in C and the fall time (Tf) is reached. After this transient time, when the signal m becomes “L”, the second
The gate G2 is also turned on, the transistor Q2 becomes fully conductive, the output terminal p is connected to the ground through this, and the state of "L" is maintained as shown in D. By the way, the output impedance of the fall time (Tf) is 400
Ω, the output impedance is 100 Ω when the transistor Q2 is fully conductive and the state of “L” is maintained. In addition, the output terminals q by the signals k and n of the other drive circuits and the signals l and o,
The same applies to changes in the signal of r.

By operating in this manner, the output impedance of the drive circuit is changed and reduced when the "H" and "L" states are held, so that one channel is driven, for example, B in FIG. In this state, even if the adjacent channel is driven, the voltage at the “H” level does not change, and one channel is in the non-driven state, for example,
Even if the adjacent channel changes from the driving state to the non-driving state in the state of D in FIG. 9, the “L” level voltage does not change. Therefore, the waveform distortion of the actuator drive signal is improved. Further, the rising time (Tr) and the falling time (Tf) of the applied voltage can be arbitrarily selected,
It can contribute to stable ink ejection. Moreover, it is possible to achieve both the reduction of the ON resistance for improving the waveform distortion and the optimization of the rise and fall times as described above, without adding a transistor to the drive circuit.

[0019]

As described above, according to the ink jet head drive circuit of the first aspect of the present invention, the first control terminal of one of the two switching elements is used to raise the voltage applied to the electrode of the actuator. Control, the second control terminal is controlled to hold the applied voltage at a high level, and the first control terminal of the other switching element is controlled to drop the applied voltage to the electrode. Since the control terminal is controlled to hold the low level state of the applied voltage, the output impedance of the switching element can be lowered in the high level state in which the applied voltage is raised and in the low level state in which the applied voltage is lowered. Therefore, it is possible to reduce the influence of the signal level in the rising or falling state of the applied voltage due to the driving of the adjacent actuator, reduce the waveform distortion of the output voltage, and increase the proper driving rise time and fall time. It is also easy to select. Therefore, stable ink ejection is possible.

According to the ink jet head drive circuit of the second aspect of the present invention, the piezoelectric elements between the electrodes of the adjacent channels are equivalently connected in series in capacitance. , The output impedance of the drive circuit connecting the electrode to the power supply side or the ground can be lowered, the influence of the drive of the adjacent channel can be reduced, and the above effect can be obtained.

According to the ink jet head drive circuit of the third aspect of the present invention, since the dual gate field effect transistor is used as the switching element, the high voltage after the rise of the applied voltage is increased without adding the switching element. It is possible to hold the level and hold the low level after the fall.

Further, according to the ink jet head drive circuit of the present invention, only the first control terminal of each switching element is turned on during the rising transition and the falling transition of the applied voltage. It is easy to select the optimum time for raising and lowering the applied voltage.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an inkjet head.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an equivalent circuit diagram of the head having the above configuration.

FIG. 4 is a diagram showing a connection relationship between an equivalent circuit of a head and a drive circuit.

FIG. 5 is a configuration diagram of one drive circuit.

FIG. 6 is a signal waveform diagram when driven by the drive circuit.

FIG. 7 is a diagram showing an equivalent circuit of an inkjet head and a driving circuit thereof according to an embodiment of the present invention.

FIG. 8 is a configuration diagram of one drive circuit according to an embodiment of the present invention.

FIG. 9 is a signal waveform diagram when driven by the drive circuit.

FIG. 10 is a characteristic diagram of drain current with respect to a first gate-source voltage.

[Explanation of symbols]

 2 Piezoelectric element substrate 3 Channels 7a, 7b, 7c, 7d, 7e Electrode 24 Driving circuit Q1, Q2 Transistor (switching element) G1 1st gate (control terminal) G2 2nd gate (control terminal)

Claims (4)

[Claims] 1. An actuator comprising a channel having a plurality of nozzles for ejecting ink formed continuously and an electrode for voltage application provided corresponding to the channel, the voltage being applied to the electrode of the actuator. In a drive circuit of an inkjet head that ejects ink from the nozzles by applying a voltage, two switching elements having a plurality of control terminals are connected in series between a power supply side and a ground side, and the connection point is the electrode. To control the voltage application to the electrode, the first control terminal of the one switching element is for starting to apply a voltage to the electrode, and the second control terminal is For holding the high level, the first control terminal of the other switching element is for lowering the applied voltage, and the second control terminal is for keeping the low level. A drive circuit for an ink-jet head, which is a portable device. 2. A channel of the actuator is continuously defined and formed on a piezoelectric element substrate, the electrode is provided on a wall of the channel, and the piezoelectric element is deformed by applying a voltage to the electrode, 2. The ink jet head drive circuit according to claim 1, wherein the volume of the ink is changed to eject the ink. 3. The switching element is a dual gate field effect transistor.
Alternatively, the drive circuit of the inkjet head according to claim 2. 4. When the applied voltage rises, only the first control terminal of the one switching element is turned on, and when the applied voltage falls, only the first control terminal of the other switching element is turned on. The inkjet head drive circuit according to claim 1 or 2, which is turned on.