JPH0531895A - Ink jet head - Google Patents

Abstract

PURPOSE:To obtain a simple-structure and high-efficiency device for driving an ink-jet print head using ink mist. CONSTITUTION:In a non-printing period, a switch SW1 is connected to a switching bias dc voltage source VB2, and a diode D1 is tuned OFF. In a printing period, the switch SW1 is connected to a switching bias dc voltage source VB1, the diode D1 is turned ON, and an ac electric signal generating source RF and the VB1 are superimposed on a head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head for recording by using ink and ink mist, and in particular, an alternating electric signal is selectively applied to cause the head structure to resonate and vibrate the ink. The present invention relates to an inkjet head for forming a mist and discharging the mist.

[0002]

2. Description of the Related Art Conventionally, a diode switch circuit has been realized by applying a DC voltage to a diode in order to control a required AC electric signal. Therefore, a DC voltage blocking capacitor is used so that the DC voltage is not superimposed on the AC electric signal oscillation source and the load device. FIG. 5 shows an example of a circuit of a driving device using a conventional technique. RF is an AC electric signal oscillation source, C51 and C5.
2 is a DC blocking capacitor, D51 is a switching diode, L51 and L52 are AC blocking coils, R51
Is a current limiting resistor, VB51 and VB52 are switching bias DC voltage sources, SW51 is a bias voltage changeover switch, and HEAD is a load device. The alternating electrical signal generated by RF is selectively HEA by D51.
It is transmitted to D. This is transmitted when SW51 switches to the VB51 side and a forward voltage is applied to D51, SW51 switches to the VB52 side, and D51
It is realized by blocking when a reverse voltage is applied to. At this time, since a DC voltage applied to the anode side of D51 does not affect the RF side, a DC blocking capacitor C51 is provided between RF and D51. Similarly, since the DC voltage generated on the cathode side of D51 does not affect the HEAD side, a DC blocking capacitor C52 is provided between HEAD and D51.

[0003]

In the above-mentioned prior art,
Since a DC blocking capacitor is provided in the propagation path of the AC electric signal, propagation attenuation becomes large especially in the low frequency range. Moreover, it is impossible to apply a DC voltage to the HEAD.

Therefore, the present invention solves such a problem, and an object of the present invention is to provide a DC voltage to the load device without a DC blocking capacitor between the switching diode and the load device. It is to provide a circuit which is not applied.

[0005]

An ink jet head according to the present invention comprises a head structure formed of a piezoelectric substrate, a common electrode and a segment electrode disposed on the front surface and the back surface of the head structure, respectively. The common electrode and the segment electrode are provided with a driving device that selectively applies an AC electric signal for causing the head structure to resonate and vibrate, and a sub-structure that is arranged in parallel to the head structure, and the driving device includes a diode. It is characterized by using a switch circuit.

[0006]

EXAMPLES Examples of inkjet heads prototyped according to the present invention will be described below. FIG. 1 is an overall view of a printing mechanism using an embodiment of the present invention. Reference numeral 1 is a head structure made of a piezoelectric material such as PZT, 2 is a segment electrode corresponding to each recording element, 3 is a common electrode, and 4 is a substructure arranged in parallel to the head structure 1. 5 is a platen, 6 is paper to be printed, 7 is ejected mist-like ink,
Liquid ink 8 is held in the gap between the head structure 1 and the sub structure 4.

FIG. 2 is a view showing the head structure 1 alone, and the substructure 4 in FIG. 1 is in contact with the surface B.

The head structure 1 made of a piezoelectric material is
Segment electrodes 2 arranged to face each other in the thickness direction
And distortion is generated by the voltage applied to the common electrode 3. When the applied voltage is an alternating current and is equal to the natural frequency of the head structure, the head structure 1 causes resonance vibration at the portion sandwiched between the segment electrode 2 and the common electrode 3, and at the surface thereof. , Large amplitude vibration is obtained. The basic principle of the inkjet head of the present invention is shown in FIG.
The energy of the piezoelectric vibration of the head structure is applied to the liquid ink 8 held between the head structure 1 and the sub-structure 4 in, and the activated ink is ejected as a mist-like ink 7. It is transferred onto the paper 6.

In the example of the trial manufacture according to the present invention, the thickness of the sub-structure, that is, the width for holding the ink relative to the head structure 1 is about 100 μm, and the head structure 1 and the sub-structure 4 are The gap was about 5 μm. PZT, which is a piezoelectric material, is used for the head structure, and the polarization direction is from the common electrode 3 to the segment electrode 2. In addition to this, as a piezoelectric material, PVDF, crystal, lithium miobate, and the like are also manufactured as prototypes. Further, the thickness of the head structure 1, that is, the distance between the segment electrode 2 and the common electrode 3 is set to 0.6 mm. The width of the segment electrode 2 and the common electrode 3 is 150 μm. The pitch between the segment electrodes is 280 μm, and 12 elements are arranged. This is a size that can be printed at a density of approximately 90 dots per inch, and by arranging two sets in a staggered manner, it is possible to print at a density of 180 dots per inch. The electrodes were formed by depositing a two-layer metal thin film of nickel chrome and gold on the PZT surface by a sputtering method or the like and forming a pattern by a photolithography method. It was also confirmed that the PZT surface was subjected to polishing treatment to improve the electrode adhesion and the like.

Even if the gap between the head structure 1 and the sub-structure 4 has a width of 1 μm to 10 μm and the thickness of the sub-structure 4 is 50 μm to 300 μm, the mist-like ink is ejected efficiently.

FIG. 3 is a view showing the structure of electrodes laid on the head structure 1, which is a view of the surface C in FIG. Reference numerals 21 to 24 show the segment electrodes 2 for four recording elements, and all of them perform the same operation as the segment electrode 2 described above. 41 to 44
FIG. 3 schematically shows a state of an electric field generated by a voltage applied between the common electrode 3 and the segment electrodes 21 to 24. Reference numerals 41, 43 and 44 in the figure denote electric fields due to a DC voltage applied from the common electrode 3 in the directions of the segment electrodes 21, 23 and 24, and 42 denotes the common electrode 3.
And the electric field by the alternating voltage applied between the segment electrodes 22 is shown. In the normal driving method, the electric field in the state of 42 is applied to the element in the driving state, and the electric field is not applied to the element in the resting state. The common electrode and each segment electrode are connected to a corresponding driving device, that is, drivers 1 to 4.

FIG. 4 is a circuit diagram of a drive device prototyped as an embodiment of the present invention. RF is an AC electric signal oscillation source, C1 is a DC blocking capacitor, D1 is a switching diode, L1 and L2 are AC blocking coils, and R1 is a current limiting resistor, VB1 and VB2 are bias DC voltage sources for switching, SW1 is a bias voltage changeover switch, and H
The EAD is a load device, that is, a head unit for one recording pixel. In this embodiment, the oscillation frequency of the AC electric signal oscillation source RF is set to 3 MHz, VB1 = 5V, VB2 = 5V. Further, as a circuit constant, C1 = 10000 pF, L
A prototype was produced with 1 = 10 mH, L2 = 10 mH, and R1 = 47Ω. The outline of the operation of this circuit is that the signal from the AC electric signal oscillation source RF is selectively supplied to the load device HEAD by the switching diode D1.
This is realized by switching the DC voltage applied to D1 in the forward direction and the reverse direction by SW1.

Specifically, the state of blocking transmission is SW
1 may be connected to the state of FIG. 4, that is, to the VB2 side. At this time, a reverse bias voltage of 5 V is applied between the cathode and the anode of D1, that is, it is turned off. Therefore, the AC electrical signal from RF is blocked at D1 and does not reach HEAD.

Similarly, the state in which SW1 can be transmitted is as shown in FIG.
The opposite state, that is, it may be connected to the VB1 side. At this time, a forward voltage of 5 V is applied to D1, and a current flows. That is, the superimposed AC electric signal is also transmitted to the cathode side and applied to the HEAD. At this time, due to the function of the current limiting resistor R1, the direct current component flowing through D1 is suppressed to about 100 mA.

Here, the circuit of FIG. 4 does not use a DC blocking capacitor between the cathode of D1 and HEAD. As can be seen from the circuit diagram, it is not necessary to prevent the DC voltage from being applied to the HEAD because the DC voltage does not appear on the cathode side of the D1, that is, the HEAD terminal regardless of whether the D1 is in the ON state or the OFF state. This is because. When the 10000 pF capacitor used in the conventional example is interposed, since the frequency is 3 MHz, it acts as a resistance of about 5.3Ω. The load of 50Ω used in this embodiment is HE.
Even considering the example connected as AD, the load resistance is reduced by about 10% by omitting the DC blocking capacitor on the output side. That is, the output voltage of the AC signal oscillation source can be set lower accordingly. Further, in terms of the circuit configuration, the number of elements is reduced, and in particular, when considering a driving device having a multi-nozzle, the effect is further enhanced.

FIG. 6 is a circuit diagram showing an example in which the switching bias DC voltage sources VB1 and VB2 used in the circuit of FIG. 4 which is an embodiment of the present invention are not used. Here, D2 and D3 are rectifying diodes, C2
And C3 are bias voltage holding capacitors. This circuit self-supplies a DC voltage for bias from an input AC signal without a dedicated voltage source. That is, as the negative voltage applied to the anode of D1, the voltage of the negative period of the AC signal from RF is selected by D2, and the voltage is held in C2 for use. Similarly, as the positive voltage applied to the anode of D1, the voltage of the positive period of the AC signal from RF is selected by D3, and the voltage is held in C3 and used. This eliminates the external DC voltage source,
The circuit configuration has been simplified. When a plurality of driving devices are used, the rectification and voltage holding unit can be shared and used, and therefore, it is not always necessary to install each for each recording pixel.

FIG. 7 shows an example of a circuit configuration for realizing a driving device for four recording pixels corresponding to FIG. 3 of the embodiment of the present invention. The basic circuit for each pixel is the same as that described in FIG. 4, but a transistor is used as the bias voltage switching means. For the circuit operation, see H at the top of FIG.
The portion connected to the EAD1 will be described as a representative.
The operation of each of the four blocks is the same.

The drive control signal to HEAD1 is GATE.
-1 is input to BUFFER-1. here,
TR6 whose signal is logically inverted is a P-channel JFET
Applied to the gate of. TR6 performs a switching operation, that is, when TR6 is conductive, a reverse voltage is applied to D61 and D61 is turned off. When TR6 is in a non-conducting state, a forward voltage is applied to D61 via the current limiting resistor R62, D61 is turned on, and an AC signal is transmitted to HEAD1.

Switching bias DC voltage source VB3
It is possible to share VB4 and a plurality of elements by using VB4 having a sufficiently low internal resistance. Although not shown in FIG. 7, the same effect was obtained by using the rectifying diode and the DC voltage holding capacitor described in FIG. 6 instead of the switching bias DC voltage source.

[0020]

According to the present invention, a drive device for an AC electric signal can be realized with a simple circuit configuration by configuring it with a circuit using a switching diode. Further, by devising the circuit configuration, it is possible to omit the bias voltage generation source, which is required in the conventional diode switch circuit. Also, because the output side has a circuit configuration that does not require a DC blocking capacitor,
As compared with the case of interposing a DC blocking capacitor, it has the effect of reducing the propagation loss of an AC electrical signal.

[Brief description of drawings]

FIG. 1 is an overall view showing a configuration of an inkjet head according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a head structure according to an embodiment of the present invention.

FIG. 3 is a diagram showing a state of an electrode laid on a head structure and an applied electric field according to an embodiment of the present invention.

FIG. 4 is a diagram showing an example of a circuit of a driving device in an example of the present invention.

FIG. 5 is a diagram showing a circuit example of a conventional driving device using a switching diode.

FIG. 6 is a diagram showing a second circuit example of the driving device in the example of the present invention.

FIG. 7 is a diagram showing a circuit example in the case where a plurality of driving devices according to the embodiment of the present invention are configured.

[Explanation of symbols]

1 head structure 2 segment electrode 3 common electrode 4 Substructure 5 Platen 6 paper 7 Mist-like ink 8 Liquid ink 21 segment electrode (HEAD1) 22 segment electrode (HEAD2) 23 segment electrode (HEAD3) 24 segment electrodes (HEAD4) 41 electric field 1 42 electric field 2 43 Electric field 3 44 electric field 4

Claims (3)

[Claims] 1. A head structure formed of a piezoelectric substrate, a common electrode and a segment electrode disposed opposite to a front surface and a back surface of the head structure, and the head structure on the common electrode and the segment electrode. A drive device for selectively applying an AC electrical signal for causing resonant vibration of the, and a sub-structure arranged in parallel to the head structure,
An inkjet head characterized in that a diode switch circuit is used in the driving device. 2. The ink jet head according to claim 1, wherein a DC voltage blocking capacitor is not used in the driving device. 3. The ink jet head according to claim 1, which has a function of selectively applying a DC voltage to the driving device in a superimposed manner.