JPH0341349B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink jet printing device using piezoelectric elements, and more particularly to a print head having multiple nozzles capable of multiplex driving.

Among inkjet printing devices that use piezoelectric elements, the ink-on-demand type inkjet, which ejects ink when it is needed, does not require expensive pumps or other equipment and does not use high voltage, making the device simpler than continuous-jet inkjet. It has the advantage of becoming However, it has the disadvantage that the response is slower than that of a continuous inkjet.

In order to eliminate this drawback, it is conceivable to use a so-called multi-nozzle in which a large number of nozzles are provided. However, as the number of nozzles increases to improve the apparent recording responsiveness of the device, the number of drivers increases, making the recording device equipped with a multi-nozzle head bulky, and furthermore, When ink is ejected, other nozzles are also interfered with, resulting in a problem where incorrect ink is easily ejected.

An object of the present invention is to eliminate such drawbacks, to suppress the increase in the number of drivers even when the number of nozzles is increased, to realize a recording device that is compact and simple in configuration, and to prevent interference with other nozzles. The main feature is to provide a nozzle head.

Another object of the present invention is to provide a multi-nozzle head that can reduce the number of drivers.

FIG. 1 shows an embodiment of the present invention. In order to simplify the explanation, a case with four nozzles is shown.

Reference numeral 1 designates a substrate made of soda lime glass, on which a nozzle 2, a pressurizing chamber 3, a supply preparation chamber 4, a filter 5, and a supply path 6 are formed by etching. A diaphragm 7 is made of the same material as the substrate 1 and is pressure-fused to the substrate 1 at high temperature. 8 is a tantalum thin film formed by sputtering on the diaphragm 7, 9 is an insulating layer of Ta ₂ O ₅ made by anodizing a part of the tantalum thin film 8, and 10 is an aluminum electrode formed by vapor deposition. , tantalum thin film 8, insulating layer 9, and aluminum electrode 10 are etched to form four MIMs (Metal-
Insulator-Metal) element 11 is configured.
The MIM element will be described later. The MIM element 11 is represented by [j, k]. Here, j is an integer from 1 to m, k is an integer from 1 to n, and in the example of FIG. 1, m=2 and n=2. Among the MIM elements 11, as shown in the figure, M[J, 1] and M[k,
2] Connecting tantalum thin films 8 to each other with a conductive member 12. 13 is a piezoelectric element, with MIM element 11 on the bottom surface
Electrodes 14 corresponding to each M[J, k] are formed by thick film printing. Although the piezoelectric element 13 is made integrally, P[j,
k]. Reference numeral 15 denotes an electrode formed on the upper surface of the piezoelectric element 13, which serves as a common electrode for P[1,k] and P[2,k]. Reference numeral 16 is a thin film resistor provided on the side surface of the piezoelectric element 13 by vapor deposition and connected to the electrode 14 and the electrode 15.

After fusing the substrate 1 and the diaphragm 7, a MIM element 11 is formed and a piezoelectric element 13 is bonded to form a printing head. Ink from an ink tank (not shown) is supplied to the print head through a supply channel 6. When a signal from a control circuit (not shown) is applied to the piezoelectric element P[j,k] corresponding to the nozzle 2 that has ejected the ink, the piezoelectric element P[j,k]
The corresponding portion of the diaphragm 7 is deformed, the internal volume of the corresponding pressurizing chamber 3 is changed, and ink is ejected from the nozzle 2.

As can be seen in FIG. 1, since the nozzles and the pressurizing chambers are arranged at periodic pitches, the pressurizing chambers and the nozzles can be directly communicated with each other. Therefore, ink inertance (inertance) and ink viscous resistance in the flow path can be reduced. On the other hand, as the nozzle pitch becomes smaller, the width of the pressurizing chamber 3 has to be increased. Therefore, the width corresponding to each pressurizing chamber of the piezoelectric element becomes narrower, and the driving voltage becomes higher.

The small flow path impedance mentioned above means that
This has the effect of suppressing an increase in drive voltage.

FIG. 2 shows the drive circuit of the embodiment shown in FIG. Here, the piezoelectric element 13 is equivalently represented by a capacitor, and each is shown as P[j,k]. r[j,
k] is a discharge resistor connected in parallel to the piezoelectric element P[j, k], which is the thin film resistor 16 shown in FIG.
and the leakage resistance of the piezoelectric element 13. The MIM element 11 is a capacitor surrounded by a dotted line in Figure 2.
It is shown as a parallel circuit of C _M and resistor R _M. The resistor R _M changes depending on the voltage applied to both ends, and exhibits a nonlinear voltage (V)-current (I) characteristic as shown in FIG.
In other words, when the applied voltage is small, the resistance value is large;
It exhibits nonlinear voltage-current characteristics in which the resistance value decreases as the applied voltage increases.

In FIG. 2, the contacts connecting the horizontal bus bars j1 and j2 to the power supply voltage V are designated as J1 and J2, and the contacts that ground the vertical bus bars k1 and k2, respectively, are designated as K1 and K2.

The operation of the above configuration will be explained. Bus line j turned on by contact J and contact K
Piezoelectric element P selected by turned ON bus line k
A signal is applied to [j, k] to perform driving.
In this way, it is generally possible to drive (m×n) piezoelectric elements using (m+n) contacts. Such multiplex driving is generally advantageous when six or more piezoelectric elements are driven, since the number of contacts is smaller than when each piezoelectric element is driven independently. The biggest problem with multiplex drive is that a loop circuit is formed through unselected piezoelectric elements, and the unselected piezoelectric elements are driven. In this example, this loop circuit is shown in Figure 3.
This is prevented by using the resistance change due to the applied voltage of the MIM element. That is, the selected piezoelectric element P[j,k]
In, MIM elements M[j,
A voltage higher than Von shown in FIG. 3 is applied to the piezoelectric element P[j, k], and a current sufficient to drive the piezoelectric element P[j, k] flows, thereby driving the piezoelectric element P[j, k]. Ten thousand unselected piezoelectric elements P [j', k'] are connected in series.
If the characteristics of the MIM element are selected so that the wrap-around voltage applied to the MIM elements [j', k'] is less than Voff shown in Figure 3, almost no wrap-around current will flow and the unselected piezoelectric element P [j ′, k′] are not driven.

After piezoelectric element P[j,k] is selected and a signal is applied, after a predetermined period of time has elapsed, it is turned off by contact J or K and the selection is canceled. Piezoelectric element P[j,
k] returns to the steady state where it is discharged through the discharge resistor r[j, k]. The charge charged in the MIM element M[j,k] is discharged by the internal resistance R _M. In this case, from the characteristics of the MIM element,
There is concern that as the terminal voltage of the MIM element decreases, its resistance will increase, making it more difficult to discharge, and that it will not be able to return to a steady state. However, by reducing the capacitance C _M of the MIM element, it is possible to construct a circuit that does not pose any practical problems.

As can be seen from the above example, by constructing an MIM element on a diaphragm fused to a glass substrate and bonding an integrated piezoelectric element having divided electrodes,
A multi-nozzle head capable of multiplex driving without generation of wrap-around circuits is created. This multi-nozzle head can be extremely easily integrated to a high degree by using thin film technology or thick film technology, so it is possible to obtain an inexpensive multi-nozzle head.

In addition, in FIG. 1 and FIG. 2, the case where m=2 and n=2 is described for ease of explanation, but in practice, for example, m=10, n=10 or m
Multiplex driving such as n = 50 and n = 40 is also possible. Furthermore, if the number of busbars n on the scanning side is too large, the actual response will drop, so increase the number of drivers, such as arranging four 50 x 10 print heads instead of a 50 x 40 multiplex. It is also possible to have sex faster.

As the conductive member 12 in FIG. 1, solder connection, wire bonding, etc. can be considered, but as with other processes, thick film and thin film technologies are more advantageous for high integration. For example, FIG. 4 shows a configuration of conductive members for a 3.times.3 multiplex. On top of the tantalum thin film 8 shown in figure a, there is a thick insulating film 4 as shown in figure b.
0 is formed by screen printing, and a conductive member 41 is further formed by screen printing as shown in FIG. Of course, these steps can also be achieved using thin film technology.

Note that contacts J and K shown in Figure 2 are transistors.
Various semiconductor devices such as SCR can be used. From the above explanation, one electrode of the MIM element and the electrode on one side of the piezoelectric element are connected, the other electrode of the MIM element and the electrode on the other side of the piezoelectric element are connected as matrix wiring, and each matrix wiring is provided with a switch means. Multiplex driving becomes possible by connecting a drive circuit (not shown) via the drive circuit.

In this embodiment, an integrated piezoelectric element is bonded on top of the MIM element to facilitate high integration and provide a multi-nozzle head that can be easily driven in multiplex mode. Of course, it is possible to create a multi-nozzle head by gluing an integral piezoelectric element, or
Multiplex driving using MIM elements has sufficient advantages even when used individually.

Note that after adhering the piezoelectric element in one piece, it is also possible to divide the piezoelectric element using a diamond cutter or the like in order to suppress the influence of vibration on neighboring parts.

Furthermore, if a piezoelectric thin film such as PZT or ZnO is used as the piezoelectric element, high integration becomes easier.

Note that the thin film resistor 16 for discharge shown in FIG.
, and instead, the characteristics of the piezoelectric element 13 are changed to
It is also possible to increase the internal leakage current.

In the embodiment described above, the diaphragm is arranged on one side of the board, but the diaphragm is placed on both sides of the board.
It is easy to install MIM elements and piezoelectric elements,
In this way, a more highly integrated multi-nozzle head can be obtained.

Note that in the above embodiments, the relationship between the application of voltage to the piezoelectric element and the ejection of ink is not described in detail. In carrying out the present invention, ink is ejected when the piezoelectric element is charged, ink is ejected when the piezoelectric element is discharged, ink is ejected by reducing the volume of the pressurized chamber, or the volume of the pressurized chamber is Whether or not to eject ink when returning to the original state after increasing the ink may be determined by the method most suitable for each case and does not limit the scope of the invention.

In the embodiment described above, on the glass diaphragm
It constitutes an MIM element and a piezoelectric element is placed on top of it. If the head is made of plastic for cost reasons, etc., the piezoelectric element may be
It would also be possible to form a MIM element and glue it to a plastic head. Also, the electrode of the piezoelectric element
It is also possible to use the same material as the electrodes of the MIM element.

FIG. 5 shows an example of printing using the multi-nozzle head according to the present invention. The printing head 50 shown in Figure a is double-sided, with the nozzles on the top and bottom surfaces being offset horizontally by one dot. Printing is performed by ejecting ink from the required nozzles while moving the print head 50 relative to the recording paper 60 in the direction of arrow B. In this case, for example, with A4 size paper, if the print head is placed on the short side, the resolution will be approximately 10 lines/mm.
2000 nozzles are required.

In figure b, nozzles 51, 52, . . . of the printing head 50 are shown.
The nozzle is moved in a direction perpendicular to the nozzle arrangement direction to scan four dots. In this way, the number of nozzles can be reduced to 1/4 compared to a. In this way, the printing speed can be suppressed and the number of nozzles can be reduced. Particularly in the case of an ink-on-demand type inkjet, the printing head itself is very light, and since contactless printing is performed, the printing head 50 can be moved at high speed as shown by arrow c while the recording paper 60 is kept stationary. Therefore, it is advantageous in planar scanning compared to thermal, discharge, etc. printing devices. The scanning direction of the print head 50 is c
Although it is possible to oscillate in the nozzle arrangement direction as shown in the figure, diagram b is usually better due to the acceleration during reversal. For example, when recording an A4 size sheet with a resolution of 10 lines/mm, one page can be recorded in 4 seconds by moving 500 nozzles back and forth at 0.5Hz in the scanning shown in figure b. The response of the head at this time is approximately 3KHz. On the other hand, in the scanning shown in figure c, if recording is performed at the same time with the same number of nozzles as in figure b, the entire head must be vibrated at approximately 1.5 KHz, and the amplitude is 0.4.
mm or more is required, which poses a problem in terms of energy and noise.If high-density recording is to be performed at high speed, it is desirable to perform recording by moving perpendicular to the nozzle arrangement direction as shown in figure b.

As can be seen from the above explanation, according to the present invention
Since an integrated piezoelectric element is bonded onto the diaphragm on which the MIM element is formed, thin film technology and thick film technology can be effectively utilized. Therefore, a highly integrated multi-nozzle head that is easy to multiplex drive can be obtained at low cost. Furthermore, even if the number of nozzles is increased, the increase in the number of drivers can be suppressed, making it possible to realize a recording device that is compact and simple in configuration, and a multi-nozzle head that can prevent interference that occurs when driving other nozzles to eject. Can be provided.

The present invention can be applied not only to ink-on-demand type heads but also to continuous jet type multi-nozzle heads, and is widely used in printers, plotters, facsimile machines, copying machines, etc.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing one embodiment of the present invention;
The figures are a drive circuit diagram using the printing head of the embodiment shown in Fig. 1, Fig. 3 is a characteristic diagram of the MIM element, Fig. 4 is a diagram showing an embodiment of the conductive member, and Fig. 5 is a diagram of the printing head of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Substrate, 7... Vibration plate, 11... MIM element, 13... Piezoelectric element, 41... Conductive member.

Claims (1)

[Scope of Claims] 1. A substrate including a plurality of nozzles for ejecting ink and pressurizing chambers each communicating with the plurality of nozzles, and a diaphragm forming a wall of the pressurizing chamber and bonded to the substrate. In the multi-nozzle head, there is provided on the diaphragm a parallel circuit of a capacitor and a resistor that exhibits a nonlinear voltage-current characteristic in which the resistance value is large when the applied voltage is small and the resistance value is small when the applied voltage is large. A MIM element that is
A piezoelectric element having electrodes on both sides is used as a pair of drive elements, and is provided corresponding to each of the pressurizing chambers, one electrode of the MIM element and an electrode on one side of the piezoelectric element are connected, and the MIM The other electrode of the element and the electrode on the other side of the piezoelectric element are each formed into matrix wiring, switch means are connected to each of the matrix wiring, and multiplex driving means is provided for driving the pair of driving elements. Multi-nozzle head.