JPH01234254A - Ink jet printing head - Google Patents

Abstract

PURPOSE:To control the attenuation characteristics of a piezoelectric vibrator independently of the characteristics of an ink flow passage or those of a piezoelectric element and the piezoelectric vibrator, by changing the intensity of a magnetic field by a magnetic field generating means in synchronous relation to the electric signal to the piezoelectric vibrator. CONSTITUTION:An on-demmand type ink jet printing head is constituted of a multinozzle. A vibrator is formed by bonding 9 piezoelectric elements to a thin plate 18 composed of a magnetostriction material and fine notches are formed to the thin plate 18 so as to independently constitute vibrators of the respective piezoelectric elements and the respective vibrators are bonded by an adhesive so as to be overlapped with a cavity to constitute a multinozzle head. A magnetic field generating means is formed by superposing a polyethylene terephthalate film 12, which has the pattern of oval ring coils 10 each having a shape matched with that of each of the vibrators formed thereto, on the vibrators. The number of windings of each coil is properly set corresponding to the intensity of a magnetic field to be generated. Each coil is connected to a power supply circuit 11 and stably operated by allowing a current to flow to the coil so as to set the min. value of the magnetic field formed in the vibrator to Hs or more.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 1 The present invention relates to an on-demand inkjet printer head.

1. Prior art) In an on-demand inkjet printer head,
By applying a pulse voltage as shown in FIG. 14(b) to the piezoelectric element, the piezoelectric vibrator undergoes a transient response and reaches the maximum displacement as shown in FIG. 14(a), and then the vibrator and ink It is damped while vibrating at the natural frequency of the system made up of. At this time, the ink droplets ejected from the nozzle are formed into ink droplets whose diameter decreases in order from the beginning depending on the amplitude of the vibrator, and the ink droplets except the beginning reach the recording medium with a time delay from the beginning. This causes disturbances in the image. Furthermore, since the next ink droplet cannot be ejected until the vibration is sufficiently damped, the printing speed cannot be increased. Therefore, in conventional inkjet printer heads, by appropriately increasing the fluid resistance of the flow path, the vibrator is damped to the extent that image disturbance is tolerated, and piezoelectric strain is applied in the direction of reducing the vibrating momentum of the vibrator. The method used was to actively provide damping by adjusting the voltage applied to the piezoelectric vibrator so as to give .

] Problems to be Solved by the Invention l However, if the fluid resistance of the ink flow path is increased, the pressure loss in the flow path will increase, resulting in problems such as slowing down the ejection speed of ink droplets, or in extreme cases, no ejection. It has points. Furthermore, if an attempt is made to compensate for the loss due to flow path resistance by increasing the vibration energy of the vibrator, a load will be placed on the vibrator driver and the system will have low energy efficiency. .

Furthermore, if we actively apply damping by adjusting the voltage applied to the piezoelectric vibrator without knowing the deformation state of the piezoelectric vibrator, there will be variations in the characteristics of individual vibrators and drive circuits. It's hard to save.

Additionally, when monitoring the voltage between the electrodes of the piezoelectric element and controlling the voltage applied to the piezoelectric vibrator based on that information, there is a problem that the control circuit system becomes extremely complicated. There is.

Therefore, the object of the present invention is to solve these problems, and its purpose is to control the damping characteristics of the piezoelectric vibrator independently of the characteristics of the ink flow path, the piezoelectric element, and the drive circuit of the piezoelectric vibrator. The purpose of the present invention is to provide a high-speed, on-demand inkjet printer head with stable print quality.

1. Means for Solving the Problems) The inkjet printer head of the present invention has a magnetic field generating means that applies a magnetic field to the magnetostrictive material of the pressure a vibrator, which is made by joining an elastic plate made of a magnetostrictive material and a piezoelectric plate. The piezoelectric vibrator is characterized in that a magnetic field is generated by the magnetic field generating means in synchronization with an electric signal to the piezoelectric vibrator.

Furthermore, the period during which the magnetic field is generated by the magnetic field generating means is from the rise time of the pulse voltage applied to the piezoelectric vibrator in response to the print signal to the time when the first maximum deflection of the deflection vibration of the piezoelectric vibrator due to the application of the pulse voltage occurs. It is characterized by including at least between times. Furthermore, the magnetic field generating means is characterized in that the strength of the magnetic field acting on the plate made of the magnetostrictive material of the piezoelectric vibrator is greater than or equal to the strength that saturates the magnetization of the magnetostrictive material.

] Effect 1 Stress when stress is applied to magnetostrictive material - strained cotton is the 12th
It has characteristics as shown by curve a in the figure.

That is, the apparent elastic modulus is smaller in a region where the strain is small than in a region where the strain is large. This property is known as the ΔE effect. A typical example of the magnetization characteristics of such a magnetostrictive material is shown in FIG. 13. When a magnetic field with a strength of Hb in FIG. 13 is applied to this magnetostrictive material, the stress-strain curve
The curve S in Figure 2, and the magnetic field He greater than Hs in Figure 13
(In this case, the magnetization of the magnetostrictive material is saturated), the stress-strain curves become as shown in curves km and c in FIG. 12, respectively. That is, as the strength of the magnetic field increases, ΔE
The effect becomes smaller and the ΔE effect disappears when the magnetization of the magnetostrictive material is saturated. In other words, the elastic modulus of the magnetostrictive material can be changed by a magnetic field.

Furthermore, when vibration is applied to a magnetostrictive material that has a ΔE effect, the relationship between stress and strain becomes hysteretic, as shown by the broken line in Figure 12, and the vibration energy is converted into thermal energy, causing the vibration to decrease. Attenuates rapidly. However, when a magnetic field is applied to this magnetostrictive material, the ΔE effect becomes smaller, so the hysteresis becomes smaller, and the vibration damping also becomes smaller accordingly.

When the magnetic field is strong enough to saturate the magnetization of the magnetostrictive material, ΔE
Since the effect is lost, the vibrations are no longer damped. In other words, the vibration absorption properties of the magnetostrictive material can be changed by a magnetic field.

According to the above configuration of the present invention, by applying a magnetic field to the magnetostrictive material of the vibrator and changing the elastic properties and vibration absorption characteristics of the vibrator, the piezoelectric vibrator responds to a pulse voltage applied to the piezoelectric vibrator in accordance with a print signal. It becomes possible to control the damping speed and amplitude of vibration independently of the shape of the ink flow path and the drive circuit of the vibrator.

(Example 1) The configuration of the ink flow path and vibrator of an inkjet printer head applied as an example of the present invention will be explained using the schematic diagram of FIG. It is formed by joining a thin plastic plate 6 to a substrate 5 having a flow path 2 leading to a nozzle 3, a flow path 4 leading to an ink supply tank, and a cavity 1 for applying pressure by a vibrator. There is.

The vibrator was constructed by bonding a thin plate 8 made of a magnetostrictive material and a piezoelectric element 7, and was bonded onto the cavity 1 using an adhesive 9. The piezoelectric element uses a unidirectionally polarized PZT measuring 4 by 2 meters by 0.1 mm thick, and wiring for voltage input is omitted. The thin plate made of magnetostrictive material was a heat-treated Fe-A1 alloy plate with a thickness of 20 μm. Magnetostrictive materials include metals and alloys such as bi-alloys, ferrite and Co.

Ferrite-based magnetostrictive materials containing Cu, Ni, etc. can be used. In addition, amorphous magnetic materials such as FeB51
Amorphous alloys are also effective as magnetostrictive materials.

Generally, ferromagnetic materials have some degree of magnetostriction, so it is thought that they can be applied even if the degree of effect is different.

Regarding the magnetostrictive material, it is the same in the following examples, so it will not be specifically mentioned.

The magnetic field generating means of the present invention is not shown in FIG. In the following, an embodiment of the magnetic field generating means will be explained in detail using FIGS. 2 to 6, but the configurations of the ink flow path and the vibrator are basically the same as those explained in FIG. is omitted. Further, in each figure, the drive circuit in the magnetic field generating means is omitted because it has a well-known configuration.

-The on-demand type inkjet printer head is composed of multiple nozzles. Figure 2(a) is
This is a flow path pattern of a multi-nozzle inkjet printer head having the basic configuration shown in FIG. 1. As shown in FIG. 2(b), the vibrator is made of a thin plate 1 made of magnetostrictive material.
Nine piezoelectric elements 17 are joined to the thin plate 18, and thin cuts are made in the thin plate 18 so that each piezoelectric element constitutes an independent vibrator. The multi-nozzle head is constructed by overlapping the two and bonding them with adhesive. The magnetic field generating means is shown in Figure 2 (C).
As shown in the figure, a polyethylene terephthalate film 12 with a pattern of an elliptical ring coil 10 that matches the shape of the vibrator is placed on top of the vibrator.Although it is omitted in the figure, the number of turns of the coil is Set appropriately depending on the strength of the magnetic field to be generated. At this time, in the case of a large number of turns, the circuit patterns of the coils overlap on a plane, so a method such as making the circuit patterns intersect with each other on the back surface of the film 12 by hole-through is used. Furthermore, a hole is made in the film at the center of the coil for wiring to the piezoelectric element. Each coil is connected to a power supply circuit 11. The connection may be made in series or in parallel, but if the drive timings of the respective vibrators do not match in time, each coil needs to be connected to the power supply via an individual switching circuit. With this structure, it is difficult to form a uniform magnetic field over the entire area of the vibrator. However, as shown in Figure 13, the magnetization of the magnetostrictive material is saturated when the strength of the external magnetic field exceeds Hs. The vibration characteristics are not affected by the apparent uniformity of the magnetic field distribution. In this example, an inkjet head that operates stably can be constructed by passing current through the coil so that the minimum value of the magnetic field that the coil forms in the vibrator is equal to or higher than Hs.

FIG. 3 shows another embodiment of the magnetic field generating means, 1: IR circuit 3
By bending the iron core around which the solenoid connected to 1 is annular and facing each other with the end faces parallel with a gap, a uniform and strong magnetic field can be applied to the vibrator placed in the gap.

FIG. 4 shows an embodiment using permanent magnets. Ink channels are formed on both sides of the substrate 45 for high density. Permanent magnets such as alnico and Ba ferrite 4Qa and 4
A uniform magnetic field is formed by opposing Nff1 of 0b and the S pole. In the case of a multi-nozzle, a permanent magnet shaped to cover all the vibrators may be used. Since it is not possible to change the strength of the magnetic field quickly with a permanent magnet, an IIT current that cancels the magnetic field of the permanent magnet is applied to the coils 41a and 41b provided surrounding each vibrator, which acts on the vibrator. It is possible to reduce the magnetic field to zero.

FIG. 5 shows an embodiment in which a Helmholtz coil is used as the magnetic field generating means. The Helmholtz coil is made up of two circular coils (50a, 50b) with radius a arranged coaxially in parallel, with a distance equal to a, and can form a uniform magnetic field inside. As explained earlier, if the strength of the magnetic field acting on the vibrator is sufficiently low to saturate the magnetization, the effects of the non-uniform magnetic field will not appear on the characteristics of the inkjet head. In some cases, the conditions for the Helmholtz coil can be relaxed somewhat, the shape of the coil does not have to be circular, and the distance of the coil can be changed, so
This example was also effective in reducing the size of the device.

FIG. 6 shows an example in which a uniform magnetic field is applied to all the vibrators 67 of the multi-nostle head using one Helmholtz coil (60a, 60b) similar to that in FIG. 5.This embodiment In the example, 12 nozzles 63 on one side are connected to the substrate 65.
on both sides.

What has been said regarding FIG. 5 applies directly to this embodiment.

Next, an embodiment will be described regarding the period during which the magnetic field is generated by the magnetic field generating means described above and the timing of the voltage pulse applied to the vibrator. In the graphs in FIGS. 8 to 11 used in the explanation, the horizontal axis represents time t, and the vertical axis represents, in order from the top graph, the deflection displacement U of the vibrator (the direction in which the volume of the cavity is decreased is positive); A voltage Vp is applied to the piezoelectric element of the vibrator, and a voltage VC is applied to the coil of the magnetic field generating means, respectively.

There are two main driving methods for the on-demand ink shed printer head, as shown in FIG. In the pulling method shown in Fig. 7(a), when a pulse voltage is applied to the piezoelectric element, the vibrator deflects to increase the volume of the cavity, and after ink is supplied from the ink supply path, the ink and the vibrator are assembled. The ink is pushed out while vibrating at the natural frequency. In the push method shown in FIG. 7(b), when a pulse voltage is applied to the piezoelectric element, the vibrator deflects to reduce the volume of the cavity, pushes out the ink, and then returns to its original state while vibrating. Ink is supplied from the supply path.

8 and 9 are FIGS. 2, 3, and 5.

Like the embodiment shown in FIG. 6, this is an embodiment of a magnetic field generating means in which a magnetic field is applied to a vibrator by passing a current through a coil.

Figure 8 shows the drawing method.The ink is sealed from the nozzle by the pressure that starts from the rise time to of Vp until the time tl when the vibration U of the vibrator first reaches its maximum, so the vibration is not attenuated during this period. It is preferable that there is no hysteresis and that the vibrations are quickly attenuated after time t1. Therefore, VC is applied to the coil including the period from time 10 to tl. It is most effective for the strength of the magnetic field formed by the coil due to Vc to be greater than or equal to the strength at which the magnetization of the magnetostrictive material is saturated, as this will minimize vibration attenuation and will not be affected by the non-uniformity of the magnetic field. This is as explained earlier. This is explained in the following 9th
This also applies to the illustrated embodiment. However, if the influence of attenuation in a short period of time can be ignored, sufficient effects can be obtained even in an embodiment that includes a period from time to to time t2 when the negative deflection first reaches its maximum.

Figure 9 is for the push-dosing method, and the ink is 1 pull-dosing.
As in the previous case, the rise time t of Vp.

When the vibration U of the oscillator starting from becomes maximum for the first time, 11t
Since the injection is made from the nozzle with a pressure of up to l, at time t
Vc is applied to the coil in a manner that includes 10 periods. The difference from the pulling method is that the time when the vibration U first reaches its maximum is as short as about 1/4 of the natural period of the vibration system.

FIGS. 10 and 11 show that, as in the embodiment shown in FIG. 4, the magnetic field statically generated by a permanent magnet or other magnetic field generating means can be canceled out by flowing a current of 'N through the coil. This is an embodiment of a magnetic field generating means for controlling the magnetic field acting on the vibrator.

The 10th (g is also two pairs of the pulling method, and the 8th rjU
Similarly, during the period from time to to tl, voltage VC is not applied to the coil so that a magnetic field acts on the vibrator. After time t1, a voltage is applied to the coil so as to attenuate vibrations during a period of time L3, when the input pulse Vp corresponding to the next print signal rises.

Figure 11 is for the pushing method, and like Figure 10,
After the time t1 when the vibration U of the vibrator first reaches its maximum and the time t3 when the next input pulse Vp rises,
A voltage is applied to the coil to dampen vibrations.

1 Effects of the Invention 1 As described above, according to the present invention, a vibrator is constructed by bonding a thin plate made of a magnetostrictive material and a piezoelectric element,
By applying a magnetic field to the vibrator using the magnetic field generating means, it is possible to control the amplitude and damping characteristics of the vibrator, and the present invention has the feature that an inkjet printer head with high printing quality and quick response can be constructed. Further, by configuring that the period during which the magnetic field is applied to the vibrator by the magnetic field generating means includes at least the period from the rise time of the pulse voltage applied to the piezoelectric element to the time when the first maximum deflection of the deflection vibration of the vibrator occurs, The vibrator is characterized in that the amplitude of the vibrator is large when the ink is ejected, and can be quickly attenuated after the ink is ejected. In addition, by setting the strength of the magnetic field that acts on the magnetostrictive material of the vibrator using the magnetic field generating means to be greater than the strength that saturates the magnetization of the magnetostrictive material, the vibration characteristics of the vibrator can be improved by making the magnetic field acting on the vibrator non-uniform. It has the characteristic that it can be prevented from being affected by

[Brief explanation of the drawing]

FIG. FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are diagrams illustrating other magnetic field generating means methods for the inkjet printer head of the present invention. FIG. 8, FIG. 9, FIG. 10, and FIG. 11 are timing charts showing an embodiment of the method for driving the magnetic field generating means of the present invention. 1...Cavity, 7, 17.67...
・Piezoelectric element, 8.18...Thin plate of magnetostrictive material, 1
0.32゜41.50.60... Electromagnetic coil,
40... Applicant for permanent magnets and above Seiko Epson Co., Ltd. Representative Patent Attorney Toku Mogami and 1 other person (a) (b) Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13

Claims (3)

[Claims] (1) In an on-demand inkjet printer head that applies pressure to ink and causes ink droplets to fly by flexing and vibrating a piezoelectric vibrator, which is made by bonding an elastic plate and a piezoelectric plate, with a pulse voltage according to a print signal. ,
The elastic plate is made of a magnetostrictive material, and has a magnetic field generating means for applying a magnetic field to the elastic plate made of the magnetostrictive material, and the magnetic field generating means is used in synchronization with an electric signal to the piezoelectric vibrator. An inkjet printer head characterized by changing the strength of a magnetic field. (2) The period during which the magnetic field is generated by the magnetic field generating means is from the rise time of the pulse voltage applied to the piezoelectric vibrator in response to the print signal to the initial bending vibration of the piezoelectric vibrator due to the application of the pulse voltage. 2. The inkjet printer head according to claim 1, wherein the inkjet printer head includes at least a time during which the maximum deflection occurs. (3) The first aspect of the invention is characterized in that the strength of the magnetic field acting on the elastic plate made of magnetostrictive material of the piezoelectric vibrator by the magnetic field generating means is greater than or equal to the strength that saturates the magnetization of the magnetostrictive material. The inkjet printer head described in Section 1.