JP3395463B2 - Ink jet head and driving method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an ink jet head mounted on an ink jet recording apparatus for ejecting ink droplets and adhering them onto a recording paper only when recording is required, and a driving method suitable for the structure. is there.

[0002]

2. Description of the Related Art As an ink jet recording apparatus, a so-called ink-on-demand type, which ejects ink droplets only when recording is required, does not require recovery of ink droplets unnecessary for recording. Is becoming mainstream because of.

The ink jet head mounted on the ink jet recording apparatus of this type is, for example, Japanese Patent Application Laid-Open Nos. 6-71882 and 6-55732 filed by the present applicant.
And the structure described in each publication of the same No. 5-50601. In this inkjet head, three substrates are stacked, a plurality of ink nozzles and an independent ink chamber communicating with each nozzle are defined and formed on the intermediate substrate, and the bottom wall of the ink chamber vibrates in the out-of-plane direction. It is configured as a vibrating plate that is possible. The vibrating plate is vibrated by using electrostatic force generated by applying a voltage between the counter electrodes arranged on the back surface and the surface of the facing wall defined by the lower substrate facing the vibrating plate. It is like this. The volume of the ink chamber is increased or decreased by the vibration of the vibrating plate, and the ink pressure generated inside by this causes ink droplets to be ejected from the ink nozzles.

Ink jet recording apparatuses are required to have high quality output images and high output speeds.
Therefore, there is an urgent need to develop an ink jet head capable of stably ejecting finer ink droplets at a higher frequency. Therefore, it is possible to appropriately set the ink droplet ejection characteristics of the inkjet head, that is, the main ink droplets are ejected at high speed to suppress the generation of unnecessary ink droplets thereafter, and the frequency of ejecting ink droplets repeatedly is increased. It is necessary to do so. For that purpose, it is important to properly control the vibration of the internal pressure due to the vibration of the diaphragm formed on the bottom of the ink chamber of the inkjet head. A technique for making the bottom wall of the ink chamber a thin vibrating plate that is deformed by ink pressure is disclosed in JP-A-6-32072.
No. 5 is disclosed. Further, the driving method is disclosed in Japanese Patent Laid-Open No. 192947/1990.
These techniques focus on the natural vibration of the vibration system determined by the structure of the inkjet head, and control the generation of the vibration unique to this system.

In order to obtain good ink ejection characteristics, it is necessary to increase the vibration peculiar to this system when the ink droplets are ejected and reduce it after the ink droplets are ejected. But,
It is very difficult to satisfy these two conditions because the natural vibration changes due to environmental changes such as temperature and manufacturing errors of the inkjet head.

[0006]

SUMMARY OF THE INVENTION Therefore, the applicant of the present invention, in an ink jet head provided with a vibrating plate that can be deformed according to the pressure generated in the ink chamber, deforms when the pressure in the ink chamber exceeds a certain value. It proposes a configuration in which an opposing wall is arranged at a position where it abuts against the diaphragm. According to this configuration, in a state where the diaphragm does not hit the facing wall,
The diaphragm flexes in proportion to the pressure. That is, the compliance defined as the volume change due to the deformation of the wall per unit pressure is kept constant. However, after the diaphragm hits the opposing wall, the deformation of the diaphragm with respect to the increase in pressure becomes small. That is, the compliance changes and becomes smaller. This compliance is a parameter involved in determining the natural period of the ink vibration system. Therefore, the natural period differs between the state where the diaphragm does not hit the opposing wall and the state where it touches the opposite wall, and the natural period becomes short in the state where it hits. Further, the natural period differs depending on the hitting condition, and when the ink is ejected, a large positive pressure is generated and the vibrating plate hits the opposing wall, the responsiveness of the system becomes faster, and the ink droplet can be ejected at high speed. vice versa,
After the ejection, the vibrating plate is separated from the opposing wall and the response system of the system becomes slow, so that the fluid motion after the ejection can be relaxed. Furthermore, since the characteristics of the system change non-linearly in this way, a specific vibration does not strongly oscillate, and unnecessary ink ejection can be suppressed.

An object of the present invention is to discharge a drop of ink by applying a voltage between the vibrating plate thus constructed and the opposing wall to bend the vibrating plate toward the opposing wall by Coulomb force. It is an object of the present invention to propose a configuration in which various types of ejection characteristics such as ejection weight of ink droplets can be easily controlled in an inkjet head of a type. Another object of the present invention is to propose an inkjet head that can achieve high density without impairing ink ejection characteristics. Another object of the present invention is to propose an inkjet head that can be driven at a low voltage. on the other hand,
An object of the present invention is to propose a driving method particularly suitable for such an inkjet head having a novel structure.

[0008]

In order to solve the above problems, an ink jet head of the present invention comprises an ink nozzle for ejecting ink and an ink chamber communicating with the nozzle and holding ink. An ink supply path that supplies ink to the ink chamber, a diaphragm that is formed on a peripheral wall that defines the ink chamber and that can vibrate in an out-of-plane direction, and the vibrating plate outside the ink chamber. and the opposing walls are located opposite each other with a gap with respect to the plate, this
And an electrode arranged on the opposite wall of the
The Coulomb force generated by applying voltage between
In the type in which the vibration plate vibrates to eject ink droplets, a relatively large gap part and a small gap part are formed as a gap between the vibration plate and the facing wall. Small gaps are formed
The portion of the diaphragm that corresponds to the
It is a low-rigidity part that has lower rigidity than the other parts. Also,
The inkjet head of the present invention is of the type described above.
As a gap between the diaphragm and the opposing wall, it is relatively large.
There are gaps and small gaps.
From the ink nozzle side to the ink supply path side
Large and small gaps to make it smaller
Minutes are formed.

Here, the large gap portion and the small gap portion can be formed stepwise, for example.

[0010]

[0011]

On the other hand, the present invention relates to a method for driving an ink jet head having the above-mentioned structure, in which the vibrating plate is vibrated while controlling the state of contact with the large gap part and the small gap part of the vibrating plate. The ejection characteristics of the ink droplets ejected from the ink nozzles are controlled.

[0013]

[0014]

[0015]

[0016]

In the ink jet head of the present invention, the diaphragm flexes in proportion to the pressure when the diaphragm is not in contact with the opposing wall. Therefore, the compliance defined as the volume change due to the deformation of the wall per unit pressure is kept constant. However, if the diaphragm is pulled toward the opposing wall by the Coulomb force between the opposing electrodes and comes into close contact with the opposing wall, the diaphragm cannot be further bent even if the ink pressure increases. Therefore, the compliance changes and becomes smaller.

Here, since there is a large gap portion and a small gap portion between the diaphragm and the opposing wall, the amount of the portion in which the diaphragm is in close contact with the opposing wall changes depending on the amount of bending of the diaphragm. Therefore, the compliance changes depending on the amount of deflection of the diaphragm even between the state where the diaphragm is completely separated from the opposing wall and the state where it is completely in close contact with the opposing wall.

For example, in the state where only the portion of the vibration plate corresponding to the small gap portion is brought into close contact with the opposing wall, the compliance is smaller than that in the completely separated state, and therefore the natural period of the vibration system of ink becomes shorter. Therefore, if the vibration plate is slightly vibrated while being held in this state, minute ink droplets can be ejected at high speed. On the contrary, if the vibration plate is vibrated in its entirety without being partially restrained in this way, the compliance is large, so that excessive pressure generation can be alleviated and large ink droplets can be stably ejected. .

Here, when the large gap portion and the small gap portion are formed stepwise, the close contact state of the vibrating plate with the opposing wall can be controlled stepwise, so that the ink ejection characteristics are stably and stepwise. It can be switched.

Further, if the rigidity of the vibration plate portion corresponding to the small gap is set lower than that of the other vibration plate portions, this low rigidity portion absorbs the generation of ink pressure in the ink chamber. However, it is possible to suppress the generation of unnecessary ink droplets and shorten the time interval until the next ink droplet is ejected. That is, the frequency of ink droplet ejection can be increased.

On the other hand, in the small gap portion, even if the driving voltage applied between the opposing electrodes is small, the portion of the diaphragm corresponding thereto is pulled to the opposing wall side and adheres thereto. Such bending is transmitted to the large gap portion, and the diaphragm is gradually pulled toward the opposite wall side from the portion corresponding to the small gap to the portion corresponding to the size gap, and as a whole, is brought into close contact with the opposite wall. It becomes a state. As a result, the portion of the diaphragm located in the small gap portion serves as a starting point, and the diaphragm is easily pulled to the side of the opposing wall by a small driving voltage and is brought into close contact there.
Further, since the diaphragm can be easily attracted to the side of the facing wall in this way, the size of the diaphragm can be reduced. Therefore, high density of the inkjet head can be realized. As described above, according to the present invention, it is possible to realize an ink jet head which can be driven with high density and low voltage.

On the other hand, according to the driving method of the present invention, the diaphragm is vibrated while controlling the contact state with respect to the large gap portion and the small gap portion of the diaphragm of the ink jet head having the above structure. By controlling the contact state of the vibrating plate with respect to the opposing wall in this manner, the ejection characteristics such as the ink ejection amount can be controlled. Therefore,
A single inkjet head can realize various ejection characteristics.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an ink jet head to which the present invention is applied, FIG. 2 is a plan view thereof, and FIG. 3 is a partial sectional view thereof.

As shown in these figures, the ink jet head 1 sandwiches a silicon substrate 2, a nozzle plate 3 also made of silicon on the upper side, and a borosilicate glass substrate 4 on the lower side having a thermal expansion coefficient close to that of silicon, respectively. It has a laminated three-layer structure. The central silicon substrate 2 is etched from its surface to form five independent ink chambers 5, one common ink chamber 6, and the ink that connects the common ink chamber 6 to each ink chamber 5. Grooves functioning as the supply paths 7 are machined. These grooves are closed by the nozzle plate 3 and each part 5, 6, 7
Are sectioned.

Ink nozzles 11 are formed in the nozzle plate 3 at positions corresponding to the front end side of each ink chamber 5, and these nozzles communicate with each ink chamber 5. Further, in the portion of the nozzle plate 3 where the common ink chamber 6 is located, an ink supply port 12 (see FIG. 2) communicating with this is formed. Ink is supplied to the common ink chamber 6 from an external ink tank (not shown) through the ink supply port 12. The ink supplied to the common ink chamber 6 passes through each ink supply passage 7 and is supplied to each independent ink chamber 5
Is supplied to.

Each of the independent ink chambers 5 has a thin bottom wall 51, and is set to function as an oscillating plate that is elastically displaceable in the out-of-plane direction, that is, in the vertical direction in FIG. Therefore, the portion of the bottom wall 51 may be referred to as a diaphragm for convenience of description below.

Next, in the glass substrate 4 located below the silicon substrate 2, the bonding surface with the silicon substrate 2, which is the upper surface, is located at a position corresponding to each ink chamber 5 of the silicon substrate 2. A shallow etched recess 9 is formed. Therefore, the bottom wall 51 of each ink chamber 5 faces the surface 92 of the opposing wall 91 made of a glass substrate in which the concave portion 9 is formed with a very small gap G therebetween. The distance between the bottom wall 51 and the opposing wall surface 92 will be described in detail later.

Here, the bottom wall 51 of each ink chamber 5 functions as a common electrode on the side of each ink chamber. The segment electrode 10 is formed on the concave surface 91 of the glass substrate 4 so as to face the bottom wall 51 of each ink chamber. The surface of each segment electrode 10 is covered with an insulating layer 15 made of inorganic glass. In this way, each ink chamber bottom wall 51 and each corresponding segment electrode 10 form an opposing electrode with the insulating layer 15 formed on the segment electrode 10 sandwiching the gap G.

As shown in FIG. 2, the voltage applying means 21 for driving the ink jet head charges and discharges these counter electrodes according to a print signal from the outside (not shown). One output of the voltage applying means 21 is connected to each segment electrode 10, and the other output is connected to a common electrode terminal 22 formed on the silicon substrate 2.
Since the silicon substrate 2 itself has conductivity, it is possible to supply a voltage from the common electrode terminal 22 to the common electrode of the bottom wall 51. Further, when it is necessary to supply a voltage to the common electrode with lower electric resistance, for example, a thin film of a conductive material such as gold may be formed on one surface of the silicon substrate by vapor deposition or sputtering. In this embodiment, the silicon substrate 2
Since anodic bonding is used to connect the and the glass substrate 4,
A conductive film is formed on the flow path forming surface side of the silicon substrate 2.

Thus, in this embodiment, the bottom wall 51,
On the other hand, an opposing electrode is formed between the insulating film 15 and the opposing wall 91 that faces the insulating film 15 with the gap G interposed therebetween. When the drive voltage from the voltage applying means 21 is applied between the counter electrodes, a Coulomb force is generated by the charges charged between the counter electrodes, and the bottom wall (vibration plate) 51 bends toward the segment electrode 10 side, and the ink The volume of the chamber 5 increases. Next, when the electric charge between the opposing electrodes is rapidly discharged by the voltage applying means 21, the diaphragm 51 is restored by its elastic restoring force, and the volume of the ink chamber 5 is rapidly contracted. Due to the pressure generated at this time, part of the ink filling the ink chamber 5 is ejected as an ink droplet from the ink nozzle 11 communicating with this ink chamber.

(Gap between Vibration Plate and Opposing Wall) Next, with reference mainly to FIG. 1, the gap G between the vibration plate 51 and the opposed wall 91 in this embodiment will be described in detail. As shown in the figure, the back surface of each diaphragm 51 is a flat surface. On the other hand, the facing wall 91 on the glass substrate 4 side has the ink chamber 5
It becomes deeper in a stepwise manner in the longitudinal direction. The base end side of the ink chamber 5, that is, the portion of the opposing wall 91 facing the bottom plate portion on the ink supply path 7 side is the smallest gap G1.
Has become. A portion of the facing wall 91 facing the bottom wall portion of the middle portion of the ink chamber 5 adjacent to the gap G1 is a medium gap G2 larger than this.
Then, the tip side of the ink chamber 5, that is, the ink nozzle 1
The largest gap G3 is formed between the bottom wall portion on the 1st side and the opposing wall 91. Of course, these gaps are precisely the distances from the front surface of the insulating layer 15 to the back surface of the bottom wall, as shown in FIG.

In the thus constructed ink jet head 1 of the present embodiment, the vibrating plate 51 as the bottom wall of each ink chamber has a pressure in a displacement state (vibration state) in which it is not elastically displaced until it hits the facing wall 91. Bends in proportion to. That is, the compliance is kept constant.
However, if the diaphragm 51 undergoes a large elastic displacement such that the diaphragm 51 is in close contact with the opposing wall, the diaphragm cannot flex further when the ink pressure is increased in the state in which the diaphragm 51 is in close contact with the opposing wall. Get smaller.

Here, a gap G between the diaphragm 51 and the opposing wall 91.
Is the smallest gap G1 in the longitudinal direction of the ink chamber.
, A medium gap G2, and a largest gap G3 are formed in this order from the base end side to the tip end side. Therefore, the compliance of the vibration system can be changed according to the bending amount of the diaphragm 51. Since compliance is one variable that determines the natural frequency of the vibration system, changing the compliance in this way can control the natural frequency of the ink vibration system,
The amount of ink droplets ejected can be adjusted.

For example, as shown in FIG. 4, if the diaphragm 51 is driven in a state where the portion 51a of the diaphragm 51 is attracted to the facing wall 91 side only in the portion of the smallest gap G1, the compliance will be completed. Since it is proportional to the length of the diaphragm, the compliance can be reduced by the length in close contact with the opposing wall 91. Therefore, as compared with the case where the entire diaphragm is vibrated, the natural period of the ink vibration system is reduced. Can be shortened, and minute ink droplets can be ejected at high speed.

When a small gap G1 is formed as in this example, the corresponding portion 51a of the diaphragm 51 is formed.
In comparison with the case where a large gap is formed, is simply attracted to the side of the facing wall 91 and is brought into close contact therewith only by applying a smaller drive voltage. As shown in FIG. 5, when such a partially adhered state is formed,
With that portion as the starting point, elastic displacement is gradually induced from that portion over the entire area. As a result, it is possible to easily cause elastic displacement of the diaphragm and bring the diaphragm into close contact with the side of the opposing wall, as compared with the case where a constant gap is formed. Therefore, if the configuration of this example is adopted, it becomes possible to vibrate the diaphragm using a small drive voltage.

This means that the size of the diaphragm can be reduced when the same drive voltage is used. That is, for example, in order to increase the density of the inkjet head, it is necessary to reduce the size of each component including the ink chamber 5. Ink chamber 5
If the dimension of is reduced, the width and length of the diaphragm that is the bottom wall is also reduced. As a result, the rigidity of the diaphragm becomes high, and a large drive voltage is required to generate appropriate vibration. Alternatively, it is necessary to reduce the gap between the diaphragm and the opposing wall. If the gap is made small, a sufficient amplitude of the vibration plate cannot be secured, so that a problem that a sufficient amount of ink liquid cannot be ejected occurs. However, by forming a small gap as in this example,
Even a small-sized diaphragm can be vibrated without requiring a large driving voltage. Also, since there is a large gap, it is possible to eject a sufficient amount of ink droplets. As described above, according to this example, it is possible to easily realize high density of the inkjet head.

Here, in this example, the gap is formed so as to increase from the base end side of the ink chamber 5 toward the front end side. Therefore, the elastic displacement of the vibration plate 5 is generated from the ink supply side which is the base end side of the ink chamber 5, and this elastic displacement propagates toward the ink ejection side. That is, as shown in FIG. 5, elastic displacement of the vibration plate 51 occurs so that the ink flows in the supply direction. Therefore, there is an advantage that the ink ejection operation can be performed efficiently.

Next, a drive voltage is applied to once bring the diaphragm 51 into close contact with the opposing wall 91, and then the voltage application is released to discharge the electric charges stored in the diaphragm 51 and the opposing wall 91. The Coulomb force disappears, and the diaphragm 51 tries to return to its original state by its elastic return force. At this time, the generated Coulomb force is the smallest in the large gap G3, and the diaphragm 51 is elastically displaced the largest in the gap G3. Therefore, when the voltage application is released and the discharge is performed, the portion 51c of the diaphragm 51 located in the portion of the large gap G3 becomes the other portions 51b, 51a of the diaphragm located in the portions of the gaps G2, G1. Compared with this, in response, the volume of the ink chamber 5 is rapidly contracted away from the facing wall 91, thereby generating a high ink pressure in the ink chamber. The portion of the diaphragm 51 corresponding to the gaps G2 and G1, especially the portion 51a of the diaphragm 51 located in the smallest gap G1 tries to recover very gently, but occurs in the ink chamber. Deformation is hindered by the applied ink pressure, and the ink is temporarily held in contact with the facing wall 91. Compliance is small in this state. That is, the rigidity of the ink chamber 5 is high at the time of ejecting the ink droplet, the ink flow is rapidly generated, and the ink droplet is ejected at high speed. The internal pressure of the ink chamber 5 rises sharply, and after the ink is ejected, it drops sharply to a negative pressure state. As a result, the portion of the vibration plate 51 located in the smallest gap G1 also bends away from the facing wall 91 toward the ink chamber 5. As described above, when the vibrating plate 51 is completely separated from the facing wall 91, the vibrating wall elastically displaces in proportion to the pressure, so that the rigidity of the ink chamber 5 is low, that is, the compliance is large and the ink flow is large. The vibration of the nozzle meniscus after ink droplet ejection is suppressed. After that, the vibration of the ink flow is gradually attenuated by the viscosity of the ink, and the vibration plate 51 vibrates so as to absorb the pressure of the ink chamber without coming into contact with the facing wall.

Therefore, if the rigidity of the portion 51a of the vibration plate 51 corresponding to the smallest gap G1 is set lower than that of the other vibration plate portions, the low rigidity portion 51a will be the ink in the ink chamber. It is possible to absorb the generation of pressure, suppress the generation of unnecessary ink droplets, and suppress the time interval until the next ink droplet ejection. That is, the frequency of ink droplet ejection can be increased.

In order to form a portion having low rigidity on the diaphragm, the width of the diaphragm at that portion may be made wider than the other portions. Alternatively, the thickness of the portion of the diaphragm whose rigidity is desired to be lowered may be made thinner than other portions.

In this example, the gap G is large, medium,
Although it is formed in three small steps, it may be formed in two steps or finely in four or more steps. Further, instead of forming the different gaps by forming the flat surface in a stepwise manner as in this example, it is also possible to form the gap that gradually changes by using a curved surface or an inclined surface.

(Driving Method of Inkjet Head) Next, a driving method of the inkjet head having the above structure will be described with reference to FIGS. 6 to 9. In particular, a control method after the drive voltage applied between the opposing electrodes by the voltage applying means 21 is released will be described.

FIG. 6 shows an example of the voltage waveform between the opposing electrodes. Charging is performed so that the voltage between the counter electrodes rises to the peak voltage Vo at time t1 (V10), and then the peak voltage Vo is maintained until time t2. After that, the discharge is performed as described below, and the ink droplets are ejected.

In this example, in the portion where the waveform portion V11 falls, that is, in the discharge process between the counter electrodes, the first section V where the slope of the voltage drop with respect to time is steep.
12 and a second section in which the slope of the voltage drop is gentle is formed following the first section. That is, after the period t1 to t2 in which the voltage between the opposed electrodes is held at the peak voltage Vo, the discharge is started at the time point t2, and the voltage drops to Va along the first section V12 where the voltage drops sharply. After the time t3 when this voltage value is reached, the voltage drops to zero along the second section V13 where the voltage drops gently.

In the voltage applying means 21 of this example, the magnitude of the voltage drop in the first section V12 can be changed. For example, as shown in the figure, the voltage V
It is possible to switch between a, Vb, and Vc. Voltage V
When the voltage is switched to b or Vc, the voltage drops to this voltage and then discharges at the same voltage drop rate as in the section V13. That is, the voltage is dropped along the lines represented by the sections V14 and V15.

The voltage applying means 21 charges and discharges the counter electrodes so that the voltage waveform between the counter electrodes changes as described above, and the ink droplet ejection operation is performed. here,
When the voltage between the opposing electrodes is dropped along the section V12 and then discharged so as to gradually drop along the waveform portion V13 from the time t3 of the voltage Va, the diaphragm 51 operates as follows. Operate. The voltage between the opposite electrodes is the voltage V
The diaphragm 5 with a large gap G3 while descending to the point a
First, the first portion 51c is elastically displaced inward of the ink chamber 5 away from the surface 91a of the facing wall 91 by the elastic return force.

FIG. 7 shows this elastically displaced state. After this, since the voltage drop is gentle, the portion 51b of the medium gap G2 and the portion 51a of the smallest gap G1 are sequentially separated from the facing wall 91 and returned to the ink chamber side by the elastic return force. Therefore, basically, the portion 51c of the diaphragm 51 facing the portion of the largest gap G3.
Ink droplets are ejected by the ink pressure in the ink chamber 5 generated by the elastic displacement of the ink. In this case, the portion 51b of the medium gap G2 and the portion 51a of the smallest gap G1 are substantially the surface 91b of the facing wall 91.
And 91a, respectively, and therefore the compliance of the ink vibration system is small. Therefore, the natural period can be shortened and minute ink droplets can be ejected at high speed.

On the other hand, when the voltage applied between the opposed electrodes is discharged, when the voltage is gradually decreased along the waveform portion V14 from the time when the voltage is decreased to the value Vb,
In the diaphragm 51, as shown by the broken line in FIG. 7, the portions 51c and 51b corresponding to the largest gap G3 portion and the medium gap G2 portion are opposite wall portions 91c and 91, respectively.
The ink is ejected by moving away from b to the ink chamber 5 side by the elastic return force. In this case, the portion 51c of the diaphragm 51 corresponding to the portion of the smallest gap G1.
Is substantially in contact with the surface 91c of the facing wall 91 without contributing to the ink ejection operation. Therefore, the compliance of the ink vibration system is large and the ejection amount of the ink droplet is large as compared with the case shown by the broken line in FIG.

On the other hand, when the discharge of the voltage applied between the opposed electrodes is rapidly performed until the voltage reaches Vc, substantially all the parts of the diaphragm 51 are shown by the phantom line in FIG. Is elastically displaced toward the inside of the ink chamber by the elastic return force, and contributes to the ink ejection operation. Therefore, in this case, there is no portion of the vibration plate that is in contact with the facing wall 91, the compliance becomes maximum, and the generation of excessive ink pressure can be alleviated. Therefore, a large ink droplet can be stably ejected.

As described above, by changing the voltage drop characteristic at the time of discharge between the opposed electrodes, it is possible to change the ink ejection characteristic of the ink nozzle 11, in particular, its cycle and ink drop weight.

Next, FIG. 8 shows another voltage waveform between the opposite electrodes applicable to the driving of the ink jet head 1 shown in FIGS. In this example, charging / discharging (V20 to V22) for ejecting ink droplets and charging / discharging (V23 to V25) for controlling the ejection amount of the ink droplets.
The charging and discharging are performed twice in total. After a lapse of a certain period from the time point t4 when the first charge / discharge is completed, the auxiliary charge V23 is further performed. This auxiliary charging V23 is performed at time t5.
Starts at, reaches the peak voltage Va at time t6, and ends. After the peak of the voltage is held from time t6 to time t7, the voltage is discharged from time t7 to time t8. Then, in this example, the peak voltage value can be switched to Va, Vb, and Vc by controlling the charging time.

When the charging / discharging is performed in this way, the diaphragm 51 is charged to the voltage Vo so that the vibrating plate 51 becomes
When it is discharged by pulling it to the side of
After time t2 in the figure, the vibration plate 51 returns to its original position by its elastic return force, and is further displaced inward of the ink chamber 5. As a result, the internal pressure of the ink chamber rapidly increases, and ink droplets are ejected from the ink nozzle 11.
The auxiliary charging V23 is started at t5, which is a time point before the ink droplets are completely ejected from the nozzles 11, that is, a time point before the ink exhaustion time.

When the peak value of the auxiliary charge V23 is set to the maximum value Va (V24a), the entire diaphragm 51 is pulled toward the facing wall 91 by the generated Coulomb force and is largely elastically displaced. As a result, the ink pressure in the ink chamber is temporarily and suddenly reduced, and the ink droplets in the process of being ejected have the effect of being sucked into the ink chamber. As a result, the amount of ejected ink is significantly reduced, and minute ink droplets are ejected to form small dot prints on the recording paper.

On the other hand, when the peak of auxiliary charging is Vb (V24b), the portion 5 of the diaphragm 51 corresponding to the medium gap G2 and the smallest gap G1.
Only the portions 1b and 51a are the surfaces 91a and 9 of the facing wall 91.
It is pulled to the side of 1b. Therefore, the elastic deformation of the vibration plate 51 is smaller than that in the above case, and the pressure drop in the ink chamber is also small. Therefore, a larger amount of ink droplets is ejected than in the above case. On the other hand, when the peak of auxiliary charging is set to the smallest Vc (V24c), only the portion 51c of the diaphragm corresponding to the smallest gap G3 is drawn to the surface 91c on the side of the facing wall. Since the elastic displacement of the diaphragm is very small, a large amount of ink droplets are ejected, and large dot printing can be performed.

As shown in the above example, by changing the value of the peak voltage at the time of auxiliary charging, the amount of ejected ink can be controlled and the size of the dots formed can be changed.

Here, such control of the ejected ink amount can also be realized by performing charging and discharging as shown in FIG. In the voltage waveform between the opposing electrodes shown in FIG. 9, charging / discharging for ink ejection (from V30 to V3
After performing 2), the auxiliary charging / discharging (V3
3 to V35). However, in this example, the ejected ink amount is controlled by changing the start time point of the auxiliary charging V33. When the auxiliary charge V33 is started at the earliest time point ta after the end of the discharge V32 (V33a), the amount of ink droplets in the process of being ejected is significantly reduced, and it is possible to realize the ejection of minute ink droplets. On the contrary, when the auxiliary charging V33 is performed from the latest time point tc (V33c), the suction action of the ink droplet having the ejection process is extremely small, so that the ink ejection amount is large, and thus large dot printing is performed. be able to. When the auxiliary charging V33 is started at a time point tb intermediate between these time points ta and tc, ink droplets of an intermediate amount are ejected. In this way, the amount of ink droplets ejected can also be adjusted by changing the start time of auxiliary charging.

Needless to say, the peak voltage value of auxiliary charging and the starting time thereof may be changed simultaneously by combining the example shown in FIG. 8 and the case of this example.

Each voltage value V in the drive voltage signal
o, V1, Va, Vb, and Vc are properties that should be set to optimum values as appropriate according to each specific example according to the elastic characteristics, dimensions, etc. of the diaphragm.

(Inkjet Head Driving Circuit) Next, an inkjet head driving circuit having the above structure will be described with reference to FIGS. 10 and 11. FIG.

FIG. 10 shows an example of a drive circuit for obtaining the voltage waveform between the opposed electrodes shown in FIG.
In the figure, IN1 is an input terminal of a charging signal for bending the diaphragm 51, the signal of the waveform shown in FIG. 11A is input, and IN2 is a counter electrode (vibration) in a charged state. The signal of the waveform shown in FIG. 11B is input to the input terminal of the discharge signal for discharging the electric charge of the plate 51 and the opposing wall 91) to restore the diaphragm 51. A first constant current circuit 40 is connected to the input terminal IN1 via a level shift transistor Q1. The constant current circuit 400 includes transistors Q2 and Q3 and a resistor R1 and is configured to charge the capacitor C with a constant current value.

Reference numeral 410 in the drawing denotes a discharge amount control circuit, which is the first and second one-shot multivibrators MV1 and M.
It is composed of V2. The first one-shot multivibrator MV1 operates when a discharge signal is input and outputs a signal having a pulse width Tx. The pulse width T output from the first one-shot multivibrator MV1
x can be controlled to a desired width, and in this example, 3
It is configured to be able to select the type of pulse width. The second one-shot multivibrator MV2 outputs a signal having a pulse width Td in synchronization with the falling edge of the pulse output from the first one-shot multivibrator MV1.

A second constant current circuit 420 is connected to the output terminal of the first one-shot multivibrator, and a third constant current circuit 430 is connected to the output terminal of the second one-shot multivibrator. . Second constant current circuit 4
20 is composed of transistors Q4 and Q5 and a resistor R2, and is configured to discharge the electric charge of the capacitor C at a constant current value while the signal Tx is being output from the ejection amount control circuit 41. In addition, the third constant current circuit 430
Is composed of transistors Q10 and Q11 and a resistor R3, and is configured to discharge the electric charge of the capacitor C at a constant current value while the signal Td is being output from the ejection amount control circuit 41. Here, the values of the resistors R2 and R3 are set so that the speed of discharge performed by the third constant current circuit is smaller than that performed by the second constant current circuit.

The terminal of the capacitor C is a transistor Q6,
It is connected to the output terminal OUT via a current amplifier circuit formed by connecting Darlington connection of Q7, Q8 and Q9.

The output terminal OUT has a transistor T,
All counter electrodes (diaphragm 51 and segment electrodes 10) forming the actuator of the inkjet head are connected via T, T ....

As a result, since the capacitor C is charged with a constant current while the charging signal is being input, the transistors T, T, T. .. are selected by dot formation signals etc. and turned on, the transistors T, T, T ...
The counter electrode is charged via the. Then, when the discharge signal is input, the capacitor C is discharged, so that the charged electric charge of the counter electrode is discharged through the diodes D, D, D ....

Next, the operation of the drive circuit thus configured will be described with reference to the waveform chart shown in FIG. When the charge signal (a) shown in FIG. 11 is input to the terminal IN1, the rising edge thereof turns on the transistor Q1, which turns on the transistor Q2 forming the first constant current circuit 400, A current flows into the connected capacitor C via the resistor R1.

The terminal voltage of the resistor R1 is the base-emitter voltage of the transistor Q3, and when the transistor Q3 is on, the base-emitter voltage thereof is constant, so that it flows into the capacitor C. The current will be maintained at a constant value.

As a result, the terminal voltage of the capacitor is as shown in FIG.
As shown in 1 (c), it rises linearly from 0 volt with a constant slope τ1. This gradient τ1 changes by adjusting the resistance value of the resistor R1 or the capacitance of the capacitor C. That is, by adjusting the resistance value of the resistor R1, the charging speed between the counter electrodes can be set to a predetermined value.

The terminal voltage of the capacitor C is amplified by the transistors Q6 and Q7 and applied between the opposing electrodes from the output terminal OUT, and the transistors T, T, T ... Which are selectively turned on by the dot formation signal. Via, only between specific counter electrodes is charged with a predetermined gradient τ1. (Fig. 11
Due to this, the vibrating plate 51 is sucked toward the segment electrode 10 side at a predetermined speed, the ink chamber 5 expands, and ink flows from the common ink chamber 6 into the ink chamber 5.

When the time defined by the pulse width To of the charge signal elapses, the transistor Q1 is turned off, so that the charging of the capacitor C is stopped. As a result, the voltage between the opposing electrodes is maintained at Vo, and the diaphragm 51 is
It is maintained at 0.

When the predetermined time Th has elapsed, the discharge signal is input to IN2. (FIG. 11B) As a result, the signal (FIG. 6C) having the pulse width Tx is output from the first one-shot multivibrator MV1 of the ejection amount control circuit 410.

The transistor Q4 forming the second constant current circuit 420 is turned on, and the electric charge of the capacitor C is discharged through the resistor R2. Since the terminal voltage of the resistor R2 is the base-emitter voltage of the transistor Q5, it operates similarly to the above-described first constant current circuit 400 to maintain the current flowing through the resistor R2 at a constant value.

As a result, the terminal voltage of the capacitor C becomes
It falls linearly with a gradient τ2 based on the adjusted resistance value of the resistor R2. This falling voltage is
The voltage is applied to the output terminal OUT via 8 and Q9, but since only the counter electrodes of the nozzles on which dots are to be formed are charged, only these counter electrodes are diodes D, D and D.
The discharge is caused by the falling gradient τ2 via ... And the diaphragm 51 is restored at a speed determined by this.

When the time determined by the pulse width Tx of the first one-shot multivibrator MV1 elapses in the process of restoring the diaphragm, the transistor Q4 is turned off. At the same time, the second one-shot multivibrator MV2 of the ejection amount control circuit 410 outputs a signal having a pulse width Td (see FIG. 6).
(D)) is output. As a result, the second constant current circuit 4
The discharge that has been performed via the resistor R2 of the transistor 20 is stopped, and the transistor Q1 forming the third constant current circuit 430 is formed.
When 0 is turned on, the electric charge of the capacitor C is discharged through the resistor R3.

Since the resistance value of the resistor R3 is set to a value larger than that of the resistor R2, the terminal voltage of the capacitor C changes to the resistance R after a lapse of the time determined by the pulse width Tx.
It falls linearly with a gradient τ3 based on the resistance value of 3. That is, the electric charge between the opposing electrodes, which has been discharged with the falling gradient τ2, has a gradient τ after the lapse of the time determined by the pulse width Tx.
The discharge is performed with a falling slope τ3 smaller than 2. The second one-shot multi-vibrator MV2
The signal having the pulse width Td output from is preset so as to fall after the electric charges between the opposite electrodes are completely discharged.

The pulse width Tx of the signal output from the first one-shot multivibrator MV1 of the discharge amount control circuit 420 is controlled according to the discharge amount control signal. The first one-shot multivibrator of this example is
Three types of pulse widths can be output according to the ejection amount control signal, and three types of ink ejection amounts can be selected.

When ejecting the smallest amount of ink droplet,
Signal with the shortest pulse width Tx (solid line part in FIG. 10C)
Is output from the first one-shot multivibrator MV1. As a result, the electric charge stored between the opposite electrodes is discharged to the voltage Va with the gradient τ2, and then the gradient τ3.
Is discharged. (Solid line part in FIG. 10E) At this time, as shown in FIG. 7, the ink pressure in the ink chamber 5 caused by the elastic displacement of the portion 51c of the diaphragm 51 facing the portion of the largest gap G3 causes the ink Droplet ejection is performed.

On the other hand, when ejecting the largest amount of ink droplets, the signal having the longest pulse width Tx is output from the first one-shot multivibrator MV1. As a result, the electric charge stored between the opposite electrodes is discharged to the voltage Vc with the gradient τ2 and then with the gradient τ3. At this time, as described above, all the portions of the vibration plate 51 are elastically displaced toward the inside of the ink chamber by the elastic restoring force and contribute to the ink ejection operation.

When a medium amount of ink droplets is ejected, the electric charge accumulated between the opposed electrodes is equal to the voltage Vb.
A signal having a medium pulse width Tx is output from the first one-shot multivibrator MV1 so that the discharge is performed up to the gradient τ2 and then the gradient τ3.

As a result, the portions 51c, 51 corresponding to the largest gap G3 and the medium gap G2 are formed.
b is separated from the opposing wall portions 91c and 91b and is displaced toward the ink chamber 5 side by the elastic return force, and ink is ejected.

Thus, using the drive circuit of this example,
It is possible to easily change the voltage drop characteristic during discharge between the opposing electrodes, and as a result, it is possible to control the weight of the ink droplets ejected from each nozzle.

Further, by applying the drive circuit of this example, a plurality of constant current circuits and a circuit for switching them,
By combining a one-shot multivibrator, a delay circuit, a plurality of constant voltage circuits and a circuit for switching them, the charge / discharge waveforms shown in FIGS. 8 and 9 can be obtained.

[0084]

As described above, in the ink jet head of the present invention, as a gap between the diaphragm forming the bottom wall of the ink chamber and the counter wall against which it vibrates,
A structure is used in which a large gap and a small gap are formed. According to this configuration, even if the driving voltage applied between the opposing electrodes therebetween is small, the portion of the diaphragm located in the small gap portion is easily elastically displaced toward the opposing wall side, and this displacement is The vibration propagates to the portion of the diaphragm located in the large gap portion, and the diaphragm as a whole is attracted and adheres to the opposing wall side by the Coulomb force. Therefore, the drive voltage can be reduced. On the contrary, even if the ink chamber is made small in order to increase the density of the ink jet head, that is, even if the size of the diaphragm which is the bottom wall is made small to increase the rigidity, this diaphragm can be easily vibrated. Because you can
It is also advantageous for realizing high density of the inkjet head.

Further, when the rigidity of the diaphragm portion located in the small gap is set to be low, this low rigidity portion absorbs the generation of ink pressure in the ink chamber after ink ejection. The generation of unnecessary ink droplets can be suppressed, and the time interval until the next ink droplet ejection can be suppressed to be short. That is, the frequency of ink droplet ejection can be increased.

Further, when the small gap portion and the large gap portion are arranged in this order in the direction of the ink supply flow, there is an effect that the ink is pushed out in the supply direction by the elastic deformation of the diaphragm. I will receive
Ink can be efficiently supplied toward the ink nozzles.

On the other hand, according to the present invention, when the ink jet head having such a small gap portion and a large gap portion is driven, the voltage drop characteristic at the time of discharging the electric charge accumulated between the opposing electrodes is changed. I have to. Alternatively, the auxiliary charging / discharging may be further performed after the charging / discharging for discharging the ink, and the peak voltage value of the auxiliary charging / discharging may be set together with or separately from the start time of charging of the auxiliary charging / discharging. I am trying to change it. If this driving method is adopted, for example, a state where only the portion of the vibration plate located in the small gap portion is sucked to the facing wall,
That is, the vibration plate can be elastically displaced while the compliance of the vibration system of the ink is reduced, and the ink ejection characteristics such as the amount of ejected ink can be variously changed.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an inkjet head to which the present invention is applied.

FIG. 2 is a plan view of the inkjet head shown in FIG.

3 is a schematic cross-sectional view showing a part of the inkjet head of FIG.

FIG. 4 is an explanatory diagram showing an elastically displaced state of a diaphragm of the inkjet head of FIG.

5 is an explanatory diagram showing an elastically displaced state of a vibration plate of the inkjet head of FIG. 1. FIG.

6 is a waveform diagram showing a voltage waveform between opposing electrodes of the inkjet head of FIG.

FIG. 7 is an explanatory diagram showing an elastically displaced state of a diaphragm in the inkjet head of FIG.

8 is a waveform diagram showing another example of the voltage waveform between the opposing electrodes of the inkjet head of FIG.

9 is a waveform diagram showing still another example of the voltage waveform between the opposing electrodes of the inkjet head of FIG.

10 is a circuit diagram showing an embodiment of a drive circuit of the inkjet head of FIG.

11 is a signal waveform diagram showing an operation of the drive circuit of FIG.

[Explanation of symbols]

1 inkjet head 2 substrates 3 nozzle plate 4 glass substrates 5 ink chamber 51 Vibration plate (bottom wall of ink chamber) 51a The diaphragm part located in the smallest gap 51b A portion of the diaphragm located in the middle gap 51c The diaphragm part located in the largest gap 6 common ink chamber 7 ink supply path 9 recess 91 Opposite wall 91a Surface of opposing wall located in smallest gap 91b Surface of opposing wall located in medium gap 91c The surface of the opposing wall located in the largest gap 92 Opposite wall surface 10 electrodes 11 ink nozzles 12 Ink supply port 21 voltage applying means 22 Common electrode terminal G Gap between diaphragm and facing wall G1 smallest gap G2 Medium gap G3 Largest gap

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/055 B41J 2/16

Claims (4)

(57) [Claims] 1. An ink nozzle for ejecting ink, an ink chamber communicating with the nozzle and holding the ink, an ink supply path for supplying the ink to the ink chamber, and the ink chamber being partitioned. Is formed on the surrounding wall,
A vibrating plate that is elastically displaceable in the out-of-plane direction, a facing wall that is disposed outside the ink chamber and faces the vibrating plate with a gap, and a facing wall that is disposed on the facing wall
An electrode, and a voltage is applied between the electrode and the diaphragm.
The vibrating plate due to the Coulomb force generated by applying
In an inkjet head that vibrates to eject ink droplets , a relatively large gap portion and a small gap portion are provided as a gap between the vibrating plate and the facing wall, and the small gap portion is formed at a position where the gap portion is formed. Before responding
The diaphragm part is more rigid than other parts of the diaphragm.
Inkjet head characterized by low rigidity and low rigidity . 2. An ink nozzle for ejecting ink, and
The ink that holds the ink while communicating with the nozzle
Ink chamber and an ink supply path that supplies ink to this ink chamber
And formed on the peripheral wall that defines the ink chamber,
The diaphragm that is elastically displaceable in the out-of-plane direction and the
Outside the ink chamber, leaving a gap between the diaphragm and
The opposite wall that is arranged opposite to each other and the opposite wall that is arranged
An electrode, and a voltage is applied between the electrode and the diaphragm.
The vibrating plate due to the Coulomb force generated by applying
Inkjet head that vibrates to eject ink droplets
The size of the gap between the diaphragm and the facing wall is relatively large.
A small gap part and a small gap part, and the gap is formed from the ink nozzle side to the ink supply path.
The large gap so that it becomes smaller toward the side of
It has a special feature that a gap and a small gap are formed.
Inkjet head to collect. 3. The ink jet head according to claim 1 or 2 , wherein the large gap portion and the small gap portion are formed in a step shape. 4. The ink jet device according to claim 1.
In the method for driving the
Abutment of the diaphragm to the minute and the small gap
The diaphragm is vibrated while controlling the
Controlling the amount of ink droplets ejected from the nozzle
And a method for driving an inkjet head.