JP2000272119A - Ink jet head and its drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply control a discharge characteristic of ink drops such as a discharge weight or the like more variously in an ink jet head of a system wherein a voltage is impressed between a diaphragm arranged via a gap for forming an ink chamber bottom face and an opposite wall, thereby deflecting the diaphragm towards the opposite wall by a Coulomb's force to discharge ink drops. SOLUTION: A bottom wall of an ink chamber 5 of an ink jet head 1 functions as a diaphragm 51, and an opposite wall 91 is set to a position where the diaphragm is pressed in contact with the opposite wall when elastically deformed. An electrode 10 opposite to the diaphragm 51 is divided to a plurality of electrode parts. The electrode parts are mutually connected by resistors, and therefore the electrode parts have different time constants. A contact state between each part of the diaphragm 51 and each surface of the opposite wall can be changed by controlling a voltage waveform of opposite electrodes, and a discharge characteristic such as a discharge weight or the like of ink drops can be variously changed.

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 only when recording is required and attaching the ink droplets onto recording paper, and a driving method suitable therefor. is there.

[0002]

2. Description of the Related Art As an ink jet recording apparatus, a so-called ink-on-demand system which discharges ink droplets only when recording is required does not require collection of ink droplets unnecessary for recording. It is becoming mainstream.

An ink jet head mounted on an ink jet recording apparatus of this type is disclosed in, for example, JP-A-6-71882 and JP-A-6-55732 filed by the present applicant.
And JP-A-5-50601. In this ink-jet head, three substrates are laminated, a plurality of ink nozzles and an independent ink chamber communicating with each nozzle are formed on an intermediate substrate, and the bottom wall of the ink chamber vibrates in an out-of-plane direction. It has a configuration formed as a possible diaphragm. The vibrating plate is vibrated by utilizing an electrostatic force generated by applying a voltage between opposing electrodes respectively disposed on the back surface of the opposing wall defined by the lower substrate facing the vibrating plate. It has become. The vibration of the diaphragm increases or decreases the volume of the ink chamber, and the ink pressure generated inside the ink chamber causes ink droplets to be ejected from the ink nozzle.

[0004] 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. For this reason, it is possible to appropriately set the ejection characteristics of the ink jet head, in which the main ink droplet is ejected at a high speed to suppress the generation of unnecessary ink droplets thereafter and the frequency of repeatedly ejecting the ink droplet is increased. It is necessary to do so. For that purpose, it is important to appropriately control the vibration of the internal pressure due to the vibration of the diaphragm formed at the bottom of the ink chamber of the ink jet head. A technique for forming the bottom wall of the ink chamber into a thin diaphragm deformed by ink pressure is disclosed in JP-A-6-32072.
No. 5 discloses this. The driving method is disclosed in JP-A-2-192947.
These techniques focus on the natural vibration of a vibration system determined by the structure of the ink jet head, and control the generation of vibration unique to this system.

It is necessary to increase the vibration inherent in this system when ejecting ink droplets and to reduce the vibration after ejecting ink droplets in order to obtain good ink ejection characteristics. However, it is very difficult to make these two conditions compatible because the natural vibration changes due to environmental changes such as temperature and manufacturing errors of the ink jet head.

[0006]

SUMMARY OF THE INVENTION Therefore, in the ink jet head provided with a vibrating plate which can be deformed according to the pressure generated in the ink chamber, when the pressure of the ink chamber becomes higher than a certain value, the present applicant has proposed A configuration in which an opposing wall is disposed at a position where the opposing wall contacts the vibrating plate is proposed. According to this configuration, when the diaphragm does not hit the opposing wall,
The diaphragm bends in proportion to the pressure. That is, the compliance defined as the volume change due to the deformation of the wall with respect to the unit pressure is kept constant. However, after the diaphragm comes into contact with the opposing wall, the deformation of the diaphragm with respect to an increase in pressure becomes smaller. That is, the compliance changes and becomes smaller. This compliance is a parameter related to the determination of the natural period of the ink vibration system. Therefore, the natural period is different between the state where the diaphragm is not in contact with the opposing wall and the state where it is in contact with the opposing wall, and the natural period is short in the state where the diaphragm is in contact. In addition, the natural period differs depending on how the diaphragm hits the opposing wall. When ink is ejected, a large positive pressure is generated, the diaphragm hits the opposing wall, the response of the system becomes faster, and ink droplets are ejected at high speed. Can be. Conversely, after ejection, the diaphragm moves away from the opposing wall and the response of the system is slowed, so that fluid movement after ejection can be reduced.
Furthermore, since the characteristics of the system change nonlinearly in this way,
Specific vibration does not oscillate strongly, and unnecessary ink ejection can be suppressed.

An object of the present invention is to discharge ink droplets by applying a voltage between the diaphragm and the opposing wall, and bending the diaphragm toward the opposing wall by Coulomb force to release the voltage. It is an object of the present invention to provide a configuration in which a discharge characteristic such as a discharge weight of an ink droplet can be easily and more variously controlled in an ink jet head of a type. Another object of the present invention is to propose an ink jet head that can achieve downsizing without impairing the ink ejection characteristics. Another object of the present invention is to propose a driving method particularly suitable for such an ink jet head having a novel configuration.

[0008]

In order to solve the above-mentioned problems, an ink jet head according to the present invention comprises an ink nozzle for discharging ink, and an ink chamber communicating with the nozzle and holding the ink. An ink supply path for supplying ink to the ink chamber, a diaphragm formed on a peripheral wall that defines the ink chamber, and elastically displaceable in an out-of-plane direction; An electrode formed opposite to the vibration plate, an electric pulse is applied between the vibration plate and the electrode, and a pressure fluctuation generated in the ink chamber in response to the vibration of the vibration plate. Use
In the ink jet head for ejecting ink droplets from the ink nozzle, the electrode is divided into a plurality of electrode portions, and the electrode portions are connected to each other by a resistor.

Here, the time required for charging the electrode portion corresponding to the ink supply path side of the ink chamber can be minimized as compared with the time required for charging the other electrode portions. In particular, it can be reduced to 1/10 or less.

The resistor is preferably a high-resistance semiconductor film, and is preferably amorphous silicon, amorphous silicon carbide, titanium oxide or diamond.

On the other hand, the present invention relates to a method for driving an ink jet head having the above-mentioned structure, and vibrates the diaphragm while controlling the contact state of the diaphragm corresponding to the electrode portion having a different charging time. The ejection characteristics of the ink droplets ejected from the ink nozzles are controlled.

[0012]

In the ink jet head according to the present invention, the electrodes are composed of a plurality of electrode parts, and the electrode parts are connected to each other by a resistor. The area where the diaphragm contacts the opposing wall changes according to the application time. Therefore, the state of close contact of the diaphragm with the opposing wall can be controlled in a stepwise manner in accordance with the application time of the electric pulse, so that the ink discharge characteristics can be stably switched in a stepwise manner.

Further, if the time required for charging the electrode portion corresponding to the ink supply path side of the ink chamber is set to be the shortest as compared with the other electrode portions, the elastic displacement of the diaphragm will be reduced from the supply port side of the ink chamber. This elastic displacement propagates toward the ink ejection side. Further, the return of the elastic displacement of the diaphragm to the standby state starts from the supply port side of the ink chamber and propagates toward the ink discharge side. As a result, the flow of ink in the ink chamber flows in the ink supply direction. Therefore, the ink discharge operation can be performed efficiently.

On the other hand, according to the driving method of the present invention, the diaphragm is vibrated while controlling the abutting state of the diaphragm corresponding to the electrode portion having a different time required for charging the ink jet head having the above configuration. . By controlling the state of close contact of the diaphragm with the opposing wall in this manner, the discharge characteristics such as the ink discharge amount can be controlled. Therefore, various ejection characteristics can be realized with one inkjet head.

[0015]

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, an ink jet head 1 has a silicon substrate 2 sandwiched therebetween, a nozzle plate 3 also made of silicon on the upper side, and a borosilicate glass substrate 4 having a thermal expansion coefficient close to that of silicon on the lower side. 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 an ink connecting the common ink chamber 6 to each ink chamber 5. Grooves each functioning as a supply path 7 are machined. These grooves are closed by the nozzle plate 3 and each part 5, 6, 7
Are formed.

In the nozzle plate 3, ink nozzles 11 are formed at positions corresponding to the front end portions of the respective ink chambers 5, and these are communicated with the respective ink chambers 5. An ink supply port 12 (see FIG. 2) communicating with the nozzle plate 3 is formed in a portion of the nozzle plate 3 where the common ink chamber 6 is located. The ink is supplied from an external ink tank (not shown) to the common ink chamber 6 through the ink supply port 12. The ink supplied to the common ink chamber 6 passes through each ink supply path 7 and passes through the independent ink chambers 5.
Supplied to

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

Next, in the glass substrate 4 located below the silicon substrate 2, the upper surface of the glass substrate 4, which is in contact with the silicon substrate 2, is located at a position corresponding to each ink chamber 5 of the silicon substrate 2. , A shallowly 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 having the recess 9 formed with a very small gap G.

Here, the bottom wall 51 of each ink chamber 5 functions as a common electrode on each ink chamber side. 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. As described above, with the insulating layer 15 formed on the segment electrode 10 and the gap G interposed therebetween, each ink chamber bottom wall 51 and the corresponding segment electrode 10 form a counter electrode. Details of the segment electrode 10 will be described later.

As shown in FIG. 2, a voltage applying means 21 for driving the ink-jet head charges and discharges between these opposing electrodes in response to an external print signal (not shown). One output of the voltage applying means 21 is connected to each segment electrode 10 via the segment electrode terminal 13, 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, a voltage can be supplied from the common electrode terminal 22 to the common electrode on the bottom wall 51. When it is necessary to supply a voltage to the common electrode with a 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, since the anodic bonding is used to connect the silicon substrate 2 and the glass substrate 4, a conductive film is formed on the flow channel forming surface side of the silicon substrate 2.

As described above, in the present embodiment, the bottom wall 51,
On the other hand, an opposing electrode is formed between the insulating film 15 and the opposing wall 91 opposing the gap G therebetween. When the driving voltage from the voltage applying means 21 is applied between the opposing electrodes, Coulomb force is generated by the electric charge charged between the opposing electrodes, and the bottom wall (diaphragm) 51 bends toward the segment electrode 10 and the ink The volume of the chamber 5 increases. Next, when the voltage between the opposing electrodes is suddenly 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, a part of the ink filling the ink chamber 5 is ejected as ink droplets from the ink nozzle 11 communicating with the ink chamber.

(Segment Electrode) Next, with reference mainly to FIG. 2, the segment electrode 10 in this embodiment will be described in detail. As shown in the figure, the segment electrode 1
0 is divided into electrode portions 10a, 10b and 10c. The divided electrode portions 10a and 10b are connected to a resistor 10x
And the electrode portions 10b and 10c are connected by a resistor 10y. One output of the voltage applying means 21 is connected to the electrode portion 10c on the ink supply path 7 side via the segment electrode terminal 13.

In the case of this type of ink jet head utilizing Coulomb force, the capacitance between the opposing electrodes is practically about 5 to 600 pF due to the limitation of the driving voltage and the resolution. If the capacitance is smaller than 5 pF, the required ink droplet cannot be ejected because the area of the diaphragm is small. Further, the gap G becomes too wide, and the driving voltage rises extremely.

If the capacitance is larger than 600 pF, the required resolution cannot be obtained because the area of the diaphragm is large. Further, since the gap G becomes narrow, the amplitude of the diaphragm becomes small, and it is not possible to secure necessary ink droplets.

On the other hand, the pulse width of the voltage applied between the opposing electrodes is such that the frequency of ink ejection (ejection frequency) is several kHz to
Since it is several tens of kHz, 2 to 40 μsec is realistic. Therefore, the resistances of the resistors 10x and 10y need to be several kΩ to several MΩ from the above-mentioned capacitance and pulse width. The resistance is determined by the resistivity, the width, the thickness, and the length of the substance, but the length is preferably short from the viewpoint of miniaturization of the ink jet head. Therefore, a high-resistance semiconductor film having a high resistivity is suitable. In this embodiment, amorphous silicon, which is a representative of the high-resistance semiconductor film, is employed. However, other examples include amorphous silicon carbide, titanium oxide, and diamond.

As a method for forming these high-resistance semiconductor films, there is a method in which a film is formed by a normal CVD method, a plasma CVD method, or a sputter deposition method, and photoetching is performed.

The resistances of the resistors 10x and 10y are determined according to the elastic characteristics and dimensions of the diaphragm and in accordance with each specific example.
It is a property that should be appropriately set to an optimal value.

In the ink jet head 1 of the present embodiment having the above-described structure, the diaphragm 51 as the bottom wall of each ink chamber is in a displaced state (vibration state) in which the diaphragm 51 does not elastically displace until it hits the opposing wall 91. Deflected 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 bend further when the ink pressure is increased in a state in which the diaphragm 51 is in close contact with the opposing wall, so that the compliance is reduced. Become smaller.

Next, the time constant will be described. FIG. 4 shows an equivalent circuit of the capacitance and resistance acting between one diaphragm and the corresponding segment electrode. Here, the electrode portion 10a and the portion of the diaphragm corresponding to this portion (hereinafter, referred to as the electrode portion 10a)
The capacitance of the diaphragm 51a) is Ca, the time constant is τa,
The capacitance of the electrode portion 10b and the portion of the diaphragm corresponding to this portion (hereinafter referred to as diaphragm 51b) is Cb, and the time constant is τ.
b, the capacitance of the electrode portion 10c and the portion of the diaphragm corresponding to this portion (hereinafter referred to as the diaphragm 51c) is Cc, and the time constant is τc. The resistance of the resistor 10x is Rx, the resistance of the resistor 10y is Ry, and the resistance between the electrode portion 10c and the segment electrode terminal 13 is Rz. The capacitance of the electrode portion has the relationship of Expression (1), and the resistance of the resistor is expressed by Expression (2).
, The time constants acting on the respective electrode portions are as shown in equations (3) to (5).

Ca ≒ Cb ≒ Cc Formula (1) Rz ≦ Ry = Rx Further, Rz <Ry <Rx In particular, Rz≪Ry≪Rx Formula (2) τa = Ca × (Rx + Ry + Rz) Formula (3) τb = Cb × (Ry + Rz) Equation (4) τc = Cc × Rz Equation (5) Here, a square wave is input to the diaphragm 51 and the segment electrode 10 and the time from the start of charging (rise of the square wave) is t1.
, The potential difference Vt acting between the counter electrodes at time t1
1 is as follows when the potential difference of the square wave is V and the time constant is τ.

Vt1 = V {1−exp (−t1 / τ)} Equation (6) The suction force acting between the diaphragm 51 and the segment electrode 10 is:
Since the equations (3) to (5) are applied to the equation (6) because the potential difference is proportional to the square of the potential difference between the opposing electrodes, the diaphragm 51
The diaphragm 51c corresponding to the electrode portion 10c having the smallest time constant has the shortest time required for contacting with the opposing wall 91. The longest time required for contact is the diaphragm 51a corresponding to the electrode portion 10a.

Similarly, at the time of discharge, when a square wave is input to the diaphragm 51 and the segment electrode 10 and the time from the start of discharge (fall of the square wave) is t2, the potential difference between the opposing electrodes at time t2. Vt2 is as follows when the potential difference of the square wave is V and the time constant is τ.

Vt2 = V {exp (−t2 / τ)} Equation (7) Similarly, when Equations (3) to (5) are applied to Equation (7),
The diaphragm 51c corresponding to the electrode portion 10c having the smallest time constant has the shortest time required for the diaphragm 51 to return from the state in which the diaphragm 51 contacts the opposing wall 91 to the standby state. The longest time required until the standby state is the diaphragm 51a corresponding to the electrode portion 10a.

The capacitance of the electrode portion is expressed as Ca = Cb = Cc = 5
0 pF, the resistance of the resistor is Rz = 3 kΩ, Ry = Rx = 3
When 0 kΩ is applied and a square-wave pulse voltage is applied between the terminals, Cc is charged after 0.5 μsec, Cb is charged after 5 μsec, and Ca is charged after 9.5 μsec. It will come in contact with a delay.

Further, by applying the time of the pulse voltage in accordance with the time constant of the electrode portion, the compliance of the vibration system can be changed. Since the compliance is one variable that determines the natural frequency of the vibration system, by changing the compliance in this way, the natural frequency of the ink vibration system can be controlled, and the amount of the ejected ink droplet can be adjusted.

For example, as shown in FIG. 5, when the portion 51a of the diaphragm 51, the portion 51b of the diaphragm 51, and the portion 51c of the diaphragm 51 are sucked toward the opposing wall 91, the time constant is the smallest. If only the portion 51c of the diaphragm 51 of τc is elastically returned to the standby state, the compliance is proportional to the length of the diaphragm. Can be reduced,
Therefore, compared to the case where the whole diaphragm is vibrated,
The natural period of the ink vibration system is shortened, and minute ink droplets can be ejected at high speed.

Here, in this example, the electrode portion 10c having the smallest time constant is set to the base end side (supply port side) of the ink chamber 5,
The electrode portion 10a having the largest time constant is formed so as to be on the tip side (nozzle side) of the ink chamber 5. Therefore, the elastic displacement of the vibration plate 5 occurs from the ink supply side, which is the base end side of the ink chamber 5, and the elastic displacement propagates toward the ink ejection side. That is, as shown in FIG.
The elastic displacement of the diaphragm 51 occurs so that the ink flows in the supply direction. Further, the return of the elastic displacement of the diaphragm 5 to the standby state occurs from the ink supply side, which is the base end side of the ink chamber 5, and the return of the elastic displacement to the standby state propagates toward the ink ejection side. To go. That is, as shown in FIG. 7, the vibration plate 51 is moved so that the ink flows in the supply direction.
Is returned to the standby state of the elastic displacement of the motor. Therefore, there is an advantage that the ink discharging operation can be performed efficiently. This means that to get the same amount of ink,
This means that the length of the diaphragm can be reduced. That is, the size of the inkjet head can be reduced.

In this embodiment, the segment electrode is divided into three and the adjacent electrode portions are connected by a resistor. However, the segment electrode may be divided into two and connected by a resistor.
It may be divided into two or more and connected with a resistor.

(Driving Method of Ink Jet Head) Next, a driving method of the ink jet head having the above configuration will be described with reference to FIGS. In particular, a control method after the driving voltage applied between the opposing electrodes by the voltage applying unit 21 is released will be described.

FIG. 8 shows an example of the voltage waveform between the opposing electrodes. Charging is performed such that the voltage between the opposing electrodes rises to the peak voltage Vo at time t1 (V10), and thereafter, the peak voltage Vo is held until time t2. Thereafter, discharge is performed as described below, and ink droplets are ejected.

In this example, in the portion where the waveform portion V11 falls, that is, in the discharging process between the opposing electrodes, the first section V has a steep slope of the voltage drop with respect to time.
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 from t1 to t2 when the voltage between the opposing electrodes is held at the peak voltage Vo, the discharge is started at the time t2, and the voltage drops to Va along the first section V12 where the voltage drop is sharp. After the time point t3 when the voltage value reaches this value, the voltage drops to zero along the second section V13 of the gentle voltage drop.

Here, in the voltage applying means 21 of the present embodiment, the magnitude of the voltage drop in the first section V12 can be changed. For example, as shown in FIG.
a, Vb, and Vc. Voltage V
When the voltage is switched to b or Vc, after the voltage drops to this voltage, discharge is performed at the same voltage drop rate as that of the section V13. That is, the voltage is decreased along the lines represented by the sections V14 and V15.

The voltage application means 21 performs charging / discharging between the opposing electrodes so that the voltage waveform between the opposing electrodes changes as described above, and discharges ink droplets. 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 point t3 of the voltage Va, the diaphragm 51 becomes as follows. Operate. The voltage between the opposing electrodes is the voltage V
While descending to the point of time a, the portion 51c of the diaphragm 51 corresponding to the smallest time constant τc is first separated from the surface 91a of the opposing wall 91 toward the inside of the ink chamber 5 by the elastic return force. Elastically displaced.

FIG. 9 shows this elastic displacement state. Thereafter, since the voltage drop is gradual, the portion 51b of the diaphragm corresponding to the medium time constant τb and the portion 51a of the diaphragm corresponding to τa having the largest time constant sequentially come from the opposing wall 91. It returns to the ink chamber side by the elastic return force. Therefore, basically, the ink droplets are ejected by the ink pressure in the ink chamber 5 generated by the elastic displacement by the portion 51c of the vibration plate 51 corresponding to the smallest time constant τc. In this case, the portion 51b of the diaphragm corresponding to the medium time constant τb and the portion 51a of the diaphragm corresponding to the largest time constant τa substantially contact the surfaces 91b and 91a of the opposed wall 91, respectively. State and therefore the compliance of the ink oscillating system is small. Therefore, its natural period can be shortened,
Fine ink droplets can be ejected at high speed.

On the other hand, when the voltage applied between the opposite electrodes is discharged, when the voltage is gradually decreased along the waveform portion V14 from the time when the voltage decreases to the value Vb,
As shown by the broken line in FIG. 9, the diaphragm 51 has a portion of the diaphragm corresponding to τc having the smallest time constant and portions 51c and 51b corresponding to τb having a medium time constant and portions 91c and 91b of the opposing wall. The ink is ejected by being displaced toward the ink chamber 5 by the elastic return force apart from the ink chamber 5. In this case, the portion 51c of the diaphragm 51 corresponding to τa having the largest time constant does not substantially contribute to the ink ejection operation, and is in contact with the surface 91c of the opposing wall 91. Therefore, the compliance of the ink vibration system is larger than that of the case shown by the broken line in FIG.

On the other hand, when the discharge of the voltage applied between the opposing electrodes is rapidly performed until the voltage becomes Vc, substantially all parts of the diaphragm 51 are substantially removed as shown by imaginary lines in FIG. Is elastically displaced into the ink chamber by the elastic return force, thereby contributing to the ink ejection operation. Therefore, in this case, there is no portion of the diaphragm in contact with the opposing wall 91, the compliance is maximized, and the occurrence of excessive ink pressure can be reduced. Therefore, large ink droplets can be stably ejected.

As described above, by changing the voltage drop characteristics at the time of discharge between the opposing electrodes, the ink discharge characteristics of the ink nozzle 11, in particular, its cycle and ink droplet weight can be changed.

Next, FIG. 10 shows a voltage waveform between other counter electrodes applicable to the driving of the ink jet head 1 shown in FIGS. In this example, charge and discharge (V30 to V32) for discharging ink droplets and charge and discharge (V33 to V3) for controlling the discharge amount of the ink droplets are performed.
The charging and discharging of 5) are performed twice in total. In the present embodiment, the discharge ink amount is controlled by changing the start time of the auxiliary charging V33.

When charging / discharging is performed as described above, the diaphragm 51 is charged to the voltage Vo, so that the diaphragm 51
When it is pulled and adhered to the side, and this is discharged,
After time t2 in the figure, the diaphragm 51 returns to its original position by its elastic return force, and is further displaced further into the ink chamber 5. As a result, the internal pressure of the ink chamber rapidly increases, and ink droplets are ejected from the ink nozzles 11.
Ta-t, which is a point in time when the ink droplet is completely ejected from the nozzle 11, that is, a point in time before the time when the ink runs out.
The auxiliary charging V33 is started from c.

When the auxiliary charge V33 is started at the earliest time ta after the end of the discharge V32 (V33a), the entire diaphragm 51 is pulled toward the opposing wall 91 and undergoes a large elastic displacement. As a result, the ink pressure in the ink chamber drops temporarily and suddenly, and the ink drops in the process of being ejected are sucked into the ink chamber. As a result, the amount of ejected ink is significantly reduced, and minute ink droplets are ejected, so that a small dot print is formed on the recording paper.

On the other hand, when the auxiliary charging V33 is started from tb (V33b), only the portions 51b and 51c of the diaphragm 51 corresponding to the medium time constant τb and the smallest time constant τc are used. Is the surface 91b of the opposing wall 91,
It is drawn to the side of 91c. Therefore, the elastic deformation of the vibration plate 51 is smaller than in the above case, and the degree of the pressure drop in the ink chamber is smaller. Therefore, a larger amount of ink droplets are ejected than in the above case.

On the other hand, when the auxiliary charging V33 is started from the latest tc (V33c), only the portion 51c of the diaphragm corresponding to τc having the smallest time constant is drawn to the surface 91c on the side of the opposing wall. Therefore, the amount of elastic displacement of the diaphragm is very small, so that a large amount of ink droplets are ejected and large dot printing can be performed.

As shown in the above example, the amount of ink droplets to be ejected can be adjusted by changing the start time of the auxiliary charging.

Here, such control of the discharge ink amount can also be realized by charging and discharging as shown in FIG. In the voltage waveform between the opposing electrodes shown in FIG. 11, charge / discharge (V20 to V22) for ink discharge is performed, and then auxiliary charge / discharge (V23 to V25) is performed as in the above-described example. However, in this example, the auxiliary charging V23 is further performed after a lapse of a certain period from the time point t4 when the first charge / discharge ends. This auxiliary charging V23 starts at time t5, reaches the peak voltage Va at time t6, and ends. After the voltage peak is held from time t6 to time t7, discharge is performed from time t7 to time t8. In the present embodiment, the value of this peak voltage is set to Va, V by controlling the charging time.
It is possible to switch to b and Vc.

When charging / discharging is performed in this manner, the diaphragm 51 is charged to the voltage Vo, so that the diaphragm 51 is moved to the opposite wall 91.
When it is pulled and adhered to the side, and this is discharged,
After time t2 in the figure, the diaphragm 51 returns to its original position by its elastic return force, and is further displaced further into the ink chamber 5. As a result, the internal pressure of the ink chamber rapidly increases, and ink droplets are ejected from the ink nozzles 11.
The auxiliary charging V23 is started at a time point t5 when the ink droplet is completely ejected from the nozzle 11, that is, a time point before the time when the ink runs out.

When the peak value of the auxiliary charge V23 is set to the largest value Va (V24a), the amount of ink droplets in the process of being discharged is greatly reduced, and the discharge of minute ink droplets can be realized. Conversely, when the peak value of the auxiliary charge V23 is set to the smallest value Vc (V24c), the suction effect of the ink droplet with the discharging process is very small, so that the ink discharge amount is large, and therefore a large dot printing is performed. It can be performed. When the peak value of the auxiliary charge V23 is set to the intermediate value Vb (V24b),
The ejection of an ink droplet of an intermediate amount between these is performed. As described above, by changing the peak value of the voltage of the auxiliary charge, the amount of the ejected ink droplet can be adjusted.

Of course, by combining the example shown in FIG. 10 described above with the case of this example, the value of the peak voltage of the auxiliary charging and the start timing thereof may be changed simultaneously.

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

(Driving Circuit of Inkjet Head) Next, a driving circuit of the ink jet head having the above configuration will be described with reference to FIGS.

FIG. 12 shows an example of a drive circuit for obtaining the voltage waveform between the opposed electrodes shown in FIG. In the drawing, reference symbol IN1 denotes an input terminal of a charging signal for bending the diaphragm 51, a signal having a waveform shown in FIG. 13A is input, and IN2 denotes a counter electrode (vibration) in a charged state. A signal having a waveform shown in FIG. 13B is input to an input terminal of a discharge signal for discharging the electric charge of the plate 51 and the opposing wall 91) and restoring the diaphragm 51. A first constant current circuit 40 is connected to the input terminal IN1 via a transistor Q1 for level shift. 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.

In the drawing, reference numeral 410 denotes a discharge amount control circuit, which includes first and second one-shot multivibrators MV1 and MV1.
V2. The first one-shot multivibrator MV1 operates when a discharge signal is input, and outputs a signal having a pulse width Tx. Pulse width T output from first one-shot multivibrator MV1
x can be controlled to a desired width, and in this example, 3
It is configured so that a type of pulse width can be selected. The second one-shot multivibrator MV2 outputs a signal having a pulse width Td in synchronization with the fall of the pulse output from the first one-shot multivibrator MV1.

The second constant current circuit 420 is connected to the output terminal of the first one-shot multivibrator, and the third constant current circuit 430 is connected to the output terminal of the second one-shot multivibrator. . Second constant current circuit 4
Reference numeral 20 includes transistors Q4 and Q5 and a resistor R2, and is configured to discharge the charge of the capacitor C at a constant current value while the signal Tx is being output from the ejection amount control circuit 41. Also, 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 with 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 such that the discharge speed performed by the third constant current circuit is lower than that performed by the second constant current circuit.

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

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

As a result, while the charging signal is being input, the capacitor C is charged with a constant current, and in this state, the transistors T, T, T, T. .. Selected by a dot forming signal or the like and turned on, the transistors T, T, T...
The counter electrode is charged via. 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 diagram shown in FIG. When the charging signal (a) shown in FIG. 13 is input to the terminal IN1, the transistor Q1 is turned on by its rising edge, and thereby the transistor Q2 constituting the first constant current circuit 400 is turned on. A current flows into the connected capacitor C via the resistor R1.

The terminal voltage of the resistor R1 is the voltage between the base and the emitter of the transistor Q3. When the transistor Q3 is on, the voltage between the base and the emitter is constant. The current will be maintained at a constant value.

As a result, the terminal voltage of the capacitor is
As shown in FIG. 3 (c), the voltage rises linearly from 0 volt with a constant gradient τ1. The 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 opposed electrodes can be set to a predetermined value.

The terminal voltage of the capacitor C is amplified by the transistors Q6 and Q7, applied from the output terminal OUT to between the opposing electrodes, and selectively turned on by the dot forming signal. The transistors T, T, T,. Only between the specific counter electrodes is charged at a predetermined gradient τ1 via (FIG. 13
As a result, the diaphragm 51 is sucked toward the segment electrode 10 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 specified by the pulse width To of the charging signal elapses, the transistor Q1 is turned off, and 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
It is maintained in a state of being sucked to zero.

After a lapse of a predetermined time Th, a discharge signal is input to IN2. (FIG. 13 (b)) Thereby, the signal (FIG. 13 (c)) of the pulse width Tx is output from the first one-shot multivibrator MV1 of the ejection amount control circuit 410.

The transistor Q4 constituting the second constant current circuit 420 is turned on, and the electric charge of the capacitor C is discharged via the resistor R2. Since the terminal voltage of the resistor R2 is the voltage between the base and the emitter of the transistor Q5, it operates in the same manner as the first constant current circuit 400 described above 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 slope τ2 based on the adjusted resistance value of the resistor R2. This falling voltage is determined by the transistor Q
8, Q9, which is applied to the output terminal OUT, but is charged only between the opposing electrodes of the nozzles on which dots are to be formed, so that only these opposing electrodes are diodes D, D, D
.., And the diaphragm 51 recovers at a speed determined by this.

In the process of restoring the diaphragm, when the time determined by the pulse width Tx of the first one-shot multivibrator MV1 elapses, the transistor Q4 turns off. At the same time, a signal of pulse width Td from the second one-shot multivibrator MV2 of the ejection amount control circuit 410 (FIG. 13)
(D)) is output. As a result, the second constant current circuit 4
The discharging that has been performed through the resistor R2 of the transistor 20 stops, and the transistor Q1 forming the third constant current circuit 430 is stopped.
0 turns on, and the electric charge of the capacitor C is discharged via 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 is changed to the terminal voltage of the resistor R after a lapse of time determined by the pulse width Tx.
3 linearly descends at a gradient τ3 based on the resistance value of “3”. In other words, the electric charge between the opposite electrodes discharged at the falling slope τ2 becomes equal to the slope τ2 after the lapse of time determined by the pulse width Tx.
The discharge is performed at a falling slope τ3 smaller than 2. Note that the second one-shot multivibrator MV2
Is set in advance so that it falls after the electric charge between the opposing electrodes is 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 discharge amount control signal, and three types of ink discharge amounts can be selected.

When ejecting the smallest amount of ink droplet,
The signal with the shortest pulse width Tx (solid line in FIG. 13C)
Is output from the first one-shot multivibrator MV1. As a result, the electric charge stored between the counter electrodes is discharged with a gradient τ2 up to the voltage Va, and thereafter the gradient τ3
It is discharged by. (The solid line in FIG. 13E) At this time, as shown in FIG. 9, the ink pressure in the ink chamber 5 generated by the elastic displacement by the portion 51c of the vibration plate 51 corresponding to the portion of τc having the smallest time constant. As a result, ink droplets are ejected.

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

When a medium amount of ink droplet is ejected, the electric charge stored between the opposing electrodes becomes 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 first one-shot multivibrator MV1 discharges at a gradient τ2 and then discharges at a gradient τ3. As a result, the portions 51c and 51b of the diaphragm 51 corresponding to the smallest time constant τc and the medium time constant τb are separated from the opposing wall portions 91c and 91b and displaced toward the ink chamber 5 by the elastic return force. Then, ink is ejected.

As described above, by using the driving circuit of this embodiment,
The voltage drop characteristics at the time of discharge between the opposing electrodes can be easily changed, and as a result, the weight of ink droplets ejected from each nozzle can be controlled.

Further, by applying the driving circuit of this embodiment, a plurality of constant current circuits and a circuit for switching between them are provided.
The charge / discharge waveforms shown in FIGS. 10 and 11 can be obtained by combining a one-shot multivibrator, a delay circuit, a plurality of constant voltage circuits, and circuits for switching between them.

[0084]

As described above, in the ink jet head of the present invention, the electrodes are constituted by a plurality of electrode portions, and the electrode portions are connected to each other by the resistor. According to this configuration, the area where the diaphragm contacts the opposing wall changes according to the application time of the electric pulse.
Therefore, it is possible to variously control the ejection amount of the ink.

Further, if the time required for charging the electrode portion corresponding to the ink supply path side of the ink chamber is set to be the shortest as compared with the time required for charging the other electrode portions, it is particularly preferable that 1 /
If the number is set to 10 or less, the ink flow in the ink chamber flows in the ink supply direction, so that the ink discharge operation can be performed efficiently. That is, the size of the inkjet head can be reduced.

On the other hand, according to the structure of the present invention, the electrode portions are connected to each other by the resistor, and the time constant is made different for each electrode portion. If the resistor is made of a high-resistance semiconductor film such as amorphous silicon, amorphous silicon carbide, titanium oxide, or diamond, it is possible to prevent an increase in the size of the ink jet head in order to secure an effective time constant.

On the other hand, according to the present invention, when driving the ink jet head having the electrode portions having different time constants as described above, the voltage drop characteristic at the time of discharging the electric charge stored between the opposing electrodes is changed. Like that. Alternatively, the auxiliary charging / discharging is further performed after the charging / discharging for discharging the ink, and the peak voltage value of the auxiliary charging / discharging, together with or separately from the start time of the charging of the auxiliary charging / discharging, is determined. I am trying to change it. If this driving method is adopted, for example, the diaphragm is pulled in a state where only the portion of the diaphragm corresponding to the electrode portion having the smallest time constant is sucked to the opposing wall, that is, the compliance of the ink vibration system is reduced. It is possible to obtain an effect that the ink can be elastically displaced and the ink ejection characteristics such as the amount of ejected ink can be variously changed.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an ink jet head to which the present invention is applied.

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

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 equivalent circuit between one vibration plate and an electrode facing the vibration plate of the ink jet head of FIG. 1;

FIG. 5 is an explanatory diagram showing an elastic displacement state of a diaphragm of the inkjet head of FIG. 1;

FIG. 6 is an explanatory diagram showing an elastic displacement state of a diaphragm of the inkjet head of FIG. 1;

FIG. 7 is an explanatory diagram showing an elastic displacement state of a diaphragm of the inkjet head of FIG. 1;

8 is a waveform diagram showing a voltage waveform between opposed electrodes of the inkjet head of FIG.

FIG. 9 is an explanatory diagram showing an elastic displacement state of a diaphragm in the ink jet head of FIG. 1;

FIG. 10 is a waveform chart showing another example of the voltage waveform between the opposing electrodes of the inkjet head of FIG.

FIG. 11 is a waveform chart showing still another example of the voltage waveform between the opposing electrodes of the ink jet head of FIG.

FIG. 12 is a circuit diagram showing one embodiment of a drive circuit of the inkjet head of FIG. 1;

13 is a signal waveform diagram illustrating an operation of the drive circuit of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink jet head 2 Substrate 3 Nozzle plate 4 Glass substrate 5 Ink chamber 51 Vibration plate (bottom wall of ink chamber) 51a Part of diaphragm corresponding to the largest time constant 51b Part of diaphragm corresponding to a medium time constant 51c The portion of the diaphragm corresponding to the smallest time constant 6 The common ink chamber 7 The ink supply path 9 The concave portion 91 The facing wall 91a The surface of the facing wall facing the portion 51a of the diaphragm 91b The surface of the facing wall facing the portion 51b of the diaphragm 91c Surface of opposing wall opposing portion 51c of diaphragm 92 Opposite wall surface 10 Segment electrode 10a Electrode portion having largest time constant 10b Electrode portion having medium time constant 10c Electrode portion having smallest time constant 10x Resistor 10y Resistance Body 11 Ink nozzle 12 Ink supply port 13 Segment electrode terminal 21 Voltage applying means 22 Common electrode terminal G Gap between diaphragm and opposing wall

Claims (6)

[Claims] 1. An ink nozzle for discharging ink, an ink chamber communicating with the nozzle and holding the ink, an ink supply path for supplying ink to the ink chamber, and partitioning the ink chamber. A vibrating plate formed on the peripheral wall and being elastically displaceable in an out-of-plane direction; and an electrode formed outside the ink chamber so as to face the vibrating plate. An electric pulse is applied between the electrode and the electrode, and an ink jet head that ejects ink droplets from the ink nozzles by utilizing a pressure change generated in the ink chamber in accordance with the vibration of the vibration plate, wherein the electrode is An ink-jet head, wherein the ink-jet head is divided into a plurality of electrode portions, and the electrode portions are connected to each other by a resistor. 2. The ink-jet apparatus according to claim 1, wherein the time required to charge an electrode portion corresponding to the ink supply path side of the ink chamber is the smallest as compared to the time required to charge another electrode portion. head. 3. The method according to claim 2, wherein the time required to charge an electrode portion corresponding to the ink supply path side of the ink chamber is 1/10 or less of the time required to charge another electrode portion. Ink jet head. 4. The ink jet head according to claim 1, wherein said resistor is a high-resistance semiconductor film. 5. The semiconductor device according to claim 4, wherein the high-resistance semiconductor film is amorphous silicon, amorphous silicon carbide,
An ink jet head comprising titanium oxide or diamond. 6. An ink nozzle for discharging ink, an ink chamber communicating with the nozzle and holding the ink, an ink supply path for supplying ink to the ink chamber, and partitioning the ink chamber. A vibrating plate formed on the peripheral wall and being elastically displaceable in an out-of-plane direction, and an electrode formed outside the ink chamber and opposed to the vibrating plate, wherein the electrode is , Divided into multiple electrode parts,
The electrode portions are connected to each other by a resistor, are formed so that the time required for charging is different, and the ink droplets are ejected from the ink nozzles by utilizing the pressure fluctuation generated in the ink chamber in response to the vibration of the diaphragm. In the method of controlling an ink jet head, the vibration plate is vibrated while controlling the contact state of the vibration plate corresponding to the electrode portion, thereby discharging ink droplets discharged from the ink nozzle. A method for driving an ink-jet head, characterized by controlling characteristics.