JPH08187847A - Driving circuit for ink jet head - Google Patents

Abstract

PURPOSE: To attempt improvement of discharge efficiency of an ink jet head and its frequency responsiveness by a method wherein driving voltage having a waveform which satisfies a specific formula in pressurizing ink and in reduced pressure of the ink, is generated. CONSTITUTION: Where variation rate in time of charging voltage of a piezoelectric element in pressurizing ink is (α) for the driving voltage Vp, maximum value of the variation rate in time (α) during the charging period tr is (αm), its minimum value is (αn), and a risen content in voltage of the driving voltage risen during charging period α=αm is taken as Vαm, the relation between (αm) and (αn) satisfies αn>=(1/8)*αm or the relation between Vαm and Vp satisfies Vαm>=(1/2)*Vp. Besides, where variation rate in time of discharge voltage of the piezoelectric element in reduced pressure of ink is taken as -β, and during discharged period (tf) when the discharged period is taken as (tf), variation rate in time just before end time of discharge is taken as (-βk), and discharge time resulting in β<(Vp/tb) is taken as tbβ, the relation between Vp/tf, βk, and β1 satisfies the formula β1>(Vp/tf)>βk.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an inkjet head, and more particularly to a drop-on-demand (DO)
The present invention relates to a drive circuit for a D) type inkjet head.

[0002]

2. Description of the Related Art As an ink jet recording system, a so-called drop-on-demand (DOD) type system in which ink is ejected only when a recording signal is input is predominant. Among the DOD methods, there is a so-called bubble jet method (Japanese Patent Publication No. 61-59913, etc.) that utilizes bubbles generated in ink by thermal energy, and a piezo actuator method that uses a piezoelectric element (Japanese Patent Publication No. 60-895).
No. 3, etc.)

The latter piezoelectric actuator type ink jet head is provided with a nozzle, a liquid chamber communicating with the nozzle, and a piezoelectric element for pressurizing the liquid chamber, and a pulsed drive voltage is applied to the piezoelectric element. By expanding and contracting the piezoelectric element, the ink in the liquid chamber is pressurized to eject ink droplets from the nozzle.

By the way, as a drive circuit for applying a drive voltage to a piezoelectric element of a conventional ink jet head, for example, as shown in FIG. 17A, a trapezoidal shape (or a triangular shape) in which a pulse is linearly raised with respect to the piezoelectric element. A drive voltage having a waveform of (shape) is generated and output (Japanese Patent Laid-Open No. 59-59135)
No. 136-266), or as shown in FIG. 2B, a driving voltage having a waveform having a time constant characteristic of smoothly charging the piezoelectric element is generated and output (Japanese Patent Laid-Open No. 51-104224). (See Japanese Patent Publication).

[0005]

However, in the above-mentioned conventional ink jet head drive circuit,
There is a problem that it is difficult to achieve both ink ejection efficiency and frequency response. That is, first, as shown in FIG.
The harmonic components due to the rising portion of the drive voltage of the waveform shown in (a) (hereinafter referred to as "waveform a") and the waveform shown in (b) in the figure (hereinafter referred to as "waveform b") are as shown in FIG. become.

Here, since the waveform a rises linearly (constant current) with respect to the piezoelectric element as described above, the change immediately before and after the end of charging is larger than that of the waveform b, and the harmonic component is large. growing. In this way, if the harmonic component is large,
The pressure wave of the liquid chamber generated when the piezoelectric element is driven is not attenuated even after the ink is ejected, and the response frequency is repeatedly lowered. on the other hand,
Since the waveform b is smoothly charged to the piezoelectric element,
The harmonic component is lower than that of the waveform a, and high frequency driving is possible.

FIG. 19 shows the relationship between the ink drop velocity Vj and the ejection volume Mj when driven by the drive voltage having the waveforms a and b.
Is shown in. Here, the waveform b has the same ejection volume Mj as the waveform a, but the ink droplet ejection speed Vj is about 3.
5% lower. This is because the ink drop velocity Vj is the drive voltage V
The discharge volume Mj depends on the drive voltage Vp and the pulse width Pw, which is determined by the magnitude of the pressure generated at the rising time tr of p.

Further, FIG. 20 shows how the waveforms a and b fall and the ink droplets are ejected. For waveform a,
As shown in FIG. 7C, the negative pressure generated in the liquid chamber becomes small because the slope is less steep than the waveform b immediately after the start of the fall, and as shown in FIG. A large drop S (satellite) is generated. In the case of the waveform b, negative pressure is generated to the extent that unnecessary satellites are not generated,
After that, it gradually falls with the passage of time so that the pressure wave does not remain.

As described above, the driving voltage of the waveform a has a good ink droplet ejection speed Vj, but since the waveform changes linearly immediately before and after the end of charging or immediately before and after the start of discharging, many harmonic components are contained. In addition, since the unnecessary residual pressure wave after ink ejection is increased, the frequency response is deteriorated and it is not suitable for high frequency driving. On the other hand, the drive voltage of the waveform b is suitable for high frequency drive, but the ink ejection speed Vj is not sufficient.

The present invention has been made in view of the above points, and an object of the present invention is to provide a drive circuit which improves the ejection efficiency and frequency response of an ink jet head.

[0011]

In order to solve the above problems, an ink jet head drive circuit according to a first aspect of the present invention pressurizes a plurality of nozzles, a plurality of liquid chambers communicating with each nozzle, and each liquid chamber. A plurality of piezoelectric elements for applying the driving voltage to the piezoelectric elements to press the ink in the liquid chamber to eject ink droplets from the nozzles. With respect to this drive voltage Vp, the rate of change in the charging voltage of the piezoelectric element during pressurization of ink (ΔVp / Δt)
Is α and the charging period is tr, the maximum value of the time change rate α during the charging period tr is αm, and the minimum value is αn, α.
= Vm, the relationship between αm and αn satisfies Formula 1, or the relationship between Vαm and Vp satisfies Formula 2, The time change rate (ΔVp / Δt) of the discharge voltage of the piezoelectric element during depressurization is set to −β, and the discharge period is tf.
, The time change rate immediately after the start of discharge is -β1, the time change rate immediately before the discharge end time is -βk,
When the discharge time for β <(Vp / tf) is tfβ, the relationship between Vp / tf and βk and β1 satisfies the formula 3, and the relationship between tfβ and tf has a waveform satisfying the formula 4. A waveform generating means for generating the drive voltage is provided.

[0012]

[Formula 5] αn ≧ (1/8) * αm (1)

[0013]

[Equation 6] Vαm ≧ (1/2) * Vp …… (2)

[0014]

[Formula 7] β1> (Vp / tf)> βk (3)

[0015]

[Formula 8] tfβ ≧ (1/2) * tf (4)

According to a second aspect of the present invention, there is provided a drive circuit for an ink jet head according to the first aspect, wherein when the power supply voltage is Vs, the relationship between the drive voltage Vp and the power supply voltage Vs is Vp. 9/10 of Vs
The configuration is as follows.

According to a third aspect of the present invention, there is provided an ink jet head drive circuit according to the first or second aspect of the present invention, in which the wave forming means is lower than the first power supply voltage Vs and the first power supply voltage Vs. The drive voltage is generated based on the second power supply voltage Vpd.

According to a fourth aspect of the present invention, there is provided an ink jet head drive circuit according to the third aspect, wherein the first power supply voltage Vs is resistance-ratio-divided to generate the second power supply voltage Vpd. Means were provided.

According to a fifth aspect of the present invention, in the ink jet head drive circuit according to the third aspect, a zener diode for generating the second power supply voltage Vpd from the first power supply voltage Vs is provided.

According to a sixth aspect of the present invention, there is provided a drive circuit for an ink jet head according to any one of the first to fifth aspects, wherein the drive voltage is commonly connected to the + side of the plurality of piezoelectric elements. It is configured to be applied to the plurality of piezoelectric elements via the.

[0021]

In the ink jet head drive circuit according to the first aspect of the present invention, by satisfying the equation (1) or (2) at the time of pressurizing the ink, the harmonic component generated at the rising portion of the waveform is small and the frequency response is improved, By satisfying the equations 3 and 4 when the ink is depressurized, unnecessary satellites can be prevented, the ink ejection speed Vj is less decreased, and the ink ejection efficiency is improved.

According to a second aspect of the present invention, there is provided a drive circuit for an inkjet head according to the first aspect, wherein the drive voltage Vp and the power supply voltage Vs have a relationship that Vp is 9/10 or less of Vs. Because,
The drive waveform of claim 1 can be easily obtained.

According to a third aspect of the present invention, there is provided an ink jet head drive circuit according to the first or second aspect, wherein the waveform generating means has a first power supply voltage Vs and a second power supply voltage lower than the first power supply voltage Vs. Power supply voltage Vpd
Since the drive voltage is generated based on the above, it is possible to obtain a highly accurate drive waveform.

According to a fourth aspect of the present invention, there is provided an ink jet head drive circuit according to the third aspect, wherein the first head power source voltage Vs is resistance-ratio-divided to generate the second power source voltage Vpd. Since it is provided, it is possible to easily control the drive voltage such as correction of variations in head characteristics at low cost.

According to a fifth aspect of the present invention, there is provided an ink jet head drive circuit according to the third aspect, wherein a zener diode for generating the second power supply voltage Vpd from the first power supply voltage Vs is provided. It can be implemented at low cost and in a small space.

According to a sixth aspect of the present invention, there is provided an ink jet head drive circuit according to any one of the first to fifth aspect of the present invention, wherein a drive voltage is applied via a common electrode commonly connected to the + side of the plurality of piezoelectric elements. Since it is configured to apply the voltage to a plurality of piezoelectric elements, the head can be downsized and the cost can be reduced, and the number of signal lines with the printer body can be significantly reduced.

[0027]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the present invention,
2 is a plan view of the inkjet head of FIG. 1 excluding the liquid chamber unit, FIG. 3 is a cross-sectional view including the liquid chamber unit taken along the line AA of FIG. 2, and FIG. 4 is taken along the line BB of FIG. FIG. 4 is a sectional view similar to FIG. 3.

The drive circuit of this ink jet head is
A waveform generation unit A that generates a voltage waveform that satisfies the above-described formula 1 or 2 when the ink is pressurized from the rectangular pulse and that satisfies the above-described formulas 3 and 4 when the ink is depressurized, and the output of the waveform generation unit A is inkjet. The low impedance means B for outputting to the plurality of piezoelectric elements P, P ... Of the head H, and the piezoelectric elements P, P.
Is supplied with a signal from the selection means C for selecting the piezoelectric element P to be driven.

The waveform generating means A can be composed of a ROM, a D / A converter or another pulse generating circuit and a waveform modifying circuit such as a calculus integrating circuit, a clipping circuit, a clamp circuit and the like. The low impedance means B is a buffer amplifier, SEPP
It is composed of a low impedance amplifier composed of (Single Ended Push Pull) or the like. The selection unit C includes a shift register circuit, a latch circuit, and an inkjet head H.
Each piezoelectric element P (channel, where a channel is
It is used to mean the part consisting of the nozzle, pressurized liquid chamber and piezoelectric element. ) Corresponding to the transistor and die dood array. By using a low impedance circuit, the output of the drive voltage waveform becomes a low impedance output to the piezoelectric element, and the waveform is not distorted due to variations in the piezoelectric element and the number of drive channels.

The ink jet head comprises an actuator unit 1 and a liquid chamber unit 2 joined on the actuator unit 1. The actuator unit 1 has a plurality of laminated piezoelectric elements arranged in a row (arranged in rows) on a substrate 3 made of ceramic, glass epoxy resin, or the like.
The two rows of piezoelectric element rows 4 and 4 and the frame member 5 that surrounds these two rows of piezoelectric element rows 4 and 4 are joined by a bonding agent 6. The piezoelectric element array 4 is provided with a plurality of piezoelectric elements (hereinafter referred to as “driving portion piezoelectric elements”) 7, to which a drive pulse is applied to make the ink droplets and fly.
7 and the driving portion piezoelectric elements 7, 7 and a plurality of piezoelectric elements (which are referred to as “fixing portion piezoelectric elements”) 8 and 8 which are simply the liquid chamber unit fixing member without being given a drive pulse.
... and a bi-pitch structure in which are alternately arranged.

The liquid chamber unit 2 includes two photosensitive resin films (dry film resists) 20 and 21 that form a pressurized liquid chamber, a common ink flow path, etc. on a diaphragm 12 having a diaphragm portion 11 formed thereon. The liquid chamber flow path forming member 13 is adhered, and a plurality of nozzles 1 are formed on the liquid chamber flow path forming member 13.
The nozzle plate 16 formed with No. 5 is adhered. The vibrating plate 12, the liquid chamber flow path forming member 13, and the nozzle plate 16 are used to drive the respective piezoelectric elements 7 of the piezoelectric element array 4.
7, a plurality of substantially independent pressurizing liquid chambers 17 each having a diaphragm portion 11 are formed, and fluid resistance portions 23, 23 are formed on both sides of the pressurizing liquid chamber 17, respectively. Common liquid chambers 24, 24 are formed outside 23.

On the substrate 3 of the actuator unit 1, a common electrode in which the + side of all the piezoelectric elements P (driving section piezoelectric element 7 and fixed section piezoelectric element 8) is connected inside each of the piezoelectric element rows 4 and 4. A pattern 25 is provided, and the common electrode pattern 25 is connected (wired) to the low impedance means B on the printer body side to apply a drive voltage. By doing so, the number of connections with the printer body side can be significantly reduced.

Further, by providing a selection electrode pattern 26 divided for each piezoelectric element P on the outside of each piezoelectric element array 4 and 4, and inputting a signal from the selection means C to this selection electrode pattern 26, driving is performed. The piezoelectric element P (only the driving portion piezoelectric element 7 is targeted) is selected. Here, a shift register circuit constituting the selecting means C,
The latch circuit and the transistor and diode array corresponding to each channel can be easily integrated into one chip, and this IC chip can be attached to a part, side surface, front surface, back surface, etc. of the head substrate 3 to reduce the size of the head. The cost can be reduced. The output terminal of the selection means C formed into a chip is connected to the selection electrode pattern 26, and the input signal (latch, clock, enable signal) system is connected to the printer main body through the FPC cable. If the selection electrode patterns 26 and the output terminal pitch of the selection means C formed into a chip substantially match each other, wire-bonding them
It can be directly joined by bumps (gold, solder, etc.).

The waveform of the drive voltage applied to the piezoelectric element P of the ink jet head H will be described. First, the waveform as shown in FIG. 5 (hereinafter referred to as “main waveform”).
An experiment was conducted by applying the driving voltage of No. 1 to the piezoelectric element P. This waveform has a pulse width Pw, and the time change rate (ΔVp / Δt) of the charging voltage of the piezoelectric element at the time of ink pressurization (the rising portion of the waveform) is α with respect to the drive voltage Vp of the piezoelectric element. , Three time change rates (slopes) α during the charging period tf
1, α2, α3, and the maximum value αm = α1 and the minimum value αn = α3 of the slope α. Further, the amount of voltage increase that rises during the charging period of the maximum value αm of the slope is Vαm.

Here, under the condition of Vαm = (1/2) * Vp, the minimum value αn (= α3) of the slope α is changed to the maximum value αm.
When the change of the ink droplet ejection speed Vj was tested by changing it with respect to (= α1), as shown in FIG.
Is smaller than ⅛ of the minimum value αm, the ink droplet ejection speed Vj sharply decreases.

From the above, the rate of change (Δ in the charging period tr of the piezoelectric element during the pressurization of the ink (the rising portion of the waveform) (Δ
Vp / Δt), that is, the maximum value αm and the minimum value α of the slope α
By setting n and n so as to satisfy the condition of Expression 1, the drop is small with respect to the ink droplet ejection speed Vj of the waveform (linear rising waveform) with the maximum value αm of the inclination α = the minimum value αn. (Within 30%) Ink drop ejection speed Vj
It turns out that

[0037]

[Equation 9] αn ≧ (1/8) * αm (1)

Under the condition that the gradient α ≧ (1/2) * αm, the voltage component V that rises during the charging time of the maximum gradient value αm.
When αm is changed with respect to the drive voltage Vp, the change in the ink drop ejection speed Vj was tested. As shown in FIG. 7, when the voltage increase Vαm becomes less than 1/2 of the drive voltage Vp, the ink drop ejection speed is reduced. Vj dropped sharply.

As a result, the rate of change (Δ in the charging period tr of the piezoelectric element during the pressurization of the ink (the rising portion of the waveform) (Δ
Vp / Δt), that is, the voltage component Vαm for which the slope α rises during the charging time of the maximum value αm is set so as to satisfy the condition of Expression 2 with respect to the drive voltage Vp, so that the ink having a linearly rising waveform is obtained. It can be seen that the ink drop ejection speed Vj that is less than the drop ejection speed Vj (within 20%) is obtained.

[0040]

[Formula 10] Vαm ≧ (1/2) * Vp …… (2)

Therefore, at the time of pressurizing the ink,
Alternatively, a desired ink droplet ejection velocity Vj can be obtained by satisfying the condition of Expression 2, and the harmonic component generated at the rising portion of the waveform having the slope α of the above condition is also small.

On the other hand, this waveform shows the drive voltage Vp of the piezoelectric element.
On the other hand, the time change rate (ΔVp / Δt) of the discharge voltage of the piezoelectric element at the time of ink pressure reduction (waveform falling portion) is −
Let β be three slopes (time change rates) −β1, −β2, −β3 during the discharge period tf, the time change rate immediately after the start of discharge is −β1, and the time change rate immediately before the discharge end time is −β.
k is -β3.

Here, when the discharge time of β <(Vp / tf) is tfβ, (Vp / tf) and βk (= β3)
And β1 satisfy Expression 3, and the discharge time tf
The relationship between β and the discharge period tf satisfies Expression 4.

[0044]

[Formula 11] β1> (Vp / tf)> βk (3)

[0045]

[Equation 12] tfβ ≧ (1/2) * tf (4)

Therefore, immediately after the start of discharge, the slope β1 becomes larger than that in the case of linear discharge, and an appropriate negative pressure is generated in the liquid chamber, so that unnecessary satellites after ink droplet ejection can be suppressed and at the same time, all (1/2) of discharge time tf
In the above time, the slope β is small (tfβ ≧ (1/2) * t
Because of f), the residual pressure wave can be efficiently reduced. When tfβ <(1/2) * tf, the residual pressure wave is not completely attenuated, and unnecessary satellites are generated depending on the driving frequency.

As described above, a waveform satisfying the conditions of the formulas 1 or 2 when the ink is pressurized (start-up part) and satisfying the conditions of the formulas 3 and 4 when the ink pressure is reduced (start-up part) is obtained. By applying the driving voltage that the piezoelectric element has to the piezoelectric element, the frequency response is improved and high frequency driving is possible, and the ink ejection speed Vj is not significantly reduced, and both can be achieved.

Other waveforms satisfying the same conditions as this waveform are shown in FIGS. 8, 9 and 10. The waveform of FIG. 8 has a maximum value αm of inclination at the start of rising (charging), a minimum value αn of inclination immediately before the drive voltage Vp, and a falling edge (discharge) has a pulse width Pw that is a smooth curve. It is a waveform.
The waveform in FIG. 9 has a maximum value of slope αm at the start of start-up (charging), a minimum value of slope αn immediately before the drive voltage Vp, and a smooth curve for start-up (discharge) immediately after start-up. This is the waveform that starts the fall. The waveform in FIG. 10 shows the maximum value αm of the slope after a lapse of a predetermined time after the start-up.
And has a minimum slope value αn immediately before the drive voltage Vp,
The fall (discharge) is a waveform with a pulse width Pw that is a smooth curve.

Next, specific examples of the waveform generating means A and the low impedance means B shown in FIG. 1 will be described with reference to FIG. This embodiment is a constant voltage drive circuit,
The drive voltage having the waveform shown in FIG. 8 is generated and output.

In this constant voltage drive circuit, an input terminal IN to which an input signal is given is connected to a transistor T via a buffer B.
The transistor T is connected to the base of r1 via the inverter I.
These transistors T are connected to the bases of r2 respectively.
The collector of r1 is supplied with the first power supply voltage Vs, and the emitter of the transistor Tr2 is grounded.

Between the emitter of the transistor Tr1 and the collector of the transistor Tr2 is connected a parallel circuit of a series circuit of a resistor ra and a diode D1 and a series circuit of a resistor rb and a diode D2, and these diodes D1 and D2 are connected.
1 and D2 are connected to a point, a capacitor Ck is connected between the a point and the ground, and a time constant circuit for charging with a resistor ra and a capacitor Ck and a time constant circuit for discharging with a resistor rb and a capacitor Ck. Are configured. Further, the point a connected between the capacitor Ck and the resistors ra and rb is a diode Dk.
To the second power supply voltage Vpd (Vpd <Vs). This diode Dk becomes the clip circuit 31.

The point a is set to the transistors Tr3 to Tr.
A low impedance circuit consisting of 6 is connected between the base of the transistor Tr3 on the input side and the base of the transistor Tr4, and the head H is connected between the emitter of the transistor Tr5 on the output side and the collector of the transistor Tr6.
Are connected to a common terminal COM of the plurality of piezoelectric elements P.

In the constant voltage drive circuit thus constructed, when a pulsed input signal is input to the input terminal IN, the transistor Tr1 is turned on via the buffer B and the transistor Tr2 is turned off via the inverter I. Then, the charging of the capacitor Ck is started by the first power supply voltage Vs with a time constant determined by the resistor ra and the capacitor Ck as shown in FIG. At this time, the second power supply voltage V is applied to the point a through the diode Dk (falling voltage Vd).
Since it is connected to p, the charging voltage of the capacitor Ck does not rise to the first power supply voltage Vs as shown in FIG.
It is clipped to the voltage Vp (Vp = Vpd−Vd), and this voltage becomes the maximum value of the drive voltage Vp.

When the pulsed input signal is not input to the input terminal IN, the transistor Tr1 is turned off via the buffer B and the transistor Tr2 is turned on via the inverter I, so that the resistance as shown in FIG. The capacitor Ck is discharged with a time constant determined by rb and the capacitor Ck.

In this way, a waveform satisfying the above-mentioned conditions as shown in the figure is generated and applied to the plurality of piezoelectric elements P of the ink jet head H from the point a through the low impedance circuit. Then, the first power supply voltage Vs
By generating the waveform of the drive voltage based on the second power supply voltage Vp and the second power supply voltage Vp, the mounting can be easily performed at low cost.

By the way, FIG. 13 shows the relationship between the second power supply voltage Vpd, the first power supply voltage Vs, and the slope (time change rate) α during charging regarding the waveform generated at this time. Here, if the second power supply voltage Vpd is a variable voltage with respect to the first power supply voltage Vs, the minimum value αn of the slope α can be made steeper as the second power supply voltage Vpd is made smaller. The drive voltage Vp is Vp <0.9 * Vs,
More preferably, by setting the second power supply voltage Vpd (Vs = constant) so as to satisfy the relationship of Vp ≦ 0.7 * Vs, αn> (1/8) * αm (αm = α1) As a result, the ink droplet ejection speed Vj hardly decreases, and the harmonic components can be reduced, so that high frequency driving becomes possible.

Further, when the second power supply voltage Vpd is kept constant, by increasing the first power supply voltage Vs, the minimum inclination value αn becomes large, and the minimum inclination value αn becomes the maximum inclination value. The ink ejection speed Vj
The efficiency of can be improved. The first power supply voltage V
When s = second power supply voltage Vpd, the waveform (αn = 0) shown by the broken line in FIG. 12 is obtained, and the ink ejection speed Vj is significantly reduced as in the conventional case.

Next, another example of the constant voltage drive circuit will be described with reference to FIGS. First, the constant voltage drive circuit shown in FIG. 14 includes a clip circuit 32 including resistors r1 and r2, a variable resistor r3, a diode Dk, and an electric field capacitor C for current compensation. In the clip circuit 32, the first power supply voltage Vs is applied to the resistor r1.
The resistance ratio is divided by the variable resistance t3 and the series circuit of the resistance r2, and the voltage at the voltage dividing point b is used as the second power supply voltage Vpd. As a result, the capacitor Ck has Vp = Vs *
It will be charged up to {(r2 + r3) / (r1 + r2 + r3)}-Vd.

As described above, by generating the second power supply voltage Vpd from the first power supply voltage Vs by dividing the resistance ratio, the drive voltage control such as temperature compensation and head characteristic variation correction can be easily performed at low cost. It will be possible to do.

The constant voltage drive circuit shown in FIG. 15 is configured so that the second power supply voltage Vpd generated by the clipping circuit 32 is supplied as the power supply voltage of the low impedance output stage. By doing so, the transistor loss of the low impedance circuit can be suppressed to a small value, but the capacitance of the electric field capacitor C of the clip circuit 32 becomes larger than that of the configuration of the constant voltage drive circuit of FIG.

The constant voltage drive circuit shown in FIG. 16 includes a clipping circuit 3 including a Zener diode ZD and a diode Dk.
It is equipped with 3. In this case, the Zener voltage Vz of the Zener diode ZD becomes the second power supply voltage Vpd (Vz = Vpd), and the drive voltage Vp applied to the piezoelectric element is determined by the Zener voltage Vz. Therefore, when performing voltage control of the head characteristics, it is sufficient to select a plurality of Zener diodes having different Zener voltages Vz.

In this way, the second power supply voltage Vpd is set to the first
By using the Zener diode to generate the power supply voltage Vs from, the mounting at low cost and space can be realized.

In the above-described embodiment, an example in which the nozzle opening direction is applied to a side shooter type ink jet head coaxial with the displacement direction of the piezoelectric element has been described, but the opening direction of the nozzle is the displacement direction of the piezoelectric element. The present invention can also be applied to an edge-shooter type inkjet head in a direction orthogonal to each other. Further, in the above embodiment, the bi-pitch structure in which the driving portion piezoelectric element and the fixed portion piezoelectric element are alternately arranged is used, but it is also possible to adopt the normal pitch structure in which all the piezoelectric elements are used as the driving portion. The fixed portion piezoelectric element 8 also becomes the drive portion piezoelectric element 7.

[0064]

As described above, according to the ink jet head drive circuit of the first aspect of the invention, the equations (1) and (2) are satisfied when the ink is pressurized, and the equations (3) and (4) are satisfied when the ink is depressurized. Since the waveform generating means for generating a driving voltage having a waveform is provided, the frequency response is improved, high frequency driving is possible, and the ink ejection speed is less decreased and the ink ejection efficiency is improved.

According to the ink jet head drive circuit of the second aspect, in the drive circuit of the first aspect, the relationship between the drive voltage Vp and the power supply voltage Vs is 9/10 of Vs being Vs.
Since the configuration is as follows, it is possible to easily obtain a drive waveform that satisfies the condition of claim 1.

According to the drive circuit of the ink jet head of claim 3, in the drive circuit of claim 1 or 2,
Since the waveform generating means is configured to generate the drive voltage based on the first power supply voltage Vs and the second power supply voltage Vpd lower than the first power supply voltage Vs, a highly accurate drive waveform can be obtained.

According to the ink jet head drive circuit of the fourth aspect, in the drive circuit of the third aspect, means for dividing the first power supply voltage Vs by the resistance ratio is provided to generate the second power supply voltage Vpd. In addition, it is easy to control the drive voltage such as correction of variations in head characteristics at low cost.

According to the ink jet head drive circuit of the fifth aspect, in the drive circuit of the third aspect, the Zener diode for generating the second power supply voltage Vpd from the first power supply voltage Vs is provided. It can be installed in a small space.

According to the drive circuit of the ink jet head of claim 6, in the drive circuit according to any one of claims 1 to 5, the drive voltage is supplied through the common electrode commonly connected to the + side of the plurality of piezoelectric elements. Since the voltage is applied to a plurality of piezoelectric elements, the size and cost of the head can be reduced, and the number of signal lines with the printer body can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a plan view of the inkjet head of FIG. 1 excluding a liquid chamber unit.

3 is a cross-sectional view including a liquid chamber unit taken along the line AA in FIG.

4 is a sectional view similar to FIG. 3 taken along the line BB of FIG.

FIG. 5 is a waveform diagram showing an example of a drive voltage waveform according to the present invention.

6 is a diagram showing an example of the relationship between the slope of the charging voltage and the ink ejection speed when the waveform of FIG. 5 is used.

7 is a diagram showing an example of the relationship between the amount of voltage increase of the maximum value of the slope of the charging voltage and the ink ejection speed when the waveform of FIG. 5 is used.

FIG. 8 is a waveform diagram showing another first example of the drive voltage waveform according to the present invention.

FIG. 9 is a waveform diagram showing another second example of the drive voltage waveform according to the present invention.

FIG. 10 is a waveform chart showing another third example of the drive voltage waveform according to the present invention.

FIG. 11 is a circuit diagram showing a specific example of a drive circuit according to the present invention.

FIG. 12 is a waveform diagram showing drive waveforms of the drive circuit of FIG.

FIG. 13 is a diagram showing the relationship between the second power supply voltage and the minimum value of the slope of the drive circuit of FIG.

FIG. 14 is a circuit diagram showing another first specific example of the drive circuit according to the present invention.

FIG. 15 is a circuit diagram showing another second specific example of the drive circuit according to the present invention.

FIG. 16 is a circuit diagram showing another third specific example of the drive circuit according to the present invention.

FIG. 17 is a waveform diagram showing a different example of conventional drive waveforms.

18 is a diagram showing harmonic components included in the drive waveform of FIG.

19 is a diagram showing a comparison of ink droplet ejection speed and ejection volume when the drive waveform of FIG. 17 is used.

20 is an explanatory diagram showing an ink droplet ejection state when the drive waveform of FIG. 17 is used.

[Explanation of symbols]

1 ... Actuator unit, 2 ... Liquid chamber unit, 3 ...
Substrate, 4 ... Piezoelectric element array, 5 ... Frame member, 7 ... Driving section piezoelectric element, 8 ... Fixed section piezoelectric element, 11 ... Diaphragm section, 12 ... Vibration plate, 13 ... Liquid chamber flow path forming member, 15 ... Nozzle, 16 ... Nozzle plate, 17 ... Pressurized liquid chamber, 25 ...
Common electrode pattern, 26 ... Selective electrode pattern, 31-3
3 ... Clip circuit, A ... Waveform generating means, B ... Low impedance output means, C ... Selection means, H ... Inkjet head, P ... Piezoelectric element.

Claims (6)

[Claims] 1. A plurality of nozzles, a plurality of liquid chambers communicating with each nozzle, and a plurality of piezoelectric elements for pressurizing the respective liquid chambers are provided, and by applying a drive voltage to the piezoelectric elements, the liquid In an ink jet head that pressurizes ink in a chamber to eject ink droplets from the nozzles, the driving voltage of the piezoelectric element is Vp, and the charging voltage time of the piezoelectric element at the time of pressurizing ink with respect to this driving voltage Vp Change rate (ΔVp / Δt) is α
When the charging period is tr, the maximum value of the time change rate α during the charging period tr is αm, the minimum value is αn, and α = α
The voltage increase of the drive voltage that rises during the charging period of m is V
When αm, the relationship between αm and αn satisfies Expression 1, or the relationship between Vαm and Vp satisfies Expression 2, and the time change rate of the discharge voltage of the piezoelectric element (ΔVp / Δt) is −β and the discharge period is tf, during the discharge period tf, the time change rate immediately after the start of discharge is −β1, the time change rate immediately before the discharge end time is −βk, β <.
When the discharge time to be (Vp / tf) is tfβ, V
p / tf and βk and β1 satisfy the formula 3, and tfβ and tf satisfy the formula 4 by providing the waveform generating means for generating the drive voltage having the waveform. Inkjet head drive circuit. [Formula 1] αn ≧ (1/8) * αm (1) [Formula 2] Vαm ≧ (1/2) * Vp (2) [Formula 3] β1> (Vp / tf)> βk (3) [Equation 4] tfβ ≧ (1/2) * tf (4) 2. The ink jet head drive circuit according to claim 1, wherein when the power supply voltage is Vs, the relationship between the drive voltage Vp and the power supply voltage Vs is 9 / where Vp is Vs.
A method of driving an inkjet head, which is 10 or less. 3. The circuit of the inkjet head according to claim 1, wherein the waveform generation means is based on a first power supply voltage Vs and a second power supply voltage Vpd lower than the first power supply voltage Vs. A driving circuit for an inkjet head, wherein the driving voltage is generated by the driving circuit. 4. The ink jet head drive circuit according to claim 3, further comprising means for generating the second power supply voltage Vpd by dividing the first power supply voltage Vs by a resistance ratio. Head drive circuit. 5. The ink jet head drive circuit according to claim 3, further comprising a Zener diode that generates the second power supply voltage Vpd from the first power supply voltage Vs. circuit. 6. The drive circuit for an inkjet head according to claim 1, wherein the drive voltage is applied to the plurality of piezoelectric elements via a common electrode commonly connected to the + side of the plurality of piezoelectric elements. A drive circuit for an inkjet head, characterized in that