JP2003226011A - Driving method for piezoelectric element, inkjet head and inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a driving voltage, a heating value and power consumption in driving piezoelectric elements used in an inkjet printer or the like. <P>SOLUTION: A rise time Tr or a fall time Tf of the driving voltage is made not smaller than 1/20 a natural oscillation period of the inkjet head, whereby the driving voltage, heating value and power consumption which increase by a loss because of resistance components of a charging/discharging system of wiring lines, switching elements and the like in consequence of a large current flowing if the rise or fall is steep are suppressed. The time Tr/the time Tf is made not larger than 1/3 the natural oscillation period, whereby an oscillation energy efficiency of piezoelectric elements which becomes higher as a voltage waveform rises or falls more steeply can be 80% or higher. The time Tr/the time Tf is made approximately 1/20 the natural oscillation period Ti, whereby a discharge energy by piezoelectric elements is nearly saturated. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a piezoelectric element, such as an inkjet head of an inkjet printer, an ultrasonic cleaner, an ultrasonic humidifier, an ultrasonic motor, or the like, which is driven by a rectangular wave or a trapezoidal wave. The present invention relates to an inkjet head using this driving method and an inkjet printer equipped with this head.

[0002]

2. Description of the Related Art An inkjet head of an inkjet printer has a large number of ink pressurizing chambers. In addition, the ink pressurizing chamber stores ink therein and has a nozzle for ejecting the ink. Further, a part of the partition wall of the ink pressurizing chamber is composed of a piezoelectric element. And in the inkjet head,
By applying a driving voltage to the piezoelectric element in the ink pressurizing chamber to deform it, ink is ejected from a nozzle onto a sheet (paper) to perform recording.

As an example of a method of driving such an ink jet head, for example, the following conventional techniques have been proposed.

That is, in the ink jet printer described in Patent Document 1, the ink pressurizing chamber is expanded by the first drive voltage and then restored (basic drive). afterwards,
By reducing the ink pressurizing chamber by the second drive voltage,
The ink ejection amount is corrected.

Further, Japanese Patent Application Laid-Open No. 2004-242242 discloses an ink jet printer head. In this head, the rise time T1 and the hold time T2 of the drive voltage of the ink pressurizing chamber are set.
And the total time is 1/2 of the natural period Tc of the ink pressurizing chamber.
That is all. This is to improve the ejection efficiency during low voltage driving.

Further, Japanese Patent Application Laid-Open No. 2004-242242 discloses a technique relating to an ink jet head and a driving method thereof.
In this technique, when the natural vibration cycle of the piezoelectric element is Ta, the natural vibration cycle of the ink in the ink pressurizing chamber is Tc, the rising time of the driving voltage of the piezoelectric element is T2, and the falling time is T1, T1 and T2 ≧ Tc and T1,
T2 ≧ Ta. This is for stabilizing the ink ejection amount and improving the print quality.

[0007]

[Patent Document 1] Japanese Patent Laid-Open No. 6-297708 (publication date: October 25, 1994)

[0008]

[Patent Document 2] Japanese Patent Laid-Open No. 10-114063 (published date May 6, 1998)

[0009]

[Patent Document 3] Japanese Patent Application Laid-Open No. 6-305134 (publication date: November 1, 1994)

[0010]

[Patent Document 4] Japanese Patent Publication No. 6-61936 (publication date 1
(August 17, 994)

[0011]

However, each of the above-mentioned prior arts aims at stabilizing the discharge amount. Moreover, the assumed drive frequency is low (about several k to several tens of k pulses / sec). Then, in order to apply these techniques to a driving system involving a high driving frequency (100 k pulse or more / sec or so) such as so-called multi-drop driving, it is necessary to shorten the rising time T2 and the falling time T1. is there. However, if these times are set too short, there is a problem that the generated heat is accumulated and the head temperature rises, the ejection characteristics fluctuate, and ejection failure occurs. In addition, there is a problem that power consumption increases.

On the other hand, if the rise time T2 and the fall time T1 are set too long in order to reduce the drive frequency of the piezoelectric element, the drive voltage must be raised in order to eject an appropriate amount of ink, and high voltage is applied. You need a power supply.

The present invention has been made to solve the above conventional problems. An object of the present invention is to provide a method of driving a piezoelectric element that can reduce driving voltage, heat generation and power consumption.

[0014]

In order to achieve the above-mentioned object, a method of driving a piezoelectric element according to the present invention (main driving method) determines a natural vibration period of a system (vibration system) vibrated by the piezoelectric element. When Ti, the rising time of the drive voltage applied to the piezoelectric element is Tr, and the falling time is Tf, at least one of Tr and Tf is set to 1/20 or more of Ti.

This driving method is a method for driving a piezoelectric element (piezoelectric body) such as an ink jet head, an ultrasonic cleaner, an ultrasonic humidifier and an ultrasonic motor by applying a rectangular wave or a trapezoidal wave.

Here, the piezoelectric element has the same structure as a capacitor in which a dielectric is sandwiched by a pair of electrodes. Then, in the present driving method, at least one of Tr and Tf in the driving voltage applied to such a piezoelectric element is set to
Natural vibration period Ti of the vibration system vibrated by the piezoelectric element
It is designed to be 1/20 or more.

Accordingly, in the present driving method, Tr, Tf
It is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current, which is caused by the too small value. Therefore, it is possible to suppress heat generation and power consumption.

Further, in the present driving method, it is also preferable that at least one of Tr and Tf is set to 1/10 or more of Ti. As a result, the amount of heat generation can be halved without significantly reducing the vibration energy efficiency (1% decrease). The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the heat radiation design of the drive circuit and reducing costs.

Further, in the present driving method, it is also preferable that at least one of Tr and Tf is set to 1/3 or less of Ti. As a result, it is possible to prevent an extreme decrease in vibration energy efficiency (to secure an efficiency of 80% or more), and as a result, it is possible to suppress an increase in drive voltage. The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the power design of the drive circuit and reducing costs.

Further, in the present driving method, it is also preferable to set at least one of Tr and Tf to 1/6 or less of Ti. This makes it possible to prevent an extreme reduction in vibration energy efficiency (ensure 80% or more efficiency) in a drive involving bidirectional deformation in which the vibration system is once expanded and then contracted. Can be suppressed. The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the power design of the drive circuit and reducing costs.

Further, in the present driving method, it is preferable that the time Tv for maintaining the driving voltage is set so as to satisfy Tv≈ (Ti-Tr) / 2.

The displacement of the piezoelectric element with respect to the driving voltage is (T
The maximum is i + Tr) / 2. Therefore, by maintaining the drive voltage with the remaining time from the rise of the drive voltage to (Ti + Tr) / 2 as the maintenance time Tv, the displacement of the piezoelectric element can reach the maximum value. Therefore, if the drive voltage sustain time Tv is set to the above value and the polarity of the drive voltage is switched when the sustain time Tv elapses, maximum efficiency can be obtained.

Further, the ink jet head of the present invention (the present head) has a large number of ink pressurizing chambers in which a part of the partition wall is composed of piezoelectric elements, and the piezoelectric elements are deformed by applying a driving voltage. The inkjet head ejects ink in the ink pressurizing chamber. In this head, the natural vibration period of the vibration system in the ink pressurizing chamber is T
i, where Tr is the rise time of the drive voltage applied to the piezoelectric element and Tf is the fall time, Tr, T
At least one of f is set to 1/20 or more of Ti.

That is, the present head is an ink jet head using the above-mentioned present driving method. Therefore, in the present head, it is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current due to the excessively small Tr and Tf. This makes it possible to suppress heat generation and power consumption.

Further, the ink jet printer of the present invention (the present printer) has a large number of ink pressurizing chambers in which a part of the partition wall is composed of piezoelectric elements, and the piezoelectric elements are deformed by applying a driving voltage. In an ink jet printer having an ink jet head for ejecting ink in the ink pressurizing chamber, Ti is the natural vibration period of the ink pressurizing chamber, Tr is the rising time of the drive voltage applied to the piezoelectric element, and Tf is the falling time. When
At least one of Tr and Tf is set to 1/20 or more of Ti.

That is, this printer is a printer provided with the above-mentioned head. Therefore, in this printer, it is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current due to the excessively small Tr and Tf. This makes it possible to suppress heat generation and power consumption.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described. The printer according to the present embodiment (this printer) receives and processes image data transmitted from an external information processing device (computer, digital camera, etc.), and prints the image on a printing sheet made of paper, plastic, or the like. It has the function of printing and outputting.

FIG. 1 is a perspective view showing the structure of this printer. As shown in this figure, the printer includes a housing 1
1, the sheet guide 12 and the inkjet head 1
3, a holding shaft 14, a conveying roller (not shown), and the like.

Further, the printer is provided with a control unit (not shown) which receives image data transmitted from an image processing device (computer or the like) not shown and controls the above-mentioned members to perform printing.

The sheet guide 12 is a paper feed tray / paper feed guide that supports the sheet P before and during printing.

The ink jet head 13 prints an image by ejecting ink (printing agent) on a sheet conveyed by a conveying roller according to an instruction from the control section.

The ink jet head 13 is set to print an image line by line on a sheet while reciprocating in a scanning space provided in the printer.

The holding shaft 14 is a guide for guiding the ink jet head 13 so as to be movable in the scanning direction, and is provided in the scanning space.

Further, FIG. 2 shows the ink jet head 13
It is explanatory drawing which shows the structure of. As shown in this figure, the inkjet head 13 includes a large number of ink pressurizing chambers K1 to K.
n is included.

Each of the ink pressurizing chambers K1 to Kn stores ink therein, has a nozzle for ejecting ink, and has a drive circuit for controlling ink ejection. There is. Further, a part of the partition walls of the ink pressurizing chambers K1 to Kn is composed of a piezoelectric element.

In the ink jet head 13, a driving voltage is applied to the piezoelectric elements in the ink pressurizing chambers K1 to Kn, and the ink pressurizing chambers K1 to Kn are once expanded and then contracted, so that ink is ejected from the nozzles. The ink is ejected to form an image on a sheet (recording paper).

Since such a driving method is described in detail in, for example, Patent Document 4, description thereof will be omitted here.

FIG. 3 is an electric circuit diagram of the drive circuit 21 provided in each of the ink pressurizing chambers K1 to Kn.

As shown in FIG. 3, in the drive circuit 21, the drive signal CK is applied to the base of the PNP type transistor Q1 via the open collector type inverter INV1 and the resistor R1. Also, this drive signal C
Further, K is given to the base of the NPN type transistor Q2 via another inverter INV2.

The emitter of the transistor Q1 is connected to the power supply of high level Vh via the emitter resistor R3.

Further, a PNP type transistor Q is provided between the base of the transistor Q1 and the power supply of high level Vh.
3 is interposed. The base of the transistor Q3 is connected to the emitter of the transistor Q1.

On the other hand, the emitter of the transistor Q2 is connected to the low level GND power source through the emitter resistor R4.

Further, an NPN type transistor Q4 is interposed between the base of the transistor Q2 and the low level GND power source. And this transistor Q4
Is connected to the emitter of the transistor Q2.

The base of the transistor Q2 is connected to the power supply of high level Vh via the pull-up resistor R2.

The collectors of the transistors Q1 and Q2 are
One terminal of the capacitor C1 is connected. Also,
The other terminal of the capacitor C1 has a low level GND.
Connected to the power supply. The output voltage from one terminal of the capacitor C1 is the output stage transistors Q5 and Q6.
Commonly given to the base of.

The collector of the NPN type transistor Q5 is connected to the high level Vh power supply. Also, P
The collector of the NP type transistor Q6 has a low level G
Connected to ND power supply. These transistors Q5,
The output voltage Vo is derived from the emitter of Q6. The output voltage Vo is selectively applied to the piezoelectric elements B1, B2, ..., Bn by the analog switches A1, A2, ..., An that are driven according to the image data.

Therefore, as shown in FIG. 4, when the drive signal CK becomes high level, the output of the inverter INV1 becomes low level, and the capacitor C1 is charged through the transistor Q1. At this time, the transistor Q2 is turned off. Further, the emitter current of the transistor Q1 is made constant by the resistor R3 and the transistor Q3. Further, the output voltage Vo of the transistor Q5 corresponding to the output voltage of the capacitor C1 also rises as shown in FIG.

When the drive signal CK becomes low level, the output of the inverter INV2 becomes high level, and the capacitor C1 is discharged through the transistor Q2. At this time, the transistor Q1 is turned off. The emitter current of the transistor Q2 is made constant by the resistor R4 and the transistor Q3. Further, the output voltage Vo of the transistor Q6 corresponding to the output voltage of the capacitor C1 also falls as shown in FIG.

In particular, in the drive circuit 21, the rising time Tr and the falling time Tf of the output voltage Vo are set.
The slew rate α is set to a preferable value so that the drive voltage, the heat generation amount, and the power consumption can be suppressed.

The slew rate α is the piezoelectric element B1.
Drive voltage pulse of rectangular wave or trapezoidal wave that drives ~ Bn
It is the rate of change from the level V ₁₀ of 10% of the peak value Vp to the level V _{90 of} 90% (unit: V
/ Sec). That is, this α is represented by α = (V ₉₀ −V ₁₀ ) / Tr = ΔV / Tr (1).

However, Tr is the time until the pulse rises from the level V ₁₀ to the level V ₉₀ . The slew rate α at the time of falling can also be expressed in the same manner by using the falling time Tf (the time until the pulse falls from the level V ₉₀ to the level V ₁₀ ) instead of Tr.
In addition, in the drive circuit 21 of FIG.
It can be set to a desired value by adjusting the resistance value of 3 · R4.

Here, the preferable value of the slew rate α will be specifically described. That is, the piezoelectric elements B1 to Bn
The pulse voltage value of the output voltage Vo given to the ink is ΔV, the vibration system of the ink pressurizing chambers K1 to Kn
In which the piezo-electric elements B1 to Bn vibrate; the ink ejection system) has a natural vibration period of Ti, the slew rate α is set to a value that satisfies α ≦ 20 × ΔV / Ti (V / sec) Preferably. Also,
It is more preferable that the slew rate α is set to a value that satisfies α ≦ 10 × ΔV / Ti (V / sec).

Since α = ΔV / Tr = ΔV / Tf, the rising time Tr and the falling time Tf of the pulse voltage (output voltage) are set to 1/20 ≦ Tr / Ti and 1/20 ≦ Tf / Ti (a) is preferable. Further, it is more preferable that these Tr and Tf are set to 1/10 ≦ Tr / Ti and 1/10 ≦ Tf / Ti (b).

In addition to the above conditions, these T
It is preferable that r and Tf are Tr / Ti ≦ 1/3 and Tf / Ti ≦ 1/3 (c).

Next, the reason why the values of α, Tr / Ti, and Tf / Ti are preferably in the above ranges will be described (hereinafter, Tr = Tf).

Generally, a piezoelectric element has the same structure as a capacitor in which a dielectric is sandwiched by a pair of electrodes. The charge Q injected into the piezoelectric element during driving
Is represented by Q = CV (2) Further, since Q = ∫idt (3), C · (V / Tr) = C · (V / Tf) = i (4). From this, it can be seen that the current i becomes a large current when the drive voltage V rises or falls sharply. For example, if the slew rate α doubles (Tr and Tf become 1/2), the current i also doubles.

When the resistance component of the charging / discharging system such as the wiring in the head and the analog switch is R, the heat generation amount U
Is represented by U = i ² · R (Tr + Tf) (5)

Therefore, it is understood that when the slew rate α becomes high, Tr and Tf become small, but the current i is influenced by the square of the current, so that the heat generation amount and the power consumption increase.

On the other hand, the ejection performance depends on the kinetic energy (speed Vmax) of the vibration system in the ink pressurizing chamber. That is, when the slew rate α (gradient) becomes gentle, the drive voltage corresponding to the displacement must be increased in order to obtain the same discharge pressure. This will be explained below.

Vibration system of ink pressurizing chamber (ink ejection system)
Can be replaced with a vibration system as shown in FIG. As shown in FIG. 6, the slew rate α is set so as to obtain a desired displacement Xr at a desired time Tr. Also, assuming that m is the equivalent mass of the vibration system of the ink pressurizing chamber, xo (t) is the position at an arbitrary time point t, xb (t) is the base point position, and k is the equivalent elasticity, vibration at time t <Tr. The motion of the system can be expressed as a function of velocity and position, as shown below.

M {d ² xo (t) / dt ² } + k {xo (t) −xb (t)} = 0 (6) The above equation is subjected to the Laplace transform of the time t into the function s, and the vibration thereafter. By solving, m · s ² · Xo (s) + k {Xo (s) −Xb (s)} = 0 (7) Then, this equation 7 and the linear function xb (t) = α
When combined with a Laplace transform of t, (s ² + k / m) Xo (s) = Xb (s) k / m = α · k / (m · s ² ) ... (8) Here, when Xo (s) is arranged, Xo (s) = α · k / {m · s ² (s ² + ωn ² )} (9) where ωn ² = k / m. Inverse Laplace transform of Equation 9 gives xo (t), and as shown in FIG. 7, xo (t) = (α · k / m) (1 / ωn ³ ) (ωn · t−sin (ωn · t )) = (Α / ωn) (ωn · t−sin (ωn · t)) = α {t− (1 / ωn) · sin (ωn · t)} (10)

The Laplace transform of the polygonal curve xb '(t) consisting of the rising part with the rising time Tr in FIG. 6 as the boundary and the upper bottom part of the trapezoid is Xb' (s) = ωn (α / s ² ) (1-ε- ^Tr.s ) (11). Further, by substituting the equation 11 into the above equation 8, Xo ′ (s) = ωn (α / s ² ) (1-ε ^−Tr.s ) / (s ² + ωn ² ) ... (12) is obtained. When the equation 12 is subjected to the inverse Laplace transform, the displacement xo ′ at the time t with respect to the polygonal curve xb ′ (t).
(T) is obtained.

Xo ′ (t) = xo (t) −xo (t−Tr) = α (t− (1 / ωn) · sin (ωn · t)) − α {(t−Tr) − (1 / ωn) · sin (ωn · (t−Tr))} (13) When this Expression 13 is rearranged, xo ′ (t) = Xr (1- (2 / (ωn · Tr)) · sin (ωn · (Tr / 2)) · cos (ωn · (2t−Tr) / 2) )… (14) can be obtained. When Xr = 1 and Tr = 0.2 are normalized and the displacement X (t) is obtained from the above equations 10 and 14,
The graph shown in FIG. 8 can be obtained.

From the equation 14 and FIG. 8, the condition tp of the maximum displacement Xp with respect to the polygonal line input is tp = (Ti + Tr) / 2 (15). Further, Tv, which is the maintenance time of the upper bottom of the trapezoidal waveform for obtaining the maximum displacement Xp, is Tv = (Ti-Tr) / 2 (16). Note that Xp is the maximum displacement at time t ≧ Tr.

Therefore, in order to maintain a predetermined repeated ejection frequency, when the drive voltage of the piezoelectric element rises and falls slowly with the drive pulse width fixed (time Tr and Tf in the above equation become long). Then, it can be understood that the maximum displacement Xp of the vibration system decreases (maximum speed decreases), the required drive voltage increases, and a high-voltage power supply is required.

FIG. 9 shows a vibration state and a heat generation state when a pulse having an arbitrary slew rate is applied to the vibration system (and the piezoelectric elements B1 to Bn) in the ink pressurizing chambers K1 to Kn. .

The vibration energy (energy contributing to ejection) given to the vibration system is obtained as a function of the square of the maximum displacement Xp.

Therefore, in FIG. 9, the vibration energy is
Xp normalized to the saturation value of "1" ²Is illustrated.
In other words, vibration energy when Tr / Ti is changed.
Saturated vibration energy when Tr / Ti is sufficiently small
Diagram showing how efficient is the energy
It can be said that it was shown. Furthermore, when driving according to equation (5)
The amount of heat generated at the time of Tr / Ti = 1/20
It is shown as normalized heating value (as "1"). This
According to this, the calorific value is linear with the decrease of Tr / Ti.
Is on the rise.

From FIG. 9, it is possible to read the ratio of Tr and Ti for obtaining the vibration energy more efficiently while suppressing the heat generation of the drive circuit. That is, Tr / Ti =
At 1/20, Xp ² = 0.99 (efficiency: 99%, the efficiency here is the ratio to the vibration energy saturated when Tr / Ti is sufficiently small), and the normalized heating value is 1. is there. Even if Tr / Ti is made smaller than this, the efficiency is hardly increased and only the amount of heat generation is increased. On the other hand, by setting Tr / Ti = 1/10, Xp ²
= 0.98 (efficiency: 98%), the efficiency is reduced by about 1%, but the normalized heating value is 0.5 and Tr / Ti = 1.
The heat generation can be reduced to half compared with the case of / 20. However, if Tr / Ti is set to be extremely large in order to further reduce the amount of heat generation, Xp ² tends to decrease sharply. Therefore, in order to obtain the same vibration energy, it is necessary to increase the driving voltage. is there. Here, Xp ² = 0.80 (efficiency: 80%) of Xp ² rapidly decreases is defined as an inflection point. Further, in order to obtain stable driving, it is necessary to avoid becoming smaller than this inflection point. Therefore, Tr / Ti should be 1 /
Must be 3 or less.

That is, in order to obtain the vibration energy more efficiently while suppressing the heat generation of the drive circuit, 1/20 ≦ Tr / Ti ≦ 1/3, and as a further heat generation measure, 1/10 ≦ Tr / Ti ≦ 1/3 is preferable.

Next, a description will be given of a case where the ink jet head 13 of the printer is constructed so that the ink pressurizing chambers K1 to Kn are once expanded and then contracted to eject ink. In this case, the time required for the process of expansion and maintenance in the ink pressurizing chambers K1 to Kn is set to 1/2 of the natural vibration period Ti ′ of the vibration system in the ink pressurizing chambers K1 to Kn. .

In the drive for expansion and contraction, the displacement Xt at the end of the expansion process becomes the initial displacement during contraction. Therefore, by setting the displacement Xt at the end of contraction to be as large as possible, the energy of the ejection vibration performed at the time of contraction can be increased. FIG. 10 shows the vibration state and the heat generation state at the end of expansion, that is, at time t = Ti ′ / 2, as in FIG. 9.

As shown in FIG. 11, the ink pressurizing chambers K1 ...
The piezoelectric elements B1 to Bn attached to Kn expand with the drive waveform of the A phase and contract with the drive waveform of the B phase. That is,
A voltage of Vh / 2 is applied to the piezoelectric elements B1 to Bn in a non-driving state, a voltage of Vh is applied during expansion, and a voltage of 0V is applied during contraction with reference to the time of contraction.

From FIG. 10, while suppressing the heat generation of the drive circuit,
Tr and Ti 'for obtaining vibration energy more efficiently
It is possible to read the ratio with. That is, Tr / T
When i '= 1/20, Xt ² = 0.98 (efficiency: 98%)
And the normalized calorific value is 1. Tr /
Even if Ti 'is made small, the efficiency hardly increases and the amount of heat generation only increases. On the other hand, Tr / Ti '= 1/10
By setting Xt ² = 0.94 (efficiency: 94%) and 4
Although the efficiency is reduced by about%, the normalized heat generation amount becomes 0.5, and the heat generation can be reduced to half as compared with the case of Tr / Ti ′ = 1/20. However, if Tr / Ti ′ is set extremely large in order to further reduce the heat generation amount, Xt
^{Since 2} tends to decrease sharply, it is necessary to increase the drive voltage when trying to obtain the same vibration energy. Here, Xt ² sharply decreases Xp ² = 0.80
(Efficiency: 80%) is defined as an inflection point. Further, in order to obtain stable driving, it is preferable to avoid becoming smaller than this inflection point. Therefore, in order to secure the inflection point or higher, Tr / Ti 'must be about 1/6 (more accurately, 1 / 5.8 in FIG. 10) or less.

That is, in order to obtain the vibration energy more efficiently while suppressing the heat generation of the driving circuit, 1/20 ≦ Tr / Ti ′ ≦ 1/6, and as a further heat generation measure, 1/10 ≦ Tr / Ti '≦ 1/6 is preferable.

Further, the sustaining time Tv after the pulse voltage rises is given by (Ti '
The maximum efficiency can be obtained by setting -Tr) / 2.

In this embodiment, the rising time Tr and the falling time Tf are equal (Tr = Tf). However, not limited to this, Tr, Tf
May have different values as long as they satisfy (a) (or (b)) and (c) described above.

Further, these Tr and Tf are not always
It is not necessary to satisfy both (a) (or (b)) or (c). By setting Tr and Tf so that either of these is satisfied, it is possible to suppress the amount of heat generation or suppress the drive voltage (and sufficient displacement of the piezoelectric element).

Further, both Tr and Tf are
Neither is it necessary to satisfy (a) (or (b)) and / or (c). By setting one of Tr and Tf so as to satisfy (a) (or (b)) and / or (c), suppression of heat generation or suppression of drive voltage (and sufficient displacement of piezoelectric element) ) Can be achieved to some extent.

The ink jet printer described above can also be expressed as an ink jet recording apparatus.

Further, this embodiment describes an ink jet printer having an ink jet head 13 to which the method for driving a piezoelectric element of the present invention is applied. However, the driving method of the present invention is not limited to the piezoelectric element of the inkjet head, and drives a piezoelectric element (piezoelectric body) such as an ultrasonic cleaner, an ultrasonic humidifier, and an ultrasonic motor by applying a rectangular wave or a trapezoidal wave. This is a method that can be preferably used.

Further, the piezoelectric element drive circuit of the present invention (2
1) is the natural vibration period of the vibration system vibrated by the piezoelectric elements (B1 to Bn), and Ti is the piezoelectric element (B1 to Bn).
When the rising time of the driving voltage given to n) is Tr and the falling time is Tf, it is expressed that at least one of Tr and Tf is set to 1/20 or more of Ti. You can also

As described above, the piezoelectric element driving method (main driving method) according to the present invention is such that the natural vibration period of the system (vibration system) vibrated by the piezoelectric element is Ti, and the driving voltage applied to the piezoelectric element. Is a method of setting at least one of Tr and Tf to 1/20 or more of Ti, where Tr is the rise time and Tf is the fall time.

This driving method is a method for driving by applying a rectangular wave or a trapezoidal wave to a piezoelectric element (piezoelectric body) such as an ink jet head, an ultrasonic cleaner, an ultrasonic humidifier and an ultrasonic motor.

Here, the piezoelectric element has the same structure as a capacitor in which a dielectric is sandwiched by a pair of electrodes. Then, in the present driving method, at least one of Tr and Tf in the driving voltage applied to such a piezoelectric element is set to
Natural vibration period Ti of the vibration system vibrated by the piezoelectric element
It is designed to be 1/20 or more.

Accordingly, in the present driving method, Tr, Tf
It is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current, which is caused by the too small value. Therefore, it is possible to suppress heat generation and power consumption.

In the present driving method, it is also preferable that at least one of Tr and Tf is set to 1/10 or more of Ti. As a result, the amount of heat generation can be halved without significantly reducing the vibration energy efficiency (1% decrease). The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the heat radiation design of the drive circuit and reducing costs.

In the present driving method, it is also preferable to set at least one of Tr and Tf to one third or less of Ti. As a result, it is possible to prevent an extreme decrease in vibration energy efficiency (to secure an efficiency of 80% or more), and as a result, it is possible to suppress an increase in drive voltage. The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the power design of the drive circuit and reducing costs.

In the present driving method, it is also preferable to set at least one of Tr and Tf to 1/6 or less of Ti. This makes it possible to prevent an extreme reduction in vibration energy efficiency (ensure 80% or more efficiency) in a drive involving bidirectional deformation in which the vibration system is once expanded and then contracted. Can be suppressed. The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the power design of the drive circuit and reducing costs.

Further, in the present driving method, it is preferable that the time Tv for maintaining the driving voltage is set so as to satisfy Tv≉ (Ti-Tr) / 2.

The displacement of the piezoelectric element with respect to the driving voltage is (T
The maximum is i + Tr) / 2. Therefore, by maintaining the drive voltage with the remaining time from the rise of the drive voltage to (Ti + Tr) / 2 as the maintenance time Tv, the displacement of the piezoelectric element can reach the maximum value. Therefore, if the drive voltage sustain time Tv is set to the above value and the polarity of the drive voltage is switched when the sustain time Tv elapses, maximum efficiency can be obtained.

Further, the ink jet head of the present invention (main head) has a large number of ink pressurizing chambers in which a part of the partition wall is composed of piezoelectric elements, and the piezoelectric elements are deformed by applying a driving voltage. The inkjet head ejects ink in the ink pressurizing chamber. In this head, the natural vibration period of the vibration system in the ink pressurizing chamber is T
i, where Tr is the rise time of the drive voltage applied to the piezoelectric element and Tf is the fall time, Tr, T
At least one of f is set to 1/20 or more of Ti.

That is, the present head is an ink jet head using the above-mentioned present driving method. Therefore, in the present head, it is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current due to the excessively small Tr and Tf. This makes it possible to suppress heat generation and power consumption.

Further, the ink jet printer of the present invention (the present printer) has a large number of ink pressurizing chambers in which a part of the partition wall is composed of piezoelectric elements, and the piezoelectric elements are deformed by applying a driving voltage. In an ink jet printer having an ink jet head for ejecting ink in the ink pressurizing chamber, Ti is the natural vibration period of the ink pressurizing chamber, Tr is the rising time of the drive voltage applied to the piezoelectric element, and Tf is the falling time. When
At least one of Tr and Tf is set to 1/20 or more of Ti.

That is, the present printer is a printer equipped with the above-mentioned head. Therefore, in this printer, it is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current due to the excessively small Tr and Tf. This makes it possible to suppress heat generation and power consumption.

Further, the present invention is preferably used when a rectangular wave or a trapezoidal wave is applied to a piezoelectric body such as an ink jet head of an ink jet recording apparatus, an ultrasonic cleaner, an ultrasonic humidifier and an ultrasonic motor to drive the piezoelectric body. It can be said that the present invention relates to a driving method of a piezoelectric element capable of performing the above, and an ink jet recording apparatus using the driving method.

Further, in the above-mentioned Patent Document 3, when the natural vibration period in the ink pressurizing chamber is Tc, the rising time of the drive voltage is T2, and the falling time is T1, T1 + T
By setting 2 ≧ Tc / 2, it can be said that an inkjet head and a driving method thereof that realize stable print quality at low cost with respect to a change in viscosity depending on the type of ink and the environment are shown.

It can be said that the present printer is an ink jet printer to which the method for driving a piezoelectric element according to the embodiment of the present invention is applied.

The ink jet head of this printer uses, for example, the drive circuit shown in FIG. 3 and has a large number of ink pressurizing chambers having nozzles, and each ink pressurizing chamber is provided with this drive circuit. ing. Then, a drive voltage is applied to the piezoelectric element forming a part of the partition wall of the ink pressurizing chamber so that the ink pressurizing chamber is once expanded and then contracted, or directly contracted without an expansion stroke. Therefore, it can be said that the ink is ejected.

The output voltage Vo shown in FIG. 3 corresponds to the analog data A1, A2, ..., A according to the image data.
, n may be selectively applied to the piezoelectric elements B1, B2, ..., Bn. Further, FIG. 5 can also be said to be a diagram of a vibration model for explaining the ejection system of the inkjet head.

The present invention can also be described as follows. That is, what should be noted in the circuit of FIG. 3 is the setting of the resistance values of the resistors R3 and R4, etc., and the slew rate α at the rising time Tr and the falling time Tf of the output voltage Vo is set as described later. Therefore, the driving voltage, the heat generation amount, and the power consumption are suppressed. Specifically, assuming that the voltage value of the pulse given to the piezoelectric elements B1, B2, ..., Bn is ΔV and the natural vibration period of the ink ejection system of the inkjet head is Ti, the slew rate α is α ≦ 20 × ΔV / Ti. (V / sec). Then, the rise time of the pulse voltage is Tr,
When the fall time is Tf, α = ΔV / Tr (=
Tf), so 1/20 ≦ Tr / Ti, Tf / Ti
And Further, preferably, 1/10 ≦ Tr / Ti,
Tf / Ti. This is because the rise time Tr and the fall time Tf do not depend on the shape of the inkjet head, and the natural vibration period T of the ink ejection system is
When normalized with i and changed it, the piezoelectric element B
This is because the amounts of displacement and heat generation (= power consumption) of 1, B2, ..., Bn change as shown in FIG. In addition,
In FIG. 9, the vibration energy of the displacement is represented by the square of the maximum displacement Xp ² .

Therefore, the rise time Tr and the fall time Tf of the pulse voltage are set to 1 / n of the natural vibration period Ti of the ink ejection system of the ink jet head as described above.
By setting the time to 20 or more, it is possible to obtain a desired displacement amount while suppressing the drive voltage, the heat generation amount, and the power consumption.

The rising time T of the pulse voltage
By setting r and the fall time Tf to be 1/3 or less of the natural vibration period Ti of the ink ejection system, the displacement of the piezoelectric element which becomes higher as the rise or fall of the voltage waveform becomes steeper is also changed. A pole point (efficiency of 80%) or more can be secured, and in particular, in the vicinity of 1/20 of the natural vibration period Ti of the ink ejection system, the ejection energy by the piezoelectric element can be substantially saturated.

Further, in the driving method in which the ink pressurizing chamber is once expanded and then contracted to eject the ink as described above, the time required for the process of expansion and maintenance is the natural vibration of the ink ejecting system. Period Ti '
FIG. 10 shows the displacement energy when it is set to ½ of the above, and FIG. 11 shows the drive waveform thereof. The piezoelectric element attached to the ink pressurizing chamber expands with the A-phase drive waveform and contracts with the B-phase drive waveform. That is, a voltage of Vh / 2 is applied to the piezoelectric element in the non-driving state, with the time of contraction as a reference voltage, the voltage of Vh is applied during the expansion, and the voltage of 0V is applied during the contraction.

As is apparent from FIG. 10, by setting the rise time Tr and the fall time Tf of the pulse voltage to be 1/20 or more of the natural vibration period Ti ′ of the ink ejection system as described above, It is possible to obtain a desired displacement amount while suppressing the drive voltage, the heat generation amount, and the power consumption.

Further, the rise time T of the pulse voltage
r and the fall time Tf are set to 1 of the natural vibration period Ti ′.
By setting the time to be / 6 or less, the displacement of the piezoelectric element, which becomes higher as the rising or falling of the voltage waveform becomes steeper, can also ensure the inflection point (efficiency of 80%) or more, and particularly the natural vibration. In the vicinity of 1/20 of the period Ti ′, the displacement of the piezoelectric element can be almost saturated.

Furthermore, the sustain time Tv after the pulse voltage rises is given by (T
The maximum efficiency can be obtained by setting i′-Tr) / 2.

The present invention can also be expressed as the following first and second piezoelectric element driving methods and first and second ink jet recording apparatuses. That is, the first method of driving a piezoelectric element is as follows: where Ti is the natural vibration period of the system vibrated by the piezoelectric element, Tr is the rise time of the drive voltage applied to the piezoelectric element, and Tf is the fall time. This is a method of setting / 20 ≦ Tr / Ti and Tf / Ti ≦ 1/3.

According to this method, when a drive voltage is applied to a piezoelectric element having a structure similar to that of a capacitor in which a dielectric is sandwiched between a pair of electrodes, a sharp rise or fall of the voltage waveform is large. The drive voltage, heat generation, and power consumption increase due to the loss due to the resistance component of the charging / discharging system such as wiring and switching elements, whereas the drive voltage rise time T
By setting r and the fall time Tf to 1/20 or more of the natural vibration period Ti of the system vibrated by the piezoelectric element as described above, the drive voltage, the heat generation amount, and the power consumption can be suppressed.

Further, the rise time Tr of the drive voltage
Or fall time Tf is 1/3 of the natural vibration period Ti
By setting the time below, it is possible to secure a vibration energy efficiency of 80% or more of the piezoelectric element that becomes higher as the rising or falling of the voltage waveform becomes steeper, and particularly in the vicinity of 1/20 of the natural vibration period Ti, The displacement energy of the piezoelectric element can be almost saturated.

The driving method of the second piezoelectric element is the first
In the method of driving a piezoelectric element, when the time for maintaining the driving voltage is Tv, this Tv is set to Tv≈ (Ti−Tr) / 2.

According to the above method, the displacement of the piezoelectric element with respect to the drive voltage becomes maximum at (Ti + Tr) / 2, so that the (Ti + T) is reached after the drive voltage rises.
By maintaining the drive voltage with the remaining time up to r) / 2 as the maintenance time Tv, the displacement of the piezoelectric element can reach the maximum value.

Therefore, the maximum efficiency can be obtained by setting the drive voltage sustaining time Tv to the above value and switching the polarity of the drive voltage when the sustaining time Tv elapses.

Furthermore, the first ink jet recording apparatus has a large number of ink pressurizing chambers having nozzles, and a drive voltage is applied to a piezoelectric element which constitutes a part of the partition wall of the ink pressurizing chamber to apply the piezoelectric element. In the ink jet recording apparatus including an ink jet head that performs recording by causing the ink stored in the ink pressurizing chamber to fly to the paper from the nozzles by performing deformation, It is characterized in that the natural vibration period is Ti and the first or second piezoelectric element driving method is used.

According to this structure, high ejection efficiency can be obtained while suppressing the drive voltage, heat generation and power consumption.

The second ink jet recording apparatus is the first ink jet recording apparatus, wherein the ink pressurizing chamber is expanded and then contracted to eject ink. And the time required for the maintenance process is 1/2 of the natural vibration period Ti of the ink ejection system, and preferably 1/20 ≦ Tr / Ti and Tf / Ti ≦ 1/6 are set. And

According to this structure, the lower limit of the rise time Tr and the fall time Tf of the drive voltage is set to 1/20 or more of the natural vibration period Ti of the ink ejection system, so that the expansion of the ink pressurizing chamber and the expansion thereof. Even when the time required for the maintenance process is set to 1/2 of the natural vibration period Ti of the ink ejection system, the driving voltage, the heat generation amount and the power consumption can be suppressed, and particularly the heat generation amount and the power consumption can be reduced by half.

[0118]

As described above, in the method of driving a piezoelectric element according to the present invention (the present driving method), the natural vibration period of the system (vibration system) vibrated by the piezoelectric element is given to Ti and the piezoelectric element. When the rising time of the driving voltage is Tr and the falling time is Tf, at least one of Tr and Tf is set to 1/20 or more of Ti.

The present driving method is a method for applying a rectangular wave or a trapezoidal wave to a piezoelectric element (piezoelectric body) such as an ink jet head, an ultrasonic cleaner, an ultrasonic humidifier, an ultrasonic motor, etc.

Here, the piezoelectric element has the same structure as a capacitor in which a dielectric is sandwiched between a pair of electrodes. Then, in the present driving method, at least one of Tr and Tf in the driving voltage applied to such a piezoelectric element is set to
Natural vibration period Ti of the vibration system vibrated by the piezoelectric element
It is designed to be 1/20 or more.

Thus, in the present driving method, Tr, Tf
It is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current, which is caused by the too small value. Therefore, it is possible to suppress heat generation and power consumption.

In the present driving method, it is also preferable to set at least one of Tr and Tf to 1/10 or more of Ti. As a result, the amount of heat generation can be halved without significantly reducing the vibration energy efficiency (1% decrease). The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the heat radiation design of the drive circuit and reducing costs.

Further, in the present driving method, it is also preferable to set at least one of Tr and Tf to 1/3 or less of Ti. As a result, it is possible to prevent an extreme decrease in vibration energy efficiency (to secure an efficiency of 80% or more), and as a result, it is possible to suppress an increase in drive voltage. The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the power design of the drive circuit and reducing costs.

In the present driving method, it is also preferable to set at least one of Tr and Tf to 1/6 or less of Ti. This makes it possible to prevent an extreme reduction in vibration energy efficiency (ensure 80% or more efficiency) in a drive involving bidirectional deformation in which the vibration system is once expanded and then contracted. Can be suppressed. The vibration energy efficiency here is the ratio to the saturated vibration energy when Tr / Ti is sufficiently small. This has the advantage of reducing the power design of the drive circuit and reducing costs.

Further, in the present driving method, it is preferable that the time Tv for maintaining the driving voltage is set so as to satisfy Tv≉ (Ti-Tr) / 2.

The displacement of the piezoelectric element with respect to the driving voltage is (T
The maximum is i + Tr) / 2. Therefore, by maintaining the drive voltage with the remaining time from the rise of the drive voltage to (Ti + Tr) / 2 as the maintenance time Tv, the displacement of the piezoelectric element can reach the maximum value. Therefore, if the drive voltage sustain time Tv is set to the above value and the polarity of the drive voltage is switched when the sustain time Tv elapses, maximum efficiency can be obtained.

Further, the ink jet head of the present invention (main head) has a large number of ink pressurizing chambers in which a part of the partition wall is composed of piezoelectric elements, and the piezoelectric elements are deformed by applying a driving voltage. The inkjet head ejects ink in the ink pressurizing chamber. In this head, the natural vibration period of the vibration system in the ink pressurizing chamber is T
i, where Tr is the rise time of the drive voltage applied to the piezoelectric element and Tf is the fall time, Tr, T
At least one of f is set to 1/20 or more of Ti.

That is, the present head is an ink jet head using the above-mentioned present driving method. Therefore, in the present head, it is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current due to the excessively small Tr and Tf. This makes it possible to suppress heat generation and power consumption.

Further, the ink jet printer of the present invention (this printer) has a large number of ink pressurizing chambers in which a part of the partition wall is composed of piezoelectric elements, and the piezoelectric elements are deformed by applying a driving voltage. In an ink jet printer having an ink jet head for ejecting ink in the ink pressurizing chamber, Ti is the natural vibration period of the ink pressurizing chamber, Tr is the rising time of the drive voltage applied to the piezoelectric element, and Tf is the falling time. When
At least one of Tr and Tf is set to 1/20 or more of Ti.

That is, this printer is a printer provided with the above-mentioned head. Therefore, in this printer, it is possible to prevent the loss due to the resistance component of the charging / discharging system such as the wiring and the switching element due to the large current due to the excessively small Tr and Tf. This makes it possible to suppress heat generation and power consumption.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an inkjet head in the inkjet printer shown in FIG.

FIG. 3 is an electric circuit diagram of a drive circuit of an inkjet head in the inkjet printer according to the embodiment of the present invention.

FIG. 4 is a waveform diagram for explaining the operation of the drive circuit shown in FIG.

FIG. 5 is a diagram of a vibration model for explaining a vibration system of the inkjet head.

FIG. 6 is a graph for explaining a slew rate (gradient) of a drive pulse of an inkjet head.

FIG. 7 is a graph for explaining the relationship between the slew rate and the displacement amount of the piezoelectric element.

FIG. 8 is a graph for explaining conditions for obtaining the maximum displacement of the piezoelectric element.

FIG. 9 is a graph for explaining changes in the displacement amount and heat generation amount (= power consumption) of the piezoelectric element with respect to changes in the rise time Tr and the fall time Tf of the drive pulse of the piezoelectric element.

FIG. 10 is a displacement amount and heat generation of the piezoelectric element with respect to changes in the rise time Tr and the fall time Tf of the drive pulse in a drive method in which ink is ejected by temporarily expanding and then contracting the ink pressurizing chamber. It is a graph for explaining the change of the amount (= power consumption).

FIG. 11 is a waveform diagram for explaining the driving method described above.

[Explanation of symbols]

A1 to An analog switch B1-Bn Piezoelectric element C1 capacitor INV1 / 2 inverter K1 to Kn ink pressurizing chamber Q1 to Q6 transistors R1 to R4 resistance

Claims (11)

[Claims] 1. When Ti is a natural vibration period of a vibration system vibrated by a piezoelectric element, Tr is a rising time of a drive voltage applied to the piezoelectric element, and Tf is a falling time, at least one of Tr and Tf is set. , 1/20 of Ti
A method for driving a piezoelectric element, which is set as described above. 2. At least one of Tr and Tf is Ti
It is set to 1/10 or more of the above.
7. A method for driving a piezoelectric element according to item 4. 3. At least one of Tr and Tf is Ti
2. The method for driving a piezoelectric element according to claim 1, wherein the piezoelectric element is set to one third or less. 4. At least one of Tr and Tf is Ti
2. The method for driving a piezoelectric element according to claim 1, wherein the piezoelectric element is set to ⅙ or less. 5. The method for driving a piezoelectric element according to claim 1, wherein the time Tv for maintaining the drive voltage is set so as to satisfy Tv≈ (Ti−Tr) / 2. 6. An ink jet which has a large number of ink pressurizing chambers in which a part of partition walls are composed of piezoelectric elements, and which deforms the piezoelectric elements by applying a driving voltage to eject ink in the ink pressurizing chambers. In the head, the natural vibration cycle of the vibration system in the ink pressurizing chamber is T
i, where Tr is the rise time of the drive voltage applied to the piezoelectric element and Tf is the fall time, Tr, T
At least one of f is set to 1/20 or more of Ti. 7. At least one of said Tr and Tf is Ti
7. The inkjet head according to claim 6, wherein the inkjet head is set to 1/10 or more of the above. 8. At least one of Tr and Tf is Ti.
7. The inkjet head according to claim 6, wherein the inkjet head is set to one-third or less. 9. The ink pressurizing chamber is set so that the ink is ejected by temporarily expanding and then contracting the ink pressure chamber, and at least one of the Tr and Tf is 6 of Ti.
The ink-jet head according to claim 6, wherein the ink-jet head has a ratio of one-tenth or less. 10. The ink jet head according to claim 6, wherein the time Tv for maintaining the drive voltage is set so as to satisfy Tv≈ (Ti-Tr) / 2. 11. An ink jet printer provided with the ink jet head according to claim 6.