JP2004025890A - Method for driving actuator, and inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To displace an actuator at a speed higher than a proper period of a basic mode of the actuator. <P>SOLUTION: Voltage is again raised after a pulsed wave form SO consisting of the rise and fall of the voltage is added, during a time period shorter than 30 μs, which is the proper period of the basic (primary) mode and the first oscillation mode of a piezoelectric oscillator. A time period from a first voltage rise PO to a voltage fall P1, and that from the voltage fall P1 to a second voltage rise P2 are approximately 6 μs, which is approximately a half value of the proper period of a secondary mode to be the second oscillation mode of the piezoelectric oscillator 60. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for driving an actuator that is displaced by input of a drive signal. More specifically, the present invention relates to a driving method for displacing an actuator at high speed. Another technical field to which the present invention pertains relates to an ink jet recording apparatus that ejects ink droplets and deposits them on a recording medium. More specifically, the present invention relates to ejecting minute ink droplets at a low voltage at a high speed. The present invention relates to a suitable inkjet recording apparatus.

(4) As a driving force generated by input of a control signal or an actuator which is displaced by a change in the driving force, for example, there are an electrostrictive actuator using an electrostrictive (piezoelectric) material and a magnetostrictive actuator using a magnetostrictive material. These actuators have a natural vibration mode determined by the shape and fixing method of the actuator.

For example, in the piezoelectric longitudinal vibrator shown in FIG. 1, when one end of a piezoelectric ceramic thin rod is fixed and a voltage is applied between drive electrodes formed on both surfaces of the thin rod, the piezoelectric longitudinal vibrator is displaced in the longitudinal direction of the thin rod by a piezoelectric transverse effect. I do. The natural frequency of the longitudinal vibration of such a rod with one end fixed is

It is represented by. Here, L: length of rod, E: longitudinal elastic modulus of rod material, γ: density of rod material, λ: dimensionless coefficient determined by natural vibration mode, λ = π / 2, 3π / 2, 5π / 2,. . . , (2n-1) π / 2 (n is a natural number). The natural vibration modes corresponding to the respective natural frequencies are as shown in FIG. In FIG. 18, the displacement state in the longitudinal direction of the rod in the first mode, the second mode, and the third mode is expressed as a displacement perpendicular to the rod for convenience.

(4) When an output voltage from an external drive circuit is applied between the drive electrodes to the piezoelectric longitudinal vibrator, a driving force is generated by a piezoelectric transverse effect, and statically generates a displacement expressed by the following equation.

Here, V: drive voltage, t: thickness of the piezoelectric thin bar between the electrodes, L: length of the bar, d ₃₁ : piezoelectric constant.

When the piezoelectric longitudinal vibrator is displaced, the transient vibration state up to the static displacement is largely governed by how the voltage rises. FIGS. 19 and 20 show the displacement response of the tip of the piezoelectric longitudinal vibrator when a pseudo step voltage that rises at a constant voltage rising rate is applied to the piezoelectric longitudinal vibrator. The horizontal axis in the figure is normalized by the fundamental period _Tm1 of the primary mode of the piezoelectric longitudinal vibrator, and the vertical displacement is normalized by the static displacement.

In FIG. 19, the rise time T ₁ of the pseudo step voltage is shorter than the natural period T _m3 = T _m1 / 5 of the third mode, and a plurality of modes of the first mode, the second mode, and the third mode are excited, and as a result, the static displacement Rise up to about twice the displacement, but saw-like ringing occurs.

In Figure 20, it is set equal to the rise time T ₁ of the pseudo-step voltage to the natural period T _m1 of the primary mode. In general, if the rise time is set to be sufficiently longer than the natural oscillation period of a certain natural mode, the excitation of the natural mode and higher-order vibrations can be suppressed low. Conversely, if the rise time is shorter than the eigenmode of a certain eigenmode, the eigenmode and a lower-order eigenmode are strongly excited. Further, when the rise time becomes equal to the natural vibration period of a certain mode, the excitation of the mode becomes minimal, and the excitation of the vibration mode can be suppressed as much as possible. In Figure 20, since the rising time T ₁ of the pseudo-step voltage is set equal to the natural period T _m1 of the primary mode, excitation of the primary and higher modes are suppressed both transducer tip is approximately equal to the rise time It rises in time (that is, a time equal to the natural period T _m1 of the first-order mode), and no overshoot or ringing occurs.

Next, an ink jet recording apparatus according to the prior art of the present invention will be described.

In general, an ink jet recording apparatus has a natural vibration of an ink flow having a Helmholtz frequency determined by the rigidity (compliance) of an ink chamber and the inertia (inertance) of an ink flow path system including a supply path and a nozzle, and this vibration mode is strongly excited. By doing so, it becomes possible to eject ink droplets from the nozzles at high speed.
Therefore, the period of the basic vibration mode of the actuator is set shorter than the period of the natural vibration of the ink flow so that the actuator is displaced in a shorter time than the period of the natural vibration of the ink flow. Such a conventional technique is disclosed in Patent Document 1.

In such an ink jet recording apparatus, when ringing (residual vibration) occurs after the actuator is driven, natural vibration of the ink flow is excited, and mist-like ink droplets are generated from the nozzles even with a very small amplitude. When the mist itself adheres to the recording medium, it degrades the recording quality.However, when the mist adheres not only to the recording medium but also to the periphery of the nozzle of the ink jet head, the nozzle opening becomes unevenly wet, and is attracted to the adhering mist. Since the ejection direction of the ink droplet changes, it is not possible to accurately record at a target position on the recording medium, and the recording quality is deteriorated.

Further, an ink jet recording apparatus disclosed in Patent Literature 2 has one of a piezoelectric vibrator as an actuator for driving the vibration plate and pressurizing the ink chamber by driving the vibration plate as a bottom wall of the partitioned ink chamber. The ends are in contact. The other end of the piezoelectric vibrator is fixed to a base via a substrate, and is driven in a longitudinal vibration mode that expands and contracts in the axial direction by applying a driving voltage to the stacked driving electrodes. When the drive voltage is increased, the piezoelectric vibrator shrinks and deforms the diaphragm out of the plane of the ink chamber to increase the volume of the ink chamber. Thereafter, when the drive voltage is lowered, the piezoelectric vibrator expands and the volume of the ink chamber is rapidly reduced. Due to the fluid pressure of the ink chamber generated at this time, an ink droplet is ejected from a nozzle communicating with the ink chamber. The drive voltage is lowered by a circuit in which the voltage drop rate is constant. By making the time of this drop substantially equal to the period of the free vibration (basic vibration of the longitudinal vibration) of the piezoelectric vibrator, The residual vibration of the piezoelectric vibrator is reduced, and the ejection of unnecessary mist-like ink droplets from the nozzles is suppressed.

Further, the ink jet recording apparatus disclosed in Patent Document 3 divides the driving voltage into two stages, and inserts a stop time of the voltage drop in the middle of the voltage drop, so that the residual vibration of the piezoelectric vibrator can be reduced as much as possible. Has been suppressed.
Japanese Patent Publication No. 4-71712 JP-A-6-8427 JP-A-6-340075

As described in the above prior art, in order to displace an actuator at a high speed and to sufficiently reduce the ringing of the displacement, a basic vibration mode related to the displacement of the actuator, for example, an actuator using a tip displacement of a longitudinal transducer as an output is used. The natural frequency of the fundamental vibration mode (primary vibration mode) of longitudinal vibration must be increased so that its natural period is equal to or less than the required displacement response time. That is, the upper limit of the speed of the displacement response is determined by the natural period of the fundamental vibration mode of the actuator. Generally, the natural vibration frequency of a mechanical structure increases as the structure decreases. For example, for a uniform longitudinal oscillator or torsional oscillator, the natural frequency is inversely proportional to the length, and for a transverse oscillator (flexible oscillator), the natural frequency is inversely proportional to the square of the length. Conversely, if the driving force is constant, the amount of displacement of the actuator decreases as the size decreases. For example, in a uniform longitudinal or torsional vibrator, the amount of displacement is proportional to the length, and in a lateral vibrator (flexible vibrator), the amount of displacement is proportional to the square of the length. Therefore, in order to increase the displacement speed, it is necessary to reduce the size of the actuator and to increase its driving force, that is, the driving voltage of the actuator including the electromechanical transducer.

However, when the drive voltage is increased, the drive circuit becomes very large and expensive, and the performance of the drive circuit and the actuator deteriorates due to heat generation. In addition, the upper limit of the characteristic is determined by the limit distortion of the actuator element itself, for example, the stress inside the actuator is increased and the reliability is reduced due to the destruction of the actuator.

In addition, in the ink jet recording apparatus, it is possible to discharge minute ink droplets at high speed by increasing the natural frequency (Helmholtz frequency) of the vibration mode of the ink chamber relating to the discharge of ink droplets. For that purpose, an actuator having a high displacement speed capable of driving the vibration mode of the ink chamber is required. However, if the rise of the drive voltage is made faster, ringing occurs, and there is a problem that unnecessary ink mist that deteriorates print quality is generated. In addition, if the actuator is miniaturized in order to increase the speed of the basic mode of the actuator, there is a problem that the driving voltage becomes extremely high.

Therefore, an object of the present invention is to provide a driving method of an actuator in which a displacement rises in a time equal to or less than a natural period of a basic mode, and drastically improve a displacement response limit limited in the basic mode of the actuator, and An object of the present invention is to provide a high-performance actuator that can be driven at high speed with a low driving voltage and low driving force.

Another object of the present invention is to provide a high-quality ink jet recording apparatus capable of ejecting minute ink droplets at a high speed with a low driving force and a low voltage by dramatically increasing the displacement speed of an actuator.

In order to solve the above-mentioned problems, the present invention provides a first vibration mode that is displaced by a driving force of a driving unit and is excited by the driving force, and a second vibration mode that is higher in order than the first vibration mode. In the driving method of the actuator, comprising: during a section shorter than the period of the first vibration mode, a pulse-like driving force having a width substantially half the natural period of the second vibration mode; By performing the fall at least once, the second vibration mode is excited, and then a driving force for driving to a necessary displacement is applied.

Here, it is desirable to set the time from the fall to the driving force for driving to the required displacement to be substantially half of the natural period of the second vibration mode.

It is desirable that the magnitude of the rise and fall of the pulse-like drive force is larger than the magnitude of the drive force for driving to the required displacement.

Preferably, the driving force for driving to the required displacement is obtained by superimposing a pulse-like driving force on a step-like driving force. Here, it is preferable that the superimposed pulsed driving force suppresses the vibration in the first vibration mode.

It is preferable that the actuator is made of an electrostrictive vibrator or a magnetostrictive vibrator.

It is preferable that the actuator is a vertical vibrator, a horizontal vibrator, or a torsional vibrator.

The present invention also provides an ink jet recording apparatus that ejects ink droplets from a nozzle communicating with the ink chamber by vibrating a part of a peripheral wall that defines an ink chamber with an actuator. A first vibration mode that is displaced by the driving force of the first vibration mode and is excited by the driving force, and a second vibration mode that is higher in order than the first vibration mode. Exciting the second vibration mode by performing at least one rise and fall of a pulse-like driving force having a width approximately half the natural period of the second vibration mode during a short section. Then, a driving force for driving the required displacement is applied.

Here, it is desirable to set the time from the fall to the driving force for driving to the required displacement to be substantially half of the natural period of the second vibration mode.

It is desirable that the magnitude of the rise and fall of the pulse-like drive force is larger than the magnitude of the drive force for driving to the required displacement.

Preferably, the driving force for driving to the required displacement is obtained by superimposing a pulse-like driving force on a step-like driving force. Here, it is preferable that the superimposed pulsed driving force suppresses the vibration in the first vibration mode.

Preferably, the actuator is an electrostrictive vibrator driven in a longitudinal vibration mode, and the driving force by the driving means is given by a voltage applied to a drive electrode formed on the electrostrictive vibrator.

Further, the ink chamber has a vibration mode of the ink chamber related to the ejection of ink, a natural period of the first vibration mode of the actuator is larger than a natural period of the vibration mode of the ink chamber, and the second vibration mode Is preferably smaller than the natural period of the vibration mode of the ink chamber.

According to the present invention, the actuator can be started up in a time shorter than the natural period of the basic mode of the actuator, and an actuator that displaces at a high speed can be realized.

Also, in order to obtain a high-speed response, it is not necessary to make the actuator more compact than necessary, and an actuator that displaces at a high speed while obtaining a necessary displacement with a low driving force and a low driving voltage can be realized. It is possible to drive an ink chamber having a response speed.

Furthermore, overshoot and residual vibration of the actuator can be suppressed, and unnecessary ink droplet ejection and ink ejection instability do not occur, and both low drive voltage and high reliability can be achieved.

Hereinafter, the driving method of the actuator of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an actuator to which an embodiment of a drive waveform described below is applied. A piezoelectric plate having a thickness H made of lead zirconate titanate (hereinafter, referred to as PZT) is cut into a plate bar having a width W, and one end thereof is formed. The portion is bonded and fixed to the substrate with a length L extending from the substrate 61. Drive electrodes 62 are formed on both surfaces of the piezoelectric plate 60, and the piezoelectric material is polarized in the thickness direction using the drive electrodes 62. The dimensions of this piezoelectric longitudinal vibrator are as follows: the thickness H is 200 μm, the width W is 500 μm, the overhang length L is 20 mm, and the approximate material constants of the piezoelectric material are specific gravity 7.5 and longitudinal elastic modulus 6 × 10 ¹⁰ N / m ² and the piezoelectric constant d ₃₁ are 200 × 10 ⁻¹² m / V. When a voltage is applied to the drive electrode, piezoelectric strain due to the piezoelectric transverse effect acts as a drive force, and the rod contracts in the longitudinal direction. When the natural frequency of the longitudinal vibration in the longitudinal direction is calculated from the formula using the above numerical values, the primary mode is 34 kHz, the secondary mode is 102 kHz, and the tertiary mode is 170 kHz. In addition, when viewed in a natural cycle, the primary mode is 29 μs, the secondary mode is 10 μs, and the tertiary mode is 6 μs. When the resonance point was actually measured using an impedance analyzer, the natural period of the first-order mode was 30 μs, which was consistent with the above calculation result.

The drive voltage waveform shown in FIG. 2A is a pseudo step waveform in which the voltage rises in 30 μs, which is equal to the natural mode natural period of the piezoelectric vibrator shown in FIG. 1, and this drive waveform is shown in FIG. , The response of the actuator displacement shown in FIG. 2B is obtained. As described in the related art, according to this driving method, the displacement rises smoothly without overshoot or ringing, but the time required for the rise of the displacement is about 30 μs, and the speed of the rise is low. I will.

3A and 3B show a driving method according to a first embodiment of the present invention. FIG. 3A shows a driving voltage waveform applied to a piezoelectric vibrator, and FIG. 3B shows a driving voltage waveform as an actuator. It is a tip displacement response of a piezoelectric vibrator. The drive voltage waveform in FIG. 3A includes a rise and fall of the voltage during a time shorter than 30 μs, which is the natural period of the basic (primary) mode, which is the first vibration mode of the piezoelectric vibrator. After adding the pulse waveform S0, the voltage is raised again. The time from the first voltage rise P0 to the voltage fall P1 and the time from the voltage fall P1 to the second voltage rise P2 is about 6 μs, and the second vibration mode of the piezoelectric vibrator 60 is The value is about a half of the natural period of the second mode. With this drive waveform, before the fundamental (primary) mode rises at the rise of the piezoelectric vibrator 60, a pressure wave that excites the secondary displacement mode propagates through the vibrator, as shown in FIG. 3B. A steep rising Q0 and a constant displacement plateau Q1 are obtained. After the plateau Q1, the ringing Q2 of the primary mode due to the rise of the drive voltage with the pulse-like drive voltage waveform remains after the time of 15 μs.

(3) By the driving method of FIG. 3, the displacement of the tip of the vibrator rises in about 8 μs, which is one third or less as compared with the prior art of FIG. 2, and a very fast rise can be realized. However, the displacement that rises sharply to the plateau Q1 is about 20% smaller than the static displacement of about 0.25 μm.

FIG. 4 shows a driving method according to a second embodiment of the present invention, which is an improvement of the embodiment shown in FIG. FIG. 4A shows a drive voltage waveform applied to the piezoelectric vibrator, and FIG. 4B shows a tip displacement response of the piezoelectric vibrator 60 as an actuator. In contrast to the drive voltage waveform shown in FIG. 3A, the drive voltage waveform shown in FIG. 4A is obtained by changing the height of the pulse-shaped waveform S10 composed of the rising P10 and the falling P11 of the initial voltage by a static displacement. By increasing the applied voltage by about 30%, it became possible to make the amount of displacement rising steeply up to the plateau Q11 almost equal to the amount of static displacement. By changing the pulse height as in this driving method, it is possible to freely adjust the amount of displacement that rises sharply up to the plateau.

5A and 5B show a driving method according to a third embodiment of the present invention. FIG. 5A shows a driving voltage waveform applied to the piezoelectric vibrator, and FIG. 5B shows a driving voltage waveform of the piezoelectric vibrator as an actuator. It is a tip displacement response. This embodiment is an improvement of the embodiment shown in FIG. That is, the rise P20 of the first voltage is performed about 30% higher than the voltage giving the static displacement amount. Subsequently, the voltage falls P21 at about 6 μs, which is about half the natural period of the second mode of the piezoelectric vibrator 60, which is the second vibration mode, to form a first pulse-shaped waveform S20. Subsequently, the second voltage rise P22 is performed at about 6 μs from the voltage fall P21 as before. The height of the start-up P22 is set to be about 30% higher than the voltage that gives a static displacement amount, similarly to the first start-up. Subsequently, a fall P23 of the second voltage is performed from the second rise P22 to a voltage that gives a static displacement in about 6 μs as before.

As can be seen by comparing FIG. 4 (A) and FIG. 5 (A), in the drive waveform of the present embodiment, the second pulse-like waveform S21 is added to the step-like drive waveform S22 for driving up to the static displacement. By superimposing, it is possible to suppress ringing after rising of the actuator displacement.

6A and 6B show a driving method according to a fourth embodiment of the present invention. FIG. 6A shows a driving voltage waveform applied to the piezoelectric vibrator 60, and FIG. 6B shows a piezoelectric vibrator as an actuator. 60 is the tip displacement response of FIG. This embodiment is an improvement of the embodiment shown in FIG. 5, in which the auxiliary superimposed second pulse is optimized so as to cancel the ringing in the fundamental (first order) mode, and the residual vibration is suppressed. . That is, the height of the rising P32 of the second voltage is made larger than that of the first rising P30, and the height is adjusted so as to cancel the ringing in the basic (primary) mode. With this drive waveform, as shown in FIG. 6B, overshoot and ringing could be suppressed to a very small level. As compared with FIG. 2B, a rising speed three times or more was obtained by using the same actuator, and the driving capability of the actuator could be significantly improved.

7A and 7B show a driving method according to a fifth embodiment of the present invention. FIG. 7A shows a driving voltage waveform applied to the piezoelectric vibrator 60, and FIG. 7B shows a piezoelectric vibrator as an actuator. 60 is the tip displacement response of FIG. The drive voltage waveform in FIG. 7A includes a rise and fall of the voltage during a time shorter than 30 μs, which is the natural period of the basic (primary) mode, which is the first vibration mode of the piezoelectric vibrator. The voltage rises after adding two pulse-like waveforms S40 and S41. The interval between the rise and fall of the voltage is 3 μs, which is approximately half of the natural period of the third mode, which is the second vibration mode of the piezoelectric vibrator, and the pressure wave for exciting the third displacement mode causes the vibrator to vibrate. Propagated.

Looking at the response to this drive voltage waveform in FIG. 7 (B), after a first rising Q40 in about 4 μs, a plateau Q41 resting for about 3 μs, followed by a second rising Q42 in about 3 μs. Shows the second plateau Q43 again resting for approximately 3 μs. Comparing this embodiment with FIG. 2B, this embodiment shows that the rising speed is about twice as high as that of the prior art, while repeating the rising and stopping.

8A and 8B show a driving method according to a sixth embodiment of the present invention. FIG. 8A shows a driving voltage waveform applied to the piezoelectric vibrator 60, and FIG. 8B shows a piezoelectric vibrator as an actuator. 60 is the tip displacement response of FIG. The drive voltage waveform in FIG. 8A is optimized for the drive waveform, focusing on the first rising Q40 in FIG. 7B. That is, the first voltage rise P50 which is 2.5 times higher than the voltage that gives a static displacement is performed, and subsequently, about half the natural period of the third mode, which is the second vibration mode of the piezoelectric vibrator. The voltage falls P51 at about 3 μs, which is the value of (1), to form a first pulse waveform S50. Subsequently, the pseudo step waveforms S51 and S52 are applied and displaced to a static displacement amount. This pseudo step waveform needs to be optimized to a waveform that suppresses ringing in the fundamental mode to cancel out when combined with the first pulse waveform S50. In the present embodiment, the rise time of the pseudo step waveform is adjusted so that the fundamental mode vibration induced by the first pulse waveform S50 and the fundamental mode vibration induced by the pseudo step waveforms S51 and S52 cancel each other. Control the phases to match. That is, the adjustment is performed at a time when the phases of the two basic modes are different by 180 °. The time required for the rise P52 of the pseudo step waveform is set to 6 μs, which is slightly shorter than the natural period of the secondary mode, so as not to induce the higher mode. The time from rising P52 of the pseudo step waveform to P53 falling to the voltage giving the static displacement amount, that is, the width of the second pulse waveform S51 superimposed on the pseudo step waveform having a constant rising gradient, is effective in reducing the oscillation in the fundamental mode. The time was adjusted to about half the natural period of the fundamental mode for better guidance. By adjusting the height of the second pulse so as to cancel the vibration of the fundamental mode induced by the first pulse-like waveform, as shown in FIG. Driving in a stepwise manner rising in 5 μs, which is half the time, can be realized.

9A and 9B show a driving method according to a seventh embodiment of the present invention. FIG. 9A shows a driving voltage waveform applied to the piezoelectric vibrator 60, and FIG. 9B shows a piezoelectric vibrator as an actuator. 60 is the tip displacement response of FIG. The drive voltage waveform of FIG. 9A is optimized by the same approach as the drive voltage waveform of FIG. 8A. Unlike FIG. 8A, in the first pulse waveform S60 and the pseudo step waveforms S61 and S62, the voltage rising gradients P60, P62 and P63, and the voltage falling gradients P61 and S61 are used to simplify the driving circuit. P64 is a constant value.

応 答 In both the responses of FIGS. 8B and 9B, the ringing can be suppressed, but the overshoots Q52 and Q62 are slightly larger. It is possible to suppress this overshoot by superimposing the third, fourth and pulse-like waveforms on the pseudo step waveform. However, when the waveform becomes complicated, the driving circuit becomes complicated, and it is expected that the expected effect or function does not function due to slight parameter fluctuation. In the embodiment shown in FIG. 8 or FIG. 9, the speed of the initial rise Q50, Q60 is improved about six times as compared with the prior art of FIG. Therefore, the speed of the actuator is more important than the high-speed positioning function of the actuator, and this is a very effective driving method in an application field in which overshoot having a frequency component on the order of the fundamental mode is not a problem.

In the above embodiments, the driving method has been described by taking the vertical vibrator made of a piezoelectric element as an example. However, it is apparent that the same operation and effect can be obtained by the same operation principle even in other vibration modes. For example, for a torsional vibrator, the equation of motion is similar to a longitudinal vibrator, and by replacing the longitudinal elastic modulus for a longitudinal vibrator with the transverse elastic modulus for a torsional vibrator, a series of formulas for torsional vibration are obtained. Is obtained. Also in the case of the transverse oscillator, the idea of the present invention that suppresses the vibration of the primary mode while realizing a steep rise by the higher mode using the vibration of the first mode, the second mode, and the third mode can be applied. . However, in the transverse oscillator, the natural frequencies of the first mode, the second mode, and the third mode are not linearly arranged like the longitudinal oscillator and the torsional oscillator, and the natural oscillation of the first mode and the higher mode is not performed. Because of the large difference between the numbers, it is more difficult to optimize the drive waveform than other transducers.

Here, since the piezoelectric vertical vibrator described so far uses the piezoelectric lateral effect, when a voltage is applied in the same direction as the voltage at the time of polarization, the piezoelectric vertical vibrator generates negative distortion (negative displacement). I do. Conversely, in the case of a piezoelectric longitudinal vibrator using the piezoelectric longitudinal effect, when a voltage is applied in the same direction as the voltage at the time of polarization, the piezoelectric longitudinal vibrator generates a positive strain (positive displacement). Therefore, in the present specification, the rise of a driving signal such as a driving force or a voltage may mean a change in a driving signal such as a driving force or a voltage in a direction in which the actuator is driven to a target displacement. Yes, in that case, the terms are used where the rise / fall does not depend on the positive / negative sign.

It is clear that the present invention can be applied not only to a piezoelectric vibrator (electrostrictive vibrator) but also to a magnetostrictive vibrator. In a piezoelectric vibrator, an electric field generated by a driving voltage generates a driving force, whereas in a magnetostrictive vibrator, the strength of a magnetic field generates a driving force. However, if the magnetic field generating means is a coil, the driving current may be interpreted as a driving force.

Next, the ink jet recording apparatus of the present invention will be described in detail with reference to the drawings.

FIG. 10 shows an ink jet recording apparatus using a piezoelectric vibrator in a longitudinal vibration mode as an actuator, in which each component is disassembled so that the internal structure can be seen. FIG. 11 is a partial cross-sectional view of the embodiment shown in FIG.

In FIG. 10, the channel forming member 3 is formed with two elongated rows of linear cavities 51, 51, 51,... One end of the cavity communicates with a window 41 that forms an ink reservoir described later. By sandwiching and sealing the flow path forming member 3 between the nozzle substrate 1 and the vibration plate 7, the elongated linear cavity 51 forms the ink chamber 5, and the window 41 forms the ink reservoir 4. . The nozzle plate 1 has perforated nozzles 2, 2, 2,... Corresponding to the ink chambers 5, and the nozzle 2 is connected to one end of the ink chamber 5.

The actuator 22 serving as a driving source of ink droplet ejection is a vertical vibrator having one end fixed to the element fixing substrate 21 so that a rod-shaped laminated piezoelectric element is projected from the element fixing substrate 21 in a beam shape. A plurality of piezoelectric elements are mounted on the element fixing substrate 21 to constitute an actuator unit. As shown in FIG. 11, the laminated piezoelectric element has an active portion in which electrode layers 26 and 27 alternately intersecting at a beam-like portion and a piezoelectric material (in this embodiment, lead zirconate titanate is used) are laminated. One electrode layer 27 is connected as an individual electrode for each actuator, and the other electrode layer 26 is connected to an external drive circuit (not shown) via a lead frame 25 as an electrode common to the actuator. The arrangement of the actuators 22 is arranged at the same interval as the ink chambers 5 so that one actuator 22 corresponds to one ink chamber 5. In the embodiment shown in FIG. 10, two actuator units are mounted corresponding to the two rows of ink chambers 5.

The ink flow path component and the actuator unit are fixed to each other by the base 11. An ink supply pipe 31 is press-fitted and adhered to the base 11. The ink is supplied from an external ink tank (not shown) to the ink reservoir 4 and further to the ink chamber 5 through the ink supply pipe 31 and the ink communication port 33 provided in the diaphragm 7. The diaphragm 7 constituting the bottom wall of each ink chamber 5 can be deformed as an elastic wall 8, and has an island-shaped leg 9 formed for each ink chamber on a surface opposite to the ink chamber 5. It has become. The tip of the beam-shaped actuator 22 is joined to the leg 9 of each ink chamber.

When a voltage is applied between the individual electrode 27 and the common electrode 26 of the laminated piezoelectric element by an external drive circuit (not shown), the active portion of the laminated piezoelectric element contracts in the longitudinal direction with the element fixing substrate 21 as a fulcrum, The elastic wall 8 of the chamber 5 is deflected downward in FIG. 11 to increase the volume of the ink chamber 5. As the volume of the ink chamber 5 increases, ink is supplied from the ink reservoir 4 to the ink chamber 5 via the supply flow path 6. When the voltage application between the individual electrode 27 and the common electrode 26 is released in a subsequent time, the active portion of the multilayer piezoelectric element expands to its original length and reduces the volume of the ink chamber 5, and the pressure generated at this time causes A part of the ink that satisfies 5 is ejected as an ink droplet from the nozzle 2 communicating with the ink chamber 5.

Next, the actuator unit will be described in more detail with reference to FIG.

FIG. 12 is an enlarged view of the actuator unit of the embodiment shown in FIG. The element fixing substrate 21 is made by processing an alumina substrate having a thickness of 1 mm. The beam-shaped protrusion 42 is provided for positioning the actuator unit and the base 11. As shown in FIG. 11, one of the stacked electrodes of the stacked piezoelectric elements (actuators 22) arranged in a row is connected to an external electrode at the beam-shaped tip of the stacked piezoelectric element, and further connected to an electrode 28 on the side surface. are doing. The other end of the laminated electrode is connected to an external electrode at the end of the laminated piezoelectric element which is fixed to the element fixing substrate 21, and is connected to an electrode 29 formed on a side surface facing the electrode 28. The electrodes 29 provided on the bonding surface of the multilayer piezoelectric element with the element fixing substrate 21 serve as electrical contacts of the individual electrodes individually provided on the multilayer piezoelectric element. It is electrically connected to a conductive pattern 24 provided on the fixed substrate 21 corresponding to each of the actuators 22. An electrode 28 provided on the other surface of the laminated piezoelectric element is connected as an electrical contact of a common electrode by a conductive member 23, and passes through dummy piezoelectric elements 32 provided at both ends of the piezoelectric vibrator row, and then to an element fixing substrate. 21 is connected to the conductive pattern. The terminals on both sides of the lead frame 25 are connected to an external drive circuit as the terminals of the common electrode, and the terminals on the inside are used as the terminals of the individual electrodes of the individual laminated piezoelectric elements except for the dummy piezoelectric elements.

In the present embodiment, the ink chambers 5 are arranged in rows at intervals of 282 μm, that is, at a density of 90 nozzles per inch, and as shown in FIG. Is configured. Therefore, the pitch of the actuators 22 of the actuator unit is also 282 μm.

The actuator is manufactured by bonding a plate-shaped laminated piezoelectric element to the element fixing substrate 21 so as to project from the element fixing substrate 21 and then cutting the laminated piezoelectric element into a strip shape having a pitch of 282 μm using a wire saw or the like. Thus, individual actuators 22 are formed. As a cutting method, a dicing saw may be used. The laminated piezoelectric element has a thickness of about 0.5 mm in the laminating direction, and a length of a portion protruding from the element fixing substrate 21 is about 8 mm. In order to arrange at a pitch of 282 μm, the width in the arrangement direction is 150 μm, and the margin for cutting is about 130 μm.

Next, the structure of the diaphragm 7 constituting the bottom wall of the ink chamber 5 will be described in detail with reference to FIG.

FIG. 13 is a partial perspective view of the diaphragm 7 forming the elastic wall 8 of each ink chamber 5 as viewed from the actuator 22 side. The actuator 22 expands and contracts perpendicularly to the diaphragm 7 by applying a voltage to the piezoelectric element. The vibrating plate 7 has, on the outside of the ink chamber 5 which is an elastic wall of each of the ink chambers 5, legs 9 which are elongated island-shaped thick portions along the elongated linear ink chamber, respectively. Is formed for each ink chamber. Conversely, the periphery of the island-shaped leg 9 is a thin plate portion 10, and wide thin plate portions 10 a and 10 b are formed at both ends of the leg portion 9. Each pattern is arranged in rows at regular intervals of 282 μm so as to correspond to the arrangement of the ink chambers 5.

お よ そ The approximate volume deformation of the ink chamber 5 due to the expansion and contraction of the actuator 22 is given by the volume excluded by the vertical movement of the wall surface of the elastic wall 8. In order to deform the ink chambers 5 arranged at a high density in this way and to discharge the amount of ink required for pixel formation from the nozzles 2 as ink droplets, the ink chamber 5 of the present invention is formed to be elongated. A large area of the elastic wall 8 which constitutes one surface thereof and is deformed in accordance with expansion and contraction of the actuator 22 is secured. In this embodiment, the width of the ink chamber 5 is 200 μm, and the length is about 1 mm. The thickness of the thick portion and the thin portion of the diaphragm 7 varies depending on the material constituting the diaphragm 7, but when nickel is used, the thick portion has a thickness of about 25 μm, and the thin portion has a thickness of about 25 μm. The thickness is about 1 μm to 3 μm.

吐出 In order to eject minute ink droplets from the nozzles at high speed, it is necessary to increase the natural frequency (Helmholtz frequency) of the vibration mode of the ink chamber related to the ejection of ink droplets.

イ ン ク In the ink flow generated in the ink flow path of the inkjet head, the mass of the ink acts as inertance when accelerating the ink in the narrow flow path. Further, since the ink chamber is elastically deformed by the ink pressure, or the ink filling the ink chamber is compressed and expanded by the ink pressure, these volume displacements act as compliance. Therefore, due to the combination of inertance and compliance, the response of the ink chamber has a unique vibration mode, the frequency of which is the Helmholtz frequency obtained by the following equation.

Here, the C _c ink chamber compliance, the M _n inertance of the ink in the nozzle, the M _s is the inertance of the ink supply channel.

C _c is the sum of the component due to the compressibility of the ink and the component due to the flexibility of the peripheral wall of the ink chamber. The component C _ink due to the compressibility of the _ink is obtained by the following equation.

Here, κ is the volume compression ratio of the ink, which is about 0.45 (GPa) ⁻¹ for the water-based ink. _Vc is the volume of the ink chamber. A component due to the flexibility of the peripheral wall of the ink chamber cannot be expressed by a simple equation in a complicated ink chamber structure, and is generally obtained by using a numerical analysis means using a finite element method or the like.

Further, M _c and M _s can be expressed by the following equations, where S is the cross-sectional area of the flow path, ρ is the ink density, and L is the length of the flow path.

Here, k is a shape factor determined by the cross-sectional shape of the flow channel, and is approximately 1.3 in a circular pipe.

When the flow path has a complicated shape, it is obtained by using a numerical analysis method using a finite element method or the like as in the case of compliance.

Now, when the Helmholtz frequency of the present embodiment is calculated using the above method, the result is as follows.

That is, the inertance _Mn of the nozzle is _Mn = 70 × 10 ⁶ kg / m ⁴ when the nozzle diameter is 40 μm, the length of the straight pipe portion is 20 μm, and the tapered portion connected to the straight pipe portion is added. The inertance M _s of the supply channel is M _s = 60 × 10 ⁶ kg / m ^{4 because the} length is 150 μm in a rectangular cross section of 60 μm × 60 μm. Most of the compliance is contributed by the thin plate portion of the elastic wall 8 of the ink chamber 5, and is approximately C _c = 1 × 10 ⁻¹⁹ m ³ / Pa. The Helmholtz frequency calculated using these values is 90 kHz, and its natural period is 11 μs.

In order to drive the actuator 22 to generate strong pressure vibration in the ink chamber 5, it is necessary to start the actuator 22 faster than the natural period of the vibration mode of the ink chamber related to ink ejection determined by the Helmholtz frequency. The basic period of the longitudinal vibration mode of the actuator 22 is about 16 μs. By applying the drive voltage waveform shown in FIG. 14 to this actuator, the actuator is started up in about 5 μs, which is about three times faster than the fundamental period of the longitudinal vibration mode. Can be done.

The driving waveform shown in FIG. 14 is the same as the driving method of the actuator shown in FIG. 3. In FIG. 3, the vertical vibrator using the piezoelectric lateral effect is contracted. The sign of the rise and fall of the drive voltage is opposite between FIGS. 3 and 14 in order to apply to extending the used longitudinal vibrator.

The drive waveform shown in FIG. 14 shows that the voltage P71 rises more slowly than the basic period of the actuator 22 and the natural period of the ink chamber 5 and then falls P71 during a time shorter than the basic period of the actuator 22. After adding a pulse-like waveform consisting of rising P72, the voltage is lowered again. The actuator 22 contracts in the longitudinal direction by the rise P70 of the voltage, causing the elastic wall 8 of the ink chamber 5 to bend downward in FIG. As the volume of the ink chamber 5 increases, ink is supplied from the ink reservoir 4 to the ink chamber 5 via the supply flow path 6. Next, by the voltage drop P71, the voltage rise P72, and the voltage drop P73, the actuator elongates in the longitudinal direction at 5 μs, which is about the natural period of the secondary mode that is the second vibration mode, and the volume of the ink chamber 5 is increased. Is rapidly reduced in a time shorter than the natural cycle of the ink chamber 5. The pressure generated at this time excites the ink filling the ink chamber 5 with a large pressure oscillation having a Helmholtz frequency, and the ink droplets are ejected at high speed from the nozzle 2 communicating with the ink chamber 5.

As in the embodiment of FIG. 3, in the drive waveform of FIG. 14, the time from the voltage fall P71 to the voltage rise P72 and the time from the voltage rise P72 to the second voltage fall P73 are about 3 μs. , About half the natural period of the second mode, which is the second vibration mode of the actuator 22.

FIG. 15 shows a second embodiment of the present ink jet recording apparatus, in which the signs of the drive voltage drop and rise are opposite to those of the actuator driving method shown in FIG.

The drive waveform shown in FIG. 15 has a voltage fall P81 during a time shorter than the basic cycle of the actuator 22 after the rise P80 of the voltage that rises more slowly than the basic cycle of the actuator 22 and the natural cycle of the ink chamber 5. After adding a pulse-like waveform consisting of the rising P82, the voltage is lowered again to perform P83, a smaller voltage rising P84 is performed, and finally the voltage is gradually reduced to perform P85 to return to the voltage 0. ing. The actuator 22 contracts in the longitudinal direction due to the voltage rise P80, causing the elastic wall 8 of the ink chamber 5 to bend downward, thereby increasing the volume of the ink chamber 5. As the volume of the ink chamber 5 increases, ink is supplied from the ink reservoir 4 to the ink chamber 5 via the supply flow path 6. Next, by the voltage falling P81, the rising P82, the falling P83, and the rising P84, the actuator elongates in the longitudinal direction for about 5 μs, which is a value of about the natural period of the secondary mode that is the second vibration mode, At this time, as shown in FIG. 5, the ringing after the extension of the actuator 22 is suppressed to be low, and unnecessary vibration of the ink chamber 5 is suppressed.

As in the embodiment of FIG. 5, in the drive waveform of FIG. 15, the time from the voltage fall P81 to the voltage rise P82, the time from the voltage rise P82 to the second voltage fall P83, and the second time The time from the falling P83 of the voltage to the rising P84 of the small voltage is about 3 μs, which is about half the natural period of the second mode, which is the second vibration mode of the actuator 22. Vibration is strongly excited. The height of the voltage rise P84 is adjusted to a value that optimally suppresses ringing in the basic mode.

FIG. 16 shows a third embodiment of the ink jet recording apparatus, in which the signs of the drive voltage drop and rise are opposite to those of the actuator driving method shown in FIG.

The drive waveform shown in FIG. 16 has a voltage fall P91 during a time shorter than the basic cycle of the actuator 22 after the rise P90 of the voltage that rises more slowly than the basic cycle of the actuator 22 and the natural cycle of the ink chamber 5. After adding a pulse-like waveform consisting of a rise P92, the voltage is lowered again, and a small voltage rise P94 is performed again. Finally, the voltage is gradually reduced to P95 to return to the voltage 0. The voltage fall P93 is larger than the voltage fall P91, and the potential after the voltage rise P94 is set higher than the potential after the voltage fall P91.

(6) As shown in FIG. 6, the ringing after the extension of the actuator 22 is suppressed to be lower than that of the previous embodiment by the present drive voltage waveform, and unnecessary vibration of the ink chamber 5 is suppressed.

In the embodiments shown in FIGS. 14, 15 and 16, slight ringing occurs after the actuator 22 is extended. Most of the ringing component is a component of the first-order mode of the actuator, and its fundamental period is about 16 μs. However, in the ink jet recording apparatus of this embodiment, the natural period of the ink chamber 5 determined by the Helmholtz frequency is about 11 μs, which is set shorter than the basic period of the actuator. Accordingly, the ink chamber 5 is excited by ringing having a cycle longer than the natural cycle of the ink chamber 5, but the response of the ink chamber 5 to this excitation is small, and the ink jet 5 does not eject unnecessary mist-like ink droplets. An excellent ink jet recording apparatus has been realized.

In addition, conventionally, to drive the actuator in 5 μs, the length of the actuator had to be shortened to about 3 mm, and a voltage of about 30 V was required to obtain a required ink droplet weight. However, according to the above embodiment, the driving voltage was at most about 10 V, and a voltage reduction of about one third could be achieved.

In the embodiments described above, since the piezoelectric lateral effect is used as the actuator, the basic mode that becomes the first vibration mode when the drive voltage drops after the drive voltage is increased and the volume of the ink chamber 5 is increased. A pulse-like waveform consisting of a voltage fall and a rise is inserted in a section shorter than the natural period of, and then the voltage falls.

On the other hand, in the actuator using the piezoelectric longitudinal effect and the actuator using the magnetostriction effect, the displacement of the ink chamber 5 is caused to be reduced in accordance with the increase of the voltage. Therefore, as shown in FIG. 17, as the driving voltage waveform, a pulse-shaped waveform consisting of a rising P100 and a falling P101 of the voltage during a period shorter than the natural period of the basic mode that is the first vibration mode when the voltage rises. , And then using a pseudo step waveform in which an auxiliary pulse composed of a rising P102 and a falling P103 of the voltage is superimposed, the same effect as in the previous embodiment can be obtained.

It is a perspective view of the actuator to which the present invention is applied. FIG. 7 is a diagram illustrating a drive voltage waveform and an actuator displacement according to a conventional drive method. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 2 is a diagram showing an example of a drive waveform of the present invention applied to the actuator of FIG. 1. FIG. 1 is a perspective view illustrating a structure of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of the ink jet recording apparatus of FIG. FIG. 11 is a perspective view illustrating an actuator structure of the ink jet recording apparatus of FIG. 10. FIG. 11 is a perspective view illustrating a structure of a diaphragm of the ink jet recording apparatus of FIG. 10. FIG. 11 is a diagram illustrating an example of a drive voltage waveform for driving the inkjet recording apparatus of FIG. 10. FIG. 11 is a diagram illustrating an example of a drive voltage waveform for driving the inkjet recording apparatus of FIG. 10. FIG. 11 is a diagram illustrating an example of a drive voltage waveform for driving the inkjet recording apparatus of FIG. 10. FIG. 3 is a diagram illustrating an example of a driving voltage waveform for driving the inkjet recording apparatus. It is a figure explaining the vibration mode of a vertical vibrator. FIG. 9 is a diagram illustrating a conventional actuator driving method and its response. FIG. 9 is a diagram illustrating a conventional actuator driving method and its response.

Explanation of reference numerals

1 nozzle substrate, 2 nozzle, 3 channel forming member, 4 ink reservoir, 5 ink chamber, 6 supply channel, 7 diaphragm, 8 elastic wall, 9 leg, 10 flexible section, 11 head frame, 21 element fixing Substrate, 22 ° actuator, 60 ° piezoelectric vibrator

Claims (14)

In a method for driving an actuator having a first vibration mode displaced by a driving force of a driving unit and excited by the driving force, and a second vibration mode higher in order than the first vibration mode,
By performing at least one rise and fall of a pulse-like driving force having a width substantially half the natural period of the second vibration mode during a section shorter than the period of the first vibration mode. Exciting the second vibration mode,
A driving method for an actuator, wherein a driving force for driving a necessary displacement is applied after that. The time from the fall of the pulse-shaped driving force to the driving force for driving to the required displacement is set to substantially half of the natural period of the second vibration mode. Actuator driving method. 3. The actuator according to claim 1, wherein the magnitude of the rise and fall of the pulse-shaped driving force is larger than the magnitude of the driving force driving the required displacement. 4. Method. 4. The method of driving an actuator according to claim 1, wherein the driving force for driving to the required displacement is obtained by superimposing a pulse-like driving force on a step-like driving force. 5. The method according to claim 4, wherein the superimposed pulse-like driving force suppresses the vibration of the first vibration mode so as to cancel the vibration. 5. The method according to any one of claims 1 to 5, wherein the actuator comprises an electrostrictive vibrator or a magnetostrictive vibrator. The method according to any one of claims 1 to 5, wherein the actuator is a vertical vibrator, a horizontal vibrator, or a torsional vibrator. In a liquid ejecting apparatus that discharges liquid droplets from a nozzle communicating with the liquid chamber by vibrating a part of a peripheral wall that defines the liquid chamber by an actuator,
The actuator is displaced by a driving force of a driving unit, and has a first vibration mode excited by the driving force, and a second vibration mode higher in order than the first vibration mode. During a section shorter than the cycle of the vibration mode, the drive force in the form of a pulse having a width substantially half of the natural cycle of the second vibration mode is raised and lowered at least once, whereby the second An ink jet recording apparatus which excites a vibration mode and then applies a driving force for driving to a required displacement. 9. The time period from the fall of the pulse-shaped driving force to the driving force for driving to the required displacement is set to substantially half the natural period of the second vibration mode. Inkjet recording device. 10. The ink jet recording apparatus according to claim 8, wherein the magnitude of the rise and fall of the pulse-shaped driving force is larger than the magnitude of the driving force for driving to the required displacement. . 11. The ink jet recording apparatus according to claim 8, wherein the driving force for driving to the required displacement is obtained by superimposing a pulse-like driving force on a step-like driving force. 12. The ink jet recording apparatus according to claim 11, wherein the superimposed pulse-like driving force suppresses the vibration in the first vibration mode so as to cancel the vibration. 9. The device according to claim 8, wherein the actuator is an electrostrictive vibrator driven in a longitudinal vibration mode, and a driving force of the driving unit is given by a voltage applied to a drive electrode formed on the electrostrictive vibrator. The inkjet recording apparatus according to any one of claims 1 to 12. The ink chamber has a vibration mode of the ink chamber related to the ejection of ink, a natural cycle of the first vibration mode of the actuator is larger than a natural cycle of the vibration mode of the ink chamber, and a natural cycle of the second vibration mode. 14. The ink jet recording apparatus according to claim 8, wherein a period is shorter than a natural period of the vibration mode of the ink chamber.

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