JPH1024570A - Ink jet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the stable discharge of an ink droplet and maintain the target position of the ink droplet constantly regardless of drive frequency, environmental temperature and flow path dimension. SOLUTION: This ink is jet recording device comprises a drive pulse generating means 120 which outputs a first pulse for enlarging a pressure generating chamber, a second pulse for shrinking the pressure generating chamber from its inflated state and thereby, discharging an ink droplet from a nozzle and a third pulse for enlarging the pressure generating chamber again after the second pulse, and a drive pulse control means 130 which controls the timing to start the second pulse and the timing to start the third pulse with the help of a means to detect environmental temperature in a accordance with the environmental temperatures. In addition, the second pulse start time is adjusted so that a position for drawing a meniscus at the time of discharging the ink droplet is constant and thus the discharge velocity of the ink droplet is set to be constant. Further, the third pulse is applied to inflate the pressure generating chamber again at the stage in which the oscillation of the meniscus generated by the discharge of the ink droplet is fully shifted to the pressure generating chamber. Consequently, the kinematic energy of the meniscus tending to move toward the nozzle is effectively attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for driving an ink jet recording head using a piezoelectric vibrator as a drive source.

[0002]

2. Description of the Related Art An on-demand type ink jet recording head communicates with a plurality of pressure generating chambers for generating ink pressure by piezoelectric vibrators and heating elements, a common ink chamber for supplying ink to each pressure generating chamber, and each pressure generating chamber. A flow path having a nozzle is provided, and a drive signal is applied to the pressure generating chamber of the nozzle corresponding to the print signal so that the ink droplet flies from the nozzle to the recording medium.

In such an ink jet recording head, there is a so-called bubble jet type in which a resistance wire for generating Joule heat is provided in a pressure generating chamber as a pressure generating means, and ink droplets are ejected by utilizing the pressure at which bubbles are generated.

On the other hand, a pressure generating chamber partially constituted by an elastic plate is formed by a piezoelectric vibrator using a piezoelectric vibrator, which is formed by alternately laminating a piezoelectric material and a conductive layer, and uses an axial extension thereof, that is, a longitudinal vibration mode. There is also known a piezoelectric vibration type that expands and contracts to suck ink and discharge ink droplets.

[0005] The former method has a drawback that the ink and the head itself are liable to be deteriorated due to the use of heat generation, while a high-density device can be easily manufactured at a low cost.

However, since the latter method does not generate heat, it does not cause deterioration of the ink, and has a wide use range of the ink.
In addition, there is a feature that the head life is semi-permanent and the running cost is low. In addition, the piezoelectric vibrator having the longitudinal vibration mode has a feature that it can be driven at high speed and can repeatedly expand and contract the pressure generation chamber at a high speed by being brought into contact with the pressure generation chamber. I have.

[0007]

The on-demand type ink jet head has the following problems.

After the pressure is generated in the pressure generating chamber and the ink droplets are ejected, pressure fluctuations remain in the pressure generating chamber, so that the meniscus in the nozzle vibrates at a resonance cycle (Helmholtz resonance cycle) unique to the pressure generating chamber. While recovering to the nozzle tip.

The cycle of the residual vibration is very small, and is shorter than the time required for the meniscus to reach the nozzle tip (hereinafter referred to as meniscus recovery time).

When high-frequency driving is performed, if the ejection of the next ink droplet is to be started before the minute residual vibration is sufficiently suppressed, the meniscus is not stable.
The ejected ink droplet may become unstable. result,
The flight direction changes, ink mist is generated,
There is a problem that the printing quality is likely to be reduced, which results in hindrance to improving the response frequency of the ink jet recording head.

The vibration behavior of the meniscus is liable to change depending on the dimensional variation of the flow path, the physical properties of the material and the ink, and further changes depending on the environmental temperature. Therefore, the residual vibration of the meniscus is effectively reduced by the fixed driving method. I can't control it.

For this reason, there is also a problem that the dimensional control of the flow path is strictly controlled, the selection range of the flow path forming material and the ink is narrowed, the manufacturing cost is increased, and the degree of freedom of design is reduced. Was.

[0013] On the other hand, the following problems also occur when ejecting ink droplets.

When the pressure generating chamber is expanded, the meniscus in the nozzle is drawn toward the pressure generating chamber, but the ink is gradually supplied to the pressure generating chamber, so that the meniscus gradually recovers to the nozzle tip side. To go.

Here, if the ink is ejected after the meniscus reaches the nozzle tip, the ejection speed of the ink droplet is always constant regardless of the ejection timing. However, when performing high-frequency driving, it is necessary to perform expansion and contraction of the pressure chamber in a short lead time.Therefore, depending on the recovery time of the meniscus, the ink is discharged before the drawn meniscus reaches the nozzle tip sufficiently. Must be ejected.

Further, in order to secure the ejection speed of the ink droplets and to stabilize the ejection, it is better to eject the ink droplets vigorously with the meniscus retracted to some extent.

From the above background, the above-described ejection method is generally used in the piezoelectric vibration method.

However, the amount of meniscus drawn in and the recovery time to the tip of the nozzle are:
Similar to the vibration of the meniscus after the ink droplet is ejected, it varies depending on the dimensional variation of the flow path, the difference in the material and physical properties of the ink, and furthermore, the environmental temperature. There is a problem in that the drawing positions of the ink droplets vary, resulting in variations in the ejection speed of the ink droplets and the amount of the ejected ink.

For this reason, there are also problems that the dimensional control of the flow channel is strictly controlled, the selection range of the flow channel material and ink is narrowed, the manufacturing cost is increased, and the degree of freedom in design is reduced. Was.

The present invention has been made in view of such a problem, and aims at ensuring stable ejection of ink droplets even at a high frequency drive, as well as dimensional variations in ink flow paths, materials, and the like. Stable discharge can be ensured against changes in the physical properties of ink and changes in environmental temperature.Furthermore, it is possible to maintain a constant ink discharge speed to maintain a constant ink droplet landing position and secure a stable image. Another object of the present invention is to provide a simple ink jet recording apparatus.

[0021]

According to the present invention, there is provided an ink jet recording apparatus comprising: a pressure generating chamber which communicates with a common ink chamber via a nozzle and an ink supply port and has a Helmholtz resonance frequency of a period Tc; An ink jet recording head comprising a piezoelectric vibrator for expanding and contracting a chamber; a first pulse for expanding the pressure generating chamber; and a first pulse for discharging the ink droplet from the nozzle by contracting the pressure generating chamber in an expanded state. Drive pulse generating means for outputting a second pulse, a third pulse for expanding the pressure generating chamber again after the second pulse, a timing of starting the second pulse, and a timing of starting the third pulse And drive pulse control means for arbitrarily controlling the driving pulse.

Further, the timing of the start of the second pulse is controlled by drive pulse control means so that the position of the meniscus in the nozzle at the timing of the start of the second pulse becomes constant. .

Further, the apparatus further comprises the drive pulse control means for arbitrarily setting the start timing of the second pulse in accordance with the flow path impedance of the nozzle and the ink supply port.

Further, the timing of starting the second pulse is set so as to be early when the flow path impedance of the nozzle or the ink supply port is small and to be late when the flow path impedance is large.

Further, the timing of starting the second pulse is set so as to be early when the cross-sectional area of the nozzle or the ink supply port is large, and to be late when the cross-sectional area is small.

Further, the timing of starting the second pulse is set to be earlier when the length of the nozzle or the ink supply port is long, and to be late when the length of the nozzle or the ink supply port is short.

[0027] Further, there is provided an environmental temperature detecting means, wherein the timing of starting the second pulse is controlled by the driving pulse control means according to the environmental temperature.

Further, the timing of starting the second pulse is set to be early when the environmental temperature is high, and to be late when the environmental temperature is low.

Further, the timing of the start of the third pulse is controlled by the drive pulse control means so that the vibration of the meniscus generated after the ejection of the ink droplets becomes almost the same as the time when the meniscus moved to the pressure generating chamber most. It is characterized by being.

The driving pulse control means for arbitrarily setting the timing of starting the third pulse in accordance with the cycle Tc of the pressure generating chamber is provided.

Further, the apparatus further comprises an environmental temperature detecting means, wherein the timing of starting the third pulse is controlled by the driving pulse control means according to the environmental temperature.

Further, the timing of starting the third pulse is set so as to be earlier when the ambient temperature becomes higher and to be later when the ambient temperature becomes lower.

Further, the duration of the second pulse and the duration of the third pulse are set to be the same, and the time from the start of the second pulse to the start of the third pulse is determined by the cycle of the pressure generating chamber. The time is set so as to substantially coincide with Tc.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of an ink jet recording head used in the ink jet recording apparatus of the present invention.

In the figure, reference numeral 1 denotes a nozzle plate in which the nozzle 2 is formed, reference numeral 7 denotes a flow path forming plate formed so that the pressure generating chamber 3, the common ink chamber 4, and the ink supply port 5 communicate with each other, and 8 denotes an elastic plate. is there. The ink flow path unit is formed by integrally forming the flow path forming plate 7 so as to be sandwiched between the nozzle plate 1 and the elastic plate 8.

The piezoelectric vibrator 9 is formed by alternately laminating a piezoelectric material and a conductive material. The piezoelectric vibrator 9 contracts in a charged state in a direction perpendicular to the lamination direction of the conductive layers, and when the charged state is released, the lamination with the conductive layers. A so-called longitudinal vibration mode vibrator extending in a direction perpendicular to the direction, in which an inactive portion at the tip where no electrode is present is in contact with the elastic plate 8 in the region of the pressure generating chamber 3 and the other end is a fixed substrate. It is fixed to 10.

The ink jet recording head configured as described above discharges ink droplets by the following drive.

When a driving voltage is applied to the piezoelectric vibrator 9 to perform charging, the piezoelectric vibrator 9 contracts to deform the abutting elastic plate 8, thereby expanding the pressure generating chamber 3 and causing the ink supply port 5 to expand.
The ink flows from the common ink chamber 4 into the pressure generating chamber 3 via.

Next, the piezoelectric vibrator 9 is stretched to its original state by the discharge and the elastic plate 8 is pressed, so that a pressure is generated in the pressure generating chamber 3 and the ink droplet is ejected from the nozzle 2. I do.

Further, the pressure generating chamber 3 is expanded again so that the ink droplets are not discharged by the subsequent charging.

Hereinafter, the driving pulse generating means, the driving pulse control means and the driving method thereof will be described in detail.

FIG. 2 is a block diagram showing one embodiment of the ink jet recording apparatus of the present invention.

In the figure, the ink jet recording apparatus includes an ink jet recording head 100 described with reference to FIG. 1, driving nozzle selecting means 110 for selecting the driving of the piezoelectric vibrators 9, 9, 9,... It comprises a driving pulse generating means 120 for generating a driving pulse, a driving pulse control means (CPU) 130 for controlling the driving pulse, and an environmental temperature detecting means 140.

The environmental temperature detecting means 140 detects the surrounding environmental temperature and sends the environmental temperature data to the drive pulse control means (CPU) 130.

The drive pulse control means (CPU) 130
The pulse control signals p1, p2,
Pulse widths pw1, pw2, pw3 according to the environmental temperature based on the relation table between the pulse width of p3.
Are sent to the drive pulse generation means 120. The pulse control signals p1, p2, p3,. Further, the print data is supplied to the drive nozzle selecting means 11 based on a print signal from the outside.
Come to 0.

The drive pulse generating means 120 generates a drive pulse having a desired peak and valley based on a plurality of pulse control signals p1, p2, p3... Sent from a drive pulse control means (CPU) 130.

The generated driving pulse is selectively sent to the piezoelectric vibrator 9 belonging to the nozzle 2 to form a dot via the driving nozzle selecting means 110. Thus, ink droplets are ejected from desired nozzles 2.

In this embodiment, the ink jet recording head 1
A driving nozzle selection unit 110 and an environmental temperature detection unit 140 are mounted on the top of the reference numeral 00. The reason why the environmental temperature detecting means 140 is mounted on the ink jet recording head 100 is to detect the environmental temperature around the ink jet recording head 100 more accurately.

FIG. 3 is a view for explaining an embodiment of the driving pulse formation of the ink jet recording head in the ink jet recording apparatus of the present invention.

The drive pulse of the ink jet recording head of the present invention is a stepped trapezoidal pulse composed of peaks and valleys as shown in FIG. 3A, a first pulse S1 for charging and a second pulse for discharging. S2, third pulse S3 for recharging
Consists of

In this embodiment, the drive pulse control means 130
Are set to p1, p2, p3
, Each of which is the first pulse S of the drive pulse.
1, the second pulse S2, and the third pulse S3, and the drive pulses S1, S2, and S3 are determined by the application timings of the pulse control signals p1, p2, and p3 and their pulse widths pw1, pw2, and pw3. Start timing and duration are determined.

In each step of the driving pulse as described above, the following driving of the ink jet recording head is performed.

When the first pulse control signal p1 is turned on, charging is performed up to a predetermined peak voltage in a time required for the pulse width pw1 and the piezoelectric vibrator 9 contracts. Accordingly, the pressure generating chamber 3 expands, and the meniscus in the nozzle 2 is drawn toward the pressure generating chamber 3 and recovers toward the nozzle tip 21 while vibrating from the most drawn position. At this time, the ink in the common ink chamber 4 flows into the pressure generating chamber 3 via the ink supply port 5.

After the end of the first pulse control signal p1, the voltage is maintained at the peak voltage, and the piezoelectric vibrator 9 also stops deforming and waits for the pulse width pwh1. During this time, the meniscus continues to recover toward the nozzle tip 21.

Subsequently, when the second pulse control signal p2 is turned on during the recovery of the meniscus, the pulse width pw
Discharging is performed until the voltage becomes zero in a period of 2 minutes, and the piezoelectric vibrator 9 is extended. With this, the pressure generating chamber 3 starts to contract, and the pressure is generated in the pressure generating chamber 3 so that the nozzle 2
Ink droplets are ejected. After the ejection of the ink droplets, the meniscus starts oscillating in the nozzle 2.

By the way, the meniscus vibrating after the ejection of the ink droplet is most drawn into the pressure generating chamber 3 side,
This time, the movement toward the nozzle tip 21 is started. If the third control pulse signal p3 is set to be turned on at this time, it takes a time corresponding to the pulse width pw3 and a predetermined intermediate time is required. Since the piezoelectric vibrator 9 is charged to a potential and slightly shrinks, the pressure generating chamber 3 expands. Due to the expansion of the pressure generating chamber 3, the kinetic energy of the meniscus toward the nozzle tip 21 is reduced, and the residual vibration of the meniscus can be rapidly attenuated as shown by the solid line L1 in FIG.

In the driving described above, in the present invention, the means for adjusting the application timing of the second pulse (S2) and the third pulse (S3) is used to keep the pull-in position of the meniscus at the time of ink droplet ejection. And effective damping of the residual vibration of the meniscus after ink droplet ejection.

First, a first embodiment for adjusting the second pulse (S2) will be described.

In the first embodiment of the present invention, the start time pw5 (= pw1 + pwh1) of the second pulse (S2) from the start of the first pulse (S1) can be adjusted.
The application timing of the second pulse (S2) (hereinafter simply referred to as ejection timing) can be adjusted.

FIGS. 4 and 5 are diagrams for explaining the relationship between the driving pulse of the ink jet recording head, the behavior of the meniscus, and the pull-in position of the meniscus during ejection in the ink jet recording apparatus according to one embodiment of the present invention.

The meniscus pull-in and recovery behavior caused by the driving of the first pulse depends on the inherent flow path impedance of the ink jet recording head, and this flow path impedance is the inertance M of the nozzle 2.
n, the resistance Rn, the inertance Ms of the ink supply port 5, and a value roughly determined by the resistance Rs.
The flow path impedance Z is as follows: Z = (Rn + Rs) + (Mn × ω + Ms × ω) Here, ω = 1 / Tc, and Tc is a Helmholtz resonance period described later.

Inertance Mn · Ms, Resistance R
Since n · Rs fluctuates due to variations in the flow path dimensions of the nozzle 2 and the ink supply port 5 and the like, and also fluctuates due to changes in ink physical properties (viscosity and density) due to environmental temperature, meniscus pull-in and Recovery behavior varies.

Nevertheless, if the drive is always performed with the ejection timing kept constant, as shown in FIG. 4B, a difference in the meniscus behavior causes a difference in the meniscus pull-in position at the ejection timing. The ejection speed of the ink droplets and the amount of the ejected ink vary (compared with La and Lb in the figure).

This is because the landing positions of ink droplets vary,
As a result, variations in the image of each head may occur, which may reduce the production yield of the inkjet recording head.

However, according to the present invention, since the ejection timing can be set arbitrarily, even if the meniscus behavior changes due to variations in the flow path dimensions of the nozzles 2 and the ink supply ports 5 and variations in the ink physical properties, By adjusting the ejection timing (pwh1 → pwh1 ′) as shown in FIG. 5A, it is possible to always eject ink droplets at the same retracted position as shown in FIG. It can be kept constant (compared with La and Lb 'in the figure).

As a result, the landing position of the ink droplet becomes stable,
A stable image can always be expressed.

Further, even if the flow path dimension varies to some extent, it is possible to cope with this by changing the driving pulse without lowering the production yield.

Further, in the present embodiment, an environmental temperature detecting means 140 is further provided to detect the environmental temperature, and the second pulse (S 2) of the driving pulse output from the driving pulse generating means 120 through the driving pulse controlling means 130. ) Is changed.

As a result, it is possible to keep the meniscus pull-in position constant at the ejection timing even if the environmental temperature changes, and it is possible to always form a high-quality image that is stable against environmental changes.

Regarding the first embodiment, the present inventor investigated the relationship between the application timing of the second pulse and the ejection speed for ink jet recording heads of a plurality of specifications having different ink supply port widths and nozzle diameters.

FIGS. 6A and 6B are diagrams for explaining the relationship between the ejection speeds in a plurality of head specifications having different ink supply port widths and nozzle diameters in a driving method in which the application timing of the second pulse is fixed. is there.

In this experiment, the application timing of the second pulse (S2) was set to two points, and the ejection speed of each specification head when ejecting the same ejection ink amount was confirmed. FIG.
(A) is pw5 = (pw1 + pwh1) = (15 + 1)
0) = 25 μs, and FIG. 6B shows pw5 = (pw1 + pw
h1) = (15 + 20) = 35 μs.

In the drawing, the drive of FIG. 6A in which the application timing of the second pulse (S2) is earlier, that is, the drive of FIG. 6A in which pw5 is shorter, discharges ink droplets at the position where the meniscus is more retracted. It can be seen that the speed can be increased.

In both the application timing driving, the ejection speed tends to decrease as the ink supply port width increases and the nozzle diameter increases. In addition, the ejection speed greatly changes due to the difference of several μm in both dimensions, and the ejection speed varies in the range of 3 to 4 m / s in the range of several μm evaluated in this experiment.

FIG. 7 is a view for explaining the relationship between the ink supply port width and the discharge speed in the head specification of the nozzle diameter when the driving method according to the first embodiment of the present invention is performed.

Using the driving method of the first embodiment,
The pwh1 was adjusted for each head specification, and for the specification in which the ink supply port width and the nozzle diameter were wide and the discharge speed was slow, the discharge speed was adjusted by shortening the application timing (pw5) of the second pulse.

As a result, as shown in FIG. 6, the variation in the discharge speed can be reduced, and in this experiment, the dispersion of the discharge speed can be reduced to 1 m / s or less in the range (in FIG. The asterisks and the asterisks indicate that adjustment was made to drive at pw5 = 25 and 35 μs, respectively.)

By adjusting the application timing (pw5) of the second pulse in this way, even if the head specifications vary, the variation in the ejection speed can be suppressed to a small value.

In this experiment, pw5 was adjusted at two points. However, if it was adjusted at finer points, the dispersion of the discharge speed could be further reduced.

In this experiment, when adjusting pw5, pw1 was adjusted.
Is fixed and adjustment is performed only with pwh1, but adjustment may be made with pw1. However, if you change pw1,
Since the pull-in behavior of the meniscus further changes, pwh1 needs to be adjusted in addition to this, and the combination of the optimal pulses for each flow path size becomes complicated. Therefore, p
It is preferable that w1 be fixed and only pwh1 be adjusted.

Next, a second embodiment will be described.

In the second embodiment of the present invention, the start time pw4 (= pw2) of the third pulse from the start of the second pulse
+ Pwh2) can be adjusted, and the application timing of the third pulse can be adjusted.

This will be specifically described with reference to the drawings.

FIG. 8 is a diagram showing a driving pulse of an ink jet recording head and a behavior of a meniscus in an ink jet recording apparatus according to an embodiment of the present invention.

Regarding the application timing of the third pulse,
When charging is started and the pressure generating chamber 3 is expanded at the timing when the meniscus is moving to the pressure generating chamber 3 side or the nozzle tip 21 side, effective vibration control of the meniscus is not performed.

That is, in this case, the kinetic energy of the meniscus is not sufficiently reduced, and the vibration of the meniscus remains as shown by a dashed line L2 in FIG. If this is the case, the shape of the meniscus at the time of ink droplet ejection becomes unstable, and as a result, mist is generated in the ejected ink droplet, and ejection ink bending or ejection blur is easily caused.

For this reason, under the drive frequency at which the next ink droplet is to be ejected at the above timing, a stable ejection of the ink droplet cannot be sufficiently ensured, which causes a problem that the print quality is likely to deteriorate.

For this reason, it is necessary to pay attention to the setting of the application timing of the third pulse. However, in the present invention, the means utilizing the Helmholtz frequency of the period Tc, which is a typical meniscus vibration characteristic, is described below. The optimum application timing of the third pulse is easily determined and set.

The representative values of the meniscus vibration characteristics will be described below.

In the ink jet recording head constructed as shown in FIG. 1, the compliance caused by the compressibility of the ink in the pressure generating chamber 3 is Ci, the elastic plate 8 forming the pressure generating chamber 3, the nozzle plate 1, and the like. Assuming that the rigidity compliance of the material itself such as the flow path constituting plate 7 is Cv, the inertance of the nozzle 2 is Mn, and the inertance of the ink supply port 5 is Ms, the Helmholtz resonance period Tc of the ink flow path.
Can be expressed by Tc = 2π × √ ((Mn + Ms) / (Ci + Cv) (Mn × Ms)).

Here, the compliance Ci is Ci = V / ρc ² where V is the volume of the pressure generating chamber 3, ρ is the density of the ink, and c is the speed of sound in the ink.

The rigidity compliance Cv of the pressure generating chamber 3 matches the volume change of the pressure generating chamber 3 when a unit pressure is applied to the pressure generating chamber 3.

Specific examples include a length of 0.5 to 2 mm,
When the pressure generating chamber 3 having a width of 0.1 to 0.2 mm and a depth of 0.05 to 0.3 mm is configured, the Helmholtz resonance period is 5 to 5.
An inkjet recording head of about 20 μs (having a resonance frequency of 50 to 200 kHz) can be configured.

The representative values shown above are largely related to the behavior characteristics of the residual vibration of the meniscus after the ejection of the ink droplet.

As shown in FIG. 8, the meniscus after the ejection of the ink droplet has a small vibration cycle (T) and a large cycle (Tm).

As described above, the effect of the third pulse is most effective when the meniscus is drawn into the pressure generating chamber 3 side. For this reason, the timing of the third pulse at which the vibration of the meniscus can be effectively suppressed exists in a very small cycle T.

That is, the third pulse is applied after a lapse of time corresponding to the oscillation cycle of T from the time of ink droplet ejection (that is, the time pw4 from the start of the second pulse to the start of the third pulse in FIG. 3). Is approximately equal to T)
Means that the meniscus can be effectively damped.

The minute oscillation period (T) of the meniscus
Is the above-mentioned Helmholtz resonance period (Tc), that is, if the minute resonance period Tc can be confirmed by the above-described formula, the optimum application timing of the third pulse can be easily set.

The present inventor investigated the resonance period Tc of the ink jet recording head and the optimum timing of applying the third pulse.

FIG. 9 is a diagram showing the relationship between the resonance period Tc and the optimal third pulse application timing for stabilizing the ejection of ink droplets in the ink jet recording apparatus according to one embodiment of the present invention.

In the figure, the optimum application timing of the third pulse is indicated by the time pw4 from the start of the second pulse to the start of the third pulse.

In this experiment, the third pulse duration pw3 is set to be substantially the same as the second pulse duration pw2. This is because the meniscus oscillation caused by the third pulse is caused by the second pulse because the meniscus oscillation caused by both pulses is generated at substantially the same period by applying the pulse for the same duration. When the phases are opposite to each other, the meniscus is more effectively damped than when the durations of both pulses are not the same.

It is apparent from FIG. 9 that the resonance period Tc and the optimum application timing (pw4) of the third pulse substantially coincide with each other. In the present invention, the Helmholtz resonance period (Tc), which is a representative value of the meniscus vibration characteristics, is determined. Depending on the means used,
It can be seen that the optimum application timing of the third pulse can be easily determined and set.

When the duration pw3 of the third pulse is not the same as the duration pw2 of the second pulse, the resonance cycle Tc does not match the pw4, but the resonance cycle Tc does not match the resonance cycle Tc.
, The resonance period Tc can be easily set to a representative value as long as the shift amount can be grasped.

Incidentally, the vibration of the meniscus after the ejection of the ink droplet also depends on the compliance caused by the compressibility of the ink and the rigidity of the pressure generating chamber 3 and the nozzle 2 and the ink supply port 5 as defined by the above-mentioned equations. And the like, due to a change in inertance due to the shape and size of the ink flow path.

The main causes of these fluctuations are variations in the shape of the ink flow path in manufacturing and changes in the environmental temperature. In particular, when the environmental temperature changes, not only the physical properties of the ink but also the pressure Since the rigidity of the material constituting the chamber 3 also changes, the fluctuation is relatively large.

Accordingly, the resonance oscillation period Tc changes, and accordingly, the optimum application timing of the third pulse also changes.

The present inventor investigated the change of the resonance period Tc of the ink jet recording head due to the environmental temperature.

FIG. 10 is a diagram showing the relationship between the resonance period Tc and the ambient temperature in the ink jet recording apparatus according to one embodiment of the present invention. FIG. 11 shows an optimum third temperature for stabilizing the ejection and the environmental temperature in the inkjet recording apparatus of the present invention.
FIG. 6 is a diagram showing the relationship between the application timings of the pulses.

Obviously, as the environmental temperature increases, the resonance cycle Tc also increases, and the optimum third pulse application timing pw4 changes accordingly.

That is, if the drive is performed with the application timing fixed at a certain constant value, if the resonance cycle Tc greatly changes due to variations in the shape of the ink flow path in manufacturing and changes in the environmental temperature, it is optimal. The vibration of the meniscus is not performed, and the ink droplet ejection becomes unstable.

In this embodiment, the environmental temperature detecting means 1
40, whereby the ambient temperature is detected, and the drive pulse generation means 130
The application timing of the third pulse of the drive pulse output from the controller is changed.

As a result, it is possible to drive at the optimum timing for applying the third pulse even when the environmental temperature changes.
Even if the vibration of the meniscus generated by the discharge of the ink droplet changes due to the environmental temperature, the pressure generating chamber 3 is expanded again by the third pulse at the stage where the meniscus has moved to the pressure generating chamber 3 most. The kinetic energy of the meniscus that is heading can be effectively attenuated.

As a result, an unstable ink droplet ejection phenomenon due to poor attenuation of the kinetic energy of the meniscus is suppressed irrespective of the environmental temperature, and the meniscus is kept at a fixed position irrespective of the repetition frequency due to the rapid stop of the meniscus. Since the ink droplets are ejected in a stationary state, the flying speed is stabilized. Therefore, stable ejection can be ensured even at a high driving frequency.

Finally, the operations at the time of preparing for the start of printing and at the end of printing will be described.

Before printing is started, the driving pulse is charged to the intermediate potential, and the piezoelectric vibrator 9 is slightly contracted to wait for a print signal to be sent. The time required for charging to the intermediate potential may be such that ink droplets are not ejected by the drive, and there is no problem if the time is about the duration of the third pulse.

On the other hand, when the print signal is no longer input, the drive pulse is discharged from the intermediate potential by a predetermined pulse to make the potential zero. There is no problem with this required time as long as ink droplets are not ejected by the drive.

With the above operation, the following effects can be obtained.

By the above operation, the piezoelectric vibrator 9 slightly expands and contracts, and the pressure generating chamber 3 expands and contracts. As a result, the meniscus in the nozzle 2 slightly vibrates, and the ink in the pressure generating chamber 3 is agitated to prevent solidification of the ink in the nozzle 2 which is exposed to the atmosphere and easily dried, thereby preventing clogging of the ink. be able to.

In the above embodiment, an ink jet recording head using a piezoelectric vibrator in the longitudinal vibration mode has been described as an example. However, it is apparent that a similar effect can be obtained when a piezoelectric vibrator in the horizontal vibration mode is used. is there.

[0122]

As described above, according to the present invention, the pressure generating chamber having the resonance frequency of the period Tc and the pressure generating chamber communicating with the common ink chamber via the nozzle and the ink supply port are expanded, A first pulse for expanding the pressure generating chamber and an ink jet recording head including a piezoelectric vibrator for contracting, a second pulse for discharging the ink droplet from the nozzle by contracting the pressure generating chamber in the expanded state, A drive pulse for controlling the timing of the start of the second pulse and the timing of the start of the third pulse by the environmental temperature by the drive pulse generating means for outputting the third pulse for expanding the pressure generating chamber again after the pulse of the above and the environmental temperature detecting means Since the control means is provided, the position where the meniscus is pulled in during the recovery by the first pulse and the meniscus is being recovered is always the same at the start of the second pulse. Since the ink can be ejected in ring can be always constant ejection speed of the ink droplet.

In addition, even when the meniscus behavior changes due to environmental temperature changes, ink can always be ejected at a constant meniscus pull-in position, so that the ink droplet ejection speed is always constant at any environmental temperature. be able to.

On the other hand, when the residual vibration of the meniscus generated after the ejection of the ink droplet has moved to the pressure generating chamber most,
Since the third pulse can be easily applied to expand the pressure generating chamber again, the kinetic energy of the meniscus going to the nozzle at this point can be effectively attenuated.

In addition, the third pulse can be started at the optimum timing for the attenuation even when the meniscus vibration behavior changes due to the environmental temperature change. It becomes possible.

Further, due to the rapid stop of the meniscus,
Ink droplets are ejected in a state where the meniscus is kept stationary at a fixed position regardless of the driving frequency, so that the flying speed is stable and the recovery time of the meniscus is short, so that the response frequency is improved.

Since the time from the start of the second pulse to the start of the third pulse, which is optimal for damping and damping the meniscus vibration after the ejection of the ink droplet, is substantially equal to the cycle Tc of the pressure generating chamber. , Tc as a representative value, and the start time of the third pulse can be set.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an ink jet recording head used in an ink jet recording apparatus of the present invention.

FIG. 2 is a block diagram showing one embodiment of the ink jet recording apparatus of the present invention.

FIG. 3 is a diagram illustrating an embodiment of forming a driving pulse of an ink jet recording head in the ink jet recording apparatus of the present invention.

FIG. 4 is a diagram for explaining the relationship between the driving pulse of the ink jet recording head and the behavior of the meniscus, and the position at which the meniscus is pulled in during ejection in the ink jet recording apparatus according to one embodiment of the present invention.

FIG. 5 is a diagram illustrating the relationship between the driving pulse of the ink jet recording head, the behavior of the meniscus, and the pull-in position of the meniscus during ejection in the ink jet recording apparatus according to one embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between ejection speeds in a plurality of head specifications having different ink supply port widths and nozzle diameters in a driving method in which the application timing of a second pulse is fixed.

FIG. 7 is a diagram illustrating the relationship between the ejection speed in the head specification of each ink supply port width and nozzle diameter when the driving method according to the first embodiment of the present invention is performed.

FIG. 8 is a diagram illustrating the relationship between the driving pulse of the ink jet recording head and the behavior of the meniscus, and the pull-in position of the meniscus during ejection in the ink jet recording apparatus according to one embodiment of the present invention.

FIG. 9 is a diagram illustrating a relationship between a resonance period Tc and an application timing of an optimal third pulse for stabilizing ejection of ink droplets in the ink jet recording apparatus according to an embodiment of the present invention.

FIG. 10 is a diagram illustrating a relationship between a resonance period Tc and an ambient temperature in the ink jet recording apparatus according to one embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between an environmental temperature and an application timing of an optimal third pulse for stabilizing ejection in the inkjet recording apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle plate 2 Nozzle 3 Pressure generating chamber 4 Common ink chamber 5 Ink supply port 6 Ink flow path 7 Flow path constituent plate 8 Elastic plate 9 Piezoelectric vibrator 10 Fixed substrate 21 Nozzle tip 100 Ink jet recording head 110 Driving nozzle selecting means 120 Driving Pulse generation means 130 Drive pulse control means (CPU) 140 Environmental temperature detection means

Claims (13)

[Claims] 1. An ink jet apparatus comprising: a pressure generating chamber having a Helmholtz resonance frequency of a period Tc communicating with a common ink chamber via a nozzle and an ink supply port; and a piezoelectric vibrator for expanding and contracting the pressure generating chamber. A recording head, a first pulse for expanding the pressure generating chamber, a second pulse for contracting the expanded pressure generating chamber to eject ink droplets from the nozzles, and the second pulse after the second pulse. A drive pulse generating means for outputting a third pulse for expanding the pressure generation chamber again; and a drive pulse control means for arbitrarily controlling the timing of starting the second pulse and the timing of starting the third pulse. Ink jet recording device having. 2. The driving pulse control unit according to claim 1, wherein the timing of the start of the second pulse is controlled by a drive pulse control unit such that the position of the meniscus in the nozzle at the timing of the start of the second pulse becomes constant. Ink jet recording device. 3. The timing of starting the second pulse is as follows:
The ink jet recording apparatus according to claim 1, further comprising the drive pulse control unit that arbitrarily sets the drive pulse according to the flow path impedance of the nozzle and the ink supply port. 4. The timing of the start of the second pulse,
4. The ink jet recording apparatus according to claim 1, wherein the setting is such that when the flow path impedance of the nozzle or the ink supply port is small, it is early, and when it is large, it is late. 5. The timing of starting the second pulse,
4. The ink jet recording apparatus according to claim 1, wherein when the cross-sectional area of the nozzle or the ink supply port is large, it is set to be early, and when it is small, it is set to be late. 6. The timing of starting the second pulse,
4. The ink jet recording apparatus according to claim 1, wherein when the length of the nozzle or the ink supply port is long, the speed is set to be early, and when the length is short, the speed is set to be low. 7. The ink jet recording apparatus according to claim 1, further comprising an environmental temperature detecting means, wherein the timing of starting the second pulse is controlled by the driving pulse control means according to the environmental temperature. 8. The timing of starting the second pulse,
8. The ink-jet recording apparatus according to claim 1, wherein the setting is such that when the environmental temperature is high, the temperature is high, and when the temperature is low, the temperature is low. 9. The start pulse timing of the third pulse is controlled by the drive pulse control means so that the vibration of the meniscus generated after the ejection of the ink droplets is almost the same as the time when the meniscus moved to the pressure generating chamber most. The ink jet recording apparatus according to claim 1. 10. The ink jet recording apparatus according to claim 1, further comprising the drive pulse control means for arbitrarily setting a timing of starting the third pulse in accordance with a cycle Tc of the pressure generating chamber. 11. The ink jet recording apparatus according to claim 1, further comprising an environmental temperature detecting means, wherein the timing of starting the third pulse is controlled by the driving pulse control means according to the environmental temperature. 12. The method according to claim 1, wherein the start timing of the third pulse is set so as to be early when the environmental temperature is high and to be late when the environmental temperature is low.
12. The ink jet recording apparatus according to 0 or 11. 13. The duration of the second pulse and the duration of the third pulse are set to be the same, and the time from the start of the second pulse to the start of the third pulse is equal to the cycle of the pressure generation chamber. 13. The ink jet recording apparatus according to claim 1, wherein the time is set to substantially coincide with Tc.