JP3522267B2 - Recording method using ink jet recording apparatus and recording head suitable for the recording method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a recording head for ejecting ink droplets from a nozzle opening by causing a pressure generation chamber, which communicates with a nozzle opening and a reservoir, to fluctuate with a piezoelectric vibrator in accordance with print data. The present invention relates to an inkjet recording apparatus, and more specifically, to an ink droplet ejection technology.

[0002]

2. Description of the Related Art An ink jet recording apparatus uses an ink jet recording head composed of a pressure generating chamber communicating with a nozzle opening and a reservoir and pressure generating means for pressurizing the pressure generating chamber. A dot is formed on a recording medium by supplying a corresponding drive signal to eject an ink droplet from a nozzle opening, and full-color printing can be easily performed by using inks of different colors. In order to print such graphic print with a quality as close to that of a photograph as possible, it is necessary to reduce the size of dots formed by ink droplets as much as possible. For such miniaturization of dots, it is effective to reduce the opening area of the nozzle opening, but there is a limit to making a fine opening with high accuracy.

Therefore, after expanding the pressure generating chamber,
In a recording apparatus using an ink jet recording head that uses a longitudinally vibrating mode piezoelectric vibrator that can be contracted as a pressure generating means, as disclosed in Patent Document 1, the kinetic energy of a meniscus is used to form a nozzle opening. Techniques have been proposed for generating ink droplets having a cross-sectional area smaller than a predetermined size.

[Patent Document 1] Japanese Patent Publication No. 4-36071

That is, first, the pressure generating chamber is expanded by the piezoelectric vibrator at a speed faster than that at the time of ink filling, and the meniscus in the vicinity of the nozzle opening is rapidly drawn to the pressure generating chamber side. As a result, a wave of ink that moves up and down due to resonance is generated on the surface of the center line of the meniscus, and when the meniscus rises, a part is separated from the main body of the meniscus and becomes a splash from the nozzle opening and flies toward the recording medium. As a result, a size much smaller than an ink droplet that can be formed in the nozzle opening, specifically, a maximum cross-sectional area of about 10 to 15 μm from the nozzle opening having an opening diameter of 51 to 56 μm, that is, about 20% of the nozzle opening diameter, It can be discharged.

[0005]

However, since the size of the ink drop that can be used for printing is too small compared to the size of the nozzle opening, the dot on the recording medium due to the ink drop ejected from the adjacent nozzle opening is formed. There is a gap between the nozzle openings and the recording medium.
Since the kinetic energy that can be held by ink droplets is too small to fly a gap of about mm in a predetermined path, flight bending or the like occurs, and furthermore, the wave that causes ink droplets greatly depends on the viscosity of the ink. There are many problems such as being unable to stably discharge due to the influence of the above. The present invention has been made in view of the above problems, and an object thereof is to use an ink jet recording head capable of stably ejecting ink droplets smaller than the mechanical size of a nozzle opening or the like. It is to propose a recording method.

Another object of the present invention is to provide an ink jet recording head suitable for carrying out the same printing method as above.

[0007]

In order to solve such a problem, according to the present invention, the pressure for communicating ink to the reservoir through the ink supply port and for ejecting the ink droplet from the nozzle opening. The volume of the generation chamber is expanded by the displacement of the piezoelectric vibrator, and the central region of the meniscus stationary at the nozzle opening is selectively pulled in relative to the wall surface side region of the nozzle opening, and the meniscus has at least a different frequency A first step of vibrating with two natural vibrations, a central region of the meniscus drawn in the first step is inverted to the nozzle opening side, and two different frequencies
When the moving direction of the meniscus vibrating due to the natural vibration of the nozzle is synchronized with the movement toward the nozzle opening side, the piezoelectric vibrator is displaced to contract the pressure generating chamber at a speed capable of ejecting an ink droplet. And a second step.

[0008]

When the central region of the vibration of the meniscus of two frequencies generated by the sudden pulling is inverted to the nozzle opening side and synchronized so as to move toward the nozzle opening side, the piezoelectric vibrator is displaced to apply pressure. The generation chamber is pressurized to eject the ink in the central region as ink droplets.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below with reference to illustrated embodiments. FIG. 1 shows a structure around a printing mechanism of a printer according to the present invention. In the figure, reference numeral 1 is a carriage, which is connected to a carriage drive motor 3 via a timing belt 2 and a guide member 4.
Is guided to reciprocate in the paper width direction of the recording paper 5, and its position can be detected by the linear encoder 6.

Ink jet recording heads 7 and 8 to be described later are attached to a surface of the carriage 1 facing the recording paper 5, that is, a lower surface in this embodiment, and ink is replenished from ink cartridges 9 and 10 mounted on the carriage 1. In response to the movement of the carriage 1, ink droplets are ejected onto the recording paper 5 to form dots, and images or characters are printed on the recording paper.

In the non-printing area, the cap member 11,
12 is provided to seal the nozzle openings of the recording heads 7 and 8 during rest and to receive ink droplets from the recording heads 7 and 8 by the flushing operation performed during the printing operation. . In addition, reference numeral 13 in the drawing
The cleaning means and the paper feed motor 14 are shown.

FIG. 2 shows an embodiment of the recording heads 7 and 8. In the drawing, reference numeral 15 is a flow path forming substrate, and the central area thereof is aligned with the array pitch of nozzle openings 20 which will be described later. A plurality of rows of pressure generating chambers 16, 16, ... Are formed, and a reservoir 17 that supplies ink to the pressure generating chambers 16 and an ink supply port 18 that connects the pressure generating chambers 16 to the reservoir 17 are formed around them. Is configured.

The nozzle plate 19 for sealing one opening surface of the flow path forming substrate 15 has a pressure generating chamber 16 in the central region.
A nozzle opening 20 is formed so as to face one end of the.

The elastic plate 21 for sealing the other opening surface of the flow path forming substrate 15 is brought into contact with a piezoelectric vibrator 22 to be described later in the central region of each pressure generating chamber 16 so that the piezoelectric vibrator 22 is displaced.
An island portion 23 having a relatively large rigidity that is efficiently transmitted to each pressure generating chamber 16 and a thin portion 24 that is elastically deformable are formed so as to surround the island portion 23. As shown in FIG. 5, the thin portion 24 has regions 24a, 24 on both sides of the island portion 23 and on the nozzle opening side and the ink supply side.
It is also formed in b and is configured to positively give compliance to the vicinity of the nozzle opening and the vicinity of the ink supply port.

Reference numeral 25 is a piezoelectric vibrator unit, and as shown in FIG. 4, a plurality of piezoelectric vibrators 22 are aligned with the arrangement pitch of the pressure generating chambers 16 and one end thereof is made of a material having high rigidity such as metal or ceramic. It is configured to be fixed to the configured fixed substrate 26, and dummy vibrators 27, 27 functioning as a positioning member and a conductive pattern forming material are arranged at both ends.

In these piezoelectric vibrators 22, a plurality of electrodes 29, 30 are sandwiched with a piezoelectric material 28 such as lead zirconate titanate sandwiched therebetween so as to be wrapped in regions other than the regions near both ends. It is configured such that the wrapping region is an active region, that is, a region involved in expansion and contraction in the axial direction.

Of these electrodes, one electrode 29 is formed on the surface of the fixed substrate 26 via the conductive pattern formed on the dummy vibrator 27 after being connected in parallel between the piezoelectric vibrators by the connection bar 31. And the other electrode 30 is connected to a conductive pattern 33 formed independently for each piezoelectric vibrator, and will be described later by a lead frame 34 via these conductive patterns 32, 33. It is connected to the drive circuit.

The nozzle plate 19, the flow path forming substrate 15, and the elastic plate 21 are integrally laminated to form a flow path unit, and then are formed in an opening of a head frame 35 made of a polymer material or the like. The piezoelectric vibrator unit 25 is fixed to the island portion 23 with an adhesive, and the fixed substrate 26 is fixed to the frame 35 with an adhesive so that the piezoelectric vibrator unit 25 is assembled into a recording head. There is. An ink tube 36 connected to an ink tank (not shown) is drawn into the frame 35, and its tip is connected to an ink introduction port 37 formed in the elastic plate 21. This allows ink to be supplied to the reservoir 17 from the outside.

Next, the characteristics of the ink jet recording head thus constructed will be described. When the ink flows while being accelerated in the narrow flow path, the mass of the ink acts as inertance. If the density of the ink is ρ, the cross-sectional area of the flow path is S, and the length is S, then the inertance M is

[Equation 1] Becomes Here, κ is a shape factor determined by the cross-sectional shape of the flow path, and is about 1.3 when the cross section is circular or the aspect ratio is close to 1. On the other hand, the compliance C of the pressure generating chamber 16 acts on the compliance component Cink due to the compressibility of the ink. This ingredient Cink is

[Equation 2] Becomes Here, κ'is the volume compression ratio of the ink, which is about 0.45 (GPa) -1 for the water-based ink, and Vin
k represents the volume of the pressure generating chamber 16. Further, since the pressure generating chamber 16 is surrounded by the elastic member, these elastic deformations also act as compliance, but since these are largely governed by the shape and the pressure generating chamber has a complicated shape, Usually, it is experimentally obtained by the finite element method or the like.

In the ink jet recording head in this embodiment, in addition to the area pressed by the piezoelectric vibrator 22, the thin portions 24a, 24b are formed in the area on the side of the nozzle opening 20 and the area on the side of the ink supply port which are distant therefrom. To form
Further, the inertance Mc of the pressure generating chamber 16 itself and the inertance Ms of the ink supply port 18 are both configured to be larger than the inertance Mn of the nozzle opening 20.

That is, the nozzle opening 20 has a diameter of 32 μm.
m, the length of the straight portion is 15 μm, the taper portion is formed on the straight portion, and the inertance Mn is 8 × 10 7 (kg / m 4), and the ink supply port 18
Is a rectangle with a cross section of 40 μm × 50 μm and a length of 300
Since it is μm, its inertance Ms is 21 × 10 7th power (kg / m 4th power), and the pressure generation chamber 16
Is a rectangle with a cross section of 40 × 100 μm and a length of 500 μ
Since it is m, its inertance Mc is 25 × 10 7th power (kg / m 4th power).

On the other hand, regarding the compliance, the component due to the thin portion 24a on the nozzle opening side is Cc1≈4 × 10 minus 21 (m cubed / Pa), and the component due to the thin portion 24b on the ink supply port side is Cc2 = 8 × 10 minus 2
It is the 1st power (mth power / Pa).

By the way, the displacement of the piezoelectric vibrator in the ink jet recording head and the flow of ink corresponding thereto are generally considered by analogy with an electric circuit. 7A, statically, as shown in FIG. 7A, a series circuit of each inertance Mn, Mc, Ms of the nozzle opening 20, the pressure generating chamber 16, and the ink supply port 18 is connected to each inertance. It can be considered as a circuit in which the compliance Cc1 by the thin portion 24a on the nozzle opening side and the compliance Cc2 by the thin portion 24b on the ink supply port side are connected to each point.

That is, when the contraction displacement amount of the piezoelectric vibrator 22 is increased, the thin portion 24b of the ink supply port 18 is
Since it vibrates up to, the compliances Cc1 and Cc2 on the nozzle opening side and the ink supply port side both function as compliances in the entire fluid circuit. Since the Helmholtz resonance frequency is 160 kHz in this vibration mode, the meniscus has a natural vibration period of 6 μs.

On the other hand, when the contraction displacement amount of the piezoelectric vibrator 22 is reduced, only the thin portion 24a on the nozzle opening 20 side vibrates, and the ink flow due to this vibrates.
Since the compliance Cc2 on the ink supply port side, which is formed larger than the compliance Cc1 by a, acts, the ink flow is mostly absorbed by the compliance Cc2 on the ink supply port side.

Therefore, the ink supply port side of the pressure generating chamber 16 is similar to being short-circuited, and as shown in FIG. 7B, the inertance Mc of the pressure generating chamber 16 and the inertance Mn of the nozzle opening 20 are connected in series. And the compliance Cc1 on the nozzle opening side is connected to these connection points. Since the Helmholtz resonance frequency is 320 kHz in this vibration mode, the meniscus has a natural vibration period of 3 μs.

As a result, the ink flow generated by the expansion and contraction of the pressure generating chamber 16 by the piezoelectric vibrator 22 performs a combined motion of two vibration modes of a natural vibration period of 6 μs and a natural vibration period of 3 μs. become. Therefore, a period shorter than the above two vibration modes of the ink flow path system involving the thin portion 24 of the pressure generating chamber 16, that is, 3 μm in this embodiment.
When the volume of the pressure generating chamber 16 is changed for s or less and shorter than the cycle of the two vibration modes of the ink flow path system, for example, 3 μs or less in this embodiment, the above-mentioned 2
It is possible to generate a motion corresponding to one vibration mode.

The piezoelectric vibrator 22 used in the recording head of this embodiment has a length of 1.5 mm, an axial natural vibration frequency of 450 kHz, a period of 2.2 μs, and axial displacement. Therefore, the rigidity thereof is extremely large as compared with the case of utilizing the flexural vibration, and is 10 times or more the rigidity of the island portion 23 of the pressure generating chamber 16. Therefore, the displacement of the piezoelectric vibrator 22 can be transmitted to the pressure generating chamber 16 without a time delay. Therefore, the piezoelectric vibrator 22
We could observe the peak of meniscus vibration in the frequency region lower than the natural vibration frequency of.

FIG. 8 shows an embodiment of a driving device for driving the recording head of the same as above. Reference numeral 40 in the drawing is a control means which is synchronized with a print signal (FIG. 9I) from a host. The output terminals 41 and 42 are configured to output a charging pulse (FIG. 9 II) and a discharging pulse (FIG. 9 III).

When the charging pulse is input to the base of the NPN type transistor 43 and the NPN type transistor 43 becomes conductive, the constant current circuit 47 constituted by the PNP type transistors 44 and 45 and the resistor 46 operates and the capacitor 48 is provided.
Constant current Ir suitable for pulling the meniscus up to voltage V1
Charge with a.

On the other hand, when a discharge pulse is input to the input terminal 42, the constant current circuit 52 including the NPN transistors 49, 50 and the resistor 51 discharges the electric charge of the capacitor 48 to a zero voltage with a constant current Ifa. The NPN type transistors denoted by reference numerals 53 and 54 in the figure constitute a current amplifier, and output a current suitable for driving the piezoelectric vibrator 22 to the output terminal 55.

Next, the operation of the apparatus thus configured will be described. First, an oscillating pressure gradient α is applied to a fluid having a narrow gap such as a nozzle opening or between two parallel flat plates.

[Equation 3] The outline of the behavior of the fluid under the action of is described (see, for example, Isao Imai, Fluid Mechanics, published by Sokabo Publishing (Part 1)). When the pressure vibration is P, the angular frequency of the pressure vibration is ω, and the flow path is a circular pipe, the diameter of the circular pipe is d and the kinematic viscosity of the fluid is υ.

[Equation 4] When the condition of is satisfied, as shown in FIG. 10, the viscosity is dominant within the range of a predetermined thickness δ from the pipe wall,
A flow in the same phase as the pressure gradient occurs, and in the region outside the boundary layer, in the region from the center in this figure, the flow is greatly affected by inertia and vibrates as a unit, but the temporal change in the pressure gradient, That is, it has a phase delayed by π / 2 with respect to the phase of vibration.

The thickness δ of the region where the influence of viscosity is dominant
From the tube wall

[Equation 5] Becomes For example, assuming that the diameter d of the circular tube portion is 30 μm, the kinematic viscosity coefficient ν of ink is 2 × 10 −6 m 2 / s, and the natural period of pressure vibration is 10 μs, the thickness δ of the boundary layer is about 2.5.
μm.

When a print command is output from the host to the control means 40, the control means 40 outputs a charge signal (FIG. 9 II) having a time width t11 to the terminal 41 in time with the print signal (FIG. 9 I). The piezoelectric vibrator 22 is a constant current circuit 47.
Due to the constant current Ira caused by the above, for a time t11, it is rapidly charged to a voltage V1 with a constant gradient and contracts at a constant rate. As a result, the pressure generating chamber 16 expands rapidly and the nozzle opening 20
In the meniscus m which is stationary (Fig. 11I), the central region is relatively larger than the thickness δ of the above-mentioned viscosity-dominant region from the wall surface of the nozzle opening 20 and suddenly drawn into the pressure generating chamber side. (Fig. 11 II).

The control means 40 holds the voltage V1 for a time t12 when the piezoelectric vibrator 22 is charged to the voltage V1, and prevents the volume change of the pressure generating chamber 16 as much as possible. On the other hand, the meniscus further moves to the pressure generating chamber side according to its own natural oscillation period, but in the process, an outward flow (arrow A in the figure) occurs in the vicinity of the boundary layer, and the central portion still has pressure. It is drawn to the generation chamber side (Fig. 11
III).

Then, with the passage of time, the boundary layer portion is extruded toward the nozzle opening side, becoming a meniscus displaced toward the pressure generating chamber side toward the central portion, and further the nozzle opening 20
Since there is less ink and the inertance is smaller in the central region of the nozzle than in the boundary layer, only the central region of the nozzle opening 20 is selectively and rapidly drawn to the pressure generating chamber side (FIG. 11I).
V).

When the central region of the meniscus m is largely pulled in toward the pressure generating chamber side, the control means 40 outputs a discharge pulse (III in FIG. 9) from the terminal 42. The piezoelectric vibrator 22 is discharged by the constant current Ifa by the constant current circuit 52 for a time t13, and rapidly expands at a constant speed to contract the pressure generating chamber 16 at a constant speed.

By contracting the pressure generating chamber 16, the pressure generating chamber 1
The flow of ink pressurized at 6, that is, the inertial flow concentratedly acts on the central region mc of the meniscus m near the pressure generating chamber side (FIG. 11V), and selectively selects only the central region mc of the meniscus m. Extrude at a very large speed (Fig. 11 VI).
In this way, without relying on the movement of the meniscus itself,
Since the central area is positively pressed, it is possible to stably eject ink droplets that are thinner than the diameter of the nozzle opening 20 from the nozzle opening 20 at a speed suitable for printing.

Thereafter, when the voltage of the piezoelectric vibrator 22 becomes zero, the input of the next print signal is awaited, and each time the print signal is input, the above steps are repeated to form dots.

The above operation will be described in more detail with reference to FIG. 12, focusing on the movement of the meniscus. When the pressure generating chamber 16 expands rapidly in the first step, as described above, the meniscus near the nozzle opening 20 is drawn toward the pressure generating chamber in a vibration mode due to the superposition of the two vibration modes.
And each natural vibration period, that is, 3μs and 6μ
By s, the movement to the pressure generating chamber side and the movement to the nozzle opening side are repeated.

As described above, since the meniscus is excited by the superposition of the two vibration modes existing as the characteristics of the recording head, when the meniscus is drawn into the pressure generating chamber side, it is caused by the vibration of a short cycle (3 μs). After the return of the meniscus (P1) starts, the meniscus is again drawn to the pressure generating chamber side, and finally reaches the maximum depth (P2).

At this point P2, a long cycle (6
Since the vibration of (μs) also overlaps, the vibrations of the two modes are synchronized, and the meniscus starts to rapidly return toward the nozzle opening 20. Therefore, if the discharge pulse (FIG. 9 III) is output at this point in time and the pressure generating chamber 16 is abruptly contracted, the ink droplet k having a small cross-sectional area described above is generated.
(FIG. 11) can be discharged at a higher speed.

In the ink jet recording head of this embodiment, the vibration of the entire meniscus is dominated by two vibrations having different periods, and each period is an integral multiple of 3 μs and 6 μs. Because there is 2
The vibration component of the meniscus due to the two modes synchronizes from the second time when the meniscus returns to the nozzle opening side, that is, after reaching the maximum depth (P2) to ink ejection, and the meniscus efficiently moves to the nozzle opening side. Be accelerated.

Therefore, the sum of the charging time t11 and the holding time t12 of the driving voltage (IV in FIG. 9) (t11 + t12).
Is set so as to coincide with the time when the meniscus reaches the maximum vibration (P2), and the extension time of the piezoelectric vibrator 22 is
That is, the discharge time t14 is made equal to the shorter cycle of the vibration mode, which is 3 μs in this embodiment, to prevent the occurrence of residual vibration.

By adopting such a driving method, in the recording head of the present invention, the ink weight is 3 μg to 8 μg.
An ink droplet of μg is ejected at a speed of 5 m / s to 10 m / s, and only the ink amount is 60 to 80% while maintaining the flight speed of the ink droplet when this inkjet recording head is driven by a normal method. Could be reduced to.

Further, in order to confirm the timing of contracting the pressure generating chamber 16 for ejecting ink droplets, only the compliance Cc2 on the ink supply port side is reduced by 14 × 10, which is about twice as much as that of the above-described embodiment. 21.sup.th power (m.sup.3 / Pa), and the natural vibration period of the meniscus caused by the thin portion 24a on the nozzle opening side is 3 .mu., While the natural vibration period of the meniscus by the thin portion 24b on the ink supply port side is 8 .mu.s. A larger ink jet recording head was manufactured and the same test was conducted.

That is, as shown in FIG. 13A, when the pressure generating chamber 16 is rapidly contracted in the same manner as described above at the same timing as P3 when the meniscus is moved to the nozzle opening side for the second time, Similarly, an ink droplet having a smaller cross-sectional area than the diameter of the nozzle opening 20 was ejected at a high speed suitable for printing.

On the other hand, as shown in FIG. 13B, when the low frequency component is returned due to the thin portion 24b on the ink supply port side where the compliance is increased (Q1).
Even when the pressure generating chamber 16 is contracted at the same timing, only the movement of the meniscus is accelerated, and an ink droplet suitable for printing cannot be formed.

FIG. 14 shows another embodiment of the ink jet recording head suitable for the driving method of the present invention. In this embodiment, the displacement of the thin portion 24a on the nozzle opening side and the piezoelectric vibrator 22 is displaced. Is formed between the thin portion 24b on the ink supply port side and the area directly receiving the displacement of the piezoelectric vibrator 22, and the compliance Cc1 on the nozzle opening side is formed. And area 6 where compliance Cc2 is generated on the ink supply port side
2, 63 and the area 6 where the pressure of the piezoelectric vibrator 22 acts
4 compliance is separated as much as possible, and
It is configured to positively express one vibration mode.

FIG. 15 shows another embodiment of the recording head of the present invention. In this embodiment, the inertance Mc 'of the pressure generating chamber 70 is substantially the same as the inertance Mn of the nozzle opening 20. And the meniscus is configured to move in a substantially single vibration. The flexibility of the thin portion 71 of the vibration plate 21 forming the pressure generating chamber 70 is adjusted so that the meniscus has an optimum natural vibration frequency.

The recording head having the above structure is shown in FIG.
6 can be represented as an equivalent electric circuit, and the Helmholtz resonance frequency of the pressure generating chamber 16 is

[0052]

[Equation 6] And about 120 kHz in this embodiment,
That is, it becomes about 5 μs. The piezoelectric vibrator 22 has the same structure as that described above, and has a natural vibration frequency of 450 kHz.
At z, the period is about 2.2 μs.

FIG. 17 shows an embodiment of a drive circuit for driving the recording head of the same as above. Reference numeral 80 in FIG.
The control means outputs the first charging pulse (II) and the second charging pulse (II) shown in FIG. 18 from the output terminals 81, 82 and 83 in synchronization with the print signal based on the print data from the host.
I) and discharge pulse (IV).

When the first charge pulse is input to the base of the NPN type transistor 84 and the NPN type transistor 84 becomes conductive, the PNP type transistors 85 and 86 and the resistor 8 are connected.
The constant current circuit 88 constituted by 7 is activated to charge the capacitor 89 to a second voltage V2 with a constant current Ira suitable for pulling the meniscus.

Similarly, when the second charging pulse output from the terminal 82 is input to the base of the NPN transistor 90 and the NPN transistor 90 becomes conductive, a constant current composed of the PNP transistors 91 and 92 and the resistor 93. The circuit 94 is activated to recharge the capacitor 89 from the voltage V2 to the voltage V1 with a constant current Irb suitable for rapidly drawing the meniscus, and thereafter maintain this voltage V1 for a predetermined time.

On the other hand, when a discharge pulse is input to the input terminal 83, a constant current circuit 98 composed of NPN type transistors 95 and 96 and a resistor 97 causes the electric charge of the capacitor 89 to reach a zero voltage, which is suitable for ejecting ink droplets. Discharge with current Ifa. Note that N shown by reference numerals 99 and 100 in the figure
The PN type transistor constitutes a current amplifier and outputs a current suitable for driving the piezoelectric vibrator to the output terminal 101.

Next, the operation of the apparatus thus configured will be described. When the print command is output from the host to the control unit 80, the control unit 80 matches the timing of the print signal (FIG. 18I) with the first charge signal (FIG. 1) having the time width t21.
8 II) is output to the terminal 81. The piezoelectric vibrator 22 is charged by the constant current Ira by the constant current circuit 88 to the voltage V2 at a constant gradient for the time t21, and contracts at a constant speed to expand the pressure generating chamber 16 at a constant speed.

As a result, the meniscus m (FIG. 11I) standing still at the nozzle opening 20 is suddenly drawn into the pressure generating chamber side, and the meniscus m starts to vibrate at its own natural vibration frequency. At this time, as described above, the central region of the wall surface of the nozzle opening 20 is selectively drawn to the pressure generating chamber side more than the thickness δ of the region where viscosity is dominant (FIG. 11).
II).

The control means 80 holds this voltage V2 for a time t22 at the time when the piezoelectric vibrator 22 is charged to the voltage V2, and prevents the volume change of the pressure generating chamber 16 as much as possible. In the meniscus, when the pressure oscillation reverses from negative to positive, an outward flow (arrow A in the figure) occurs in the boundary layer part, and the central part is still drawn to the pressure generating chamber side, and the boundary changes with time. The layer portion is pushed out toward the nozzle opening side, and becomes a meniscus that is displaced toward the pressure generating chamber side toward the center portion (FIG. 11 III).

The control means 80 controls the second unit after the elapse of a predetermined time.
The charging pulse (Fig. 18 III) is output. The piezoelectric vibrator 22 uses the constant current Irb generated by the constant current circuit 94 for the time t23.
During this period, the voltage V1 is charged with a constant gradient, and the pressure generating chamber 16 is greatly contracted at a constant rate to further expand the pressure generating chamber 16 at a constant rate. As a result, since there is less ink in the central area of the nozzle opening 20 and the inertance is smaller than that in the boundary layer, only the central area mc of the nozzle opening 20 is selectively and rapidly drawn to the pressure generating chamber side (FIG. 11 IV). ).

When the central area of the meniscus is largely drawn to the pressure generating chamber side, the control means 80 outputs a discharge pulse (IV in FIG. 18) from the terminal 83. The piezoelectric vibrator 22 uses the constant current Ifa generated by the constant current circuit 98 for the time t.
Discharged during 25, the pressure generating chamber 16 contracts at a constant speed by greatly and rapidly expanding at a constant speed.

The ink flow pressurized by the contraction of the pressure generating chamber 16, that is, the inertial flow, acts intensively on the central region mc of the meniscus near the pressure generating chamber side (FIG. 11 V),
Only the central area of the meniscus is extruded at a very large speed (Fig. 11 VI). In this way, to positively pressurize the central region without relying solely on the movement of the meniscus itself,
Ink droplets smaller than the diameter of the nozzle opening 20 can be stably ejected from the nozzle opening 20 at a speed suitable for printing.

Thereafter, when the voltage of the piezoelectric vibrator 22 becomes zero, the input of the next print signal is awaited, and each time the print signal is input, the above steps are repeated to form dots.

By the way, in this embodiment, the pulling-in of the meniscus as the first step (FIG. 11I) is as follows.
Since this is a process for generating a boundary layer between the meniscus and the wall surface of the nozzle opening 20, it is desirable to reduce the amount of drawing in the boundary layer.
As IV), the inertance at the central portion of the meniscus is dynamically reduced and the subsequent action of the inertial flow of the ink is greatly exerted. Therefore, the larger the amount of pulling in, the more effective. Therefore, the voltage ratio between the charging voltage V2 of the piezoelectric vibrator 22 and the additional charging voltage V1-V2 is
It is set to be 1: 3, preferably 1: 4, and preferably 1: 6 or more.

Then, the first rising time t21 and the second rising time t21
It has been experimentally confirmed that the rising time t23 of 1 is shorter than the natural vibration period of the piezoelectric vibrator 22. Therefore, in this embodiment, the time t21 + t23 is set to 2 μm.
It is set to s to 3 μs. Further, if the fall time t25 for ejecting the ink droplets is equal to or less than the natural vibration period of the piezoelectric vibrator 22 as in the above-described embodiment, preferably, the fall time t25, the residual vibration can be prevented.

Specifically, assuming that the final saturation voltage V1 is 20 volts, the charging voltage V2 in the first step is 3 to 5 volts, and the fall time t25 for ejecting ink droplets is 2.
When the recording head is driven with a setting of μs to 4 μs, an ink droplet having an ink weight of about 5 ng to 7 ng will have a velocity of 10%.
It was possible to eject at a rate of m / s to 15 m / s.

On the other hand, according to the conventional driving method of continuously charging the piezoelectric vibrator 22 from zero volt to V1, although the ink amount of the ink droplet does not change greatly,
The speed was reduced to about 1/2 from 4 m / s to 8 m / s.

More specifically, the hold time t22 that defines the time difference between the end of the first rising edge and the start of the second rising edge is also an important factor, and the period of the meniscus oscillation due to the Helmholtz resonance frequency of the pressure generating chamber 70 is also an important factor. By setting it to about 1/2 (5 μs in this embodiment) (2 μs to 3 μs), the ink amount of the ink droplet can be reduced and the flight speed of the ink droplet can be increased.

On the other hand, if the hold time t22 is set to be long, not only the ink amount of the ink droplets increases, but also the flight speed decreases and it becomes impossible to achieve the initial purpose. This is because when the hold time t22 becomes long, the meniscus drawn in by the first-stage charging is reversed and starts to move toward the nozzle opening side, that is, in the state where the central portion of the meniscus is convex toward the nozzle opening side, The meniscus is pulled in at the second stage, and the pulling force of the meniscus is canceled by the movement of the meniscus.

Therefore, in the central region of the boundary layer, the flow is greatly affected by inertia and vibrates as a unit, but the time gradient of the pressure gradient, that is, the phase of vibration is delayed by π / 2. This is because the above-described effect of having a phase cannot be used. In other words, it is an essential requirement to execute the second-stage meniscus pull-in within a time shorter than one cycle of the meniscus vibration after the first-stage charge meniscus pull-in.

FIG. 19 is a diagram showing the relationship between the displacement of the piezoelectric vibrator 22 and the position of the central portion of the meniscus in the above-described driving method. The piezoelectric vibrator 22 by the first-stage charging is shown.
The meniscus is pulled in by the reduction of. Then, when the piezoelectric vibrator 2 is returned with a displacement amount smaller than the retracted amount,
2 is greatly reduced and the meniscus is largely retracted, and the vibration of the meniscus due to this reversal is reversed and the nozzle opening 2
At the time of going to 0, the piezoelectric vibrator 22 is discharged to eject an ink droplet.

As a result, when the central portion of the meniscus comes closest to the pressure generating chamber and heads toward the nozzle opening side,
Since the pressure generating chamber 16 is pressurized, it is possible to reduce the amount of ink in the ink droplet and to fly the ink droplet without reducing the flight speed.

In the above embodiment, the piezoelectric vibrator having the longitudinal direction of the piezoelectric vibrator as the displacement direction has been described as an example. However, as shown in FIG.
0 through the reservoir 111, the nozzle communication holes 112, 1
Pressure generating chamber 1 communicating with the nozzle opening 114 via 13
A part of 15 is sealed by an elastically deformable lid body 116,
The same effect can be obtained by sticking the piezoelectric vibrator 117 that is displaced in the flexure mode on the surface of the lid body 116 or applying the piezoelectric vibrator to a recording head formed by sputtering.

[0074]

As described above, according to the present invention, only the central region of the meniscus is effectively and selectively pressurized,
At a flight speed suitable for printing ink drops with a small amount of ink,
Moreover, it is possible to eject the ink with the influence of the viscosity of the ink being reduced as much as possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an ink jet apparatus of the present invention centering on a recording mechanism.

FIG. 2 is an assembled perspective view showing an embodiment of a recording head of the same apparatus.

FIG. 3 is a diagram showing a sectional structure of the recording head of the same for one pressure generating chamber.

FIG. 4 is a diagram showing an embodiment of a piezoelectric vibrator unit used in the recording head of the same.

FIG. 5 is an enlarged perspective view showing the vicinity of the pressure generating chamber of the recording head.

FIG. 6 is an enlarged view showing the structure of an elastic plate that seals the pressure generating chamber of the recording head.

FIG. 7A and FIG. 7B are diagrams showing the fluid characteristics of the recording head as a model, respectively.

FIG. 8 is a circuit diagram showing an embodiment of a drive device for driving the recording head of the above.

FIG. 9 is a waveform chart showing signals of the drive device of the same.

FIG. 10 is a diagram showing two different fluid characteristic ranges generated in the vicinity of the nozzle opening by the driving method of the present invention.

11 (I) to (VI) are diagrams schematically showing the movement of a meniscus according to the driving method of the present invention.

FIG. 12 is a diagram showing a temporal change in the position of the central portion of the meniscus according to the driving method of the present invention.

13A and 13B are diagrams showing temporal changes in the position of the central portion of the meniscus shown as a comparative example, respectively.

FIG. 14 is a cross-sectional view showing another embodiment of the ink jet recording head suitable for the driving method of the present invention in the vicinity of the pressure generating chamber in an enlarged manner.

FIG. 15 is a cross-sectional view showing another embodiment of the ink jet recording head suitable for another driving method of the present invention in the vicinity of the pressure generating chamber in an enlarged manner.

FIG. 16 is a diagram showing a modeled fluid characteristic of the recording head.

FIG. 17 is a circuit diagram showing an embodiment of a driving device suitable for driving the recording head of the above.

FIG. 18 is a waveform chart showing signals of the driving device of the above.

19 (a) and 19 (b) are diagrams showing temporal changes in displacement of the piezoelectric vibrator and temporal changes in displacement of the central portion of the meniscus according to the second driving method of the present invention. .

FIG. 20 is a diagram showing another embodiment of an ink jet recording head to which the recording method of the present invention can be applied.

[Explanation of symbols]

16 Pressure Generating Chamber 17 Reservoir 18 Ink Supply Port 20 Nozzle Opening 21 Elastic Plate 22 Piezoelectric Vibrator 23 Island Part 24 Thin Part

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (5)

(57) [Claims] 1. The nozzle opening is communicated with a reservoir via an ink supply port to receive ink supply, and the volume of a pressure generating chamber for ejecting ink droplets from the nozzle opening is expanded by displacement of a piezoelectric vibrator, thereby forming the nozzle opening. A first step of selectively pulling in a central area of the meniscus stationary at a position more than an area on the wall surface side of the nozzle opening, and vibrating the meniscus with at least two natural vibrations having different frequencies; When the central region of the meniscus is inverted to the nozzle opening side, and the moving direction of the meniscus vibrating with the solid vibration of two different frequencies is synchronized with the movement to the nozzle opening side. And a second step of displacing the piezoelectric vibrator to contract the pressure generating chamber at a speed capable of ejecting ink droplets. Recording method. 2. The recording method by an ink jet recording apparatus according to claim 1, wherein the displacement time of the piezoelectric vibrator in the first step and the second step is equal to or less than the cycle of the natural vibration of the meniscus. 3. A reservoir for supplying ink from the outside, a pressure generating chamber which is partially sealed by an elastically deformable lid member, pressurizes the ink due to volume change, and ejects an ink droplet from a nozzle opening, In a recording head including an ink supply port that connects the reservoir and the pressure generating chamber, and a piezoelectric vibrator that elastically deforms the lid member, an ink flow is provided on the nozzle opening side region and the ink supply port side, respectively. An elastically deformable region is formed, and the inertance of the pressure generating chamber itself and the inertance Ms of the ink supply port are both larger than the inertance Mn of the nozzle opening, and the Helmholtz resonance of the region on the ink supply port side. Inkjet recording head whose frequency is set lower than other areas. 4. The ink jet recording according to claim 3, wherein the Helmholtz resonance frequency in the area on the ink supply port side and the Helmholtz resonance frequency in the other area are set to have an integer multiple relationship. head. 5. An area that is elastically deformable by the ink flow on the nozzle opening side and an area that is elastically deformable by the piezoelectric vibrator are partitioned by a diaphragm , and the ink flow on the ink supply port side is defined. The ink jet recording head according to claim 3, wherein an elastically deformable area and an area elastically deformable by the piezoelectric vibrator are partitioned by a diaphragm portion.