JP3099653B2 - Fluid ejection device and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ink jet printing, and more particularly, to an apparatus and method for ejecting ink droplets (fluids) from an ink jet head at a substantially constant ejection speed over a wide range of ejection repetition rates. About.

[0002]

2. Description of the Related Art Apparatus and methods for ejecting ink droplets from an ink jet print head at a high repetition rate are known in the art. The physical laws governing the structure and ejection of an ink jet drop interact in a complex way. Accordingly, U.S. Pat. No. 4,730,197 issued on Mar. 8, 1988, entitled "Impulse Ink Jet System" describes the ink jet geometry, transducer drive waveforms, ink meniscus and pressure chamber resonance, Also, many interactions between ink drop ejection characteristics are described and characterized. Is described can have multiple orifice print head Nitsu, provided a "dummy channels" and flexible room wall, and the non-uniformity of ink droplets caused by the cross talk between the injection and to minimize. Piezoelectric transducer (PZ
T) The drive waveform compensation technique can increase the ink droplet ejection rate (the number of ink droplet ejections per unit time).
This technique allows for print head resonance, fluid resonance, and timing compensation of past drops. Adapted PZT drive waveform circuits and complex ink jet head structures have increased the drop ejection rate to over 7 KHz.

US Pat. No. 5,170,177, issued Dec. 8, 1992 and assigned to the assignee of the present invention, describes a method for operating an ink jet to achieve high print quality and a high print rate. The PZT drive waveform is explained, and the spectrum of this drive waveform
The energy distribution is minimized at the "dominant (dominant) acoustic resonance frequency". Regarding the main frequency, a meniscus resonance frequency, a Helmholtz resonance frequency, a PZT
It is described as including any of the drive resonance frequencies and the various acoustic resonance frequencies of the different channels and paths forming the ink jet print head.
PZ at the resonant frequency of the ink jet outlet channel
It is also described that the T energy is suppressed to make the amount of ink droplets constant and the ejection speed constant at an ink droplet ejection rate higher than 10 KHz.

[0004] It is known that ink droplets are governed by an electric field.
U.S. Patent Application Serial No. 07/89249 by Roy et al., Filed on June 3, 1992 and assigned to the present assignee.
No. 4, entitled "Printing Method and Apparatus by Drop-on-Demand Ink-Jet Print Head Using Electric Field". An electric field that does not change with time allows time-to-paper compensation for different amounts of ink droplets, allows ink droplets to be ejected in a wide range of amounts, and allows ink droplets to be ejected with low PZT drive energy. Therefore, the maximum ink droplet ejection rate can be increased to 8 KHz or more.

[0005]

Unfortunately, however, electric field devices are complex, expensive, and vulnerable to impact. In addition, reliability and print quality are also issues because the electric field attracts dust.

Therefore, a simple ink jet that keeps the ink droplet ejection speed substantially constant for ink droplets ejected at a rate ranging from 0 to 13,000 ink droplets per second without using an electric field. -There is a need for a print head system.

It is, therefore, one object of the present invention to provide a fluid ejection apparatus and method for ejecting ink drops from an ink jet head at a substantially constant ejection velocity over a wide range of ejection repetition rates.

It is another object of the present invention to provide an improved method of driving a conventional ink jet head to enhance jetting performance without requiring an electric field.

[0009]

According to the ink jet apparatus and method of the present invention, high resolution and high speed printing can be performed by supplying a transducer driving waveform having a specific energy distribution. According to this energy distribution, energy is concentrated near the frequency associated with the main (Helmholtz) ink drop ejection mode or its integral fraction or multiple (subharmonics or harmonics), and the ink jet head At the resonance frequency associated with the structure of the ink inlet and the ink outlet,
Energy is suppressed.

According to the present invention, since the ejection speed of ink droplets is substantially the same over a wide range of ejection repetition rates, high-speed printing with high resolution can be performed.

Further, the present invention achieves a driving waveform shaping principle capable of enhancing the ejection performance of a conventional ink jet head.

Other objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention can be understood from the following description with reference to the accompanying drawings, in which: FIG. FIG. 1 is a cross-sectional view of an ink jet 10 that is part of a multi-orifice ink jet print head suitable for using the present invention. Ink jet 10 includes a body that defines an ink manifold 12 through which ink is supplied to an ink jet print head. The body defines an ink drop forming orifice 14 and an ink flow path from the ink manifold 12 to the orifice 14. Typically,
The ink jet print head preferably includes an array of orifices 14 that are closely spaced from one another for use in printing ink drops on a print medium (not shown).

A typical ink jet printhead has at least four manifolds for receiving black, cyan, magenta and yellow inks for use in black and color printing. However, the number of such manifolds will vary depending on whether printing is done with black ink alone or less than the full range of colors. The ink is supplied from the manifold 12 to the inlet port 16, the inlet channel (groove) 18, the pressure chamber port 2
0 flows into the ink pressure chamber 22. Ink is supplied to the pressure chamber 22 via the offset channel port 24.
And flows to the nozzle 14 via an optional offset chamber 26 and output channel 28. An ink droplet is ejected from the nozzle 14.

The ink pressure chamber 22 has a flexible partition (diaphragm) 30 on one side. An electromechanical transducer 32, such as PZT, is secured to the septum 30 with a suitable adhesive and covers the ink pressure chamber 22. In a conventional manner, the transducer 32 comprises a metal film layer 34
An electrical transducer driver is electrically connected to the metal film layer. Although other types of transducers may be used, the voltage is applied to the metal film layer 34.
Supplied to the transducer 3 in a bending mode such that the transducer 32 attempts to change its shape.
2 works. However, since the transducer 32 is securely and firmly attached to the partition 30, when the transducer 32 bends, the partition 30 is deformed. Therefore, when ink is supplied to the ink pressure chamber 22, the ink flows to the nozzle 14 via the passage 26. After the ink droplets have been ejected, the transducer 32 bends in the opposite direction and the partition 3
Since 0 also moves incidentally, ink is supplied to the ink pressure chamber 22 again.

To facilitate the manufacture of an ink jet print head that can be used in the present invention, the ink jet 10 is preferably formed from a number of thin plates or sheets, such as stainless steel. . These sheets are stacked in a stacking relationship. In the embodiment of the invention shown in FIG.
An ink pressure chamber plate 42 defining an ink pressure chamber 22; defining a pressure chamber port 20; contacting one side of the ink pressure chamber 22; Separation plate 44 defining a part of boundary
And inlet channel 18 and outlet channel port 24
An inlet channel plate 46 delimiting a portion of the manifold 12; the inlet port 16 and other separator plates 48 identifying the outlet channel port 24 and a portion of the manifold 12; the outlet offset channel 26 and the manifold 12 An offset channel plate 50 delimiting a portion of the outlet channel 28 and a separation plate 52 delimiting a portion of the manifold 12.
Exit plate 5 delimiting part of exit channel 28
4 and an orifice plate 56 that bounds the ink jet orifice 14.

Using more or less plates than shown, ink jet print printing can be used.
The various ink flow paths, manifolds and pressure chambers of the head may be defined. For example, multiple plates may be used to delimit ink pressure chambers instead of the single plate shown in FIG. Also, separate sheets or layers of metal are not required for all of the various functions. For example, the pattern in the photoresist used as a template to chemically etch the metal (if chemical etching is used in manufacturing) is different on each side of the metal sheet. Therefore,
As a more specific example, the pattern for the ink inlet path can be located on one side of the metal sheet, while the pattern for the pressure chambers can be located on the other side in front-to-back registration. Thus, with carefully controlled etching, separate ink inlet paths and pressure chambers containing layers can be combined into one common layer.

To minimize assembly costs, except for the orifice plate 56, all metal layers of the ink jet print head are fabricated using relatively inexpensive conventional light patterning and etching processes for metal sheets. To be assembled. No machining or other metalworking steps are required. The orifice plate 56 is suitably made using any number of processes, including electroforming with a nickel sulfide bath, micro-discharge machining in 300 series stainless steel, and 300 series stainless steel. There is punching in steel. The last two approaches use all features of the orifice plate 56, except for the orifices themselves, to light pattern and etch. Another suitable approach is to pierce the orifice and use a standard blanking process to create any features that remain on the orifice plate.

Table 1 shows the permissible dimensions of the ink jet of FIG. The actual dimensions used will depend on the capabilities of the ink jet arrangement and the package for the particular application. For example, the orifice diameter of orifice 14 in orifice plate 56 may range from about 25 microns to about 1 micron.
It may vary between 50 microns.

[Table 1]

The electromechanical transducer selected for the ink jet print head of the present invention comprises a hexagonal cut ceramic transducer glued to the septum plate 40 by epoxy, each of the transducers comprising: It is located at the center of each ink pressure chamber 22. For this type of transducer mechanism, the hexagon is approximately circular, which is the highest electromechanical efficiency in terms of the amount placed in a given area of the piezoceramic element.

In order to eject a controllable amount of ink droplets from an ink jet head as shown in FIG. 1, a number of selectable drive waveforms must be supplied from the transducer driver 36 to the transducer 32. Transducer 32 responds to the selected waveform by inducing a pressure wave in the ink. This pressure wave causes the ink fluid to flow within the orifice 14.

FIGS. 2A, 2B and 2C are enlarged sectional views of the orifice portion of the print head of FIG. An ink column 60 having a meniscus 62 is located in the orifice 14. The meniscus 62 is excited in three operation modes, which are modes (shapes) 0, 1, and 2 in FIGS. 2A, 2B, and 2C. FIG. 2C
Indicates a central movable range (excursion) Ce of the meniscus surface in a high-order oscillation mode.

FIG. 2A shows the operation mode 0. this is,
It corresponds to the volume forward displacement of the ink column 60 in the wall 64 of the orifice 14. In the past, ink jet and drive waveforms were based on mode 0 operation, but the potential was not fully exploited. Due to the effects of the ink surface tension and the viscous boundary layer associated with the wall 64, the meniscus 62 has a rounded shape in the form of a lack of high order mode. The natural (natural) resonance frequency of mode 0 is determined primarily by the movement of the volume of the ink mass interacting with the pressure of the ink inside the ink jet (ie, like a Helmholtz oscillator). Note that the "capacitive" pressure chamber 22 comprises an "inductance" inlet channel 18, a combined outlet channel structure 24,26,
28 and the orifice 14 together form a parallel resonant circuit.
Channels 18, 26, 28, manifold 1 all shown in FIG.
2. The geometric dimensions of the various fluidly coupled ink jet elements, such as components 16, 20, 22, and pressure chamber 22, are such that unnecessary or parasitic resonant frequencies interacting with the orifice oscillation mode are avoided. Is set.

To set the drive waveform to be suitable for a constant ink drop ejection speed over a wide range of ejection rates,
It is further necessary to know the natural frequencies of the orifice and meniscus system elements. Therefore, the energy can be concentrated at a frequency near the natural frequency of the desired mode, and the waveform can be set so as to suppress the energy at the natural frequency of another mode or at an unnecessary or parasitic resonance frequency that competes with the energy of the desired mode. These unwanted and parasitic resonance frequencies are dependent on the size of the ink drop, the speed of the ink drop, or the orifice.
In some ways, including, but not limited to, the time it takes for the ink droplets ejected from the ink jet to reach the print media, it adversely affects the ejection of the ink droplets from the ink jet orifice.

To set the waveform used to operate the ink jet 10 of FIG. 1, the fundamental (fundamental) resonance frequency of the inlet channel 18 and the offset
Channel port 24, offset channel 2
6. It is necessary to know the fundamental resonance frequency of the combined outlet channel structure including the outlet channel 28 and the orifice 14.

Using the basic organ pipe frequency calculations and assuming that the manifold 12 and the ink pressure chamber 22 operate in a constant pressure range, using the equation f = a / 2L,
The approximate resonance frequency of the inlet channel can be calculated.
Note that “a” is the speed of sound in the ink flow,
"L" is the length of the inlet channel. In the same manner as for the combined outlet channel structure, the outlet 14
Assuming that acts as a closed (zero velocity) boundary, the approximate resonant frequency of the combined exit channel structure can be calculated from the equation f = a / 4L.

Referring to Table 1, the ink jet 10
Has a length of about 6.35 millimeters and the combined outlet channel has a length of about 3.50 millimeters. The speed of sound in the fluid is about 1000 meters per second. Therefore, the entrance resonance frequency is about 79 KHz, and the exit resonance frequency is about 73 KHz.

Japanese Patent Application No. 6-189062 filed by the present applicant
The above theory together with the fluid flow theory described in
This was applied to the setting of the PZT drive waveform for the ink jet 10. The electrical waveform generated by the transducer driver 36 has energy concentrated in the frequency range of the desired mode, while energy is suppressed at the resonant frequency of the inlet and outlet channel structures of the ink jet 10 in other competing modes.

FIG. 3 is a prior art device representing a transducer driver 36 suitable for generating a PZT drive waveform according to the present invention. Of course, other waveform generators can be used.

Processor 100 provides a trigger pulse to negative pulse timer 102. This negative pulse timer 102 drives a field effect transistor 104,
During a period determined by the processor 100, the resistor network 106 is electrically connected to the negative voltage source -Vo.

When the negative pulse timer 102 times out, a wait period timer 108 is triggered for a wait period determined by the processor 100. When the waiting period timer 108 finishes counting, the positive pulse timer 110 drives the field effect transistor 112 to
0, the resistor network 106 is connected to the positive voltage source + V
o to be electrically connected.

Whether timers 102 and 110 are inactive,
While timer 108 is active, resistor network 106 is electrically disconnected from power supplies + Vo and -Vo. Therefore, a two-pole (bipolar) electric drive is performed to connect the film layer 3 of the transducer 32 through the resistor network 106.
4 electrically connected to one of the metals.

The resistor network 106 has values of 5000 and 6
A series resistor 114 in the range of 1000 ohms and a value of about 55
And a parallel resistor 116 of 60 ohms. As described in commonly assigned U.S. Pat. No. 5,212,497, issued May 18, 1993, entitled "Normalization of Array Firing Velocity", series resistor 114 is used to provide ink from ink jet 10. Trimming is performed so that the ejection speed of the droplet becomes a predetermined value. This application does not directly relate to establishing a predetermined firing velocity, but describes how to maintain a substantially constant firing velocity over a wide range of ink drop firing rates.

FIG. 4 shows a preferred PZT drive waveform 160 which makes the ink drop ejection speed in mode 0 almost constant at an ink drop ejection rate aiming at 14 KHz. Drive waveform 16
The shape of 0 is such that energy concentrates near the main (Helmholtz) resonance frequency and energy is suppressed near the resonance frequency of the inlet channel 18 and the combined outlet channel structure. While many drive waveform shapes can achieve the same result, drive waveform 160 can achieve the desired result by generating a bipolar drive waveform 162 in transducer driver 36 (FIG. 3). Note that this 2
The polar drive waveform 162 has a positive 50 for a period of 12.5 milliseconds.
12.5 millisecond waiting period 1 from volt pulse 168
It includes a 12.5 millisecond negative 50 volt pulse 164 separated by 66. Although an appropriate driving waveform can be generated, each of the above-described pulse period and waiting period is about 4 times.
It may be in the range from milliseconds to about 30 milliseconds.

The characteristic capacitance of the pressure transducer 32 is approximately 500 picofarads, and the resistive network 106 forms a simple resistive capacitance (RC) filter, which causes the drive waveform 160 to have a rolled-off characteristic shape. . It will be apparent to those skilled in the art that other combinations of RC values are possible and that the bipolar waveform 162 can be properly adjusted and compensated.

FIG. 5 shows an energy distribution 1 as a result of driving the pressure transducer 32 by the driving waveform 160.
4 shows an approximation of the Fourier series of frequencies to 70. The energy distribution 170 is 19 KH for the ink jet 10.
concentrated at a peak 172 near the main resonance frequency of z, 79
It is suppressed at null points 174 near the KHz and 73 KHz entry and exit channel resonance frequencies, respectively.

FIG. 6 shows a comparison of the ejection performance based on the driving result of the ink jet 10 between the case of the conventional waveform and the case of the preferred driving waveform 160 of FIG. The conventional drive waveform is of the type described in U.S. Pat. No. 5,170,177, where the energy is concentrated around the 19 KHz main frequency, but the energy is minimized only at the 73 KHz resonance frequency of the exit channel. A two-pole drive waveform having a negative 50 volt pulse of 12.0 microseconds separated by a 3.0 microsecond wait period from a positive 50 volt pulse of 11.0 microseconds was converted to transducer driver 36 ( When FIG. 3) occurs, the waveform becomes a conventional waveform.

FIG. 6 shows the time required for the ink jet 10 to be driven from the orifice 14 on the print medium 0.81 mm apart by driving the ink jet 10 with a conventional waveform, with respect to the ink drop ejection rate. . Curve 180 shows that the time variation to the medium is 100 microseconds when the ink jet 10 is driven with a conventional waveform over a range of firing rates from 1 KHz to 10 KHz. Time variation to media is 50
% Will cause errors in ink drop placement and limit printing speed in high resolution printing applications.

Next, the ink jet 10 is driven by the preferred drive waveform 160, and the time required for the ejected ink drop from the orifice 14 to the print medium 0.81 millimeters apart is again recorded relative to the ink drop ejection rate. did. Curve 182 shows that driving the ink jet 10 with the preferred drive waveform 160 over a firing rate range of 1 KHz to 13 KHz results in a 65 microsecond variation in time to media. ink·
If the jet rate of the jet 10 is limited to 12.5 KHz, the time variation to the medium will be 40 milliseconds. As a result of the time variation up to the medium of 20 to 30%, the time variation is improved by 50% in addition to the improvement of the ink droplet ejection rate by 25 to 30%.

The use of transducer drive waveforms set and shaped according to the principles described herein can similarly improve high speed, high resolution printing applications.

Some alternative embodiments of the present invention include, but are not limited to, for example, aqueous inks of various colors and phase change inks, as well as jetting of various fluid types including these inks and the like. May be applied.

[0042] with the desired result can be achieved also by the waveform 16 2 other than the waveform, spectrum analyzer or fast while Fourier transform (FFT) using the display oscilloscope to observe a spectrum results of the energy, waveform to a predetermined energy distribution It will be understood by those skilled in the art that Furthermore, a desired drive waveform energy distribution can be achieved without using a filter other than RC filtering or performing filtering at all.

It should be noted that the present invention is useful when combined with various conventional techniques, such as dithering and accelerating the ink drops by an electric field, with further improvements in image quality and ink drop placement accuracy.

In summary, the present invention is applicable to any fluid ejection drive mechanism and can provide the necessary drive waveform energy distribution for the appropriate orifice.

Various modifications can be made to the above-described embodiments of the present invention without departing from the spirit of the invention. For example, electromechanical transducers other than the PZT bending mode type described above may be used. Alternatives include shear mode, annular compression, electrostriction,
Transducers of the type such as electromagnetism and magnetostriction are suitable. Similarly, although described above in terms of electrical energy waveforms driving the transducers, any other suitable form of energy may be utilized to operate the transducers, including but not limited to acoustic or microwave energy. . When using electrical waveforms, unipolar, dipole pairs or groups of pulses can achieve the desired energy distribution equally. Thus, the present invention is applicable to fluid ejection applications other than those used in ink jet printers.

[0046]

As described above, according to the present invention, the ejection speed of ink droplets ejected from the ink jet head can be made substantially constant over a wide range of ejection repetition rates.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a PZT driven ink jet, one of the typical ink jet print heads of the type used in the present invention.

FIG. 2 is an enlarged cross-sectional view of the orifice portion of the print head of FIG. 1 in orifice fluid flow operating modes 0, 1, and 2 to which the present invention is applied.

FIG. 3 is a block diagram of a conventional device used to generate a PZT drive waveform according to the present invention.

FIG. 4 is a preferred voltage versus time waveform diagram of a PZT drive waveform used in generating ink droplets at a high repetition rate according to the method of the present invention.

FIG. 5 is a diagram illustrating an energy spectrum with respect to a frequency of the PZT driving waveform illustrated in FIG. 4;

FIG. 6 is a diagram illustrating a relationship between an ink droplet ejection rate and a time of an ink droplet reaching a medium based on a preferred driving waveform illustrated in FIG. 4 and a conventional PZT driving waveform.

[Explanation of symbols]

 10 Ink Jet 12 Ink Manifold 14 Orifice 18 Inlet Channel 22 Pressure Chamber 28 Outlet Channel 32 Transducer 36 Transducer Driver

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (2)

(57) [Claims] 1. The method of claim 1, wherein the inlet channel has a first length.
In both cases, the speed of sound in the fluid is twice the first length.
A fluid having a first resonant frequency determined by division, an outlet channel having a second length,
Divided by four times the second length
Having a second resonance frequency, and forcing the fluid from the manifold through the inlet channel
And the outlet channel from the pressure chamber
Flow through the orifice to the injection repetition rate range
The droplet of the fluid is sprayed at a substantially constant
A device for injecting from a fiss over a range of the ejection repetition rate of the fluid droplet.
A transducer driver for generating an electrical waveform that repeats and transmitting each of the electrical waveform repetitions to the pressure chamber.
The fluid from the orifice at a substantially constant injection speed.
An electromechanical transducer for injecting drops of each of the electrical waveforms into the orifice.
Spectrum around the main resonance frequency of the above fluid
An energy peak exists, and the first resonance frequency and
And the above-mentioned spectrum energy around the second resonance frequency.
Predetermined spectrum energy where energy is substantially reduced
A fluid ejecting apparatus having a lug distribution and expanding the range of the ejection repetition rate of the fluid droplet. 2. The method of claim 1, wherein the inlet channel has a first length and a first length.
And the outlet channel has a second length and a second length.
It has a resonance frequency, and the ink droplets
It has a wave number and allows ink to enter the inlet channel from the manifold.
Through the pressure chamber through the outlet chamber.
Flow through the orifice through a channel
Drops are jetted almost constant over the repetition rate range
Jetting from the orifice at a velocity, wherein the velocity of the sound in the ink is twice the first length.
The first resonance frequency is obtained by division, and the speed of sound in the ink is four times the second length.
Dividing the second resonance frequency to obtain a value near the main resonance frequency of the fluid at the orifice
There is a spectrum energy peak at
In the vicinity of the first resonance frequency and the second resonance frequency,
The predetermined spectrum at which the spectrum energy is substantially reduced
Each of the repeats has a spectrum energy distribution
An electrical waveform is obtained, and the electrical waveform is spread over the range of the injection repetition rate.
And the electromechanical transducer repeats the electrical waveform.
Each return is transmitted to the above-mentioned pressure chamber, and the injection speed is almost constant.
Ejecting the ink droplets from the orifice at an angle
A method for ejecting ink droplets, characterized in that :