JPH0640031A - Driving method of ink-jet printing head - Google Patents

Abstract

PURPOSE:To conduct uniform printing having high quality efficiently at high printing speed by reducing the relative errors of the speed of ink droplets at each repeating speed. CONSTITUTION:The relative errors of the speed of ink droplets at each repeating speed are brought to approximately fifteen% or less within the range of repeating speed to ink droplets of ink at maximum speed from intermittent ink droplet injection from an ink injection outlet. Bipolar electric pulses 100 including a supply pulse component 102 and an infection pulse component 104 are used as a driving signal effective for driving an ink jet employing an acoustic driving apparatus. The pulse components 102 and 104 represent voltage, voltage amplitude of which often differs and has mutually reverse polarity. These electric pulses, the pulse components 102 and 104, are separated by the state of a standby time shown in 106.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an ink jet print head, and more particularly to a method for driving an ink jet print head that improves print quality.

[0002]

Ink jet printers, and in particular drop-on-demand (DOD) ink jet printers having print heads that use acoustic drivers for ink drop formation, are well known to those skilled in the art. The principle of this type of inkjet printhead is to generate a pressure wave in the ink chamber which continuously ejects ink drops from the ink pressure chamber through a nozzle orifice or ink drop ejection orifice outlet. . Various acoustic drivers are used in this type of inkjet printhead. For example, the driver consists of a pressure transducer (transducer) made of a piezoceramic material adhered to a thin diaphragm. In response to the applied voltage, the piezoelectric ceramic deforms and the partition moves the ink in the ink pressure chamber. This movement of ink causes a pressure wave to cause a flow of ink through one or more nozzles.

Piezoelectric ceramic drivers are circular, polygonal,
It may have any suitable shape such as a cylindrical shape or an annular cylindrical shape.
In addition, the piezo driver has bending mode, shear
Mode and various deflection modes such as longitudinal mode. Other acoustic drivers that generate pressure waves in the ink include heated bubble source drivers (so-called bubble or thermal inkjet printheads) and electromagnetic solenoid drivers. In general, inkjet printheads
It is desirable to have a shape that allows a plurality of nozzles to be arranged in a dense array. Here, each nozzle is driven by an associated acoustic driver.

Hawkins US Pat. No. 4,523,2
No. 00 describes a method of stabilizing inkjet printhead operation by producing high speed ink drops without unwanted ambient (satellite) ink drops and orifice clogging. In this method, an electromechanical transducer is coupled to the ink chamber and driven with a synthetic waveform. This composite waveform comprises independent consecutive first and second pulses, which in some cases are of opposite polarity and which may be separated by a time delay. The first electric pulse is an injection pulse having a pulse width sufficiently larger than the pulse width of the second pulse. When the second pulse has the opposite polarity to the first pulse, the trailing edge exponentially attenuates. Upon application of the first pulse, the ink chamber of the inkjet printhead contracts rapidly and the ejection of ink drops begins from the associated orifice. When the second pulse is supplied, the ink chamber expands rapidly, and the ejection of ink droplets from the orifice stops quickly. However, this specification does not describe the adjustment of the position of the meniscus (unevenness of the liquid surface in the capillary) of the ink before the ejection of the ink droplet, and the uniform printing is performed at a high ink droplet repetition rate. There is a problem when you need it.

It is understood that this conventional example is effective in printing with ink droplets whose amount is selectively changed. For example,
The amount of ink drop can be selected to create the optimum spot size for efficient high resolution printing.
Draft mode print quality is also obtained by using only larger drops. Such a printer is
It is useful for applications that require half tone images, such as with adjustment of color saturation, hue and brightness.

US Pat. No. 4,513,329 to Lee et al.
No. 9 describes a method of changing the size of ink droplets. In this way, the electromechanical transducer
It is coupled to the ink chamber and is driven by one drive signal or a plurality of drive signals of the same polarity, each of which is separated by a certain time delay. This time delay is shorter than the DOD ink drop generation rate. Each drive signal ejects a predetermined amount of ink with a large amount of ejected ink that merges to form one ink drop. As the drive signal during ink drop formation and ejection increases, the volume of the ink drop increases. This patent states that ink droplets of different sizes move to the print medium at a constant velocity. Further, this patent states that since the print head is moving at a constant velocity during printing, changes in the velocity of the ink drop cause the ink drop to shift from the desired position on the print medium, resulting in poor print quality. There is. However, as long as all the energy for the formation and ejection of the drops comes from the drive pulses supplied to the transducer, the change in drop size is limited to some extent, the velocity of individual drops is limited, and Changes in travel time to tend to occur. Moreover, the capacity of the ink jet to produce large drops using a large number of consecutive pulses limits the maximum drop velocity. Mizuno et al., U.S. Pat. No. 4,491,851, describes a method of using continuous drive pulses to generate drops of varying size.

US Pat. No. 45610 by Tsuzuki et al.
No. 25 describes a printer that prints halftone images with drops or ink dots of varying size. The diameter of each dot is controlled by controlling the energy content of the drive pulse that causes the dot, for example by changing the amplitude or pulse width.

US Pat. No. 4,56, by Murakami et al.
3,689 describes a method of operating an inkjet printhead to deliver different sized drops of ink onto a print medium for halftone printing. In this method, the leading pulse is applied to the electromechanical transducer before the main pulse. The leading pulse is a voltage pulse that is applied to the piezoelectric transducer to oscillate the ink in the nozzle. The energy of this voltage pulse is below the threshold level required to eject a drop of ink. The preceding pulse controls the size of the ink drop by controlling the position of the ink meniscus within the nozzle. In FIGS. 4 and 8 of Murakami et al., The leading and main pulses are of the same polarity, whereas in FIGS. 9 and 11, these pulses are of opposite polarity. The typical delay time from the start of the preceding pulse to the start of the main pulse is about 500 μs. Therefore, in this method, ink drop ejection is limited to a relatively low repetition rate. Moreover, this patent specification does not mention that a bipolar waveform with a waiting time has the lowest energy content at the fundamental acoustic resonance frequency of the inkjet.

[0009]

U.S. Pat. No. 4,403,223 to Tsuzuki et al. Describes a drop-on-demand ink jet printer in which drive pulses are applied to a piezoelectric transducer to eject ink drops from a nozzle. . The size of the ink drop is changed by adjusting the energy content of the drive pulse supplied for the purpose of performing halftone printing. The ejected ink drop passes between the charging electrodes and is charged by the voltage supplied when the ink drop is ejected from the nozzle. In the embodiment of FIG. 10 of this patent, the charged ink drop produces an electric field oriented transverse to the direction of movement of the ink drop for the purpose of altering the ink drop flight path. In the device of FIG. 1 of this patent, a charged drop of ink passes between a pair of plates 40 and a pair of plates 60 having a deflector between them. The plates 40 and 60 form an electric field directed in the direction of movement of the ink drop in order to accelerate it.

The Tsuzuki et al. Patent requires a relatively complex drive circuit because the charging voltage changes with changes in the drive pulse. In addition, the use of deflection voltage adds further complexity to the device.

Although these conventional apparatuses are known, it is possible to perform uniform high quality printing efficiently at a high printing speed.
Required for inkjet printers.

Therefore, an object of the present invention is to provide a method for driving an ink jet print head which can perform uniform and high quality printing efficiently at a high printing speed.

Another object of the present invention is to provide a method of driving an ink jet print head which can print a medium with high reliability and high efficiency with ink containing a heat-melt ink.

Another object of the present invention is to drive an inkjet printhead for reliable and efficient operation to perform halftone or gray scale printing without the need for complex electric field switching or time delay circuits. It is in the provision of methods.

Another object of the present invention is to provide a method of driving an ink jet print head which can selectively generate ink droplets of different sizes.

[0016]

A DOD type ink jet system includes an ink chamber connected to an ink source and an ink chamber.
An ink drop forming orifice having an ejection outlet and coupled to the ink chamber. Acoustic drivers are used to generate pressure waves in the ink as it exits through the ink drop orifices and ejection outlets. The driver expands and contracts the ink chamber to eject ink droplets from the ink droplet ejection orifice outlet and initially expands the volume of the ink chamber to replenish the ink chamber with ink from the ink supply. Operate. During this expansion, ink is withdrawn toward the ink chamber and away from the ink drop ejection orifice outlet. The waiting time is
It is time for the ink chamber to return to its original volume and for the ink in the orifice to leave the ink chamber and travel toward the ink drop ejection orifice outlet. Further, the driver operates to contract the volume of the ink chamber to eject ink drops. In this way, the expansion of the ink chamber, the waiting period, and the contraction of the ink chamber occur sequentially during the ejection of ink droplets.

In another feature of the invention, these ink jetting steps are repeated, for example, at high speed to provide high speed printing. Furthermore, in each standby step, the ink in the orifice waits until it reaches a position substantially the same as the position in the orifice to which the ink advances during another standby step.

According to another feature of the invention, in the waiting step, before the ink chamber volume is contracted to eject the ink droplets, the ink is near the ink droplet ejection orifice ejection outlet but does not cross the orifice. Wait until you reach the position.

In another feature of the invention, the shrinking step is performed as the ink progresses toward the drop ejection orifice outlet.

In another aspect of the invention, the driver comprises a piezoelectric driver driven by drive pulses comprising first and second pulse components of opposite polarities separated by a waiting period. These pulse components or electric drive pulses may be square waves or trapezoidal waves.

According to the present invention, when the first voltage pulse called "replenishment pulse component" is supplied, the acoustic driver increases the volume of the ink pressure chamber by the expansion of the ink pressure chamber and the ink pressure from the ink supply source is increased. Refill the chamber with ink. During expansion of the ink pressure chamber, ink is drawn back within the orifice from the orifice outlet toward the ink pressure chamber. When the replenishment pulse component is no longer supplied, the waiting period state is set next, and during this period, the ink pressure chamber returns to its original volume, and the ink in the orifice advances from the ink pressure chamber toward the orifice outlet. When the second voltage pulse, which is referred to as the “ejection pulse component” of relatively opposite polarity, is supplied, the acoustic driver reduces the volume of the ink pressure chamber due to the contraction of the ink pressure chamber, and ejects the ink droplet. In this manner, by supplying these voltage pulses to the acoustic driver, the ink droplets are ejected by the series of expansion of the ink pressure chamber, the waiting period, and the contraction of the ink pressure chamber.

According to the present invention, these steps are repeated at high speed for high speed printing. The replenishment pulse component, the waiting period state and the ejection pulse component form a drive signal. The supplemental pulse component and the injection pulse component are rectangular waves or trapezoidal waves.

A preferred embodiment of the drive signal of the present invention comprises a bipolar electrical pulse having a replenishment pulse component and a firing pulse component that vary about a zero amplitude reference voltage maintained during a wait period condition. However, it will be apparent to those skilled in the art that the reference pulse need not have zero voltage amplitude. The drive signal includes pulse components of relatively opposite polarity that vary around a positive or negative reference voltage amplitude maintained during the waiting period state.

In another aspect of the invention, the drive signal is tuned to the characteristics of the inkjet printhead in a known manner such that there is no high energy component at the fundamental acoustic resonant frequency of the inkjet printhead. Generally, the most important factor affecting the fundamental resonant frequency of an inkjet printhead is the resonant frequency of the ink meniscus. One important factor affecting the fundamental acoustic resonant frequency of an inkjet printhead is the length of the path from the ink pressure chamber outlet to the orifice outlet of the inkjet printhead. This passage is referred to as an "offset
Channel ”. The amount of energy of the complete drive pulse at different frequencies is also determined.

A complete electric drive pulse includes a replenishment pulse component, a drive pulse component and a waiting period used in ejecting ink drops. The drive pulse is adjusted so that the energy content of the drive pulse is lowest at the fundamental acoustic resonance frequency of the inkjet. When using an ink jet of the type having an offset channel between the ink chamber and the drop ejection orifice outlet, the fundamental acoustic resonance frequency corresponds to the standing wave resonance frequency through the liquid ink in the offset channel of the ink jet. In such a method, the drive signal is tuned to the characteristics of the inkjet to prevent the generation of high energy components at the fundamental resonant frequency of the inkjet.

The drive signal is tuned to the characteristics of the inkjet printhead, preferably by adjusting the duration of the wait period state and the duration of the first or replenishment pulse component, including rise and fall times. The rise and fall times of the supplement pulse component are the change from 0V to the voltage amplitude of the supplement pulse component and the change from the voltage amplitude of the supplement pulse component to 0V, respectively. A standard spectrum analyzer may be used to determine the amount of energy in the drive signal at various frequencies. After tuning adjustment, the energy content of the drive signal is minimized at the fundamental acoustic resonance frequency of the inkjet printhead.

According to another feature of the present invention, if necessary, the minimum energy content of the drive pulse having a frequency substantially equal to the fundamental acoustic frequency of the inkjet is the maximum of the drive pulse having a frequency other than the frequency substantially equal to the fundamental acoustic resonance frequency. The drive pulse is adjusted to be at least about 20 db below the amount of energy. Further, the drive pulse may be adjusted so that the maximum amount of energy of the drive pulse does not occur at a frequency sufficiently close to any of the main resonance frequencies of the inkjet print head (for example, 10 kHz or less). These main resonance frequencies include the meniscus resonance frequency, the Helmholtz resonance frequency, the piezoelectric drive resonance frequency, and the different acoustic resonance frequencies of the different channels and passages forming the inkjet printhead.

According to another feature of the present invention, the drive pulse may have trapezoidal supplemental and ejection pulse components of pulse components having different rising speeds from the maximum amplitude to the falling speed with respect to the maximum amplitude. More specifically, the first
The drive pulse or supplemental pulse component has a rise time of about 1 to 4 μsec, a maximum amplitude period of about 2 to 7 μsec, and a fall time of about 1 to 7 μsec. Furthermore, the waiting time is
Greater than about 8 μsec. The second drive pulse, that is, the ejection pulse, has the same rising period, maximum amplitude period, and falling period as the first driving pulse, but the polarities are opposite. More specifically, the rise time of the first and second drive pulse components is preferably about 1 μ to 2 μ seconds, the maximum amplitude period is about 4 μ to 5 μ seconds, and the fall period is about 2 μ to 4 μ. Seconds, and the waiting period is about 15μ-2
2 microseconds.

An important advantage of the present invention is that the improved inkjet printhead produces drops that arrive at the print medium with a substantially uniform transit time at a wide range of drop repetition rates, or firing rates. This directly affects the print finish. Conversely, if the velocity of ink droplets ejected from a single outlet is different over time or the velocity of ink droplets ejected from several outlets operating at the same time is different, the print finish is distorted. This is because the ink jet moves or the print medium moves during printing and the ink jet print head scans the print medium. DOD ink jet printers using the various features of the present invention may include an array of ink jets each having an orifice or nozzle outlet.

Another major feature of the invention is the control of the drive pulses applied to the acoustic driver to selectively vary the amount of ink within the ink drops ejected through the individual ink jets. is there.

Another feature of the invention is that the drop volume is controlled by controlling one or more characteristics of at least one bipolar pulse applied to the acoustic driver of the ink jet printer. . The bipolar pulse consists of a replenishment pulse and a firing pulse component having opposite polarities separated by a waiting period. The amount of ink in the ink drop selectively changes the duration of the waiting period, the duration or pulse width of the ejection pulse component, the amplitude of the ejection pulse component, the ejection pulse component relative to the pulse width of the replenishment pulse component. Can be changed by changing the ratio of the pulse width of the injection pulse component, changing the ratio of the amplitude of the injection pulse component to the amplitude of the supplemental pulse component, and a combination of these techniques.

Another method of varying the amount of ink in an ink drop is to use multiple bipolar pulses to form multiple pulses. The number of pulses used to form an individual drop controls the amount of ink in that drop. Each of these bipolar pulses is separated from each other for a period of time insufficient to separate ink drops at the orifice outlet until a selected number of bipolar drive pulses are delivered. In one particular method, these bipolar pulses are separated from each other for a period of at least about twice the pulse width of the individual bipolar pulses. More specifically, the bipolar pulses provided to form a single drop may be separated from each other in about 40-100 μsec.

In another method, the acoustic driver is driven by a monopolar pulse, and changing the amplitude and pulse width of the monopolar pulse changes the ink volume of the ink drop. In addition, a series or group of consecutive drive pulses may be used to vary the ink volume of the ink drops.

In addition to the factors above that affect the nature of the drive signal, the drive pulse has a predetermined threshold to prevent the maximum negative pressure in the ink jet chamber from the opposite effect of "rectified diffusion." It is configured to limit to a value less than the hold limit. "Rectifying diffusion" means the growth of bubbles dissolved in ink by repeatedly supplying a pressure wave or pressure pulse to the ink in the ink pressure chamber of an inkjet printhead at a pressure below ambient pressure. . Excessively repeated negative pressure pulses can cause air bubbles in the ink to grow to a point that adversely affects print quality, resulting in malfunctioning of the inkjet. This is not detailed here, but in U.S. patent application Ser. No. 07/665615, there is described a drive signal pulse shape which prevents the problem of rectifying diffusion. This is January 22, 1992
Published European patent application No. 467656
It is also disclosed in the issue.

[0035]

FIG. 2 shows an example of an inkjet print head to which the method for driving an inkjet print head of the present invention is applied. The DOD inkjet printhead 9 has an internal ink pressure chamber (not shown in this figure) coupled to an ink source 11. The inkjet printhead 9 includes one or more ink drop ejection orifice outlets (hereinafter simply orifice outlets) 14, 14a and 14b that couple into the ink chambers through the ink orifices. The ink passes through the orifice outlet 14 in forming the ink drop.
Ink drops travel in a first direction along a path from an orifice outlet 14 to a print medium 13 spaced from the orifice outlet. A typical inkjet printer includes a plurality of ink pressure chambers, each coupled to one or more respective orifices and orifice outlets.

Acoustic driver 36 is used to generate pressure waves or pulses. This pulse is delivered to the ink within the ink pressure chamber, causing the ink to pass outward through the orifice and its associated orifice outlet 14. The acoustic driver 36 operates in response to a signal from the signal source 37 and supplies a pressure wave to the ink.

The present invention is particularly applicable and effective when a piezoelectric driver is used to form ink droplets.
One preferred embodiment of an inkjet printhead using this type of acoustic driver is described in US Patent Application No. "Drop-on-Demand Inkjet Printhead" by Joy Roy and John Moore in November 1989. No. 07 / 430,213.
For example, electromagnetic solenoid drivers may be used, as well as piezoelectric actuators of other shapes (eg, circular, polygonal, cylindrical, annular cylindrical). In addition, the bending mode,
The piezoelectric driver may be deflected and used in various modes such as a shear mode and a longitudinal mode.

The above-mentioned Japanese Patent No. 508793 shown in FIG.
Inkjet head 9 as described in specification No. 0
In, the body 10 has an ink inlet 12 through which ink is supplied to the inkjet printhead. Further, the body 10 along with the orifice outlet or jet 14 is the ink flow path 2 from the ink inlet 12 to the jet 14.
Have eight. Typically, this type of inkjet printhead includes an array of jets 14 located immediately in front of the print medium and closely spaced from one another for printing ink drops on the print medium.

Ink entering the ink inlet 12 from the ink supply source 11 shown in FIG. 2 passes through the ink supply manifold (manifold) 16. A typical color inkjet printhead has at least four manifolds that are supplied with black, cyan, magenta and yellow inks, respectively, and are used for black and three color subtractive printing. However, the number of ink supply manifolds differs depending on whether the printer prints only with black ink or not with a full range of colors. From the ink supply manifold 16, ink flows into the ink pressure chamber 22 through the ink inlet passage 18 and the ink inlet 20.
The ink leaves the ink pressure chamber 22 through the ink pressure chamber outlet 24 and flows through the ink passage 26 to the ejection port 14 where ink droplets are ejected. The arrow 28 indicates the path of ink flow.

The ink pressure chamber 22 is in contact with one side surface of the flexible partition wall 34. In this case, the partition wall 34 made of epoxy
A pressure transducer, which is a piezoceramic disk 36 affixed to, is affixed to the ink pressure chamber 22. In the conventional method, the piezoelectric ceramic disk 36 is used.
Although not shown in FIG. 3, the metal film layer 38 electrically connected to the electronic circuit driver indicated by the reference numeral 37 shown in FIG.
Have. The transducers shown operate in a bending mode, although other types of pressure transducers can be used. That is, when a voltage is applied to the piezoceramic disk 36, the disk changes its volume. However, since the disk 36 is fixedly attached to the partition wall 34, the disk 36 is curved. This curve causes the ink in the ink pressure chamber 22 to move, causing a flow of ink through the ink passage 26 toward the ejection port 14. The replenishment of ink in the ink pressure chamber 22 after the ejection of ink drops is increased by the reverse curvature of the pressure transducer 36.

In addition to the ink flow path 28 described above, an additional ink outlet or purging path 42 is formed in the body 10 of the inkjet print head 9. The purification passage 42 is connected to the ink passage 26 at an inner portion near the ejection port 14. The purifying passage 42 leads from the ink passage 26 to an outlet or purifying manifold 44 connected to the purifying outlet 48 by the purifying outlet passage 46. Purification manifold 44 is typically connected by a similar purification passage 42 to a similar ink passage 26 associated with multiple jets 14. During the purifying operation, a flows in the direction indicated by arrow 50 to the purifying outlet 48 via the purifying passage 42, the purifying manifold 44, and the purifying outlet passage 46.

To facilitate the manufacture of the inkjet printhead of FIG. 3, body 10 is preferably formed of a plurality of laminated stainless steel plate-like plates or sheets. These sheets are stacked in a stacked relationship.
In the form of the inkjet printhead shown in FIG. 3, these sheets include a partition plate 60 that forms the partition and limits the ink inlet 12 and the purification outlet 48, the ink pressure chamber 22, a portion of the ink supply manifold and the purification. The ink pressure plate 62 that limits a part of the passage 42 is in contact with one side of the ink pressure chamber 22, and the inlet 20 and the outlet 24 of the ink pressure chamber
Of the ink supply manifold 16 and a part of the purification passage 46, a part of the passage 26, the inlet channel 18 and a part of the purification passage 46. Of the ink inlet plate 66 defining a portion of each of the passages 26 and 46, a second separating plate 68 defining a portion of each of the passages 26 and 46, and a major or offset portion of the passage 26 and the cleaning manifold 44
An offset channel plate 70 that limits a portion of the purification channel 42, a third separation plate 72 that limits a portion of the passage 26 and the purification manifold 44, respectively, and an outlet plate that limits a portion of the purification channel 42 and the purification manifold. 74, a jet plate 76 that defines the jets 14 of the array, and a stiffener plate 78 that reinforces the jet plate and minimizes the possibility of scratching or otherwise damaging the jet plate. Further plates may be used besides those shown to define various ink outlets, manifolds and pressure chambers. For example, multiple plates may be used rather than the single plate shown in FIG. 6 to limit the ink pressure chambers.
Furthermore, in all cases it is not necessary to use individual plates or layers of metal.

An example of the dimensions of the components of the inkjet printhead of FIG. 3 is shown in Table 1 below.

[0044]

[Table 1] Dimensions and resonance characteristics of the inkjet print head shown in FIG. 3 Components Cross-section length Resonance frequency Ink supply passage 18 0.203mm × 0.254mm 6.81mm 60-70kHz Septum plate 60 Diameter 2.79mm 0.102mm 160-180kHz Pressure chamber 22 Diameter 2.79mm 0.457mm Separation plate 64 1.02mm × 0.914mm 0.559mm Offset passage 71 0.508mm × 0.914mm 2.95mm 65-85kHz Purification passage 42 0.102mm × 0.254mm 8.89mm 50-55kHz Orifice outlet 14 50-70μm 60-76μm 13-18kHz

The various layers forming the ink jet print head may be arranged and joined by other suitable means, including using suitable mechanical fasteners. However, Anderson et al., U.S. Pat. No. 4,883,219, entitled "Manufacturing Inkjet Printheads by Diffusion Bonding and Brazing," describes a method of bonding metal layers.

FIG. 1 shows a first embodiment of drive signals useful for driving an inkjet using an acoustic driver. This particular drive signal is a bipolar electrical pulse 100 including a replenishment pulse component 102 and a firing pulse component 104. The pulse components 102 and 104 are voltages of opposite polarities that may have different voltage amplitudes. These electrical pulses or pulse components 102 and 104 are 106
They are separated by the waiting period state shown by. This waiting period 1
The duration of 06 is indicated by "B" in FIG. The relative polarities of the pulse components 102 and 104 may be opposite to the example shown in FIG. 5, which is the piezoelectric ceramic driver 3.
6 (FIG. 2).

Although FIG. 1 shows a typical shape of the drive signal, it does not show typical values for various attributes of the signal or pulse component such as voltage amplitude, duration, or rise and fall times. . Further, the pulse components of the drive signal shown in FIG. 1 are trapezoidal waves or rectangular waves, but in actual operation, these pulse components have rising and falling edges that change exponentially.

The preferred embodiment of the drive signal has a waiting period of 1
It includes a bipolar electrical signal having a replenishment pulse component and a firing pulse component that varies around a zero voltage amplitude maintained during 06. The drive signal may include pulses of opposite polarities that vary about a positive or negative reference voltage amplitude that is maintained during the waiting period state.

In the operation of the ink jet print head using this drive signal, when the replenishment pulse component 102 is supplied, the ink pressure chamber 22 expands, and from the ink supply source 11 to the ink pressure chamber 22 for ejecting ink. Pull in ink and refill ink. Replenishment pulse component 102
At the end of the, as the voltage drops towards zero, the ink pressure chamber 22 begins to contract and the ink orifice 103
The front ink meniscus in (FIG. 2) is moved toward the orifice outlet 14. During the waiting period B, the ink meniscus continues to move toward the orifice outlet 14. Upon supplying the ejection pulse component 104, the ink pressure chamber 22 contracts rapidly to eject an ink drop. When the replenishment pulse component 102 is supplied after the ink droplet is ejected, the ink meniscus is drawn back from the orifice outlet 14 into the ink orifice 103. Replenishment pulse component 10 including rise and fall times
The duration of 2 is less than the time required for the ink meniscus to return to a position near the orifice outlet 14 for the ejection of ink drops.

Typically, the duration of the replenishment pulse component 102, including rise and fall times, is less than half the time period associated with the resonant frequency of the ink meniscus. More preferably, this duration is less than about 1/5 of the time period associated with the resonant frequency of the ink meniscus. The resonant frequency of the ink meniscus within the inkjet printhead orifice can be readily calculated from the properties of the ink, including the amount of ink inside the inkjet printhead and the size of the orifice.

As the duration of the waiting period B increases, the ink meniscus moves closer to the orifice outlet 14 at the time the ejection pulse component 104 is supplied. Typically, the duration of the wait period 106 and the duration including the rise and fall times of the firing pulse component 104 is less than one-half of the period associated with the resonant frequency of the ink meniscus. In order to control the operation of the inkjet print head to achieve high quality printing and high speed printing by the above-mentioned driving signals, the period related to the resonance frequency of the ink meniscus is determined by the structure of the specific inkjet print head and the specific frequency. It depends on the ink and is in the range of about 50 μsec to about 160 μsec.

The pulse components 102 and 104 of the drive signal for controlling the operation of the ink jet print head so as to perform high quality printing and high speed printing are usually shown in FIG.
It is a trapezoidal wave of opposite polarity. However, a rectangular wave pulse component may be used. A conventional signal source 37 may be used to generate pulses of this shape. Other shaped pulses may be used. In general, a suitable replenishment pulse component 102 expands the ink pressure chamber 22 to increase the volume of the ink pressure chamber and replenishes the ink pressure chamber with ink from the ink supply 11 while the ink in the ink orifice 103 is replenished. Toward the ink pressure chamber 22 and away from the orifice outlet 14. The standby period 106 is a period in which approximately 0 volts is supplied to the acoustic driver. During the standby period, the ink pressure chamber 22 returns to its original volume due to contraction,
The ink meniscus in the orifice 103 separates from the ink pressure chamber 22 in the orifice and leaves the orifice outlet 14
Head towards. The injection pulse component 104 has a waiting period 1
After 06, the ink pressure chamber 22 is rapidly contracted to reduce the volume of the ink pressure chamber and eject ink droplets.

A drive signal composed of pulses having the shape shown in FIG. 1 is repeatedly supplied to eject ink droplets. Although one or more pulses may be provided to fire each drop, the preferred embodiment uses at least one such composite signal to form each drop. Further, the duration of the waiting period 106 is such that the ink meniscus in the ink orifice 103 advances to approximately the same position in the orifice during each waiting period before the ink pressure chamber 22 contracts to eject an ink drop. Is set as follows. During the waiting period 106, the ink that retracts between the replenishment pulse components can return to the position adjacent the orifice outlet 14 before the ink drop ejection pressure pulse arrives with the pulse component 104. By positioning the meniscus at substantially the same position prior to the ink droplet ejection pressure pulse component, the uniformity of the ink droplet flight time on the print medium is enhanced over a wide range of ink droplet ejection speeds. Furthermore, the duration of the waiting period is the ink chamber 22
Before the ink shrinks and ejects the ink drop, the ink meniscus is properly positioned so that it advances to the position of approximately the ink drop ejection orifice outlet 14 in the orifice 103 and does not cross the orifice outlet. If ink ejects past the orifice outlet 14 before the ejection pulse 104 is delivered,
The surface around the orifice outlet gets wet. This wetting causes the ink drops to have asymmetrical deflection and non-uniform ink drops, resulting in the formation and ejection of different ink drops. Placing the ink meniscus at approximately the same position prior to the pressure pulse enhances the uniformity of drop flight time on the print medium over a wide range of drop ejection velocities.

Further, at the point in time when the pressure pulse arrives in response to the jet pulse component 104, the ink meniscus preferably still has a forward velocity toward the orifice outlet 14 within the orifice 103. In this state, the liquid train traveling out of the inkjet print head will properly coalesce into one ink drop, minimizing the formation of unwanted ambient (satellite) ink drops. Inkjet pulse component 1
Reference numeral 04 designates the partition wall 34 of the pressure transducer as the ink chamber 2
It moves rapidly inward towards 2, causing a sudden pressure wave. This pressure wave ejects the ink drop present at the orifice exit at the end of the waiting period. Injection pulse component 1
Subsequent to the end of 04, the septum returns to its original position, during which a negative pressure wave begins to help break the ink drop.

In a specific example of the duration of different pulse components to achieve high print quality and high printing speed, the A portion of the supplemental pulse component 102 is 5 μsec and its rise time and fall time are 1 μsec, respectively. And 3 μsec, the waiting period B is 15 μsec, and the injection pulse component 10
The C portion of 4 has a duration of 5 μs, and its rise time and fall time are the same as those of the supplement pulse component 102. As mentioned above, FIG. 5 shows the shape of the drive signal, but not the individual values of its various attributes. In order to achieve high quality printing and high speed printing, it is effective to reduce these durations in order to return the fluid system to the initial state as quickly as possible, which enables high printing speed. . Another way to increase the ink drop repetition rate for the drive signal is to decrease the period from the trailing edge of the firing pulse component to the leading edge of the replenishment pulse component. This method has the advantage that it does not affect the duration of pulse components, including rise and fall times.

FIG. 4 is a diagram modeling the change in the shape of the ink row ejected when the ink jet print head of the type shown in FIG. 3 is driven by the drive signal including the duration of the above-described specific example. . 4a, 4b and 4c show the effect of varying the waiting period 106. Figure 4
In a, the duration of the waiting period B is 18 μsec, the main volume of the ink 120 forms a spherical head connected to a long tapered tail 122, the position between the tail of this filament and the orifice outlet 14. Then, ink separation occurs. After the ink drops have separated, the tail 122 begins to coalesce into the head 120 and does not form spherical drops until it reaches the print medium. However, due to the relatively high velocity of the ink train relative to the print medium, the spots (spots) that occur on the print medium are close to spheres.

In FIG. 4b, the duration of the waiting period B is 8 μ
In seconds, the ink drop separation point 124 is adjacent to the main volume of ink 120 and the ink drop is well formed. In this case, the tail portion 122 of the ink droplet is sequentially blocked with respect to the orifice outlet 14, and an unnecessary peripheral ink droplet that moves at a lower speed than the main ink droplet is formed. Therefore, the main ink drop 120 and the unwanted ambient ink drop 112 form two distinct spots on the print medium.

In FIG. 4c, the waiting period 102 is 0 μs and the drop separation point 124 occurs near the main drop volume 120. However, the remaining ink filaments 122 have weaknesses, indicated by 126 and 128, where the filaments may separate and form unwanted ambient ink drops.

FIG. 4 uses the drive signal shown in FIG.
4 illustrates the results of a theoretical model of the operation of the inkjet printhead of FIG. In each of FIG. 4, only the upper half of the formed ink drop on the centerline of the ink orifice 103 is shown.

Only a supplemental pulse, such as pulse component 102,
Alternatively, even with only the ejection pulse such as the pulse component 104, satisfactory printing performance cannot be obtained. In fact, using only the replenishment pulse component 104, the drop ejection velocity is
For example, it tends to be limited to about 3.5 m / s or less. Further, in order to increase the speed of the ink drop, the replenishment pulse 10
Increasing the amplitude and duration of 2 pulls the meniscus back to the upstream end of the ink orifice 103, causing air bubble suction. To enhance the functionality of an inkjet printer to operate at a high drop ejection speed, 6m /
A high ink drop velocity of s or more is required.

When only the ejection pulse component 106 is used without the replenishment pulse and the waiting period component, the ink velocity changes in a rhythmic vibration according to the change of the ink droplet ejection velocity. The frequency of this rhythmic vibration is modified from the information in Table 1 to be the same as the frequency of the reverberant resonance in the channel portion forming the ink flow path between the ink chamber 22 and the ink orifice outlet 14. As shown in FIG. 6, the drive signal of the injection pulse component only smoothes the velocity or flight time change by using a drive pulse having a frequency spectrum that slowly removes energy from reverberation. However, in this case, the ink volume / droplets decrease with increasing ejection velocity. In other words, the ink pressure chamber does not properly refill ink between ink ejections at all ink drop ejection velocities. Another drawback is that each ink ejected, regardless of ink refill, delivers the same amount of energy to the piezoelectric element, which tends to cause small ink droplets to travel at a fast rate. As shown in FIG. 6, the ink drop velocity normally increases as the ink drop ejection speed increases (corresponding to the decrease in the ink drop flight speed), although there is no remarkable rhythmic ink drop velocity oscillation of FIG. .

The drawback of the drive signal of only the ejection pulse is that the replenishment pulse component 104 for replenishing the ink chamber 22 first is supplied.
Can be eliminated by applying the action. Furthermore, the inkjet print head is
If designed to have a channel 71, this channel is also refilled with ink. By enlarging the ink inlets 18 and 20 from the ink supply sump, the ink chamber is fully replenished with ink without using the active replenishment pulse component 104. But in that case,
As the septum is moved inward to eject ink drops from the ink ejection orifice 14, pressure pulses established within the ink chamber 22 also flow through the conduit leading to the orifice 26 and the ink inlets 18, 20. A portion of the pressure wave traveling to the ink inlet is energy that is not used to form ink drops. The use of the replenishment pulse component allows the inlet to be smaller in order to reduce the loss of energy not used to form the ink drop, and if the inkjet is part of an array, an ink reservoir or manifold 1.
Ink chamber 22 and passage 2 from pressure pulse disturbance 6
Separate 6 This separation decreases progressively as the inlet opening 20 is made larger. Therefore, there is a balance between the size of the ink inlet, the strength of the replenishment pulse component 102, and the ejection pulse component 104. Strong replenishment pulse component 1
02 draws ink into the pressure chamber 22 via the inlet opening 20. If the replenishment pulse component is too strong, it will suck air bubbles through the orifice outlet. Similarly, the injection pulse component 1
If 04 is too strong, the replenishment pulse component will eject more ink than the ink drop that can be drawn through the ink inlet 20. A preferred relationship for these parameters is shown in Table 1 and described in the pulse component duration example above.

It should be noted that the inclusion of a replenishment pulse in the drive signal can pull ink back from the outer surface around ink orifice outlet 14. By this action, there is no possibility that the surface around the ink outlet is wetted with the ink, and the progress of the ink is delayed or blocked at the orifice outlet.

The duration of the waiting period B is such that the retracted meniscus in the orifice 103 is at the orifice outlet 1
4 is a composite function of the time required to reach 4 and the velocity of the ink when the positive pressure pulse generated by the ejection pulse component 104 arrives. The retracted meniscus preferably reaches the orifice outlet 14 at a low velocity just before the pressure pulse from the pulse component is delivered.

FIG. 5 is a graph showing ink droplet flight time versus ink droplet ejection repetition speed when the ink jet print head shown in FIG. 3 is driven by the drive signal shown in FIG.
FIG. 5 is a graph showing ink droplet flight time vs. ink droplet ejection repetition speed when the inkjet print head shown in FIG. 2 is driven only by the ejection pulse component of the drive signal shown in FIG. In FIG. 5, the ink flight time is 10,000
It is substantially constant over the entire range up to the ink droplet ejection repetition speed for ejecting an ink droplet of drops / second. In the example of FIG.
The print medium is spaced 1 mm from the orifice exit 14 of the inkjet printhead, and ink drop velocities in excess of 6 m / sec are obtained. As shown in FIG.
A maximum deviation of 30 μs was observed at ink drop ejection repetition rates ranging from 0 drops / second to 10,000 drops / second. Further, at 8,500 drops / second or less, this deviation becomes smaller. In this way, the supplemental pulse component 102 and the waiting period 10
By appropriately selecting the drive signal having 6 and the ejection pulse component 104, it is possible to obtain a substantially constant ink droplet flight time in a wide range of ink droplet ejection repetition rates.
High quality printing is obtained when the ink flight time is substantially constant.

Further, the speed of the ink droplet is relatively high,
Ink droplets of uniform size can be used. The replenishment pulse component of the drive signal reduces wetting of the surrounding surface of the orifice outlet 14 which causes the ejected ink droplet to be displaced from the desired trajectory, so that the trajectory of the ink droplet will be an orifice at all ink droplet ejection repetition rates.・ It becomes almost right angle to the face plate. Further, this drive signal is an internal cavity acoustic absorber of pressure pulses in which a highly viscous ink, such as hot melt ink in the conduit of the ink orifice 103, reverberates in the offset channel 71 of the inkjet printhead shown in FIG. Therefore, the formation of unnecessary surrounding ink can be minimized. Also, relatively simple drive signals of the type shown in FIG. 1 can be generated by conventional commercially available digital electronic drive signal sources.

A suitable relationship between the drive pulse components 102, 104 and 106 for performing high quality printing and high speed printing is experimentally determined. In particular, with an inkjet printhead such as that shown in FIG. 3, the wait period 106 can be at least about 8 μsec, and preferably longer, to form uniform and consistent ink drops. A shorter wait period increases the likelihood of unwanted ambient ink drops being formed than using a wait period set at or above the 8 microsecond level. Further, preferably, the dilation pulse component or supplemental pulse component 102 is about 16-20 μm.
Seconds. The greater the duration of the refill pulse, the greater the likelihood that bubbles will be drawn into the orifice outlet 14. For high quality and high speed printing, the duration of the replenishment pulse component, including rise and fall times, is greater than or equal to the time required to return the ejected ink to its original position during ink drop formation. Should not be long. The shorter the duration of the replenishment pulse component, the higher the achievable ink repetition rate. Generally, the duration of the supplemental pulse component 102 is preferably about 7 μsec or less. In addition, the duration of the injection pulse component 104 is typically up to 16-
20 μsec, which is about 6 μsec at the shortest. In addition, the pulse components in these ranges have a wide range of ink drop ejection speed,
Increasing the uniformity of ink drop formation and ink drop movement speed.

In the range of these drive signal parameters that control the operation of the inkjet printhead for high quality printing and high speed printing, an inkjet printhead of the type shown in FIG. It operated at the drop ejection repetition rate. Droplet velocity non-uniformities were observed to be less than 15% for continuous and intermittent drop ejection conditions. As a result, the error of the ink drop position is 11.81 drops / mm printed at the maximum repetition rate of 8 kHz, which is significantly smaller than 1/3 of one pixel. In addition, a measured ink drop volume of 170 pl / drop ± 15 pl was observed, suitable for printing with an addressability of 11.81 drops / mm when using hot melt inks. Moreover, in this state, little or no unwanted ambient ink drops are generated.

As shown in FIG. 1, the first pulse component, the replenishment pulse 102, reaches the voltage amplitude and holds this amplitude until the end of the replenishment pulse. Furthermore, the second pulse component, the injection pulse component 104, reaches a negative voltage amplitude and holds this amplitude until the end of the injection pulse. Although this amplitude value can be changed, in order to perform high-quality printing and high-speed printing, as shown in the figure, these drive pulse components are trapezoidal and the rise time to the fall time to each voltage amplitude is increased. Until time is different. In the drive signal for performing high quality printing and high speed printing, the rise time of the two pulse components 102 and 104 is about 1 μsec to about 4 μsec, and the voltage amplitude is maintained for about 2 μsec to about 7 μsec. The subsequent waiting period 106 is made longer than about 8 μsec. For other driving signals for high quality printing and high speed printing, the rise time of the first pulse or replenishment pulse is about 2 μsec, the voltage amplitude is maintained for about 3 μsec to about 7 sec, and its fall time is Is about 2 μsec to about 4 sec, and the waiting period 106 is about 1
It is 5 microseconds to about 22 seconds. Furthermore, in this case, the firing pulse component 104 is similar to the replenishment pulse component 102, but with opposite polarities.

In order to perform high quality printing with high speed printing,
Note that these durations are different due to inkjet printhead design and ink differences.
At the time of generation of each pressure wave generated by the supply of the ejection pulse component 104, the ink meniscus is traveling forward, and it is desirable that the ink meniscus is at a common position. The parameters of the drive signal can be changed to achieve this condition.

It has been found that the optimum print quality and print repetition rate are determined which shape the drive signal so as to provide a minimum amount of energy at the fundamental acoustic resonance frequency of the inkjet printhead. The fundamental acoustic resonance frequency of the inkjet printhead is determined by a well-known method.
The fundamental resonant frequency of the inkjet printhead corresponds to the resonant frequency of the ink meniscus. When using the inkjet printhead with offset channel 71 shown in FIG. 3, the fundamental resonant acoustic frequency typically corresponds to the standing wave resonant frequency through the liquid ink in the orifice channel. By using the lowest energy content drive signal at the fundamental acoustic resonance frequency of the inkjet printhead, reverberation at this fundamental acoustic resonance frequency is minimized. Reverberation interferes with the uniformity of the flight time of ink drops from the inkjet printhead to the print medium.

Generally, a Fourier transform or spectral analysis is performed on the complete drive signal to assist in adjusting the drive signal for high quality printing and high speed printing. A complete drive signal refers to the complete set of pulses used to form a single drop. In the case of a drive signal of the type shown in FIG. 5, the complete signal comprises a replenishment pulse component 102, a waiting period 106 and an injection pulse component 104. A conventional spectrum analyzer may be used to determine the energy content of the drive signal at different frequencies. This amount of energy varies with frequency, from height or peak to valley or bottom. The lowest energy content of the drive signal at some frequencies is well below the peak energy content of other frequencies. For example, the minimum amount of energy is at least about 20 dB less than the maximum amount of energy of drive signals at other frequencies.

The drive signal is adjusted by shifting the frequency of this minimum energy amount so as to be substantially equal to the fundamental acoustic resonance frequency of the ink jet print head. Using a drive signal tuned in this way, the energy of the drive signal is minimal at the fundamental acoustic resonance frequency. As a result, the effect of the resonant frequency of the inkjet printhead in forming ink drops is minimized. Without limitation to a particular method, the preferred method of adjusting the drive signal for high quality printing and high speed printing is the duration of the first pulse or replenishment pulse component 102, including the rise and fall times, and the wait. Adjust the period 106. These pulse components are adjusted at a frequency approximately equal to the fundamental acoustic resonance frequency of the inkjet printhead until the amount of energy in the drive signal is minimized.

In addition to the above effects, the main effect of the present invention is to effectively perform halftone, that is, gray scale printing with a DOD type ink jet printer. Phrase grayscale printing refers to the modulation or variation of drop volume. 1 and 2 show a waveform and a circuit for generating it, respectively, for controlling the ink drop volume.

Generally, the amount of ink contained in each individual ink drop is controlled by the diameter of the inkjet orifice and the waveform used to drive the acoustic driver. If the waveform is adjusted so that the ink amount increases, the ink droplet becomes larger. Conversely, if the waveform is adjusted so that the ink amount decreases, the ink droplet becomes smaller.

FIG. 7 shows an effective drive signal according to the present invention for performing gray scale printing. This special drive signal includes a replenishment pulse component 162 and an injection pulse component 16
4 is a bipolar electrical pulse 160 having 4. Ingredient 162
And 164 are voltages of opposite polarity. Pulse component 16
2 and 164 are separated by a waiting period X. Ingredient 1
The polarities of 62 and 164 may be opposite to those shown in FIG. 7 depending on the polarity produced by the piezoelectric drive mechanism 36 (see FIGS. 4 and 6). In operation, supplying the replenishment pulse component 162 causes the ink chamber 22 to expand and draw ink into the chamber. When the voltage reaches a value of 0 at the end of the refill pulse, the ink chamber begins to contract and the ink meniscus draws orifice 1
It moves in 03 toward the orifice outlet 14. When the ejection pulse component 164 is supplied, the ink chamber rapidly contracts to eject an ink drop. In this method of forming ink drops, the duration of the refill pulse component is shorter than the time required for the meniscus drawn into the orifice 103 by the refill pulse to return to its initial position near the orifice outlet 14. The duration of the supplemental pulse component is less than half the period of the natural or resonant frequency of the meniscus. More preferably, this duration is less than about 1/5 of the period of the meniscus's natural resonant frequency. The resonant frequency of the ink meniscus within the inkjet orifice can be calculated in a known manner from the properties of the ink and the dimensions of the ink orifice. As the waiting period increases, the ink meniscus approaches the orifice outlet 14 as the ejection pulse component 164 is delivered. At a point before the meniscus advances in the orifice and reaches the orifice exit,
If the waiting time is sufficiently short so that the ejection pulse component is supplied, the amount of ejected ink droplets decreases.
On the contrary, if the waiting time is made sufficiently long so that the ink reaches the orifice outlet before the ejection pulse component is supplied, the amount of ejected ink droplets increases. At a later point in time, the orifice is completely filled with ink. The desired waiting period and pulse width of the firing pulse for a particular drop volume depends on the characteristics of the particular inkjet used and can be observed by monitoring the performance of the inkjet. Usually, the waiting period and the period of the injection pulse component are shorter than about half the period of the natural or resonant frequency of the meniscus. A normal meniscus has a resonance period of 50 μ to
It is in the range of 160 μs and depends on the inkjet construction and the ink used. Further, increasing the duration of the ejection pulse component 64 or increasing the amplitude of the ejection pulse component increases the drop volume.

As a specific example, US Pat. No. 508793.
Suppose an inkjet of the type described in No. 0 operates at a drop repetition rate of 4 kHz. in this case,
The level or amount within an individual ink drop is varied by changing the drive waveform in FIG. When printed with hot melt ink on Mylar print media and prior to melting, the spot or dot size will be in the range of about 0.056 to 0.1 mm. If the ink is a hot melt ink and pressure is applied to melt the ink dots on the print medium, the dot size will increase, for example, in the range of about 0.066 to 0.14 mm. To minimize the dot size, for example,
The waiting period X is set to 9 μsec and the duration Y of the injection pulse component 64 is set to 3 μsec. To bring the dot size to a slightly larger second level, for example, set X to 11 μsec and Y to 5 μsec. To bring the dot size to the third level, for example, set X to 11 μsec and Y to 9 μsec. To bring the dot size to the fourth level, for example, set X to 12 μsec and Y to 15 μsec. Finally, to maximize the dot size,
Set X to 12 μs and Y to 20 μs. In each of these cases, the amplitude and pulse width of the supplemental pulse component are, for example, 40 V and 5 μsec, respectively. Further, the amplitude of the injection pulse component is, for example, 40V. By adjusting these component values of the bipolar drive pulse, the ink drop volume and ink dot size are adjusted accordingly. Similarly, by increasing the amplitude of the ejection pulse component, one or a combination of the duration of the waiting period and the duration of the pulse width of the ejection pulse component, or a combination thereof, changes the ink drop volume. As the amplitude of the ejection pulse component 64 increases, the ratio of the amplitude of the ejection pulse component to the supplement pulse component increases, and the amount of ink in the ink droplet increases. Similarly, when the pulse width of the ejection pulse increases, the ratio of the pulse width of the ejection pulse component to the pulse width of the replenishment pulse component increases, and the amount of ink drops also increases.

Further, a plurality of bipolar pulses of the type shown in FIG. 7 may be used to produce individual ink drops. Furthermore,
Increasing the number of bipolar pulses used to form the drop increases the amount of ink in the drop. In effect, each bipolar pulse causes an additional amount of ink to be added to the ink drop, increasing the amount of ink contained in the ink drop before it leaves the orifice exit.
In order to separate the individual inks formed in this way,
Increase the time interval between bipolar pulses. Alternatively,
A desired number of 2 to produce a desired size drop
After using the polar pulse, the high energy pulse is applied to separate the drops.

In a specific example, a normal bipolar pulse of a series of pulses containing a replenishment component, a standby component and an injection component is about 2
It has a duration of 0-40 μs. Furthermore, the time delay between the individual bipolar pulses is approximately 30 μ-100 μsec. In inkjet printheads of the type shown in FIGS. 2 and 3, ink drops are separated when the time delay between individual pulses is greater than about 100 μsec. Assuming that the duration of the bipolar pulses is 20 μsec, the time interval between the bipolar pulses is, for example, 40 μsec. in this case,
The time interval is approximately twice the duration of each bipolar pulse. If the time interval between the bipolar pulses is less than about 100 μs or any other time when ink drop separation occurs, successive bipolar pulses will instead produce separate ink drops, but instead will produce a quantity of individual ink drops. Add ink to.

Combining one or more pulses to produce independent drops reduces the maximum drop repetition rate at which the inkjet can operate. But,
High drop repetition rates are still possible. For example,
If up to three bipolar pulses were combined to produce the largest drop size, up to a repetition rate of 8 kHz could be achieved.

Finally, it is applicable to inkjet printers that use a wide variety of inks. Ink that is liquid at room temperature can be used as well as phase change inks that are solid at room temperature. One suitable phase change ink was the "Phase Change Ink Carrier Com" filed on August 3, 1988.
No. 4,889,560 entitled "Position and Phase Ink Produced There from". Furthermore, the present invention is not limited to any particular type of ink.

FIG. 8 is an example of a circuit within the signal source 37 that can be used to generate the bipolar electrical pulse 160 applied to the piezoceramic material 36. Referring to FIG.
The central processing unit (CPU) 200 uses the pulse component 16
It outputs a trigger pulse that feeds the pulse timer 202 to generate 2. In response to the trigger pulse,
The replenishment pulse timer 202 generates a replenishment pulse drive signal at its output terminal 206 and causes the transducer driver 2
04, the transducer driver 204 outputs the pulse component of FIG. The duration of component 162 is controlled by the count value loaded from CPU 200 via counter preset line 208.

When the count value of the supplement pulse timer 202 becomes 0, the signal at the output terminal 206 becomes 0,
(1) Set the value 0 to the negative input of the transducer driver 204.
Then, (2) the waiting period timer 210 is started. When the transducer driver 204 input returns to 0, the pulse component 162 ends and the waiting period begins. During the waiting period, the CP is set via the counter preset line 212.
It is controlled by the count value loaded from U200.

When the count value of the waiting period timer 210 becomes 0, the signal at the output terminal 214 becomes the value 0 which starts the injection pulse timer 218. The output of the fire pulse timer 218 on line 222 causes the positive input of the transducer driver 204 to go high and the pulse component of the figure begins. Component 164 has a duration Y controlled by a count value loaded from CPU 206 via counter preset line 216. Injection pulse
When the counter value of the timer 218 becomes 0, the output signal of its output terminal 22 becomes the value 0, whereby the pulse component 164 ends.

FIG. 9 shows a unipolar drive pulse. As mentioned above, the bipolar pulse drive signal of FIG. 1 is preferred, but in some cases a unipolar signal can also be used. This unipolar drive pulse is
It can be generated in a conventional manner by the signal generator 37 and is supplied to the acoustic drive mechanism 36. In the first method for varying the drop volume, the amplitude modulation method, the pulse amplitude in FIG. 9 is increased from Vo to V1. This increases the amount of ink contained in the ink droplet. Conversely, if the voltage is reduced from Vo to a low level, the amount of ink in the ink drop will decrease. Pulse width modulation techniques may be used. For example, by increasing the pulse duration or pulse width shown in FIG. 9 from t1 to t2 to t1 to t3, the amount of ink contained in the ink droplet increases. On the other hand, by reducing the pulse width of the illustrated pulse, the amount contained in the ink droplet is reduced. A combination of amplitude and pulse width modulation techniques may be used, and different waveforms may be provided beyond those shown in FIG. For example, a series of pulses may be used with a large number of pulses applied to the driver 30 during initial drop formation and drop separation that determines drop volume.

In addition to the above, controlling the amount and movement of ink drops from the ink head orifices to the print medium is aided by providing a control voltage electric field in the space between them.

[0087]

As described above, the relative error of the ink drop velocity at each repetition speed is about 15% or less over the repetition speed range from the intermittent ink drop ejection from the ink ejection outlet to the highest speed ink droplet ejection. The error in the ink drop position on the print medium is significantly reduced, and in this state, little or no unwanted ambient ink drops are generated.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing an example of drive signals used in a method for driving an inkjet print head according to the present invention.

FIG. 2 is a simplified diagram showing an inkjet print head and a print medium.

FIG. 3 is a cross-sectional view showing an example of an inkjet print head to which the driving method of the present invention can be applied.

FIG. 4 is an explanatory diagram showing a shape of an ink row ejected from an inkjet print head.

FIG. 5 is a graph showing the ink droplet flight time versus the ink droplet ejection repetition speed when driven by the drive signal of FIG.

FIG. 6 is a graph showing ink droplet flight time versus ink droplet ejection repetition speed when an inkjet print head is driven only by ejection pulse components.

FIG. 7 is a waveform diagram showing another embodiment of drive signals used in the method for driving an inkjet print head of the present invention.

8 is a block diagram showing a signal source for generating the bipolar drive signal shown in FIG. 7. FIG.

FIG. 9 is a waveform diagram showing still another embodiment of the drive signal used in the method for driving the inkjet print head of the present invention.

[Explanation of symbols]

 11 ink supply source 14 ink ejection outlet 22 ink pressure chamber 103 ink droplet ejection orifice 36 drive means

Front Page Continuation (72) Inventor Susan Sea Shauning Oregon, USA 97210 Portland North West Irving Street 2247 (72) Inventor Jeffrey J. Anderson Washington, USA 98607 Camath South East Thirty Fo Sue Way 16509

Claims (1)

[Claims] 1. An ink pressure chamber coupled to an ink supply for storing phase change ink in a liquid state when heated, an ink droplet ejection orifice having an ink droplet ejection outlet and coupled to the ink chamber, and the ink. A drive unit that supplies a drive signal to the pressure chamber to expand and contract, and repeatedly ejects ink from the ink ejection outlet toward the print medium through the ink droplet ejection orifice. A method of driving an ink jet print head that moves relative to each other, wherein the ink pressure chamber is expanded to replenish the pressure chamber with ink from the ink supply source, and the ink droplet ejection outlet is provided in the ink droplet ejection orifice. From the ink to the ink chamber, the ink pressure chamber is returned to its original volume, and Link advances toward the injection outlet,
Waiting for a predetermined time until reaching almost the same position, contracting the ink pressure chamber, ejecting ink from the ink ejection outlet, intermittent ink droplet ejection from the ink ejection outlet A method for driving an inkjet print head, characterized in that the relative error of the velocity of ink drops at each repetition rate is about 15% or less over the range of the repetition rate.