CA2199725A1 - Method and apparatus for continuous ink jet printing - Google Patents
Method and apparatus for continuous ink jet printingInfo
- Publication number
- CA2199725A1 CA2199725A1 CA002199725A CA2199725A CA2199725A1 CA 2199725 A1 CA2199725 A1 CA 2199725A1 CA 002199725 A CA002199725 A CA 002199725A CA 2199725 A CA2199725 A CA 2199725A CA 2199725 A1 CA2199725 A1 CA 2199725A1
- Authority
- CA
- Canada
- Prior art keywords
- waveform
- ink
- drops
- periodic non
- satellite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/015—Ink jet characterised by the jet generation process
- B41J2/02—Ink jet characterised by the jet generation process generating a continuous ink jet
- B41J2/025—Ink jet characterised by the jet generation process generating a continuous ink jet by vibration
Abstract
An apparatus and method for producing a stream of ink drops in a continuous ink jet printer (20) having a maximum allowable number of fast satellite drops. An ink, which may be a hot-melt ink in its liquid phase, is pressurized for continuous flow to a nozzle (26) and a rectangular or triangular waveform is generated at a fixed frequency. The waveform is applied to a transducer (30) coupled to the nozzle (26) such that nozzle vibrates and the ink flow is perturbed and discharged from the nozzle as primary drops with satellite drops formed therewith. The harmonic content of the rectangular or triangular waveform is adjusted until the desired number of fast satellite drops suitable for desired image formation are formed in the stream of primary drops. In a preferred embodiment, the desired number of fast satellites is a maximum of three.
Description
W096/0837~ 7 2 ~ P~ 95/01886 I~ ~ nOL~ ~ND A~PARATUS FOR
CO~-11~U~JU~ IN~C JET PR
The present invention relates generally to ink jet printers, and more particularly to an apparatus and method in a continuous ink jet printing system for producing crops of ink having desirable satellite formation characteristics.
Contin.uous ink jet printing systems operate by continuously discharging a stream of pressurized ink through a n.ozzle toward a substrate to be marked. The nozzle is coupled to a piezoelectric transducer or the like which. is vibrated with a sinusoidal waveform at a frequency that causes the stream of ink to break off into substa.ntially uniform drops shortly after being discharged. from the nozzle.
Upon breakoff, each of the drops is subsequently passed through a selectively variable electric field associated with a charging electrode which selectively charges the drop. The amount of charge received by each drop is ordinarily con~rolled by ad~usting the level of a voltage on the charging electrode that . 25 generates the electric field. Thereafter, an electric field generated by deflection plates deflect the drop according to the charge thereon. By appropriately varying the charging voltage and synchronizing it with the formation of each drop according to the amount of deflection desired therefor, drops are selectively deflected to form characters or other images on a moving target substrate. Drops that are not used for character or image fo~ation are substantially uncharged and intercepted by a catcher for recirculation through the system. Two such systems are described in U.S. Patent Nos. 3,683,396 and 3,972,474.
W096/08374 ~ 7 ~ ~ P~-l/~b95/01886 During the formation of a drop, the drop r~m~;n~
temporarily connected to the stream by a thin filament of ink. Eventually the drop and filament separate from each other and from the stream, whereby the filament may form its own, smaller drop known as a satellite.
If the satellite has a speed that is greater than that of its associated primary drop, it is known as a fast satellite. Conversely, if the satellite has a speed that is slower than that of its primary drop, it is known as a slow satellite. Factors in determining how the drops and satellites will break off from the stream include the frequency and amplitude of the driving signal, the physical properties of the ink, and the geometric characteristics of the nozzle.
A fast satellite catches up to and recombines with its primary drop, while a slow satellite is caught by and combines with the next subsequently-formed primary drop that trails it. Since each satellite may be charged with charge that was removed from its associated primary drop, fast satellites recombine with the primary drop without adversely affecting the charge-dependent amount of deflection of the primary drop. However, a slow satellite may alter the desired amount of charge on the subsequent drop.
This results in an unintended amount of charge on either the primary drop or the subsequent drop, or on both drops, and therefore results in an unintended amount of deflection of the drops, thereby adversely affecting the quality of the resultant image. Thus, typical continuous ink jet printers are arranged to suppress satellite formation as much as possible, or at least to produce fast satellites in a manner that does not degrade the resultant image. This is W096/08374 ~ ~ 9 ~ 7 2 5 PCT/GB95tO1886 ordinarily accomplished by increasing the amplitude of a sinusoidal driving waveform producing the nozzle vibration until satellite formation suitable for desirable image cluality is achieved.
A condition wherein no more than three fast satellites are present in the drop stream (i.e., the third primary drop from the nozzle and its corresponding fast satellite have recombined before a new satellite is formed near the breakoff point with the next primary drop) has been found to be an acceptable condition for many printing operations.
Accordingly, it is often desirable to arrange the system and the parameters influencing the breakoff characteristics so that no more than three fast satellites ~re produced in the drop stream, a printing condition ]~lown as a "three fast satellite~ condition.
However, with certain inks and/or nozzles, desirable satellite conditions cannot be consistently achieved us:ing conventional methods of breaking up an ink stream. While increasing the amplitude of the excitation signal producing the vibration to some extent des-irably regulates satellite formation in some ink and nozzle combinations, other ink and nozzle combinationc; are unable to achieve acceptable satellite conditions, or recIuire increases in driving amplitude t:hat exceed the power driving capabilities of current] existing nozzle drive circuitry. For example, even at very large amplitudes, sinusoidal waveforms c:cmnot achieve a fast satellite condition suitable for desirable image cluality with certain inks .
In particular, continuous ink jet printing with hot-melt ink:s poses a subs~antial difficulty. Hot-melt inks exist in a solid phase at room temperature and are heated to a liquid phase for discharging.
7 2 ~
Satellite f-ormation difficulties arise primarily as a result of t:he relatively low surface tension and high viscosity of hot-melt inks.
For e~.ample, typical lic~uid inks have a viscosity of 2 centipoise, a surface tension of 40 millinewtons per meter cmd a density of 1000 kilograms per cubic meter, versus a typical hot-melt ink viscosity of 10 centipoise, a surface tension of 18 millinewtons per meter and a density of 950 kilograms per cubic meter.
As a result, even large increases in driving amplitude have been found incapable of adecIuately breaking off hot-melt ink drops to form desired satellite c:onditions. Nevertheless, despite the drawbacks, continuous ink jet printing with hot melt inks is desirable to the industry because hot-melt inks have laster drying times compared to licIuid inks.
In addition, hot-melt inks substantially do not contain environmentally harmful volatile organic compounds.
GB-A--1544493 discloses an apparatus for producing a stream oi substantially ecIual sized, uniformly spaced lic~lid droplets, said apparatus comprising means for causing a continuous filament of licIuid to issue under pressure from a nozzle orifice, electrically actuable means for periodically perturbating the licIuid filament to cause it initially to form perturbations interconnected by ligaments and thereafter to break up into discrete droplets, and electric s gnal generating means for actuating the perturbating means with a composite signal comprising a first cornponent hav-ing a fundamental frecIuency at the recIuired droplet repetition frecIuency and a second component having a frecIuency which is a harmonic of the fundar~ental frecIuency, the relative amplitudes and A~EN~
CO~-11~U~JU~ IN~C JET PR
The present invention relates generally to ink jet printers, and more particularly to an apparatus and method in a continuous ink jet printing system for producing crops of ink having desirable satellite formation characteristics.
Contin.uous ink jet printing systems operate by continuously discharging a stream of pressurized ink through a n.ozzle toward a substrate to be marked. The nozzle is coupled to a piezoelectric transducer or the like which. is vibrated with a sinusoidal waveform at a frequency that causes the stream of ink to break off into substa.ntially uniform drops shortly after being discharged. from the nozzle.
Upon breakoff, each of the drops is subsequently passed through a selectively variable electric field associated with a charging electrode which selectively charges the drop. The amount of charge received by each drop is ordinarily con~rolled by ad~usting the level of a voltage on the charging electrode that . 25 generates the electric field. Thereafter, an electric field generated by deflection plates deflect the drop according to the charge thereon. By appropriately varying the charging voltage and synchronizing it with the formation of each drop according to the amount of deflection desired therefor, drops are selectively deflected to form characters or other images on a moving target substrate. Drops that are not used for character or image fo~ation are substantially uncharged and intercepted by a catcher for recirculation through the system. Two such systems are described in U.S. Patent Nos. 3,683,396 and 3,972,474.
W096/08374 ~ 7 ~ ~ P~-l/~b95/01886 During the formation of a drop, the drop r~m~;n~
temporarily connected to the stream by a thin filament of ink. Eventually the drop and filament separate from each other and from the stream, whereby the filament may form its own, smaller drop known as a satellite.
If the satellite has a speed that is greater than that of its associated primary drop, it is known as a fast satellite. Conversely, if the satellite has a speed that is slower than that of its primary drop, it is known as a slow satellite. Factors in determining how the drops and satellites will break off from the stream include the frequency and amplitude of the driving signal, the physical properties of the ink, and the geometric characteristics of the nozzle.
A fast satellite catches up to and recombines with its primary drop, while a slow satellite is caught by and combines with the next subsequently-formed primary drop that trails it. Since each satellite may be charged with charge that was removed from its associated primary drop, fast satellites recombine with the primary drop without adversely affecting the charge-dependent amount of deflection of the primary drop. However, a slow satellite may alter the desired amount of charge on the subsequent drop.
This results in an unintended amount of charge on either the primary drop or the subsequent drop, or on both drops, and therefore results in an unintended amount of deflection of the drops, thereby adversely affecting the quality of the resultant image. Thus, typical continuous ink jet printers are arranged to suppress satellite formation as much as possible, or at least to produce fast satellites in a manner that does not degrade the resultant image. This is W096/08374 ~ ~ 9 ~ 7 2 5 PCT/GB95tO1886 ordinarily accomplished by increasing the amplitude of a sinusoidal driving waveform producing the nozzle vibration until satellite formation suitable for desirable image cluality is achieved.
A condition wherein no more than three fast satellites are present in the drop stream (i.e., the third primary drop from the nozzle and its corresponding fast satellite have recombined before a new satellite is formed near the breakoff point with the next primary drop) has been found to be an acceptable condition for many printing operations.
Accordingly, it is often desirable to arrange the system and the parameters influencing the breakoff characteristics so that no more than three fast satellites ~re produced in the drop stream, a printing condition ]~lown as a "three fast satellite~ condition.
However, with certain inks and/or nozzles, desirable satellite conditions cannot be consistently achieved us:ing conventional methods of breaking up an ink stream. While increasing the amplitude of the excitation signal producing the vibration to some extent des-irably regulates satellite formation in some ink and nozzle combinations, other ink and nozzle combinationc; are unable to achieve acceptable satellite conditions, or recIuire increases in driving amplitude t:hat exceed the power driving capabilities of current] existing nozzle drive circuitry. For example, even at very large amplitudes, sinusoidal waveforms c:cmnot achieve a fast satellite condition suitable for desirable image cluality with certain inks .
In particular, continuous ink jet printing with hot-melt ink:s poses a subs~antial difficulty. Hot-melt inks exist in a solid phase at room temperature and are heated to a liquid phase for discharging.
7 2 ~
Satellite f-ormation difficulties arise primarily as a result of t:he relatively low surface tension and high viscosity of hot-melt inks.
For e~.ample, typical lic~uid inks have a viscosity of 2 centipoise, a surface tension of 40 millinewtons per meter cmd a density of 1000 kilograms per cubic meter, versus a typical hot-melt ink viscosity of 10 centipoise, a surface tension of 18 millinewtons per meter and a density of 950 kilograms per cubic meter.
As a result, even large increases in driving amplitude have been found incapable of adecIuately breaking off hot-melt ink drops to form desired satellite c:onditions. Nevertheless, despite the drawbacks, continuous ink jet printing with hot melt inks is desirable to the industry because hot-melt inks have laster drying times compared to licIuid inks.
In addition, hot-melt inks substantially do not contain environmentally harmful volatile organic compounds.
GB-A--1544493 discloses an apparatus for producing a stream oi substantially ecIual sized, uniformly spaced lic~lid droplets, said apparatus comprising means for causing a continuous filament of licIuid to issue under pressure from a nozzle orifice, electrically actuable means for periodically perturbating the licIuid filament to cause it initially to form perturbations interconnected by ligaments and thereafter to break up into discrete droplets, and electric s gnal generating means for actuating the perturbating means with a composite signal comprising a first cornponent hav-ing a fundamental frecIuency at the recIuired droplet repetition frecIuency and a second component having a frecIuency which is a harmonic of the fundar~ental frecIuency, the relative amplitudes and A~EN~
2~9~72~
~ . .
-4a-phases of t:he component signals being such that each ligament fi.rst breaks off from the same predetermined one of the two pertubations it interconnects and subsequent]y merges with the other of the pertubations it intercoImects.
GB-A--1544493 is concerned with control of initial break off and subsequent merging of satellite drops from/into primary drops such that a particular type of break off cmd merging process takes place. GB-A-1544493 is not concerned with ensuring that at any given time there is present in the drop stream a desired number of fast satellite ink drops.
According to the present invention there is provided an apparatus for perturbing a pressurized ink in a continuous ink jet printer into a stream of primary ink drops and satellite ink drops with a desired ~lcmtity of fast satellite ink drops present in said strearn at any given time, the apparatus comprising, a transducer for imparting mechanical vibration t;o an ink discharge nozzle of the ink jet printer, which nozzle is in fluid commlln;cation with a pressurizecl supply of ink, a periodic non-sinusoidal waveform signal generator for driving the transducer with a periodic non-sinusoidal waveform, and a harrnonic controller arranged to adjust the harmonic content oi- the periodic non-sinusoidal waveform to obtain said desired quantity of fast satellite ink drops.
Further according to the invention there is provided a method of producing, in a continuous ink jet printing system, a stream of ink drops having a desired n~nber of fast satellite ink drops present in said stream at any given time, the method comprising the steps of:
pressurizing a fluid for continuous flow to an ink discharge nozzle;
A~EN~ HEET
- 2~7~ -~ .
generating a periodic non-sinusoidal waveform at a fixed frec~ency;
applying the waveform to a transducer coupled to the nozzle such that the ink flow is perturbed and discharged from the nozzle as primary ink drops and satellite ink drops associated therewith; and adjusting the harmonic content of the waveform to obtain saicL desired number of fast satellite drops in the ink stream.
The present invention has an advantage that it provides an apparatus and method for producing drops of ink in 2. continuous ink jet printing system wherein desirable satellite formation, resulting in desirable printing conditions, are achieved for an increased lS variety of inks. The apparatus and method as characteriz;ed above functions with an increased variety of nozzle types.
Further the present invention has an advantage that it recluces the amount of power recluired to drive a nozzle while achieving desired satellite and printing conditions.
The apparatus and method embodying the present invention zchieves desired satellite conditions without increasing the amplitude of the driving signal above customary excitation levels. The method and apparatus embodying the present invention simplifies the electrical circuitry for driving a continuous ink jet nozzle.
The apparatus and method embodying the present invention facilitates the use of hot-melt inks in a continuous ink jet printing system.
A~EN~ Slt~T
W096/08374 ~ 7 2 ~ 55/01886 It is a resulting feature of the invention that improved cost savings and reliability are attained.
The irl~ention will now be further descri~ed by way of exan~ple with reference to the accompanying drawings in which:
FIGURE 1 is a functional block diagram illustrating components of a continuous ink jet printing system constructed in accordance with a preferred en~odiment of the present invention;
FIGs. ~ and 4 are graphs representing two distinct types of rectangular waveforms which can be applied via a transducer to a continuous ink jet printing noz;zle to generate desirable satellite conditions according to the invention;
FIGs. 3 and 5 are graphs representing the Fourier coefficients of the waveforms of FIGs. 2 and 4, respectively;
FIGs. 6 and 8 are graphs representing two distinct types of triangular waveforms that generate desirable satellite conditions according to the invention;
FI~s. 7 and 9 are a graphs representing the Fourier coefficients of the waveforms of FIGs. 6 and 8, respectively;
FIGs. lO, 12, 14 and 16 are graphs representing four distinct types of trapezoidal waveforms that generate desirable satellite conditions according to the invention;
FIGs. ll, 13, 15 and 17 are graphs representing the Fourier coefficien~s of the waveforms of FIGs. lO, 12, 14 and 16, respectively;
FIGs. 18, 20, 22 and 24 are graphs representing four distinct types of quasi-rectangular waveforms that generate desirable satellite conditions according to the invention;
WO 96/08374 ~ 'I 9 ~ 7 ;2 ~ PCTIGB95/01886 plates 34 onto a target substrate 35 at an appropriate location for forming a desired image. Because not all of the available drops are needed to form a given image, an ink recirculation system (not shown) is provided to collect and reuse the extra drops.
In accordance with one aspect of the invention, a non-sinusoidal periodic waveform having a controllable harmonic content is employed to drive the transducer 30. Examples of such a waveform include rectangular, quasi-rectangular, triangular, quasi-triangular, trapezoidal, and quasi-trapezoidal waveforms.
To generate such a periodic non-sinusoidal waveform, a suitable electronic waveform generation means comprising a periodic non-sinusoidal waveform generator 36 and an amplifier 38 is provided to supply the desired waveform of a suitable driving frequency and amplitude to the transducer 30. A typical frequency is on the order of 66 kilohertz and a typical amplitude is on the order of 100 volts peak to peak, which is not necessarily symmetric about ground.
By way of example, the waveform generator 36 may be a rectangular waveform generator (FIG. 26) or alternatively may be a triangular waveform generator (FIG. 27) as described in more detail below.
Although not necessary to practice the invention, a controller 40 is provided to control certain waveform parameters such as the amplitude and frequency. As can be readily appreciated, the controller 40 comprises a set of potentiometers or the like. Alternatively, the controller 40 may comprise more complex electronic circuitry such as a microprocessor-based frequency and gain control circuit.
In accordance with another aspect of the invention, there is provided a means for adjusting the W096/08374 ~ 7 ~ ~ P~-l/~b95,~l886 .
FIGs. :L9, 21, 23 and 25 are graphs representing the Fourier coefficients of the waveforms of FIGs. 18, 20, 22 and 24, respectively;
FIGs. 26 and 27 are block diagrams representing sui~able waveform generators and harmonic content controllers for FIG. 1 that generate rectangular and triangular ~aveforms, respectively; and FIG. 2~3 is a block diagram representing a programmab]e rectangular waveform generator and harmonic corltent controller for FIG. 1.
Turninsr now to the drawings and re~erring first to FIG. 1, t:here is shown a continuous ink jet printing system 20 constructed in accordance with a preferred embodiment of the present invention. The lS printing sy,tem 20 comprises a pressurized supply of ink 22 con~e~cted by a suitable conduit 24 to a nozzle 26 which provides a pressurized ink stream. A
pressure source (not shown) may be utilized to pressurize the ink. In the embodiment described, the ink is of a type known as hot-melt and a heater 28 is provided to liquify the ink in a known manner. One such hot-meit ink Je~ printing system is described in US patent application number 08/307,195. Of course, other t~pes of inks may alternatively be used with the present invention, including inks that exist in a liquid phase at room temperature and-which consequently do not require a heater.
To break the ink into droplets of substantially uniform size, a transducer 30 is provided and coupled with the nozzle 26 in a manner that imparts vibration to the nozzle 26, thereby breaking the continuous flow of ink into primary drops and satellite drops. Once broken from the stream, the ink drop~s are charged by a charging electrode 32 and deflected using deflection W096l08374 ~ 7 2 ~ PCT/GB95/01886 harmonic content of the periodic non-sinusoidal waveform, designated as a harmonic content controller 42. ~y altering the harmonic content of the driving ~ waveform, the formation and relative motion of satellites is affected.
In a rectangular or triangular waveform, a change in the harmonic content appears as a change in the duty cycle of the waveform. Duty cycle is defined for a rectangular waveform as the percentage of time that the waveform is at its high amplitude over the total period of one waveform cycle (high amplitude plus low amplitude):
Duty cycle = [rh~gh / (Th.gh + T1OW)] 100%
For a triangular wave, duty cycle is defined as the time the signal takes to rise from its lowest to highest amplitude divided over the to.tal period of one waveform cycle (the rise time from lowest amplitude to highest amplitude plus fall time from highest amplitude to lowest amplitude~:
Duty cycle = [Trise / (Trise + Tfall)] 100%
~5 By way of example, FIG. 2 illustrates one cycle of a rectangular wavefor... havlng a twenty=flve percer.t duty cycle (twenty-five percent high, seventy-five perce~t low over one complete waveform period To)~
FIG. 6 illu.strates one cycle of a triangular waveform having a twenty-five percent duty cycle (twenty-five percent of the period rising, seventy-five percent falli~g).
Any repetltive waveform of period To can be represented. as a Fourier series according to the formula:
W096/08374 ~ ~ Q ~ 7 ~ ~ PCT/GB95/01886 f(t) = aO/2 + ~; [(an cos(2nnt/T0) + (bn sin(2n~t/T0)]
r To where ar. = 2/To J f(t) cos(2n~t/T0) dt for n = 0, 1, 2, ...
To and br = 2/To ~0 f(t) sin(2n~t/T0) dt for n = 1, 2, When an ~ and bn ~ 0, an alternate form of the Fourier series can be expressed as:
f(t) = aO/2 + ; cn sin(2n~t/T0 + ~n) where an = cn sin ~n bn = Cn COS ~t)n Cn = ~/ an + bn and ~n = arctan(an/bn).
The coefficients cO through cn correspond to the harmonics of the Fourier expansion, and are commonly referred to as the Fourier coefficients.
For a rectangular waveform of amplitude A, period To and duty cycle ~, the Fourier coefficients are given by:
45 aO = 4A ( ~ /2 ) W096l08374 ~ 7 ~ 5 P~-l/~b5SJ~l886 cn = (A ~ / n~)~ 1 - cos(2n~) for n = 1, 2, ...
and the pha.se angles by:
~)n = arctan [sin (2n~ cos (2n~o))]
for n = 1, 2, The FoL;rier coefficients for the twenty-five percent duty cycle rectangular waverorm of FIG. 2 for n = 0 to 40 are shown in FIG. 3. As can be seen from FIG. 3 and/or by solving the formula for cnl in this rectangular waveform every multiple of a fourth harmonic (C4, C8, Cl2 an.d so on) equals 0. This plays a significant role in acceptable satellite formation for certain types of inks and nozzles.
Similarly, for a triangular waveform, of amplitude ~, period To~ and duty cycle ~, the Fourier coefficientc are given by:
ao =
cn = [A ~ / n2~2~ )] ~1 - cos(2n~) : ~ for n = 1, 2, and the pha.se angles by:
~n = arctan [cos (2n~) - 1 / sin (2n~)]
- for n = 1, 2, The Fou.rier coefficients for the twenty-five percent duty cycle triangular waveform of FIG. 6 for n = 0 to 40 are shown in FIG. 7. As can be seen from FIG. 7 and/or by solving the formula for cn, in this triangular waveform every multiple of a fourth harmonic (C4, C8, C12 and so on) equals 0, as with the rectangular waveform.
W096/08374 2 ~ ~ 9 7 ~ ~ PCTIGB95/01886 .
The waveforms (and their corresponding Fourier coefficients) illustrated in FIGs. 10-25 will not be described in detail herein for purposes of simplicity.
However it can be readily appreciated from an inspection of the drawings and/or by solving well-known equations that multiples of the fourth harmonic are either zero or near zero for these waveforms.
Again, this plays a significant role in acceptable satellite formation for certain types and combinations of inks and nozzles.
The waveforms illustrated herein were found to successfully break up continuous jets of various types of inks using prototype nozzles, achieving a three fast satellite condition suitable for desirable image formation when the transducer was driven by a commercially available signal generator and power amplifier at a frequency of 66 kilohertz at various peak-to-peak amplitudes between 50 and 200 volts. In particular, rectangular waves were found to successfully break up hot-melt inks in a prototype nozzle. In contrast, a conventional sine wave with comparable amplitude and frequency was unable to acceptably break up the hot-melt ink jet using this same ink and nozzle combination. Indeed, acceptable breakoff did not occur even when driving the transducer with a 300 volt peak-to-peak sine wave, the maximum test voltage available, which is an amplitude that far exceeds the power driving capabilities of currently existing nozzle drive circuitry.
It should be noted that certain of the waveforms have the same Fourier coefficients as their effectively inverted counterpart waveforms. For exam~le, the rectangular waveform of FIG. 2 having a twenty-five percent duty cycle has Fourier coefficients that are equivalent to the Fourier WO 96108374 ~ 7 ~ ~ PCIIGB95/01886 coefficients of the rectangular waveform of FIG. 4 having a seventy-five percent duty cycle. However, the phase shifts ~ are different for the two duty cycles. It has been found that one of the duty cycles provides better print quality when the driving frequency is less than the frequency at which the nozzle fluid chamber resonates, while the counterpart duty cycle provides better print quality when the driving frequency is greater than this resonant frequency.
Periodic non-sinusoidal waveforms having other duty cycles can also produce desired satellite formations suitable for desirable image formation in other types of ink and nozzle combinations, and at ~ar lower drive levels than required by sine waves. For example, with certain inks and nozzles, periodic non-sinusoidal waves having du~y cycles ranging from between sixty and ninety percent high, or alternatively between forty and ten percent high are far more effective in achieving acceptable print quality than. comparable sinusoidal driving waveforms.
As an added. benefit, the electronics required to generate su.ch waveforms are less complex and more cost-effective than the electronics required to generate sin.e waves, and thus rel-iability and cost benefits are achieved with the present invention.
It can. be readily appreciated that rectangular waveforms in. general have finite rise and/or fall times and to this extent may not be exactly rectangular, but for practical purposes, a waveform such as depicted in FIG. 2 may be considered as purely rectangular because of its sufficiently fast rise and fall time relative to the ~otal time period of one complete waveform cycle.
W096/08374 ~ 1 9 9 7 ~ h PCTIGB95/01886 .~
Moreover, a waveform having a substantially rectangular shape, such as the waveforms of FIGs. 18, 20, 22 and 24 which have slower and more rounded rise and fall times, have essentially similar Fourier coefficients as pure rectangular waveforms, and have similarly beneficial nozzle drive characteristics. As shown in FIGs. 19, 21, 23 and 25, wherein the coefficients for the exemplary quasi-rectangular waveforms of FIGs. 18, 20, 22, and 24 are graphed for the first forty harmonics, every fourth coefficient is nearly zero. Accordingly, as used herein, the phrase l~rectangular waveform" is intended to include all substantially rectangular waveforms, including pure rectangular waveforms, quasi-rectangular waveforms, and trapezoidal waveforms such as those depicted in FIGs. 10, 12, 14 and 16.
Analogous to the rectangular waveform, quasi-triangular waveforms have essentially similar Fourier coefficients as pure triangular waveforms, and have similarly beneficial nozzle driving characteristics.
Thus, the phrase "triangular waveform~ is intended to include all substantially triangular waveforms, including pure triangular waveforms and quasi-triangular waveforms.
Turning now to an explanation of the operation of the invention, the tailoring of the h~rmonl C content of the periodic non-sinusoidal waveform for a particular ink and nozzle combination is ordinarily performed by carefully observing the actual satellite formation and/or studying the placement accuracy of the resultant dots forming an image on a target surface. To initialize the printing system 20 of FIG.
1, the duty cycle of the periodic non-sinusoidal waveform, and if necessary the amplitude thereof, is varied until the desired satellite condition suitable -W096/08374 ~ ~ ~ 9 7 2 ~ PCTIGB95/01886 .
for desirable image formation is achieved. Once achieved, the waveform is then established for a given ink and nozzle combination.
By way of example, as shown in FIG. 26 wherein the periodic non-sinusoidal waveform generator 36 comprises a rectangular waveform generator, the harmonic content of the waveform is varied by adjusting the resistance settings of one or more variahle resistors 56, 58 (potentiometers) in the RC
circuit 60. As can be appreciated, one type of waveform generator that is controllable to generate a rectangula:r wave of an appropriate frequency and duty cycle acco:rding to the values of resistors and a capacitor 6:2 comprises an astable multivibrator.
Altenlc~tively, as shown in FIG. 27, the periodic non-sinusoidal waveform generator 36 may comprise a triangular wave~orm generator. With this particular circuit, operational amplifiers 64 and 66 are employed to generate the triangular waveform. Fixed resistors 68-71 and capacitor 72 are selected in a known manner.
The duty c~c:le of the waveform is adjusted by ~djusting t:he harmonic content controller 42, comprising a variable resistor 74 connected to vary the voltage on the non-inverting input of the operational amplifier 66.
Once acljusted, the harmonic content for the chosen waveform is established in the settings of the variable resistors 56, 58 (rectangular waveform generator) cr in the setting of the variable resistor 74 (triangular waveform generator). In general, if a voltage controlled oscillator (not shown) serves as the waveform generator, an input voltage, which may originate from any suitable source, is provided to vary the harmonic content.
W096108374 ~ ~ ~ 9 7 2 ~ PCTIGB95101886 .
Regardless of how the harmonic content of the waveform is adjusted, the adjustment takes place in conjunction with an analysis of a resultant printed image and/or by viewing the actual drop formations, (for example by employing a microscope and a strobe light). According to the invention, the harmonic content is varied until the desired satellite condition and resultant desirable image formation are regularly achieved.
By way of example, to select and adjust a suitable non-sinusoidal waveform for a given ink and nozzle combination when a conventional sinusoidal waveform is unacceptable, a rectangular waveform having a twenty-five percent duty cycle is initially employed as the driving waveform. The quality of the printed image or the actual formation of the drops is then analyzed for various driving amplitudes of the rectangular waveform. If the results obtained at the twenty-five percent duty cycle are less than ideal, the rectangular waveform may be effectively inverted to have a seventy-five percent duty cycle in order to determine if the arop formation or the resultant image quality is consequently enhanced as analyzed at various driving amplitudes.
If improvements to the image quality beyond those provided by the rectangular waveform are still likely or necessary, a triangular waveform having a twenty-five percent duty cycle may be subsequently selected and utilized as the driving waveform, and the results again analyzed at various driving amplitudes. As with the rectangular waveform, this triangular waveform may be inverted to have a seventy-five percent duty cycle in order to determine the effect on the quality of the printed image. Other waveforms may be selectively applied to the transducer in a similar manner, W096/08374 ~ 7 ~ ~ r~ 95/01886 .
although typically ei~her a rectangular or triangular waveform provides acceptable results.
Finally, once an appropriate waveform is established, the harmonics, or symmetries, of the waveform may be adjusted as desired in order to fine-tune the drop formation as evidenced by the quality of the printed image. As described above, a change in the harmonic content of a waveform alters the duty cycle thereof. While a twenty-five or a seventy-five percent duty cycle typically provides the desired results, e;~amples of duty cycles ranging from ten to thirty-five (or ninety to sixty-five) percent have produced prl-ferable results with other ink and nozzle combinations. If a range of duty cycles is determined to provide ~cceptable image formation, the duty cycle may be set ,ubstantially in the middle of the range.
Since :Eormulations of inks may vary over time, and since one type of printer may be used with several different t:~pes of inks and/or nozzles, an alternate embodiment of the invention shown in FIG. 28 includes means for e3ectrically varying the waveform. This enabies the driving waveform to be controlled by co~mAn~s frc)m a printer controller, a personal computer, or the like.
In FIG. 28, a microprocessor 80 is connected- to a storage device 82 which may be a RAM, ROM, a computer disk or the like. The storage device 82 has previously c;tored therein the optimal waveform parameters for a number of inks and/or nozzles. Based on the type of ink and/or nozzle, which are input (along with any other variables that are deemed significant) as values into the microprocessor 80 via input means 84, the microprocessor 80 accesses the storage device 82 to o~tain the corresponding optimal waveform parameters to adjust the waveform generator W096/0837~ ~ 1 9 9 ~ 2 ~ r~ll~b5510l886 36. For example, the microprocessor 80 may be arranged to reference a database in the storage device 82 to obtain the optimal waveform duty cycle, amplitude and frequency for a given ink and nozzle combination. Of course, the microprocessor 80 may alternatively receive waveform information directly from the input device 84.
The microprocessor 80 may be present in an external device such as a personal computer, however it can be appreciated that many ink jet printing systems already are equipped with a printer controller for controlling other aspects of the printing operation. Thus, such a printer controller can be modified to perform the functions of the microprocessor 80 described herein.
As shown in FIG. 28, the programmable variable resistors 90, 92 are electrically adjustable by the computer signals, such as in a programmable resistor network. These resistors comprise an RC circuit 94 that controls the operation of the astable multivibrator as in the previously described circuit of E'IG. 2~. Alternatively, a latched digital-to-analog voltage converter (not shown) coupled to a voltage controlled resistor may act as a programmable 25- resistor.
Output signals from the microprocessor 80 set the values of the resistors 90, 92, thus determ; n; ng the corresponding duty cycle and/or frequency. Similar output signals are also used to set the gain of a variable gain amplifier 98. Once the waveform characteristics are set, the system may be arranged such that the microprocessor-based device can subsequently be disconnected from the printing apparatus, such as by unplugging a portable personal computer. In this manner, a consistent and rapid W096l08374 ~ ~hi ~ 9 7 2 ~ P~ 5S,~l886 -- 19 ._ change to the waveform may be accomplished as inks or nozzles are varied.
Moreover, it is feasible to remotely set the parameters of the driving waveform to match given ink and nozzle combinations. For example, the parameters may be set via telephone, modem, transmission cable, or other transmission means from a central or remote location. Alternatively, each time a new ink is developed, the ink may be shipped with a set of waveform parameters stored on a floppy disk or the like that may be used by the customer to tailor the system to the new type of ink. Indeed, other methods of supplying in~ormation to adjust the duty cycle or harmonics of the waveform are feasible. For example, the input me,~ns 84 may comprise DIP switches operatively ,-onnected to the microprocessor 80 such that the settings thereof corresponding to selected parameters for known ink and/or nozzle configurations.
Of course, DIP switches may alternatively be arranged to directly vary the resistance settings of resistors and thus adjust the waYeform duty cycle or harmonics withou~ a microprocessor.
While F:[G. 28 describes a programmable rectangular waveform with a corresponding rectangular waveform generator, it can be readily appreciated that other waveforms may be set by programmably controlling a similar waveform generator and/or harmonic content controller. For example, the h~rmoni C content of a triangular wclveform may be electrically controlled by utilizing a programmable resistor as the variable resistor 74 in FIG. 27, and similarly connecting it for adjustment by the output of a microprocessor.
Moreover, a microprocessor may further be employed to select the t:~pe of periodic non-sinusoidal driving W096l08374 ~ 7 ~ ~ P~-ll~h5J~l886 waveform from a waveform generator capable of outputting multiple types of waveforms (not shown).
Finally, although not necessary to the invention, by utilizing a camera in a computerized vision system to compare the actual drop formation or to analyze printed images against changes to the duty cycle and other parameters, it is further feasible to automate the adjustment process in a closed-loop control system. This may be performed during installation or in real-time during actual printing operations.
As can be seen from the foregoing detailed description, there is provided an apparatus and method for producing drops of ink in a continuous ink jet printing system that achieves desirable satellite formation thereby resulting in desirable printing conditions. The desired satellite formation is achieved for an increased variety of inks and nozzle types, including hot-melt inks, and with a reduced amount of power consumption. The desired satellite conditions are achieved with simplified electrical driving circuitry that provides improved cost savings and reliability, and without increasing the amplitude of the driving signal above customary excitation levels.
~ . .
-4a-phases of t:he component signals being such that each ligament fi.rst breaks off from the same predetermined one of the two pertubations it interconnects and subsequent]y merges with the other of the pertubations it intercoImects.
GB-A--1544493 is concerned with control of initial break off and subsequent merging of satellite drops from/into primary drops such that a particular type of break off cmd merging process takes place. GB-A-1544493 is not concerned with ensuring that at any given time there is present in the drop stream a desired number of fast satellite ink drops.
According to the present invention there is provided an apparatus for perturbing a pressurized ink in a continuous ink jet printer into a stream of primary ink drops and satellite ink drops with a desired ~lcmtity of fast satellite ink drops present in said strearn at any given time, the apparatus comprising, a transducer for imparting mechanical vibration t;o an ink discharge nozzle of the ink jet printer, which nozzle is in fluid commlln;cation with a pressurizecl supply of ink, a periodic non-sinusoidal waveform signal generator for driving the transducer with a periodic non-sinusoidal waveform, and a harrnonic controller arranged to adjust the harmonic content oi- the periodic non-sinusoidal waveform to obtain said desired quantity of fast satellite ink drops.
Further according to the invention there is provided a method of producing, in a continuous ink jet printing system, a stream of ink drops having a desired n~nber of fast satellite ink drops present in said stream at any given time, the method comprising the steps of:
pressurizing a fluid for continuous flow to an ink discharge nozzle;
A~EN~ HEET
- 2~7~ -~ .
generating a periodic non-sinusoidal waveform at a fixed frec~ency;
applying the waveform to a transducer coupled to the nozzle such that the ink flow is perturbed and discharged from the nozzle as primary ink drops and satellite ink drops associated therewith; and adjusting the harmonic content of the waveform to obtain saicL desired number of fast satellite drops in the ink stream.
The present invention has an advantage that it provides an apparatus and method for producing drops of ink in 2. continuous ink jet printing system wherein desirable satellite formation, resulting in desirable printing conditions, are achieved for an increased lS variety of inks. The apparatus and method as characteriz;ed above functions with an increased variety of nozzle types.
Further the present invention has an advantage that it recluces the amount of power recluired to drive a nozzle while achieving desired satellite and printing conditions.
The apparatus and method embodying the present invention zchieves desired satellite conditions without increasing the amplitude of the driving signal above customary excitation levels. The method and apparatus embodying the present invention simplifies the electrical circuitry for driving a continuous ink jet nozzle.
The apparatus and method embodying the present invention facilitates the use of hot-melt inks in a continuous ink jet printing system.
A~EN~ Slt~T
W096/08374 ~ 7 2 ~ 55/01886 It is a resulting feature of the invention that improved cost savings and reliability are attained.
The irl~ention will now be further descri~ed by way of exan~ple with reference to the accompanying drawings in which:
FIGURE 1 is a functional block diagram illustrating components of a continuous ink jet printing system constructed in accordance with a preferred en~odiment of the present invention;
FIGs. ~ and 4 are graphs representing two distinct types of rectangular waveforms which can be applied via a transducer to a continuous ink jet printing noz;zle to generate desirable satellite conditions according to the invention;
FIGs. 3 and 5 are graphs representing the Fourier coefficients of the waveforms of FIGs. 2 and 4, respectively;
FIGs. 6 and 8 are graphs representing two distinct types of triangular waveforms that generate desirable satellite conditions according to the invention;
FI~s. 7 and 9 are a graphs representing the Fourier coefficients of the waveforms of FIGs. 6 and 8, respectively;
FIGs. lO, 12, 14 and 16 are graphs representing four distinct types of trapezoidal waveforms that generate desirable satellite conditions according to the invention;
FIGs. ll, 13, 15 and 17 are graphs representing the Fourier coefficien~s of the waveforms of FIGs. lO, 12, 14 and 16, respectively;
FIGs. 18, 20, 22 and 24 are graphs representing four distinct types of quasi-rectangular waveforms that generate desirable satellite conditions according to the invention;
WO 96/08374 ~ 'I 9 ~ 7 ;2 ~ PCTIGB95/01886 plates 34 onto a target substrate 35 at an appropriate location for forming a desired image. Because not all of the available drops are needed to form a given image, an ink recirculation system (not shown) is provided to collect and reuse the extra drops.
In accordance with one aspect of the invention, a non-sinusoidal periodic waveform having a controllable harmonic content is employed to drive the transducer 30. Examples of such a waveform include rectangular, quasi-rectangular, triangular, quasi-triangular, trapezoidal, and quasi-trapezoidal waveforms.
To generate such a periodic non-sinusoidal waveform, a suitable electronic waveform generation means comprising a periodic non-sinusoidal waveform generator 36 and an amplifier 38 is provided to supply the desired waveform of a suitable driving frequency and amplitude to the transducer 30. A typical frequency is on the order of 66 kilohertz and a typical amplitude is on the order of 100 volts peak to peak, which is not necessarily symmetric about ground.
By way of example, the waveform generator 36 may be a rectangular waveform generator (FIG. 26) or alternatively may be a triangular waveform generator (FIG. 27) as described in more detail below.
Although not necessary to practice the invention, a controller 40 is provided to control certain waveform parameters such as the amplitude and frequency. As can be readily appreciated, the controller 40 comprises a set of potentiometers or the like. Alternatively, the controller 40 may comprise more complex electronic circuitry such as a microprocessor-based frequency and gain control circuit.
In accordance with another aspect of the invention, there is provided a means for adjusting the W096/08374 ~ 7 ~ ~ P~-l/~b95,~l886 .
FIGs. :L9, 21, 23 and 25 are graphs representing the Fourier coefficients of the waveforms of FIGs. 18, 20, 22 and 24, respectively;
FIGs. 26 and 27 are block diagrams representing sui~able waveform generators and harmonic content controllers for FIG. 1 that generate rectangular and triangular ~aveforms, respectively; and FIG. 2~3 is a block diagram representing a programmab]e rectangular waveform generator and harmonic corltent controller for FIG. 1.
Turninsr now to the drawings and re~erring first to FIG. 1, t:here is shown a continuous ink jet printing system 20 constructed in accordance with a preferred embodiment of the present invention. The lS printing sy,tem 20 comprises a pressurized supply of ink 22 con~e~cted by a suitable conduit 24 to a nozzle 26 which provides a pressurized ink stream. A
pressure source (not shown) may be utilized to pressurize the ink. In the embodiment described, the ink is of a type known as hot-melt and a heater 28 is provided to liquify the ink in a known manner. One such hot-meit ink Je~ printing system is described in US patent application number 08/307,195. Of course, other t~pes of inks may alternatively be used with the present invention, including inks that exist in a liquid phase at room temperature and-which consequently do not require a heater.
To break the ink into droplets of substantially uniform size, a transducer 30 is provided and coupled with the nozzle 26 in a manner that imparts vibration to the nozzle 26, thereby breaking the continuous flow of ink into primary drops and satellite drops. Once broken from the stream, the ink drop~s are charged by a charging electrode 32 and deflected using deflection W096l08374 ~ 7 2 ~ PCT/GB95/01886 harmonic content of the periodic non-sinusoidal waveform, designated as a harmonic content controller 42. ~y altering the harmonic content of the driving ~ waveform, the formation and relative motion of satellites is affected.
In a rectangular or triangular waveform, a change in the harmonic content appears as a change in the duty cycle of the waveform. Duty cycle is defined for a rectangular waveform as the percentage of time that the waveform is at its high amplitude over the total period of one waveform cycle (high amplitude plus low amplitude):
Duty cycle = [rh~gh / (Th.gh + T1OW)] 100%
For a triangular wave, duty cycle is defined as the time the signal takes to rise from its lowest to highest amplitude divided over the to.tal period of one waveform cycle (the rise time from lowest amplitude to highest amplitude plus fall time from highest amplitude to lowest amplitude~:
Duty cycle = [Trise / (Trise + Tfall)] 100%
~5 By way of example, FIG. 2 illustrates one cycle of a rectangular wavefor... havlng a twenty=flve percer.t duty cycle (twenty-five percent high, seventy-five perce~t low over one complete waveform period To)~
FIG. 6 illu.strates one cycle of a triangular waveform having a twenty-five percent duty cycle (twenty-five percent of the period rising, seventy-five percent falli~g).
Any repetltive waveform of period To can be represented. as a Fourier series according to the formula:
W096/08374 ~ ~ Q ~ 7 ~ ~ PCT/GB95/01886 f(t) = aO/2 + ~; [(an cos(2nnt/T0) + (bn sin(2n~t/T0)]
r To where ar. = 2/To J f(t) cos(2n~t/T0) dt for n = 0, 1, 2, ...
To and br = 2/To ~0 f(t) sin(2n~t/T0) dt for n = 1, 2, When an ~ and bn ~ 0, an alternate form of the Fourier series can be expressed as:
f(t) = aO/2 + ; cn sin(2n~t/T0 + ~n) where an = cn sin ~n bn = Cn COS ~t)n Cn = ~/ an + bn and ~n = arctan(an/bn).
The coefficients cO through cn correspond to the harmonics of the Fourier expansion, and are commonly referred to as the Fourier coefficients.
For a rectangular waveform of amplitude A, period To and duty cycle ~, the Fourier coefficients are given by:
45 aO = 4A ( ~ /2 ) W096l08374 ~ 7 ~ 5 P~-l/~b5SJ~l886 cn = (A ~ / n~)~ 1 - cos(2n~) for n = 1, 2, ...
and the pha.se angles by:
~)n = arctan [sin (2n~ cos (2n~o))]
for n = 1, 2, The FoL;rier coefficients for the twenty-five percent duty cycle rectangular waverorm of FIG. 2 for n = 0 to 40 are shown in FIG. 3. As can be seen from FIG. 3 and/or by solving the formula for cnl in this rectangular waveform every multiple of a fourth harmonic (C4, C8, Cl2 an.d so on) equals 0. This plays a significant role in acceptable satellite formation for certain types of inks and nozzles.
Similarly, for a triangular waveform, of amplitude ~, period To~ and duty cycle ~, the Fourier coefficientc are given by:
ao =
cn = [A ~ / n2~2~ )] ~1 - cos(2n~) : ~ for n = 1, 2, and the pha.se angles by:
~n = arctan [cos (2n~) - 1 / sin (2n~)]
- for n = 1, 2, The Fou.rier coefficients for the twenty-five percent duty cycle triangular waveform of FIG. 6 for n = 0 to 40 are shown in FIG. 7. As can be seen from FIG. 7 and/or by solving the formula for cn, in this triangular waveform every multiple of a fourth harmonic (C4, C8, C12 and so on) equals 0, as with the rectangular waveform.
W096/08374 2 ~ ~ 9 7 ~ ~ PCTIGB95/01886 .
The waveforms (and their corresponding Fourier coefficients) illustrated in FIGs. 10-25 will not be described in detail herein for purposes of simplicity.
However it can be readily appreciated from an inspection of the drawings and/or by solving well-known equations that multiples of the fourth harmonic are either zero or near zero for these waveforms.
Again, this plays a significant role in acceptable satellite formation for certain types and combinations of inks and nozzles.
The waveforms illustrated herein were found to successfully break up continuous jets of various types of inks using prototype nozzles, achieving a three fast satellite condition suitable for desirable image formation when the transducer was driven by a commercially available signal generator and power amplifier at a frequency of 66 kilohertz at various peak-to-peak amplitudes between 50 and 200 volts. In particular, rectangular waves were found to successfully break up hot-melt inks in a prototype nozzle. In contrast, a conventional sine wave with comparable amplitude and frequency was unable to acceptably break up the hot-melt ink jet using this same ink and nozzle combination. Indeed, acceptable breakoff did not occur even when driving the transducer with a 300 volt peak-to-peak sine wave, the maximum test voltage available, which is an amplitude that far exceeds the power driving capabilities of currently existing nozzle drive circuitry.
It should be noted that certain of the waveforms have the same Fourier coefficients as their effectively inverted counterpart waveforms. For exam~le, the rectangular waveform of FIG. 2 having a twenty-five percent duty cycle has Fourier coefficients that are equivalent to the Fourier WO 96108374 ~ 7 ~ ~ PCIIGB95/01886 coefficients of the rectangular waveform of FIG. 4 having a seventy-five percent duty cycle. However, the phase shifts ~ are different for the two duty cycles. It has been found that one of the duty cycles provides better print quality when the driving frequency is less than the frequency at which the nozzle fluid chamber resonates, while the counterpart duty cycle provides better print quality when the driving frequency is greater than this resonant frequency.
Periodic non-sinusoidal waveforms having other duty cycles can also produce desired satellite formations suitable for desirable image formation in other types of ink and nozzle combinations, and at ~ar lower drive levels than required by sine waves. For example, with certain inks and nozzles, periodic non-sinusoidal waves having du~y cycles ranging from between sixty and ninety percent high, or alternatively between forty and ten percent high are far more effective in achieving acceptable print quality than. comparable sinusoidal driving waveforms.
As an added. benefit, the electronics required to generate su.ch waveforms are less complex and more cost-effective than the electronics required to generate sin.e waves, and thus rel-iability and cost benefits are achieved with the present invention.
It can. be readily appreciated that rectangular waveforms in. general have finite rise and/or fall times and to this extent may not be exactly rectangular, but for practical purposes, a waveform such as depicted in FIG. 2 may be considered as purely rectangular because of its sufficiently fast rise and fall time relative to the ~otal time period of one complete waveform cycle.
W096/08374 ~ 1 9 9 7 ~ h PCTIGB95/01886 .~
Moreover, a waveform having a substantially rectangular shape, such as the waveforms of FIGs. 18, 20, 22 and 24 which have slower and more rounded rise and fall times, have essentially similar Fourier coefficients as pure rectangular waveforms, and have similarly beneficial nozzle drive characteristics. As shown in FIGs. 19, 21, 23 and 25, wherein the coefficients for the exemplary quasi-rectangular waveforms of FIGs. 18, 20, 22, and 24 are graphed for the first forty harmonics, every fourth coefficient is nearly zero. Accordingly, as used herein, the phrase l~rectangular waveform" is intended to include all substantially rectangular waveforms, including pure rectangular waveforms, quasi-rectangular waveforms, and trapezoidal waveforms such as those depicted in FIGs. 10, 12, 14 and 16.
Analogous to the rectangular waveform, quasi-triangular waveforms have essentially similar Fourier coefficients as pure triangular waveforms, and have similarly beneficial nozzle driving characteristics.
Thus, the phrase "triangular waveform~ is intended to include all substantially triangular waveforms, including pure triangular waveforms and quasi-triangular waveforms.
Turning now to an explanation of the operation of the invention, the tailoring of the h~rmonl C content of the periodic non-sinusoidal waveform for a particular ink and nozzle combination is ordinarily performed by carefully observing the actual satellite formation and/or studying the placement accuracy of the resultant dots forming an image on a target surface. To initialize the printing system 20 of FIG.
1, the duty cycle of the periodic non-sinusoidal waveform, and if necessary the amplitude thereof, is varied until the desired satellite condition suitable -W096/08374 ~ ~ ~ 9 7 2 ~ PCTIGB95/01886 .
for desirable image formation is achieved. Once achieved, the waveform is then established for a given ink and nozzle combination.
By way of example, as shown in FIG. 26 wherein the periodic non-sinusoidal waveform generator 36 comprises a rectangular waveform generator, the harmonic content of the waveform is varied by adjusting the resistance settings of one or more variahle resistors 56, 58 (potentiometers) in the RC
circuit 60. As can be appreciated, one type of waveform generator that is controllable to generate a rectangula:r wave of an appropriate frequency and duty cycle acco:rding to the values of resistors and a capacitor 6:2 comprises an astable multivibrator.
Altenlc~tively, as shown in FIG. 27, the periodic non-sinusoidal waveform generator 36 may comprise a triangular wave~orm generator. With this particular circuit, operational amplifiers 64 and 66 are employed to generate the triangular waveform. Fixed resistors 68-71 and capacitor 72 are selected in a known manner.
The duty c~c:le of the waveform is adjusted by ~djusting t:he harmonic content controller 42, comprising a variable resistor 74 connected to vary the voltage on the non-inverting input of the operational amplifier 66.
Once acljusted, the harmonic content for the chosen waveform is established in the settings of the variable resistors 56, 58 (rectangular waveform generator) cr in the setting of the variable resistor 74 (triangular waveform generator). In general, if a voltage controlled oscillator (not shown) serves as the waveform generator, an input voltage, which may originate from any suitable source, is provided to vary the harmonic content.
W096108374 ~ ~ ~ 9 7 2 ~ PCTIGB95101886 .
Regardless of how the harmonic content of the waveform is adjusted, the adjustment takes place in conjunction with an analysis of a resultant printed image and/or by viewing the actual drop formations, (for example by employing a microscope and a strobe light). According to the invention, the harmonic content is varied until the desired satellite condition and resultant desirable image formation are regularly achieved.
By way of example, to select and adjust a suitable non-sinusoidal waveform for a given ink and nozzle combination when a conventional sinusoidal waveform is unacceptable, a rectangular waveform having a twenty-five percent duty cycle is initially employed as the driving waveform. The quality of the printed image or the actual formation of the drops is then analyzed for various driving amplitudes of the rectangular waveform. If the results obtained at the twenty-five percent duty cycle are less than ideal, the rectangular waveform may be effectively inverted to have a seventy-five percent duty cycle in order to determine if the arop formation or the resultant image quality is consequently enhanced as analyzed at various driving amplitudes.
If improvements to the image quality beyond those provided by the rectangular waveform are still likely or necessary, a triangular waveform having a twenty-five percent duty cycle may be subsequently selected and utilized as the driving waveform, and the results again analyzed at various driving amplitudes. As with the rectangular waveform, this triangular waveform may be inverted to have a seventy-five percent duty cycle in order to determine the effect on the quality of the printed image. Other waveforms may be selectively applied to the transducer in a similar manner, W096/08374 ~ 7 ~ ~ r~ 95/01886 .
although typically ei~her a rectangular or triangular waveform provides acceptable results.
Finally, once an appropriate waveform is established, the harmonics, or symmetries, of the waveform may be adjusted as desired in order to fine-tune the drop formation as evidenced by the quality of the printed image. As described above, a change in the harmonic content of a waveform alters the duty cycle thereof. While a twenty-five or a seventy-five percent duty cycle typically provides the desired results, e;~amples of duty cycles ranging from ten to thirty-five (or ninety to sixty-five) percent have produced prl-ferable results with other ink and nozzle combinations. If a range of duty cycles is determined to provide ~cceptable image formation, the duty cycle may be set ,ubstantially in the middle of the range.
Since :Eormulations of inks may vary over time, and since one type of printer may be used with several different t:~pes of inks and/or nozzles, an alternate embodiment of the invention shown in FIG. 28 includes means for e3ectrically varying the waveform. This enabies the driving waveform to be controlled by co~mAn~s frc)m a printer controller, a personal computer, or the like.
In FIG. 28, a microprocessor 80 is connected- to a storage device 82 which may be a RAM, ROM, a computer disk or the like. The storage device 82 has previously c;tored therein the optimal waveform parameters for a number of inks and/or nozzles. Based on the type of ink and/or nozzle, which are input (along with any other variables that are deemed significant) as values into the microprocessor 80 via input means 84, the microprocessor 80 accesses the storage device 82 to o~tain the corresponding optimal waveform parameters to adjust the waveform generator W096/0837~ ~ 1 9 9 ~ 2 ~ r~ll~b5510l886 36. For example, the microprocessor 80 may be arranged to reference a database in the storage device 82 to obtain the optimal waveform duty cycle, amplitude and frequency for a given ink and nozzle combination. Of course, the microprocessor 80 may alternatively receive waveform information directly from the input device 84.
The microprocessor 80 may be present in an external device such as a personal computer, however it can be appreciated that many ink jet printing systems already are equipped with a printer controller for controlling other aspects of the printing operation. Thus, such a printer controller can be modified to perform the functions of the microprocessor 80 described herein.
As shown in FIG. 28, the programmable variable resistors 90, 92 are electrically adjustable by the computer signals, such as in a programmable resistor network. These resistors comprise an RC circuit 94 that controls the operation of the astable multivibrator as in the previously described circuit of E'IG. 2~. Alternatively, a latched digital-to-analog voltage converter (not shown) coupled to a voltage controlled resistor may act as a programmable 25- resistor.
Output signals from the microprocessor 80 set the values of the resistors 90, 92, thus determ; n; ng the corresponding duty cycle and/or frequency. Similar output signals are also used to set the gain of a variable gain amplifier 98. Once the waveform characteristics are set, the system may be arranged such that the microprocessor-based device can subsequently be disconnected from the printing apparatus, such as by unplugging a portable personal computer. In this manner, a consistent and rapid W096l08374 ~ ~hi ~ 9 7 2 ~ P~ 5S,~l886 -- 19 ._ change to the waveform may be accomplished as inks or nozzles are varied.
Moreover, it is feasible to remotely set the parameters of the driving waveform to match given ink and nozzle combinations. For example, the parameters may be set via telephone, modem, transmission cable, or other transmission means from a central or remote location. Alternatively, each time a new ink is developed, the ink may be shipped with a set of waveform parameters stored on a floppy disk or the like that may be used by the customer to tailor the system to the new type of ink. Indeed, other methods of supplying in~ormation to adjust the duty cycle or harmonics of the waveform are feasible. For example, the input me,~ns 84 may comprise DIP switches operatively ,-onnected to the microprocessor 80 such that the settings thereof corresponding to selected parameters for known ink and/or nozzle configurations.
Of course, DIP switches may alternatively be arranged to directly vary the resistance settings of resistors and thus adjust the waYeform duty cycle or harmonics withou~ a microprocessor.
While F:[G. 28 describes a programmable rectangular waveform with a corresponding rectangular waveform generator, it can be readily appreciated that other waveforms may be set by programmably controlling a similar waveform generator and/or harmonic content controller. For example, the h~rmoni C content of a triangular wclveform may be electrically controlled by utilizing a programmable resistor as the variable resistor 74 in FIG. 27, and similarly connecting it for adjustment by the output of a microprocessor.
Moreover, a microprocessor may further be employed to select the t:~pe of periodic non-sinusoidal driving W096l08374 ~ 7 ~ ~ P~-ll~h5J~l886 waveform from a waveform generator capable of outputting multiple types of waveforms (not shown).
Finally, although not necessary to the invention, by utilizing a camera in a computerized vision system to compare the actual drop formation or to analyze printed images against changes to the duty cycle and other parameters, it is further feasible to automate the adjustment process in a closed-loop control system. This may be performed during installation or in real-time during actual printing operations.
As can be seen from the foregoing detailed description, there is provided an apparatus and method for producing drops of ink in a continuous ink jet printing system that achieves desirable satellite formation thereby resulting in desirable printing conditions. The desired satellite formation is achieved for an increased variety of inks and nozzle types, including hot-melt inks, and with a reduced amount of power consumption. The desired satellite conditions are achieved with simplified electrical driving circuitry that provides improved cost savings and reliability, and without increasing the amplitude of the driving signal above customary excitation levels.
Claims (29)
1. An apparatus for perturbing a pressurized ink in a continuous ink jet printer (20) into a stream of primary ink drops and satellite ink drops with a desired quantity of fast satellite ink drops present in said stream at any given time, the apparatus comprising, a transducer (30) for imparting mechanical vibration to an ink discharge nozzle (26) of the ink jet printer, which nozzle is in fluid communication with a pressurized supply of ink (22), a periodic non-sinusoidal waveform signal generator (36) for driving the transducer with a periodic non-sinusoidal waveform, and a harmonic controller (42) arranged to adjust the harmonic content of the periodic non-sinusoidal waveform to obtain said desired quantity of fast satellite ink drops.
2. An apparatus as claimed in claim 1, wherein said harmonic controller (42) determines which harmonics are present in said periodic non-sinusoidal waveform.
3. An apparatus as claimed in claim 1 or 2, wherein the harmonic controller (42) includes means (56, 58, 60) for adjusting the harmonic content of the waveform such that the fourth harmonic and multiples thereof of said waveform are zero or near zero.
4. An apparatus as claimed in claim 1 or 2 or 3, wherein the periodic non-sinusoidal waveform is a rectangular waveform and wherein the waveform signal generator (36) includes a rectangular waveform generator.
5. An apparatus as claimed in claim 4, wherein the rectangular waveform generator comprises an astable multivibrator, and the harmonic controller includes a variable resistor (56, 58).
6. An apparatus as claimed in claim 1 or 2 or 3, wherein the periodic non-sinusoidal waveform is a triangular waveform (36) and the signal generating means includes a triangular waveform generator.
7. An apparatus as claimed in claim 6, wherein the harmonic controller includes a variable resistor (56, 58, 74).
8. An apparatus as claimed in claim 1, further comprising means for adjusting the amplitude of the waveform.
9. An apparatus as claimed in claim 1, further comprising means for adjusting the frequency of the waveform.
10. An apparatus as claimed in any one of the preceding claims, wherein the ink comprises a hot-melt ink that is in a solid phase at ambient room temperatures and at a liquid phase at increased temperatures, and further comprising a heater (28) coupled to the supply of ink (22) for liquefying the ink.
11. An apparatus as claimed in any one of the preceding claims, further comprising a microprocessor (80) which provides electrical signals to vary the duty cycle of the periodic non-sinusoidal waveform.
12. An apparatus as claimed in claim 11, further comprising a data storage device (82) operatively connected to the microprocessor (80), wherein the microprocessor (80) references the data storage device to provide electrical signals to vary the duty cycle of the periodic non-sinusoidal waveform.
13. An apparatus as claimed in any one of the proceeding claims, further comprising DIP switches for varying the duty cycle of the periodic non-sinusoidal waveform.
14. An apparatus as claimed in any one of the preceding claims, wherein said waveform generates a maximum of three fast satellite ink drops.
15. A method of producing, in a continuous ink jet printing system, a stream of ink drops having a desired number of fast satellite ink drops present in said stream at any given time, the method comprising the steps of:
pressurizing a fluid for continuous flow to an ink discharge nozzle (26);
generating a periodic non-sinusoidal waveform at a fixed frequency;
applying the waveform to a transducer (30) coupled to the nozzle (26) such that the ink flow is perturbed and discharged from the nozzle (26) as primary ink drops and satellite ink drops associated therewith; and adjusting the harmonic content of the waveform to obtain said desired number of fast satellite drops in the ink stream.
pressurizing a fluid for continuous flow to an ink discharge nozzle (26);
generating a periodic non-sinusoidal waveform at a fixed frequency;
applying the waveform to a transducer (30) coupled to the nozzle (26) such that the ink flow is perturbed and discharged from the nozzle (26) as primary ink drops and satellite ink drops associated therewith; and adjusting the harmonic content of the waveform to obtain said desired number of fast satellite drops in the ink stream.
16. A method as claimed in claim 15, wherein said step of adjusting the harmonic content determines which harmonics are present in said periodic non-sinusoidal waveform.
17. A method as claimed in claim 15 or 16, further comprising the step of adjusting the amplitude of the waveform.
18. A method as claimed in claim 15 or 16, further comprising the step of varying the frequency of the waveform.
19. A method as claimed in any one of claims 15 to 18, wherein the step of adjusting the harmonic content includes the step of varying the resistance of a variable resistor (56, 58, 74).
20. A method as claimed in any one of claims 15 to 19, wherein the desired number of fast satellite drops is a maximum of three.
21. A method as claimed in claim 20, further comprising the step of inspecting the drop formation to determine when no more than three fast satellites are present in the ink stream.
22. A method as claimed in any one of claims 15 to 21, wherein the step of generating a periodic non-sinusoidal waveform comprises the step of generating a rectangular waveform.
23. A method as claimed in claim 22, wherein the step of adjusting the harmonic content of the rectangular waveform comprises the step of setting the duty cycle between sixty and ninety percent high.
24. A method as claimed in claim 22, wherein the step of adjusting the harmonic content of the rectangular. waveform comprises the step of setting the duty cycle between forty and ten percent high.
25. A method as claimed in any one of claims 15 to 21, wherein the step of generating a periodic non-sinusoidal waveform comprises the step of generating a triangular waveform.
26. A method as claimed in claim 25, wherein the step of adjusting the harmonic content of the triangular waveform comprises the step of setting the duty cycle between sixty and ninety percent high.
27. A method as claimed in claim 25, wherein the step of adjusting the harmonic content of the triangular waveform comprises the step of setting the duty cycle between forty and ten percent high.
28. A method as claimed in any one of claims 15 to 27, wherein the ink is a hot-melt ink that is in a solid phase at ambient room temperatures and in a liquid phase at increased temperatures, and further comprising the step of heating the ink to convert it to its liquid phase.
29. A method as claimed in any one of claims is to 28, wherein the harmonic content of the periodic non-sinusoidal waveform is adjusted such that the fourth harmonic and multiples thereof of said waveform are zero or near zero.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/307,193 | 1994-09-16 | ||
| US08/307,193 US5646663A (en) | 1994-09-16 | 1994-09-16 | Method and apparatus for continuous ink jet printing with a non-sinusoidal driving waveform |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2199725A1 true CA2199725A1 (en) | 1996-03-21 |
Family
ID=23188657
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002199725A Abandoned CA2199725A1 (en) | 1994-09-16 | 1995-08-09 | Method and apparatus for continuous ink jet printing |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5646663A (en) |
| AU (1) | AU3186895A (en) |
| CA (1) | CA2199725A1 (en) |
| GB (1) | GB2307451B (en) |
| WO (1) | WO1996008374A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH09262970A (en) * | 1996-03-28 | 1997-10-07 | Canon Inc | Ink-jet recording apparatus |
| US6491737B2 (en) * | 2000-05-22 | 2002-12-10 | The Regents Of The University Of California | High-speed fabrication of highly uniform ultra-small metallic microspheres |
| US6520402B2 (en) * | 2000-05-22 | 2003-02-18 | The Regents Of The University Of California | High-speed direct writing with metallic microspheres |
| US6883904B2 (en) * | 2002-04-24 | 2005-04-26 | Eastman Kodak Company | Apparatus and method for maintaining constant drop volumes in a continuous stream ink jet printer |
| NL1021319C2 (en) * | 2002-08-22 | 2004-02-24 | Tno | Device and method for printing a viscous substance. |
| US20050243144A1 (en) * | 2004-04-09 | 2005-11-03 | Synergy Innovations, Inc. | System and method of manufacturing mono-sized-disbursed spherical particles |
| US20070291058A1 (en) * | 2006-06-20 | 2007-12-20 | Fagerquist Randy L | Continuous ink jet printing with satellite droplets |
| GB2554924A (en) * | 2016-10-14 | 2018-04-18 | Domino Uk Ltd | Improvements in or relating to continuous inkjet printers |
| CN107933090B (en) * | 2017-12-20 | 2023-05-26 | 北京赛腾标识系统股份公司 | Device and method for setting nozzle drive and ink jet system |
Family Cites Families (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE756224A (en) * | 1969-09-23 | 1971-03-01 | Teletype Corp | ELECTROSTATIC INK AND PRINTING APPARATUS |
| US3683396A (en) * | 1970-08-05 | 1972-08-08 | Dick Co Ab | Method and apparatus for control of ink drop formation |
| US4056741A (en) * | 1973-04-18 | 1977-11-01 | Airco, Inc. | Audible signal generating apparatus having selectively controlled audible output |
| US3935783A (en) * | 1974-07-08 | 1976-02-03 | The Wurlitzer Company | Electronic piano circuit |
| US3972474A (en) * | 1974-11-01 | 1976-08-03 | A. B. Dick Company | Miniature ink jet nozzle |
| US3928855A (en) * | 1974-12-18 | 1975-12-23 | Ibm | Method and apparatus for controlling satellites in an ink jet printing system |
| US3979756A (en) * | 1974-12-18 | 1976-09-07 | International Business Machines Corporation | Method and apparatus for merging satellites in an ink jet printing system |
| GB1543155A (en) * | 1975-05-02 | 1979-03-28 | Nat Res Dev | Transponders |
| GB1544493A (en) * | 1975-09-05 | 1979-04-19 | Ibm | Apparatus for liquid droplet generation |
| JPS54137320A (en) * | 1978-04-18 | 1979-10-25 | Matsushita Electric Ind Co Ltd | Ultrasonic liquid atomizer |
| JPS56139973A (en) * | 1980-04-01 | 1981-10-31 | Sharp Corp | Ink jet recording |
| JPS5738159A (en) * | 1980-08-20 | 1982-03-02 | Ricoh Co Ltd | Exciting system of printing head in ink jet printing device |
| JPS5759766A (en) * | 1980-09-27 | 1982-04-10 | Sharp Corp | Driving circuit for ink jet head |
| JPS5766974A (en) * | 1980-10-10 | 1982-04-23 | Ricoh Co Ltd | Fluid spray method |
| JPS585272A (en) * | 1981-07-02 | 1983-01-12 | Seiko Epson Corp | Ink jet printer |
| US4897665A (en) * | 1986-10-09 | 1990-01-30 | Canon Kabushiki Kaisha | Method of driving an ink jet recording head |
| US5146236A (en) * | 1989-12-14 | 1992-09-08 | Ricoh Company, Ltd. | Ink jet record apparatus |
| US5206944A (en) * | 1990-06-07 | 1993-04-27 | The United States Of America As Represented By The Secretary Of The Air Force | High speed analog to digital converter board for an IBM PC/AT |
| JP2663077B2 (en) * | 1991-03-25 | 1997-10-15 | テクトロニクス・インコーポレイテッド | Ink supply device |
-
1994
- 1994-09-16 US US08/307,193 patent/US5646663A/en not_active Expired - Lifetime
-
1995
- 1995-08-09 CA CA002199725A patent/CA2199725A1/en not_active Abandoned
- 1995-08-09 WO PCT/GB1995/001886 patent/WO1996008374A1/en active Application Filing
- 1995-08-09 GB GB9704406A patent/GB2307451B/en not_active Expired - Fee Related
- 1995-08-09 AU AU31868/95A patent/AU3186895A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| GB2307451B (en) | 1997-11-12 |
| GB2307451A (en) | 1997-05-28 |
| US5646663A (en) | 1997-07-08 |
| AU3186895A (en) | 1996-03-29 |
| GB9704406D0 (en) | 1997-04-23 |
| WO1996008374A9 (en) | 2008-03-06 |
| WO1996008374A1 (en) | 1996-03-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |