DE3513442A1 - Method for the selective, multicycle resonant operation, serving to control the dot size, of an ink jet printing device - Google Patents

Description

PROCESS FOR THE SELECTIVE, MULTICYCLE, RESONANT OPERATION OF AN INK JET DEVICE, USING THE CONTROL OF THE DOT SIZE

The invention relates to ink jet devices, in particular a method of operating an inkjet device in FIG a resonance mode to enable high resolution printing.

The implementation of practical inkjet devices and devices, which are used to generate a single droplet of ink on demand is relatively new in the art. In known "drop-on-demand" inkjet devices, the volume of each is Ink droplets typically from the geometry of the inkjet device, the type of ink used and the size of one in the ink chamber for ejecting an ink droplet overpressure developed from an associated opening. The effective diameter and structure of the opening, the volume and structure of the ink chamber associated with the opening, the transducer construction and the method of coupling of the transducer with the ink chamber are other factors that affect the volume of the orifice ejected, determine individual ink droplets. With every such Ink jet apparatus is required for high resolution imaging to be relatively small in size Bulky ink droplets ejected from the device will. Typically, such ink droplets with a small size by reducing the diameter of the orifices of the ink jet apparatus. However is it is difficult to make jet orifices with a small diameter, and the operation of an ink jet apparatus provided with such small diameter openings

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is equipped with orifice clogging problems (due to dried-up ink, contamination in the ink, paper dust, etc.), by adverse effects as a result a high ratio of surface tension forces to inertia forces, by a poor result etc. adversely affected.

Many attempts have been made to improve the print density as well as the print resolution or rasterization in an ink jet printer to control. For example, in US Pat. No. 3,977,007, shades of gray are reproduced in an ink jet printer by using is the number of ink droplets deposited at a predetermined point in a dot matrix, selectively changes by one. In US Pat. No. 4,018,383 there is disclosed a method of eliminating satellite droplets in one continuous ink jet system, the method further selectively eliminates or traps the ink droplets when printing to improve density to control the droplet streams. In a continuous ink jet apparatus disclosed in U.S. Patent No. 4,047,183 a laser is used to control the formation and shape of the ink droplets forming the stream of ink droplets, around the frequency components of a continuous ink jet stream to control the characteristics of a die Device controlling fault control signal.

In U.S. Patent 4,281,333, the volume or size of the "drop-on-demand" ink jet ejected ink droplets simply by varying the amplitude or power envelope of the control signal waveform used to operate the ink jet apparatus. In U.S. Patent 4,337,470 Dot size generated by an inkjet printer by varying the frequency of the vibration of a vibrator

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controls that vibrate the ink in the ink head to eject ink droplets. These To control the print density, droplets are electrostatically directed toward or away from a receiving medium. U.S. Patent 4,393,384 teaches a method of operating an ink jet device for the purpose of controlling volume and the speed of ink droplets, which are the absolute Control of print quality can be generated. This control is accomplished by being controllable and successively first reducing the volume of the associated ink chamber, then increasing the volume and then immediately that Volume decreased by an amount less than the first volume decrease and then the volume the ink chamber for ejecting the ink droplet is enlarged.

U.S. Patent 4,493,388 discloses a method of operating a Ink jet device disclosed, in which the oscillo ram of the signal fed to the transducer has an interruption period of time which is longer than a predetermined period of time is followed by the time segments of three consecutive electrical signals, at least the The amplitude or width of the second of the three electrical signals relative to the other two is increased by to prevent a decrease in the radius of the second ink droplet ejected after the interruption portion.

In none of the patents briefly described above it is disclosed that, in order to operate an ink jet device, certain resonances of that device are excited in order to allow control over the size and volume of the ink droplets ejected.

In accordance with the invention there is provided a method of operating an inkjet device proposed to control the dot size printed on a recording medium. This

Procedure has the following procedural steps: one operates a converter device to synchronously either one or one Combination of the fluidic and mechanical resonance frequencies of the inkjet device to generate a dominant one Resonance frequency in the ink chamber and the adjunct Excite ink; you can either leave a single cycle or generate a subharmonic cycle of the dominant resonant frequency to essentially predictably volume of an ink droplet ejected from an orifice of the device by the resulting printing disturbance generated in the associated ink chamber; the two steps mentioned above are repeated successively synchronously with the dominant resonance frequency as often as desired, in order to generate a large number of ink droplets within one Period of time to generate the merging of the droplets during flight or in the air or on the recording medium enables.

The invention is explained in more detail below with reference to the drawing. It shows:

Fig. 1 shows an ink jet device in section

opinion ;

Fig. 2 shows a detail of the ink jet device

according to FIG. 1 in an enlarged view;

Fig. 3 is a projection view of the ink

blasting device in expanded

Arrangement, the ink jet apparatus being those shown in Figs Embodiments includes;

Figure 4 shows the waveform for electrical pulses

of a preferred embodiment;

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Fig. 5 is a sinusoidal waveform for elek

tric signals of another embodiment of the invention;

Fig. 6 is a half sine wave curve for a third one

Embodiment of the invention;

Fig. 7 is a quarter wave sine curve for elek

tric pulses of a fourth embodiment of the invention;

Figure 8 is a sawtooth waveform for a fifth

Embodiment of the invention;

Fig. 9 is a triangular waveform for elek

tric pulses of a sixth embodiment of the invention;

Fig. 10 Printouts (A) to (F), which are taken from the shown

th ink jet device under use

application of the process according to the invention were and

11 printouts (A) to (C) showing the

Typical print density controls illustrated by the use of the

Inkjet device using of the method according to the invention can be achieved and

Fig. 12 using the inventive method

driving generated droplets during the

In flight

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In Figs. 1 to 3, an ink jet apparatus is shown in FIG U.S. Patent 4,459,601, which is incorporated herein by reference. The present invention was achieved during the development of improved methods of operating the aforementioned ink jet apparatus made of a printing process with high resolution or high rasterization. The various embodiments of the invention, which are described below, however, with a variety of inkjet devices (especially "drop-on-demand" inkjet devices) Find application. The ink jet apparatus explained below is therefore to explain the invention provided and does not imply any limitation. As a result, the following paragraphs only describe the basic mechanical features as well as the operation of this device are discussed.

The ink jet apparatus illustrated in Figures 1-3 includes a chamber 200 having an orifice 202 for ejection of ink droplets in response to excitation of a transducer, with a series of such for each jet Radiation (see Fig. 3) a transducer 204 is provided. The transducer 204 expands along its axis of extension and contracts along its axis of extension (in the directions shown by the arrows in Fig. 2), where this movement is coupled to the chamber 200 via a coupling device 206. The coupling device 206 comprises a foot 207, a viscoelastic material 208 adjoining the foot 207 and a membrane 210 which is inserted into the in the position shown in Figs. 1 and 2 is biased.

Ink flows through restricted inlet means in the form of a restricted orifice 214 from an unpressurized one Container 212 in the chamber 200. The limiting! Ο opening 214 is through a flow restriction plate

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216 provided opening is formed (see FIG. 3). As can be seen from FIG. 2, the has in a chamber plate 220

222 formed container 212 has a beveled edge which leads into the opening 214. As can be seen from Fig. 3, is the container 212 is equipped with an inlet pipe 223 and an outlet pipe 225. The container 212 is due to the membrane 210 compliant. This membrane 210 stands over a large opening provided in the flow restriction plate 216 227, which adjoins a recess 229 provided in the plate 226, in communication with the ink.

One end of each transducer 204 is provided by the cooperation of the foot 207 with one in a plate 226 Hole 224 out. As shown, the feet 207 of the transducers 204 are slidably received in the holes 224. The others Ends of transducers 204 are in a block 228 by means of a resilient or elastic provided in slots 232 Materials 230 resiliently attached to provide support for the other ends of transducers 204. Likewise is a electrical contact with the transducers 204 made in a resilient manner by means of a compliant printed circuit board 234, which is coupled to an electrode 260 of the transducers by any suitable means such as solder. On the Printed circuit board 234, printed circuit boards 238 are provided. {_ The plate 226 (see Figures 1 and 3) faces at the base

237
of a slot has holes 224 which, as mentioned above,

226 take up the feet 207 of the transducers 204. The plate is also equipped with a receptacle 239 for a heating pad 240. This intermediate heating layer 240 comprises a heating element 242 with spirals 244, a hold-down plate 246, one of the Spring 248 assigned to plate 246 and a support plate 250 arranged directly below heating element 242. A slot 253 for receiving a thermistor 252 is also provided. The thermistor 252 is used to control the

Monitor the temperature of the heating element 242. The entire heating pad 240 is covered by a cover plate 254 in FIG in the plate 226 provided receptacle 239 held.

As can be seen from Fig. 3, the various are described Components of the inkjet device by means of screws 256 extending upwardly through openings 257, and held together by screws 258 extending downwardly through openings 259, the Screws 258 hold circuit board 234 in place on plate 228. The dashed lines in Fig. show the connections 263 to the printed circuit on the circuit board 234. The connections 263 couple Controller 261 with the ink jet device to control its operation.

In normal operation of the ink jet apparatus, this is

261

The controller is programmed to have it connected to the printed circuit board at an appropriate time the transducer 204 supplies a voltage to a particular one or to some of the heated electrodes 260. The supplied Voltage causes an electric field that is generated perpendicular to the extension axis of the selected transducers 204, thereby causing the transducers 204 to contract along their elongated axis. If there is a special When transducer 204 contracts after excitation, that part of the transducer 204 located under foot 207 moves Diaphragm 210 toward the contracting transducer 204, effectively increasing the volume of the attached chamber 200 increases. As the volume of the particular chamber 200 expands in this way, a negative pressure is initially established generated in the chamber, whereby the ink therein tends to move away from the opening 202 during at the same time, ink can flow from the container 212 through the associated, restricted opening 214 into the chamber 200. The selected

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The amount of ink flowing into the chamber 200 during the refill is greater than the amount that flows back through the restricted opening 214 during the firing of the ink. The time between refilling and firing is during the blasting operation not changed, thus providing a "refill before launch" cycle. The control unit is like that programmed that shortly thereafter the voltage or the control signal of a certain or some of the selected Transducer 204 is removed, whereby the transducer or transducers 204 expand very rapidly along their elongated axes and via the viscoelastic material 208 and the feet 207 against the part of the membrane 210 lying below them bump. In this way, there is a rapid contraction or reduction in the volume of the associated chamber or chambers 200 scored. This rapid reduction in volume of the affiliated Chambers 200 generates a pressure pulse or an overpressure disturbance in the chamber 200, whereby the associated Orifices 202 an ink droplet is ejected. It should be noted that with such excitation one certain transducer 204 both reduces its length and increases its thickness. However, the magnification is its thickness for the illustrated ink jet device insofar as the changes in length of the transducer control the use of each ink jet in the ink jet array. It should also be noted that with the present Technology, i.e. by energizing the transducer for the purpose of contraction along its elongated axes, accelerated aging of the transducers is prevented. In extreme cases, depolarization is also avoided.

As mentioned above, it is known that the droplet size produced by an impulse inkjet printer is closely tied to the size of the opening of the associated ink jet device and that generally only small

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Variations in droplet size, e.g. Variation of the control signal amplitude or control signal waveform, can be generated. However, on the other hand, for high quality halftone printing, the droplet size must be in be controllable over a wide range. In addition, for certain inks that do not spread far on the paper, such as wax-based inks, require larger than the ink droplets already obtainable by current methods of operating inkjet devices Achievement of the desired pressure point diameter can be generated.

According to the invention, the operation described above has been carried out Ink jet device recognized that by synchronously exciting one or a combination of the fluidic and mechanical Resonance frequencies of the inkjet device for generating a dominant resonance frequency disturbance in the corresponding, associated chamber and the ink and by causing a single cycle or a subharmonic cycle to be generated the dominant resonance frequency is the volume of the ejected Can control ink droplets. According to the invention it was further found that by repeating this Operation in an iterative or successive manner, with each subsequent cycle synchronous with the dominant resonance frequency of the ink jet apparatus, a plurality of ink droplets are ejected within a period of time which allows the droplets to merge as they fly through the air or on the recording medium can. This allows substantial control over what results on the recording medium Dot size relative to the dot size achieved by a single ink droplet. The resulting point size is depending on how often the method according to the invention for operating the device within a given period of time is repeated. Figure 12 shows nine droplets through 309 in flight to create a point on one

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Recording medium using the inventive Procedure.

In accordance with the invention, it was also recognized that, for the illustrative inkjet apparatus of this example, the Helmholtz resonance frequency is the dominant resonance frequency of the subject inkjet device. Other inkjet devices, which can also be operated using the method according to the invention can be used as dominant resonance frequency a different resonance frequency than have the Helmholtz resonance frequency. For the purpose of further description and clarification of the invention A method of operating an inkjet device is disclosed assumed that the Helmholtz resonance frequency is the dominant Is resonance frequency. However, such an assumption means no limitation as to the scope and use of the invention.

The present method represents a multi-pulse method for operating an inkjet device, which is the dominant resonance frequency of the inkjet device Excitation of ink droplets with controllable volume Pulsation of the transducer 204 (in this example) with a repetition frequency of the dominant resonance frequency is used, and using a single pulse or a plurality of pulses depending on the required Point size. Where the Helmholtz frequency is the dominant frequency, this frequency results from the interaction of the Compliance of the ink chamber 200 (in this example) and the ink or fluid inertia, expressed by the formula

_F. ^H

where C is the ink chamber compliance, L is the

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For example, inertia and 1 / L equals 1 / L opening 202 + 1 / L limited opening 214 ~ | is.

By laboratory testing and analysis it was found that the illustrated ink jet device has a Helmholtz frequency of about 30 kHz. As can be seen from FIG. 4, essentially rectangular or square wave pulses were used to operate the illustrated ink jet device in accordance with the method according to the invention. The pulse characteristics of this particular waveform, found to provide substantial control over the size of the ink droplet ejected, were determined for the various time periods shown as follows: T. = 1.0 microsecond pulse rise time, T "= 13.0 microseconds Pulse duration, T _Q = 1.0 microsecond pulse fall time and T. = = 15.0 microsecond dead time, thereby providing a pulse repetition rate close to the 30 kHz Helmholtz resonance frequency of the illustrated device. It should be noted that, in this example, the dead time T. It was found that by applying two pulses as shown in FIG the two pulses were supplied. It has also been found that the droplet volume appears to increase linearly in direct correspondence with the number of such pulses applied to transducer 204. Further, by applying two or more pulses of suitable amplitude having the waveforms shown in FIG. 4 and the characteristics described above, it was found that this multiple

pulse process in a merging of the ink droplets in the Flight or when hitting the recording medium, resulting in an enlarged spot size on the recording medium compared to using a single pulse to create such a point on the medium.

It should be noted that the waveform of Fig. 4 and the waveforms of Figs. 5 through 9 described below are below Laboratory test conditions can be generated with a commercially available wave generator. With a practical device For example, the controller 261 must be specially designed or programmed to the desired Waveforms and the number required to create a particular point size on the recording medium To generate pulses.

Tests carried out have shown that the illustrated device, which, as mentioned above, has a Helmholtz frequency of 30 kHz, using any combination of pulse duration T and dead time T ranging between 8.0 microseconds and 16.0 microseconds can work, with the rise time T and the fall time T _{3 being set} to one microsecond, for example. The lower limit of this range is determined by the response time of the transducer or transducers 204, while the upper limit of this range is determined by the design of the inkjet device, which can effectively control or operate the device at or near its Helmholtz frequency limited. The complexity of the electronic construction of the control unit 261 is decreased when the waveform of the control pulses as shown in Fig. 4 substantially corresponds to that shown, with the total pulse duration (T. + T + T _Q) and the dead time T is substantially

are the same. Optimal operation of the illustrated ink jet apparatus was also obtained when all of the periodicity of the pulse train (T + T + T + T) essentially

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equal to _s the reciprocal of the dominant resonance frequency, in this example 1 / F ₁ . is made. It was also determined that

that due to the limitations of the response time of the transducer 204 coupled to the relatively high frequency of the dominant resonant frequency mode of the control and operation of the ink jet apparatus using the multi-pulse method of the present invention, many other different waveforms other than those of Figure 4; but have the same or similar periodicity, can be used. Other waveforms that have been found to provide satisfactory control over spot size using the method of the present invention include, for example, a sine waveform, a half sine waveform, a quarter sine waveform, a sawtooth waveform, and a triangular waveform as shown in Figs. 5 to 9 is shown in this order. When using such alternative waveforms for operating the device shown, the 30 kHz Helmholtz frequency of the device was determined as the dominant frequency, as mentioned above. Accordingly, for the sinusoidal waveform of Fig. 5, 1/2 T _{5 can be} made substantially equal to 30 kHz. Similarly, for the sine half-wave curve of FIG. 6, the pulse duration T_ and the dead time T _{7 should be} approximately equal to 15 microseconds. Similar remarks apply to the pulse durations T ₀ , T._. or T. “the

ο TU \ d. 7 to 9 and the dead times T _Q , T and T ₁₃ of FIGS. 7 to 9.

When testing various pulse or waveforms, it was found that that uses the rectangular or square waveform with a much lower voltage pulse amplitude than any other waveforms tested,

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such as those of Figures 5 through 9, and likely due to the faster rise and fall times. Indeed, it was found that the quarter-wave sine curve of Fig. 7 requires pulses with 20% greater amplitude than the substantially square or rectangular Pulses of Figure 4 to be obtained from the illustrated ink jet device to get an equivalent printing process. As mentioned above, in general, the waveform of Figure 4 relative to the other waveforms of Figures 5-9 relative to still other different waveforms much easier to provide electronically.

When testing the method according to the invention and during operation The ink jet device shown was also discovered that, due to the dominance of the Helmholtz frequency in the tested Device the multi-pulse method according to the invention can also be provided by changing the periodicity of the control pulses on subharmonic cycles of the Helmholtz frequency founds. It is believed that the same result can be obtained for the dominant resonance frequency of some other inkjet devices would have been obtained if tested using the method of the invention. Using the example of a 30 kHz Helmholtz main frequency however, for a particular inkjet device, a subharmonic frequency would be in control pulse widths result, which would be very large, what an undesirable reduction in the usable printing frequency of the special Device or inkjet device. Accordingly, the inventors tested an ink jet device, which is similar to the device shown, but with a smaller ink chamber 200 (relatively low compliance) has to a Helmholtz resonance frequency of about 100 kHz to be provided. With the help of the method according to the invention

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could this device with a satisfactory pressure operated using multiple pulses with a periodicity of 30 microseconds, which is the corresponds to the third subharmonic of the 100 kHz Helmholtz resonance or main frequency. Multiple pulses that have a periodicity made subharmonic to 100 kHz, e.g. 20 kHz, were tested, but the performance was found to be relatively weak at this subharmonic level.

As can be seen from Fig.10, bands of successive Dots are printed by a progressively larger number of multiple pulses for printing each dot in the corresponding Ribbons of views (A) to (F) were used. The multiple pulses used to generate the dot bands in FIG were quarter-sine waves according to FIG. 7, the pulse durations T and the dead times T each being 15 microseconds cheat. The voltage amplitude of the pulses was kept constant at approximately 33 volts. In the point band of view (A) only one such pulse was used to achieve the points shown. The points of the in the view (B) bands shown were generated during the same cycle time as those in view (A), but instead of a pulse two multiple pulses were used to generate each point on the ribbon shown in view (B). In a similar way wui— the points of the bands shown in views (C) to (F) using 3, 4, 5 and 6 multiple pulses, respectively generated using an equal time cycle to print each dot. As expected, the The bands in views (A) to (F) are progressively bold, due to the progressively larger point size that is shown with the help of of the process according to the invention is obtained.

Similar multiple pulses were used to produce the Fonts shown in views (A) to (C) of Fig. 11

used with progressively greater fatness. The characters printed in view (A) required a control pulse for Generation of each of the points that form a particular character, whereas two pulses are used to generate each of the individual ones Points of the writing of view (B) were used as well as three impulses to generate each of the individual points that which form the characters of view (C) were used.

The summary of the mode of operation of the invention can be seen in the fact that when an ink jet device is operated for generating of a printing point on a recording medium certain period of time depending on the ink jet printing system is allotted to the ink droplet or droplets for printing the dot on the recording medium. The fatness of a particular one The dot can be controlled by controlling the volume of ink or the number of ink droplets that are drawn from the inkjet device for the allotted time Generation of this point can be generated. The invention provides a method of operating an inkjet device which to generate ink droplets with a known volume of ink a control pulse or a plurality of control pulses for operating the device during a specific Dot creation time is generated by carefully choosing the shape and periodicity of the control pulses used is controlled, whereby the periodicity of the control pulses used is substantially equal to the dominant resonance frequency the ink jet apparatus is made.

The controller 261 can perform the required Control functions e.g. with hard-wired logic or with a programmed microprocessor or a combination to be equipped by both. In order to generate the waveforms shown in FIGS. 4 through 9, the inventors a Wavetek waveform generator, model 175,

manufactured by Wavetek, San Diego, California. In a practical embodiment of the device, the control device 261 would typically be configured in this way that it has the required waveforms and functions, as explained above, provides for each specific application.

Claims (8)

FCJNER EBBINGHAUS FINCK PATENTANWÄLTE EUROPEAN PATENT ATTORNEYS MARIAHILFPLATZ 2 & 3, MÖNCHEN 9O POST ADDRESS: POSTBOX 95 O1 6O1 D-8OOO MUNICH 95 Q ζ 1 ^ Λ. Λ EXXON RESEARCH AND DEAB-32633.0 ENGINEERING COMPANY April 15, 1985 METHOD FOR THE SELECTIVE, MULTICYCLE, RESONANCE OPERATING AN INKJET DEVICE FOR CONTROL OF THE POINT SIZE A method of operating an inkjet apparatus for controlling the size of the ink dot printed on a recording medium, the inkjet apparatus comprising transducer means for generating an overpressure disturbance in an associated ink-filled chamber to eject a droplet of ink from an associated orifice;
characterized in that one (1) the converter device is operated to synchronously generate a or a combination of the fluidic or mechanical resonance frequencies of the inkjet device ORIGINAL BATHROOM device to generate a dominant resonance frequency in the chamber and in the associated ink to excite and (2) can generate either a single cycle or a subharmonic cycle of the dominant resonance frequency, by essentially predictably the volume of an ink droplet to control that due to the resulting pressure disturbance from the opening generated in the chamber is expelled. 2. The method according to claim 1, characterized in that steps (1) and (2) are repeated repeated as desired continuously and in synchronization with the dominant resonance frequency to generate a plurality of ink droplets within a period of time that allows the droplets to be in the air or on the Recording medium can merge, and thus relative to the resulting point size on the recording medium to controllably increase the dot size achieved by a single ink droplet. 3. The method according to claim 1 or 2, characterized in that the converter means for generating of the pressure disturbance is responsive to an electrical signal, and in method step (1) the period of the electrical signal is either substantially equal to or substantially equal to the period of the Helmholtz resonance frequency makes equal to the period of a subharmonic of the Helmholtz frequency and the electrical signal of the Converter device supplies. 4. The method according to claim 3, characterized in that the electrical signal is shaped so that it is essentially a pulse with an exponential leading edge and a stepped trailing edge represents. ßAD ORIGINAL 5. The method according to claim 2, characterized in that the converter means for generating the pressure disturbance is responsive to an electrical signal, and in method step (1) furthermore the electrical signal essentially to a square wave, a rectangular wave, a triangular wave, a half sine wave, a full sine wave, a quarter sine waveform, a sine waveform with less than a quarter wave or a pulse with a exponential leading edge and a stepped trailing edge forms and feeds this electrical signal to the converter. 6. The method according to claim 5, characterized in that the period of the electrical Signal either equal to a period of the selected fluidic and mechanical resonance frequencies of the inkjet device or a combination of the periods of the selected fluidic and mechanical resonance frequencies the ink jet device makes. 7. The method according to claim 6, characterized in that one further to control the dot size of each individual ink droplet, the electrical Controls signal selectively "ON" and "OFF". 8. The method according to claim 7, characterized in that the period of the electrical signal substantially equal to the period of the Helmholtz resonance frequency of the ink jet device or the period of a subharmonic of the Helmholtz frequency. BATH ORIGINAL