Patent Application
20120120163
This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet systems capable of printing at multiple resolutions.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of its non-impact, low-noise characteristics, its use of plain paper, and its avoidance of toner transfer and fixing. Other applications, requiring very precise, non-contact liquid pattern deposition, may be served by drop emitters having similar characteristics to very high resolution ink jet printheads. By very high resolution liquid layer patterns, it is meant, herein, patterns formed of pattern cells (pixels) having spatial densities of at least 300 per inch in two dimensions. Ink jet printing mechanisms can be categorized by technology as either drop-on-demand ink jet or continuous ink jet. The first technology, “drop-on-demand” ink jet printing, provides ink droplets that impact upon a recording surface by using a pressurization actuator (thermal, piezoelectric, etc.). Many commonly practiced drop-on-demand technologies use thermal actuation to eject ink droplets from a nozzle. A heater, located at or near the nozzle, heats the ink sufficiently to boil, forming a vapor bubble that creates enough internal pressure to eject an ink droplet. Other well known drop-on-demand droplet ejection mechanisms include piezoelectric actuators.
Drop-on-demand drop emitter systems are limited in the drop repetition frequency that is sustainable from an individual nozzle. In order to produce consistent drop volumes and to counteract front face flooding, the ink supply is typically held at a slightly negative pressure. The time required to re-fill the drop generation chambers and passages, including some settling time, limits the drop repetition frequency. Drop repetition frequencies ranging up to ˜50 kHz may be possible for drops having volumes of 10 picoLiters (pL) or less. However, a drop frequency maximum of 50 KHz limits the usefulness of drop-on-demand emitters for high quality patterned layer deposition to process speeds below ˜0.5 msec.
The second ink jet technology, commonly referred to as “continuous” ink jet (CU) printing, uses a pressurized ink source that produces a continuous stream of ink droplets from a nozzle. The stream is perturbed in some fashion causing it to break up into uniformly sized drops at a nominally constant distance, the break-off length, from the nozzle. Since the source of pressure is remote from the nozzle (typically a pump is used to feed pressurized ink to the printhead), the space occupied by the nozzles is very small. CIJ drop generators do not have a “refill” limitation since the drop formation process occurs after ejection from the nozzle, and thus can operate at frequencies approaching a megahertz.
CIJ drop generators rely on the physics of an unconstrained fluid jet, first analyzed in two dimensions by F. R. S. (Lord) Rayleigh, “Instability of jets,” Proc. London Math. Soc. 10 (4), published in 1878. Lord Rayleigh's analysis showed that liquid under pressure, P, will stream out of a hole, the nozzle, forming a jet of diameter, Dj, moving at a velocity, vj. The jet diameter, Dj, is approximately equal to the effective nozzle diameter, Dn, and the jet velocity is proportional to the square root of the reservoir pressure, P. Rayleigh's analysis showed that the jet will naturally break up into drops of varying sizes based on surface waves that have wavelengths, λ, longer than πDj, i.e. λ≧πDj. Rayleigh's analysis also showed that particular surface wavelengths would become dominate if initiated at a large enough magnitude, thereby “stimulating” the jet to produce mono-sized drops. Individual CU drop generators or low density arrays of CIJ drop generators may be configured to produce the 100's of 1000's of small (<50 pL) drops per second per nozzle, which is one of the requirements needed for high quality patterned layered deposition process speeds above 0.5 msec.
Thermally stimulated CU devices may be fabricated using emerging microelectromechanical (MEMS) fabrication methods and materials. By applying microelectronic fabrication process accuracies to the construction of a thermally stimulated CIJ drop emitter, a liquid pattern deposition apparatus may be provided having a wide range of resolution and process speed capabilities. The physical parameters relating to continuous stream drop formation are constrained within certain boundaries to ensure the capability of providing a desired combination of pattern resolution, grey scale, drop volume uniformity, minimization of mist and spatter, and process speed. Such an apparatus has application for very high speed, photographic quality printing as well as for manufacturing applications requiring the non-contact deposition of high precision patterned liquid layers.
Ink jet printing systems that are capable of printing at different resolutions are known in the market. Such printing systems allow the user to select whether to print in a high quality mode at one print resolution at a certain print speed or in a lower quality mode at a lower print resolution at a higher print speed. Typically the lower quality mode, sometimes referred to as a draft mode, increases the spacing between pixels while printing with the same size drops. As a result, the print quality is reduced not only by the resolution reduction, but also by the lower ink coverage. There are some drop-on-demand (DOD) printing systems in which larger ink drops are used for the printing at the lower resolution to produce similar ink coverage levels in both the high and low quality print modes. A need exists to have a continuous ink jet system capable of printing quality prints at multiple resolutions. A system capable of printing at multiple resolutions needs to have a method for adjusting the spot size on paper to achieve the correct ink laydown and coverage for each of the resolutions.
There are documented systems which print at multiple resolutions using DOD technologies. In one example, as described in European Patent No. 0692386 (Onishi et al.) print using a fixed print droplet volume from a DOD ink jet device. In order to achieve multiple resolutions, ink media pairs are chosen such that the repellency of the ink on the media controls the diameters of the ink dots to the proper size. With this approach to multiple resolution printing, there is no flexibility for ink media selection, and it would be difficult to make quality prints at multiple resolutions on a single media type. U.S. Pat. No. 6,419,336 (Takahashi) describes another system capable of printing at multiple resolutions. In this second example, the volume of print drops formed is varied using a peizo system DOD, and is independently controlled. However, as a DOD technology it is fundamentally limited in the frequency at which drops can be made, thereby limiting the attainable process speeds.
In commonly-assigned U.S. Pat. No 7,249,829 (Hawkins et al.) describes a drop deposition apparatus capable of forming drops of predetermined volumes having a unit volume, V0, and drops having volumes that are integer multiples of the unit volume mV0 using a continuous ink jet system. The disclosure is related to gray level printing, and does not address the problems associated with using drops of mV0 increments in a multiple resolution continuous printing system.
The need exists for a continuous ink jet system capable of printing high quality images at multiple resolutions at fast process speeds.
Briefly, according to one aspect of the present invention a continuous ink jet printing system capable of printing at multiple predetermined print resolutions is disclosed. The system comprises a drop generator having an array of nozzles for emitting a plurality of continuous streams of liquid for applying ink to media driven in a media advance direction having a source for pressurized liquid for supplying pressurized liquid to the plurality of nozzles, wherein the plurality of nozzles have effective nozzle diameters D0 and a stimulation device associated with each nozzle of the plurality of nozzles for forming ink drops having predetermined drop volumes from the continuous streams of liquid, wherein the predetermined drop volumes include non-print drops of a unit volume V0, and print drops having volumes that are integer multiples of the unit volume, mV0, wherein m is an integer greater than 1; a catcher to collect the non-print drops; and a selector for selecting a predetermined print resolution, wherein each predetermined print resolution has a corresponding print drop volume mV0.
It is an advantage of the present invention that it provides an apparatus capable of printing images having different resolutions within a single system. The apparatus and method of the present invention allows the user to select predetermined resolutions and print speed combinations that were not previously achievable with a single continuous ink jet system, providing the user greater print job flexibility and lower overall equipment costs.
These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
a, 6b, and 6c illustrate ideal spot placement for (a) 100% fill spots, 6b 110% fill spots and 6c undersized spots resulting in unwanted “white” space;
a and 8b illustrate spots from single print drops and multiple drop merged spots on the recording media for 600×1200 dpi and 600×1800 dpi prints; and
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements.
The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention.
As described herein, the example embodiments of the present invention provide a printhead or printhead components typically used in ink jet printing systems. However, many other applications are emerging which use ink jet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid” and “ink” refer to any material that can be ejected by the printhead or printhead components described below. Referring to
Recording medium 32 is moved relative to printhead 30 by a recording medium transport system 34, which is electronically controlled by a recording medium transport control system 36, and which in turn is controlled by a micro-controller 38. The recording medium transport system shown in
The process speed of the multiple resolution continuous ink jet system 20 shown in
Ink is contained in an ink reservoir 40 under pressure. In the non-printing state, continuous ink jet drop streams are unable to reach recording medium 32 due to an ink catcher 42 that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit 44. The ink recycling unit reconditions the ink and feeds it back to reservoir 40. Such ink recycling units are well known in the art. The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir 40 under the control of ink pressure regulator 46. Alternatively, the ink reservoir can be left unpressurized, or even under a reduced pressure (vacuum), and a pump is employed to deliver ink from the ink reservoir under pressure to the printhead 30. In such an embodiment, the ink pressure regulator 46 can comprise an ink pump control system. As shown in
The ink is distributed to printhead 30 through an ink channel 47. The ink preferably flows through slots or holes etched through a silicon substrate of printhead 30 to its front surface, where a plurality of nozzles and drop forming mechanisms, for example, heaters, are situated. When printhead 30 is fabricated from silicon, drop forming mechanism control circuits 26 can be integrated with the printhead. Printhead 30 also includes a deflection mechanism (not shown in
Referring to
Liquid, for example, ink, is emitted under pressure through each nozzle 50 of the array to form filaments of liquid 52. In
Jetting module 48 is operable to form liquid drops having a first size or volume and liquid drops having a second size or volume through each nozzle. To accomplish this, jetting module 48 includes a drop stimulation or drop forming device 28, for example, a heater or a piezoelectric actuator, that, when selectively activated, perturbs each filament of liquid 52, for example, ink, to induce portions of each filament to breakoff from the filament and coalesce to form drops 54, 56.
In
Typically, one drop forming device 28 is associated with each nozzle 50 of the nozzle array. However, a drop forming device 28 can be associated with groups of nozzles 50 or all of nozzles 50 of the nozzle array.
When printhead 30 is in operation, drops 54, 56 are typically created in a plurality of sizes or volumes, for example, in the form of large drops 56, a first size or volume, and small drops 54, a second size or volume. The ratio of the mass of the large drops 56 to the mass of the small drops 54, herein referred to as print drop ratio, is typically approximately an integer between 2 and 10. A drop stream 58 including drops 54, 56 follows a drop path or trajectory 57. The multiple resolution continuous printing system 20 is capable of operating at multiple print drop ratios, resulting in the generation of print drops 56 that are integer (m) multiples of the volume of drop 54. These drop volumes mV0 correspond to the predetermined print resolutions.
Printhead 30 also includes a gas flow deflection mechanism 60 that directs a flow of gas 62, for example, air, past a portion of the drop trajectory 57. This portion of the drop trajectory is called the deflection zone 64. As the flow of gas 62 interacts with drops 54, 56 in deflection zone 64 it alters the drop trajectories. As the drop trajectories pass out of the deflection zone 64 they are traveling at an angle, called a deflection angle, relative to the undeflected drop trajectory 57.
Small drops 54 are more affected by the flow of gas than are large drops 56 so that the small drop trajectory 66 diverges from the large drop trajectory 68. That is, the deflection angle for small drops 54 is larger than for large drops 56. The flow of gas 62 provides sufficient drop deflection and therefore sufficient divergence of the small and large drop trajectories so that catcher 42 (shown in
Drop stimulation or drop forming device 28 (shown in
Positive pressure gas flow structure 61 of gas flow deflection mechanism 60 is located on a first side of drop trajectory 57. Positive pressure gas flow structure 61 includes first gas flow duct 72 that includes a lower wall 74 and an upper wall 76. Gas flow duct 72 directs gas flow 62 supplied from a positive pressure source 92 at downward angle θ of approximately a 45° relative to liquid filament 52 toward drop deflection zone 64 (also shown in
Upper wall 76 of gas flow duct 72 does not need to extend to drop deflection zone 64 (as shown in
Negative pressure gas flow structure 63 of gas flow deflection mechanism 60 is located on a second side of drop trajectory 57. Negative pressure gas flow structure includes a second gas flow duct 78 located between catcher 42 and an upper wall 82 that exhausts gas flow from deflection zone 64. Second gas flow duct 78 is connected to a negative pressure source 94 that is used to help remove gas flowing through second gas flow duct 78. An optional seal(s) 84 provides an air seal between jetting module 48 and upper wall 82.
As shown in
Gas supplied by first gas flow duct 72 is directed into the drop deflection zone 64, where it causes large drops 56 to follow large drop trajectory 68 and small drops 54 to follow small drop trajectory 66. As shown in
As shown in
A greater understanding of generating drops of volumes V0 and mV0 can be gained by examining
Returning now to drops 54 and 56 of
For the purpose of understanding the present inventions the jet diameter will be approximated by the diameter of nozzle 50, D0, i.e. Dj=D0. The jet diameter will be only a few percent smaller than the nozzle diameter for liquids having relatively low viscosities, i.e. v<20 centipoise. Further it is customary to relate the wavelength, λ0, of surface waves to the jet diameter, D0, using a dimensionless “wave ratio”, L. In the explanation of the present invention herein, the dimensionless wave ratio, L, will be frequently used in place of the wavelength, λ0=L D0.
It is well known that surface waves having wave ratios less than π have negative growth factors and so decay with time rather than grow to cause the jet to break up (reference Lord Rayleigh, -H. C. Lee, “Drop formation in a liquid jet,” IBM Journal of Research and Development, July, 1974, pp. 364-369, and U.S. Pat. No. 7,249,829 issued to Hawkins et al.). The reported values for the optimum wave ratio ranges from Lopt=π√2=4.443 from a one-dimensional analysis by H. C. Lee (H. C. Lee, “Drop formation in a liquid jet,” IBM Journal of Research and Development, July, 1974, pp. 364-369) to Lopt=4.51 determined from the more rigorous two-dimensional analysis by Lord Rayleigh. The growth factor rises quickly to its peak value from π and then more slowly falls off as L increases. Surface waves having L values of 10 or more may still result in drop break off. However, if spontaneous waves having a smaller wave ratio (closer to the optimum wave ratio) are present with equal or larger initial amplitude, the smaller wave ratio waves will grow much faster and lead to earlier jet break-up. The practice of stimulating continuous ink jet requires that a perturbing surface wave is created on the continuous streams of liquid at a chosen wave ratio and with sufficient amplitude to overwhelm the spontaneous surface waves that would otherwise lead to natural break-up. Preferably, drop formation device 28 is operated to create drops of unit volume V0 by creating perturbation surface waves on the continuous streams of liquid having a wave ratio L0 between 4 and 7; and more preferably having wave ratio L0 is between 4.4 and 4.6.
By reexamination of the drop volume equation, V0≈λ0(πD02/4), in terms of L: V0≈L(πD03/4), one can see that in order to operate near the optimal wave ratio the selection of the nozzle diameter is limited by the desired drop volume. Since the print drops are integer (m) multiples of the fundamental drop volume, mV0 the obtainable print drop volumes are then limited by the fundamental drop volume. The multiple resolution continuous printing system 20 is operated such that the predetermined print resolutions have corresponding print drop volumes, mV0.
There are many stimulation schemes useful for creating drops 54 and 56.
Thermal pulse stimulation of the break-up of continuous liquid jets is known to provide the capability of generating streams of drops of predetermined volumes wherein some drops may be formed having volumes equal to mV0, where m is an integer V0 is the unit volume. Integer m is called the print drop ratio. For additional details, see for example, commonly-assigned U.S. Pat. No. 6,588,888 (Jeanmaire et al.). In
As described in relationship to
Assuming that the spots are arranged on the page in a regular grid pattern, the center to center distance between each spot in both the scan and array directions is the corresponding pitch. In practice, it is useful to increase the 100% fill spot size by 10% to account for small errors in spot placement on the page. As such, a preferred spot size can be defined to guarantee covering the paper with 10% margin for spot placement error. A spot diameter Dspot with 10% margin can be calculated for square resolutions (R) by Dspot=1.1*sqrt(2)*25400/R, where Dspot is in microns and R is in dpi.
a, 6b, and 6c illustrate the overlap of spots of different sizes as placed on a regular grid.
For asymmetric resolutions that are less than a factor of two from square, it is not unreasonable to use the same logic as put forth for square resolutions. For example, a print resolution of 600×900 dpi using a 10% overfill criteria, the optimum spot size is 56 um, as calculated by
where Rarray and Rscan are the resolutions in the array and scan direction in units of dpi. This is simple modification to the Dspot calculation allows for independent scan and array resolutions.
In addition to asymmetric resolutions, it is possible to devise printing schemes which purposely offset the spot placement of adjacent spots of some fraction of a pixel in either direction. For example, to reduce the effect of drop-drop interactions on the trajectory of a given drop, every other nozzle may be fired so that the drops on the page are offset by ½ a pixel in the scan direction, as described in commonly-assigned U.S. Pat. No. 7,758,171 (Brost). Also, in instances where multiple printheads are used to create an image, the relative spacing in the array direction may also be staggered by ½ pixel. Generally, in order to have complete coverage (no unwanted “white” space) for any regular arrangement of equally sized ink jet spots, the radius the 100% spot is defined as the circumcenter of the triangle formed by three adjacent spots.
In the instance where the spots are placed in a regular grid pattern as resolutions increase in asymmetry, using to
calculate spot size overestimates the spot size necessary to give 100% fill on the page. Looking closely at the equation, it is clear that the minimum Dspot is governed by the lowest resolution in the system—scan or array. For example, calculating a target spot size for a 600 npi printhead printing at 600 dpi in the array direction an optimum 10% overfill spot size of 46.6 microns is obtained as the Rscan goes to infinity, and practically speaking a target spot size of 46.9 microns is calculated for Rscan=4800 dpi. For resolutions with asymmetry ratio, A=Rscan/Rarray, greater than or equal to 2, the simple calculation for Dspot is only valid when a print is made in a manner that allows one drop to fully dry and form a spot on the page prior to deposition of the next drop, and if the next drop does not interact with the ink already on the page. One can think about this as if each spot on the page was placed as sticker, where the boundary of the ink (ie sticker size) is fixed by the drop volume. It is worth noting that for other printing technologies, such as offset lithography, the sticker analogy holds.
In ink jet printing, and particularly for single printhead printing, as the scan resolution increases for a fixed array resolution (Rarray), the likelihood that a subsequent drop will land on the previous drop while it is still wet on the surface of the recording media increases. It has been found that for resolutions that are a factor of two or more from square (A>2), it is likely that the print drops from two adjacent pixels will merge to form a single spot on the recording media. From this observation, one can view the resolution of a 100% filled area to be the square resolution. As an example, when printing a 600 dpi by 1200 dpi image with a printhead 30 that has 600 nozzles per inch (npi), 100% fill areas can be considered to be 600 dpi by 600 dpi. It is known that for a square resolution 600 dpi image the spot size should be approximately 65.9 microns in diameter on the recording media. Therefore the size of the merged spot formed by 2 print drops, in this example, should also be 65.9 um in diameter. This concept may be generalized for resolutions where A≦2. Generally, a predetermined resolution with Rarray equal to the npi and Rscan equal to the integer multiple A of the Rarray can be expressed as Rarray×Rarray*A, where A is the asymmetry ratio and is equal to the number of drops that will form the Rarray×Rarray required spot size.
The diameter of the final spot on the page is highly dependent on ink-media interactions. It is therefore, best to determine the optimum print drop volume using two empirical models: 1) the asymmetry (A) correlation of a single print spot (mV0) to merged spot sizes as printed at the corresponding resolutions (A*mV0), printed at Rarray×Rarray*A) and 2) a print spot Dspot to drop volume (mV0) correlation. It has been found that an empirical model to determine merged spot sized based normalized drop diameter ratios is valid for multiple drop volumes (mV0).
As noted above, to form the appropriate sized spot for a Rarray×Rarray*A resolution, A print drops merge on the page. The volume of ink which forms each merged spot is therefore A times the print drop volume. A theoretical print drop can be imagined which represents the collection of A drops, and has a volume of A times print drop volume (A*mV0). The diameter of the actual and theoretical print drops can be calculated. Since the volume of the theoretical print drops scales with A, an effective drop diameter ratio (EDDR) can be determined for any value of A by taking the ratio of a drop of A*mV0 to a single print drop (mV0). This ratio results the simple relationship of EDDR=A1/3.
To validate the spot size determination for asymmetric resolutions where A≧2, a series of prints were made using both pigmented ink and dye based ink on a single batch of a glossy coated paper. (The glossy coated paper yields a more consistent dot size and shape and uncoated papers.) A 600 npi head was used to print images which contained single pixel spots, as well as spots formed with A number of drops/pixels (2 drops/pixels for 1200 dpi, etc). The diameters of the single spots (Dspot) and the A spots (Dspot-A) were measured using a hand-held CCD device from Quality Engineering Associates, Inc. (QEA) and associated software. The ratio of the Dspot-A to Dspot was taken over a range of drop volumes (mV0) and Rscan. These ratios were correlated to the EDDR and found to have a single straight-line correlation, as shown in
a and 8b illustrate the spots generated by single drops and merged drops, from a 600 npi printhead, at 600×1200 dpi (A=2) and 600×1800 dpi (A=3) respectively. In
The second step in determining the target drop volume (mV0) is correlation of drop volume to spot size (Dspot).
The methods presented herein for determining the desired spot size on the media are intended to serve as examples useful in the present invention, and are not intended to be limiting. Other methods for determining the desired spot size, and corresponding drop volume are also valid under the current invention as long as each predetermined resolution has a corresponding drop volume mV0, where m is an integer between 2 and 10, and preferably if the spot size for each predetermined resolution results in 100% fill areas with no unwanted “white” space on the recording media and
The maximum paper speed of ink jet systems is fixed by the frequency of the print drop formation and the resolution in the scan direction. Rscan sets the number of print drops (spots) on the page per inch in the media advance (scan) direction, while the print frequency sets how fast those drops can be generated. The maximum paper speed for any given print frequency (Fp) and scan resolution (Rscan) can be determined using the relationship PaperSpeedmax=Fp/Rscan. The print frequency is the frequency associated with making print drops mV0, and is therefore the fundamental frequency divided by the print drop ratio m (Fp=f0/m). For a fixed Rarray, images with larger Rscan values will have a lower maximum print speed for a given print drop ratio (m). Similarly images printed at the same resolution but with larger values of m will have a lower print frequency and therefore a slower maximum print speed than their lower print drop ratio counterparts. Multiple resolution continuous ink jet printing system will present users with the option to tradeoff print speed and resolution depending on the requirements of a given print job. Printing selected higher resolutions with the multiple resolution continuous printing system 20, the system runs at a lower maximum print speed, but gives higher image quality with lower grain. Conversely, at lower resolutions, higher print speeds are obtainable with higher grain and fewer obtainable gray levels. This allows the user to determine which factor is important on a job by job basis, rather that having to choose a system preconfigured for one condition. The Rscan and process speed are independently controllable up to the limit of PaperSpeedmax. The multiple resolution continuous ink jet printing system may be operated at different process speeds for different resolutions, or may optionally fix the process speed for a given job (a job represents a collection of documents printed together) such that all system resolutions are obtainable. Similarly, the selected operating resolution may vary job-to-job, image-to-image, or within an image. That is, different ones of the predetermined print resolutions can be selected for different print jobs, for different documents within a print job, or for different portions of a document.
The multiple resolution continuous printing system 120 utilizing two printheads had additional range in quality and speed, since the system may be operated such that each printhead is effectively doubling the maximum print speed over a single printhead system. Alternatively, the two printhead system may be used to create images at higher resolution in the array direction at slower speeds.
The following examples are presented as further understandings of the present invention and are not to be construed as limitations thereon.
In this example a series of prints were made on glossy paper using a 600 npi printhead at resolutions of 600×900, 600×1200 and 600×2400. The printhead used in this example had a nominal nozzle diameter D0 of 8 microns, and was operated at a nominal jet velocity of 20 m/s. The frequency for forming the fundamental drop V0 was 451 kHz, resulting in a value of L of 5.7 and a drop volume V0 of 2.3 pL. Quality images were obtained with equivalent 100% fill at all three resolutions. The drop volumes used to image the three resolutions of 600×900 dpi, 600×1200 dpi and 600×2400 dpi were produced at values of m of 4, 3 and 2 respectively. Where Rscan=1200, A=2 and when Rscan=2400, A=4 consistent with the previous discussion, the Dspot-A was set to be equivalent to the Dspot for the Rarray×Rarray image of 600×600 dpi. In this example the operation conditions of the deflection mechanism were different for each printed resolution. Table 1 summarizes the results from Example 1.
The multiple resolution continuous printing system of Example 2 is similar to that of Example 1, except that the operating parameters of the deflection mechanism were kept the same for each of the print resolutions. The quality of the images and the values for the fill spot diameter were equivalent to Example 1. The deflection control mechanism was run at a negative air flow of 1050 and a positive air flow of 1650 for the same three resolutions as Example 1. In this example, the operating parameter values are kept the same for each of the selectable predetermined print resolutions. In both the first and second examples, the same jet velocity, vj0, is employed for each of the selectable predetermined print resolutions.
Table 1 contains details for four model multiple resolution continuous ink jet systems, A-D. All four systems A-D are designed to operated at an optimal wave ratio for the fundamental drop of L=4.5, and with a common jet velocity vj0. The systems of Table 1 are intended to be operated in single pass mode, where each color is addressed by a single array of nozzles. These four system models each provide three or four selectable predetermined print resolutions each of which has a corresponding print drop volume mV0 with a distinct value of the print drop ratio m, with the values of the print drop ratio m are integers that are greater than 1 and less than 7. As can be seen in Table 2, the print resolutions have asymmetry ratios A=Rscan/Rarray of 1, 1.5, 2, 3, and 4. That is, the predetermined print resolutions have asymmetry ratios A, where A is 1.5 or an integer greater than or equal to 1.
Table 3 contains details for two model multiple resolution continuous ink jet systems operating with two printheads. Both systems E and F are designed to operated at an optimal wave ratio of L=4.5.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
