System and methods for fluid drop ejection

TECHNICAL FIELD

0001This application relates to the field of fluid drop ejection.

BACKGROUND

0002Ink jet printers typically include an ink path from an ink supply to a nozzle path. The nozzle path terminates in a nozzle opening from which ink drops are ejected. Ink drop ejection is controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electro statically deflected element. A typical printhead has an array of ink paths with corresponding nozzle openings and associated actuators, and drop ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image as the print head and a printing substrate are moved relative to one another. An ink jet recording head designed to control the discharging of ink highly accurately, even when a pressure or a flow of the ink in a pressure generation chamber becomes instable, is known from the Japanese patent publication <patcit id="pcit0001" dnum="JP2002248774A"><text>JP 2002248774 A</text></patcit>. It generally discloses an ink-jet recording head having a plurality of nozzle openings for forming one ink drop. The ink-jet recording head discharges ink as ink drops by pressuring the stored ink. The ink in the ink conduit of an ink jet printing system is usually kept at a negative pressure to keep the ink from spilling over the nozzle plate. In addition, the ink nozzles are required to be primed by the ink fluid for proper ink drop ejection.

SUMMARY

0003In one aspect of the invention a drop ejection device comprises a group of orifices in a nozzle plate adapted to eject fluid drops, wherein the orifices in the group are arranged in a 2D array. A fluid conduit is fluidly coupled to the group of orifices and an actuator is provided which is capable of ejecting fluid in the fluid conduit through at least two of the orifices in a group. Further a controller is coupled to the actuator and the orifices and the controller are configured such that the fluids ejected from the orifices merge into a fluid drop having a particular drop volume on the nozzle plate. Each orifice has a bubble pressure over 6 inch wg (one inch of water is 249.0889 Pascal) with an ink having a surface tension of 30 dynes/cm, (1 dyn = 10^-5 Newton) the bubble pressure in each orifice being greater than a bubble pressure of a single nozzle ejecting the same drop volume. Further a pressure regulator is provided which is configured to apply a negative pressure to the fluid at the orifices, wherein the negative pressure is pressure that is below atmospheric pressure and the magnitude of the pressure is smaller than the bubble pressure in each orifice.

0004In another aspect the invention is directed to a corresponding method for ejecting fluid.

0005In one implementation, a drop ejection device has a group of orifices adapted to eject fluid drops, a fluid conduit fluidly coupled to the group of orifices, an actuator to eject fluid contained in the fluid conduit through at least two of the orifices, and a controller coupled to the actuator. The orifices and controller are configured such that the fluids ejected from the orifices merge into a fluid drop.

0006In another implementation, a drop ejection device has a plurality groups of orifices adapted to eject fluid drops, a fluid conduit fluidly coupled to each group of orifices, and an actuator associated with each group of orifices. The actuator is capable of ejecting fluid from the fluid conduit through the orifices. The orifices are closer to other orifices in the same group than to the orifices from a different group and the orifices within a group are disposed in a substantially non-linear pattern.

0007In yet another implementation, an ink jet print head has a group of orifices adapted to eject ink drops, a fluid conduit fluidly coupled to the group of orifices, an actuator capable of ejecting an ink fluid in the fluid conduit through at least two of the orifices, and a controller coupled to the actuator. The orifices and controller are configured such that the ink fluids ejected from the orifices merge into an ink drop.

0008In still another implementation, an ink jet print head has a plurality groups of orifices adapted to eject ink drops, a fluid conduit fluidly coupled to each group of orifices, and an actuator associated with each group of orifices. The actuator is capable of ejecting an ink fluid from the fluid conduit through the orifices. The orifices are closer to other orifices in the same group than to the orifices from a different group and the orifices within a group are disposed in a substantially non-linear pattern.

0009In another, a method for ejecting fluid includes providing a fluid conduit fluidly coupled to a group of orifices, ejecting a fluid from the in the conduit fluidly through at least two orifices in the group, and merging the ejected fluid into a fluid drop.

0010In another implementation, a method for ejecting fluid includes providing a plurality groups of orifices adapted to eject fluid drops, disposing the orifices within a group in a substantially non-linear pattern, and coupling a fluid conduit to each group of orifices. The orifices are closer to other orifices in the same group than to the orifices from a different group.

0011Further implementations may include one or more of the following. A drop ejection device can have a group of orifices adapted to eject fluid drops, a fluid conduit fluidly coupled to the group of orifices, an actuator to eject fluid contained in the fluid conduit through at least two of the orifices, and a controller coupled to the actuator, wherein the orifices and controller are configured such that the fluids ejected from the orifices merge into a fluid drop. The drop ejection device can include at least two orifices having substantially the same dimensions or different dimensions. The group of orifices can include a first orifice and a plurality of second orifices, wherein the first orifice is surrounded by the plurality of second orifices. The opening of the first orifice can be wider than the openings of the second orifices. The fluid ejected from all the orifices in the group of orifices can be merged into a single fluid drop. The nozzle plate portions separating the orifices can be substantially equal or smaller than the widths of the fluid ejected from the orifices. The drop ejection device can comprise a fluid ejection actuator that can actuate the fluid ejection through the orifices. The fluid ejection actuator can include a piezoelectric transducer or a heater. An electronic control unit can provide control to the fluid ejection actuator. The electronic control unit can control the fluid ejection actuator to eject fluid drops to form an image on a substrate.

0012The drop ejection device can further include an electronic selector that can actuate the ejection of fluid. The fluid drop can vary in volume in response to different drive voltage waveforms applied to the fluid ejection actuator by the electronic control unit. The fluid drop can form a substantially single fluid dot on a fluid-receiving substrate. Separate meniscuses can be formed at different orifices in the group of orifices. The orifices can be in the shape of a circle, a hexagon, a triangle, or a polygon. The group of orifices can formed in a substantially circular area on the nozzle plate. The controller can be configured to select one of a plurality of different drive voltage waveforms. A first of the plurality of different drive voltage waveforms can cause fluid not to be ejected from at least one of the orifices, and a second of the plurality of different drive voltage waveforms can cause fluid to be ejected from the at least one of the orifices.

0013The orifices can have opening dimensions in the range from 1 µm to 100 µm, or in the range from 3 µm to 50 µm. The orifices can have bubble pressure over 6 inch wg or over 8 inch wg. The drop ejection device can further comprise a silicon substrate. The orifices can be fabricated using one or more of etching, laser ablation, and electroforming. The fluid can include at least one colorant that optionally comprises a dye or pigment.

0014Implementations can also include one or more of the following. A drop ejection device can include a plurality groups of orifices adapted to eject fluid drops, a fluid conduit fluidly coupled to each group of orifices, and an actuator associated with each group of orifices, the actuator being capable of ejecting fluid from the fluid conduit through the orifices. The orifices are closer to other orifices in the same group than to the orifices from a different group and the orifices within a group are disposed in a substantially non-linear pattern. The fluids ejected from two or more of orifices in a group of orifices can merge into a fluid drop. The orifices within a group of orifices can have substantially the same dimensions. The orifices within a group of orifices can have the different dimensions. The orifices within a group include a first orifice and a plurality of second orifices surrounding the first orifice. The fluid ejection actuator can include a piezoelectric transducer or a heater. The drop ejection device can further comprise an electronic control unit controls the fluid ejection actuator to eject fluid drops and to form an image on a substrate. The drop ejection device can further comprise an electronic selector that can select the fluid ejection actuator to actuate the ejection of the fluid drop. The fluid drop can vary in volume in response to different drive voltage waveforms applied to the fluid ejection actuator by the electronic control unit. Separate meniscuses can be formed at different orifices in each group of orifices. Each group of orifices can be formed in a substantially compact area on the nozzle plate. At least one group of orifices can be formed in a substantially circular area on the nozzle plate. The orifices can be in the shapes of one or more of a circle, a hexagon, a triangle, or a polygon. The orifices can have opening dimensions in the range from 1 µm to 100 µm, e.g., opening dimensions in the range from 3 µm to 50 µm. The orifices can have bubble pressures over 6 inch wg, e.g., bubble pressures over 8 inch wg. The drop ejection device can further comprise a silicon substrate. The orifices can be fabricated using one or more of etching, laser ablation, and electroforming. The fluid can comprises at least one colorant.

0015Embodiments may include one or more of the following advantages. The ink jet printing system disclosed provides reliable performance under a wide range of operating conditions. The disclosed system is capable of ejecting large ink drops. The ink nozzles are properly primed while the ink fluid is kept from spilling over the nozzle plate. The ink jet print head can provide consistent ink ejection direction and thus precise ink dot placement on ink receiver. The ink jet printing system disclosed is capable of providing the above performance at high acceleration of printheads.

0016Another advantage of the disclosed ink jet printhead is that it provides robust performance in the presence of mechanical vibrations in the environment or when the printhead is subject to significant accelerations. Ink meniscuses can be held in position within the ink orifices even when the printhead is perturbed by environmental forces.

0017Yet another advantage is that the disclosed ink jet printhead can be fabricated using silicon-based fabrication technologies. The disclosed system and methods are also compatible with piezoelectric, thermal and MEMS-based ink jet printing systems. The disclosed system and methods are also applicable to water-based inks, solvent-based inks, hot-melt inks, which can include colorants such as dye or pigment, as well as other fluids without containing colorants.

0018The details of one or more embodiments are set forth in the accompanying drawings and in the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

0019<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is a block diagram of ink jet printing system having ink nozzles.</li><li><figref idref="f0002">Figure 2A</figref> is a top view of one implementation of an ink nozzle.</li><li><figref idref="f0003">Figure 2B</figref> illustrates a cross-sectional view of the ink nozzle of <figref idref="f0002">Figure 2A</figref>.</li><li><figref idref="f0004">Figure 3A</figref> is a top view of another implementation of an ink nozzle.</li><li><figref idref="f0005">Figure 3B</figref> illustrates a cross-sectional view of the ink nozzle of <figref idref="f0004">Figure 3A</figref>.</li><li><figref idref="f0006">Figure 4A</figref> is a top view of a plurality of ink nozzle with each ink nozzle having a plurality of ink orifices.</li><li><figref idref="f0007">Figure 4B</figref> illustrates a cross-sectional view of the ink nozzles of <figref idref="f0006">Figure 4A</figref></li></ul>

DETAILED DESCRIPTION

0020<figref idref="f0001">FIG. 1</figref> illustrates an ink jet printing system 100 that includes an ink jet print head module 110 having a plurality of ink nozzles 120 typically arranged in arrays on a nozzle plate 121, a fluid conduit 130 for supplying ink to the ink jet print head module 110, an ink reservoir 140 for storing the ink to be supplied to the fluid conduit 130, and an ink passage 150 that provides fluid connection between the ink reservoir 140 and the fluid conduit 130. During printing, ink drops are ejected from the ink nozzles 120 under the control of an electronic control unit 190 in response to input image data to form an image pattern of ink dots on an ink receiver 180. The ink jet printing system 100 can include a plurality of ink nozzles 120, each nozzle associated with one or more ink ejection actuators. The ink ejection actuators can include a piezoelectric transducer, a heater, or an MEMS transducer device. The ink jet printing system 100 can further comprise an electronic selector that can select the ink ejection actuators associated with the ink nozzle 120 from which the fluid drop will be ejected.

0021As shown in <figref idref="f0001">Figures 1</figref>, <figref idref="f0002">2A</figref> and <figref idref="f0003">2B</figref>, each ink nozzle 120 comprises a plurality of closely distributed orifices 230. Ink nozzles 120 are separated by distances significantly larger than those between neighboring orifices 230 within each ink nozzle. The ink fluid contained in the fluid conduit 130 is ejected from the orifices corresponding to each ink nozzle 120 under the control of the control unit 190. The ink fluid ejected from the orifices can merge into an ink drop after the ejection. The ejected ink drop can vary in volume in response to different drive voltage waveforms applied to the ink ejection actuator by the electronic control unit 190.

0022The ink jet print head module 110 can exist in the form of piezoelectric ink jet, thermal ink jet, MEMS based ink jet print heads, and other types of ink actuation mechanisms. For example, <patcit id="pcit0002" dnum="US5265315A"><text>Hoisington et al. U.S. Patent 5,265,315</text></patcit>, describes a print head that has a semiconductor print head body and a piezoelectric actuator. The print head body is made of silicon, which is etched to define a fluid conduit. Nozzle openings are defined by a separate nozzle plate 121, which is attached to the silicon body. The piezoelectric actuator has a layer of piezoelectric material, which changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a fluid conduit that supplies the ink to the ink orifices.

0023Other ink jet print heads are disclosed in commonly assigned <patcit id="pcit0003" dnum="US10189947B"><text>US Patent Application No. 10/189,947</text></patcit>, US Patent Publication No. <patcit id="pcit0004" dnum="US20040004649A1"><text>US20040004649A1</text></patcit>, titled "Printhead", filed on 7/3/2002, and <patcit id="pcit0005" dnum="US60510459B"><text>US Provisional Patent Application No. 60/510,459</text></patcit>, titled "Print head with thin membrane", filed 10/10/2003. <patcit id="pcit0006" dnum="US60510459B"><text>US Provisional Patent Application No. 60/510,459</text></patcit> discloses a printhead having a monolithic semiconductor body with an upper face and a lower face. The body defines a fluid path including a fluid conduit, and a nozzle opening. The nozzle opening is defined in the lower face of the body and the nozzle flow path includes an accelerator region. A piezoelectric actuator is associated with the fluid conduit. The actuator includes a piezoelectric layer having a thickness of about 50 micron or less.

0024The ink reservoir 140 includes an ink-feeding path 160 having an ink filter 161 that supplies ink to the ink reservoir 140. The ink reservoir 140 also has an air inlet 155 having an air filter 156 that allows the ink level to vary in the ink reservoir 140.

0025Ink types compatible with the described ink jet printing system include water-based inks, solvent-based inks, and hot melt inks. The ink fluids may include colorants such as a dye or a pigment. The fluids also may not include any colorant. Other fluids compatible with the system may include polymer solutions, gel solutions, solutions containing particles or low molecular-weight molecules.

0026The hydrostatic pressure in fluid conduit 130, the ink reservoir 140, and ink passage 150 needs to be controlled for proper ink jet printing and head maintenance operations. Insufficient hydrostatic pressure at the ink jet nozzles 120 can cause the ink meniscus at the nozzles to retract within the ink jet nozzles 120. On the other hand, excessive hydrostatic pressure at the ink jet nozzles 120 can cause the ink to leak from the ink jet nozzles 120, producing ink spilling on the nozzle plate 121.

0027The pressure of air in the space 165 over the fluid in the ink reservoir 140 is typically controlled to keep the pressure at the nozzles slightly below atmospheric pressure (e.g. at - 1 inch to - 4 inches of water). The air pressure in the space 165 is regulated by an air pressure regulator 170 that can pump air from the space 165 under the control of the control unit 190.

0028The ink jet printing system 100 can also include a mechanism 185 that transports an ink receiver 180 along a direction 187. In one embodiment, the ink jet print head module 110 can move in reciprocating motion driven by a motor via an endless belt. The direction of the motion is often referred to as the fast scan direction. A second mechanism can transport the ink receiver 180 along a second direction (commonly referred as the slow scan direction) that is perpendicular to the first direction. During the ink jet printing operations, the ink jet print head module 110 disposes ink drops to form a swath of ink dots on the ink receiver 180. In another embodiment, a page-wide ink jet print head module 110 is formed by a print head bar or an assembly of print head modules. The ink jet print head module 110 remains still during printing while the ink receiving media is transported along the slow scan direction under the ink jet print head module 110. The ink jet system and methods are compatible with different print head arrangements known in the art. For example, the system and methods are applicable to a single pass ink jet printer with offset ink jet modules disclosed in the commonly assigned <patcit id="pcit0007" dnum="US5771052A"><text>US Patent 5,771,052</text></patcit>.

0029As described previously, the ink pressure in the ink conduit of an ink jet printing system is kept negative to keep the ink from spilling on the nozzle plate, especially during the high-acceleration movement of the inkjet print head. In addition, the ink nozzles are required to be primed by the ink fluid for proper ink drop ejection. Under certain system configurations and certain operating conditions, an operating pressure cannot be found at which the ink can be kept from spilling on the nozzle plate while keeping ink nozzles primed. Such a situation can occur when a print head needs to produce a large ink drop volume and to experience high-acceleration movement. The nozzle diameter needs to be large for the ejection of large ink drops. A large negative pressure is needed to keep the ink from spilling on the nozzle plate during acceleration or deceleration. But the nozzle opening prevents the ink from being primed the nozzles.

0030In one embodiment, the ink jet printing system 100 overcomes the above described problem by providing a large ink drop volume as well as the proper priming of the ink nozzles. An ink's ability to prime an opening such as an ink nozzle is determined by a property called bubble pressure. The bubble pressure is a function of the nozzle diameter (or opening dimensions) and the surface tension of the ink. As shown in Table I, the bubble pressure decreases as the nozzle diameter increases. When the magnitude of the negative pressure in the ink fluid is higher than the bubble pressure of a nozzle, the ink will pulled back from the nozzle. Air bubbles will be ingested into the ink body in fluid conduit 130. The nozzle is not properly primed. In other words, the magnitude of the negative ink pressure has to be smaller than the bubble pressure. <tables id="tabl0001" num="0001"><table frame="all"><title><b>Table I. Fluid Bubble Pressure * as a Function of the Orifice Diameter</b></title><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52mm" /><colspec colnum="2" colname="col2" colwidth="52mm" colsep="1" /><thead><row><entry align="center" valign="top"><b>Orifice Diameter (microns)</b></entry><entry align="center" valign="top"><b>Meniscus Pressure (inch wg)</b></entry></row></thead><tbody><row><entry align="center">30</entry><entry align="center">16.1</entry></row><row><entry align="center">40</entry><entry align="center">12.0</entry></row><row><entry align="center">50</entry><entry align="center">9.6</entry></row><row><entry align="center">60</entry><entry align="center">8.0</entry></row><row><entry align="center">70</entry><entry align="center">6.9</entry></row><row><entry align="center">80</entry><entry align="center">6.0</entry></row><row><entry align="center">90</entry><entry align="center">5.4</entry></row><row><entry align="center">100</entry><entry align="center">4.8</entry></row><row><entry align="center">110</entry><entry align="center">4.4</entry></row><row><entry align="center">120</entry><entry align="center">4.0</entry></row><row><entry align="center">130</entry><entry align="center">3.7</entry></row><row rowsep="1"><entry align="center">140</entry><entry align="center">3.4</entry></row></tbody></tgroup><tgroup cols="2" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52mm" /><colspec colnum="2" colname="col2" colwidth="52mm" /><tbody><row><entry namest="col1" nameend="col2" align="justify">* At ink surface tension of 30 dynes/cm.</entry></row></tbody></tgroup></table></tables>

0031In one aspect, the ink jet print head module 110 in ink jet printing system 100 provides ink nozzles having high bubble pressure while still being able to deliver large ink drop volume. In another aspect, the increase of drop volume and the decrease of the nozzle bubble pressure are decoupled.

0032In one embodiment, <figref idref="f0002">Figure 2A</figref> illustrates a top view of an ink nozzle 210 on the nozzle plate 121 compatible with the ink jet print head module 110. The ink nozzle 210 defines a nozzle region 220 comprising a group of orifices 230. In one implementation, the orifices 230 are disposed in a compact formation within a substantially circular area defined by the nozzle region 220. In one implementation, the orifices 230 in the group are in hexagon shape having substantially the same dimensions. Alternatively, the group of orifices may be of other shapes such as triangles, squares, or circles. The orifices in each group can be in the same or different dimensions. The nozzle region 220 typically spans in a range of 1 µm to 300 µm. The orifice opening dimensions are typical in the range from 1 µm to 100 µm, preferably in the range of 3 µm to 50 µm.

0033<figref idref="f0003">Figure 2B</figref> illustrates a cross-sectional view of the ink nozzle 210 of <figref idref="f0002">Figure 2A</figref> along the line of 2B-2B. The ink nozzle 210 is formed in a nozzle plate 215. The cross section of the ink nozzle 210 includes a group of orifices 230 separated by separation walls 235. The ink fluid is supplied from the fluid conduit 130 along the direction 240. Separate meniscuses 250 are formed in the orifices 230. In non-ejection states, the meniscuses 250 form concave shapes curving toward the direction of the fluid conduit 130 due to the negative pressure applied to the ink body. The negative ink pressure holds the ink meniscuses 250 at the inner ends of the ink orifices 230 and prevents the ink from spilling over the nozzle plate 215. Before ink ejection, an outward pressure wave is generated in the ink fluid by the ink actuator under the control of the control unit 190. The ink fluid is pushed outward along direction 260. The ejected ink fluid from separate orifices 230 merge to form a common ink surface 270 moving along an outward direction 280. An ink drop is then broken off which may finally land on an ink receiver 180. Thus, in this implementation, the ejected ink merges as it emerges from the different orifices 230.

0034In one implementation, the ink ejected from different orifices 230 can form separate ink drops in flight and merge together as an ink dot on the ink receiver 180. The location where ink mergers can depend on a number of factors such as the volume of the ink drops, the spacing between the orifices 230, and the waveform applied to the actuators by the control unit 190. As discussed below in relation to <figref idref="f0006 f0007">FIG. 4</figref>, the ink fluids ejected from orifices belonging to different nozzles cannot be merged before they arrive at the ink receiver 180 because a significantly longer distance between the orifices in neighboring nozzles.

0035In another implementation, the ink ejected from different orifices 230 can first form separate ink drops before merging into one or more ink drops in flight. The widths of the separation walls 235 are substantially equal or smaller than the widths of the fluid ejected from the orifices 230 such that the fluid ejected from the orifices 230 can be merged into a fluid drop. The merging of ink fluids can occur right after the ink fluids emerged from the orifices or "in flight" after individual ink drops have been formed in the air.

0036The orifices 230, the nozzle plate 215 and the fluid conduit 130 can be formed in a silicon substrate. The orifices are fabricated using one or more of etching, laser ablation, and electro forming. For example, fabrication techniques disclosed in commonly assigned <patcit id="pcit0008" dnum="US5265315A"><text>U.S. Patent 5,265,315</text></patcit>, <patcit id="pcit0009" dnum="US10189947B"><text>US Patent Application No. 10/189,947</text></patcit>, US Patent Publication No. <patcit id="pcit0010" dnum="US20040004649A1"><text>US20040004649A1</text></patcit>, titled "Printhead", filed on 7/3/2002, and <patcit id="pcit0011" dnum="US60510459B"><text>US Provisional Patent Application No. 60/510,459</text></patcit>, titled "Print head with thin membrane", filed 10/10/2003.

0037The bubble pressures in the ink nozzle 210 are determined by the ink surface tension and the dimensions of the orifices 230. The volume of the merged ink drop is determined by all the ink ejected collectively from several or all the orifices 230 in the nozzle region 220. In comparison, a large single-opening nozzle is required if the same ink drop is ejected from one nozzle having one opening. The bubble pressures of the orifices 230 can thus be significantly higher than the bubble pressure of the single-opening nozzle. The bubble pressures of the orifices 230 can be designed to be above a predetermined ink pressure. For example, as shown in Table 1, orifices at diameters of 50 µm or smaller can result in bubble pressures above 8 inch wg at a surface tension of 30 dyne/cm, no matter how large an ink drop is ejected. The volume of the merged ink drop can be flexibly increased by scaling up the number of the orifices 230. For a fixed group of orifices 230, the merged ink drop volume can also be varied by varying the waveforms applied to the ink actuator from the control unit 190.

0038In another embodiment, <figref idref="f0004">Figure 3A</figref> illustrates a top view of another implementation of an ink nozzle 310 compatible with the ink jet print head module 110. The ink nozzle 310 defines a nozzle region 320 comprising a first orifice 325 in the center and a plurality of second orifices 330 surrounding the first orifice 325. The orifices 325, 330 are disposed in a compact formation within a substantially circular area defined by the nozzle region 320. The orifices 325 and 330 can take the shape of hexagons, triangles, a square, a circle, or a polygon, etc. The orifices 330 can have substantially the same dimensions whereas the orifice 325 has a wider dimension. The nozzle region 220 typically spans in a range of 1 µm to 300 µm. The orifice opening dimensions are typically in the range of 1 µm to 100 µm, preferably in the range of 3 µm to 50 µm.

0039<figref idref="f0005">Figure 3B</figref> illustrates a cross-sectional view of the ink nozzle 310 of <figref idref="f0004">Figure 3A</figref> along 3B-3B. The ink nozzle 310 is formed in a nozzle plate 315. The cross section of the ink nozzle 310 includes the orifice 325 and orifices 330 separated by separation walls 335. The ink fluid is supplied from the fluid conduit 130 along the direction 340. In non-ejection states, separate meniscuses 350 and 355 are formed in the orifice 325 and orifices 330. The meniscuses 350 and 355 are in concave shapes curving toward the direction of the fluid conduit 130 as a result of the negative pressure applied to the ink body. The negative ink pressure holds the ink meniscuses 350, 355 at the inner ends of the ink orifices 325, 330 and prevents the ink from spilling over the nozzle plate 315. Before ink ejection, an outward pressure wave is generated in the ink fluid by the ink actuator under the control of the control unit 190. The ink fluid is pushed outward along direction 360. The ejected ink fluid from separate ink orifices 325, 330 merge to form a common ink surface 370 moving along an outward direction 380. An ink drop is then broken off which may finally land on an ink receiver 180.

0040In one implementation, the ink ejected from different orifices 325 and 330 can first form separate ink drops while emerging before merging into one or more ink drops in flight or on the ink receiver 180. In another implementation, the widths of the separation walls 335 are substantially equal or smaller than the widths of the fluid ejected from the orifices 325 and 330 such that the fluid ejected from the orifices 325 and 330 can be merged into a fluid drop.

0041The wider orifice 325 serves several functions in comparison to the ink nozzle 210 in which the orifices are substantially equal. First, the orifice 325 produces a larger ejected ink fluid in the center of the nozzle region 320, which better defines the symmetric direction of the merged ink drop. Second, the orifice 325 has a lower bubble pressure than those of orifices 330. The waveform applied to the ink actuator by the control unit 190 can thus be manipulated so that ink is ejected only from the orifice 325 but not from orifices 330. The ability to eject a smaller ink drop is very desirable especially for high-resolution ink printing applications.

0042The orifices 325 and 330 of different dimensions and the nozzle plate 315 can be formed in a silicon substrate. The orifices are fabricated using one or more of etching, laser ablation, and electroforming. For example, fabrication techniques disclosed in commonly assigned <patcit id="pcit0012" dnum="US5265315A"><text>U.S. Patent 5,265,315</text></patcit>, <patcit id="pcit0013" dnum="US10189947B"><text>US Patent Application No. 10/189,947</text></patcit>, US Patent Publication No. <patcit id="pcit0014" dnum="US20040004649A1"><text>US20040004649A1</text></patcit>, titled "Printhead", filed on 7/3/2002, and <patcit id="pcit0015" dnum="US60510459B"><text>US Provisional Patent Application No. 60/510,459</text></patcit>, titled "Print head with thin membrane", filed 10/10/2003.

0043In one implementation, the print head can include a plurality of ink nozzles 410, 450 each comprising groups of orifices 430, 470 on a nozzle plate 400 as shown in <figref idref="f0006">FIG 4A</figref>. The ink nozzle 410 includes a group of ink orifices 430 distributed in a nozzle region 420. Similarly, the ink nozzle 450 includes a group of ink orifices 470 disposed in a nozzle region 460. The nozzle regions 420, 460 can be generally circular.

0044The spacing between adjacent ink nozzles 410, 450 is significantly larger than the distances between neighboring ink orifices 430, 470 within each nozzle group, which enables the merging of ejected ink from different orifices within a nozzle group. In contrast, the ink fluids ejected from different nozzles can merge before they arrive at the ink receiver 180 because the larger distance between adjacent nozzles than the distances between the adjacent orifices within the same nozzle. The ink nozzles 410, 450 can form linear arrays or other patterns for effective depositions of ink drops. The nozzles in linear arrays can be aligned orthogonal or oblique to the fast scan direction of the printhead module 110 relative to the ink receiver 180. Different ink nozzles each comprising groups of orifices can be optimized to be suitable for ejecting ink drops of different volumes.

0045Fluid conduits 440, 480, formed in a silicon body 405, provide the ink to the nozzles 410, 450, respectively. Each fluid conduit 440, 480 can have its own associated actuator 445, 485, respectively, such that fluid in one of the conduits 440, 480 can be independently ejected from the associated nozzle 410, 450. As illustrated, all of the orifices defining a particular nozzle are fluidly coupled to the same conduit, but each particular nozzle has its own conduit. Alternatively, two or more nozzles from a plurality of nozzles could be fluidly coupled to a common conduit with a common actuator. As yet another alternative, some orifices from the group of orifices that form a nozzle could be connected to a different conduits with separate actuators. In this case, the action of the actuators could be coordinated by the controller to cause the actuators associated with a given nozzle to fire simultaneously so as to cause the ink emerging from the orifices to merge into a fluid drop.

0046A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the invention. Accordingly, other embodiments are within the scope of the following claims.