Reference is made to commonly-assigned, U.S. patent applications Ser. No. 12/767,833, entitled “PRINTHEAD INCLUDING SECTIONED STIMULATOR/FILTER DEVICE”, Ser. No. 12/767,840, entitled “PRINTHEAD STIMULATOR/FILTER DEVICE PRINTING METHOD”, Ser. No. 12/767,836, entitled “STIMULATOR/FILTER DEVICE THAT SPANS PRINTHEAD LIQUID CHAMBER”, all filed concurrently herewith.
This invention relates generally to the field of digitally controlled printer systems and in particular, to the stimulation and filtering of liquids that are subsequently emitted through a nozzle of a printhead of the system.
Traditionally, digitally controlled color printing capability is accomplished by one of two technologies Ink is fed through channels formed in the printhead. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited upon a medium. Typically, each technology requires separate ink delivery systems for each ink color used in printing. Ordinarily, the three primary subtractive colors, i.e. cyan, yellow and magenta, are used because these colors can produce, in general, up to several million shades or color combinations.
The first technology, commonly referred to as “droplet on demand” ink jet printing, selectively provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of an ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle helping to keep the nozzle clean.
Conventional droplet on demand ink jet printers utilize a heat actuator or a piezoelectric actuator to produce the ink jet droplet at orifices of a print head. With heat actuators, a heater, placed at a convenient location, heats the ink to cause a localized quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, a mechanical force causes an ink droplet to be expelled.
The second technology, commonly referred to as “continuous stream” or simply “continuous” ink jet printing, uses a pressurized ink source that produces a continuous stream of ink droplets. Traditionally, the ink droplets are selectively electrically charged. Deflection electrodes direct those droplets that have been charged along a flight path different from the flight path of the droplets that have not been charged. Either the deflected or the non-deflected droplets can be used to print on receiver media while the other droplets go to an ink capturing mechanism (catcher, interceptor, gutter, etc.) to be recycled or disposed. U.S. Pat. No. 1,941,001, issued to Hansell, on Dec. 26, 1933, and U.S. Pat. No. 3,373,437 issued to Sweet et al., on Mar. 12, 1968, each disclose an array of continuous ink jet nozzles wherein ink droplets to be printed are selectively charged and deflected towards the recording medium.
In another form of continuous ink jet printing, for example, as described in U.S. Pat. No. 6,491,362 B1, issued to Jeanmaire, on Dec. 10, 2002, commonly assigned, included herein by reference, stimulation devices are associated with various nozzles of the printhead. These stimulation devices perturb the liquid streams emanating from the associated nozzle or nozzles in response to drop formation waveforms supplied to the stimulation devices by control means. The perturbations initiate the separation of a drop from the liquid stream. Different waveforms can be employed to create drops of a plurality of drop volumes. A controlled sequence of waveforms supplied to the stimulation device yields a sequence of drops, whose drop volumes are controlled by the waveforms used. A drop deflection device applies a force to the drops to cause the drop trajectories to separate based on the size of the drops. Some of the drop trajectories are allowed to strike the print media while others are intercepted by a catcher or gutter.
While conventional thermal stimulation devices are effective in initiating the break off of drops from the liquid streams, the stimulation amplitudes can be relatively low. Under certain conditions it is desirable to employ higher stimulation amplitudes. As such, there is an ongoing need for a thermal stimulation actuator capable of providing higher stimulation amplitudes that is suitable for use in a continuous printer system.
According to an aspect of the present invention, a jetting module includes a nozzle plate, a thermal stimulation membrane, and an enclosure. Portions of the nozzle plate define a nozzle. The thermal stimulation membrane includes a plurality of pores. At least one of the plurality of pores overlaps the nozzle when viewed from a direction through the nozzle. The enclosure includes a wall that extends from the nozzle plate to the thermal stimulation membrane to define a liquid chamber positioned between the nozzle plate and the thermal stimulation membrane. The liquid chamber is in fluid communication with the nozzle. The liquid chamber is in fluid communication with the plurality of pores of the thermal stimulation membrane.
According to another aspect of the present invention, a printhead includes a jetting module and a liquid source. The jetting module includes a nozzle plate, a thermal stimulation membrane, and an enclosure. Portions of the nozzle plate define a nozzle. The thermal stimulation membrane includes a plurality of pores. At least one of the plurality of pores overlaps the nozzle when viewed from a direction through the nozzle. The enclosure includes a wall that extends from the nozzle plate to the thermal stimulation membrane to define a liquid chamber positioned between the nozzle plate and the thermal stimulation membrane. The liquid chamber is in fluid communication with the nozzle. The liquid chamber is in fluid communication with the plurality of pores of the thermal stimulation membrane. The liquid source provides a liquid under pressure sufficient to jet an individual stream of the liquid from the nozzle of the jetting module.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
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 inkjet printing systems. However, many other applications are emerging which use inkjet 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
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 is 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 which is described in more detail below with reference to
Referring to
Liquid, for example, ink, is emitted under pressure through each nozzle 50 of the array to form streams 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 (shown
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 is typically approximately an integer between 2 and 10. A drop stream 58 including drops 54, 56 follows a drop path or trajectory 57.
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
When catcher 42 is positioned to intercept large drop trajectory 68, small drops 54 are deflected sufficiently to avoid contact with catcher 42 and strike the print media. As the small drops are printed, this is called small drop print mode. When catcher 42 is positioned to intercept small drop trajectory 66, large drops 56 are the drops that print. This is referred to as large drop print mode.
Referring to
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 the stream of liquid 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 duct 78 is connected to a negative pressure source 94 that is used to help remove gas flowing through second 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
Different methods known in the art can be employed to produce components within a printhead 30. Some techniques that are employed to form micro-electro-mechanical systems (MEMS) can also be employed to form components of printhead 30. MEMS fabrication processes typically include modified semiconductor device fabrication technologies. MEMS fabrication techniques also typically combine photo-imaging techniques with etching techniques to form features in a substrate. The photo-imaging techniques are employed to define desired regions of a substrate that are to be etched from other regions of the substrate that should not be etched. MEMS fabrication techniques can be employed to produce nozzle plate 49 along with other printhead elements such as ink feed channels, ink reservoirs, electrical conductors, electrodes and insulator and dielectric components.
Nozzle plate 49 is formed from a substrate 85 using MEMS fabrication techniques. Silicon-based substrates are typically employed for this application because of their relatively low cost, their generally defect-free compositions, and due to the highly developed fabrication processes that have been developed for it. A printhead element can be formed from a single component substrate or a multi-component substrate. In some example embodiments, an employed substrate includes a single material layer, while in other example embodiments the employed substrate includes a plurality of material layers. The printhead element can be formed from a substrate which includes at least one material layer formed by a deposition process, or that includes at least one material layer applied by a lamination process.
In this example embodiment, features such as nozzles 50 and liquid chambers 53 are formed in substrate 85 by an etching process. The etching process includes forming a patterned mask (not shown) on a surface of substrate 85. The patterned mask can be formed by a photolithography process. The patterned mask is typically formed from a photo-imageable polymeric material layer known as a photoresist. Suitable photoresists can include liquid photoresists and dry film photoresists. Uniform coatings of liquid photoresists can be applied to a surface of substrate 85 by methods including spin coating by way of non-limiting example. Dry-film photoresists usually include an assemblage comprising a backing layer and a resist layer. The assemblage is laminated to a surface of substrate 85 and the backing layer is removed while leaving the resist layer in contact with substrate 85.
Regardless of the form that the photoresist takes, it is patterned to define the regions of the substrate 85 that should be substantially etched and other regions of substrate 85 that should not be substantially etched. In example embodiments employing photoresists, these regions can be defined by exposing the photoresist to radiation so as to pattern it. The photoresist can be patterned by radiation that is image-wise conditioned by an auxiliary mask or the photoresist can be patterned directly by one or more radiation beams that are selectively controlled to expose specific regions of the photoresist. The type of radiation that is employed is typically motivated by the composition of the photoresist and can include ultra-violet radiation by way of non-limiting example. The photoresist can undergo additional chemical development steps, and heat treatment steps to form a patterned mask.
Once a patterned mask has been formed, elements such as nozzles 50 are formed by exposing portions of substrate 85 to a suitable etchant though openings in the patterned mask. Without limitation, etching processes suitable for forming elements in printhead 30 can include wet chemical etching processes, vapor etching processes, inert plasma etching processes and chemically reactive plasma etching processes.
Nozzles 50 and liquid chambers 53 can be formed in separate etching processes. For example, both nozzles 50 and liquid chambers 53 can be formed by etching a same surface of substrate 85. Alternatively, different surfaces of substrate 85 can be etched. The different surfaces can include opposing surfaces of substrate 85 by way of example. Different layers of material can be deposited between etching steps.
Each of the liquid chambers 53 is formed from an enclosure whose sidewalls diverge as the enclosure extends away from an associated one of the nozzles 50. Sloped sided structures such as the illustrated liquid chambers 53 can be formed by processes including anisotropic etching techniques. Unlike isotropic etching processes, different etch rates along different directions are associated with anisotropic etching processes. Silicon is an example of a single crystal material that exhibits preferential etching characteristics along crystal planes in the presence of certain chemicals such as potassium hydroxide (KOH). For example, when an opening is etched in a <100> silicon substrate 85, the <111> crystal plane sidewalls of the substrate 85 will be exposed, thereby rendering the opening with sloped or diverging sidewalls.
Referring back to
Thermal stimulation membrane 100 can include various material layers and can be formed by various suitable techniques including MEMS fabrication techniques. In this example embodiment, thermal stimulation membrane 100 includes a plurality of insulator material layers 105A and 105B and a resistive material layer 115. Insulator material layers 105A and 105B and resistive material layer 115 can be formed by any suitable process including by deposition or lamination methods as provided by MEMS fabrication techniques. Features in insulator material layers 105A and 105B and resistive material layer 115 can be formed by any suitable process including photolithography and material deposition or etching techniques as provided by MEMS fabrication techniques. Resistive material layer 115 can include materials suitable for use in resistive heating applications. For example, tantalum silicon nitride (TaSiN) is a material employed in resistive heating applications. Insulator material layers 105A and 105B can be formed by various techniques including the use of tetraethyl orthosilicate (TEOS). The present invention is not however limited to these materials and can readily employ other suitable materials having the required resistive or insulator properties as the case may be.
Pores 110 allow for fluid communication between channel 47 and liquid channels 53. The pores 110 can be arranged in either a regular or random pattern. Pores 110 are grouped together in sets 120, each set 120 corresponding to a different one of the fluid chambers 53. All the liquid 52 entering a given one of the liquid chambers 53 passes through the pores 110 in the set 120 that span the liquid chamber 53. At least one of the pores 110 overlaps a nozzle 50 when viewed from a direction of fluid flow through the nozzle. The walls of the pores 110 include insulator material layers 105A and 105B. Insulator material layer 105A includes a planar surface positioned to intercept a direction of flow of liquid 52 through thermal stimulation membrane 100 from channel 47.
Thermal actuators 150 include one or more resistive heating elements 155 located in resistive material layer 115. As shown in
The drop generator assembly including the nozzles 50, the fluid chambers 53, and the thermal stimulation membrane 100 can be fabricated using any suitable technique. For example, the nozzles 50 and the fluid chambers 53 can be fabricated in substrate 85, as described previously. The fluid chambers can then be filled with a sacrificial material. The layers to form the thermal stimulation membrane can then be formed by appropriate deposition processes, after which the sacrificial material is removed.
Alternatively one can start by forming the thermal stimulation membrane on a substrate. Deposition processes can then be used to form the walls of the fluid chambers 53. The fluid chambers can then be filled with a sacrificial material. The layer that includes the nozzles can then be deposited onto the chamber walls and the sacrificial material. The sacrificial material can then be removed from the fluid chambers. The substrate upon which this structure was formed can then be etched from the back side to form the channel 47 that supplied fluid to the thermal stimulation membrane 100. This process can also be used to create walls that extend beyond the thermal stimulation membrane 100 and then into channel 47. When this is done, liquid chamber 53 can be referred to as a first liquid chamber with the walls that extend beyond the thermal stimulation membrane 100 defining a second liquid chamber. The thermal stimulation membrane 100 is suspended between the first liquid chamber 53 and the second liquid chamber.
A drop forming device control circuit 26 is associated with each nozzle 50 since each nozzle 50 is selectively controlled to form combinations of drops comprising different characteristics. In other example embodiments in which each nozzle 50 is employed to provide a uniform stream of drops including substantially constant characteristics (e.g. a substantially constant volume), a single drop forming control circuit 26 can be employed.
Portions of liquid 52 are subjected to the pulses of thermal energy as they travel through their respective pores 110. These portions of liquid 52 subsequently combine to form a liquid thermal layer 170 within liquid chamber 53. Accordingly, different liquid thermal layers 170 can be formed within liquid chamber 53 in accordance with the characteristics of the electrical pulses that are provided to thermal stimulation membrane 100. Factors such as the duration and the voltage of the electrical pulses can be adjusted to create a plurality of liquid thermal layers 170 in which one or more of the liquid thermal layers 170 have different characteristics than others of the liquid thermal layers 170. Different characteristics can include different amounts of thermal energy, different temperatures, velocities, pressures, different densities, viscosities, surface tensions, or combination of these characteristics by way of non-limiting example. In
As shown in
While conventional thermal stimulation techniques using a heater embedded in the nozzle plate adjacent to the nozzles have been effective in controlling the formation of drops, the amount of heat that can be transferred to the fluid, and therefore the stimulation amplitude are limited. The present invention, which locates portions of the heater adjacent to a plurality of pores in the thermal stimulation membrane is able to more effectively transfer heat to the fluid, and therefore more effectively stimulate the formation of drops from the stream of liquid flowing from the nozzle.
Thermal actuators 150 can take various forms in the present invention. For example,
The resistive heating element 155 comprises a single element with a plurality of openings 156, each opening corresponding to one of the pores 110. Conductors 165 made from an electrically conductive material (e.g. aluminum) are arranged to provide the pulses of electrical energy to resistive heating element 155 as provided by drop forming device control circuit 26 (not shown in
Each of the resistive heating elements 155B is connected to a common set of conductors 165 adapted to distribute an electrical energy pulse to each of the resistive heating elements 155B. In other embodiments, one or more of the resistive heating elements 155B can be connected to different sets of one or more conductors 165, each set of conductors 165 being adapted to distribute electrical energy pulses having different characteristics to their respective resistive heating elements 155B. Different characteristics of the electrical energy pulses can include different pulse-widths, pulse voltages and pulse timings by way of non-limiting example. In this manner, different thermal characteristics can be selectively imparted to different portions of liquid 52 as they flow through their respective pores 110. For example, pulse delay timings may be employed to cause different portions of liquid 52 to be heated at slightly different times. The delays may be desired for different reasons including to account for possible different flow characteristics or different flow paths of outboard portions of liquid 52 as compared to inboard portions of liquid 52 in fluid chamber 53. Alternatively, deflection of the subsequently formed stream of liquid 52 can be accomplished by applying heat asymmetrically to portions of liquid 52 entering liquid chamber 52. When used in this capacity, the present invention operates as the drop forming device in addition to a deflection mechanism. This type of drop formation and deflection is known having been described in, for example, U.S. Pat. No. 6,079,821, issued to Chwalek et al., on Jun. 27, 2000.
Another example embodiment is shown in
The example embodiments of the invention increase the transfer of heat to the liquid 52 that is stimulated to eventually form a stream of drops when jetted from nozzle 50. This is accomplished by employing the plurality of pores 110 to divide liquid 52 into numerous small portions and by transferring thermal energy to these portions as they flow through their respective pores 110. It is understood that additional and/or alternate components can be employed to further enhance the workings of the present invention. For example, the path traveled by liquid 52 through any of the pores 110 should be kept short to avoid excessive pressure losses. This can lead to a relatively thin thermal stimulation membrane 100 that may not be well suited to withstanding the high fluid pressures associated with the continuous printer systems. Accordingly, support features (not shown) can be provided. Support features can be formed in substrate 85 or other members. Additional components comprising cooling, heat dissipation or heat sink properties (not shown) can be formed to dissipate residual heat in thermal stimulation membrane 100, as described, for example, in US 2008/0043062 for use with thermal stimulator devices located in the nozzle plate around the nozzle.
The plurality of pores 110 can include pores of different sizes. In some example embodiments, the plurality of pores 110 have more than one pore dimension. Some of the pores 110 can be employed for alternate and/or additional functions. For example, a set 120 of pores 110 can include at least one pore 110 that is adapted for filtering particulate matter from liquid 52 without serving to couple heat into the fluid passing through the pore. Such pores would not have any resistive material located on any side. The size of the at least one pore 110 can vary in accordance with a measured or predicted size of particulate matter within liquid 52. The number of pores 110 employed can be tailored to account for the flow impedance through the pores 110 and therefore the pressure drop across the thermal stimulation membrane 100 and the quantity of liquid 52 that is desired to be thermally stimulated. Combining stimulation and filtration function as per the example embodiments of the invention can simplify the manufacture of a continuous printer system printhead.
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.
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