FIELD OF THE INVENTION

This invention relates generally to the field of digitally controlled liquid dispensing devices and, in particular, to liquid dispensing devices that include a flexible membrane.

BACKGROUND OF THE INVENTION

Inkjet 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. Inkjet printing mechanisms can be categorized by technology as either drop on demand ink jet (DOD) or continuous ink jet (CD).

Continuous inkjet printing uses a pressurized liquid source that produces a stream of drops some of which are selected to contact a print media (often referred to a "print drops") while other are selected to be collected and either recycled or discarded (often referred to as "non-print drops"). For example, when no print is desired, the drops are deflected into a capturing mechanism (commonly referred to as a catcher, interceptor, or gutter) and either recycled or discarded. When printing is desired, the drops are not deflected and allowed to strike a print media. Alternatively, deflected drops can be allowed to strike the print media, while non-deflected drops are collected in the capturing mechanism.

Drop on demand printing only provides drops (often referred to a "print drops") for impact upon a print media. Selective activation of an actuator causes the formation and ejection of a drop that strikes the print media. The formation of printed images is achieved by controlling the individual formation of drops. Typically, one of two types of actuators is used in drop on demand printing devices - heat actuators and piezoelectric actuators. When a piezoelectric actuator is used, an electric field is applied to a piezoelectric material possessing properties causing a wall of a liquid chamber adjacent to a nozzle to be displaced, thereby producing a pumping action that causes an ink droplet to be expelled. When a heat actuator is used, a heater, placed at a convenient location adjacent to the nozzle, heats the ink. Typically, this causes a quantity of ink to phase change into a gaseous steam bubble that displaces the ink in the ink chamber sufficiently for an ink droplet to be expelled through a nozzle of the ink chamber.

In some applications it may be desirable to use an ink that is not aqueous and, as such, does not easily form a vapor bubble under the action of the heater. Heating some inks may cause deterioration of the ink properties, which can cause reliability and quality issues. As described in US Patent No. 4,480,259 and US Patent No. 6,705, 716, one solution is to have two fluids in the print head with one fluid dedicated to respond to an actuator, for example, to create a vapor bubble upon heating, while the other fluid is the ink. The performance capabilities of these types of print heads is often limited due to the resistance of the membrane or diaphragm that separates the actuator fluid from the ink which reduces the amount of volumetric displacement that occurs in ink chamber as a result of the pressure caused by the vaporization of the actuator fluid.

Although US Patent No. 4,480,259 and US Patent No. 6,705, 716 both describe flexible diaphragms, it is well understood by one skilled in the art that it is difficult to manufacture a micro-fluidics device such as an ink jet print head using conventional MEMS technology while incorporating a sufficiently elastic material for use as a diaphragm. Additionally, repeated cycles of stretch and relax cause material fatigue in the diaphragm resulting in reduced device reliability and poor device performance.

As such, there is an ongoing effort to increase the reliability and performance of print heads that include two fluids and a flexible membrane.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a liquid dispenser includes a first liquid chamber and a second liquid chamber. The first liquid chamber includes a nozzle. A liquid supply channel is in fluid communication with the second chamber. A liquid return channel is in fluid communication with the second chamber. A heater is associated with the second liquid chamber. A flexible membrane is positioned to separate and fluidically seal the first liquid chamber and the second liquid chamber relative to each other. A liquid supply provides a liquid that flows continuously from the liquid supply through the liquid supply channel through the second liquid chamber through the liquid return channel and back to the liquid supply.

According to another aspect of the present invention, a method of printing includes providing a liquid dispenser made in accordance with the invention described herein and using it to dispense liquid drops.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:

Figure 1 is a schematic cross sectional view of an example embodiment of a liquid dispenser made in accordance with the present invention;

Figure 2 is a schematic cross sectional view of the example embodiment shown in Figure 1 in an actuated state;

Figure 3 is a schematic top view of an example embodiment of a heater included in an example embodiment of a liquid dispenser made in accordance with the present invention;

Figure 4 is a schematic cross sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention;

Figure 5 is a schematic cross sectional view of another example embodiment of a liquid dispenser made in accordance with the present invention;

Figures 6A-6C are schematic top views of example embodiments of flexible membranes included in example embodiments of liquid dispensers made in accordance with the present invention; and

Figure 7A-7C are schematic cross sectional and top views of example embodiments of flexible membranes included in example embodiments of liquid dispensers made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

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 liquid dispenser, often referred to as a print head, which is particularly useful in digitally controlled inkjet printing devices in which drops of ink are ejected from a print head toward a print medium. However, many other applications are emerging which use liquid dispensers, similar to inkjet print heads, 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" are used interchangeably and refer to any material, not just inkjet inks, which can be ejected by the example embodiments of the liquid dispenser described below.

In addition to inkjet printing applications in which the fluid typically includes a colorant for printing an image, the liquid dispenser of the present invention is also advantageously used in ejecting other types of fluidic materials. Such materials include functional materials for fabricating devices (including conductors, resistors, insulators, magnetic materials, and the like), structural materials for forming three-dimensional structures, biological materials, and various chemicals. The liquid dispenser of the present invention provides sufficient force to eject fluids having a higher viscosity than typical inkjet inks, and does not impart excessive heat into the fluids that could damage the fluids or change their properties undesirably.

Referring to Figure 1, a liquid dispenser 100 including a membrane MEMS actuator is shown. Liquid dispenser 100 includes a first liquid chamber 111 and a second liquid chamber 112. A flexible membrane 140 is positioned in liquid dispenser 100 to separate and fluidically seal the first liquid chamber 111 and the second liquid chamber 112. As shown in Figure 1, flexible membrane 140 is corrugated when flexible membrane 140 is in an unactuated position or state (often referred to as an at rest position or state). The overall shape of fiexible membrane 140 is planar when viewed, as shown in Figure 1, from end to end of flexible membrane 140. First liquid chamber 111 includes a nozzle 120.

Liquid dispenser 100 includes a selectively actuatable thermal actuator that uses heat energy to divert a portion of a liquid (often referred to as a first liquid) located in first liquid chamber 111 through nozzle 120. The thermal actuator includes a heater in one example embodiment of the invention that is commonly referred to as a "bubble jet" heater. When selectively actuated, the heat generated by this type of thermal actuator vaporizes a portion of a liquid (often referred to as a second liquid) in the vicinity of the actuator creating a vapor bubble 160 (shown in Figure 2) which causes the first liquid to the ejected through nozzle 120.

Referring back to Figure 1, a heater 130 is associated with second liquid chamber 112. Heater 130 is located in a wall of the second liquid chamber

112 opposite flexible corrugated membrane 140. As shown in Figure 1, heater 130 is a "bubble jet" type heater. A center axis A-A' extends through the center of nozzle 120. Nozzle 120 includes a center point, heater 130 includes a center point, and fiexible corrugated membrane 140 includes a center point. As shown in Figure 1, the center points of nozzle 120, heater 130, and flexible corrugated membrane 140 are collinear relative to each other and located on center axis A-A'. The overall shape of flexible membrane 140 is symmetric relative to center axis A-A' when viewed, as shown in Figure 1, from end to end of flexible membrane 140.

First chamber 111 is adapted to receive a liquid that is supplied to first chamber 111 in a conventional manner. Second chamber 112 is adapted to receive a liquid that is supplied to second chamber 112 in a conventional manner or in a manner according to one aspect of the present invention (described in more detail below). As flexible membrane 140 fluidically seals first chamber 111 and second chamber 112 from each other, first chamber 111 and second chamber 112 are physically distinct from each other which allows the first liquid and the second liquid present in each respective chamber to be different types of liquid when compared to each other in example embodiments of the invention.

Referring to Figure 2, a portion of a liquid (often referred to as a second liquid) located in second liquid chamber 112 is vaporized, forming a vapor bubble 160, when electric energy is applied to heater 130. The pressure resulting from the expanding vapor bubble 160 pushes flexible corrugated membrane 140 toward nozzle 120 (up as shown in Figure 2) and causes flexible corrugated membrane 140 to bend and straighten. This can also be referred to as an actuated position or state of flexible membrane 140. The displacement of the flexible corrugated membrane 140 pressurizes a liquid (often referred to as a first liquid) located in first liquid chamber 111 causing a liquid drop 170 to be ejected through nozzle 120.

Referring to Figure 3, heater 130 includes a split heater structure as viewed along the direction of center axis A-A'. The split heater 130 includes two halves 130a and 130b symmetrically positioned relative to a plane B-B' that includes the center point 135 of the heater 130. Vapor bubble 160 is shown in Figure 3 as concentric rings. The split heater configuration allows vapor bubble 160 to collapse at the center point 135 of the heater 130, reducing or even avoiding cavitation damage to the heater. Other heater 130 structures or configurations can be included in alternative example embodiments of the invention.

Referring to Figure 4, a liquid dispenser 200 including a circulating working fluid is shown. Liquid dispenser 200 includes a first liquid chamber 211 that is in fluid communication with a nozzle 220. A heater 230 is associated with a second liquid chamber 212. A flexible membrane 241 is positioned to separate and fluidically seal the first liquid chamber 211 and the second liquid chamber 212 from each other. A thermal actuator, for example, a heater 230, is located in a wall of second liquid chamber 212 opposite flexible membrane 241.

As described above and shown in Figure 4, flexible membrane 241 is corrugated when in an unactuated or at rest position. The overall shape of flexible membrane 241 is planar when viewed from end to end of flexible membrane 241. The overall shape of flexible membrane 241 is symmetric relative to center axis A- A' when viewed, as shown in Figure 1, from end to end of flexible membrane 241. A center point of nozzle 220, heater 230, and flexible membrane 241 are collinear relative to each other and located along center axis A- A' that extends through the center of nozzle 220.

A liquid supply channel 251 is in fluid communication with second chamber 212 and a liquid return channel 252 is in fluid communication with second chamber 212. Liquid supply channel 251 and liquid return channel 252 are also in fluid communication with a liquid supply 255. During a drop ejection or dispensing operation, liquid supply 255 provides a liquid (commonly referred to as a working fluid or a working liquid) that flows continuously from liquid supply 255 through liquid supply channel 251 through second liquid chamber 212 through liquid return channel 252 and back to liquid supply 255. The circulating working fluid helps to increase the drop ejection frequency by removing at least some of the heat generated by heater 230 when it is actuated during drop ejection. The circulating working fluid can help increase the drop ejection frequency by pushing at least some of vapor bubble 160 off of and away from the heater 230 area as vapor bubble 160 collapses or increasing the speed of liquid replenishment relative to heater 230. As shown in Figure 4, the liquid moves over heater 230.

Typically, liquid is supplied to first chamber 211 in a manner similar to liquid chamber refill in a conventional drop on demand device. For example, during a drop dispensing operation using liquid dispenser 200, the liquid is not continuously flowing to first chamber 211 during a drop ejection or dispensing operation. Instead, first chamber 211 is refilled with liquid on an as needed basis that is made necessary by the ejection of a drop of the liquid from first chamber 211 through nozzle 220.

Typically, a regulated pressure source 257 is positioned in fluid communication between liquid supply 255 and liquid supply channel 251.

Regulated pressure source 257, for example, a pump, provides a positive pressure that is usually above atmospheric pressure. Optionally, a regulated vacuum supply 259, for example, a pump, can be included in order to better control liquid flow through second chamber 212. Typically, regulated vacuum supply 259 is positioned in fluid communication between liquid return channel 252 and liquid supply 255 and provides a vacuum (negative) pressure that is below atmospheric pressure. Liquid supply 255, regulated pressure source 257, and optional regulated vacuum supply 259 can be referred to as the liquid delivery system of liquid dispenser 200.

In one example embodiment, liquid supply 255 applies a positive pressure provided by a positive pressure source 257 at the entrance of liquid supply channel 251 and a negative pressure (or vacuum) provided by a negative pressure source 259 at the exit of liquid return channel 252. This helps to maintain the pressure inside second liquid chamber 212 at substantially the same pressure (for example, ambient pressure conditions) at the exit of nozzle 220 when the heater 230 is not energized. As a result, flexible membrane 241 is not deflected during a time period of drop dispensing when the heater 230 is not energized.

A high degree of flexibility in flexible membrane 241 is preferred to effectively transmit the pressure generated by vapor bubble 160 in the working fluid (a second liquid) to the fluid or liquid of interest (a first liquid), for example, ink, located in first chamber 211. In one example embodiment of the invention, this aspect of the invention is achieved by incorporating a corrugated shape in a high modulus material membrane. The corrugated membrane can be made out of high modulus materials such as alloys, metals, or dielectric materials, to meet fabrication requirements of mechanic strength, durability, or thinness of the flexible membrane. These types of relatively strong materials may not have a high degree of elasticity, but the effect of the corrugation helps to greatly increase the membrane flexibility without requiring the use of an elastic material when compared to non-corrugated membranes.

As flexible membrane 241 fiuidically seals first chamber 211 and second chamber 212 from each other, first chamber 211 and second chamber 212 are physically distinct from each other which allows the first liquid and the second liquid present in each respective chamber to be different types of liquid when compared to each other in example embodiments of the invention. For example, the second liquid can include properties that increase its ability to remove heat while the second liquid can be an ink. The second liquid can include properties that lower its boiling point when compared to the first liquid. The second liquid can include properties that make it a non-corrosive liquid, for example, nonionic liquid, in order to improve and maintain the functionality of heater 230 or increase its lifetime.

Referring to Figure 5, another example embodiment of a liquid dispenser 200 including a circulating working fluid is shown. In this example embodiment, liquid dispenser includes a flexible membrane 240 that includes no corrugation when flexible membrane 240 is in an unactuated or at rest position. In this sense, flexible membrane is flat. The overall shape of flexible membrane 240 is planar when viewed from end to end of flexible membrane 240. The overall shape of flexible membrane 240 is symmetric relative to center axis A- A' when viewed, as shown in Figure 1, from end to end of flexible membrane 240. Center points of nozzle 220, heater 230, and flexible membrane 240 are collinear relative to each other and are located along center axis A- A' that extends through the center of nozzle 220.

A liquid supply channel 251 is in fluid communication with second chamber 212 and a liquid return channel 252 is in fluid communication with second chamber 212. Liquid supply channel 251 and liquid return channel 252 are also in fluid communication with a liquid supply 255. During a drop ejection or dispensing operation, liquid supply 255 provides a liquid (commonly referred to as a working fluid or a working liquid) that flows continuously from liquid supply 255 through liquid supply channel 251 through second liquid chamber 212 through liquid return channel 252 and back to liquid supply 255. The circulating working fluid helps to increase the drop ejection frequency by removing at least some of the heat generated by heater 230 when it is actuated during drop ejection. The circulating working fluid can help increase the drop ejection frequency by pushing at least some of vapor bubble 160 off of and away from the heater 230 area as vapor bubble 160 collapses or increasing the speed of liquid replenishment relative to heater 230. As shown in Figure 5, the liquid moves over heater 230.

Typically, a regulated pressure source 257 is positioned in fluid communication between liquid supply 255 and liquid supply channel 251.

Regulated pressure source 257, for example, a pump, provides a positive pressure that is usually above atmospheric pressure. Optionally, a regulated vacuum supply 259, for example, a pump, can be included in order to better control liquid flow through second chamber 212. Typically, regulated vacuum supply 259 is positioned in fluid communication between liquid return channel 252 and liquid supply 255 and provides a vacuum (negative) pressure that is below atmospheric pressure. Liquid supply 255, regulated pressure source 257, and optional regulated vacuum supply 259 can be referred to as the liquid delivery system of liquid dispenser 200.

In one example embodiment, liquid supply 255 applies a positive pressure provided by a positive pressure source 257 at the entrance of liquid supply channel 251 and a negative pressure (or vacuum) provided by a negative pressure source 259 at the exit of liquid return channel 252. This helps to maintain the pressure inside second liquid chamber 212 at substantially the same pressure (for example, ambient pressure conditions) at the exit of nozzle 220 when the heater 230 is not energized. As a result, flexible membrane 240 is not deflected during a time period of drop dispensing when the heater 230 is not energized.

A high degree of flexibility in flexible membrane 240 is preferred to effectively transmit the pressure generated by vapor bubble 160 in the working fluid (a second liquid) to the fluid or liquid of interest (a first liquid), for example, ink, located in first chamber 211. Since flexible membrane 240 is not corrugated, an elastic material can be included with or substituted for a high modulus material during flexible membrane fabrication.

As flexible membrane 240 fluidically seals first chamber 211 and second chamber 212 from each other, first chamber 211 and second chamber 212 are physically distinct from each other which allows the first liquid and the second liquid present in each respective chamber to be different types of liquid when compared to each other in example embodiments of the invention. For example, the second liquid can include properties that increase its ability to remove heat while the second liquid can be an ink. The second liquid can include properties that lower its boiling point when compared to the first liquid. The second liquid can include properties that make it a non-corrosive liquid, for example, nonionic liquid, in order to improve and maintain the functionality of heater 230 or increase its lifetime.

Referring to Figure 6A-6C, example embodiments of corrugated flexible membranes 241 are shown in which the corrugations of the corrugated membrane include a variable height, a variable pitch, or a combination of both. In Figure 6A, the height of the corrugation is larger near the edge or end region of the flexible membrane when compared to the center region of the flexible membrane. In Figure 6B, the height of the corrugation is smaller near the edge or end region of the flexible membrane when compared to the center region of the flexible membrane. In Figure 6C, a portion of the flexible membrane in the center region is flat and a portion of the flexible membrane near the edge or end region is corrugated. As shown in Figures 6A-6C, the corrugations of corrugated flexible membrane 241 are symmetric about the center point of flexible membrane 241. In Figure 6C, the flat center region of corrugated flexible membrane 241 is symmetric about the center point of flexible membrane 241.

A corrugated flexible membrane including corrugations including a variable height, a variable pitch, or a combination of both is advantaged in some applications when compared to other types of membranes. One advantage includes the ability to provide a flexible membrane having a reduced overall stiffness which helps increase displacement capabilities of the flexible membrane. Another advantage includes the ability to provide a flexible membrane having a reduced variation of stress which helps increase the life of the flexible membrane. Another advantage includes the ability to direct the pressure wave in the fluid on the other side of the flexible membrane which helps increase or enhance the efficiency of the actuator. For example, this type of flexible membrane can focus the pressure wave toward or at a nozzle located on the other side of the fiexible membrane in a manner that is similar to the function of a Fresnel lens.

Referring to Figure 7A-7C, various contour shapes of the corrugation(s) of corrugated flexible membrane 241 are shown. The contour shapes are viewed in a direction perpendicular to flexible membrane 241 along center axis A- A'. As shown in Figures 7A-7C, the contour shape of the corrugation(s) of corrugated flexible membrane 241 is similar to or the same as the shape of first fluid chamber 211 (the chamber above flexible membrane 241 as shown in Figures 7A-7C). In the perpendicular view of flexible membrane 241 shown in Figures 7A-7C, solid line 215 refers to the outer contour of first fluid chamber 211. In Figure 7A, the outer contour is a circular shape. In Figure 7B, the outer contour is an oval shape. In Figure 7C, the outer contour is a complex shape and, as shown, is a rectangular shape including corners that have a radius of curvature.

In the perpendicular view of flexible membrane 241 shown in Figures 7A-7C, the dashed lines 145 trace the troughs of corrugations of corrugated flexible membrane 241 and illustrate the contour shape of the corrugation(s) of corrugated flexible membrane 241. As shown in Figures 7A-7C, the troughs of corrugations of corrugated flexible membrane 241 and contour shape of the corrugation(s) of corrugated flexible membrane 241 are symmetric about the center point of flexible membrane 241.

Liquid dispenser 100, 200 is typically formed from a semiconductor material (for example, silicon) using semiconductor fabrication techniques (for example, CMOS circuit fabrication techniques, micro-electro mechanical structure (MEMS) fabrication techniques, or a combination of both). Alternatively, liquid dispenser 100, 200 can be formed using conventional materials and fabrication techniques known in the art.

A liquid dispenser array structure made according to the present invention includes a plurality of liquid dispensers 100, 200 described above with reference to Figures 1-7C. The plurality of liquid dispensers 100, 200 are formed, for example, integrally formed through a series of material layering and processing steps, on a common substrate typically using the fabrication techniques described above to create a monolithic liquid dispenser structure. When compared to other types of liquid dispensers, monolithic liquid dispenser configurations help to improve the alignment of each nozzle opening relative to other nozzle openings which improves drop deposition accuracy. Monolithic liquid dispenser configurations also help to reduce spacing in between adjacent nozzle openings which can increase the dots per inch (dpi) capability of the device.

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.

PARTS LIST

100 liquid dispenser

111 first liquid chamber

112 second liquid chamber

120 nozzle

130 heater

130a,b split heater

135 center point of the heater

140 flexible corrugated membrane

145 trough pattern of corrugation

160 vapor bubble

170 liquid drop

200 liquid dispenser with a circulating working fluid

21 1 first liquid chamber

212 second liquid chamber

215 outer contour of the first liquid chamber

220 nozzle

230 heater

240 flexible membrane

241 flexible membrane

251 liquid supply channel

252 liquid return channel

255 liquid supply

257 pressure source

259 pressure source