PRE-HEATING LIQUID EJECTED FROM A LIQUID DISPENSER

A liquid dispenser array structure includes a substrate including a plurality of liquid dispensers. The plurality of liquid dispensers includes a liquid supply channel, a liquid dispensing channel including an outlet opening, and a liquid return channel including a vent located downstream relative to the location of the outlet opening of the liquid dispensing channel. A selectively actuatable first heater heats a portion of the liquid flowing through the liquid supply channel. A selectively actuatable second heater diverts the portion of the liquid previously heated by the first heater toward the outlet opening of the liquid dispensing channel. A liquid supply provides liquid under pressure to the plurality of liquid dispensers.

DETAILED DESCRIPTION OF THE INVENTION

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 spirit and scope of the 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 printhead, which is particularly useful in digitally controlled inkjet printing devices in which drops of ink are ejected from a printhead toward a print medium. However, many other applications are emerging which use liquid dispensers, similar to 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” 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.

Referring toFIGS. 1A and 1B, an example embodiment of a liquid dispenser is shown. Liquid dispenser1is conventional having been described in US Patent Application Publication NO. 2012/0098902 A1, published by Xie et al., on Apr. 26, 2012, the disclosure of which is incorporated by reference in its entirety herein. Liquid dispenser1includes a liquid supply channel10that is in fluid communication with a liquid return channel50through a liquid dispensing channel25. Liquid dispensing channel25includes a liquid diverter member80. Diverter member80determines the size (for example, volume) of a drop ejected through an outlet opening30. Typically, the size of drops created is proportional to the amount of liquid displaced by the actuation of diverter member80. Liquid supply channel10includes an exit20while liquid return channel50includes an entrance. The downstream edge40of outlet opening30at least partially defines the entrance of liquid return channel50.

Diverter member80, associated with liquid dispensing channel25, is selectively actuated to divert a portion of the liquid traveling through liquid dispensing channel25toward and through outlet opening30of liquid dispensing channel25in order to form and eject a drop (not shown). The flow path of the liquid is indicated using the arrows included inFIG. 1A. Diverter member80can include a heater or can incorporate using heat in its actuation. As shown inFIG. 1, diverter member80includes a heater that vaporizes a portion of the liquid flowing through liquid dispensing channel25so that another portion of the liquid is diverted toward downstream edge of the outlet opening40. This type of heater is commonly referred to as a “bubble jet” heater. As shown inFIGS. 1A and 1B, the liquid moves over heater80.

As shown inFIGS. 1A and 1B, liquid supply channel10, liquid dispensing channel25, and liquid return channel50are partially defined by portions of substrate100. These portions of substrate100can also be referred to as a wall or walls of one or more of liquid supply channel10, liquid dispensing channel25, and liquid return channel50. A wall35defines outlet opening30and also partially defines liquid supply channel10, liquid dispensing channel25, and liquid return channel50. Portions of substrate100also define a liquid supply passage42and liquid return passages44,45. Again, these portions of substrate100can be referred to as a wall or walls of liquid supply passage42and liquid return passages44,45. Liquid supply passage42and liquid return passages44,45are perpendicular to liquid supply channel10, liquid dispensing channel25, and liquid return channel50.

Referring toFIG. 1C, a liquid supply and recirculation system is connected in fluid communication to liquid dispenser1. The liquid supply and recirculation system provides liquid to liquid dispenser1at a pressure +P that is above atmospheric pressure at the liquid supply passage42. The liquid supply and recirculation system recovers liquid from the liquid dispenser1by supplying a negative pressure −P at the outlet of liquid return passages44,45. A regulated vacuum supply source, for example, a pump, can be included in the liquid return system of the liquid supply and recirculation system in order to better control liquid flow through liquid dispenser and provide a vacuum (negative) pressure that is below atmospheric pressure.

As shown inFIG. 1C, liquid supply passage42and liquid return passages44,45are also in fluid communication with a liquid supply255. During a drop ejection or dispensing operation, liquid supply255provides a pressurized liquid that flows continuously from liquid supply255through liquid supply passage42, through liquid supply channel10, through liquid dispensing channel25, through liquid return channel50, through liquid return passages44,45, and back to liquid supply255. Liquid circulation helps to increase the drop ejection frequency by removing at least some of the heat generated by heater80when it is actuated during drop ejection. Liquid circulation can also help increase the drop ejection frequency by pushing at least some of the vapor bubble formed when heater80is actuated off of and away from heater80area as the vapor bubble collapses.

Typically, a regulated pressure source257is positioned in fluid communication between liquid supply255and liquid supply passage42. Regulated pressure source257, for example, a pump, provides a positive pressure that is usually above atmospheric pressure. Optionally, a regulated vacuum supply259, for example, a pump, can be included in order to better control liquid flow through second chamber212. Typically, regulated vacuum supply259is positioned in fluid communication between liquid return passages44,45and liquid supply255and provides a vacuum (negative) pressure that is below atmospheric pressure. Liquid supply255, regulated pressure source257, and optional regulated vacuum supply259can be referred to as the liquid delivery system of liquid dispenser1.

Liquid supply channel10or liquid supply passage42can optionally include a porous member71, for example, a filter, which provides particulate filtering of the liquid flowing through liquid dispenser1. Liquid return channel50or liquid supply return passages44,45can optionally include a porous member70, for example, a filter, which, in addition to providing particulate filtering of the liquid flowing through liquid dispenser, helps to accommodate liquid flow and pressure changes in liquid supply return channel50associated with actuation of diverter member80and a portion of liquid in the liquid dispensing channel25being deflected toward and through outlet opening30. This reduces the likelihood of liquid spilling over outlet opening30of liquid dispensing channel25during actuation of diverter member80. The likelihood of air being drawn into liquid return passages44,45is also reduced when porous member70is included in liquid dispenser1.

Liquid return channel50includes a vent60that opens liquid return channel50to atmosphere. Vent60helps to accommodate liquid flow and pressure changes in liquid return channel50associated with actuation of diverter member80and a portion of liquid in the liquid dispensing channel25being deflected toward and through outlet opening30. This reduces the likelihood of liquid spilling over outlet opening30of liquid dispensing channel25during actuation of diverter member80. In the event that liquid does spill over outlet opening30, vent60also acts as a drain that provides a path back to liquid return channel50for any overflowing liquid. As such, the terms “vent” and “drain” are used interchangeably herein.

As shown inFIG. 1, there is a plurality of liquid return passages44,45. The overall (aggregate) size of liquid return passage44,45is greater than the size of liquid supply passage42but the size and shape of individual liquid return passages44and45is approximately equal to the size and shape of liquid supply passage42. It is believed that this feature not only accommodates liquid flow and pressure changes in liquid return channel50which reduces the likelihood of liquid spilling over outlet opening30of liquid dispensing channel25, but also facilitates the manufacturing of liquid dispenser1and improves the heat dissipation from diverter member80to the liquid flowing through individual liquid return passages44and45.

Liquid dispenser1is typically formed from a semiconductor material (for example, silicon) using known semiconductor fabrication techniques (for example, CMOS circuit fabrication techniques, microelectromechanical system (MEMS) fabrication techniques, or combination of both). Alternatively, liquid dispenser1can be formed from any materials using any fabrication techniques known in the art. The liquid dispensers of the present invention, like conventional drop-on-demand inkjet printheads, only create drops when desired, eliminating the need for a gutter and the need for a drop deflection mechanism which directs some of the created drops to the gutter while directing other drops to print receiving media. The liquid dispensers of the present invention, like conventional continuous inkjet printheads, use a liquid supply that supplies liquid, for example, ink under pressure to the printhead. The supplied ink pressure serves as the primary motive force for the ejected drops, so that most of the drop momentum is provided by the pressurized liquid from the liquid supply rather than by a drop ejection actuator located, for example, at the nozzle.

Liquid ejected by liquid dispenser1of the present invention does not need to travel through a conventional nozzle which typically has a smaller area than outlet opening30. This helps to reduce the likelihood of outlet opening30becoming contaminated or clogged by particle contaminants. Using a larger outlet opening30(as compared to a conventional nozzle) also reduces latency problems at least partially caused by evaporation in the nozzle during periods when drops are not being ejected. The larger outlet opening30also reduces the likelihood of satellite drop formation during drop ejection because drops are produced with shorter tail lengths.

The liquid dispenser array structure of the present invention includes a plurality of liquid dispensers1, also referred to as liquid dispensing elements, on a common substrate100. In this sense, substrate100typically includes a plurality of liquid dispensers1. The liquid dispensers are typically arranged in an array on substrate100. The liquid dispensers can be integrally formed on the common substrate using the fabrication techniques described above thereby creating a monolithic liquid dispenser array structure. When compared to other types of liquid dispensers, monolithic dispenser configurations help to improve the alignment of each outlet opening relative to other outlet openings which improves image quality. Monolithic dispenser configurations also help to reduce spacing in between adjacent outlet openings which increases dots per inch (dpi).

Referring toFIGS. 2A-3B, example embodiments of a liquid dispenser made with the present invention is shown. Liquid dispenser1includes a liquid supply channel10that is in fluid communication with a liquid return channel50through a liquid dispensing channel25including an outlet opening30as well as the other elements described above. InFIGS. 2A-3B, liquid supply channel10includes a selectively actuated first heater81that heats a portion of the liquid flowing through the liquid supply channel10. Liquid dispensing channel25includes a selectively actuated second heater80that diverts the portion of the liquid previously heated by the first heater81toward the outlet opening of the liquid dispensing channel. The characteristics of the selectively actuated first heater81of liquid dispenser1are different when compared to the characteristics of the selectively actuated second heater80because each heater performs a different function. The different characteristics of the selectively actuated first heater and the selectively actuated second heater are, typically, one of heater area, heater aspect ratio, or heater resistance.

As shown inFIGS. 2A and 2B, first heater81is a single heater that is positioned in liquid supply channel10. InFIGS. 3A and 3B, selectively actuated first heater81of liquid dispenser1includes a plurality of heater segments81a,81b,81c(as shown in this example embodiment) that incrementally heat the portion of the liquid flowing through the liquid supply channel10. Each segment of the plurality of heater segments of heater81is individually addressable and can be activated in sequence to incrementally heat the same portion of the liquid flowing through the liquid supply channel10. The number of heater segments activated can be changed by a controller to provide wide range of heating to the portion of the liquid flowing through the liquid supply channel10.

Referring toFIGS. 4A-4C, a controller110is configured to provide a first pulsed waveform to selectively actuated first heater81that heats a portion of the liquid90aflowing through the liquid supply channel10. Sometime after the first pulsed waveform is turned off, the portion of the liquid90apreviously heated by the selectively actuated first heater81flows downstream to a new location90bover selectively actuated second heater80in the liquid dispensing channel25. Controller110is configured to provide a second pulsed waveform to selectively actuated second heater80that heats liquid portion90bpreviously heated by first heater81(and referred to as liquid portion90a) and now flowing through liquid dispensing channel25. An example embodiment of the first pulsed waveform provided by controller110to the selectively actuated first heater81is shown inFIG. 4C. An example embodiment of the second pulsed waveform provided by controller110to the selectively actuated second heater80is shown inFIG. 4B.

The first pulsed waveform provided to first heater81and the second pulsed waveform provided to second heater80are coordinated to cause the selectively actuatable first and second heaters to act upon the same liquid portion90a,90bas the liquid portion moves in the direction indicated by the arrows included inFIG. 4A. The energy level of the first pulsed waveform provided to the selectively actuatable first heater81is used to control the temperature of the liquid portion90bover the second heater80immediately before the start of the second pulsed waveform provided by the controller to the second heater80.

Second heater80determines the size (for example, volume) of the ejected drop. Typically, the size of drops created is proportional to the amount of liquid displaced by the actuation of the second heater80. The amount of liquid displaced by the actuation of the second heater80depends on the size of the second heater80, the energy level of the second pulsed waveform to second heater80, and the temperature of the liquid portion90bover the second heater80immediately before the start of the second pulsed waveform provided by the controller to the second heater80.

Referring toFIG. 5, another example embodiment of a liquid dispenser1made with the present invention is shown. Liquid dispenser1includes a temperature sensing element, sensor85, in the liquid supply channel10that is in thermal communication with a liquid in the liquid supply channel10that senses the temperature of the liquid moving through liquid dispenser1. The temperature of the liquid dispenser1changes during printing depending on the coverage of the printed document as well as the time of continuous printing. For example, for the same time of continuous printing, the higher the coverage of the printed document, the higher the liquid dispenser1temperature. Also, for the same coverage of the printed document, the longer the time of continuous printing, the higher the liquid dispenser1temperature.

As the temperature of the liquid dispenser1increases, the temperature of the liquid portion over the selectively actuatable first heater80rises. The drop volume or drop velocity of the drops produced by liquid dispenser1will increase if the energy level of first pulsed waveform provided by controller110to the selectively actuatable first heater81and the energy level of second pulsed waveform provided by controller110to the selectively actuatable second heater80is unchanged. To keep the drop volume and drop velocity produced by the liquid dispenser1constant during printing, the energy level of first pulsed waveform provided by controller110to first heater81is adjusted during operation depending on the temperature measured by the temperature sensing element85. At a relatively low temperature, the energy level of first pulsed waveform provided by controller110to first heater81is correspondingly relatively high. As the temperature of liquid dispenser1rises during operation, the energy level of first pulsed waveform provided by controller110to first heater81is decreased to help maintain a constant drop volume and drop velocity.

In another embodiment of the present invention, controller110of liquid dispenser1is configured to provide a constant activation current to the selectively actuatable first heater81. The complexity of controller110so configured is less than that of a controller configured to provide the pulsed waveform described above. This example embodiment also can include a temperature sensing element85to measure the temperature of the liquid dispenser1. As described above, the temperature of the liquid dispenser1depends on the coverage of the printed document as well as the time of continuous printing. For the same time of continuous printing, the higher the coverage of the printed document, the higher the liquid dispenser1temperature. For the same coverage of the printed document, the longer time of continuous printing, the higher the temperature of liquid dispenser1. During operation, the level of activation current provided by controller110is adjusted depending on the temperature measured by the temperature sensing element. At low temperature, the level of activation current is high. As the temperature of the liquid dispenser rises during operation, the level of activation current provided by the controller to the selectively actuatable first heater81decreases to help maintain a constant drop volume and drop velocity.

The example embodiments described above can be implemented individually (by themselves) or in combination with each other to obtain the desired performance of the liquid dispenser of the present invention. 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

10liquid supply channel

20liquid supply channel exit

40downstream edge of outlet opening

42liquid supply passage

44liquid return passage

45liquid return passage

50liquid return channel

60vent or drain

90bliquid portion over the second heater

90aliquid portion over the first heater