Printer including temperature gradient fluid flow device

A method and printing system are provided. The printing system includes a liquid drop ejector, a fluid passage, and a fluid flow. The liquid drop ejector is operable to eject liquid drops having a plurality of volumes along a first path. The fluid passage includes a temperature gradient in the passage. The fluid flow source is operable to cause a fluid to flow in a direction through the passage, wherein interaction of the fluid flow and the liquid drops causes liquids drops having one of the plurality of volumes to begin moving along a second path.

FIELD OF THE INVENTION

This invention relates generally to the management of gas flow and, in particular to the management of gas flow in printing systems.

BACKGROUND OF THE INVENTION

The device that provides gas flow to the gas flow drop interaction area can introduce turbulence in the gas flow that may augment and ultimately interfere with accurate drop deflection or divergence. Turbulent flow introduced from the gas supply typically increases or grows as the gas flow moves through the structure or plenum used to carry the gas flow to the gas flow drop interaction area of the printing system.

Drop deflection or divergence can be affected when turbulence, the randomly fluctuating motion of a fluid, is present in, for example, the interaction area of the drops (traveling along a path) and the gas flow force. The effect of turbulence on the drops can vary depending on the size of the drops. For example, when relatively small volume drops are caused to deflect or diverge from the path by the gas flow force, turbulence can randomly disorient small volume drops resulting in reduced drop deflection or divergence accuracy which, in turn, can lead to reduced drop placement accuracy.

Turbulence reduction can be achieved by reducing the magnitude of disturbances and instability in the fluid flow. Local cooling has been theorized to be an effective technology for turbulence suppression. Cooling of a fluid flow surface cools the flow boundary layer which in turn will slow the development of turbulence instability. Local cooling to suppress turbulence was also experimentally demonstrated in Russia during 1980's. (See for example, Dovgal, Levchenko, and Timofeev, (1990) “Boundary layer control by a local heating of a wall,” from IUTAM Laminar-Turbulent Transition, eds. D. Arnal and R. Michel, Springer-Verlag, pp. 113-121). U.S. Pat. No. 6,027,078, issued on Feb. 22, 2000, to J. D. Crouch and L. L. Ng, discloses aircraft boundary-layer flow control system incorporated a local heating for laminar flow.

However, one of the problems related to these types of turbulence reduction techniques is that each technique is concerned with external flow for an object, and thus can't be directly implemented in an internal flow through a channel that a printing system encounters.

Accordingly, a need exists to reduce turbulent gas flow in the gas flow drop interaction area of a printing system.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a printing system includes a liquid drop ejector, a fluid passage, and a fluid flow source. The liquid drop ejector is operable to eject liquid drops having a plurality of volumes along a first path. The fluid passage includes a wall with the wall including a first wall portion and a second wall portion. The second wall portion is located closer to the first path when compared to the location of the first wall portion. The first wall portion has a first temperature and the second wall portion has a second temperature with the second temperature being lower than the first temperature. The fluid flow source is operable to cause a fluid to flow in a direction through the passage. Interaction of the fluid flow and the liquid drops causes liquid drops having one of the plurality of volumes to begin moving along a second path.

According to another aspect of the present invention, a method of printing includes providing drops having a plurality of volumes traveling along a first path; causing a fluid to flow through a passage; creating a temperature gradient in the passage; and causing the fluid flow to interact with the liquid drops such that liquid drops having one of the plurality of volumes to begin moving along a second path.

According to another aspect of the present invention, a printing system includes a liquid drop ejector, a fluid passage, and a fluid flow. The liquid drop ejector is operable to eject liquid drops having a plurality of volumes along a first path. The fluid passage includes a temperature gradient in the passage. The fluid flow source is operable to cause a fluid to flow in a direction through the passage, wherein interaction of the fluid flow and the liquid drops causes liquid drops having one of the plurality of volumes to begin moving along a second path.

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.

The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of ordinary skill 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. In the following description, identical reference numerals have been used, where possible, to designate identical elements.

Although the term printing system is used herein, it is recognized that printing systems are being used today to eject other types of liquids and not just ink. For example, the ejection of various fluids such as medicines, inks, pigments, dyes, and other materials is possible today using printing systems. As such, the term printing system is not intended to be limited to just systems that eject ink.

FIG. 1is a schematic side view of a printing system with the fluid flow device incorporating an example embodiment of the present invention. The printing system100includes a printhead102, a fluid flow device106, a drop recycle system108and medium112. The printhead102includes a drop forming mechanism114operable to form and eject liquid drops having a plurality of volumes traveling along a first path116. The gas flow device106includes a first wall portion118and a second wall portion119that define a fluid passage110. The second wall portion119is located closer to the first path116when compared to the location of the first wall portion118. The first wall portion118and the second wall portion119can be straight or include a radius of curvature depending on the geometrical configuration of the printing system100.

A fluid flow source104is operatively associated with the fluid passage110and is operable to cause a fluid flow (represented by arrows120, hereafter) to flow through the fluid passage110along the first wall portion118and the second wall portion119. The interaction of the fluid flow and the liquid drops causes liquid drops having one of the plurality of volumes diverge (or deflect) from the first path116and begin traveling along a second path124while liquid drops having another of the plurality of volumes remain traveling substantially along the first path116or diverge (deflect) slightly and begin traveling along a third path117. Medium112is positioned along one of the first, second and third path while the drop recycle system108is positioned along another of the first, second or third paths depending on the specific application contemplated.

The fluid flow source104can be any type of mechanism commonly used to create a gas flow. For example, the fluid flow source104can be a positively pressured fluid flow source such as a fan or a blower operatively associated with an air front side130of the fluid passage110. Alternatively, the fluid flow source104can be of the type that creates a negative pressure or a vacuum operatively associated with the air backside131of the fluid passage110. Or, the fluid source104can be of the type that combines the positively pressured fluid flow source and the negative pressure source or a vacuum. The gas of the first fluid flow source104can be air, vapor, nitrogen, helium, carbon dioxide, or other, commonly available gases. However, one example of the gas of the first fluid flow source104is air. Often air is the preferred gas simply due to economical reasons.

Printheads like printhead102are known and have been described in, for example, U.S. Pat. No. 6,457,807 B1, issued to Hawkins et al., on Oct. 1, 2002; U.S. Pat. No. 6,491,362 B1, issued to Jeanmaire, on Dec. 10, 2002; U.S. Pat. No. 6,505,921 B2, issued to Chwalek et al., on Jan. 14, 2003; U.S. Pat. No. 6,554,410 B2, issued to Jeanmaire et al., on Apr. 29, 2003; U.S. Pat. No. 6,575,566 B1, issued to Jeanmaire et al., on Jun. 10, 2003; and U.S. Pat. No. 6,588,888 B2, issued to Jeanmaire et al., on Jul. 8, 2003. At least some of the liquid drops contact medium112, such as paper or other medium, while other drops are collected by the drop recycle system108such as a catcher. Liquid drops received by the drop recycle system108are circulated through a liquid recirculation mechanism commonly available for reuse.

Referring toFIG. 1, the first wall portion118has a first temperature and the second wall portion119has a second temperature. It is preferred that the first temperature is higher than the second temperature. As the fluid flow flows through the fluid passage110, the fluid flow is heated up by the higher temperature first wall portion118, and then the heated fluid flow is cooled down by the lower temperature second wall portion119. As the fluid flow flows over the first wall portion118and the second wall portion119, a steady temperature gradient that is parallel to the fluid passage110can be formed in the fluid flow along the fluid passage110. The fluid flow being cooled in the fluid passage110over the second wall portion119also includes a center region133and a boundary region135. The temperature gradient in the fluid passage includes a temperature gradient that is normal to the fluid flow120such that the temperature is lower in a boundary region135of the fluid flow as compared to a center region133of the fluid flow.

The fluid flow at the air front side130of the fluid passage110can be any temperature that is suitable for a desired temperature gradient. The temperature of the fluid flow near the first path116, however, should be controlled so that it is lower than the ink boiling point to avoid undesired intensive ink drop vaporization. For example, if the ink is aqueous-based, the temperature of the fluid flow120near the first path116should not exceed 100° C. Preferably, the temperature of the fluid flow near the first path116is close to ambient temperature to minimize adversary temperature effects on liquid drop forming mechanism114. The temperature of the fluid flow near the first path116can be controlled by adjusting the first temperature of the first wall portion118, and/or adjusting the second temperature of the second wall portion119. A heating mechanism operatively associated with the first wall portion118can be configured to heat the first wall portion118to the first temperature. A cooling mechanism operatively associated with the second wall portion119can be configured to cool the second wall portion119to the second temperature. The first temperature and the second temperature should be adjusted according to the flow rate of fluid flow120, and flow residual time in the fluid passage110. Thermal sensing device such as temperature sensing resistors can be integrated into the first wall portion118and the second wall portion119to measure the temperatures of the walls. Non-intrusive thermal sensing device such as inferred thermal cameras can be used to monitor the temperature of the fluid flow if needed.

The materials for the first wall portion118and the second wall portion119can be tantalum, silicon, stainless steel, plastics, aluminum, nickel, or other composite materials, etc., depending on mechanical integrity and thermal property requirements. Generally it is preferred that the second wall portion119is made from a material having a higher effective thermal conductivity than that of the first wall portion118. Materials with high coefficients of thermal expansion (CTE) should be avoided to minimize shape distortion of the first wall portion118and the second wall portion119that can be induced by the temperature gradient in the fluid passage110.

FIG. 2is a schematic side view of a printing system with the fluid flow device incorporating another example embodiment of the present invention. The printing system200shown inFIG. 2is similar to the printing system100shown inFIG. 1with the recognition that applying a heat source202to heat up the fluid flow being pumped or sucked out from the fluid flow source104. As an alternative of practice, the heat source202can also be placed upstream of the fluid flow source104. The fluid flow source104and the heat source202can be operatively connected by a fluid passage such as a pipe204. The heat source202can be any kind heat source that is operatively associated with the fluid flow source104to heat up the fluid flow. For example, the heat source202can be an electrical stove, or a heat exchanger. The heat source202causes the temperature of the fluid flow to increase prior to the fluid flow entering the fluid passage110. In the embodiment as shown inFIG. 2with the heat source202, the first wall portion118can or can not include a heating mechanism. For an embodiment that includes no heating mechanism in the first wall portion118, low thermal conductivity material is desired for the first wall portion118, in order to minimize heat dissipation through the first wall portion118. The first wall portion118can also be wrapped with layers of thermal insulation materials for improved heat preservation purpose. Of course, the heat source202and a heating mechanism in the first wall portion118can coexist, but not necessary.

FIG. 3Ashows a portion of a gas flow device106that includes the first wall portion118and the second wall portion119defined the fluid passage110. The fluid flow source104is operatively associated with the gas flow device106. A heating mechanism is operatively associated with the first wall portion118to heat the first wall portion118to the first temperature, and a cooling mechanism is operatively associated with the second wall portion119to cool the second wall portion119to the second temperature. For clarity graphic presentations, a close-up representation of a portion of the first wall portion118is shown inFIG. 3B, and a close-up of a portion of the second wall portion119is shown inFIG. 3F, respectively.

Referring toFIG. 3B, the heating mechanism includes a structure, for example, a series of resistive electro-thermal heaters118aoperatively configured to the first wall portion118to heat the first wall portion118to the first temperature. The resistive electro-thermal heaters118ainclude arrays of high electrical resistance wires embedded in the first wall portion118. Resistive electro-thermal heaters are well known and as such are not discussed herein.

In one example embodiment, the electro-thermal heaters118aare aligned parallel to each other and perpendicular to the fluid flow direction120.FIG. 3Cschematically shows a three-dimensional representation of the first wall portion118with such aligned electro-thermal heaters118aembedded. Such parallel-aligned electro-thermal heaters118acan substantially eliminate temperature nonuniformity across the width320of the flow passage110. The electro-thermal heaters118acan be embedded in the first wall portion118, attached to the fluid flow side118bof the first wall portion118, or attached to the outer side118cof the first wall portion118. In the case of the electro-thermal heaters118abeing attached to the fluid flow side118bof the first wall portion118, the wall surface has to be polished very smooth to eliminate adversary effects any surface roughness may introduce to the fluid flow.

FIG. 3Dshows another example embodiment of the electro-thermal heater118a, in which the electro-thermal heater118ais integrally formed with the first wall portion118. For example, the first wall portion118is made from an electrically conductive metallic material. A direct current (DC) or an alternative current (AC) power source can be used to power the resistive electro-thermal heater118a.

For the heat preservation purpose, the first wall portion118can also be wrapped with layers of thermal insulation materials.FIG. 3Eshows a portion of the first wall portion wrapped with such a layer of thermal insulation material330. The thermal insulation material330has a very low thermal conductivity and, typically, is not electrically conductive.

Referring toFIG. 3F, which is a close-up representation of a portion of the second wall portion119shown inFIG. 3A, the cooling mechanism includes a structure configured to sink heat away from the second wall portion119to cool the second wall portion119to the second temperature, and in turn sink heat away from the fluid flow120. Typically, the second wall portion is made from a high thermal conductivity material to facilitate heat transfer. To make heat transfer even faster, as shown inFIG. 3F, the cooling structure can be micro heat pipes119clocated in the second wall portion119. A micro heat pipe is a sealed vessel as a thermal conductance device. Working fluid phase is changed in heat pipe. The phase of working fluid at evaporator section (the fluid side119aof the second wall portion119) is changed from liquid to vapor and contrarily changed at condenser section (the outside wall119bof the second wall portion119) and cooled. Cooled working fluid is returned to from condenser to evaporator by capillary action within wick structure of the micro heat pipe. It dissipates energy from inside wall119aof the second wall portion119by the latent heat of evaporation in a nearly isothermal operation. Working fluid is circulated inside heat pipe accompanying with the phase change at both evaporator and condenser. The working fluid is formed of a material such as ammonia, pentane or the like. The wick structure can be aluminum, stainless steel, nickel, and carbon composite, just as with most micro heat pipes. Details on micro heat pipes operating principles and its construction techniques can be found, for example, in Chapter Eight: “Micro Heat Pipes” (pp. 295-337) in the book “Microscale Energy Transport,” edited by Tien, Majumdar and Gerner, published by Taylor & Francis in 1998. The micro heat pipes119cembedded in the second wall portion119should be in high density and well aligned to ensure temperature uniformity across the width of the flow passage110.

FIG. 3Gis another cooling mechanism operatively associated with the second wall portion119wherein cooling fins332are attached to the outer side119bof the second wall portion119. Cooling fins332are well known and as such are not discussed herein. It is preferred that the cooling fins are made from a material having high thermal conductivity.

FIG. 3His another cooling mechanism operatively associated with the second wall portion119wherein thermoelectric cooling devices350are attached to the outer side119bof the second wall portion119. A temperature controller352is operatively associated with the thermoelectric cooling devices350via cable354to control the cooling effects of the thermoelectric cooling devices350. The thermoelectric cooling device350, (also known as Peltier devices, thermoelectric cooler) is a device in which a current is applied to a semiconductor causing a temperature reduction and cooling. Thermoelectric cooling devices are well known and as such are not discussed in detail herein. Details on thermoelectric cooling device operating principles, materials and its construction techniques can be found, for example, “Thermoelectrics Handbook: Macro to Nano-Structured Materials” edited by D. M. Rowe, published by CRC Press in 2006. Thermoelectric cooling devices are commercially available. The Thermoelectric cooling devices can also be custom-made to unusual size, a different performance parameter, an embedded sensor, and such. A known manufacturer of such thermoelectric cooling devices is Custom Thermoelectric, Inc.

FIG. 4Ais a portion of a gas flow device106that includes a first wall portion118and a second wall portion119defined a fluid passage110. A fluid flow source104is operatively associated with the gas flow device106. A heating mechanism is operatively associated with the first wall portion118to heat the first wall portion118to the first temperature, and a cooling mechanism is operatively associated with the second wall portion119to cool the second wall portion119to the second temperature. Referring toFIG. 4A, the heating mechanism includes a heated fluid flow402that heats the first wall portion118to the first temperature. The heated fluid flow402can be static constant-temperature hot liquid bath electrically controlled by a temperature controller410through a conductive path420. The temperature controller410can turn on/off a power source to maintain the hot liquid bath at a constant preset temperature, such as the preferred first temperature of the first wall portion118. The fluid can be ink, water, air, oil, etc., depending on specific temperature requirement for each heating application. For example, if the temperature of the first wall portion118is lower than 100° C., the heated fluid flow can be ink or water; if the temperature of the first wall portion118exceeds 100° C., then high boiling point oils can be used for the heating purpose. The heated fluid flow can also be flowing fluid, but this is not preferred.

Still referring toFIG. 4A, the cooling mechanism includes a cooled fluid flow404that cools the second wall portion119to the second temperature. The cooled fluid flow404can be flowing cold fluid, for example, cold ink, water, oil, or air. A heat dissipation mechanism430, such a heat exchanger, is operatively associated with the cooled fluid flow404to cool the fluid, and a mass transfer mechanism428, for example a fluid pump, is operatively associated with the cooled fluid flow404and the heat dissipation mechanism430through fluid channel426to drive the cooled fluid flow404flowing over the second wall portion119. The cooled fluid flow404can flow in a direction413aagainst the fluid flow120; or the cooled fluid flow404can flow in a direction413bparallel to the fluid flow120as shown inFIG. 4B.

The cooling mechanism sinks heat away from the second wall portion119to the second temperature and in turn cools the fluid flow120in the flow passage110. With the heating mechanism and the cooling mechanism inactive, a temperature gradient can form in the fluid passage. The cooling fluid404either flows in a direction413aagainst or opposite the fluid flow direction120, or in a direction413bparallel to the fluid flow direction120to ensure temperature uniformity across the width of the flow passage110. Attentions have to be paid to ensure that little or no vibration is introduced to the gas flow device106should a mass transfer mechanism428be used in the system. The cooled fluid flow can also be a static constant-temperature fluid bath controlled by a temperature controller and connected to a heat dissipation mechanism such as a heat exchanger.

It is preferred that the heating and cooling activities occur concurrently and continuously to achieve a desired temperature gradient in the fluid passage110. However, obviously it is acceptable to create the temperature gradient in the fluid passage110by heating the first wall portion only, or, by cooling the second wall portion only, or by pre-heating the fluid flow only, or by combining any of these approaches.

The invention has been described in detail with particular reference to certain example embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.

PARTS LIST