Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-11-15
2001-01-23
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06176573
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to devices and methods for controlling gas flow through a liquid and more particularly to air flow management within a liquid container, such as an inkjet cartridge.
BACKGROUND ART
Valving mechanisms may be used to control the flow of gas through a liquid. Such valving mechanisms are employed in systems which require a precisely timed release of gas in order to cause the gas to perform work or in order to provide a desired gaseous state within the environment in which the gas is released. Alternatively, the valving mechanism may be used to retain the gas until a time when the effects of the release will be minimal. A gas management valving mechanism may be a large scale device or may be formed using micromachining techniques, depending upon the desired application.
Air management is desirable in inkjet printing to prevent inkjet cartridges from “depriming” due to the accumulation of an air bubble in the ink flow path. Air bubble accumulation is a particular worry near a thermal inkjet printing head, which typically comprises a silicon chip containing an array of heating resistors which boil ink and expel it, through an array of orifices adjacent to the resistors and onto nearby paper. The ink to be expelled is typically at a small negative pressure with respect to atmosphere to prevent it from drooling out of the orifices, but too large a negative pressure can suck air in through the orifices, forming bubbles in the ink. In addition, heat from the boiling of the ink causes air dissolved in the ink to outgas and form small bubbles. These bubbles may coalesce in the ink over the silicon chip to form large bubbles which can impede ink flow, causing print quality to suffer. The impeding of ink flow by this air bubble is called depriming.
Trapped bubbles cannot simply float away from the inkjet chip because the inkjet pen typically requires a filter screen over the inkjet chip to prevent particles in the ink from clogging the inkjet orifices. The filter screen must be placed in the inkjet cartridge near the inkjet chip to reduce the likelihood that particles will be trapped in the volume between chip and screen during manufacturing. Typically, the screen is placed at the top of a “standpipe” region in which trapped air accumulates until the air bubbles become so large that print quality suffers.
Introducing a capability to remove the trapped air bubbles from the standpipe region can thus greatly increase the service life of the inkjet cartridge before print quality begins to suffer from mechanisms other than air accumulation.
A potential solution is described in U.S. Pat. No. 4,931,811 to Cowger et al., which is also assigned to the assignee of the present invention. The ink supply of an inkjet pen is connected to the thin film printhead by way of a large diameter standpipe. The diameter of an air accumulating section of the standpipe is sufficiently great to enable ink to pass through the standpipe, despite the presence of air in the air accumulating section. Large diameter air bubbles which form in the air accumulating section are deformed by suction force from the printhead, allowing ink to pass through the standpipe between the air bubbles and the walls of the standpipe. However, once the standpipe is completely filled with an air bubble which contacts the upper surface of the silicon chip, depriming can still be expected to occur.
Depriming continues to be a main contributor to premature failures of ink cartridges. Moreover, while the solutions described in Cowger et al. may provide an improvement within ink cartridges, the approaches may not be applicable to other systems in which gas-release management is desirable.
What is needed is a gas flow control device and method which achieve gas management without requiring movable components and which may be used in such applications as selectively releasing air through an ink supply of an ink cartridge.
SUMMARY OF THE INVENTION
A gas flow control device uses capillary forces to manage gas retention and uses thermal energy to manage gas release. A capillary path has an opening within a reservoir of liquid and has a geometry by which gas flow through the path is inhibited by capillary forces on a volume of the liquid within the capillary path. An equilibrium condition is established at the interface of the liquid and gas. However, a heater is in thermal communication with the capillary path for selectively heating the liquid sufficiently to free the flow of gas through the path.
In one application, the gas flow control device is employed in an ink cartridge. The capillary path may be formed in an upright member having a resistive trace that follows the capillary path. When no current is conducted through the resistive trace, liquid enters the capillary path. Air accumulates at the lower opening of the capillary path as a result of outgassing and reverse flow from repeated firings of ink from a printhead having multiple firing chambers. An equilibrium condition is established at an ink/gas interface in the region of the lower capillary opening. The accumulated air can be released at a preselected time, such as when the ink cartridge is in a service position within a conventional inkjet printer. The air is released by conducting current through the resistive trace to overcome the capillary forces on the liquid within the capillary path. By heating the ink to a temperature above its boiling point, the surface tension on the ink goes discontinuously to zero. Heating the capillary path to drive the liquid from the path permits the air to escape.
Following a release of air, current through the resistive trace is terminated, allowing the capillary path to refill with ink. Preferably, there is a second path that ensures that the capillary path is refilled with ink following a release operation. An ink-fill maintenance path may be formed to extend from the supply of ink to a region of the capillary path above the air accumulation region, but below the upper level of the ink supply.
An optional upper mesh filter may be formed at the upper opening of the capillary path to prevent contaminants from entering the path. The resistive trace may include a serpentine section that is used to dry the filter mesh during air release operations.
As an alternative to a capillary path that is substantially vertical, the gas flow control device may be formed by two closely spaced horizontal membranes having through holes. The spacing between the membranes defines the capillary region for regulating the gas flow by means of capillary forces and thermal energy. Resistor elements may be formed within the capillary region to boil liquid within the region when gas release is desired. The through holes of the lower membrane are misaligned from the through holes of the upper membrane. The resistor elements are positioned advantageously to provide a continuous heated path between lower and upper through holes. Upon termination of a release operation, the liquid re-enters the capillary region, which is dimensioned to establish a condition in which subsequent gas flow through the device is inhibited by capillary forces. Preferably, the membranes are formed of a material that has a low thermal conductivity and a low thermal diffusivity, so that liquid at exterior surfaces of the membranes is not heated during the release operation. The membrane material should also be chemically inert with respect to the liquid (e.g., ink) with which contact is made by the membranes.
A third embodiment is similar to the second embodiment with respect to spacing apart two membranes to define a liquid path through which gas flow is to be regulated. However, in this third embodiment, only the upper membrane has a through hole. When the membranes are positioned horizontally, the gas enters laterally to reach the through hole in the upper membrane. Prior to release, capillary forces act on liquid within the through hole to inhibit escape of the gas. In a release operation, a heater is activated to apply thermal energy to the liquid within the
Barth Phillip W.
Cheung Karen C.
Hoen Storrs
McAllister William H.
Agilent Technologie,s Inc.
Le N.
Vo Anh T. N.
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