Patent Application
20090115814
It is often desirable to determine fluid-dispense rates from fluid-ejecting substrates, e.g., similar to those used for thermal or piezoelectric ink-jet print heads. Exemplary applications include fluid-ejecting substrates used as fuel injectors, IV dispensers, inhalation devices, such as nebulizers, fluid-ejecting substrates used to deposit drugs on a substrate, etc. Present methods for determining fluid-dispense rates are usually complicated, destructive, or time consuming.
In the following detailed description of the present embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice disclosed subject matter, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the claimed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the claimed subject matter is defined only by the appended claims and equivalents thereof.
Fluid-ejecting substrate 120 includes a wafer 122, e.g., of silicon. A dielectric layer 124, such as a silicon dioxide layer, is formed on wafer 122. For one embodiment, a barrier layer 128 is formed on dielectric layer 124. For another embodiment, chambers 126, e.g., often called firing chambers, as illustrated by a single chamber in
Liquid droplets are ejected from chambers 126 in response to heating the resistors. The liquid droplets are ejected through orifices (or nozzles) 132 (one of which is shown cut away in
Fluid-dispensing device 300 includes fluid-ejecting substrate 120, shown in cross-section, with the cross-hatching omitted for clarity. For one embodiment, a controller 305 is connected to a voltage source 310 and a data acquisition unit 323. For another embodiment, controller 305 includes a processor 306 for processing computer/processor-readable instructions. These computer-readable instructions, for performing the methods described herein, are stored on a computer-usable media 308, and may be in the form of software, firmware, or hardware. As a whole, these computer-readable instructions are often termed a device driver. In a hardware solution, the instructions are hard coded as part of a processor, e.g., an application-specific integrated circuit (ASIC) chip. In a software or firmware solution, the instructions are stored for retrieval by the processor 306. Some additional examples of computer-usable media include static or dynamic random access memory (SRAM or DRAM), read-only memory (ROM), electrically-erasable programmable ROM (EEPROM or flash memory), magnetic media and optical media, whether permanent or removable. Most consumer-oriented computer applications are software solutions provided to the user on some removable computer-usable media, such as a compact disc read-only memory (CD-ROM).
In response to instructions from controller 305, voltage source 310 selectively sends voltage pulses V1 to VN respectively to resistors 1301 to 130N, where the voltage pulses V1 to VN each has a pulse time, in seconds, of Δt. One or more thermal sensors 324 are disposed on wafer 122 for monitoring the temperature of fluid-ejecting substrate 120 by measuring the temperature of fluid-ejecting substrate 120 at a high enough frequency to capture the system's overall thermal dynamics. For one embodiment, each thermal sensor 324 is connected to a temperature measurement unit 320. For one embodiment, each of the thermal sensors 324 is a temperature sense resistor or temperature sense diode. For another embodiment, temperature measurement unit 320 includes circuitry 322 for measuring the resistance of each of the temperature sense resistors. Circuitry and methods for measuring the resistance of temperature sense resistors are well known in the art. For one embodiment, a data acquisition unit 323 of temperature measurement unit 320 receives analog signals from temperature sensors 324 or from circuitry 322, converts them into digital signals, and sends them to controller 305.
For one embodiment, fluid-ejecting substrate 120 includes a plurality (or bank) of nozzles 132 and resistors 130 in planes parallel to the plane of
For another embodiment, resistors 130 may be replaced with actuators, such as piezoelectric actuators. For this embodiment, voltage pulses, e.g., from voltage source 310, are applied to the piezoelectric actuators, causing them to expand. The expansion acts to eject the fluid from chambers 126 (
For other embodiments, pre-pressurized fluid is supplied to each of chambers 126 via channels 136 and feed channel 140 from a pressurized fluid reservoir, located externally of fluid-ejecting substrate 120, for preselected instants of time, such as is commonly done for continuous inkjet (CIJ) printing, and is ejected under pressure though nozzles 132. For these embodiments, the fluid is continuously supplied under pressure by feed channel 140. For a non-fluid ejecting state, the fluid is blocked from entering channels 136 by a deflector (or gutter) (not shown), the use of which is well known in the art. For these embodiments, the fluid may be preheated using resistors 130 or 170 prior to ejection. For another embodiment, a heater 180 may be located at an outlet of each nozzle 132, as shown in
For each voltage pulse supplied by voltage source 310, the energy input to fluid-ejecting substrate 120 is determined from
E
in=[(Δt×V2)/R]in (1)
where R is the total resistance of the number of resistors 130, 170, or 180 activated during the pulse. The primary energy output from fluid-ejecting substrate 120 for each voltage pulse is determined from
E
out=(mcpΔT)out (2)
where mout, cp out, and ΔTout are respectively the mass of the ejected liquid, specific heat of the ejected liquid, and the temperature change of the ejected liquid. It will be appreciated by those of skill in the art that Eout may include various energy losses, e.g., convective losses to the environment and ink supply source as well as conduction losses to a body integral with fluid-ejecting substrate 120. The energy stored in fluid-ejecting substrate 120 is determined from
E
subs=(mcpΔT)subs (3)
where msubs, cp subs, and ΔTsubs are respectively the mass of fluid-ejecting substrate 120, specific heat of fluid-ejecting substrate 120, and the temperature change of fluid-ejecting substrate 120. Note that this embodiment assumes that the entire mass msubs experiences the same temperature change, i.e., a substantially infinitesimal temperature propagation time through mass msubs.
The mass of the ejected liquid may be determined from an energy balance on fluid-ejecting substrate 120, as follows:
E
out
=E
in
−E
subs (4)
Substituting equations (1)-(3) into equation (4), gives
(mcpΔT)out=[(Δt×V2)/R]in−(mcpΔT)subs (5)
Each term on the right side of equation (5) either can be determined from measurements or is a known property. For one embodiment, ΔTsubs can be measured using thermal sensors 324, where ΔTsubs is the difference between the measured temperature of fluid-ejecting substrate 120 at the end of the voltage pulse and the measured temperature at the start of the voltage pulse. Note that for this embodiment it is assumed that the entire mass msubs experiences the same temperature change as temperature sensor 324. This enables the energy of the ejected liquid for each voltage pulse to be determined.
Note that summing (or integrating) the right side of equation (5) over a predetermined number of voltage pulses gives the total energy of the ejected liquid for the predetermined number of voltage pulses. Note further that Δt and/or R may vary from pulse to pulse, where the variation in R is due to the variation in the number of resistors 130 activated for each pulse. Note, too, that for large number of pulses, a steady state may occur, reducing equation (4) to Eout=Ein, i.e., the energy storage term Esubs, drops out. For another embodiment, the first term on the right side of equation (5), the energy in, is substantially constant, as are msubs, cp subs of the second term on the right side of equation (5), the stored energy. This suggests that the ejected mass mout correlates with the temperature change of fluid-ejecting substrate 120 ΔTsubs or the sum (or integral) of ΔTsubs over a plurality of voltage pulses.
Since the mass of the ejected liquid mout is the quantity that is to be determined, and ΔTout cannot be easily determined, a calibration equation (or curve or look-up table) is used. For one embodiment, the calibration equation determined as follows: The fluid ejecting substrate is operated under the same conditions as the intended application, and the ejected mass is collected and determined for different values of the right side of equation (5), e.g., by blocking some percentage of the fired nozzles so that Ein is constant in all cases but Eout varies depending on how many nozzles are capable of firing. The calibration equation can then be used to determine the ejected mass for values of the right side of equation (5), i.e., the energy of the ejected fluid, during actual operation. For another embodiment, a calibration equation may be determined by operating the fluid ejecting substrate and collecting and measuring the ejected mass for different values of the temperature change of fluid-ejecting substrate 120 ΔTsubs or the integral of ΔTsubs over a plurality of voltage pulses. This calibration equation can then be used to determine the ejected mass for different values of the temperature change of fluid-ejecting substrate 120 ΔTsubs or the integral of ΔTsubs over a plurality of voltage pulses, during actual operation. Note that for one embodiment, the calibration equations are obtained under substantially the same conditions that are encountered during actual operation of the fluid ejecting substrate. In this way, the calibration equations account for the various energy losses discussed above.
Optionally, for another embodiment, after determining that one or more nozzles are defective, the method continues in
At block 530, the temperature change, e.g., temperature increase, of fluid-ejecting substrate 122 is measured. If the temperature change of fluid-ejecting substrate 122 does not exceed a second predetermined temperature change at decision block 535, it is indicated that the portion of nozzles is not defective at block 540. Otherwise, it is likely that one or more nozzles are defective, and it is indicated that one or more nozzles of the portion of nozzles are defective at block 545. For one embodiment, the method proceeds to decision block 550, as indicated by the dashed line between block 545 and decision block 550. For this embodiment, if all the portions of nozzles have been checked at decision block 550, the method ends at block 555. Otherwise, the method continues until all of the portions of nozzles have been checked.
Optionally, for another embodiment, after determining that one or more nozzles of a portion of nozzles are defective, the method may proceed from block 545 of
For another embodiment, the first, second, and/or third predetermined temperature changes may be equal. For this embodiment, activating a portion of nozzles at block 525 of
For one embodiment, the first, second, and third predetermined temperature changes may be determined using experimental simulations where one or more nozzles are defective. For another embodiment, fluid-ejecting substrates with known nozzle defects may be used in the simulations. For some embodiments, the simulations are performed under substantially the same operating conditions as the actual operation of fluid-ejecting substrate 122. For other embodiments, the second predetermined temperature change may be determined using fluid-ejecting substrates known to have at least one portion with one or more nozzle defects, while the first predetermined temperature change may be determined using fluid-ejecting substrates known to have one or more nozzle defects. For another embodiment, the third predetermined temperature change may be determined using fluid-ejecting substrates known to have a single nozzle defect.
Note that since it is likely that more nozzles are active during operation of the fluid-ejecting substrate than when a portion of the fluid-ejecting substrate is being operated, and the first predetermined temperature difference is likely to be higher than the second predetermined temperature difference for some embodiments. Moreover, for other embodiments, it is likely that more nozzles are active when a portion of the fluid-ejecting substrate is being operated than when a single nozzle is being operated, the second predetermined temperature difference is likely to be higher than the third predetermined temperature difference.
For another embodiment, if the mass ejected from the fluid-ejecting substrate, determined as described above, falls below an expected ejected mass during a particular activation event, e.g., including one or more activation pulses, the current or subsequent activation event may be extended until the mass ejected from the fluid-ejecting substrate is substantially equal to the expected ejected mass.
For another embodiment the, if the mass ejected from the fluid-ejecting substrate, determined as described above, falls below an expected ejected mass during a particular activation event, e.g., including one or more activation pulses, the defective nozzle identification routine (
Although specific embodiments have been illustrated and described herein it is manifestly intended that the scope of the claimed subject matter be limited only by the following claims and equivalents thereof.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11142625 | Jun 2005 | US |
| Child | 12351763 | US |
