Acoustic and ultrasonic monitoring of inkjet droplets

Abstract
A monitoring system monitors a pressure wave developed in the surrounding ambient environment during inkjet droplet formation. The monitoring system uses either acoustic, ultrasonic, or other pressure wave monitoring mechanisms, such as a laser vibrometer, an ultrasonic transducer, or an accelerometer sensor, for instance, a microphone to detect droplet formation. One sensor is incorporated in the printhead itself, while others may be located externally. The monitoring system generates information used to determine current levels of printhead performance, to which the printer may respond by adjusting print modes, servicing the printhead, adjusting droplet formation, or by providing an early warning before an inkjet cartridge is completely empty. During printhead manufacturing, an array of such sensors may be used in quality assurance to determine printhead performance. An inkjet printing mechanism is also equipped for using this monitoring system, and a monitoring method is also provided.
Description




FIELD OF THE INVENTION




The present invention relates generally to inject printing mechanisms, and more particularly to a system for monitoring a pressure wave developed in the surrounding ambient environment during the process of inkjet droplet formation. The system uses the pressure wave information to determine current levels of printhead performance, and if required, the system then adjusts the print routine, services the printhead, or alerts an operator, for instance, that an inkjet cartridge is nearly empty.




BACKGROUND OF THE INVENTION




Inkjet printing mechanisms use cartridges, often called “pens”, which shoot drops of liquid colorant, referred to generally herein as “ink,” onto a page. Each pen has a printhead formed with very small, pin-hole-sized nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanism are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization or firing chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).




To clean and protect the printhead, typically a “service station” mechanism is mounted within the print chassis so the printhead can be moved over the station for servicing and maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as “spitting,” with this non-image producing waste ink being collected in a “spittoon” reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.




To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide faster drying, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigments based inks have a higher solid content than the earlier dye based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solid within the new inks themselves. Partially or completely blocks nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Besides merely forcing clogs out of the nozzles, spitting also heats the ink near the nozzles, which decreases the ink viscosity and assists in dissolving ink clogs. Spitting to clear the nozzles becomes even more important when using pigment based inks, because the higher solids content contributes to the clogging problem more than the earlier dye based inks.




The pen body may serve as an ink containment reservoir that protects the ink from evaporation and holds the ink so it does not leak or drool from the nozzles, Ink leakage is prevented using a force known as “backpressure,” which is provided by the ink containment system. Desired backpressure levels may be obtained using various types of pen body designs, such as resilient bladder designs, spring-bag designs, and foam-based designs.




To maintain reliability of the inkjet printing mechanism during operation, it would be helpful to have advanced warning for an operator as to when the ink level in a cartridge is getting low. This would allow an operator to procure a fresh inkjet cartridge before the one in use is completely empty. If the cartridge is refillable, an early warning would allow an operator to replenish the ink supply before the pen is dry-fired. Dry-firing an inkjet cartridge when empty may cause permanent damage to the printhead by overheating the resistive heater elements, causing the resistors to burn out.




A variety of solutions have been proposed for monitoring the level of ink within inkjet cartridges, with many incorporating measuring devices inside the cartridge. For example, several mechanism devices have been proposed to determine when the ink supply falls below a predetermined level. One system uses a ball check valve within an ink bag to interrupt ink flow when the pen is nearly empty. Unfortunately, this system has no early warning capability and it may abruptly interrupt a printing job when a certain level of ink is reached.




Other earlier ink level monitoring systems kept a running count of the number of drops fired, which worked well until cartridges were exchanged. Unfortunately, these drop counting systems had no way of determining whether a new or a partially used cartridge was installed, so they failed to detect upcoming empty conditions for the partially used cartridges. Several more sophisticated detection systems have been devised, based upon measuring printhead temperature changes after spitting specific amounts of ink into the spittoon. These temperature monitoring systems were slow to use, and they wasted ink that could otherwise have been used for printing. Other systems have been proposed using specially designed nozzles which are more sensitive to changes in the ink reservoir backpressure than the remaining nozzles, with these backpressure changes indicating ink depletion.




In operating an inkjet printing mechanism, it would be helpful to provide feedback to a print controller, such as a printer driver residing in an on-board microprocessor and/or in the host computer, as to whether or not the printhead nozzles are firing as instructed. This information would be useful to determine whether a nozzle had become clogged and required purging or spitting to clear the blockage. This information would streamline the spitting process and conserve ink because only the clogged nozzle(s) would be spit to clear the blockage. Moreover, if damaged nozzles or heating elements could be detected, then other nozzles may be substituted in the firing scheme to compensate for the damaged nozzles. Feedback as to nozzle firing could also be used to test the electro-mechanical interconnect between a replaceable inkjet cartridge and the printing mechanism. Over time, this interconnect may be contaminated with ink, interrupting the electrical connections. When this happens, it would be desirable to notify the user to clean the interconnect.




As a manufacturing quality control check, it would also be desirable to monitor nozzle performance, for instance, to verify correct nozzle-to-nozzle alignment. It would also be helpful to check for any nozzle telecentricity, that is, any lack of perpendicularly of the orifice hole through the nozzle plate relative to the plate surface. Another important feature to monitor would be nozzle directionality, that is whether a nozzle was firing at an angle other than perpendicular to the orifice plate and/or to the media.




It would also be useful to determine from merely firing ink droplets at media, what type of media was inserted into the printing mechanism, such as plain paper, glossy high-quality paper, or transparencies. This information would then allow the printer controller to adjust the print mode to correspond to the type of media in use. One desirable energy saving would be to use only the minimum “turn-on” energy required to eject ink from each of the nozzles. Using only the minimum amount of firing energy would extend printhead life by minimizing overheating of the heaters in the printhead. This minimum firing energy operation could be accomplished by providing drop feedback to the printer controller.




In the past, some inkjet printing mechanism have detected drops using optical means. For example, one system measured the change in drop volume for a given firing temperature by firing smaller and smaller droplets until the drops could no longer be seen by the optical detector. Unfortunately, the target drop volume has decreased in newer inkjet cartridges, for example, some droplets are now on the order of 30 picoliters. These small droplets require precise positioning of such an optical drop detector, which is difficult to implement consistently and reliably in production printing mechanisms. Other drop detect systems addressed the nozzle-to-nozzle and the printhead-to-printhead alignment issues by printing several test patterns, from which a user then selects the best pattern or compares the test pattern to a reference pattern in the instruction manual. In these visual tagging systems, the printer controller or driver then adjusts the printing mode to an optimum level that corresponds the pattern selected by the user. Another visual system uses a tab connected to the internal spring-bag reservoir to retract the tab as the pen empties, giving the user a visual ink level indicator on the pen body. Unfortunately, these visual tagging systems required user intervention or judgment, so they were not automatic or “transparent” to the user in operation.




In multi-printhead systems, such as those carrying two, three, four or more cartridges, it would also be desirable to have an automatic method of monitoring the pen-to-pen alignment. This pen-to-pen alignment could then be used to adjust the firing sequence of the nozzles to compensate for any misalignment of the pens. Pen-to-pen misalignment may be caused by improper seating within the pen carriage, or an accumulation of tolerance variations within a specific pen body and printhead of a particular cartridge. Pen-to-pen misalignment may also be caused by an accumulation of tolerance variations within a specific printer carriage which holds the cartridges.




Thus, a need exists for a system to provide inkjet droplet information to the printing mechanism controller. This information would allow the controller to respond by adjusting droplet formation or print modes, servicing the pen, or alerting the operator of a particular condition, for instance, that an inkjet cartridge is nearly empty.




SUMMARY OF THE INVENTION




According to one aspect of the present invention, an ultrasonic monitoring method of operating an inkjet printing mechanism is provided for a printing mechanism having an inkjet printhead installed therein, with the printhead having plural nozzles. The method includes the steps of applying an enabling signal to a selected nozzle of the inkjet printhead, and normally generating a pressure wave in response to the applying step. The method also includes the steps of ultrasonically detecting the pressure wave emitted by the selected nozzle during the generating step, and then responding to the detecting step.




According to another aspect of the invention, an inkjet printing mechanism is provided as including an inkjet printhead with plural nozzles that each normally, in response to an enabling signal, eject ink therethrough and generate a pressure wave comprising both audio and ultrasonic frequency components. The printing mechanism has an ultrasonic pressure wave sensor located to detect the ultrasonic pressure waves normally generated by the plural nozzles and in response thereto, the sensor generates a wave signal. The printing mechanism also has a controller that responds to the wave signal by generating an action signal.




According to an additional aspect of the invention, a method of monitoring the performance of an inkjet printhead having plural nozzles is provided. The method includes the steps of applying an enabling signal to a selected nozzle of the inkjet printhead, and normally generating a pressure wave in response to the applying step. In a detecting step, the pressure wave emitted by the selected nozzle during the generating step is detected from plural locations, and in response to the detected pressure wave, a wave signal is generated from each of the plural locations. In an analyzing step, the wave signal from each of the plural locations is analyzed to determine performance of the selected nozzle.




In a further aspect of the invention, an inkjet printhead is provided for an inkjet printing mechanism that generates plural firing signals. The printhead has an ink reservoir holding a supply of ink and an orifice plate defining plural nozzles extending therethrough. An ink ejection mechanism fluidicly couples the ink reservoir to the orifice plate nozzles. The ink ejection mechanism comprises plural in ejection chambers each responsive to at least one of the plural firing signals to normally eject ink through an associated one of the plural nozzles. An accelerometer mechanism is located adjacent to the ink ejection mechanism to detect a pressure wave normally generated in response to at least one of the plural firing signals, and to generate a wave signal in response thereto.




An overall goal of the present invention is to provide an inkjet droplet formation monitoring system to generate information that may be used to determine current levels of performance, which is then used by the printer controller to optimize performance. This information may be used for a variety of other purposes, such as to give an early warning before an inkjet cartridge is completely empty, allowing an operator to refill, replace or service the cartridge.




An additional goal of the present invention is to provide a monitoring system that may be used during printhead manufacture to verify the quality of printhead performance.




Another goal of the present invention is to provide a monitoring system that may be used with any type of inkjet printhead, and to provide a special printhead that has a sensor integrally formed therein.




A further goal of the present invention is to provide an inkjet droplet formation monitoring system, as well as a printing mechanism and a method which optimizes the print quality of an image in response to this monitoring.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a fragmented perspective view of one form of an inkjet printing mechanism employing a monitoring system of the present invention for monitoring pressure waves developed during inkjet droplet formation, and for adjusting operation in response thereto.





FIG. 2

is a sectional perspective view of one form of a sensor of the present invention, taken along line


2





2


of FIG.


1


.





FIG. 3

is a side elevational view of two alternate forms of a sensor of the present invention, any of which may be substituted for the sensor of FIG.


2


.





FIG. 4

is an enlarged sectional elevational view of one form of the third embodiment of the sensor of the present invention, shown integrally formed in a portion of an inkjet printhead in a view taken from the perspective along line


4





4


of FIG.


2


.





FIGS. 5 and 6

are graphs illustrating sensor information generated using two different sensor embodiments in the monitoring system of FIG.


1


.





FIG. 7

is a graph of the transverse vibration velocity of a printhead orifice plate next to a nozzle which is firing.





FIG. 8

is a graph of the amplitude spectrum of the waveform of FIG.


7


.





FIG. 9

is a graph of a sound pressure wave generated from the droplet formation or nozzle firing process, measured by a wide frequency band microphone sensor.





FIG. 10

is a graph of the audible and ultrasonic frequency components of the waveform of FIG.


9


.





FIG. 11

is a flow chart illustrating one manner of operating the inkjet printing mechanism and monitoring system of FIG.


1


.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS





FIG. 1

illustrates an embodiment of an inkjet printing mechanism, here shown as an inkjet printer


20


, constructed in accordance with the present invention, which may be used for printing for business reports, correspondence, desktop publishing, and the like, in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the present invention include plotters, portable printing units, copies, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts of the present invention are illustrated in the environment of an inkjet printer


20


.




While it is apparent that the printer components may vary from model to model, the typical inkjet printer


20


includes a chassis


22


surrounded by a housing or casing enclosure


24


, typically of a plastic material. Sheets of print media are fed through a print zone


25


by a print media handling system


26


. The print media may be any type of suitable sheet material, such as paper, card-stock, transparencies, mylar, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The print media handling system


26


has a feed tray


28


for storing sheets of paper before printing. A series of conventional or other motor-driven paper drive rollers (not shown) may be used to move the print media from tray


28


into the print zone


25


for printing. After printing, the sheet then lands on a pair of retractable output drying wing members


30


, shown extended to receive a the printed sheet. The wings


30


momentarily hold the newly printed sheet above any previously printed sheets still drying in an output tray portion


32


before retracting to the sides to drop the newly printed sheet into the output tray


32


. The media handling system


26


may include a series of adjustment mechanism for accommodating different sizes of print media, including letter, legal, A-4 , envelopes, etc., such as a sliding length adjustment lever


34


, and an envelope feed slot


35


.




The printer


20


also has a printer controller, illustrated schematically as a microprocessor


36


, that receives instructions from a host device, typically a computer, such as a personal computer (not shown). Indeed, many of the printer controller functions may be performed by the host computer, by the electronics on board the printer, or by interactions therebetween. As used herein, the term “printer controller


36


” encompasses these functions, whether performed by the host computer, the printer, an intermediary device therebetween, or by a combined interaction of such elements. The printer controller


36


may also operate in response to user inputs provided through a key pad (not shown) located on the exterior of the casing


24


. A monitor coupled to the computer host may be used to display visual information to an operator, such as the printer status or a particular program being run on the host computer. Personal computers, their input devices, such as a keyboard and/or a mouse device, and monitors are all well known to those skilled in the art.




A carriage rod


38


is supported by the chassis


22


to slideably support an inkjet carriage


40


for travel back and forth across the print zone


25


along a scanning axis


42


defined by the guide rod


38


. One suitable type of carriage support system is shown in U.S. Pat. No. 5,366,305, assigned to Hewlett-Packard Company, the assignee of the present invention. A conventional carriage propulsion system may be used to drive carriage


40


, including a position feedback system, which communicates carriage position signals to the controller


36


. For instance, a carriage drive gear and DC motor assembly may be coupled to drive an endless belt secured in a conventional manner to the pen carriage


40


, with the motor operating in response to control signals received from the printer controller


36


. To provide carriage positional feedback information to printer controller


36


, an optical encoder reader may be mounted to carriage


40


to read an encoder strip extending along the path of carriage travel.




The carriage


40


is also propelled along guide rod


38


into a servicing region, as indicated generally by arrow


44


, located within the interior of the casing


24


. The servicing region


44


houses a service station


45


, which may provide various conventional printhead servicing function. For example, a service station frame


46


may hold a conventional or other mechanism that has caps to seal the printheads during periods of inactivity, wipers to clean the nozzle orifice plates, and primers to prime the printheads after periods of inactivity. Such caps, wipers, and primers are well know to those skilled in the art. A variety of different mechanism may be used to selectively bring the caps, wipers and primers (if used) into contact with the printheads, such as translating or rotary devices, which may be motor driven, or operated through engagement with the carriage


40


. For instance, suitable translating or floating sled types of service station operating mechanisms are shown in U.S. Pat. Nos. 4,853,717 and 5,155,497, both assigned to the present assignee, Hewlett-Packard Company. A rotary type of servicing mechanism is commercially available in the DeskJet® 850C and 855C color inkjet printers, sold by Hewlett-Packard Company, the present assignee.

FIGS. 1 and 2

show a spittoon portion


48


of the service station, defined at least in part by the service station frame


46


.




In the print zone


25


, the media sheet receives ink from an inkjet cartridge, such as a black ink cartridge


50


and/or a color ink cartridge


52


. The cartridges


50


and


52


are also often called “pens” by those in the art. The illustrated color pen


52


is a tri-color pen, although in some embodiments, a set of discrete monochrome pens may be used. While the color pen


52


may contain a pigment based ink, for the purposes of illustration, pen


52


is described as containing three dye based ink colors, such as cyan, yellow and magenta. The black ink pen


50


is illustrated herein as containing a pigment based ink. It is apparent that other types of inks may also be used in pens


50


,


52


, such as paraffin based inks, as well as hybrid or composite inks having both dye and pigment characteristics.




The illustrated pens


50


,


52


each include reservoirs for storing a supply of ink. In the illustrated embodiment, pen


50


has a spring-bag reservoir to provide the desired levels of backpressure to prevent nozzle leakage or “drool,” while in contrast, the pen


52


has a foam-based reservoir design. The pens


50


,


52


have printheads


54


,


56


respectively, each of which have an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The illustrated printheads


54


,


56


are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. The printheads


54


,


56


typically include substrate layer having a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed to eject a droplet of ink through the nozzles and onto a media sheet in the print zone


25


. The printhead resistors are selectively energized in response to enabling or firing command control signals, which may be delivered by a conventional multi-conductor strip (not shown) from the controller


36


to the printhead carriage


40


, and through conventional interconnects between the carriage and pens


50


,


52


to the printheads


54


,


56


.




Acoustic and Ultrasonic




Monitoring System




Sonic or audible sound waves are longitudinal waves that can be liquids and gases, such as air, and that can be detected by the human ear, as well as other sensors, typically in an audible range up to about 20,000 Hz (20 kHz). Above the audible range, they referred to as ultrasonic waves. When traveling through solids, these also have transverse components, so they may be generally referred to as a “stress wave.” In firing an inkjet printhead nozzle, a pressure wave may be generated that has a variety of components, some of which may be in the audible range, while others may be in the ultrasonic range. Unless otherwise specified, as used herein the term “pressure wave” is understood to include longitudinal mechanical waves in both the acoustic and ultrasonic frequency ranges, typically traveling through air, as well as vibrations when traveling through a solid.




A. First Embodiment





FIG. 2

shows a first embodiment of a monitoring system


60


constructed in accordance with the present invention for monitoring a pressure wave developed in the surrounding ambient environment, here in air, during ink droplet formation as the printhead


54


of pen


50


is fired into spittoon


48


, as illustrated by arrow


62


. For clarity, the color pen


52


, carriage


40


, and remaining printer and service station components are omitted from the view of

FIG. 2

, although it is apparent that the concepts illustrated herein are also applicable to operation of the color pen


52


. A support member


64


is mounted to the service station frame


46


, near the spitting location.




The monitoring system uses either vibratory, acoustic, audible, ultrasonic, or other pressure wave monitoring mechanisms, such as a laser vibrometer or an accelerometer sensor, for instance, a microphone device


65


supported by member


64


. The support


64


may also house microphone electronics, indicated generally at location


66


, which are in communication with the controller


36


via conductors preferably routed through the interior of enclosure


24


. Preferably, the microphone


65


is a directionally oriented, line-of-sight transducer, positioned toward the printhead


54


to “listen” for droplet formation, as indicated by the dashed line


68


. Line-of-sight monitoring is preferred to avoid contamination of the pressure wave by ambient noise generated by the printer itself, by other background sources in the local environment adjacent the printer


20


, or by reflections of the pressure wave (although if captured, these reflections may be used to help amplify or attenuate the monitored pressure wave to obtain a better transducer signal). Before discussing the various methods of operating the monitoring system


60


, several alternate sensor locations will be illustrated with respect to

FIGS. 3 and 4

.




B. Second Embodiment




In

FIG. 3

, two additional embodiments of a monitoring system constructed in accordance with the present invention are illustrated, although it is apparent that only one such system would typically be used on a given printing mechanism, but in other implementations, two or more of these monitoring locations may be used. For instance, in a manufacturing context, a linear array of sensors may be used to sonically or ultrasonically detect nozzle performance to monitor printhead quality at the factory or in other noisy environments. The illustrated second embodiment of a chassis-mounted monitoring system


70


has a support member


72


mounted to the printer chassis


22


in a location adjacent either the print zone


25


, or adjacent the service station


45


. The support


72


is located for a line-of-sight positioning, indicated by the dashed line


74


, of a microphone device


75


, which may be as described above for system


60


. The support


72


may also house microphone electronics


66


, as described above.




C. Third Embodiment





FIG. 3

shows a third embodiment of a carriage-mounted monitoring system


80


, constructed in accordance with the present invention, and having a support member


82


mounted to the printer carriage


40


. The support


82


is located for a light-of-sight positioning, indicated by the dashed line


84


, of a microphone device


85


or other type pressure wave monitoring mechanism, as described above for the system


60


. The support


82


may also house microphone electronics


66


, as described above. Communication between the controller


36


and the microphone electronics


66


may be accomplished via a portion of the same conductor system that delivers firing signals to the carriage


40


from controller


36


. For example, one or more conductors within a conventional flexible conductor strip (not shown) that couples the carriage


40


to the controller


36


may be dedicated to the monitoring system


60


, rather than to printhead firing or printhead temperature monitoring (typically accomplished using a temperature sensing resistor integrally constructed within the printhead silicon).




D. Fourth Embodiment





FIG. 4

shows a fourth embodiment of an printhead-mounted monitoring system


90


, constructed in accordance with the present invention as having either a laser vibratory, acoustic, audible, ultrasonic, or other type of pressure wave monitoring mechanism, such as an accelerometer sensor


92


integrally formed within the silicon of the printhead. The sensor


92


is integrally formed within printhead


54


′ of pen


50


′, which otherwise may be of the same construction as described above for pen


50


, which otherwise may be of the same construction as described above for pen


50


, and in particular, as described in U.S. Pat. No. 5,420,627, which is assigned to the present assignee, Hewlett-Packard Company. The illustrated printhead


54


,


54


′ has 300 nozzles total, arranged in two mutually parallel linear arrays of 150 nozzles, with each nozzle array spanning a length of around 12.7 mm (0.5 inches). It is apparent that the principles of sensor


92


illustrated with respect to the black pen


50


′ may also be applied to the tri-color pen


52


, or to other printhead assemblies, including piezo-electric printheads. The technology for fabricating the sensor


92


within a silicone integrated circuit chip is known to those skilled in the art, and can be accomplished with the same economical bulk micro-machining techniques used to fabricate pressure sensors and accelerometers, such as to form one or more cantilevered reed or beam type accelerometers


93


. Either the printhead


54


′, the cartridge


50


′, or the controller


36


may house all or a portion of the sensor electronics package


66


(omitted for clarity from FIG.


4


). Communication between the printhead sensor


92


and controller


36


is preferably accomplished in parallel with the communication path of the firing signal and printhead temperature monitoring signals, as described above for system


80


, except that the electrical interconnect between the pen


50


′ and the carriage


40


is also used.




The illustrated cartridge


50


′ has a plastic body


94


that defines an ink feed channel


95


, which is in fluid communication with an ink reservoir located within the upper rectangular-shaped portion of the cartridge, such as reservoir


96


shown in FIG.


2


. The body


94


also has a raised wall


98


that defines a cavity


99


at the lower extreme of the feed channel


95


. An ink ejection mechanism


100


is centrally located within cavity


99


, and held in place through attachment by an adhesive layer


102


to a flexible polymer tape


104


, such as Kapton® tape, available from the 3M Corporation, Upilex® tape, or other equivalent materials known to those skilled in the art. The illustrated tape


104


serves as a nozzle orifice plate by defining two parallel columns of offset nozzle holes or orifices


106


formed in tape


104


by, for example, laser ablation technology. The adhesive layer


102


, which may be of an epoxy, a hot-melt, a silicone, a UV curable compound, or mixtures thereof, forms an ink seal between the raised wall


98


and the tape


104


.




The ink ejection mechanism


100


includes a silicone substrate


110


that contains a plurality of individually energizable thin film firing resistors


112


, each located generally behind a single nozzle


106


. The firing resistors


112


, each located generally behind a single nozzle


106


. The firing resistors


112


act as ohmic heaters when selectively energized by one or more enabling signals or firing pulses


228


(FIG.


11


), which are delivered from the controller


36


through a flexible conductor to the carriage


40


, and then through electrical interconnects to conductors (omitted for clarity) carried by the polymer tape


104


. A barrier layer


114


may be formed on the surface of the substrate


110


using conventional photolithographic techniques. The barrier layer


114


may be a layer of photoresist or some other polymer, which in cooperation with tape


104


defines vaporization chambers


115


, each surrounding an associated firing resistor


112


. The barrier layer


114


is bonded to the tape


104


by a thin adhesive layer


116


, such as an uncured layer of polyisoprene photoresist. Ink from the supply reservoir


96


(

FIG. 2

) flows through the feed channel


95


, around the edges of the substrate


110


, and into the vaporization chambers


115


. When the firing resistors


112


are energized, ink within the vaporization chambers


115


is ejected, as illustrated by the emitted droplets of ink


118


.




As shown in

FIG. 4

, the sensor


92


is housed within a resonance chamber


120


that is defined by cooperation of the substrate


110


, barrier layer


114


, tape


104


, and the adhesive layer


116


. The resonance chamber


120


isolates sensor


92


from ink flowing through the cavity


99


and vaporization chambers


115


, which is believed to enhance the sensor's performance. It is apparent that in some implementations, it may be preferable to locate all or a portion of the sensor in the ink, such as within cavity


99


, in the vaporization chambers


115


, or adjacent thereto. As mentioned above, the illustrated sensor


92


may be constructed with the same techniques used to fabricate pressure sensors and accelerometers to form one or more cantilevered reed or beam type accelerometers


93


, two of which are shown in

FIG. 4

, preferably in the same plane as the firing resistors


112


. Alternatively, the accelerometers may be replaced with a polysilicon strain gauge that detects electrical current changes in response to deflection. The resonance chamber


120


may run along the length of the two linear nozzle arrays (each represented by a single nozzle


106


in FIG.


4


), with a group of these reeds


93


distributed along the entire length of the chamber, or clustered in one or more locations. For instance, only one reed


93


, or more preferably two reeds for redundancy, may be located in the middle region of the substrate


110


, at a corner, or perhaps one (or two) on each end of the nozzle arrays.




The sensor reeds


93


are believed to detect the vibration of the silicon substrate


110


during firing, either in the acoustic or ultrasonic frequency ranges. For the illustrated cartridge


50


′, the firing frequency is about 12 kHz, so the sensor reeds


93


may be tuned to oscillate at a natural vibratory frequency of 12 kHz. If other frequencies are to be detected, then the reeds


93


may be tuned to these other frequencies by adding a seismic mass near the end of the reed that is suspended in the resonance chamber


120


. Indeed, the sensor


92


may have several reeds


93


all tuned to detect different frequencies, or groups of frequencies. In operation, a small current is run through the reeds


93


, which deflect when encountering the resulting pressure initiated or radiated during pen firing. Here, the accelerometer reeds


93


operate in the same manner as a polysilicon strain gauge, detecting electrical current changes in response to deflection. This deflection changes the electrical resistance of the reeds


93


, which may then measured and correlated to the frequency detected using conventional techniques known to those skilled in the art to generate a wave signal


204


(FIG.


11


).




In conclusion, the selection of which sensor system


60


,


70


,


80


or


90


to use may vary depending upon the type of printing mechanism being designed, and its priority of desired features. For example, one advantage of mounting the sensor


85


of system


80


to the carriage


40


, is that the signal may also be measured during printing, not just during spitting as for system


60


, or when located near a chassis mounted sensor


75


. Thus, a carriage based measuring system


80


, or a printhead mounted system


90


may increase throughput (rate usually measured in pages per minute), as monitoring does not require the printhead to be stopped in a particular location. Indeed, in some implementations, it may be desirable just to learn whether a nozzle is firing or not, and then to substitute other nozzles for a misfiring or a damaged nozzle to maintain print quality. Other systems may look at the actual level of the signal being detected, for instance, to determine optimal turn-of energy, such as by making amplitude measurements, so more precise sensor to printhead positioning is required, with the most precise embodiment being the on-board system


90


.




Wave Signal Graphs




In response to monitoring of inkjet droplet formation


62


by any of the monitoring systems


60


,


70


,


80


or


90


, the illustrated sensor electronics


66


generate a wave signal


204


(

FIG. 11

) in response to the pressure wave produced during droplet formation. This wave signal


204


is typically an analog signal that can be illustrated graphically, for instance as shown in

FIGS. 5 and 6

. The trace


130


in

FIG. 5

was made by monitoring the firing of one nozzle of the back printhead


54


using a 40 kHz piezo-electric microphone. This 40 kHz microphone is commercially available and relatively inexpensive (cost of about $2.00), so that it may be economically installed on inkjet printers for home and business use, for example. The trace


130


was initiated at time zero, which corresponded to the time the firing pulse was applied to the resistor associated with the fired nozzle.




Now if cost is not a constraint,

FIG. 6

shows the results for using a very sensitive and costly broad band microphone (cost of around $2500.00, including the associated electronics,), which was used during initial conceptual tests to prove the overall ultrasonic drop detection principle. This broad band microphone had a bandwidth of 160 kHz, so it detected all frequencies up to 160 kHz, rather than focusing on a single frequency like the inexpensive piezo-electric microphone used to generate curve


130


in FIG.


5


. Two traces are shown in FIG.


6


. The dashed trace


132


shows the ultrasonic pressure wave emitted or radiated by pen


50


when firing a single drop of ink


118


from a single nozzle


106


when the pen is full of ink. The solid trace


134


was made by firing a single nozzle


106


when the pen was empty. Only one firing frequency was used in

FIG. 6

with the frequency between firing the full ink nozzle and the empty nozzle being about 10 kHz. This 10 kHz value was just a convenient interval selected to locate the two pulses in the same time window, while spreading the traces


132


and


134


apart enough so the waveform of the first nozzle will have dampened out enough to avoid interference with the waveform of the next nozzle. The full pen waveform


132


has a different wave signature, as well as a higher peak amplitude, than that of the empty pen waveform


134


.




Indeed, even when using the more economical 40 kHz piezo-electric microphone of

FIG. 5

, the signal strength (amplitude) was found to drop when the pen had emptied during use. For example, a full pen had a peak-to-peak voltage amplitude of around 1.0 volts, whereas an almost empty pen had an amplitude decrease to about 0.6 volts peak-to-peak, while a dry pen had a peak-to-peak voltage of only 0.2 volts. This difference shows that the pressure wave is not solely due to ink injection, but the pressure wave also reflects other contributing factors occurring within the cartridge. Comparison of the full cartridge trace


132


with the empty trace


134


clearly shows a change in signal level, which may be compared with given threshold values to signal an imminent out-of-ink condition. This signal may be used to warn an operator of a nearly empty state, so a new pen may be available when the pen finally empties (see step


250


in FIG.


11


).




If laser vibrometer were used as the sensor


65


,


75




85


to detect the vibration using a laser beam, as was done during conceptual testing, the deflection in shape or transverse velocity of the orifice plate


104


can be measured to indicate functionality of individual nozzles. In this laser measurement technique, the vibration velocity of the orifice plate is measured by detecting changes in the frequency shift or the angle at which a laser beam is reflected off of the orifice plate


104


. These changes in the angle of the reflected laser beam may be translated into the degree of orifice plate deflection. For example,

FIG. 7

shows a trace


136


of the transverse vibration velocity of the orifice plate


104


next to a nozzle


106


which is firing.

FIG. 8

shows a trace


138


of the amplitude spectrum of the waveform of FIG.


7


. While such a laser beam sensor solution may not be cost effectively incorporated in the final printer product, it may be a very promising technique to use in the manufacturing process to monitor the quality of the printhead assemblies. It is apparent that as technology advances, it may be possible to design a cost effective laser beam sensor system for the final printer product.





FIG. 9

shows a sound pressure wave trace


140


, with a duration of less than 50 microseconds, generated from the droplet formation process or nozzle firing process. This pressure wave of

FIG. 9

is very impulsive, being rich in frequency components, including both audible and ultrasonic frequency components, as shown for trace


142


in FIG.


10


.




Method of Operation





FIG. 11

is a flow chart


200


that illustrates one embodiment of a method of controlling an inkjet printing mechanism, here, an inkjet printer


20


, in response to monitoring of inkjet droplet formation by any of the illustrated monitoring systems


60


,


70


,


80


or


90


. In a detection or monitoring step


202


, the sensors


65


,


75


,


85


,


92


monitor pressure waves in the acoustic or audible range, for instance, and in response thereto, the sensors generate a wave signal


204


, such as an analog signal, that is received by the electronics


66


associated with each microphone. The microphone electronics


66


may include signal conditioning features required by the particular type of sensor


65


,


75


,


85


,


92


being used. For example, these electronics may include amplifiers and band pass filters, such as a high gain, high Q band pass filter, for analog signal conditioning of the wave signal


204


. The sensors


65


,


75


,


85


and electronics


66


are preferably mounted on a single printed circuit board assembly


206


, which may be supported in the printer


20


by members


64


,


72


,


82


respectively, whereas the electronics


66


associated with the printhead mounted sensor


92


may be located anywhere between the print


54


′, the controller


36


and the host computer. Where ever the electronics


66


are located, in response to the wave signal


204


, the electronics


66


preferably perform a signal conditioning function, such as analog signal conditioning including analog signal amplification and filtering, to generate a conditioned wave signal


208


.




In the detection or monitoring step


202


, the sensors


65


,


75


,


85


,


92


monitor the sound field radiated by nozzle firing (or by the application of firing signals) pressure waves. These pressure waves may be in the acoustic or audible range, 10 Hz to 20 kHz, or in the ultrasonic range, for instance, 20 kHz to 500 kHz, or greater, depending upon the technology available for monitoring. Indeed, while the illustrated embodiment anticipates an upper frequency level of 500 kHz, the true upper limit may actually be in the megahertz band, assuming the technical ability exists to monitor such high frequencies. For instance, due to the inverse relationship of the signal strength amplitude and the monitoring distance, the sensor must be located physically close enough to the printhead to receive the pressure wave. Other technicalities to address before monitoring pressure wave frequencies in the megahertz band include data sampling constraints, which are presently a function of the available electronics. However, it is apparent that there is an upper limit that may be measured when transmitting through air, due to the upper limit on the compressibility of air. The relatively inexpensive piezo-electric disk-type microphone used to generate curve


130


of

FIG. 5

measured in the 40 kHz ultrasonic range.




Before completing the description of flow chart


200


, the phenomena of the pressure wave monitored in step


202


will be discussed, with reference to studies of the concept. For convenience, refer to

FIG. 4

for basic printhead construction, realizing that the tests were conducted using printhead


54


, without sensor


92


. The various merits of acoustic monitoring versus ultrasonic monitoring will also be compared. Another factor effecting pressure wave monitoring discussed below is sensor placement relative to the printhead. But first, the question to be answered is, “What generates the acoustic and ultrasonic components of the pressure wave that is monitored?”




A. Acoustic Pressure Wave Studies




Initial conceptual testing centered on measuring pressure waves developed in the audible range using a microphone as the sensor. These initial tests were directed toward a method of determining the out-of-ink condition, and more particularly to give an early warning of an impending empty condition. Unfortunately, too much background noise from other audio sources nearby printer


20


was also picked up by the microphone. The magnitude of the background noise yielded such a poor signal to noise ratio that the system failed to give consistently reliable results.




Other early studies looked at the vibration of the printhead silicon


110


and the orifice plate


104


, as well as the sound perceived versus the drop volume emitted. In one of these early vibratory studies, the operational shape deflection of the orifice plate


104


was measured using scanning laser vibrometer, where the change in phase or frequency shift was determined between a laser beam reflected by the orifice plate


104


and a reference laser beam. According to Doppler theory, this frequency shift is proportional to the velocity at which the object is moving. There is a vibration signal for each point that is scanned, as shown in FIG.


8


. The deflection shape may be obtained by integrating the vibration velocity, which is directly measured using the laser vibrometer. One advantage of this technique is that it does not affect the measured system because it is a non-contacting measurement technique. Furthermore, synchronizing the nozzle firing with the velocity measurements can help to reduce noise in the signal.




In the acoustic studies, the printhead silicon


110


was found to vibrate at its resonances after the initial impulsive response of the printhead. Specifically, when using a 3 kHz firing frequency, in one study a 12 kHz acoustic signal was measured, while in another study the orifice plate


104


also resonated at 9 kHz. Thus, it is expected that other firing frequency harmonics may also be measured, such as 6 kHz, 12 kHz, 15 kHz, etc. Unfortunately, other problems with resonance in the audible range were encountered. For example, the two metal side panels on the pen body of the black cartridge


50


were found to resonate at around 9 kHz, which was also the same frequency at which the orifice plate


104


was found to resonate. Thus, it would be difficult to distinguish whether the measured sound was emitted by the orifice plate


104


, by the printhead silicon


110


, or by the pen body.




In these audio frequency range, below 20 kHz, it also is believed that that the sound source may be the vibration during firing of the printhead silicon


110


, or the thermal expansion of the heater resistor


112


, or possibly both. This belief is based on the fact that the microphone sensors detected pressure waves when a droplet


118


was formed, and when firing signals were sent to an empty cartridge. Another theory is that the sudden very hot and very fast heating of the resistor


112


forms a “heat” bubble, that is, a localized expansion of air in the firing chamber


115


when the pen is empty. As the heat bubble of the empty pen expands and occupies more space, the heat bubble creates a pressure field in the ink and air. When an empty pen is fired, the pressure wave is developed in air, whereas when a full (or partially full) pen is fired, the pressure wave is developed in the fluid ink. The amplitude of the pressure wave changes because air and ink have very different acoustic impedances, and thus different acoustic wave radiation efficiencies. The difference in the signal amplitude from full to empty is believed to be due to the pen structure and related fluid properties, as well as bubble formation.




Indeed, while the exact source of the pressure wave generated is not completely understood at this time, this is not critical to the present invention. The essential factor is that an acoustic or ultrasonic pressure wave is generated, detected, and then actions are taken in response to this detection.




B. Ultrasonic Pressure Wave Studies




Following the initial audible range tests, ultrasonic monitoring of drop formation was tested. At the ultrasonic frequencies, the sound source may be the actual creation of a single inkjet bubble, with the ultrasonic signal occurring in the range of the time it takes to create the bubble. Bubble expansion due to thermal diffusion was found to generate a pressure wave of around 80 kHz in the illustrated embodiment, whereas the pressure wave from bubble collapse occurred at a frequency of around 160 kHz. These terms will be better understood after discussing the droplet formation process.




Referring to the printhead cross section in

FIG. 4

, the drop ejection process starts with the firing chamber


115


filling with ink and electric current being applied to the thin film resistor


112


in the chamber. The electric current heats the resistor


112


, and the heat energy is then transferred from the resistor to the ink, which begins to build pressure in the firing chamber. Eventually, the ink begins to boil and a vapor bubble is formed. This bubble grows to a maximum size, a droplet


118


of ink is ejected or pushed out of the nozzle


106


and then the bubble collapses. The act of pushing the droplet


118


out creates an opposite force that may cause the orifice plate


104


to vibrate. The heat of the firing process may also cause the silicon


110


to expand and contract, creating a thermal stress wave. When the ink droplet


118


is ejected, the remaining ink is pulled back into the firing chamber


115


as the bubble collapses. This collapse may also cause the silicon substrate


110


to vibrate. More ink then flows into the chamber


115


to replenish it for firing another droplet.




When the pen has run out of ink, applying electric current to the resistor


112


still causes it to heat up. When no ink is present in the firing chamber


115


, the thermal expansion of the local air or the silicon resistor


112


may be the cause of the signal that is monitored with a dry pen. Alternatively, when the resistor


112


of an empty pen is energized, the heat builds up in the chamber


115


and may be sent out as a pressure wave through the nozzle


106


, generating the ultrasonic signal. The 80 kHz signal measured with the illustrated pen


50


may be due to bubble growth in a full pen, and due to thermal shock of the resistor


112


when the pen is empty. The 160 kHz signal may be due to the bubble collapse immediately following droplet ejection. Of course, other physical phenomena, thus far unknown, may be occurring within the printhead


54


,


54


′ to generate the pressure wave when a dry pen is fired, but this remains to be verified.




Indeed, originally it was through that the orifice plate


104


itself was vibrating, causing both the acoustic and ultrasonic signatures. However, in one test the orifice plate was completely removed from a full pen and the signal amplitude was approximately four times larger than the signal measured with the orifice plate


104


in place. For a dry pen, removing the orifice plate


104


had not effect at all upon the signal amplitude. Even the material of the orifice plate


104


may have some bearing upon these measurements. Ink viscosity variations were also tested, and without an orifice plate the signal amplitude increased as the ink viscosity increased. However, with the orifice plate in place, the dampening effect of the orifice plate negated the change in ink viscosity. Thus, in a commercial inkjet pen with an orifice plate, fortunately, ink viscosity has little if any effect upon the signal amplitude. Another way of amplifying the ultrasonic signal is to induce the ultrasonic frequency by supplying a series of firing pulses to either multiple nozzles or to the same nozzle at the desired ultrasonic rate.




Thus, while the original thinking was that the ultrasonic sound was generated during bubble collapse, the fact that an ultrasonic signal is still detectable when the pen is empty leaves the question open as to what exactly within the pen and printhead is generating the ultrasonic pressure wave, if not bubble collapse. Thus, while the source of the signal is not completely understood, it is detectable and useable to increase print quality. It is interesting to note that when a plugged nozzle was fired,


no


signal was measured, perhaps because it did not exist, or if it did, because it was buried in the signal noise. Thus, detection of ink clogs or other nozzle blockages using the monitoring system is quite viable. Various pens of the same type were also tested, and fortunately the variation in waveform signature between different pens was very small, leading to the belief that indeed this can be implemented in a commercial printing mechanism, which receives many different pens over its lifetime.




An alternate analysis of the test results has been proposed. Here, the analysis begins by understanding that as the electric current heats the resistor


112


, this heat energy is then transferred from the resistor to the ink


and


to the surrounding solid material, including the silicon


110


, the orifice plate


104


, the barrier layer


114


, etc. The heat transmitted into the ink generates a vapor layer around the firing resistor


112


. This vapor layer then develops into a vapor bubble which deflects the ink toward the nozzle


106


and eventually pushes a droplet


118


out of the firing chamber


115


. The heat transmitted into the surrounding solid material develops thermal stress waves in both the transverse and radial directions.




These stress waves in the solid material, and the force applied on the orifice


106


by the bubble generated ink deformation, may be the main source of vibration of the orifice plate


104


, as well as the source of the sound pressure wave detected in the air surrounding the firing nozzle. The fact that a pressure wave detected with and without the orifice plate


104


confirms the theory that the orifice plate


104


is not a primary source of the sound, but rather a secondary source. Furthermore, without the orifice plate


104


, the pressure wave has a larger amplitude than with the orifice plate installed. This fact implies that the orifice plate


104


is acting as a damper to the transmission of the vibrations, and thus, as a damper to the radiation of sound from the nozzle firing act.




Since the acoustic impedance of ink is about 100 times larger than that of air, it is more efficient to radiate sound in ink than in air. On the other hand, less sound is transmitted by the air/ink interface than if the pressure wave travels only in air because of the impedance mismatch at the interface. Tests showed a slight amplitude change between when the pressure wave travels through the ink/air interface for a pen containing ink (a “wet” pen), and when the pressure wave travels through only air for an empty (“dry”) pen. This will not produce the significant difference is amplitude between the dry pen signal and the wet pen sound signals. The major difference between the wet and dry pen scenarios, is that there is a bubble formation process associated with a wet pen, but not with a dry pen. The bubble formation process generates a large deformation of ink and creates a large vibration at the orifice plate


104


, so a larger sound signal is emitted from a wet pen than from a dry pen. Since the sound pressure wave is generated by the variation of pressure above or below atmospheric pressure, the nozzle


106


provides a free link for a dry pen from the air inside the firing chamber


115


to the surrounding atmosphere. Thus, the signal amplitude for a dry pen remains at substantially the same level both with and without the orifice plate


104


in place. Both the vibration and sound pressure signals are very impulsive, as illustrated by trace


142


in

FIG. 10

, which means that they both are rich in audible and ultrasonic frequency components, as shown in FIG.


9


. The dominant frequency components are related to droplet formation.




Another factor influencing pressure wave detection is the type of ink containment system selected for the cartridge reservoir. As mentioned above, the black pen


50


has a spring bag design, whereas the tri-color pen


52


has three foam-filled reservoirs, one for each color. During studies the spring bag inside the pen


50


was found to vibrate the sides of the pen body wall. Once this phenomenon was understood, then adjustments could be made to account for these vibrations, for instance, using a filtering scheme. The foam-based pen


52


has a more complex performance that resulted in a perceived inconsistency in the way it runs out of ink. This perceived inconsistency originally made it difficult to predict an upcoming out-of-ink condition. In the foam-based design, during printing or spitting the ink is randomly depleted from the foam cells around the printhead. This depleted region is then refilled through capillary action by ink wicking through the cells from remote regions of the reservoir. This refilling action often occurred so rapidly that the region around the printhead actually refilled before the pen could be positioned for testing. This quick refill lead to inconsistent test results, but of course, once the phenomenon was finally understood, the solution of more rapid testing became apparent. Thus, for a foam-based pen, the carriage-mounted sensor system


80


or the printhead-based system


90


may be more preferable, or suitable test timing modifications may be made to adapt the remaining systems


60


and


70


for accurate reporting.




Presently, the exact source which generates the ultrasonic signal is not fully understood, but indeed a measurable ultrasonic pressure wave is emitted during drop formation, and the information carried by this wave can be used to improve printer performance, as described below with respect to FIG.


11


.




C. Acoustic vs. Ultrasonic




Now that the question of what generates the acoustic and ultrasonic components of the pressure wave has been answered with, “We're not sure yet, but we have a few ideas, ” the various merits of monitoring the two frequency ranges will be discussed.




While detection of fundamental or harmonic acoustic frequencies may be useful for the currently available cartridges, it was believed this would be too limiting as a lasting solution. For example, if the material for the sides of the black pen


50


was changed, for instance from metal to a plastic, then the resonant frequency range may also change, so the whole measuring scheme would not work with the new pen architecture without upgrading the control system


200


. Of course, these concerns could be addressed, for example, by assuming that the pen architecture will remain static curing the lifetime of the printer.




The adverse effect of extraneous environmental noise on acoustic monitoring could be addressed in several ways. For instance, a second microphone could monitor the environmental noise and then subtract the noise from the sound heard by the drop detect microphone. The sensors


65


,


75


,


85


, and possibly


92


, may also be used to monitor the extraneous environmental sounds, which are then filtered out so only the firing or drop formation pressure waves are realized. Another option would be to isolate the drop detect microphone from the extraneous environmental sounds. Other means may also be used, such as averaging the sound detected, using time correlation, and then comparing measured values with a threshold. To improve a poor signal-to-noise ratio, more nozzles may be fired together at an instant, to increase the signal, but then single nozzle detection will probably be more difficult. Alternatively, the preferred minimum sampling rate for an audio range monitoring system needs to be at the Nyquist frequency, that is, at least twice the band width of the frequency of interest being measured to avoid aliasing, i.e. mixture of low and high frequency components. For instance, if a 6 kHz pressure wave was measured, then the optimal sampling rate would be at least 12 kHz. If the signal of interest is narrower in bandwidth, the sampling rate may be greatly reduced, which is more efficient. However, the design of the printer electronic


36


may impose an upper limit this sampling rate.




This ultrasonic system may depend at least in part upon bubble dynamics, that is, the creation of the ink droplet, rather than upon resonance of the pen body and printhead in response to droplet creation. While the particular cartridge studied had a thermal inkjet head, it is believed that these concepts may also be expanded to other types of inkjet printheads, such as piezo-electric printheads. As mentioned above, the current commercial embodiment anticipated uses a piezo-electric microphone which measures in the 40 kHz range. While higher frequencies may be more preferable, currently available microphones capable of measuring these higher frequencies are not cost effective for the home and business inkjet printer market, which typically sell inkjet printers in the cost range of $200-$1,000. However, it is believed that higher frequency ranges may provide better results. For example, an 80 kHz microphone is believed to provide better results than the commercially feasible 40 kHz microphone.




Thus, while the piezo-electric microphone used for ultrasonic monitoring may be slightly more expensive than an audio microphone, the immunity of the ultrasonic system to environmental noise contamination may render it more viable than an acoustic system. Furthermore, the ultrasonic system is not as dependent on pen architecture as the acoustic system, which monitors harmonics of the firing frequency. Some implementations may justify use of acoustic sensors, while other considerations may lead to ultrasonic monitoring for other implementations.




D. Sensor Placement




Another consideration in implementing the monitoring system


60


,


70


or


80


, is the location of the sensor


65


,


75


,


85


with respect to printhead


54


. Indeed, the line of sight distance


68


,


74


,


84


was found to effect both the amplitude and the energy of the monitored signal. Specifically, when the microphone is located beyond the near field of the sound source, the amplitude measured in the far field is proportional to the reciprocal of the distance, 1/(distance), whereas the power level is proportional to the reciprocal of the square of the distance, 1/(distance)


2


. If the microphone is located in the near field, small variations in the location of the printhead or microphone, such as due to manufacturing tolerances or shifting during use, may generate large fluctuations in the wave signal


204


. Conversely, if the microphone is located too far away from the printhead, then it may be unduly influenced by background nose, with a loss in sensitivity. Also, if the distance is too great the signal-to-noise ratio may be too low to adequately process signal


204


. Thus, there is a trade-off between the signal amplitude and the system stability as affected by the sensor position relative to the firing nozzle. Using the commercially viable 40 kHz microphone, it is believed that the optimal distance for the line of sight path


68


,


74


,


84


is approximately 12-15 mm (about 0.5-1.0 inch), although in the conceptual illustration of

FIG. 3.

, the distance 74 is illustrated as being somewhat longer.




Indeed, while the line-of-sight or external sensors


65


,


75


,


85


are located a certain distance from the printhead, the printhead mounted or internal sensor


92


is directly in contact with the silicon substrate


110


. Thus, sensor


92


is mechanically coupled to the printhead, rather than being coupled through air as illustrated by the line of sight distance


68


,


74


and


84


. In a broader sense, air itself may be considered to be a mechanical coupler, linking the printhead


54


to sensors


65


,


75


,


85


. In other inkjet implementations, it is conceivable that the ink or other substances ejected from the printhead may travel through a liquid before hitting a recording surface, so the liquid would serve as the mechanical coupler between the printhead and sensor


65


,


75


,


85


. On multiple cartridge printing mechanisms, using a single microphone to monitor the performance of each printhead may be more cost effective than providing a separate external sensor for each printhead. However, for increased printing speed, using one external sensor per printhead system may be preferred in some implementations.




E. Flow Chart




Referring back to flow chart


200


of

FIG. 11

, the controller


36


includes a commercially available analog to digital (A/D) converter


210


that receives the conditioned signal


208


from electronic


66


. Besides the frequency range monitored, another constraint of current hardware is the sampling rate. Currently, commercially available A/D converters in a typical inkjet printer


20


are limited to processing about 125,000 samples per second. While a faster sampling rate may be preferred, the current embodiment is limited by this hardware constraint of the A/D converter


210


. The conversion performed by the A/D converter


210


produces a digital wave signal


212


.




The digital signal


212


then passes from the A/D converter


210


to a firmware decision making portion


214


of the printer controller


36


, and more particularly to a digital signal processing portion


216


of the firmware


214


. It is apparent that, while the illustrated preferred embodiment implements the decision making functions in firmware, that these functions may also be implemented in software, hardware, or combinations thereof, including firmware components if desired. Moreover, these functions may take place in the printer controller


36


, in the host computer, or a combination thereof. To encompass the concepts of these various physical manifestations of the system of flow chart


200


, the various steps are referred to herein as “portions” of the system. Another input to the firmware portion


214


is a desired query signal


218


, received from a desired query input portion


220


. The desired query may be any of those listed in Table I below. The desired query signal


218


is also sent to an initiate test portion


222


of the control system. In response to the desired query signal


218


, the initiate test portion


222


generates an initiated test signal


224


.




Depending upon the desired query


220


chosen, the initiate test signal


224


may selected a single nozzle, all nozzles, or a selected group of nozzles to be fired. Upon receiving the initiate test signal


224


, a nozzle firing command portion


226


generates a nozzle firing or enabling signal


228


. In response to receiving the nozzle firing signal


228


, the particular resistor(s)


112


associated with the selected nozzle(s)


106


is fired in a firing step portion


230


of flow chart


200


, with firing being conducted as described above with respect to the bubble formation discussion. Upon nozzle firing in step


230


, a pressure wave


232


is normally emitted, which is then detected by the sensor in step


202


, as described above.




Referring back to the firmware portion


214


, the digital wave signal


212


is processed by the digital signal processing portion


216


, which may be more like a data conditioning step or amplitude determination, for instance to yield a peak-to-peak value of the wave signal which may be used to look for a low ink condition. Indeed, a variety of different values may be processed and provided as a digitally processed output signal


234


. For example, besides the amplitude, other signal conditioning may be performed by the processing portion


216


, such as determining the duration of the signal, the phase shift, and the variation of he amplitude of the signal within a sampling time. For instance, the ambient noise may be filtered out to get amplitude data at a specific frequency, which may then be compared to a reference value.




The output signal from the digital signal processing portion


216


is fed to a determining portion


236


of the printer firmware


214


. The desired query signal


218


is received by a test conditions and parameters portion


238


of firmware


214


. The test conditions and parameters portion


238


communicates bi-directionally via a signal link


240


with the determination portion


236


. Table I shows a variety of different actions that may be queried and determined by these two processors


236


,


238


. The determine action portion


236


then generates a determined action signal


242


, which is supplied to a printer reaction and adjustment portion


244


. The printer reaction portion


244


then generates a reaction signal


246


, which is fed to the nozzle firing command portion


226


. The nozzle firing command portion


226


then adjusts the nozzle firing command signal


228


in response to the reaction signal


246


and the initiate test signal


224


to maintain print quality. The printer reaction portion


244


may also notify the operator of any needed operator intervention. If no adjustments or further queries are needed, then the reaction portion issues a resume signal


252


to a resume printing portion


254


, and the printer


20


continues with the normal printing and servicing routines until the desired query


220


is activated again.




For example, if droplet size or volume was being optimized by adjusting the energy applied to the firing resistors, this process may take several iterations. If instead, a low ink condition had been determined by portion


236


, then information about this low ink level would be conveyed by signal


242


to the printer reaction portion


244


. The reaction portion


244


then generates an alert operator signal


248


, which is received by an alert operator portion


250


. The operator alert step


250


may be accomplished audibly or visually, for instance by flashing a warning light supported by the printer casing


24


, or by displaying a warning message on a computer screen via the host computer.




The desired query may again be performed, if desired, to verify that the correct action has occurred. Upon verifying that the correct adjustment has been made, the desired query portion then remains dormant until another desired query input is received from either the operator, or from a higher level portion of the printer controller


36


. For instance, an automatic desired query may be made at the beginning of start up when the printer is initially energized. Alternatively, a desired query of the various nozzle operations may be made at certain intervals for example daily if a printer is left on continuously, or at the completion of printing a selected number of pages.












TABLE 1











Operational Adjustments in Response to Monitoring














Test Conditions




Determine Printer






Desired Query (220)




and Parameters (238)




Action (236)









Pen








Characteristics:






Nozzle




Max./Min. Sig. Direction




Change Firing Sequence






Telecentricity






Nozzle




Signal <or> Threshold




Change Firing Sequence






Directionality






Nozzle-to-Nozzle




Find Maximum Signal




Change Firing Sequence






Alignment






Pen-to-Pen




Fire to Detect Time




Adjust Carriage/Re-seat






Alignment






Nozzle Operation:






Clogged Nozzles




No Signal = Clog




Spit/Prime/Wipe






Nozzle Damaged




Signal <or> Threshold




Change Dither Pattern








and/or Print Pattern






Turn-On Energy




Find Minimum Energy




Adjust Firing Energy







for Stable Firing






Drop Volume




Too Large? Too Small?




Adjust Pulse Width






or Size






Printer Interface:






Interconnect




No Signal = Open Circuit




Clean Pen Interconnect;






Integrity





Re-seat/Replace Pen






Media Type




Determine Type




Adjust Drop Size






Identification






Pen Ink Level:






Low Ink




Amplitude < Threshold




Signal Operator






Detection






Out-of-Ink




Amplitude < Threshold




Stop Print Job






Detection














E. Operational Adjustments in Response to Monitoring




The various desired queries, test conditions, parameters, and printer actions are shown in Table I merely for illustration, and other queries may be developed over time, using the inputs provided by monitoring systems


60


,


70


,


80


,


90


. The queries


220


are divided into functional groups, with the first group comprising pen characteristics, the second group nozzle operation, the third group printer interface, and the fourth group pen ink level.




(1) Pen Characteristics




In the first group of desired queries


220


, the characteristics of nozzle telecentricity, nozzle directionality, nozzle-to-nozzle alignment and pen-to-pen alignment are tested. While all four characteristics may be tested by the printer, testing of the first three characteristics may be more practically implemented during the cartridge manufacturing process.




In a manufacturing context, the monitoring systems


60


,


70


,


80


, and possibly system


90


, may be used to determine printhead performance on the assembly line, for instance in quality inspections. In this context, the pen


50


may be installed in a stationary carriage-like mechanism, rather than in the reciprocating carriage


40


. Instead of a single sensor, it may be advantageous to use an array of discrete sensors, preferably in a linear array aligned either perpendicular to, or more preferably parallel with the linear arrays of nozzles


106


. The linear nozzle arrays


106


are shown parallel to the drawing sheet of

FIGS. 2 and 3

.




For example, the stationary sensor


75


may be interpreted as representing one sensor in a sensor array running perpendicular with the plane of the drawing sheet of

FIG. 3

, and thus perpendicular with the nozzle arrays. Conversely, and perhaps more preferably, the stationary sensor


75


may represent one sensor of a sensor array running parallel with the drawing sheet of

FIG. 3

, and parallel with the nozzle arrays. Of course, in some implementations it may be desirable to partially or completely surround the cartridge with sensors for quality inspection tests. Then, rather than receiving a single distal wave signal


234


, the determine action portion


236


receives multiple signals, each generated by one of the discrete sensors in the array. It is apparent that the same function of a sensor array may be accomplished using a single sensor and moving the printhead


54


relative to the sensor (or moving the sensor relative to the printhead) while making multiple drop ejections and pressure wave readings at different locations. The multiple sensor embodiment is preferred because it is faster to use and speeds the assembly and test process, yet the single sensor embodiment may be preferred for use in the printer


20


.




Now the various multiple sensor embodiments are understood, more preferably for use in a manufacturing context than in a printer, the manner of testing the first three pen characteristics will be described. First, the term nozzle telecentricity refers to a tilt in the nozzle, that is, when forming the nozzle


106


by laser ablation, the nozzle was not formed perpendicular to the plane of the orifice plate


104


. This telecentricity may be detected by using a routine stored in the test conditions portion


238


that determines the direction of the maximum and minimum wave signals emitted by a nozzle


106


. Once it is found that a nozzle suffers telecentricity, then the determination portion


236


may decide the action to be taken is to change the nozzle firing sequence, and this information is passed along as signal


242


to the printer reactions and adjustments portions


244


. For example, depending upon which nozzle(s) is non-telecentric, and depending upon the direction of the non-telecentricity, then the determination to change the firing sequence may be manifested are a re-mapping of the nozzle firing sequence, or a nozzle substitution may be made.




The second pen characteristic is nozzle directionality, which is similar nozzle telecentricity, but rather than being caused by a misaligned laser, nozzle directionality may be caused by a deformation or blemish at the outlet of the nozzle


106


. Such a nozzle blemish may be permanent and caused by damage to the nozzle


106


, or it may be temporary, caused by a partial blockage at the nozzle


106


. IF spitting fails to remedy the directionality, then the system may assume that the nozzle directionality is a permanent deformation. This nozzle directionality may be detected by using threshold values stored in the test parameters portion


238


to determine whether the pressure wave detected in step


202


is less than (<) or greater than (>) these thresholds. Once nozzle directionality is found, then the determination portion


236


may decide the action to be taken is to change the nozzle firing sequence, for example, as described above when for compensating for telecentricity.




The third pen characteristic is nozzle-to-nozzle alignment, where for instance, one nozzle may be located slightly out of alignment with the other nozzles in the array, or it may not be at the desired spacing between adjacent nozzles. This condition may be discovered by using a routine stored in the test conditions portion


238


that looks for the location of the maximum pressure wave by comparing the values received by the discrete sensors in the manufacturing context, or by comparing the values received by a single sensor sampling at different locations relative to the printhead. Once nozzle-to-nozzle misalignment is found, then the determination portion


236


may decide that the action to be taken is to change the nozzle firing sequence, for instance, as described above when for compensating for telecentricity. For example, the nozzles in the two linear arrays are preferably staggered, rather than being directly side-by-side to allow more even ink placement on the page. If one nozzle is mis-located, this defect may show on the printed image as a horizontal colorless band, e.g. as a white stripe when printing on white paper. If the printer is aware of this misalignment, then such a print defect may be hidden or camouflaged by alternately printing with adjacent nozzles in the print pattern, whether in the same array as misaligned nozzle or in the other array.




The fourth pen characteristic is pen-to-pen alignment, where for instance, one cartridge


50


,


52


is not properly seated in the carriage


40


, or perhaps there is a misalignment in the carriage or pen reference datums used to align the pens with respect to the carriage. Pen-to-pen misalignment may be found using a routine stored in the test conditions portion


238


that finds the time between when firing signal


228


is sent to the firing resistors


112


, and when the microphone detects firing in step


202


. Alternatively, a routine stored in portion


238


may be used to determine when a maximum pressure wave is monitored, and at that location the nozzle array will be considered to be aligned with respect to the sensor. Examination of pen-to-pen alignment during printer manufacture may be useful to adjust the carriage for proper angular alignment (know in the art as O-Z alignment, referring to the degree of rotation about a vertical axis). During printing, pen-to-pen misalignment may be corrected by alerting an operator in step


250


to re-seat the pen in the carriage. If re-seating fails to correct the problem, then the determination portion


236


may decide to change print modes, for instance by adjusting the line feed rate of the print media, or by turning off (or on) certain print mode features, such as the shingling print mode.




(2) Nozzle Operation




The second group of queries


220


concerns nozzle operation, and it includes checks for clogged or damaged nozzles, turn-on energy adjustments, and drop volume or size adjustments.




First, to determine whether any nozzles are clogged, each nozzle may be sequentially fired. When the test conditions portion


238


finds no wave signal is detected, then a clogged nozzle condition exists. The determination portion


236


then determines that a printhead servicing routine needs to be performed. To cure a clogged nozzle, the printhead may be primed if the service station is equipped with a printing mechanism, or the clogged nozzle(s) may be spit in the spittoon


48


(fired when positioned over the spittoon), or a combination of spitting and priming may be used to clear the obstruction.




Second, if upon repeated testing, the nozzle is still appears to be clogged it may be determined by portion


236


that a permanently damaged nozzle condition exists, and that the firing sequence should be changed to substitute a good nozzle for the permanently damaged one. This may be done by re-mapping the firing sequence, firing timing, etc., for example, as described above with respect to the cures for nozzle telecentricity, directionality, and nozzle-to-nozzle alignment.




Third, to run the printer


20


in a most economical fashion, it is desirable to energize the firing resistor


112


at the lowest energy level at which it will still eject a drop of ink


118


, that is, to minimize the turn-on energy. Using a routine stored in the test conditions portion


238


, the minimum turn-on energy for a particular nozzle or printhead may be found by initiating a series of nozzle spitting at decreasing power levels, until eventually no droplet is ejected. Then, the immediately preceding energy level may be selected as the minimum turn-on energy, and the action determined by portion


236


is to adjust the firing energy to this value.




Fourth, the monitoring system


60


,


70


,


80


,


90


may also be used to determine drop volume or size. For instance, this may be done by using a routine stored in the test parameters portion


238


to monitor the amplitude of the pressure wave and then determine whether the signal is within threshold limits. When beyond these limits, the determination portion


236


may decide that the pulse width of the firing signal


228


needs to be adjusted to vary the drop volume or size to a desired level.




(3) Printer Interface




The next group of desired queries


220


concerns what may be called printer interface queries, here being illustrated as interconnect integrity and media type identification.




First, in interconnect integrity, the parameter being measured is the electrical connection between the pen and the carriage. Failure to make good electrical contact between the carriage and pen can result in nozzles not firing, since an open circuit condition between the nozzle firing command


226


and the nozzle resistors


112


would fail to energize the resistor so no droplet would be ejected. Upon detecting this condition, an initial instruction


250


to the operator may be to clean the electrical interconnect on the pen where it receives firing signals from the carriage terminals, and/or to re-seat the pen


50


,


52


in the carriage


40


. If cleaning or re-seating does not cure the problem, then the operator may instructed to replace the pen with a fresh pen. If pen replacement still fails to rectify the problem, then perhaps there is a break in the electrical connection between the carriage


40


and the controller


36


, at which point the operator may be asked 250 whether to continue the print job, perhaps using nozzle substitution for the afflicted nozzle, or to cancel the print job and return the printer for servicing.




Second, in media type identification, the type of media in the printzone is determined. This media identification query may be most easily monitored using either the carriage based monitoring system


80


, or the printhead system


90


, where the sensor


85


,


92


is used to listen to the impact of a given size droplet upon the media. For instance, a transparency type media is expected to have a different impact sound than plain paper or a fabric media. The test parameter portion


238


has a routine with certain thresholds corresponding to the various media types. Upon determining the type of media from this droplet landing sound, then the determination portion


236


may decide to adjust the drop size to accommodate the particular media. For instance, transparencies have lower absorbency than paper, and paper has a lesser absorbency than a fabric, so transparencies may receive a smaller drop size, while plain paper, and more particularly fabric, will receive an even larger drop size to accommodate for media absorption of the ink.




(4) Pen Ink Level




The final group of desired queries illustrated concern the ink levels within the cartridges


50


,


52


. As discussed above, it may be particularly helpful to given an operator an indication of an impending low ink condition, before the pen actually dries out, to allow an operator to purchase a fresh cartridge to have on hand when the cartridge actually empties. This, it is also useful to indicate when the cartridge is finally empty. As discussed above with respect to

FIG. 6

, the wave signal amplitude has been found to decrease as the pen empties of ink. The test parameters portion


238


may have threshold limits stored therein corresponding to certain levels of ink with a cartridge, from full to partially full to empty. Upon passing a selected partially full level, the determine action portion alerts an operator in step


250


that the pen is nearing empty. Upon reaching an out-of-ink condition, the wave signal falls below another threshold, and at the time the determination portion


236


may decide to stop the print job and alert the operator in step


250


so the pen may be replaced or refilled without damaging the printhead.




Conclusion




Thus, a variety of advantages are realized using this monitoring system


60


,


70


,


80


,


90


, whether implemented in the audio frequency range or the ultrasonic frequency range. The exact type of sensor being used, whether a microphone, accelerometer, ultrasonic transducer, laser vibrometer, or pressure wave sensor (internal or external to the printhead), as well as the printer design and pen architecture, may require adjustments in the various levels and sampling parameters, etc., illustrated herein, but such adjustments are within the level of those skilled in the art. Moreover, other conditions may be monitored and measured using such a monitoring system, for instance, at some point the system may develop such sophistication that the type of ink being used may be discernible, such as the manufacturer's recommended ink composition, or an inferior substitute that may be lacking in print quality. The operator may be alerted in step


250


of these different ink types, and then make a decision as to whether to continue using an inferior ink, or to delay the print job until a pen containing higher quality manufacturer's recommended ink is obtained.




Moreover, the test parameters stored in portion


238


may also be varied depending upon various environmental conditions, such as ambient noise levels, print cartridge type, the number of nozzles used in the test, the ambient temperature or humidity, as well as the type of query being made. For instance, a microphone-type sensor may also be used to monitor the ambient noise levels, then using these levels, the controller


36


may adjust the test parameter levels in portion


238


to accommodate the environmental intrudances. Otherwise, the influence of this environmental “static” may be reduced by taking sound sampling over very short time durations.




One advantage of using ultrasonic monitoring over acoustic monitoring is that ultrasonic monitoring is independent of the firing frequency of the printhead. Moreover, ultrasonic monitoring can detect the firing of a single nozzle on the printhead. Additionally, the ultrasonic monitoring system experiences a good signal-to-noise ratio, being relatively immune to contamination from external environmental sound sources. Furthermore, while the concepts described herein are shown for a replaceable inject cartridge, it is apparent that these concepts may be extended to printing mechanism having permanent or semi-permanent printheads, such as those which have a stationary ink supply that is fluidicly coupled to the printhead, for instance, by flexible tubing.




The on-board sensor system


90


may be preferred in some implementations because it may be more cost effective to incorporate the sensor directly into the printhead. The illustrated printheads


54


′ may be manufactured using bulk silicon processes which are inherently less expensive than purchasing discrete sensors


65


,


75


and


85


. Furthermore, the discrete sensors


65


,


75




85


require separate mounting fixtures


64


,


72


,


82


, as well as separate assembly steps when manufacturing the printer


20


, both of which contribute to increased printer cost. The on-board sensor


92


uses the existing communication pathways between the carriage


40


and the printer controller


36


which are used to communicate the firing signals to the firing resistors


112


, as well as to provide printhead temperature sensor feedback to the controller


36


.




Moreover, using an array of external sensors the printhead nozzles may be checked during manufacture on the assembly line for printhead quality assurance checks, such as to look for nozzle directionality, nozzle-to-nozzle alignment, nozzle telecentricity, ink trajectory, etc. For example, by looking for the highest wave signal generated by such multiple sensors, it is possible to determine a nozzle trajectory error. In an advanced printhead/printing mechanism combination, this printhead performance information may be recorded on an electronic integrated circuit on-board the cartridge


50


,


52


for later reading by the printer controller


36


, which in response thereto adjusts the print modes or firing sequence accordingly to mask the nozzle defect. For example, this information may be stored in a ROM (read only memory) or other equivalent storage device on-board the cartridge, which for example, may be incorporated into the silicon substrate


110


, or in communication with the substrate. Such an advanced system leads to less printheads being rejected during manufacture, which lowers the scrap rate and the associated waste overhead, yield a lower manufacturing cost that can easily be passed along to consumers in the form of lower cost cartridges.



Claims
  • 1. An ultrasonic monitoring method of operating an inkjet printing mechanism having an inkjet printhead installed therein, with the printhead having plural nozzles, comprising the steps of:applying an enabling signal to a selected nozzle of the inkjet printhead; normally generating a pressure wave in response to the applying step; ultrasonically detecting the pressure wave emitted by the selected nozzle during the generating step; and responding to the detecting step.
  • 2. An ultrasonic monitoring method according to claim 1 wherein:the method further includes the step of selecting a desired query; and the responding step comprises the step of acting in accordance with the desired query.
  • 3. An ultrasonic monitoring method according to claim 2 wherein the acting step is made in accordance with test conditions or parameters corresponding to the desired query.
  • 4. An ultrasonic monitoring method according to claim 2 wherein the acting step comprises the step of adjusting the enabling signal.
  • 5. An ultrasonic monitoring method according to claim 2 wherein the acting step comprises the step of alerting an operator.
  • 6. An ultrasonic monitoring method according to claim 2 wherein:the desired query comprises determining whether the selected nozzle is clogged; and when the detecting step fails to detect a pressure wave generated in response to the applying step, the acting step comprises the step of attempting to clear a clog in the selected nozzle.
  • 7. An ultrasonic monitoring method according to claim 2 wherein:the inkjet printhead is installed in a replaceable inkjet cartridge carrying a supply of ink; the desired query comprises determining whether the cartridge ink supply is at a selected low level; and when the cartridge ink supply is at the selected low level, the acting step comprises the step of alerting an operator.
  • 8. An ultrasonic monitoring method according to claim 2 wherein:the inkjet printhead is installed in a replaceable inkjet cartridge carrying a supply of ink; the desired query comprises determining whether the cartridge ink supply is depleted; and when the cartridge ink supply is depleted, the acting step comprises the step of alerting an operator.
  • 9. An ultrasonic monitoring method according to claim 2 wherein:the inkjet printhead is installed in a replaceable inkjet cartridge carrying a supply of ink; the desired query comprises determining whether the cartridge ink supply is depleted; and when the cartridge ink supply is depleted, the acting step comprises the step of stopping any print job that is in progress.
  • 10. An ultrasonic monitoring method according to claim 1 wherein the responding step comprises the steps of:determining an amplitude of the detected pressure wave; comparing the determined amplitude to a selected threshold; and when the determined amplitude passes the selected threshold, implementing a selected action.
  • 11. An ultrasonic monitoring method according to claim 10 wherein:the method further includes the step of selecting a desired query; and the action of the implementing step is selected in accordance with the desired query.
  • 12. An ultrasonic monitoring method according to claim 1 wherein the responding step comprises the step of adjusting a duration of the enabling signal.
  • 13. An ultrasonic monitoring method according to claim 1 wherein the responding step comprises the step of adjusting of the enabling signal to change the size of ink droplets ejected from the selected nozzle in response to the applying step.
  • 14. An ultrasonic monitoring method according to claim 1 wherein the responding step comprises the step of adjusting an energy of the enabling signal.
  • 15. An ultrasonic monitoring method according to claim 14 further including the steps of:repeating the detecting and adjusting steps, with subsequent adjusting the energy of the enabling signal; reaching a stopping level when the detecting step reaches a threshold where the detecting step either fails to detect or begins to detect a pressure wave generated in response to the applying step, and then stopping the repeating step; and wherein the responding step further comprises the step of adjusting the energy of the enabling signal to a turn-on energy level selected above the stopping level for printing.
  • 16. An ultrasonic monitoring method according to claim 1 wherein the responding step comprises the step of changing the firing sequence of at least one of the plural nozzles.
  • 17. An ultrasonic monitoring method according to claim 1 wherein:the applying step comprises the step of applying enabling signal to a selected group of the plural nozzles; and detecting the pressure wave emitted by the selected group of nozzles during the generating step.
  • 18. An ultrasonic monitoring method according to claim 1 wherein:the inkjet printhead is installed in a replaceable inkjet cartridge seated in a cartridge receiving portion of the inkjet printing mechanism; the applying step comprises the step of applying an enabling signal to at least two selected nozzles; and when the detecting step fails to detect a pressure wave generated in response to the step of applying the enabling signal to at least two selected nozzles, the responding step comprises the step of alerting an operator to re-seat the inkjet cartridge in the cartridge receiving portion.
  • 19. An ultrasonic monitoring method according to claim 1 wherein:the method further includes the step of positioning the inkjet printhead adjacent a spittoon portion of the inkjet printing mechanism; and the detecting step comprises the step of detecting the pressure wave from a position in the spittoon.
  • 20. An ultrasonic monitoring method according to claim 1 wherein:the method further includes the step of positioning the inkjet printhead adjacent a stationary portion of the inkjet printing mechanism; and the detecting step comprises the step of detecting the pressure wave from the stationary portion.
  • 21. An ultrasonic monitoring method according to claim 1 wherein:the inkjet printhead is installed in a moveable carriage portion of the inkjet printing mechanism; wherein the method further includes the step of normally generating a vibration in the carriage in response to the applying step; and the detecting step comprises the step of detecting the pressure wave or the vibration from the carriage portion.
  • 22. An ultrasonic monitoring method according to claim 1 wherein:an ultrasonic sensor is located at the inkjet printhead; and the detecting step comprises the step of detecting the pressure wave using the ultrasonic sensor.
  • 23. An ultrasonic monitoring method according to claim 22 wherein:the inkjet printhead sensor is an accelerometer constructed integrally with the printhead; and the detecting step comprises detecting the pressure wave using the printhead accelerometer.
  • 24. An ultrasonic monitoring method according to claim 1 wherein the detecting step comprises the step of detecting the pressure wave using an ultrasonic microphone.
  • 25. An ultrasonic monitoring method according to claim 1 wherein the detecting step comprises the step of detecting the pressure wave using a laser vibrometer.
  • 26. An ultrasonic monitoring method according to claim 1 wherein the detecting step comprises the step of detecting the pressure wave using an ultrasonic transducer.
  • 27. An ultrasonic monitoring method according to claim 26 wherein the detecting step comprises the step of detecting the pressure wave from a location inside the printhead.
  • 28. A method of monitoring the performance of an inkjet printhead having plural nozzles, comprising the steps of:applying an enabling signal to a selected nozzle of the inkjet printhead; normally generating a pressure wave in response to the applying step; detecting the pressure wave emitted by the selected nozzle during the generating step from plural locations and generating a wave signal from each of the plural locations; and analyzing the wave signal from each of the plural locations to determine performance of the selected nozzle.
  • 29. A method according to claim 28 wherein the detecting step comprises detecting the pressure wave using an array of plural sensors.
  • 30. A method according to claim 28 wherein the detecting step comprises detecting the pressure wave using plural sensors comprising ultrasonic transducers.
  • 31. A method according to claim 28 wherein the detecting step comprises detecting the pressure wave using plural sensors comprising accelerometers.
  • 32. A method according to claim 28 wherein the detecting step comprises detecting the pressure wave using plural sensors comprising acoustic microphones.
  • 33. A method according to claim 28 wherein the detecting step comprises detecting the pressure wave using plural sensors comprising laser vibrometers.
  • 34. A method according to claim 28 wherein the analyzing step comprises the step of determining performance of the selected nozzle for directionality.
  • 35. A method according to claim 28 wherein the analyzing step comprises the step of determining performance of the selected nozzle for nozzle-to-nozzle alignment with respect to at least one other nozzle of the printhead.
  • 36. A method according to claim 28 wherein the analyzing step comprises the step of determining performance of the selected nozzle for nozzle telecentricity.
  • 37. A method according to claim 28 wherein the analyzing step comprises the step of determining performance of the selected nozzle for a direction of ink trajectory.
CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of copending application Ser. No. 09/289,481 filed on Apr. 9, 1999 which is a continuation of application Ser. No. 08,687,000 filed on Jul. 24, 1996 granted U.S. Pat. No. 5,929,875, issued on Jul. 27, 1999

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Continuations (2)
Number Date Country
Parent 09/289481 Apr 1999 US
Child 09/841386 US
Parent 08/687000 Jul 1996 US
Child 09/289481 US