Patent Application
20110141191
The present disclosure relates generally to inkjet printheads for inkjet printers wherein the printhead includes a plurality of nozzles in fluid communication with an ejection chamber, and ink is ejected from the chamber through the nozzles in drops for printing on a medium. More specifically, this disclosure pertains to systems or methods for maintaining or recovering nozzle function affected by ink clogging at the nozzles.
An inkjet printhead for an inkjet printing system includes a plurality of nozzles through which ink is ejected in drops responsive to printing commands from a controller for printing on a print medium. Whether the printhead is of the type that is permanently mounted on a printing system and linked to an ink source or of a disposable nature that includes a cartridge supporting an ink reservoir, each of the nozzles is disposed on the printhead in fluid communication with an ink ejection chamber. In the case of thermal ink jet printers and printheads, ink is ejected in drops by the application of heat to ink in the ejection chamber responsive to the printing commands. One or more resistive heater is associated with each ejection chamber and generates heat that causes solvents in the ink to vaporize generating bubble in the ejection chamber. The rapid expansion of the bubbles forces ink through the nozzles in drop form.
Other types of printing systems and printheads have a piezoelectric transducer integrated in the printhead forming a wall in the ink ejection chamber, or in some other chamber that that holds ink and is in fluid communication with the ejection chamber. Responsive to printing commands the wall, or the piezoelectric transducer, expands and contracts forcing ink from the ejection chamber in droplet form for printing.
In either of the above-described inkjet printheads, the ink solvent may tend to evaporate at the nozzles causing the ink at or in the nozzles to become more viscous when the printhead and nozzles are not performing a printing operation. More viscous ink at the nozzle area tends to plug the nozzle directly affecting the performance of the printhead and printing quality. Some systems or methods for maintaining or restoring nozzle function include capping the nozzle plate, wiping the printhead with an elastomeric blade and spitting ink through the nozzles, all of which are performed when the printhead is not performing a printing operation.
Printing systems incorporating such methods typically include printheads that move back and forth on a carriage during printing operations, and the printheads are moved to a station when printing operations are stopped or suspended. Capping the nozzle prevents fluid evaporation in the nozzles and the formation of the viscous plug. Wiping the nozzle plate with the elastomeric blade clears the nozzles of the viscous plugs and dried ink residue. Spitting processes flush ink from the nozzle to clear the fluidic column of viscous ink in the nozzle including the ejection chamber. However, such processes can not be practically used in printing systems for which a printhead remains stationary during printing and does not move on a carriage during printing. Wiping or spitting methods can foul the printing medium and area surrounding a print area. In production line printing for printing bar codes, dates or other data on product packaging, the wiping and spitting techniques may interrupt a production line. In addition, the printheads for stationary printing systems in some instances are positioned so close to the print medium a cap is difficult to place on the nozzle plate.
The wiping and spitting processes may be effective for clearing the nozzles of the viscous plugs, but are inherently wasteful because ejected ink is not used for printing. In addition, printing systems monitoring an ink volume available for printing by counting ink drops ejected from the printhead may not factor ink used during cleaning operations. Accordingly, a remaining volume of ink may be over estimated and an ink cartridge may be commanded to perform printing operations with an insufficient amount of remaining ink to perform or complete a printing operation. This may lead to dry firing at the nozzles of the printhead, which may damage the printhead. In addition, an over-estimation of remaining ink volume may result in the printing system missing codes or prints on the packaging in production line printing.
Both U.S. Pat. No. 5,329,293 and JP 57061576 disclose printheads incorporating piezoelectric elements activated to discharge ink drops for printing responsive to a first signal from a controller. A second sub-firing, or voltage signal that is below a threshold voltage signal required for discharging ink, activates the piezoelectric elements to prevent clogging of ink in the nozzle. In addition, U.S. Pat. No. 6,431,674 (the “'674 patent”) discloses an inkjet printhead that minutely vibrates an ink meniscus at nozzle openings before or after a printing operation to prevent clogging of the printhead nozzles. More specifically, the '674 patent discloses an inkjet printhead of the type that utilizes the above-described piezoelectric transducers and ejection chambers, referred to as a pressure generating chamber. The printhead includes a plurality of the pressure generating chambers wherein each chamber is associated with a nozzle and each chamber has its own transducer. The piezo-transducers are activated to pressurize their respective chambers to eject ink drops from the chamber for printing. In addition, during printing inactivity, each piezo-transducer may pressurize their respective chamber to vibrate the meniscus to an extent insufficient to eject an ink drop. Because the transducer is used to pressurize the chamber for both ejecting ink and minutely vibrating the meniscus, the transducer is activated for a plurality of successive timed intervals to avoid fatiguing the transducer.
Such above-described piezo-transducer systems can not be practically incorporated in thermal inkjet printheads. Incorporating a piezoelectric transducer for each print cartridge would be cost prohibitive for manufacturing thermal inkjet cartridges or printheads. In addition, the resistive heaters incorporated in thermal inkjet printheads may not practically be used to oscillate the meniscus without ejecting ink as compared to the piezoelectric ink ejection technologies. In thermal inkjet printheads, a voltage is applied to a resistive heater associated with each firing chamber and nozzle and heats the ink in the firing chamber causing the rapid expansion of an ink bubble forcing an ink drop through the nozzle. A threshold voltage at which an ink drop may or may not be ejected from a thermal inkjet printhead is far less predictable as compared to the piezo-transducer inkjet printheads. Indeed, in printing systems incorporating thermal inkjet printheads an algorithm is used to estimate the voltage necessary to discharge ink drops. The algorithm considers such parameters such as physical properties (vapor pressure) of the ink used and dimensions of the ink channels, firing chambers and nozzles. Once the threshold voltage is determined, the algorithm is configured to select a voltage that is a predetermined percentage over the calculated threshold to ensure that ink drops will be ejected when voltage signals are applied to the resistive heaters. Application of voltage at or below a threshold voltage may or may not oscillate a meniscus, or it may cause an ink discharge. In addition, heating the ink in a firing chamber when printing has stopped or been suspended may cause ink in the firing chamber to dry and clog the nozzles.
A system or method for maintaining nozzle function for an inkjet printing system comprises a printhead in fluid communication with an ink supply, and for printing on a print medium. The printhead has a plurality nozzles and each nozzle is associated with an ink ejection chamber in which ink is stored for ejecting ink drops from the chamber through the nozzle. An ink fluidic column is associated with each nozzle and may comprise an ink meniscus formed at the one or more nozzles and ink in the ejection chambers. In order to maintain or recover nozzle function in the cartridge, a transducer is provided for transmitting vibrational energy to the fluidic column to simultaneously vibrate at least a portion of each of a plurality of the ink fluidic columns. The transducer is linked to a controller of the printing system, which controller generates a signal to activate the transducer during the periods of printing inactivity or during printing operations. In an embodiment the printhead is mounted on a cartridge and vibrational energy may be transmitted to the fluidic column from a location external of the cartridge. In other embodiments, a transducer may be mounted internally in a cartridge housing, or may be provided as a component of a printhead circuit.
In an embodiment, an inkjet cartridge is mounted in a pocket that has walls configured for receiving and holding the cartridge in spaced relation to the print medium for printing. A vibrational force may be applied to a wall of the pocket and the interface between pocket wall and cartridge surface couple the vibrational energy to the printhead. In another embodiment, the vibrational force may be applied directly to the exterior surface of the cartridge. In this manner, the vibrational energy is transmitted to a fluidic column in the printhead to vibrate the fluidic column to maintain or recover nozzle function.
A more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained. For purposes of describing embodiments of the present invention, references in the drawings and specification are made to a printhead for a thermal inkjet cartridge; however, the invention is not so limited. The present disclosure may be used with inkjet cartridges that incorporate means other than heat to eject ink drops from the printhead. For example, the described invention may be used for those cartridges that incorporate piezoelectric transducer technologies to eject ink drops for printing or other operations. In addition, the described system and method for maintaining or recovering nozzle function is not limited to application with a printhead assembly mounted to a cartridge housing as shown in
With respect to
The term printhead as used herein shall include that component of the ink cartridge 10 to which ink is supplied from a bulk ink source for ejection of ink drops. In the embodiments described herein for a thermal inkjet cartridge, the printhead 14 may comprise a silicon substrate 15 with an ink slot 16, fluidic channels 17, firing chambers 18, nozzles 22 and the necessary integrated circuitry formed thereon and the nozzle plate 23. In other types of printheads that do not have an ink slot for example, the printhead comprises the ejection, pressure or firing chambers adjacent to the nozzles and the structural parts that define these components. In addition, at least for those inkjet cartridges utilizing piezoelectric technologies, the printhead also includes the piezo-elements integrated with the printhead for generating ink drops.
In
A nozzle plate 23 is bonded to the barrier layer 19 and has a plurality of nozzles 22 each of which corresponds to a respective firing chamber 18. Ink provided from the bulk source via the ink slot 16 forms an ink fluidic column including ink at nozzles 22 and ink in the firing chamber 18, fluidic channel 17 and ink slot 16. A negative pressure is generated and maintained at the ink bulk source forming a meniscus 33 (shown in
For each firing chamber 18 there is a corresponding resistive heater 20. Responsive to a print command from the controller, a power supply to the resistive heater 20 causes the heater 20 to heat ink in the firing chamber 18. As represented schematically in
With respect to the present disclosure, nozzle function is maintained or recovered for an inkjet cartridge by transmitting vibrational energy, preferably via sonic energy, from an external source through an exterior of the inkjet cartridge to the fluidic column to vibrate or oscillate the fluidic columns, the menisci 33 at one or more of the plurality of nozzles 22, the entire cartridge 10, the pocket 26 (described below), or any combination of these. For purposes of convenience of explanation of the disclosure the term sonic energy as used herein shall include ultrasonic energy (>20 kHz). The sonic energy induces an oscillation or vibration of ink in at least a portion of the fluidic column. The fluidic column as used herein shall include the ink present between the ink bulk supply and the nozzle 22, or ink at or in the nozzle 22 and ink ejection chamber 18. In the present example described herein, the fluidic column comprises the ink present in the nozzle 22 (including the meniscus 33), the firing chamber 18, fluid channel 17 and the ink slot 16. The rapid vibration or oscillation of the fluidic column maintains the ink composition and properties by replenishing ink solvent in the fluidic column and preventing ink crusting that may plug or clog the nozzle. The vibrational energy can serve to recover all nozzles in an array, including those that are not actively printing. The transmission of vibrational energy can be used in conjunction with other means to prevent nozzle clogging such as spitting, wiping and mechanical capping.
With respect to
The transducer 25 may be positioned on the printing system so that the transducer 25 imparts the vibrational force to the pocket 26. The transducer 25 may be positioned in contact with pocket 26 or an exterior of the cartridge 10 to impart the vibrational force at a frequency or within a range of frequencies necessary to vibrate or oscillate the fluidic column and/or meniscus 33. In one embodiment, the vibrational force vibrates the fluid column and/or meniscus 33 without ejecting ink drops. In another embodiment, the transducer pulse and ensuing vibration may lead to ink actively jetting from the nozzles 22. As shown in
In addition, the composition of the materials making up the pocket 26 or 36, cartridge housing 11 and the snout 13 should be considered in application of this system and method. More specifically, materials composition of these components should provide an adequate coupling of the vibrational forces or energy generated by the transducer 25 to the fluidic column. For examples a metal such as steel or a glass-filled plastic such as polyethylene terephthalate, or a combination of the two may provide an adequate coupling.
The point at which the transducer 25 contacts the pocket 26, or cartridge 10, relative to the printhead 14 and nozzles 22, the frequency or range of frequencies or amplitude or range of amplitudes necessary to oscillate or vibrate the ink in the fluidic column and at the nozzles 22 may vary among cartridge types. Variables or parameters to consider when determining a contact point or energy frequency may comprise the material composition of the cartridge housing 11, snout 13 and pocket 26; the architecture of the components of the fluidic column comprising the dimensions of the ink slot 16, fluidic channel 17, firing chamber 18 and nozzles 22; and, properties of the ink namely ink viscosity may be taken into consideration. In addition, ink properties may be considered in determining the frequency or amplitude of the vibrational energy or the area of application of the transducer 25. Such ink properties may include the dry time of the ink (amount of time necessary for the ink to dry at the nozzle), the ink viscosity and the sound velocity (speed at which sound may travel through an ink medium).
In addition, these parameters may also influence the time duration required for application of vibration or energy, which in turn may be influenced by the time duration of a period of printing inactivity or a printing operation. For example, taking into consideration the above-described parameters, it may be determined that a vibrational force should be applied to the inkjet cartridge 10, if a printing system has not performed a printing operation for an elapsed predetermined time duration T1, where the vibrational force is applied for a predetermined time duration T2 to maintain nozzle function. The controller 29 may be programmed to generate a signal to activate the transducer 25 once the time duration T1 has elapsed. The transducer 25 may remain activated until the controller 29 generates another print command in order to maintain nozzle function. Alternatively, the controller 29 may generate multiple signals to activate the transducer 25 in spaced time intervals during a period of inactivity or during printing in order to maintain nozzle function of the cartridge 10.
These above-listed parameters are provided as examples of parameters that may be considered and are not intended to provide an exhaustive list. Indeed, the contact point for the transducer 25 and ink oscillating frequency may have to be determined for individual cartridges or cartridge types empirically. To that end, for types of cartridges having similar physical properties that are filled with the same or similar inks, the location of the transducer contact point and the ink oscillating or vibrating frequency may be predicted and refined.
As previously noted, the vibrational energy may include a continuous application of vibrational energy or vibrational energy applied in periodic bursts, pulses or cycles or applied as a single or repetitive waveform. In particular, the waveforms may be provided by a signal generator to create the drive waveform. Any standard waveform is appropriate, such as sinusoidal, triangular, square, sawtooth, step (pulse), other piecewise linear or curvilinear waveform, or an arbitrary waveform. If two or more transducers are present, the transducers may be provided with the same or different signals, including same or different waveforms. A suitable transducer is a piezo electric device composed of one or more piezo crystals mounted in a housing, constructed such that the transducer expands and contracts in length in the presence of a varying electrical field. In such a suitable transducer, the housing may act as a passive return spring as well as providing environmental protection. The housing may also be used compressionally to pre-load the piezo crystal stack, commonly used to improve crystal reliability.
The vibrational intensity transmitted by the transducer can be controlled by adjusting the transducer voltage levels, amperage levels, waveform, vibrational frequency and/or duration of the pulse, or any combination thereof. In particular, in one embodiment, the peak-to-peak voltage may be less than 200 V, preferably between 10 V and 100 V. In one embodiment, the current may be between 0.1 and 2 amps, preferably less than 0.8 amps. The vibrational frequency may range from about 1 kHz to about 40 kHz, preferably between 2 kHz to about 30 kHz, more preferably between 3 kHz to about 12 kHz and most preferably about 6 kHz to about 10 kHz. The vibrational frequency may be less than 40 kHz, less than 30 kHz, or less than 20 kHz. The duration of pulse is preferably at least 0.1 sec, more preferably at least 0.5 sec, and most preferably 1 sec or longer. If two or more transducers are present, they may be provided with the same or different voltage levels, amperage levels, vibrational frequency and/or duration of the pulse, or any combination thereof. The waveforms of the two or more transducers may also be in phase or out of phase with each other.
Application of the transducer pulse can be initiated and terminated at any point within a printing cycle and can be of any arbitrary duration. The pulse can be applied between prints and/or during printing. The specific sequence required to recover nozzle function may be adjusted based on the time between prints. In one embodiment, a transducer pulse is applied for about 1 sec before the first print at startup.
With respect to the present disclosure testing was conducted in both a nozzle maintenance mode and a nozzle recovery mode. The nozzle maintenance mode includes those time intervals of printing inactivity when a cartridge may be exposed to vibrational excitation to prevent ink from drying or become more viscous to a point of plugging the nozzles 22. A recovery mode may involve an extended time interval of printing inactivity that results in the ink drying or becoming more viscous to the point of plugging the nozzles.
Comparison testing was conducted by allowing a cartridge filled with a methyl ethyl ketone (MEK)/methanol solvent-based ink (Videojet experimental ink No. D6-5614) and allowed to remain uncapped for a period of fifteen minutes without vibrational excitation. In reference to a sample of the testing, an HP45A thermal inkjet cartridge having a similar integral snout configuration as shown in
The identical cartridge was then exposed to vibrational excitation during another fifteen minute period. A piezoelectric transducer was activated to apply a vibrational force for the duration of the fifteen minute period of printing inactivity. The piezoelectric transducer 25 was placed in contact with the pocket 26 at an area adjacent the snout 13 about 1½″ above the printhead 14. In reference to
In other testing, nozzles on the printhead of the HP45A were observed with a video system using a strobed illumination source to observe the motion of ink meniscus in the nozzle. An HP45A inkjet cartridge as described above filled with the VideoJet Product No. D6-5614 ink was allowed to remain uncapped for 15 minutes without vibrational excitation, and a dried film on the nozzles was easily observed with the video system. Upon application of vibrational energy to the cartridge, the crusted nozzles re-solvated in approximately thirty seconds. A similar test was conducted with the cartridge remaining decapped for two hours. In that case, the nozzles re-solvated in approximately sixty seconds.
Using a strobed illumination source, it was possible to observe “snapshots” of the meniscus position in the nozzles. By delaying the illumination source with respect to the application of vibrational energy, one could observe the meniscus in various positions, dependent upon the amount of delay. In this way, the fluid could be observed in positions that range from the bottom of the nozzle to the top of the nozzle, and even slightly bulging above the nozzle.
Using the described video observations test setup described above, a range of frequencies from about 2.5 kHz to about 30 kHz vibration were evaluated, with each frequency creating meniscus oscillation. Vibrational energy at a frequency of about 2.0 KHz may also be effective. However, the frequency of meniscus oscillation does not match the input frequency. Instead, meniscus oscillation appeared to be fixed by the resonant frequency associated with the cartridge fluidic column architecture. That is, the oscillation can only proceed as fast as the fluidic column can move between the bulk ink source and the meniscus. While the meniscus of the fluidic column may vibrate, oscillate or modulate there may also occur some flooding around a localized region at a nozzle which may also aid in maintaining nozzle function.
In addition or alternatively, vibrational energy may be applied to the fluidic column during or when the printhead is performing a printing operation. Testing was conducted on cartridges containing an ink with a MEK or MEK with methanol solvent and having 40 μm×40 μm fluidic channel. The volume of ink in an ink reservoir providing ink to a printhead ranged from about 15 cc to about 45 cc. The printheads printed at print frequencies of 2 KHz and/or 8 KHz, and vibrational energy was applied to the fluidic columns at a frequency of 6 KHz and 30 V.
Vibrational energy was applied continuously during printing operations and during intervals of printing inactivity. The intervals of printing inactivity between printing operations included 6 seconds, 32 seconds, 169 seconds (3 minutes) and 893 seconds (15 minutes). Print samples generated from these cartridges were compared to print samples from the same cartridges for which vibrational energy was not applied either during printing activity or during the same time intervals of printing inactivity. With respect to
Further comparison testing was performed for a variety of transducer frequencies, waveforms, and voltages. A thermal inkjet cartridge having a similar integral snout configuration as shown in
In Table 1, “Interval” is the time period where the printing was suspended. “Waveform” is the waveform applied to the transducer. “Voltage” is the voltage supplied to the transducer. The transducer was activated for 1 sec immediately prior to the resumption of printing after the interval. “Recovery” indicates how quickly the printhead recovered normal print quality after resumption of printing. It can be seen that without applying the vibrational energy, the printhead was not able to recover normal printing after 5 min interval of no printing. It can be seen that for all of the tested operating conditions of the transducer, the 1 sec of applied vibrational energy was able to provide 100% nozzle recovery on the first printed code.
As described above, the frequency at which a meniscus may vibrate or oscillate and the time duration for application of a vibrational force necessary to maintain or recover nozzle function may vary among different cartridge types or ink types. Accordingly, the controller 29 may access a database 32 that includes data relative to the identity of a plurality of inkjet cartridge types and/or an identity of a plurality of ink types. In addition, the database 32 may include data relative to one or more frequencies or ranges of frequencies associated with each cartridge type and/or ink type, and a schedule of one or more timed intervals for activating the transducer 25 during a period of printing inactivity or during a printing operation. As described above certain parameters associated the cartridges may control the frequencies or range of frequencies selected to oscillate a fluidic column. For example, cartridge types may use different inks (i.e., water-based vs. solvent-based, or inks that differ in viscosity) or differ in fluidic column architecture. In addition, a selected printing mode for a cartridge or printing system may also affect the oscillation frequency ink in a fluidic column. For example, a draft print mode may have less stringent printing quality standards as a speed print mode; therefore, the ink in a fluidic column may be oscillated at a lower frequency or for a shorter period of time. Accordingly, the database 32 may include data relative to one or more frequencies or ranges of frequencies that are associated with one or more printing modes.
The cartridge 10 preferably has an identification circuit that generates a signal indicative of the cartridge type and/or ink type when the cartridge 10 is mounted in the pocket 26, and electrically interconnected with the controller 29. In this manner, the controller 29 is configured access the database 32 to select a frequency or range of frequencies associated, one or more time duration for activation, with the cartridge to control the activation of the transducer 25 to maintain or recover nozzle function of the cartridge 10 during periods of printing inactivity or during printing operations.
The printing system may also include a closed loop system that continuously monitors nozzle function using optical sensors or other sensing systems for detecting whether ink is being ejected from the printhead. Such optical sensors are known to those skilled in the art and may include one or more through beam sensors that detect an ink drop that passes through a light beam. Another optical system may incorporate sensors that detect ink drops or spots printed on a medium according to a predetermined image and responsive to a print command. In addition, electrostatic systems may utilize an electrical charge plate that displays certain electrical properties according to a predetermined image printed on the plate. In the above examples, responsive to a print command, nozzles are selected or predetermined through which ink drops are ejected for printing. One or more sensors are provided to determine whether ink drops are ejected through a nozzle according to the print command. When a nozzle does not fire on demand, a sensor transmits a signal to the controller 29; responsive to which the controller 29 may activate the transducer 25 to initiate a nozzle recovery mode to unplug the nozzle.
While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only and not of limitation. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the teaching of the present invention. For example the transducer may be mounted internally of the cartridge and/or included as a component of the printhead. Accordingly, it is intended that the invention be interpreted within the full spirit and scope of the appended claims.
This application is a continuation-in-part of U.S. application Ser. No. 12/432,863 filed Apr. 30, 2009, which in turn claims benefit of U.S. Provisional Application No. 61/049,490 filed May 1, 2008, the contents of both of which are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 61049490 | May 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12432863 | Apr 2009 | US |
| Child | 12971200 | US |
