Thermal monitoring system for determining nozzle health

The concepts presented herein generally eject an exact amount of fluid through one or more nozzles in response to a firing signal, including those used in inkjet printing mechanisms. It relates to a thermo-fluid injection system, and more particularly to a thermal monitoring system for determining whether a nozzle is in a healthy state.

[0002] One thermo-fluid injection system is used in an inkjet printing mechanism comprising a cartridge often referred to as a "pen" that ejects droplets of a liquid colorant, commonly referred to as an "ink". Each pen has a fluid jet printhead with very small pinhole-sized nozzles formed, and ink droplets are jetted through the nozzles. To print an image, the printhead is propelled left and right across the page, ejecting ink droplets in the desired pattern as it moves. Two early ink heat injection mechanisms are described in US Pat. Nos. 5,278,584 and 4,683,481, both of which are the assignees of the present invention, Hewlett-Packard. It has been transferred to Company). In a thermal system, a barrier layer containing an ink channel and an evaporation or injection chamber is arranged between the nozzle orifice plate and the substrate layer. This substrate layer typically includes a linear array of heating elements such as resistors that heat the ink in the evaporation chamber by applying a voltage. When heated, ink droplets are ejected from a nozzle associated with a voltage-applied resistor. By selectively applying voltage to the resistor as the printhead moves across the page, ink is ejected onto the print medium in a pattern that forms the desired image (eg, picture, chart, or text). To do.

[0003] Non-functional nozzles in inkjet printers contribute to print quality defects when attempting to print a desired image on a medium sheet such as paper. Also, when applying other fluids, the non-functional nozzles result in an improper amount of fluid on the surface to be received or inaccurate placement of the fluid. Non-functional nozzles can: (1) contaminate the internal injection head, (2) air bubbles in the injection head, (3) fluid clumps across the nozzle, (4) contaminate the external injection head, and (5) inject. There are various possible causes, including resistors that cannot. Depending on the particular practice, there may be other causes for the non-functional nozzle. In multipath fluid injection routines or print modes, there are various ways to replace non-functional nozzles with functional nozzles, for example by using backup nozzles to help restore some of the fluid placement quality lost by defective nozzles. It has been proposed. These various fluid injection routines or print mode schemes rely on the ability to reliably detect and determine when nozzles are not functioning.

[0004] Unfortunately, in inkjet printing, the combination of small nozzles and quick-drying inks causes the printhead to not only dry ink and tiny dust particles or paper fibers, but also solids in the new ink itself. It also becomes easy to get clogged. Partially or completely blocked nozzles can cause the drops to disappear or misorient on the print medium, both of which degrade print quality. Nozzle "spitting" routines eject ink to push out dry ink clogging and place it in a waste tray called a "spittoon" in the art. In addition to pushing the clogging out of the nozzle, the ejection also heats the ink near the nozzle, which reduces the viscosity of the ink and helps clear the clogging.

Bubbles in the printhead can also interfere with nozzle ejection. These bubbles are evacuated from the printhead in priming routines such as those taught in US Pat. Nos. 5,592,201 and 5,714,991, both of which were assigned to the assignee of the invention, Hewlett-Packard. be able to. In devices that are not equipped with a priming system, air bubbles can be pushed out of the printhead by applying a positive force to the ink fountain that supplies the printhead. For example, the body of the inkjet pen can serve as an ink storage tank that holds the ink so that it does not evaporate and the ink does not leak or drip from the nozzles. Ink leakage is prevented using a force known as "back pressure" provided by the ink storage system. The desired back pressure level is elastic bladder (resilient) It can be obtained using various types of pen body designs such as bladder) designs, spring-bag designs, and foam-based designs. By applying force to the ink stored in these tanks, the ink itself can be used to push out air bubbles from the nozzle.

[0006] In operating a precise fluid injection system such as an inkjet printing mechanism, whether or not the printhead nozzle injects as instructed is determined by the built-in microprocessor and / or the printer driver in the host computer or the like. It is helpful to provide feedback to your print controller. This information is useful in determining if the nozzle is clogged and needs to be purged or ejected to clear the clog. This information streamlines the ejection process and saves ink, as only the clogged nozzles are ejected to clear the clogs. Further, if a damaged nozzle or heating element can be detected, the damaged nozzle is compensated by substituting another nozzle in the firing method.

[0007] Various different methods have been used to detect failed nozzles. For example, a special circuit in the printer that examines the resistance of the drive circuit can detect a failed firing resistor. If the resistor indicates an open circuit, then obviously the resistor will not fire because it cannot receive the firing pulse. Various sensors have traditionally been used to detect whether a drop has been ejected from a nozzle. For example, one method uses a photodiode and light emitting diode (LED) pair to detect the shadow of a drop passing between the photodiode and the LED. One optical system measured an appropriate amount of change at a given firing temperature by firing smaller and smaller drops until the optical detector could no longer see the drops. Unfortunately, the drop volume of the target is lower for newer inkjet cartridges, and some drops are now around 5 picolitres. With these small drops, multiple shots need to be fired to increase the signal, or such optical drop detectors need to be accurately positioned, which is done consistently and reliably in the manufacture of printing mechanisms. Is difficult.

[0008] In another system, a piezoelectric film is used as the drop target to detect whether the drop collides with the target. The electrostatic detection method detects positive or negative charges from the ejected droplets. Yet another method uses piezoelectric crystals to detect the acoustic signal generated as the droplets are ejected from the printhead. All of these methods have been constructed and tested, at least in prototype environments, and have been found to be effective in detecting nozzle failures and, in some cases, for weak or misaligned droplets.

[0009] Unfortunately, all of these early detection methods have two serious drawbacks. First, these early methods cannot detect nozzle failure "on the fly" during fluid injection activities such as normal printing. Second, these early methods cannot detect nozzle failure at all injection frequencies of the injection head. Nozzle health can change during any fluid injection routine or print job. Therefore, failure to detect non-functional nozzles immediately during a print job or other fluid injection activity can lead to serious problems. Nozzles can fail instantly, so non-functional nozzles are detected immediately and the resulting fluid injection or printing job is replaced with the correct system applied to ensure that the resulting fluid injection or printing job is performed as originally intended with high quality. It is desirable to have a nozzle replacement system that immediately utilizes the nozzle.

[0010] [Means for Solving the Problems] According to one aspect of the present invention, there is a method of monitoring the sound state of a fluid injection nozzle that injects fluid in a normal state in response to a firing signal, which is firing. Whether or not the nozzle ejected a fluid in response to a step of giving a signal to the nozzle, then a step of monitoring the temperature change of the nozzle, and finally a step of giving a firing signal from the monitored temperature change. Steps to determine and methods are provided.

[0011] According to another aspect of the present invention, the fluid tank containing the fluid and a nozzle flowing through the tank and receiving the fluid are included, and in a normal state, in response to a firing signal, the nozzle passes through the nozzle. A fluid injection mechanism comprising a fluid injection head for injecting a liquid is provided. Unfortunately, the nozzles are sometimes in an "poor health", clogged or blocked, and may not be able to eject fluid when required. In order to deal with this problem, the fluid injection mechanism also includes a temperature sensor that monitors the temperature change of the nozzle and generates a temperature signal in response to the change. The fluid injection mechanism also includes a controller that generates a firing signal. The controller also determines from the temperature signal whether the nozzle has ejected fluid in response to the firing signal.

[0012] According to another aspect of the present invention, the fluid injection mechanism is provided with a fluid tank for accommodating the fluid and a fluid injection head. The head includes a nozzle that flows through the tank and receives the fluid, and under normal conditions ejects the liquid through the nozzle in response to a firing signal. The fluid injection mechanism also includes means for giving a firing signal to the nozzle and means for monitoring the temperature change of the nozzle. The fluid injection mechanism also comprises means of determining from the monitored temperature change whether or not the nozzle has injected fluid in response to the firing signal.

[0013] An object of the present invention is to immediately determine whether or not a thermo-fluid injection nozzle is in a healthy state without unnecessary intervention, and if an unhealthy nozzle is found, It is to provide a monitoring system that employs a nozzle recovery or replacement routine.

[0014] Another object of the present invention is to provide a thermal monitoring system that monitors the sound state of printhead nozzles when installed in an inkjet printing mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows an example of an embodiment of a fluid injection system constructed in accordance with the present invention, where business reports, contacts, in industry, offices, homes, or other environments. It is shown as an inkjet printing mechanism that can be used for printing such as desktop publishing, more specifically, an inkjet printer 20. Various inkjet printing mechanisms are commercially available. For example, there are plotters, portable printing units, copiers, cameras, video printers, and facsimile machines, to name just a few examples of printing mechanisms that can embody the present invention. For convenience, the concept of the present invention will be described in the environment of the inkjet printer 20.

[0016] While it is clear that the components of the printer can vary from model to model, a typical inkjet printer 20 includes a chassis 22 enclosed in a housing or casing enclosure 23. Most of the housing or casing enclosure 23 has been omitted so that the internal components are clearly visible. The print media processing system 24 supplies the print media sheet through the print zone 25. The print medium may be any type of suitable sheet material such as paper, card stock, envelopes, textiles, transparent sheets, Mylar (registered trademark), etc., but for convenience, paper is used as the print medium for illustration. The form will be described. The print medium processing system 24 includes a supply or a medium input such as a paper feed tray 26, to which the medium is supplied and stored before printing. A conventional series of media feeds or drive rollers (not shown) powered by a motor and gear assembly 27 can be used to move the print media from the feed tray 26 to the print zone 25 for printing. After printing, the media sheet is shown as a pair of retractable output drying vane members (output) that are extended to receive the printed sheet. Landing on drying wing members) 28. The blade 28 temporarily pulls the newly printed sheet aside and drops the newly printed sheet into the output tray portion 30 while it is still dry and any previously printed sheet. Hold above the seat. The media processing system 24 can include a set of adjustment mechanisms for adapting to different sized print media including letters, legals, A4s, envelopes and the like. The processing system 24 generally includes a sliding length adjusting lever 32 for fixing a rectangular medium sheet in the vertical direction along the length of the medium, and for fixing the medium sheet in the width direction across the width of the medium. In some cases, a sliding width adjusting lever 34 is provided.

[0017] The printer 20 also includes a printer controller that receives instructions from a host device, which is usually a computer (not shown), such as a personal computer, which is schematically shown as a microprocessor 35. In fact, many of the functions of a printer controller can be performed by a host computer, an electronics circuit built into the printer, or an interaction between them. The term "printer controller 35" as used herein includes these functions, whether performed by a host computer, a printer, an intermediate device between them, or a combination of interactions between such elements. A monitor attached to the host computer may be used to display to the operator visual information such as the status of the printer or a particular program running on the host computer. Input devices such as personal computers, keyboards and / or mouse devices, and monitors are all well known to those of skill in the art.

[0018] The chassis 22 supports the guide rod 36 that defines the scanning axis 38, and can slide the inkjet printhead cartridge 40 to the left and right across the printing zone 25 so as to reciprocate along the scanning axis 38. Support. The cartridge 40 is driven by a carriage propulsion system, which is shown here as including an endless belt 42 coupled to a carriage driven DC motor 44. The carriage propulsion system also includes a position feedback system that communicates the carriage position signal with the controller 35, such as a conventional optical encoder system. An optical encoder reader can be attached to the carriage 40 to read the encoder strip 45 that extends along the carriage transition path. Then, the carriage drive motor 44 operates in response to a control signal received from the printer controller 35. Using the conventional flexible multi-core strip 46, an enable or fire command control signal can be sent from the controller 35 to the printhead carriage 40 for printing, as described further below.

Along the guide rod 36, the carriage 40 is propelled into a service area 48 capable of accommodating a service station unit (not shown) that provides various conventional printhead service functions. To clean and protect the printhead, a service station mechanism is typically installed within the printer chassis so that the printhead can be moved to the station for service provision and maintenance. For storage or during non-printing periods, service stations are typically equipped with a capping system that hermetically seals the printhead nozzles from contaminants and drying. Some caps are designed to facilitate priming, such as by being connected to a pump unit that draws a vacuum into the printhead. During operation, a large number of ink droplets are fired through each nozzle in a process known as "spitting" to periodically clear the blockage in the printhead. Wasted ink that does not produce this image is collected in the "spit" tank portion of the service station. After ejection, after removing the cap, and sometimes during printing, most service stations wipe the surface of the printhead to leave residual ink, as well as any dust and other debris collected on the printhead orifice plate. ) Is provided with an elastomer wiper.

Motor driven or with carriage 40 to selectively contact the printhead with components that service the printhead, such as caps, wipers, and primers (if used). A variety of different mechanisms can be used, such as translating or rotating devices that can operate through the engagement of the. For example, a suitable translational or floating The sled) service station operating mechanism is found in US Pat. Nos. 4,853,717 and 5,155,497, both of which have been assigned to Hewlett-Packard, the assignor of the present invention. The rotary service mechanism is commercially available on the DeskJet® 850C, 855C, 820C, 870C, and 895C models of color inkjet printers (see also US Pat. No. 5,614,930 assigned to Hewlett-Packard). ). Meanwhile, other types of translational service mechanisms are commercially available on the DeskJet® 690C, 693C, 720C, and 722C and 2000C Professional Series models of color inkjet printers, all sold by Hewlett-Packard. Has been done.

[0021] In the print zone 25, the medium is ink from ink jet cartridges such as the black ink cartridge 50 and the three monochromatic ink cartridges 52, 54, and 56 secured to the carriage 40 by the latch mechanism 58 shown open in FIG. Receive. Cartridges 50-56 are also commonly referred to by those skilled in the art as "pen". The ink applied by the pens 50-56 can be a pigment-based ink, a dye-based ink, or a combination thereof, and a hybrid or composite ink having the characteristics of both a paraffin-based ink, a dye, and a pigment. Of course, in non-printing contexts, fluid injection cartridges can be used to accurately inject other types of fluid.

[0022] Each of the illustrated pens 50 to 56 includes a tank for storing an ink supply source inside. Each pen 50-56 tank can incorporate the entire ink source into the printer for each color, which is typical of replaceable cartridges or "off". In what is known as an "axis)" ink delivery system, only a small source of ink is stored. The replaceable cartridge system carries the entire ink source as a pen that reciprocates along the scan axis 38 across the print zone 25. Therefore, a replaceable cartridge system can be thought of as an "on-axis" system, while a system that stores the main ink source in a fixed location away from the print zone scan axis is called an "off-axis" system. .. In off-axis systems, the main ink sources for each color are stored in fixed locations within the printer, such as four refillable or replaceable main tanks 60, 62, 64, and 66, which are supported by chassis 22. The stationary ink source is housed in the receptacle 68. Pens 50, 52, 54, and 56 have printheads 70, 72, 74, and 76, respectively, which are built-in tanks adjacent to printheads 70-76 from stationary tanks 60-66. Ink is ejected through the conduit or the tube system 78.

[0023] The printheads 70 to 76 representing the fluid injection or ejection head each have an orifice plate, through which a plurality of nozzles are formed in a manner well known to those skilled in the art. Each printhead 70-76 nozzle is typically formed by at least one but generally two linear arrays along the orifice plate. Therefore, the term "linear" as used herein can be interpreted as "substantially linear" or substantially linear, and may also include nozzle configurations that are slightly offset from each other, for example in a zigzag configuration. Each linear array is typically aligned longitudinally perpendicular to the scan axis 38, and the length of each array determines the maximum single-pass image swath for the printhead. Illustrated printheads 70-76 are thermal inkjet printheads, each of which comprises a plurality of resistors associated with nozzles, which will be described in more detail with reference to FIG. When a voltage is applied to the selected resistor, one bubble of gas is formed, and the bubbles eject ink droplets from the nozzles onto a paper sheet in the printing zone 25 under the nozzles. A voltage is selectively applied to the printhead resistor in response to a firing command control signal received from the controller 35 via the multi-core strip 46.

[0024] FIG. 2 shows a form of a fluid injection head, which is shown here as an inkjet printhead 70 of a cartridge 50 that supplies black ink. The illustrated cartridge 50 comprises a plastic body 80 bisected by a central shaft 81. The body 80 defines an ink supply channel 82, which circulates with an ink fountain in the upper rectangular portion of the cartridge 50. The body 80 also includes a raised wall 84 defining the cavity 85 at the lower end of the supply channel 82. The conventional fluid injection or ejection mechanism is centrally located within the fluid cavity 85 and is commercially available from 3M on Kapton® tapes, Upilex® tapes, or other known to those of skill in the art. It is held in place through attachment by an adhesive layer 86 to a flexible polymer tape 88 of equivalent material or the like. The illustrated tape 88 also includes, for example, laser ablation. It also functions as a nozzle orifice plate by defining two parallel rows of offset nozzle holes or orifices 90 formed in tape 88 by ablation) technology. The adhesive layer 86, which can be an epoxy, hot melt, silicone, ultraviolet (UV) curable compound, or a mixture thereof, forms a fluid seal between the raised wall 84 and the tape 88.

The ink ejection mechanism comprises a silicon substrate 96, each generally located behind a single associated nozzle 90 and comprising a plurality of individually voltage-applied thin film emission resistors 95. The firing resistor 95 is sent from the controller 36 via a flexible conductor to the carriage 40 and via an electrical interconnect to the conductor carried by the polymer tape 88 (omitted for clarity). Ohmic when a voltage is selectively applied by an enable signal or firing pulse Acts as a heater). Communication between the printhead resistor 95 and the controller 35 is preferably made via an electrical interconnect between the pen 50 and the carriage 40. The barrier layer 92 can be formed on the surface of the substrate 92 using conventional photolithography techniques. The barrier layer 92 is a layer of photoresist or some other polymer that, in cooperation with tape 88, defines an evaporation chamber 93 that surrounds each associated firing resistor 95. The barrier layer 92 is bonded to the tape 88 by a thin film adhesive layer 94 such as an uncured layer of polyisoprene photoresist. Ink from the cartridge supply tank flows through the fluid supply channel 82, as indicated by a pair of curved arrows 98, around the edges of the substrate 96, and into each evaporation chamber 93. When a voltage is applied to the firing resistor 95, the ink in the evaporation chamber 93 is ejected, as indicated by the ejected ink droplet 99.

FIG. 3 shows an embodiment of a thermal monitoring system 100 constructed according to the present invention. The thermal monitoring system 100 uses the thermal properties created during the injection of the ink droplet 99 or during the attempted injection to determine if the droplet was actually ejected in response to the emission pulse received from the controller 35. To do. The surveillance system 100 eliminates the need to waste unnecessary time while positioning the printhead to a special sensor within the service area 48, as in the case of the early system described in the prior art section above. , "On the fly", i.e. during a normal fluid injection or printing routine. In addition, by monitoring nozzle health and substituting functional nozzles for non-functional nozzles, the printer 20 or other fluid injection mechanism needs to ensure that any non-functional nozzle does not affect the underlying job. Can be modified.

The thermal monitoring system 100 is in between any one of several initiating activities 102, such as during normal printing 104, during normal nozzle purging or ejection routine 106, or during special nozzle inspection routine 108. Is started. When any of these activation activities 104, 106, or 108 occurs, the printer controller 35 sends a signal to the firing pulse generator 110, which applies the firing voltage over the selected resistor 95. .. In measurement step 112, changes in the resistance of the firing resistor are measured over time in the time frame in which the selected resistor 95 is expected to fire. After this resistance measurement, in conversion step 114, analog / digital (A / D) conversion is performed on the resistance measured in step 112. This change in the resistance of the launch resistor 95 over time can be drawn as a curve 115 as shown in the graph of FIG. After generating the trace 115, signal analysis step 116 is performed with respect to FIG. 4, as described below.

[0028] In the determination step 118, it is determined whether or not the resulting curve, such as the curve 115 in FIG. 4, is a good signal indicating a properly functioning nozzle 90. If a good signal is actually found in step 118, a YES signal 120 is issued in continuation step 122, in which normal fluid injection is continued with the properly functioning nozzle 90. However, if a good signal is not found in the determination step 118, the NO signal 124 is emitted. The next action taken depends on which of the particular activation steps 104-108 occurred when the selected nozzle 90 was being inspected.

[0029] When the start-up step 104 during normal printing occurs, the NO signal 124 proceeds to the replacement step 126, and in the next printing swath, the defective nozzle that is not functioning is replaced with the nozzle that is functioning correctly. .. When the subsequent print swath using the replacement nozzle in step 126 is complete, querying step 128 asks if the print job is complete. If not completed, a NO signal 130 is issued in continuation step 132 and the print job is continued using the replacement nozzles. If it is determined in query step 128 that the print job is complete, a YES signal 134 is issued in special inspection step 135, where special inspection routine 108 is initiated to inspect suspected defective nozzles. ..

If NO signal 124 is emitted after returning to good signal determination step 118 and starting the inspection routine using step 106 or 108 during ejection or special inspection routine, nozzle recovery step 136 is NO signal 124. To receive. The type of nozzle recovery routine attempted after step 136 depends on the type of nozzle clogging and the type of recovery equipment available in the fluid injection unit, which is the printer 20 in this embodiment. First, in determination step 138, the exact type of nozzle clogging, either by analyzing the thermal properties of the firing resistor 95 or through tabulation of such data, if shown in a graph similar to FIG. 4, as described below. Is judged. Next, in query step 140, the question is asked whether the nozzle clogging is solid. If the nozzle clogging is actually solid, a YES signal 142 is issued and a printhead wiping or solvent recovery routine 144 is performed. After this recovery routine 144, a signal 146 is issued in inspection step 135 and special nozzle inspection start step 108 is performed.

If it is determined in query step 140 that the clogging is not solid, the NO signal 148 is emitted. Depending on the type of fluid injection unit, such as the printer 20, non-solid clogging, i.e. steam or bubble clogging, is cleared in a variety of different ways. For example, if the printer 20 comprises a priming system, such as that disclosed in US Pat. No. 5,714,991, which is now assigned to Hewlett-Packard, priming step 150 is initiated. During this priming routine, air or steam is purged from the printhead by applying negative or reduced pressure to the orifice plate 88. After this priming routine 150, a signal 152 is sent to the special inspection step 135 and the special inspection start step 108 is restarted to determine if the priming operation of step 150 was effective in clearing the nozzle clogging.

If the particular fluid injection system does not include a priming system, the positive pressure application step 154 receives the NO signal 148 from the query step 140. Next, step 154 applies positive pressure to the ink supply source by sending pressure to the printhead 70 through the ink supply line 78, pushing out air bubble clogging from the nozzle 90. After this positive pressure application step 154, a signal 156 is issued to inspection step 135, special inspection start step 108 is activated, and is the positive pressure application in step 154 actually successful in removing air bubble clogging from the defective nozzle? Judge whether or not. Of course, if any of the wiping / solvent recovery step 144, the priming step 150, or the positive pressure application step 154 fails to clear the blockage, these steps can be repeated continuously for the monitoring routine 100. Nozzle replacement routine 132 can be initiated if possible or if printing is required.

[0033] As described above, analysis step 116 and step 138 determining the type of clogging use the thermal properties of the firing resistor shown in FIG. Curve 115 shows the behavior of a properly functioning nozzle 90 that ejects fluid droplets 99. This curve 115 has several different segments and sections. The time zero (0) seconds indicates when the launch signal was first sent to the resistor 95 by the controller 35. Prior to time zero, the resistor 95 has an ambient temperature curve section 158, which is shown as approximately room temperature. After applying the firing pulse, the resistor temperature begins to rise as indicated by the first arc section 160 followed by the second arc section 162, and eight seconds have passed since the firing pulse was started at time zero. Not long ago, it reached a maximum temperature of about 330 degrees. After this maximum temperature, curve 115 drops sharply in temperature as shown in curve section 164 and returns to ambient temperature again before the time point of 9 seconds.

During the first arc portion 160 of the curve 115, the energy from the resistor 95 is transferred here to the resistor surrounding the liquid, which is the ink. The second arc portion 162 of the curve 115 exhibits heat transfer, where the resistor 95 heats the bubbles formed as the liquid boils. A properly functioning nozzle produces thermal properties with transition 165, where the two arc curve sections 160 and 162 meet. During this transition period 165, bubbles are formed as the liquid, which is here the ink, begins to boil. When the air bubbles finally burst, ink droplets 99 are ejected from nozzle 90, which is shown at the sharply bent portion 166 of the curve 115 where the curved portions 162 and 164 are combined.

Therefore, good signal determination step 118 looks for transition 165 of curve 115, which is about 1 second somewhere between 3 and 5 seconds with respect to printhead 70, as shown in FIG. Occurs over the area of. In determining whether transition point 165 is present, the first and second arc curve sections 160 and 162 can be mathematically approximated as straight line traces. For example, when the resistor 95 is heating a bubble, the curve 162 can be approximated by a straight-line curve 168. Similarly, when the resistor 95 is heating the liquid, the first arc curve 160 can be approximated by a straight line curve 170. If the intersection 172 of these two mathematical approximation curves 168 and 170 is found, step 118 determines that the bubbles are actually formed and that the nozzle 90 is functioning properly. Mathematical approximation to generate curves 168 and 170 to determine if inflection point 172 occurs is preferable to graph analysis of raw data. This is because point 172 is easier to detect than the actual signal inflection point 165 of curve 115.

[0036] Therefore, the operation of the good signal determination step 118 is understood here. As mentioned above, the thermal properties of FIG. 4 can also be used by determination step 148 to determine which type of clogging, solid or air, is occurring. Once the type of nozzle clogging is known, it is used to determine which type of nozzle recovery routine to perform the wiping / solvent application routine 144, the priming routine 150, or the positive pressure application routine 154. For example, if there is no transition 165 in the trace 115, a solid blockage can be found. In the case of solid nozzle clogging, the resistor 95 heats up along the first arc portion 160 and then instead of the transition at point 165, the temperature extends as shown in curve 174, where curve 115 Heat continues to be dissipated into the liquid without bursting bubbles, such as at point 166. Therefore, if the thermal properties of the nozzle follow the path of curve 174, it is considered that a solid clogging has been found, a YES signal 142 is generated, and the wiping and / or solvent recovery routine 144 is initiated.

In the case of steam or bubble nozzle clogging, after the initial application of the firing pulse, the thermal properties of the resistor follow a trace of curve 175, and then the monitoring system 100 determines that the nozzle is clogged with bubbles. Note how the steam / bubble clogging curve 175 follows approximately the same arc as the second portion 162 of the thermal trace 115 in the graph of FIG. Here, the thermal energy of the resistor 95 is consumed by the gas or bubbles. Therefore, when bubble clogging is detected, a NO signal 148 is generated, which initiates either the priming routine 150 or the positive pressure application routine 154 to draw or push bubbles out of the nozzle 90.

[0038] In summary, the temperature history of the inkjet resistor 95 during droplet ejection is shown in the pre-nucleation stage 176, the nucleation stage 178, and the post-nucleation stage. Stage) 180 can be divided into the three stages shown in Fig. 4. During the pre-nucleation stage 176, the ink is in contact with the resistor 95 when a drive current is applied by the firing pulse generator 110. At nucleation stage 178, some phase of the liquid at the interface between the launch register and the liquid changes from liquid to gas. In post-nucleation post-nucleation stage 180, the hot resistor 95 is only in contact with the ink vapor, called gas or foam, in this embodiment. As shown in FIG. 4, since the fluid in the liquid phase and the fluid in the gas phase have different heat capacities and heat transfer properties, the thermal characteristics 160 and 162 of the pre-nucleation stage 176 and the post-nucleation stage 180 are different, respectively. Knowing these characteristics of the healthy nozzle trace 115 allows the thermal profile to be used to determine if the nozzle is in good health.

[0039] Instead of simply applying a curve approximation routine to generate curves 168 and 170 to look for inflection point 172, a mathematical routine can be performed on the input data. In this mathematical routine, the quadratic derivative of the thermal properties is calculated to find the rate of temperature rise. If this quadratic derivative curve does not pass the value zero (0), which represents the inflection point 165, then the firing chamber of nozzle 90 did not succeed in nucleation, corresponding to the trace of curve 174, and bubbles were formed. It is judged that there was no such thing. Therefore, step 140 determines that the blockage is actually solid and produces a YES signal 142.

An alternative method of thermally detecting nozzle health involves observing an increase in the temperature of the resistor 95 after the firing pulse is provided by generation step 110. As mentioned above, gas clogging appears as a thermal characteristic shown by curve 175, which indicates that the resistor 95 is in contact with air and the nozzle 90 has been deprimed. Moreover, in the event of an air blockage, the resulting rate of temperature drop is significantly reduced, as evidenced by the sharp rise in curve 175 well above the healthy nozzle trace 115.

[0041] In one embodiment, the measurement of the resistor temperature is made by using a change in the resistance or conductivity of the resistor 95 itself. Alternatively, a heat sensing resistor or other heat sensor, such as a heat sensor 182, is embedded in the printhead near the firing resistor 95. It is clear that the separate thermal sensors 182 may be placed in a variety of different locations and only one preferred location for the particular printhead design illustrated is shown in FIG. However, in simple cases it may be easier to use only the firing resistor 95 to determine if the associated nozzle 90 is functioning properly.

[0042] Further, the thermal properties of FIG. 4 are shown for one particular type of printhead nozzle, but are in good health, depending on the nozzle type and fluid injection head design, as well as the type of fluid used. It is clear that the exact shape and placement of the nozzle traces, as well as the clogged nozzle traces 174, 175, differ from those shown in FIG. Further, although it has been described here that the fluid injected about the thermal monitoring system 100 is ink and the printhead carrying vehicle is an inkjet printer 20, the nozzle health monitoring system 100 is manufactured, electronically engineered, and It is clear that it can also be used in other fluid injection applications, such as fluid injection processes used in medicine, appliances, food, automobiles, and other industries where accurate fluid injection is desired. In addition, by monitoring nozzle health during normal fluid injection activity, unhealthy nozzles can be easily detected and recovered using various recovery routines such as 144, 150, and 154, permanently. It can be easily restored to a healthy state before it suffers any damage.

BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] FIG. 1 is a perspective view of an example of one fluid injection system, and here, an embodiment of an exemplary thermal monitoring system for determining the sound state of a fluid injection nozzle supported inside. Is shown as an inkjet printing mechanism using.

FIG. 2 is an enlarged front sectional view of a form of a fluid injection head, which is shown here as an inkjet printhead with two nozzles for ejecting ink droplets.

FIG. 3 is a flowchart of a form of the thermal monitoring system of FIG.

FIG. 4 is a graph of thermal characteristics used by the thermal monitoring system of FIG. 1 to determine the sound state of the nozzle.

[Code Description] 90 Fluid Injection Nozzle 95 Launch Resistor 99 Ink Drop 100 Thermal Monitoring System 108 Nozzle Inspection Routine 110 Launch Pulse Generator 112 Measurement Step 115 Curve 118 Judgment Step 126 Malfunctioning Bad Nozzle Replacing with existing nozzle Step 128 Query step 132 Continuation step 136 Nozzle recovery step 138 Judgment step 142 YES signal 144 Recovery routine 148 NO signal 150 Priming step 154 Positive pressure application step 165 Transition point