IN A FLUID EJECTION SYSTEM

BACKGROUND

[0001] Fluid ejection dies may be implemented in fluid ejection devices and/or fluid ejection systems to selectively eject/dispense fluid drops.

Example fluid ejection dies may include nozzles, ejection chambers and fluid ejectors. In some examples, the fluid ejectors may eject fluid drops from an ejection chamber out of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The disclosure herein is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements, and in which :

[0003] FIG. 1A illustrates an example fluid ejection system to evaluate a drive bubble device;

[0004] FIG. I B illustrates an example printer system to evaluate a drive bubble device;

[0005] FIG. 2 illustrates an example cross-sectional view of an example drive bubble device including a nozzle, a nozzle sensor, and nozzle sensor control logic;

[0006] FIG. 3 illustrates an example method for modulating fire pulse lengths for assessing sensor control logic of a fluid ejection system; and

[0007] FIG. 4 illustrates example DBD (drive bubble detect) Voltage Response Curves.

[0008] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown . Moreover the drawings provide examples and/or implementations consistent with the description. However, the description is not limited to the examples and/or implementations provided in the drawings. DETAILED DESCRIPTION

[0009] Examples provide for a fluid ejection system to assess a nozzle sensor control logic of a fluid ejection die. In some examples, a fluid ejection system can assess the operability of the nozzle sensor control logic by detecting a first signal response of a drive bubble device being fired at a first pulse length. Furthermore, based at least in part on the first signal response, the fluid ejection system can determine a state of operability of the nozzle sensor control logic. In some examples, a fluid ejection system can evaluate nozzle sensor control logic after the components of the fluid ejection system has been fully assembled. Such examples recognize that the fluid ejection system can evaluate nozzle sensor control logic with the presence of ink in the fluid ejection system. Among other benefits, examples are described that enable the fluid ejection system to assess the nozzle sensor control logic in a fluid ejection system.

[0010] SYSTEM DESCRIPTION

[0011] FIG. 1A illustrates an example fluid ejection system to evaluate a drive bubble device. As illustrated in FIG. 1A fluid ejection system 100 can include controller 104, fluid ejection die 106 and communication interface 110. Controller 104 can be configured to implement processes and other logic to manage operations of the fluid ejection system 100. For example, controller 104 can determine or evaluate a state of operability of DBD (drive bubble detect) 102. For instance, controller 104 can transmit instructions 112 to fluid ejection die 106 to modulate or vary the fire pulse length of drive bubble device 108. Additionally, controller 104 can transmit instructions 112 to DBD 102 to monitor the resulting signal responses and transmit data related to those signal responses back to controller 104. In some examples, controller 104 can communicate with fluid ejection die 106 to fire/eject fluid out of drive bubble device(s) 108. As herein described, any fluid, for example fluid, can be used can be fired out of drive bubble device(s) 108. In other examples, controller 104 can transmit instructions 112 to DBD 102 to make assessments on drive bubble device(s) 108. In other examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to implement servicing or pumping of drive bubble device(s) 108. In yet other examples, controller 104 can transmit instructions 112 DBD 102 to make assessments on some drive bubble devices 108, and concurrently transmit instructions 112 to fluid ejection die 106 to implement servicing or pumping of other drive bubble devices 108. In some examples, controller 104 can include one or more processors to implement the described operations of fluid ejection system 100.

[0012] Drive bubble device(s) 108 can include a nozzle, a fluid chamber and a fluid ejection component. In some examples, the fluid ejection component can include a heating source. Each drive bubble device can receive fluid from a fluid reservoir. In some examples, the fluid reservoir can be fluid feed holes or an array of fluid feed holes. In some examples, the fluid can be ink (e.g. latex ink, synthetic ink or other engineered fluidic inks).

[0013] Fluid ejection system 100 can fire fluid from the nozzle of drive bubble device(s) 108 by forming a bubble in the fluid chamber of drive bubble device(s) 108. In some examples, the fluid ejection component can include a heating source. As such, fluid ejection system 100 can form a bubble in the fluid chamber by heating the fluid in the fluid chamber with the heat source of drive bubble device(s) 108. The bubble can drive/eject the fluid out of the nozzle, once the bubble gets large enough. In some examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to drive a signal (e.g. power from a power source or current from the power source) to the heating source in order to create a bubble in the fluid chamber (e.g. fluid chamber 202). Once the bubble in the fluid chamber gets big enough, the fluid in the fluid chamber can be fired/ejected out of the nozzles of drive bubble device(s) 108.

[0014] In some examples, the heating source can include a resistor (e.g. a thermal resistor) and a power source. In such examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to drive a signal (e.g. power from a power source or current from the power source) to the resistor of the heating source. The longer the signal is applied to the resistor, the hotter the resistor becomes. As a result of the resistor emitting more heat, the hotter the fluid gets resulting in the formation of a bubble in the fluid chamber.

[0015] Fluid ejection system 100 can make assessments of drive bubble device(s) 108 by electrically monitoring drive bubble device(s) 108. Fluid ejection system 100 can electrically monitor drive bubble device(s) 108 with DBD 102 and a nozzle sensor or DBD sensing component operatively communicating with drive bubble device(s) 108. DBD sensing component can be a conductive plate. In some examples DBD sensing component can be a tantalum plate.

[0016] In some examples, DBD 102 may electrically monitor the impedance of the fluid in drive bubble device(s) 108, during the formation and dissipation of the bubble in drive bubble device(s) 108. For instance, DBD 102 can be operatively connected to a DBD sensing component that itself is operatively connected to the fluid chamber of drive bubble device 108. In such a configuration, DBD 102 can drive a signal or stimulus (e.g. current or voltage) into the DBD sensing component in order to detect response signals (e.g. response voltages) of the formation and dissipation of the bubble in a drive bubble device. If the fluid chamber is empty, the remaining air has a high impedance, meaning the detected voltage response would be high . If the fluid chamber had fluid, the detected voltage response would be low because the fluid at a completely liquid state has a low impedance. If a steam bubble is forming in the fluid chamber, while a current is driven into the DBD sensing component, the detected voltage response would be higher than if the fluid in the fluid chamber were fully liquid. As the heating source gets hotter and more fluid vapors are generated, the voltage response increases because the impedance of the fluid increases. The detected voltage response would climax when the fluid from the fluid chamber is ejected from the nozzle. After which, the bubble dissipates and more fluid is introduced into the fluid chamber from reservoir.

[0017] In some examples, DBD 102 can drive the current (to the DBD sensing component) at precise times in order to detect one or more voltage responses, during the formation and dissipation of a bubble in the fluid chamber. In other examples, DBD 102 can drive a voltage to the DBD sensing component and monitor the charge transfer or voltage decay rate, during the formation and dissipation of a bubble in the fluid chamber 202.

[0018] Fluid ejection system 100 can determine the state of operability of the components of the drive bubble device, based on the assessments. In some examples, the data of the detected signal response(s) can be compared with a DBD signal response curve. In some examples, the signal response(s) are voltage responses. In other examples, the signal response(s) are the charge transfer or voltage decay rate. Based on the comparison, fluid ejection system 100 can determine the state of operability of the drive bubble device being DBD assessed (e.g. whether the components of the drive bubble device are working properly).

[0019] Controller 104 can determine the state of operability of drive bubble device(s) 108, based on data on DBD characteristics 110 transmitted from DBD 102. In some examples, data of DBD characteristics includes, the data of signal responses transmitted from DBD 102. Furthermore, controller 104 can compare data of signal responses to a DBD signal response curve. In some examples, the DBD signal response curve can include a signal response curve of a full functioning drive bubble device. For example, if controller 104 determines that the signal response at a pulse length is similar to the measured signal at the same delay time as the time of the pulse length, then controller 104 can determine that DBD 102 and/or drive bubble device(s) 108 is working properly. On the other hand, if controller 104 determines that the signal response at a pulse length is different than the measured signal at the same delay time as the time of the pulse length, then controller 104 can determine that DBD 102 and/or drive bubble device(s) 108 is not properly working.

[0020] In some examples, fluid ejection system 100 can monitor the state of operability of drive bubble device 108 (e.g. whether drive bubble device(s) 108 is working properly) by modulating the fire pulse length of drive bubble devise 108. For example, controller 104 can modulate the fire pulse length (e.g., the amount of current or power being driven into a heating source of drive bubble device 108) of drive bubble device 108, from a minimum amount to a maximum amount and run an assessment on device 108. Furthermore, during the assessment, controller 104 can receive signal response(s) data of each fire pulse length applied to drive bubble device 108, from DBD 102. Subsequently, controller 104 can compare the signal responses to a DBD signal response curve of a known functioning drive bubble device. Based on the comparison, controller 104 can determine whether DBD 102 is working properly. Furthermore, in some examples, if controller 104 determines that DBD 102 is working properly, then controller 104 can also determine that the components of drive bubble device 108 is working properly. [0021] In other examples, controller 104 can modulate the magnitude or characteristic of the fire pulse (e.g. greater current on resistor to generate more heat) of drive bubble device 108, from a minimum amount to a maximum amount and run an assessment on device 108.

[0022] Fluid ejection die 106 can include columns of drive bubble devices 108. In some examples, fluid ejection die 106 can include a column of drive bubble devices 108. Making a DBD (drive bubble detect) assessment of an entire fluid ejection die can take too long and the later assessed drive bubble devices on the fluid ejection die may have been idle too long and become too degraded to be able to undergo an assessment. One approach to combat this problem, is by halting assessment of the entire fluid ejection die to service (e.g. eject/pump fluid currently in the drive bubble device or recirculate the fluid currently in the drive bubble device) the degraded drive bubble device. However such an approach extends the time for an

assessment and can even contribute to the degradation of the drive bubble device to degrade further. In some examples, fluid ejection system 100 can simultaneously perform an assessment of drive bubble device 108 and service the remaining drive bubble devices 108 not undergoing assessment. In other examples, printer device 100 can simultaneously perform an assessment of one drive bubble device 108 of one column of drive bubble devices and service all drive bubble devices 108 of the remaining columns not selected for assessment.

[0023] In some examples, fluid ejection die system 100 can be a printer system. FIG. IB illustrates an example printer system to evaluate a drive bubble device. Printer system 150 can include modules/components similar to fluid ejection system 100. For example, as illustrated in FIG. I B, printer system 150 can include controller 152 and fluid ejection die 156. Controller 152 can be configured to implement processes and other logic to manage operations of fluid ejection die 156. For example, controller 152 can transmit instructions 162 to fluid ejection die 156 to modulate or vary the fire pulse length of drive bubble device 158. Additionally, controller 152 can transmit instructions 162 to DBD 154 to monitor the resulting signal responses and transmit data related to those signal responses back to controller 152. In some examples, controller 152 can evaluate the health and functionality of fluid ejection die 156 by controller 152 making assessments on drive bubble device(s) 158. Furthermore, while controller 152 is making assessments on drive bubble device(s) 158, controller 152 can instruct fluid ejection die 156 to concurrently implement servicing or pumping of other drive bubble device(s) 158.

[0024] FIG. 2 illustrates an example cross-sectional view of an example drive bubble device including a nozzle, a nozzle sensor, and nozzle sensor control logic. As illustrated in FIG. 2, drive bubble device 220 includes nozzle 200, ejection chamber 202, and fluid ejector 212. In some examples, as illustrated in FIG. 2, fluid ejector 212 may be disposed proximate to ejection chamber 202.

[0025] Drive bubble device 220 can also include a DBD sensing component 210 operatively coupled to and located below fluid chamber 202. DBD sensing component can be a conductive plate. In some examples DBD sensing component 210 is a tantalum plate. As illustrated in FIG. 2, DBD sensing component 210 can be isolated from fluid ejector 212 by insulating layer 218.

[0026] In some examples, a fluid ejection die, such as the example of FIG. 1A, may eject drops of fluid from ejection chamber 202 through a nozzle orifice or bore of the nozzle 200 by fluid ejector 212. Examples of fluid ejector 212 include a thermal resistor based actuator, a piezo-electric membrane based actuator, an electrostatic membrane actuator,

magnetostrictive drive actuator, and/or other such devices.

[0027] In examples in which fluid ejector 212 may comprise a thermal resistor based actuator, a controller can instruct the fluid ejection die to drive a signal (e.g. power from a power source or current from the power source) to electrically actuate fluid ejector 212. In such examples, the electrical actuation of fluid ejector 212 can cause formation of a vapor bubble in fluid proximate to fluid ejector 212 (e.g. ejection chamber 202). As the vapor bubble expands, a drop of fluid may be displaced in ejection chamber 202 and expel led/ejected/fi red through the orifice of nozzle 200. In this example, after ejection of a fluid drop, electrical actuation of fluid ejector 212 may cease, such that the bubble collapses. Collapse of the bubble may draw fluid from fluid reservoir 204 into ejection chamber 202. In this way, in some examples, a controller (e.g. controller 104) can control the formation of bubbles in fluid chamber 202 by time (e.g. longer signal causes hotter resistor response) or by signal magnitude or characteristic (e.g. greater current on resistor to generate more heat).

[0028] In examples in which the fluid ejector 212 includes a

piezoelectric membrane, a controller can instruct the fluid ejection die to drive a signal (e.g. power from a power source or current from the power source) to electrically actuate fluid ejector 212. In such examples, the electrical actuation of fluid ejector 212 can cause deformation of the piezoelectric membrane. As a result, a drop of fluid may be ejected out of the orifice of nozzle 200 due to the deformation of the piezoelectric membrane. Returning of the piezoelectric membrane to a non-actuated state may draw additional fluid from fluid reservoir 204 into ejection chamber 202.

[0029] Examples described herein may further comprise a nozzle sensor or DBD sensing component 210 disposed proximate ejection chamber 202. DBD sensing component 210 may sense and/or measure characteristics associated with the nozzle 200 and/or fluid therein. For example, the nozzle sensor 210 may be used to sense an impedance corresponding to the ejection chamber 202. In such examples, the nozzle sensor 210 may include a first sensing plate and second sensing plate. In some examples DBD sensing component 210 is a tantalum plate. As illustrated in FIG. 2, DBD sensing device 210 can be isolated from fluid ejector 212 by insulating layer 218. Based on the material disposed between the first and second sensing plates, an impedance may vary. For example, if a vapor bubble is formed proximate the nozzle sensor 210 (e.g. in fluid chamber 202), the impedance may differ as compared to when fluid is disposed proximate the nozzle sensor 210 (e.g. in fluid chamber 202). Accordingly, formation of a vapor bubble, and a subsequent collapse of a vapor bubble may be detected and/or monitored by sensing an impedance with the DBD sensing component 210.

[0030] A fluid ejection system can make assessments of drive bubble device 220 and determine a state of operability of the components of drive bubble device 220 (e.g. whether the components of drive bubble device 220 are working properly). For example, as illustrated in FIG. 2, nozzle sensor control logic 214(including current source 216) can be operatively connected to DBD sensing component 210 to monitor characteristics of the drive bubble device, during the formation and dissipation of the a bubble in fluid chamber 202. For instance, some examples, nozzle sensor control logic 214 can be operatively connected to DBD sensing component 210 to electrically monitor the impedance of the fluid in fluid chamber 202, during the formation and dissipation of the bubble in fluid chamber 202. Nozzle sensor control logic 214 can drive a current from current source 216 into DBD sensing component 210 to detect a voltage response from fluid chamber 202 during the formation and dissipation of a bubble. In some examples, nozzle sensor control logic 214 can drive the current (to DBD sensing component 210) at precise times in order to detect one or more voltage responses, during the formation and dissipation of a bubble in fluid chamber 202. In other examples, nozzle sensor control logic 214 can drive a voltage to DBD sensing component 210 and monitor the charge transfer or voltage decay rate, during the formation and dissipation of a bubble in fluid chamber 202. Nozzle sensor control logic 214 can transmit data related to the voltage responses to a controller (e.g. controller 104) of the fluid ejection system (e.g. fluid ejection system 100). Similar to the principles described earlier, the controller can then determine the state of operability of drive bubble device 200, based on the received data. In some examples, nozzle sensor control logic 214 can include DBD circuitry.

[0031] METHODOLOGY

[0032] FIG. 3 illustrates an example method for modulating fire pulse lengths for assessing sensor control logic in a fluid ejection system. As herein described a firing event is when one drive bubble device ejects/fires fluid and undergoes assessment. In the below discussions of FIG. 3 may be made to reference characters representing like features as shown and described with respect to FIG. 1A, FIG. I B and/or FIG. 2 for purpose of illustrating a suitable component for performing a step or sub-step being described.

[0033] FIG. 3 illustrates an example method for modulating fire pulse lengths for assessing sensor control logic of a fluid ejection system. In some examples, fluid ejection system 100 can detect a first signal response of a drive bubble device at a first pulse length (300). For example, controller 104 can transmit instructions 112 to fluid ejection die 106 to select drive bubble device 108 and to apply a pulse length to the selected drive bubble device. Instructions 112 to fluid ejection die 106 can specify the pulse length (e.g. how long power or current is to be applied to the fluid ejector that is operatively connected to the fluid chamber of drive bubble device 108). Additionally, in such examples, the fluid ejector may be a thermal resistor based actuator. As a result, the longer the pulse length (e.g., the amount of time power or current is applied to the fluid ejector) the more heat is produced by the fluid ejector. The more heat the fluid ejector produces, the hotter the fluid in the fluid chamber (e.g. fluid chamber 202) becomes, resulting in the formation of a vapor bubble in the fluid chamber. In other examples, the fluid ejector can include a piezoelectric membrane.

[0034] Controller 104 can transmit instructions 112 to DBD 102 to detect a signal response while a pulse length is applied to drive bubble device 108. Based on instructions 112 from controller 104, DBD 102 can drive stimuli (e.g. current or voltage) into a DBD sensing component operatively connected to the fluid chamber of drive bubble device 108. The stimuli driven into the DBD sensing component, enables DBD 102 to detect a signal response from the fluid chamber of drive bubble device 108, while a pulse length is applied to drive bubble device 108. Controller 104 can then receive from DBD 102 data related to the detected signal responses, for a pulse length applied to drive bubble device 108.

[0035] In some examples, controller 104 can transmit instructions 112 to DBD 102 to take multiple signal response measurements while a pulse length is applied to drive bubble device 108. As a result, based on

instructions 112 from controller 104, DBD 102 can drive multiple stimuli pulses at precise times in order to detect multiple signal responses while a pulse length is applied to drive bubble device 108.

[0036] In some examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to apply to the drive bubble device a minimum pulse length. Furthermore, controller 104 can transmit instructions 112 to DBD 102 to detect the signal response of the drive bubble device at that minimum pulse length and transmit data related to the signal responses to controller 104. In some examples, the minimum pulse length can be the minimum amount of power/current required to begin the formulation of the bubble in the fluid chamber (e.g. fluid chamber 202) of the drive bubble device. In other examples, the minimum pulse length correlates to the minimum signal response DBD 102 can detect. For example, the minimum pulse length is the minimum amount of power/current applied to the heating source that causes the smallest reaction (e.g., the vaporization of fluid in the fluid chamber of the drive bubble device) that DBD 102 can detect (via a signal response) when driving stimuli into a DBD sensing component operatively connected to the drive bubble device.

[0037] In some examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to apply to the drive bubble device a maximum pulse length . Furthermore controller 104 can transmit instructions 112 to DBD 102 to detect the signal response of the drive bubble device at that maximum pulse length and transmit data related to the signal responses to controller 104. In some examples, the maximum pulse length that can be applied to the heating source is the maximum amount of power/current that can be applied to the heating source without damaging the heating source.

[0038] In some examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to apply multiple pulse lengths to a drive bubble device. Furthermore, controller 104 can transmit instructions 112 to DBD 102 to detect the signal responses of each pulse length and transmit data related to each signal response to controller 104. In some examples, controller 104 transmits to fluid ejection die 106 instructions 112 indicating that each pulse length is to be different and randomly applied to drive bubble device 108. In other examples, controller 104 transmits to fluid ejection die 106 instructions 112 indicating that each pulse lengths applied to drive bubble device 108 are to be same. In yet other examples, controller 104 transmits to fluid ejection die 106 instructions 112 indicating that each pulse length applied to drive bubble device 108 is to be incrementally longer than the pulse length previously applied to drive bubble device 108. In some examples, controller 104 can transmit instructions 112 to fluid ejection die 104 to order the pulse lengths incrementally, beginning with the minimum pulse length up to the maximum pulse length. In other examples, controller 104 can transmit instructions 112 to fluid ejection die 104 to order the applied pulse lengths incrementally, between the minimum pulse length and maximum pulse length. In some examples, controller 104 can transmit instructions 112 to fluid ejection die 104 a cool down period before the next pulse length is applied to drive bubble device 108.

[0039] In some examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to apply a pulse length for the selected drive bubble device 108 while simultaneously servicing the other drive bubble devices 108. In some examples, controller 104 can transmit instructions 112 to fluid ejection die 106 to apply multiple pulse lengths to the selected drive bubble device 108, while servicing the other drive bubble devices 108.

[0040] Based on the detected signal response of the drive bubble device, fluid ejection system 100 can determine a state of operability of the sensor control logic (302). For example, controller 104 can compare the data of signal responses to a signal response curve. Based on the comparison, the controller 104 can determine a state of operability of DBD 102 (e.g. whether DBD 102 is working properly). Furthermore, in some examples, controller 104 can determine the state of operability of drive bubble device 108 (e.g. whether drive bubble device 108 is working properly) based on the

determined state of operability of DBD 102.

[0041] In some examples, fluid ejection system 100 can provide an assessment report of the state of operability of the DBD circuit. For example based on the determined state of operability of DBD circuit 102, controller 104 can provide an assessment report of the state of operability of DBD circuit 102. In other examples, fluid ejection system 100 can provide an assessment report of the state of operability of the drive bubble device, based on the determination of the state of operability of the DBD circuit. For example, based on the determined state of operability of DBD circuit 102, controller 104 can provide an assessment report of the state of operability of drive bubble device 108.

[0042] FIG. 4 illustrates example DBD voltage response curves. A signal response curve (e.g. a voltage response curve) can represent a state of operability of a drive bubble device. For example, as illustrated in FIG. 4, Voltage response curve 404 represents a fully functioning drive bubble device with ink. Voltage response curve 406 represents a drive bubble device with ink that is 60% blocked (e.g. a drive bubble device with a nozzle that is 60% blocked). Voltage response curve 408 represents a drive bubble device with ink that is 2/3 blocked (e.g. a drive bubble device with an ink intake channel that is 2/3 blocked). Voltage response curve 410 represents a drive bubble device that only has air in the drive bubble device. In some examples, the signal response curve can be based on the time the signal response curve was detected and the magnitude of the signal response. For example, as illustrated in FIG. 4, the voltage response curves are based on the time the response voltages were detected 402 and measured voltage(s) 400 of the detect voltage response.

[0043] In some examples, controller 104 can compare the data of signal response(s) to a signal response curve representing a fully functioning drive bubble device (e.g. voltage response curve 404). For example, controller 104 determines that the voltage response at a pulse length is similar to the measured voltage of voltage curve 404 at the same delay time as the time of the pulse length. Based on the comparison, controller 104 can determine that DBD 102 is working properly. Furthermore, in some examples, based on the determination that DBD 102 is working properly, controller 104 can further determine that drive bubble device 108 is also working properly.

[0044] In another example, controller 104 determines that the voltage response at a pulse length is different than the measured voltage of voltage curve 404 at the same delay time as the time of the pulse length. Based on the comparison, then controller 104 can determine that drive bubble device 108 is not properly working. Furthermore, in some examples, based on the determination that DBD 102 is not working properly, controller 104 can further determine that drive bubble device 108 may also be not working properly.

[0045] In other examples, controller 104 can compare the data of signal responses to signal response curve representing a drive bubble device not working properly (e.g. voltage response curve 406 or 408). For example controller 104 determines that the voltage response at a pulse length is similar to the measured voltage of voltage response curves 406 or 408 at the same delay time as the time of the pulse length . Based on the comparison, controller 104 can determine that DBD 102 is not working properly.

Furthermore, based on the determination that DBD 102 is not working properly, depending on which voltage response curve (e.g. voltage response curve 406 or 408) the detected voltage response is similar to, controller 104 can determine the state of operability of drive bubble device 108. For example, if the detected voltage response is similar to voltage response curve 406, then drive bubble device 108 is likely to be operating with a nozzle that is 60% blocked. In another example, if the detected voltage response is similar to voltage response curve 408, then drive bubble device 108 is likely to be operating with a nozzle that is 2/3 blocked.

[0046] In some examples, controller 104 can store the signal response curve representing a fully functioning drive bubble device. In other examples, controller 104 can store the signal response curve(s) of a drive bubble device not working properly. In yet other examples, controller 104 can store the signal response curves representing both a fully functioning drive bubble device and a drive bubble device that is not working properly.

[0047] Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific examples discussed herein . Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.