Patent Description:
<CIT> describes a liquid discharge head comprising a first and a second substrate which are to be mutually adjoined to form plural liquid paths respectively communicating with plural discharge apertures.

Printheads may be serviced by a service station assembly within an inkjet printing system to maintain nozzle health and extend the life of the printheads. Some inks used in inkjet printing systems may be difficult to jet and may suffer from puddling, crusting, and/or decap. Accordingly, one type of printhead servicing includes periodically wiping the printheads to remove the excess ink from the printheads. Optimal nozzle servicing is critical to provide the highest print quality and minimal customer interruptions. Therefore, it would be advantageous to be able to determine the force applied to the printhead due to servicing. Pressures that are too high may damage the printhead while pressures that are too low may ineffectively service the printhead.

In addition, it would be advantageous to be able to detect and react to a printhead impact to the print medium or other object before further damage occurs. Being able to detect the severity of impacts to determine whether a printhead change is necessary would also be useful. Some printhead to print medium impacts result in contact to the printhead surface that smear print results but do not completely halt the medium. In these cases, if a portion of the medium (e.g., corrugate packaging) is torn and drags across the printhead, the printhead may be damaged if the printhead is not stopped immediately. The print job may also need to be discarded if the printhead is not stopped immediately. Printhead impacts and the defective print jobs resulting therefrom often go undetected until print quality audits are completed, resulting in large waste to the customer. Latent detection of printhead impacts may also result in permanent damage to the printhead.

Currently, no measurement capability exists in production printheads that provides insight as to the strain experienced by the printhead throughout the life of the printhead. The primary indicator that strain levels have exceeded safe limits is a cracked die. This results in downtime for customers, lost print jobs, and a reactive response to something that may have been easily detectable and avoided. Accordingly, it would be advantageous to be able to detect and react to impending printhead failure before the failure actually happens. Further, it would be advantageous to be able to detect when a fluid ejection system is exhibiting significant vibration, which may either indicate damaged components or an otherwise hostile operating environment.

Accordingly, disclosed herein is a fluid ejection system including one or a plurality of strain gauge sensors integrated within a fluid ejection die of a printhead assembly of the fluid ejection system. The strain gauge sensors sense strain during servicing of the fluid ejection die to calibrate a servicing station or stop servicing based on the sensed strain. The strain gauge sensors sense strain during operation of the fluid ejection system to detect impacts or vibration of the fluid ejection die based on the sensed strain. The strain gauge sensors sense strain over time to detect whether the fluid ejection die is close to failure based on the sensed strain. Operation of the fluid ejection system may be stopped or a user of the fluid ejection system may be alerted based on the sensed strain.

<FIG> is a block diagram illustrating one example of a fluid ejection system <NUM>. Fluid ejection system <NUM> includes a fluid ejection die <NUM>, a controller <NUM>, and a service station assembly <NUM>. Fluid ejection die <NUM> includes at least one strain gauge sensor <NUM> to sense strain. Service station assembly <NUM> services fluid ejection die <NUM>. Controller <NUM> receives the sensed strain from the at least one strain gauge sensor <NUM> during servicing of the fluid ejection die <NUM> and adjusts or stops servicing of fluid ejection die <NUM> in response to the sensed strain exceeding a servicing threshold. The servicing threshold may be set to prevent servicing station assembly <NUM> from applying a pressure to fluid ejection die <NUM> that could damage the die.

In one example, fluid ejection die <NUM> includes a plurality of strain gauge sensors, where each of the plurality of strain gauge sensors sense a strain of fluid ejection die <NUM>. In this example, controller <NUM> receives the sensed strain from each of the plurality of strain gauge sensors during servicing of fluid ejection die <NUM>. In another example, controller <NUM> receives a baseline sensed strain from the at least one strain gauge sensor <NUM> in response to installing fluid ejection die <NUM> in fluid ejection system <NUM> and alerts a user of the fluid ejection system in response to the baseline sensed strain exceeding a baseline threshold. The baseline threshold may be set such that a strain exceeding the baseline threshold indicates a defective or damaged fluid ejection die.

In another example, controller <NUM> receives the sensed strain from the at least one strain gauge sensor <NUM> over time, compares the sensed strain to a failure threshold indicating proximate failure of fluid ejection die <NUM>, and alerts a user of fluid ejection system <NUM> in response to the sensed strain exceeding the failure threshold. In this way, the user of fluid ejection system <NUM> may be notified of a fluid ejection die that is close to failure so that the fluid ejection die can be replaced prior to failure.

In another example, controller <NUM> receives the sensed strain from the at least one strain gauge sensor <NUM> during operation (e.g., printing) of the fluid ejection die, determines whether the fluid ejection die <NUM> has impacted an object (e.g., print media) based on the sensed strain, and stops operation of the fluid ejection die in response to an impact. In another example, controller <NUM> receives the sensed strain from the at least one strain gauge sensor <NUM> during operation of the fluid ejection die, determines whether the fluid ejection die is vibrating based on the sensed strain, and adjusts or stops operation of the fluid ejection die in response to vibration exceeding a vibration threshold. The vibration threshold may be set to prevent damage to the fluid ejection die and/or other fluid ejection system components, and/or to prevent a defective print job.

<FIG> is a block diagram illustrating another example a fluid ejection system <NUM>. Fluid ejection system <NUM> includes a fluid ejection assembly, such as printhead assembly <NUM>, and a fluid supply assembly, such as ink supply assembly <NUM>. In the illustrated example, fluid ejection system <NUM> also includes a service station assembly <NUM>, a carriage assembly <NUM>, a print media transport assembly <NUM>, and an electronic controller <NUM>. In other examples, fluid ejection system <NUM> may include a plurality of service station assemblies <NUM>. While the following description provides examples of systems and assemblies for fluid handling with regard to ink, the disclosed systems and assemblies are also applicable to the handling of fluids other than ink.

Printhead assembly <NUM> includes at least one printhead or fluid ejection die <NUM> which ejects drops of ink or fluid through a plurality of orifices or nozzles <NUM>. In one example, the drops are directed toward a medium, such as print media <NUM>, so as to print onto print media <NUM>. In one example, print media <NUM> includes any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, fabric, and the like. In another example, print media <NUM> includes media for three-dimensional (3D) printing, such as a powder bed, or media for bioprinting and/or drug discovery testing, such as a reservoir or container. In one example, nozzles <NUM> are arranged in at least one column or array such that properly sequenced ejection of ink from nozzles <NUM> causes characters, symbols, and/or other graphics or images to be printed upon print media <NUM> as printhead assembly <NUM> and print media <NUM> are moved relative to each other.

Fluid ejection die <NUM> also includes a plurality of strain gauge sensors <NUM>. The strain gauge sensors <NUM> sense strain within fluid ejection die <NUM>. In one example, strain gauge sensors <NUM> sense strain within fluid ejection die <NUM> during servicing of fluid ejection die <NUM> by service station assembly <NUM>. In another example, strain gauge sensors <NUM> sense strain within fluid ejection die <NUM> during operation (e.g., printing) of fluid ejection system <NUM>. In another example, strain gauge sensors <NUM> sense strain within fluid ejection die <NUM> over time during the life of fluid ejection die <NUM>.

Ink supply assembly <NUM> supplies ink to printhead assembly <NUM> and includes a reservoir <NUM> for storing ink. As such, in one example, ink flows from reservoir <NUM> to printhead assembly <NUM>. In one example, printhead assembly <NUM> and ink supply assembly <NUM> are housed together in an inkjet or fluid-jet print cartridge or pen. In another example, ink supply assembly <NUM> is separate from printhead assembly <NUM> and supplies ink to printhead assembly <NUM> through an interface connection <NUM>, such as a supply tube and/or valve.

Carriage assembly <NUM> positions printhead assembly <NUM> relative to print media transport assembly <NUM> and print media transport assembly <NUM> positions print media <NUM> relative to printhead assembly <NUM>. Thus, a print zone <NUM> is defined adjacent to nozzles <NUM> in an area between printhead assembly <NUM> and print media <NUM>. In one example, printhead assembly <NUM> is a scanning type printhead assembly such that carriage assembly <NUM> moves printhead assembly <NUM> relative to print media transport assembly <NUM>. In another example, printhead assembly <NUM> is a non-scanning type printhead assembly such that carriage assembly <NUM> fixes printhead assembly <NUM> at a prescribed position relative to print media transport assembly <NUM>.

Service station assembly <NUM> provides for spitting, wiping, capping, and/or priming of printhead assembly <NUM> to maintain the functionality of printhead assembly <NUM> and, more specifically, nozzles <NUM>. For example, service station assembly <NUM> may include a rubber blade, wiper, or roller which is periodically passed over printhead assembly <NUM> to wipe and clean nozzles <NUM> of excess ink. In addition, service station assembly <NUM> may include a cap that covers printhead assembly <NUM> to protect nozzles <NUM> from drying out during periods of non-use. In addition, service station assembly <NUM> may include a spittoon into which printhead assembly <NUM> ejects ink during spits to insure that reservoir <NUM> maintains an appropriate level of pressure and fluidity, and to insure that nozzles <NUM> do not clog or weep. Functions of service station assembly <NUM> may include relative motion between service station assembly <NUM> and printhead assembly <NUM>.

Electronic controller <NUM> communicates with printhead assembly <NUM> through a communication path <NUM>, service station assembly <NUM> through a communication path <NUM>, carriage assembly <NUM> through a communication path <NUM>, and print media transport assembly <NUM> through a communication path <NUM>. In one example, when printhead assembly <NUM> is mounted in carriage assembly <NUM>, electronic controller <NUM> and printhead assembly <NUM> may communicate via carriage assembly <NUM> through a communication path <NUM>. Electronic controller <NUM> may also communicate with ink supply assembly <NUM> such that, in one implementation, a new (or used) ink supply may be detected.

Electronic controller <NUM> receives data <NUM> from a host system, such as a computer, and may include memory for temporarily storing data <NUM>. Data <NUM> may be sent to fluid ejection system <NUM> along an electronic, infrared, optical or other information transfer path. Data <NUM> represent, for example, a document and/or file to be printed. As such, data <NUM> form a print job for fluid ejection system <NUM> and includes at least one print job command and/or command parameter.

In one example, electronic controller <NUM> provides control of printhead assembly <NUM> including timing control for ejection of ink drops from nozzles <NUM>. As such, electronic controller <NUM> defines a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print media <NUM>. Timing control and, therefore, the pattern of ejected ink drops, is determined by the print job commands and/or command parameters. In one example, logic and drive circuitry forming a portion of electronic controller <NUM> is located on printhead assembly <NUM>. In another example, logic and drive circuitry forming a portion of electronic controller <NUM> is located off printhead assembly <NUM>.

Electronic controller <NUM> also receives the sensed strain from each of the plurality of strain gauge sensors <NUM> during servicing of fluid ejection die <NUM> during which a servicing component (e.g., wiper) comes into contact with fluid ejection die <NUM>. In one example, electronic controller <NUM> calibrates the servicing component of service station assembly <NUM> in response to the sensed strain from each of the plurality of strain gauge sensors <NUM>. In another example, electronic controller <NUM> provides data to a user of fluid ejection system <NUM> for manual calibration of service station assembly <NUM> by the user in response to the sensed strain from each of the plurality of strain gauge sensors <NUM>.

By monitoring the output of the strain gauge sensors <NUM> during servicing, electronic controller <NUM> may determine whether components of service station assembly <NUM> are appropriately adjusted. If components of service station assembly <NUM> are found to not be appropriately adjusted, electronic controller <NUM> may take appropriate actions to address the issue. Too little pressure may result in ineffective servicing of fluid ejection die <NUM> while too much pressure may damage fluid ejection die <NUM> and/or force air into nozzles <NUM>, which creates additional problems. In addition, the output of the strain gauge sensors <NUM> may be monitored to determine if the pressure is too low at one end of fluid ejection die <NUM> while too high at the other end of fluid ejection die <NUM>. In this case, a tilt adjustment of components of service station assembly <NUM> may be made to appropriately adjust the pressures on both ends of fluid ejection die <NUM>. Based on the output of strain gauge sensors <NUM>, electronic controller <NUM> may alert a user of fluid ejection system <NUM> that there is a problem, adjust components of service station assembly <NUM>, and/or stop servicing of fluid ejection die <NUM>.

In one example, electronic controller <NUM> may also receive the sensed strain from each of the plurality of strain gauge sensors <NUM> during operation of the fluid ejection die <NUM>. By monitoring the output of the strain gauge sensors <NUM> during operation of fluid ejection die <NUM>, electronic controller <NUM> can determine if fluid ejection die <NUM> comes into contact with the print media or some other object (i.e., a crash) and then take appropriate actions to address the issue. The actions may include alerting the user of fluid ejection system <NUM> that there is a problem or stopping operation of fluid ejection system <NUM>.

In another example, electronic controller <NUM> may also receive the sensed strain from each of the plurality of strain gauge sensors <NUM> to monitor vibrations of fluid ejection die <NUM>. The vibrations may be due to sources external to fluid ejection system <NUM> (e.g., fluid ejection system <NUM> being moved while operating or placed in a mobile environment) or may be due to sources internal to fluid ejection system <NUM> (e.g., worn or defective rollers and/or motors). By monitoring the output of strain gauge sensors <NUM>, electronic controller <NUM> can take appropriate actions in response to detecting vibration. For larger fluid ejection systems <NUM>, these actions may include alerting the user that there is a part approaching its end of life. For smaller (e.g., more mobile) fluid ejection systems <NUM>, these actions may include alerting the user that the vibrations are too strong to allow the fluid ejection system to operate effectively or that the fluid ejection system is in an inappropriate orientation.

In another example, electronic controller <NUM> may also receive the sensed strain from each of the plurality of strain gauge sensors <NUM> to monitor the strain over time to which the fluid ejection die <NUM> is subjected. The measured strain may be related to ambient factors (i.e., the fluid ejection system's external environment) such as temperature cycling that leads to a cracked die failure. The measured strain may also be related to conditions created by the fluid ejection die <NUM> itself, such as rapid temperature change due to firing nozzles that stress the die and headland interfaces (i.e., the interfaces between fluid ejection die <NUM> and printhead assembly <NUM>) hundreds of thousands of times over the life of the fluid ejection die. It is known that over time ink soaks into structural adhesives in the headland causing swelling that increases stress to the die joints. This results in increasing warpage of the printhead assembly headland. By monitoring the output of strain gauges <NUM> over time, and after establishing known safe limits of strain for the die, electronic controller <NUM> can determine if the fluid ejection die <NUM> is trending toward near-term failure, and then take appropriate actions to address the issue. These actions may include alerting the user of fluid ejection system <NUM> that there is a fluid ejection die approaching wear out or stopping operation of fluid ejection system <NUM>.

<FIG> illustrates a front view of one example of a fluid ejection die <NUM>. In one example, fluid ejection die <NUM> provides fluid ejection die <NUM> previously described and illustrated with reference to <FIG> or fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. Fluid ejection die <NUM> includes a plurality of nozzles <NUM> and a plurality of strain gauge sensors <NUM>. In one example, fluid ejection die <NUM> is a silicon die and each of the plurality of strain gauge sensors <NUM> is integrated within the die. Each strain gauge sensor <NUM> senses the strain within fluid ejection die <NUM> at a unique location within fluid ejection die <NUM>.

While fluid ejection die <NUM> includes a rectangular shape in this example, in other examples fluid ejection die <NUM> may have another suitable shape, such as a square shape. Fluid ejection die <NUM> may include any suitable number of nozzles <NUM> and any suitable number of strain gauge sensors <NUM>. While fluid ejection die <NUM> includes nozzles <NUM> arranged in two columns and strain gauge sensors <NUM> arranged in two columns, in other examples nozzles <NUM> and strain gauge sensors <NUM> may have other suitable arrangements, such as one column of nozzles and/or one column of strain gauge sensors or more than two columns of nozzles and/or more than two columns of strain gauge sensors. Also, while fluid ejection die <NUM> includes strain gauge sensors <NUM> aligned with respect to each other, in other examples, strain gauge sensors <NUM> may be staggered with respect to each other. In other examples, fluid ejection die <NUM> may include strain gauge sensors <NUM> between the two columns of nozzles <NUM>.

<FIG> illustrates one example of a strain gauge sensor <NUM>. In one example, strain gauge sensor <NUM> provides each strain gauge sensor <NUM> of fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. Strain gauge sensor <NUM> includes a first electrode <NUM>, a second electrode <NUM>, and a piezoelectric sensor element <NUM> electrically coupled between first electrode <NUM> and second electrode <NUM>. Piezoelectric sensor element <NUM> exhibits a change in resistance in response to stress in one axis. Therefore, by biasing strain gauge sensor <NUM> (e.g., with a constant current) and measuring the voltage across piezoelectric sensor element <NUM>, the strain on piezoelectric sensor element <NUM> may be sensed.

<FIG> illustrates another example of a strain gauge sensor <NUM>. In one example, strain gauge sensor <NUM> provides each strain gauge sensor <NUM> of fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. Strain gauge sensor <NUM> includes a first electrode <NUM>, a second electrode <NUM>, a third electrode <NUM>, a fourth electrode <NUM>, a first piezoelectric sensor element <NUM>, a second piezoelectric sensor element <NUM>, a third piezoelectric sensor element <NUM>, and a fourth piezoelectric sensor element <NUM>. First piezoelectric sensor element <NUM> is electrically coupled between first electrode <NUM> and second electrode <NUM>. Second piezoelectric sensor element <NUM> is electrically coupled between second electrode <NUM> and third electrode <NUM>. Third piezoelectric sensor element <NUM> is electrically coupled between third electrode <NUM> and fourth electrode <NUM>. Fourth piezoelectric sensor element <NUM> is electrically coupled between fourth electrode <NUM> and first electrode <NUM>.

Strain gauge sensor <NUM> exhibits a change in resistance in response to stress in two axes. Strain gauge sensor <NUM> may be configured in a Wheatstone bridge configuration in which an external biasing voltage is applied across two opposing electrodes (e.g., first electrode <NUM> and third electrode <NUM>) while the voltage is measured across the other two opposing electrodes (e.g., second electrode <NUM> and fourth electrode <NUM>). Therefore, by biasing strain gauge sensor <NUM> with an external voltage and measuring the voltage across piezoelectric sensor elements <NUM>-<NUM>, the strain on strain gauge sensor <NUM> may be sensed.

<FIG> is a block diagram illustrating one example of a circuit <NUM> for processing signals from a plurality of strain gauge sensors. Circuit <NUM> includes biasing circuits <NUM><NUM> to <NUM>N, strain gauge sensors <NUM><NUM> to <NUM>N, and analog to digital converters <NUM><NUM> to <NUM>N, where "N" is any suitable number of strain gauge sensors on a fluid ejection die. The signals from each strain gauge sensor are passed to a controller, such as controller <NUM> previously described and illustrated with reference to <FIG> or electronic controller <NUM> previously described and illustrated with reference to <FIG>. Strain gauge sensors <NUM><NUM> to <NUM>N are integrated on a fluid ejection die, such as fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. Biasing circuits <NUM><NUM> to <NUM>N and analog to digital converters <NUM><NUM> to <NUM>N may be integrated in the fluid ejection die, in a printhead assembly, in other components of the fluid ejection system, or in a combination thereof.

Each biasing circuit <NUM><NUM> to <NUM>N is electrically coupled to a strain gauge sensor <NUM><NUM> to <NUM>N through a signal path <NUM><NUM> to <NUM>N, respectively. Each strain gauge sensor <NUM><NUM> to <NUM>N is electrically coupled to an analog to digital converter <NUM><NUM> to <NUM>N through a signal path <NUM><NUM> to <NUM>N, respectively. Each analog to digital converter <NUM><NUM> to <NUM>N is electrically coupled to the controller through a signal path <NUM><NUM> to <NUM>N, respectively.

Each biasing circuit <NUM><NUM> to <NUM>N provides a biasing voltage or current to a corresponding strain gauge sensor <NUM><NUM> to <NUM>N. Each strain gauge sensor <NUM><NUM> to <NUM>N may be provided by a strain gauge sensor <NUM> previously described and illustrated with reference to <FIG> or a strain gauge sensor <NUM> previously described and illustrated with reference to <FIG>. The voltage signal from each strain gauge sensor <NUM><NUM> to <NUM>N is converted to a digital signal by a corresponding analog to digital converter <NUM><NUM> to <NUM>N. The digital signal corresponding to the sensed strain of each strain gauge sensor <NUM><NUM> to <NUM>N is then passed to the controller. In this way, the strain of each strain gauge sensor may be sensed simultaneously.

<FIG> is a block diagram illustrating another example of a circuit <NUM> for processing signals from a plurality of strain gauge sensors. Circuit <NUM> includes a biasing circuit <NUM>, analog multiplexers <NUM><NUM> to <NUM>M, strain gauge sensors <NUM><NUM> to <NUM>M, and an analog to digital converter <NUM>, where "M" is any suitable number of strain gauge sensors on a fluid ejection die. The signals from each strain gauge sensor are passed to a controller, such as controller <NUM> previously described and illustrated with reference to <FIG> or electronic controller <NUM> previously described and illustrated with reference to <FIG>. Strain gauge sensors <NUM><NUM> to <NUM>M are integrated on a fluid ejection die, such as fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. Biasing circuit <NUM>, multiplexers <NUM><NUM> to <NUM>M, and analog to digital converter <NUM> may be integrated in the fluid ejection die, in a printhead assembly, in other components of the fluid ejection system, or in a combination thereof.

Biasing circuit <NUM> is electrically coupled to each analog multiplexer <NUM><NUM> to <NUM>M through a signal path <NUM>. Each analog multiplexer <NUM><NUM> to <NUM>M also receives a select signal through a signal path <NUM>. Each analog multiplexer <NUM><NUM> to <NUM>M is electrically coupled to a strain gauge sensor <NUM><NUM> to <NUM>M through a signal path <NUM><NUM> to <NUM>M, respectively. Each strain gauge sensor <NUM><NUM> to <NUM>M is electrically coupled to an analog multiplexer <NUM><NUM> to <NUM>M through a signal path <NUM><NUM> to <NUM>M, respectively. Each analog multiplexer <NUM><NUM> to <NUM>M is electrically coupled to analog to digital converter <NUM> through a signal path <NUM>. Analog to digital converter <NUM> is electrically coupled to the controller through a signal path <NUM>.

Biasing circuit <NUM> provides a biasing voltage or current to each analog multiplexer <NUM><NUM> to <NUM>M. In response to the select signal on signal path <NUM> corresponding to an analog multiplexer <NUM><NUM> to <NUM>M, the selected analog multiplexer <NUM><NUM> to <NUM>M passes the biasing voltage or current to the corresponding strain gauge sensor <NUM><NUM> to <NUM>M through the corresponding signal path <NUM><NUM> to <NUM>M. Each strain gauge sensor <NUM><NUM> to <NUM>M may be provided by a strain gauge sensor <NUM> previously described and illustrated with reference to <FIG> or a strain gauge sensor <NUM> previously described and illustrated with reference to <FIG>. The voltage signal from the selected strain gauge sensor <NUM><NUM> to <NUM>M is passed to the selected analog multiplexer <NUM><NUM> to <NUM>M through the corresponding signal path <NUM><NUM> to <NUM>M. The selected analog multiplexer <NUM><NUM> to <NUM>M then passes the voltage signal to analog to digital converter <NUM>. Analog to digital converter <NUM> converts the voltage signal to a digital signal. The digital signal corresponding to the sensed strain of the selected strain gauge sensor <NUM><NUM> to <NUM>M is then passed to the controller. In this way, a single biasing circuit and a single analog to digital converter may be used to sense the strain of multiple strain gauge sensors by sensing the strain of one strain gauge sensor at a time.

<FIG> illustrates a side view of one example of a service station assembly <NUM> servicing a fluid ejection die <NUM>. In one example, service station assembly <NUM> provides service station assembly <NUM> and fluid ejection die <NUM> provides fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. In another example, service station assembly <NUM> provides service station assembly <NUM> and fluid ejection die <NUM> provides fluid ejection die <NUM> previously described and illustrated with reference to <FIG>. Fluid ejection die <NUM> includes strain gauge sensors <NUM> indicated by dotted lines, such as strain gauge sensors <NUM> previously described and illustrated with reference to <FIG> or strain gauge sensors <NUM> previously described and illustrated with reference to <FIG>.

Service station assembly <NUM> includes a servicing component <NUM> (e.g., wiper). Servicing component <NUM> may be moved relative to fluid ejection die <NUM> as indicated at <NUM>. Servicing component <NUM> may be moved into contact with fluid ejection die <NUM> for servicing of fluid ejection die <NUM> and moved out of contact with fluid ejection die <NUM> when fluid ejection die <NUM> is not being serviced as indicated at <NUM>. During servicing, servicing component <NUM> may be moved across fluid ejection die <NUM> to remove excess ink from fluid ejection die <NUM>. The servicing component <NUM> indicated by solid lines indicates a first position of servicing component <NUM> while the servicing component <NUM> indicated by dashed lines indicates a second position of servicing component <NUM>.

Strain gauge sensors <NUM> measure the strain exerted upon fluid ejection die <NUM> by servicing component <NUM> when fluid ejection die <NUM> is being serviced by service station assembly <NUM>. The sensed strain from each strain gauge sensor <NUM> may be used to calibrate service station assembly <NUM> including servicing component <NUM> so that service station assembly <NUM> applies optimal pressure on fluid ejection die <NUM> during servicing. The sensed strain from each strain gauge sensor <NUM> may also be compared to a servicing threshold and servicing of fluid ejection die <NUM> may be stopped in response a sensed strain exceeding the servicing threshold.

<FIG> illustrates one example of a strain gauge sensor signal <NUM> corresponding to a fluid ejection die impact event. Prior to an impact event, the strain gauge sensor outputs a baseline strain indicated at <NUM>. The baseline strain indicated at <NUM> may be sensed during a fluid ejection system idle time when the fluid ejection system is neither operating nor being serviced. Upon an impact event in which the fluid ejection die comes into brief contact with an object (e.g., print media), the strain gauge sensor outputs a signal that rises rapidly to a peak value as indicated at <NUM> and then falls rapidly back to the baseline strain <NUM>. The peak value at <NUM> may be used to determine the severity of the impact. The peak value at <NUM> may be compared to an impact threshold to determine whether damage to the fluid ejection die likely occurred or not, whether operation of the fluid ejection system should be stopped, or whether the user of the fluid ejection system should be alerted.

<FIG> illustrates another example of a strain gauge sensor signal <NUM> corresponding to a fluid ejection die impact event. Prior to an impact event, the strain gauge sensor outputs a baseline strain indicated at <NUM>. The baseline strain indicated at <NUM> may be sensed during a fluid ejection system idle time when the fluid ejection system is neither operating nor being serviced. Upon an impact event in which the fluid ejection die comes into contact with an object (e.g., print media), the strain gauge sensor outputs a signal that rapidly rises and falls back to the baseline strain <NUM> multiples times as indicated by peak values <NUM>-<NUM>. While the peak values <NUM>-<NUM> are indicated as being equal, the peak values may vary depending upon the impact. The number of peaks may also vary depending upon the impact. The peak signal values at <NUM>-<NUM> may be used to determine the severity of the impact. The peak values <NUM>-<NUM> may be compared to an impact threshold to determine whether damage to the fluid ejection die likely occurred or not, whether operation of the fluid ejection system should be stopped, or whether the user of the fluid ejection system should be alerted.

<FIG> illustrates one example of a strain gauge sensor signal <NUM> corresponding to a fluid ejection die servicing event. Prior to a servicing event, the strain gauge sensor outputs a baseline strain indicated at <NUM>. The baseline strain indicated at <NUM> may be sensed during a fluid ejection system idle time when the fluid ejection system is neither operating nor being serviced. Upon the start of a servicing event in which the fluid ejection die comes into contact with a component of a service station assembly, the strain gauge sensor outputs a signal that rises rapidly to a peak value as indicated at <NUM>. The peak value at <NUM> is maintained while the component of the service station assembly remains in contact with the fluid ejection die. Once servicing of the fluid ejection die is complete and the component of the service station assembly is moved away from the fluid ejection die, the strain gauge sensor outputs a signal that falls rapidly back to the baseline strain <NUM>. The peak value at <NUM> may be used to calibrate the service station assembly including the servicing component so that an optimal pressure is applied to the fluid ejection die during servicing. The strain gauge signal may also be compared to a servicing threshold to determine whether servicing of the fluid ejection die should be stopped or whether the user of the fluid ejection system should be alerted.

<FIG> illustrates one example of a strain gauge sensor signal <NUM> corresponding to an increase in strain within a fluid ejection die over time. Initially, the fluid ejection die exhibits a baseline strain as indicated at <NUM>. The baseline strain indicated at <NUM> may be sensed when the fluid ejection die is first installed in the fluid ejection system during a fluid ejection system idle time when the fluid ejection system is neither operating nor being serviced. Over time, the strain may gradually rise as indicated at <NUM>. The sensed strain over time may be used to determine whether the fluid ejection die is close to failure. The strain gauge signal may also be compared to a failure threshold to determine whether the use of the fluid ejection die should be stopped or whether the user of the fluid ejection system should be alerted.

<FIG> illustrates one example of a strain gauge sensor signal <NUM> corresponding to vibration of a fluid ejection die. Prior to detecting vibrations, the strain gauge sensor outputs a baseline strain indicated at <NUM>. The baseline strain indicated at <NUM> may be sensed during a fluid ejection system idle time when the fluid ejection system is neither operating nor being serviced. When the fluid ejection die is subjected to vibrations, the strain gauge sensor outputs a signal that rapidly oscillates above and below the baseline strain <NUM> multiples times as indicated at <NUM> until the vibrations dissipate. The peak signal values and the length of time the vibrations persist may be used to determine the severity of the vibrations. The peak values and/or the length of time the vibrations persist may be compared to vibration thresholds to determine whether operation of the fluid ejection system should be stopped or whether the user of the fluid ejection system should be alerted.

<FIG> illustrates one example of a strain gauge sensor signal <NUM> that does not return to a baseline strain after an event. Prior to detecting an event, such as an impact or vibrations, the strain gauge sensor outputs a baseline strain indicated at <NUM>. The baseline strain indicated at <NUM> may be sensed during a fluid ejection system idle time when the fluid ejection system is neither operating nor being serviced. When the fluid ejection die is subjected to an event, the strain gauge sensor may output a signal that rapidly oscillates above the baseline strain <NUM> multiples times as indicated at <NUM> until the signal settles at a strain <NUM> above the baseline strain <NUM>. The peak signal values and the strain at <NUM> may be used to determine the severity of the event. The peak values and/or the strain at <NUM> may be compared to thresholds to determine whether the fluid ejection die has been damaged, whether operation of the fluid ejection system should be stopped, or whether the user of the fluid ejection system should be alerted.

<FIG> is a flow diagram illustrating one example of a method <NUM> for maintaining a fluid ejection system. At <NUM>, method <NUM> includes sensing, during servicing of the fluid ejection system, strain on a fluid ejection die due to a servicing component, the strain sensed via at least one strain gauge sensor integrated within the fluid ejection die. In one example, sensing strain on the fluid ejection die includes sensing strain on the fluid ejection die via a plurality of strain gauge sensors integrated within the fluid ejection die. At <NUM>, method <NUM> includes calibrating the servicing component based on the sensed strain. In one example, method <NUM> also includes stopping servicing of the fluid ejection system in response to the sensed strain exceeding a threshold.

<FIG> is a flow diagram illustrating another example of a method <NUM> for maintaining a fluid ejection system. At <NUM>, method <NUM> includes sensing strain on the fluid ejection die during operation of the fluid ejection system. At <NUM>, method <NUM> includes detecting whether the fluid ejection die has impacted an object based on the sensed strain. At <NUM>, method <NUM> includes detecting whether the fluid ejection die is vibrating based on the sensed strain. At <NUM>, method <NUM> includes stopping the operation of the fluid ejection system or alerting a user of the fluid ejection system in response to detecting an impact or detecting vibration exceeding a threshold.

Claim 1:
A fluid ejection system (<NUM>, <NUM>) comprising:
a service station assembly (<NUM>, <NUM>) including a service component (<NUM>);
a fluid ejection die (<NUM>, <NUM>, <NUM>) comprising at least one strain gauge sensor (<NUM>, <NUM>, <NUM>, <NUM>) being the strain gauge sensor to sense a strain exerted by the service component of the service station assembly upon the fluid ejection die when the fluid ejection die is being serviced by the service station assembly; and
a controller (<NUM>) to receive the sensed strain from the at least one strain gauge sensor during servicing of the fluid ejection die, wherein the controller is to adjust or stop servicing of the fluid ejection die in response to the sensed strain exceeding a servicing threshold.