BACKGROUND

[0001] Printing devices, such as standalone printers, are devices that output colorant onto print media like paper to form images on the print media. One type of printing device is an inkjet-printing device, which is more generally a fluid-ejection device. An inkjet-printing device can print ink of different colors corresponding to the colors of a color space to form full color images on print media. Another type of printing device is a three-dimensional (3D) printing device, which creates physical objects over three dimensions by printing multiple thin layers of print material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a diagram of a portion of an example fluid-ejection device.

[0003] FIG. 2 is a table of different operational states of an example fluid-ejection device.

[0004] FIG. 3 is a flowchart of an example method for cross-calibrating an extraction pump of a fluid-ejection device and a fluid level gauge sensor for a reservoir of the device.

[0005] FIG. 4 is a flowchart of an example method for using a fluid- ejection device after an extraction pump of the device and a fluid level gauge sensor for the reservoir have been cross-calibrated.

[0006] FIG. 5 is a block diagram of an example fluid-ejection device. DETAILED DESCRIPTION

[0007] As noted in the background section, one type of printing device is an inkjet-printing device, which is more generally a fluid-ejection device. Inkjet-printing devices can include those used in smaller residential, office, and even enterprise environments, in which ink supplies may be integrated within printheads and self-contained within the devices themselves. In large- scale commercial and some enterprise environments, however, due to the continuous nature of the printing that occurs within these environments or for cost considerations, the ink supplies may be located external to the printing devices, permitting the usage of larger supplies of ink. In a sort of hybrid of these two types of printing devices, a printing device may include an internal reservoir that is periodically refilled from an external ink supply.

[0008] The printing device may include a sensor to detect when the reservoir has become empty or is running low on ink, due to consumption during printing for example, and alert the user that the reservoir should be refilled soon by fluidically connecting an ink supply to the printing device.

Such a sensor can be particularly useful where the reservoir is disposed within the printing device in such a way that it is hidden from view, preventing the user from easily visually inspecting the reservoir without opening the device. The sensor can also be used to monitor the reservoir as the reservoir is emptied in preparation for printing device storage or transport.

[0009] The internal reservoir of such a printing device can be fluidically connected within the device to a print mechanism, including an inkjet printhead, or multiple printheads, which can output the fluid onto a print medium like paper to form an image on the medium. The internal reservoir may be fluidically coupled to the print mechanism via an interconnecting extraction pump. During printing, then, the extraction pump is run to provide fluid to the print mechanism from the reservoir. The extraction pump is also run to empty (i.e. , drain) the reservoir.

[0010] As a mechanical part, the extraction pump can degrade in performance over time, and indeed can suffer from failure. During printing, this means that the print mechanism may be starved for ink, even though the reservoir contains a ready supply. If the pump has failed, the mechanism may fail to output ink. Perhaps more ominously, if the pump has degraded in performance, the print mechanism may not receive a sufficient amount of ink, resulting in image quality issues that a user may incorrectly ascribe to printhead failure. Furthermore, in some situations, starving the print mechanism of ink can permanently damage the mechanism, resulting in costly service.

[0011] During emptying of the reservoir, a failed extraction pump will result in the reservoir in fact not being emptied. If the reservoir is hidden from view, a user who may have initiated reservoir emptying in preparation for storage or shipment of the printing device may assume that the device is ready for such storage or shipment, when fluid indeed still remains within the reservoir. This scenario can at a minimum potentially cause a mess, because the printing device may be positioned during storage or shipment in such a way that the remaining ink within the reservoir leaks out. If the printing device is stored with ink in its reservoir for long periods of time, the ink may dry, resulting in potentially costly reservoir service or even replacement. [0012] Ink may also be desired to be extracted from the reservoir for other reasons. For example, a printing device may reach the end of its operable life, be replaced by a new printing device, or have to be removed from service in accordance with a print service contract. In such instances, the ink can be recovered from the reservoir for use in a different printing device.

[0013] An extraction pump that has degraded in performance over time can similarly be problematic during reservoir emptying. The pump may be run a set length of time to empty the reservoir, based on assumed specifications of the pump. However, if the extraction pump is currently operating less efficiently, then this set length of time will not be long enough to empty the reservoir, resulting in some ink remaining in the reservoir.

[0014] The presence of the sensor within the reservoir mitigates the potential for issues, such as the foregoing, from occurring, but the sensor itself may fail. The co-filed patent application entitled“Supply Pump and Fluid Level Gauge Sensor Cross-Calibration,” describes a way to cross-calibrate a supply pump that fluidically interconnects the reservoir to a fluid supply to fill the reservoir. Such cross-calibration can then be used to detect failure of the sensor within the reservoir.

[0015] By comparison, techniques described herein cross-calibrate the extraction pump and the sensor. Such cross-calibration permits detection of wear and malfunction of the extraction pump. For example, after cross- calibration, the efficiency or performance of the extraction pump can be monitored over the pump’s lifetime. When the pump has degraded due to wear, it may be run for a longer period of time to empty the reservoir, or may be run more quickly during printing as well as during reservoir emptying. The sensor can be used to detect when the pump has failed as well.

[0016] FIG. 1 shows a portion of an example fluid-ejection device 100. The fluid-ejection device 100 can be an inkjet-printing device, in which case the fluid that the device 100 ejects can include ink. The fluid-ejection device 100 can include a reservoir 102, a fluid level gauge sensor 104 for the reservoir 102, and a supply pump 106. The reservoir 102 and the supply pump 106 are fluidically interconnected via a fluid channel 108, which can include tubing, and by which the supply pump 106 inlets the fluid 1 16 into the reservoir 102.

[0017] Another fluid channel 114 is fluidically connected to the reservoir

102, from which the fluid 1 16 is outlet towards a fluid-ejection engine 1 18 of the device 100. The fluid channel 114 can also include tubing. The fluid- ejection engine 1 18 is or includes the components of the fluid-ejection device 100 that actually eject fluid from the device 100. For instance, in the case of an inkjet-printing device, the fluid-ejection engine 1 18 can be or include an inkjet printhead, or multiple printheads, which can output the fluid onto a print medium like paper to form an image on the medium. Such printheads can be considered a print mechanism by which images are printed on print media.

[0018] A fluid supply 1 10 can be external and removably connectable to the fluid-ejection device 100. The fluid supply 1 10 can be a starter fluid supply that is provided with the fluid-ejection device 100, and which can be of a known volume to permit cross-calibration of the supply pump 106 and the fluid level gauge sensor 104, such as according to the co-filed patent application referenced above. The fluid supply 1 10 can be a non-starter fluid supply, which may not be of known volume in a sufficiently precise manner to permit cross-calibration, and/or which may be of greater volume than a starter fluid supply.

[0019] The supply pump 106 is fluidically interconnected with the fluid supply 1 10 via a fluid channel 1 12. The fluid channel 1 12 can, like fluid channels 108 and 1 14, include tubing. The supply pump 106 thus fluidically interconnects the reservoir 102 and the external fluid supply 1 10, via the fluid channels 108 and 1 12. It is noted that there can be a supply pump 106 and a reservoir 102, with associated fluid channels 108, 1 12, and 1 14 and an associated fluid supply 1 10, for each different type of fluid that the fluid- ejection device 100 uses. For instance, if the fluid-ejection device 100 is an inkjet-printing device, then there may be a supply pump 106, a reservoir 102, and so on, for each different color of ink that the device 100 can output.

[0020] The fluid-ejection device 100 can also include an extraction pump 120, a valve 122, and a pressure control device 124. The reservoir 102 and the extraction pump 120 are fluidically interconnected via the fluid channel 1 14, by which the pump 120 extracts the fluid 1 16 from the reservoir 102. Another fluid channel 126 fluidically connects the extraction pump 120 to both the fluid-ejection engine 1 18 and the valve 122. At the other side of the valve 122, a fluid channel 128 fluidically interconnects the valve 122 to the tubing 1 12, and thus to the supply pump 106 and the external fluid supply 1 10. The fluid channels 126 and 128 can also each include tubing. The valve 122 controls whether fluid is permitted to flow from the tubing 126 to the tubing 128 when the extraction pump 120 is running. [0021] The pressure control device 124 fluidically connects to the reservoir 102 via a fluid channel 130, and to the fluid-ejection engine 1 18 via a fluid channel 132. Like the other fluid channels, the channels 130 and 132 can each include tubing. The pressure control device 124 can also be referred to as a fluid flow restriction device, and is connected between the reservoir 102 and the fluid-ejection engine 1 18 in parallel with the extraction pump 120. When the extraction pump 120 is running to supply the fluid 116 from the reservoir 102 to the fluid-ejection engine 118 during printing, the pressure control device 124 maintains the fluidic pressure at the engine 1 18 at a relatively constant level. As such, the pressure control device 124 permits the pump 120 to constantly run during printing, regardless of the amount of fluid that the engine 1 18 is outputting (i.e. , consuming) at any given time. Therefore, the pump 120 does not have to be controlled to explicitly meter the amount of fluid delivered to the engine 1 18 in correspondence with instantaneous fluid usage by the engine 1 18.

[0022] FIG. 2 shows a table 200 of how the supply pump 106, the extraction pump 120, and the valve 122 are controlled in various example operational states of the printing device 100. The idle state of the printing device 100 can include when the device 100 is ready to print but is not currently being used, as well as during shipment or storage of the device 100. In this state, the pumps 106 and 120 are both off and not running, and the valve 122 is closed.

[0023] The reservoir fill state of the printing device 100 includes when the reservoir 102 is first filled with a starter external fluid supply 1 10 of known volume for cross-calibration of the supply pump 106 and the fluid level gauge sensor 104, such as in accordance with the patent application referenced above. The reservoir fill state also includes when the reservoir 102 is being filled by the supply pump 106 while the printing device is not actively printing using the fluid-ejection engine 1 18. In the reservoir fill state, the supply 106 is turned on to transfer fluid from the fluid supply 1 10 to the reservoir 102, while the extraction pump 120 remains off and is not running and the valve 122 stays closed.

[0024] The printing or engine recirculation state of the printing device 100 includes when the fluid-ejection engine 1 18 of the device 100 is ejecting fluid from the device 100, such as to form an image on print media, when there is sufficient fluid 116 within the reservoir 102. This state does not include when the fluid-ejection engine 1 18 has consumed enough of the fluid 1 16 during printing to necessitate refilling of the reservoir 102 from the fluid supply 1 10, which is a different state of the printing device 100. The printing or engine recirculation state also does include, however, when fluid is being recirculated between the reservoir 102 and the fluid-ejection engine 118, even when the engine 1 18 is not currently being used. Such recirculation may be periodically performed, for instance, to prevent the printheads of the engine 1 18 from drying out and/or for air management within the ink system, such as in preparation for printing or during extended periods of disuse of the printing device.

[0025] In the printing or engine recirculation state, the supply pump 106 remains turned off and the valve 122 remains closed, while the extraction pump 120 is turned on. Running of the pump 120 provides fluid to the fluid- ejection engine 1 18 via the fluid channels 1 14 and 126, whereas the fluid channels 130 and 132 provide a return path for the fluid that the engine 1 18 does not use. As noted above, the pressure control device 124 fluidically connecting the fluid channels 130 and 132 maintains a relatively constant pressure at the fluid-ejection engine 1 18, regardless of the instantaneous fluid usage by the engine 1 18. Therefore, during printing the extraction pump 120 can remain on continuously, without having to meter fluid to the fluid-ejection engine 1 18 in correspondence with fluid consumption by the engine 1 18. The presence of the return path of the fluid channels 130 and 132 also permits fluid to recirculate between the reservoir 102 and the fluid-ejection engine 1 18 when the engine 1 18 is not printing.

[0026] In the reservoir fill during printing state, the supply pump 106 is also turned on while the extraction pump 120 is on and the valve 122 remains closed. Refilling of the reservoir 102 during printing occurs, for instance, when consumption of fluid 1 16 by the fluid-ejection engine 1 18 has sufficiently emptied the reservoir 102 to necessitate refilling, permitting continued printing while refilling occurs. In this state, the supply pump 106 can be independently turned on (and then off) to selectively refill the reservoir 102 from the fluid supply 1 10 as needed, while the extraction pump 120 remains on to maintain continued printing by the engine 1 18.

[0027] In the reservoir recirculation state, both the supply pump 106 and the extraction pump 120 are turned on, and the valve 122 is opened. As such, the extraction pump 120 transfer fluid from the reservoir 102 via the fluid channels 1 14 and 126 towards the valve 122. Because the valve is open, the supply pump 106 then transfers this fluid back to the reservoir 102 through the fluid channels 128 and 108. The fluid channels 1 14, 126, 128, and 108, in other words, form a recirculation path. The printing device 100 may periodically enter the reservoir recirculation state to ensure during prolonged periods of disuse of the device 100, the constituent mixture components of ink or other fluid 1 16 do not undesirably separate from one another, for instance.

[0028] In the reservoir emptying state, the supply pump 106 remains turned off while the extraction pump 120 is turned on and the valve 122 opened. The extraction pump 120 empties the fluid 1 16 from the reservoir 102 back to the fluid supply 1 10, through the fluid channels 1 14, 126, 128, and 1 12. The reservoir 102 may be emptied, for example, to prepare the printing device 100 for long-term storage or transport.

[0029] The fluid level gauge sensor 104 may monitor the level, or volume, of fluid 1 16 within the reservoir 102 while the printing device 100 is operating in a given operational state. In the context of the printing or engine recirculation, reservoir fill during printing, reservoir recirculation and reservoir emptying operational states of the printing device 100 - i.e., when the extraction pump 120 is running - monitoring of this fluid level can permit the detection of wear or malfunction of the extraction pump 120. Such wear and malfunction can be detected using the monitored fluid level within the reservoir 102 once the extraction pump 120 has been cross-correlated against the fluid level gauge sensor 104.

[0030] FIG. 3 shows an example method 300 for cross-calibrating the extraction pump 120 of the fluid-ejection device 100 and the fluid-level gauge sensor 104 of the reservoir 102 of the device 100. The method 300 can be implemented as instructions or other program code stored on a non-transitory computer-readable data storage medium and executed by the fluid-ejection device 100. For example, a processor or other hardware logic of the device 100 can perform the method 300. The cross-calibration of extraction pump 120 and the fluid-level gauge sensor 104 may be performed according to the method 300 after the cross-calibration of the supply pump 106 has been performed according to the patent application referenced above.

[0031] The method 300 can begin when the reservoir 102 has been filled with fluid 1 16 of a known volume (302). For instance, the reservoir 102 may have been filled with the fluid 1 16 of a known volume pursuant to preceding cross-calibration of the supply pump 106 and the fluid-level gauge sensor 104. More generally, when the reservoir 102 is in an empty state, the supply pump 106 may pump a starter fluid supply 1 10, or another fluid supply 1 10 of known volume, into the reservoir 102. That the reservoir 102 is an empty state means that the reservoir 102 is in a dry or a near-dry state.

When the fluid-ejection device 100 is first deployed, for instance, the reservoir 102 may be in a dry state. If the fluid-ejection device 100 is subsequently recalibrated, the reservoir 102 may be in a near-dry state, since there may be some fluid 1 16 remaining at the bottom of the reservoir 102 that cannot be pumped or drained from the reservoir 102.

[0032] Pumping of the fluid 1 16 from the reservoir 102 back to the external fluid supply 1 10 via the extraction pump 120 is then initiated (304). That is, the extraction pump 120 starts pumping the fluid 1 16 from the fluid channel 1 14, through the fluid channels 126 and 128, and to the fluid channel 1 12. The valve 122 is opened to permit fluid transfer from the fluid channel 126 to the fluid channel 128, while the supply pump 106 remains off to prevent fluid transfer back into the reservoir 102. To move fluid from the reservoir 102, a component of the extraction pump 120, such as an electric motor, rotates. The pump 120 can thus be considered a rotary, or centrifugal, pump. Within the extraction pump 120, there may be vanes or an impeller that rotates along an axis, as caused by the motor, or there can be a long screw, or auger, that rotates.

[0033] As the fluid 1 16 is pumped from the reservoir 102 to the external fluid supply 1 10 through the fluid channels 1 14, 126, 128, and 1 12, the number of pump revolutions is counted (306). The pump revolutions can be counted by using a pump revolution sensor, which may be integrated within the extraction pump 120 itself. For example, the pump revolution sensor may be an optical or magnetic encoder.

[0034] In one implementation, there are what are referred to as specified numbers of revolution. For instance, the specified numbers of revolutions can be multiples of a base revolution count, such as 500 or 1 ,000 revolutions. In this respect, the specified number of revolutions can be based on time: if the extraction pump 120 rotates at 1 ,000 rotations per minute (rpm), then the specified number of revolutions can be every thirty seconds or every minute, which corresponds to every 500 or 1 ,000 revolutions, respectively.

[0035] In such an implementation, each time a specified number of revolutions of the extraction pump 120 has been reached (308), the fluid level gauge sensor 104 has its value sampled (310). If the specified number of revolutions is 1 ,000, for example, then this means at 1 ,000 revolutions, at 2,000 revolutions, and so on, the fluid level gauge sensor 104 has its value sampled. The specified number of revolutions can further include zero; that is, the fluid level gauge sensor 104 can have its value sampled at the time of, or prior to, starting the extraction pump 120.

[0036] The value of the fluid level gauge sensor 104 can be a raw electrical value, such as voltage or current, that corresponds linearly or non- linearly with the level - and thus volume - of the fluid 1 16 within the reservoir 102. The fluid level gauge sensor 104 may be a float sensor, or a hydrostatic measurement device like a differential pressure level sensor. The fluid level gauge sensor 104 may be a load cell or strain gauge device. Other types of fluid level gauge sensors include magnetic level gauges, capacitance transmitters, and magnetorestrictive, ultrasonic, laser, and radar level transmitters.

[0037] The extraction pump 120 continues until the fluid 1 16 has been pumped from the reservoir 102 (312) - i.e. , the pump 120 is no longer pumping any fluid from the reservoir 102 while running, and the reservoir 102 is empty. The reservoir 102 at this time can therefore be in a near dry state. The reservoir 102 can be detected as being empty at the reservoir 102 itself, at one of the channels 1 14, 126, 128, and 1 12, or at the extraction pump 120. At the reservoir 102, the fluid level gauge sensor 104 may be employed to detect when the reservoir 102 is empty, reaching a value corresponding to the reservoir 102 being empty as recorded during prior cross-calibration of the sensor 104 and the supply pump 106. At the channel 1 14, 126, 128, or 1 12, a flow sensor may be employed to detect when there is no fluidic flow, even though the pump 120 is running. At the extraction pump 120, a dry running sensor may be employed to detect that the pump 120 is not actively moving fluid from the reservoir 102 to the fluid supply 1 10. [0038] When the reservoir 102 becomes empty, the number of revolutions that the extraction pump 120 rotated to empty the reservoir 102 is recorded (314). The value of the fluid level gauge sensor is also sampled (316), and corresponds to both the number of pump revolutions recorded in part 314 and thus the volume of the fluid 1 16 as the known volume initially within the reservoir 102. The displacement of the supply pump 106 can be computed as the known volume of the starter fluid supply 1 10 divided by the number of revolutions to empty this volume of fluid from the reservoir 102, as recorded in part 314 (318). This pump displacement is the volume of fluid that the extraction pump 120 can move from the channel 1 14 to the channel 126 in one revolution.

[0039] The extraction pump 120 and the fluid level gauge sensor 104 can thus be cross-calibrated (320). Cross-calibration of the extraction pump 120 and the fluid level gauge sensor 104 in this respect can include

correlating the number or revolutions that it takes for the extraction pump 120 to empty the known volume of the fluid 1 16 from the reservoir 102 with the resulting value of the sensor 104 when the reservoir 102 becomes empty. If the fluid level gauge sensor 104 is linear, then dividing by the latter by the former is indicative of the decrease in value of the sensor 104 each time the extraction pump 120 completes one rotation when emptying the reservoir 102.

[0040] The fluid level gauge sensor 104 may not have to be linear, however, which means that as the level of the fluid 1 16 in the reservoir 102 linearly decreases, the sampled value of the sensor 104 does not linearly decrease. In this case, in the implementation in which the value of the fluid level gauge sensor 104 is sampled at different specified numbers of revolutions as the extraction pump 120 empties the reservoir 102, a non-linear profile of the sensor value by number of pump rotations can be constructed. For instance, a non-linear function can be fitted to the values sampled in part 310 at the specified numbers of pump revolutions and to the value sampled in part 316 corresponding to the number of pump revolutions recorded in part 314. As another example, a lookup table (LUT) can be maintained that has entries which each include a number of pump revolutions and the sampled value of the fluid level gauge sensor 104 at that number of pump revolutions.

[0041] It is noted that the method 300 that has been described can be repeated as needed. For example, the method 300 may be performed when the fluid-ejection device 100 is first setup, or after the printer has been removed from storage. The method 300 may then be performed periodically for recalibration purposes.

[0042] FIG. 4 shows an example method 400 for using the fluid-ejection device 100 after the extraction pump 120 and the fluid level gauge sensor 104 have been cross-calibrated. The method 400 can, like the method 300, be implemented as instructions or other program code stored on a non-transitory computer-readable data storage medium and executed by the fluid-ejection device 100. For instance, a processor other hardware logic of the device 100 can perform the method 400. Like the method 300, the method 400 can be repeated as needed.

[0043] The method 400 begins when the fluid-ejection device 100 has entered the printing state or the reservoir emptying state (402). The latter state, for instance, may be initiated from the idle state to empty the reservoir of fluid (404), by starting and running the extraction pump 120 to transfer fluid 1 16 from the reservoir 102 to the fluid supply 1 10. The former state may be initiated by initiating output of fluid by the print mechanism (406) - i.e. , by the fluid-ejection engine 118 - and includes starting and running the extraction pump 120 to supply fluid to the print mechanism. As noted above, the extraction pump 120 may run continuously during fluid ejection.

[0044] While the fluid-ejection device 100 remains in the printing state or the reservoir emptying state, the volume of fluid 1 16 exiting the reservoir 102 is monitored (408). Monitoring of the fluid 1 16 in part 408 can include monitoring the number of revolutions of the extraction pump 120 is monitored (410), as well as the value of the fluid level gauge sensor 104 (412). The number of revolutions of the extraction pump 120 is indicative of the amount of fluid 1 16 that the pump 106 is pumping from the reservoir 102, and is particularly relevant when the fluid 1 16 does not reenter the reservoir 102 - i.e., when the fluid-ejection device 100 is in the reservoir emptying state as opposed to the printing state. The value of the fluid level gauge sensor 104 is indicative of the level (and thus the volume) of the fluid 1 16 within the reservoir 102.

[0045] When the fluid-ejection device 100 is in the printing state, monitoring of the fluid 1 16 exiting the reservoir 102 can also include monitoring the amount of fluid output by the print mechanism (414), which the mechanism may itself measure, or which can be computed from the image that the mechanism is printing. The fluid 1 16 exiting (and not reentering) the reservoir 102 can thus separately and independently be monitored more than one way. During reservoir emptying, the pump revolutions of the extraction pump and the fluid level gauge sensor value can be monitored in parts 410 and 412. During printing, the fluid level gauge sensor value and the amount of fluid that the print mechanism outputs can be monitored in parts 412 and 414.

[0046] Wear and/or malfunction of the extraction pump 120 may be detected during printing or reservoir emptying via this monitoring, based on the pump 120 and the fluid level gauge sensor 104 as have been cross- calibrated, for instance. Malfunction of the extraction pump 120 may be detected during reservoir emptying when the monitored value of the fluid level gauge sensor 104 does not decrease (416), or otherwise decreases less than expected. Malfunction of the extraction pump 120 may be similarly detected during printing when the monitored value of the fluid level gauge sensor 104 does not decrease (416), or otherwise decreases less than expected, both of which may be verified if the print mechanism reports being starved of fluid. In either case, extraction pump malfunction may be further corroborated or indicated if no revolutions of the extraction pump 120 are measured.

[0047] In response to detecting extraction pump malfunction in part 416, an error can be reported to alert the user to this malfunction (418). Because such malfunction is indicative of the extraction pump 120 having failed and being inoperative, the fluid-ejection device 100 may be transitioned to an idle state (420) before the method 400 terminates (422), to abort the reservoir emptying or printing that has been initiated. Transitioning the fluid-ejection device 100 to an idle state ensures that the device 100 is not damaged, which may occur in the printing state if the print mechanism continues to attempt fluid ejection even though the mechanism is starved of fluid. Transitioning the fluid-ejection device 100 to an idle state after initiating reservoir emptying can be useful, since reservoir emptying is not in all likelihood in fact occurring.

[0048] Extraction pump wear may be detected during reservoir emptying when the monitored value of the fluid level gauge sensor 104 does not decrease as quickly as expected for the number of revolutions of the extraction pump 120 (424). Extraction pump wear may be detected during printing when the monitored value of the fluid level gauge sensor 104 does not decrease in correspondence with the expected amount of fluid output by the print mechanism (424). In either case, the extraction pump 120 may have begun starting to wear, such that it runs less efficiently. That is, for a given number of pump revolutions, the extraction pump 120 is now pumping less fluid than previously.

[0049] In response to detecting extraction pump wear, an error can be reported to alert the user to such wear (426). The error may be in the form a warning that may just be logged, as opposed to an alert necessitating immediate user attention. Because the extraction pump wear is unlikely to be catastrophic, the fluid-ejection device 100 does not have to exit its current state. Rather, a remedial action can be performed to compensate for the detected extraction pump wear (428).

[0050] For example, the extraction pump 120 may be run at a faster rate, so that the pump 120 is capable of providing sufficient fluid to the print mechanism during printing, recirculation, or emptying the reservoir 102 within a specified length of time. The extraction pump 120 may during reservoir emptying run for a longer time so that emptying of the reservoir 102 is completed. The extraction pump 120 and the fluid level gauge sensor 104 may be recalibrated against one another to account for the detected wear of the pump 120. Such recalibration, however, may not be performed until after the fluid-ejection device 100 exits its current state. After any remedial action has been performed, the method 400 may thus continue with the fluid-ejection device 100 in its current state, such that the method 400 proceeds back to part 408.

[0051] If no extraction pump malfunction is detected and no extraction pump wear is detected, the method 400 is repeated at part 408 while the fluid- ejection device 100 remains in its current state (430). For instance, the monitoring of part 408 and the detection of parts 416 and 424 is repeated until the reservoir 102 has been emptied or until the print mechanism has finished printing, at which time the method 400 is finished (422). The monitoring of part 408 and the detection of parts 416 and 424 may also cease even though printing has not finished, if the fluid-ejection device 100 transitions from the printing state to the reservoir fill during printing state. The method 400 in this case may restart once the reservoir has been sufficiently refilled - i.e. , when the fluid-ejection device 100 has transitioned back to the printing state from the reservoir fill during printing state.

[0052] FIG. 5 shows an example printing device 500. The printing device 500 is an implementation of the fluid-ejection device 100 that has been described, and may be an inkjet-printing device, or another type of printing device that ejects fluid like ink. The printing device 500 may be a standalone printer, for instance, or an all-in-one (AIO) or a multifunction device (MFD) that includes printing functionality in addition to other functionality, such as copying, scanning, faxing, and so on. The printing device 500 may be a three- dimensional (3D) printing device, which creates a physical object over three dimensions by printing multiple thin layers of print material, which is encompassed under the rubric ink herein.

[0053] The printing device 500 includes a print engine 518, which is an implementation of the fluid-ejection engine 1 18 that has been described. The print engine 518 outputs fluid, such as ink, onto print media like paper. The print engine 518 can thus form images on the print media using the fluid. The printing device 500 includes a reservoir 502, a supply pump 506, and a fluid level gauge sensor 504, which respectively correspond to the reservoir 102, the supply pump 106, and the fluid level gauge sensor 104 that have been described. Similarly, the printing device 500 can include an extraction pump 520, a recirculation valve 522, and a pressure control device 524, which respectively correspond to the extraction pump 520, the recirculation valve 522, and the pressure control device 524 that have been described.

[0054] The printing device 500 includes a pump revolution sensor 526, such as an encoder or another type of sensor, which can indicate when the extraction pump 520 has completed a revolution. The printing device 500 includes hardware logic 528. The hardware logic 528 includes a non- transitory computer-readable data storage medium that stores program code. For instance, the hardware logic 528 can include a general purpose processor that executes the program code, or can include special purpose hardware, like an application-specific integrated circuit (ASIC), which effectuates the program code. The hardware logic 528 can perform the methods 300 and 400 of FIGs. 3 and 4 that have been described. As such, the hardware logic 528 can cross-calibrate the extraction pump 520 and the fluid level gauge sensor 504, and subsequently monitor fluid exiting the reservoir 502.

[0055] The techniques that have been described cross-calibrate an extraction pump of a fluid-ejection device against a fluid level gauge sensor of the device. Because the extraction pump and the fluid level gauge sensor have been cross-calibrated, malfunction and wear of the extraction pump can thus be detected or otherwise predicted. Therefore, printing by the fluid- ejection device can be prematurely terminated to stop potential damage to the device, and further the extraction pump may be run more quickly as it loses efficiency over time.