[0001] Many printing systems utilise printheads to deposit printing liquid by firing the printing liquid from nozzles of the printheads, in such systems a printhead may become damaged if operated without a sufficient supply of printing liquid. For example, the firing of a nozzle may include heating the printing liquid in the nozzle by way of a resistor, if less printing liquid is present in the nozzle than expected, the heating by the resistor may overheat the nozzle and damage the printhead to beyond a point of repair. Solutions for ensuring that printing liquid is continuously supplied to a printhead (or nozzles thereof) during operation may include, providing the printing liquid under pressure to the printhead.

BRIEF INTRODUCTION OF THE DRAWINGS

[0002] Example implementations are described below with reference to the accompanying drawings, in which:

[0003] Fig. 1 is an example flowchart for determining a fault relating to a printing liquid pump for a printhead;

[0004] Fig. 2 is an example flowchart for determining a fault relating to a printing liquid pump for a printhead, which may, in some examples, be based on a comparison of printing liquid consumption information and pump initiation information;

[0005] Fig. 3 is an example flowchart for determining a fault relating to a printing liquid pump for a printhead based on a determination of whether a printing liquid consumption threshold has been reached and a comparison of printing liquid consumption information and pump initiation information;

[0008] Fig. 4 is an example flowchart for determining a fault relating to a printing liquid pump for a printhead based on sensor data;

[0007] Fig. 5 is a schematic diagram of functional blocks of an apparatus for determining a fault relating to a printing liquid pump for a printhead;

[0008] Fig. 6 is a schematic diagram of functional blocks of an apparatus for determining a fault relating to a printing liquid pump for a printhead, the apparatus comprising a printing liquid supply chamber;

[0009] Fig. 7 is a schematic diagram of functional blocks of an apparatus for determining a fault relating to a printing liquid pump for a printhead, the apparatus comprising sensors; [0010] Fig. 8 is a schematic diagram of circuitry and memory of an apparatus for determining a fault relating to a printing liquid pump for a printhead. DETAILED DESCRIPTION

[0011] The present disclosure may be applicable to any type of apparatus that supplies printing liquid to a printhead, or liquid ejection device. The apparatus may be part of or integrable with, for example, a 2D or 3D printing system. For example, the apparatus may be a part of a 2D inkjet printing system, such as a 2D design printing system or a 2D desktop inkjet printing system. Alternatively, the apparatus may be a part of a 3D printing system for additive manufacture. The printing liquid may be any applicable printing liquid. For example, the printing liquid may comprise e.g. ink, conditioning liquids, or a liquid polymer etc.

[0012] Fig. 1 depicts flowchart 100 according to an example method for determining (e.g. identifying) a fault relating to a printing liquid pump for a printhead. The fault may be a fault of the pump itself, such as a fault (e.g. jamming) of at least one moving part of the pump inhibiting or preventing the pump from pressurising printing liquid for use by the printhead. Additionally or alternatively, the fault may be a fault of a sensor associated with the pump, such as a sensor for triggering a pumping action of the pump. Flowchart 100 may be performed by processing circuitry, such as processing circuitry of the apparatus that supplies printing liquid to the printhead or of an apparatus such as a 2D or 3D printing system which deposits printing liquid via a printhead.

[0013] At block 110, printing liquid consumption information relating to a consumption of printing liquid by the printhead is obtained. It is to be understood throughout the description, that obtaining may include receiving (e.g, from a sensor), retrieving (e.g. from a memory), determining, or deriving from other information etc.

[0014] The printing liquid consumption information may be indicative of a quantity of printing liquid consumed by the printhead. For example, the printing liquid consumption information may indicate a quantity of printing liquid consumed by the printhead, or may indicate a quantity of printing liquid available (under pressure) to the printhead. The quantity of printing liquid available under pressure to the printhead may in turn be indicative of a quantity of printing liquid which has been consumed by the printhead, e.g. because, during normal operation, the quantity of printing liquid available under pressure to the printhead may (e.g. cyclically) vary between a predetermined minimum value and a predetermined maximum value, e.g. due to a cyclical operation of the printing liquid pump. The printing liquid consumption information may be based on (e.g. the printing liquid consumption information may comprise) an estimate of a quantity of printing liquid consumed by the printhead. The printing liquid consumption information may comprise data (e.g. a flag) specifying whether the quantity of printing liquid consumed by the printhead has reached a threshold. [0015] At block 120, pump initiation information may be obtained. It may be that the pump initiation information relates to initiation of a pumping action of the pump.

[0016] At block 130, the fault relating to the printing liquid pump is determined based on the printing liquid consumption information and the pump initiation information, in some examples, if may be determined that there is a fault relating to the pump based on the printing liquid consumption information and pump initiation information together indicating that the printing liquid consumption by the printhead has reached a printing liquid consumption threshold without a corresponding initiation of pumping action of the pump. In some examples, the determination at block 130 may be based on a comparison of the printing liquid consumption information and the pump initiation information. For example, it may be that the obtained printing liquid consumption information is compared to the obtained pump initiation information, in these cases, the determination of whether the printing liquid consumption by the printhead has reached a predetermined printing liquid consumption threshold without a corresponding initiation of a pumping action of the pump having occurred may be based on the output of the comparison.

[0017] At block 140 an error signal is generated. In some examples, it may be that the error signal comprises an error message. For example, the error signal may comprise an error message that may be displayed or issued for display to a user of the apparatus. Additionally or alternatively, the error signal may comprise a signal such as an interrupt signal, for example a system interrupt signal, to pause or terminate the operation of the printhead (e.g. to prevent damage to the printhead by its continued operation).

[0018] Fig. 5 is a schematic diagram of functional blocks of an apparatus 500 for performing the method illustrated in Fig. 1 . The apparatus 500 may correspond to any type of apparatus included in a printing system. For example, the apparatus may be part of a 2D (e.g. inkjet) or 3D printing system.

[0019] Processing circuitry 501 may be to obtain the printing liquid consumption information relating to the consumption of printing liquid by the printhead, referred to in Fig. 5 as printhead 504. Processing circuitry 501 may also be to obtain the pump initiation information relating to initiation of the pumping action of the pump, referred to in Fig. 5 as pump 502.

[0020] Processing circuitry 501 may be to determine the fault relating to the pump based on the printing liquid consumption information and the pump initiation information, the printing liquid consumption information and pump initiation information indicating that the printing liquid consumption by the printhead has reached a printing liquid consumption threshold without a corresponding initiation of pumping action of the pump. [0021] Processing circuitry 501 may be to generate the error signal in response to the determination of said fault. As described above with respect to Fig. 1 , the error signal may comprise an (e.g. interrupt) error signal to cause pausing or termination of printing liquid consumption (i.e. pausing or termination of the operation of the printhead) and/or may comprise an error message to be presented to a user/operator of the apparatus or a maintenance/repair engineer to indicate the fault. The processing circuitry 501 may aiso be to cause transmission (for example, by way of a communication unit/ transceiver of the apparatus) of the error signal. The error signal may be to prevent damage to the printhead. It may be that the error message (where provided) may provide information identifying the fault (e.g. to aid a maintenance/repair engineer). For example, the error message may identify the fault as a fault relating to the pump 502.

[0022] The apparatus 500 may further comprise the printhead 504 and may further comprise the pump 502. It may be that the pump 502 is to provide, during fault-free operation of the pump 502, printing liquid under pressure 503 to the printhead 504. For example, the printing liquid may be supplied under pressure via a path 507 to the printhead 504 during operation of the printhead. In some examples, it may be that a (e.g, non-return) valve is disposed at a point along path 507, where the valve is to inhibit or prevent backward flow of printing liquid i.e. flow back along path 507 in a direction away from the printhead 504 towards the pump 502.

[0023] it may be that the processing circuitry 501 is to obtain (e.g, receive) the printing liquid consumption information by way of channel 505, which may be an information transfer channel, such as a communication channel. It may also be that the pump Initiation information is to be obtained (e.g. received) by the processing circuitry 501 by way of channel 506 which may aiso be an information transfer channel, if may be that the information transfer channels 505, 506 may be wired or wireless paths over which the information is communicated or otherwise shared. It may be that the processing circuitry 501 may comprise receiver circuitry to obtain the information.

[0024] As discussed above with respect to Fig. 1 , it may be that the printing liquid consumption information is indicative of a quantity {or volume) of printing liquid consumed by the printhead. It may be that the printing liquid consumption information (e.g. directly or indirectly) indicates a quantity (or volume) of printing liquid that has been consumed by the printhead (e.g. based on a sensed quantity or volume of printing liquid supplied to or dispensed by the printhead - see below).

[0025] As also discussed above with respect to Fig. 1 , it may be that the printing liquid consumption information may indicate (e.g. may directly or indirectly indicate) a quantity (or volume) of printing liquid that is available (e.g. under pressure) to the printhead. With reference to Fig. 5, it may be that the printing liquid provided under pressure 503 to the printhead 504 is provided by way of a printing liquid supply chamber (e.g. see below with respect to Fig. 6 and Fig. 7). in this case, it may be that the printing liquid consumption information indicates (e.g. comprises an estimate of) a quantity of printing liquid remaining in the printing liquid supply chamber.

[0026] As discussed above in respect of Fig. 1 , a quantity (or volume) of printing liquid consumed by the printhead 504 may be indicative of a quantity (or volume) of printing liquid available under pressure to the printhead (and vice versa), for example because, during normal operation, the quantity of printing liquid under pressure 503 available to the printhead 504 may cyclically vary between a predetermined minimum value and a predetermined maximum value, e.g. due to a cyclical operation of the printing liquid pump 502. This is explained in more detail below with reference to Fig. 6.

[0027] it may be that the printing liquid consumption information obtained e.g. by processing circuitry 501 , is based on an estimate of a quantity of printing liquid consumed by e.g. printhead 504, which may be, for example, an estimate of an absolute or fractional quantity of consumed printing liquid, it may be that the estimate of the quantity of consumed printing liquid may be based on an empirical analysis of printing liquid consumption (for example, as a function of printhead operation, time, printing job type etc). Alternatively, it may be that the estimate of the quantify of consumed printing liquid may be based on e.g, a model of printing liquid consumption, historic printing liquid consumption data, or sensor data. The estimate of the quantity (or volume) of printing iiquid consumed by the printhead may be based on a sensed quantity or volume of printing liquid supplied to or dispensed by the printhead.

[0028] in some examples, the estimate of the quantity of printing Iiquid consumed by the printhead may be based on a monitored flow of printing liquid out of the printing iiquid supply chamber by way of which printing iiquid under pressure 503 may be provided to the printhead 504. For example, a monitored flow of printing liquid out of the printing liquid supply chamber may be based on a monitored flow of printing liquid along a path 507 between the printing Iiquid supply chamber and the printhead 504.

[0029] In some examples, the printing liquid consumption information may be based on sensor data.

[0030] For example, Fig. 8 illustrates an example 600 of apparatus 500 further comprising a sensor 809 to provide printing Iiquid consumption information to the processing circuitry 601 . The pump 602, printhead 604, channels 605, 606, path 607 and processing circuity 601 may perform the same or similar functionality to pump 502, printhead 504, channels 505, 506, path 507 and processing circuitry 501 of Fig, 5. During fault-free operation, the pump 602 may be to provide printing liquid under pressure to the printhead 604 by way of a printing liquid supply chamber 603. The printing liquid supply chamber 603 may be to receive printing liquid from a printing liquid reservoir 611 (e.g, under gravity). The pump 602 may be to pressurise printing liquid in the printing liquid supply chamber 603 for supply to the printhead 604 by way of channel 607. The sensor 609 may be to estimate a quantity of printing liquid consumed by the printhead 604, or to provide sensor data by which the quantity of printing liquid consumed by the printhead 604 can be determined by the processing circuitry 601. The printhead 604 may be to deposit printing liquid on print medium 608.

[0031] it may be that the printing liquid supply chamber 603 is of variable volume. For example, it may be that the volume of the printing liquid supply chamber 603 is to be increased to reduce the pressure In the printing liquid supply chamber 603 and thereby receive printing liquid from the reservoir 611 , for example under gravity, it may be that the pump 602 is to, after the printing liquid supply chamber 603 has received printing liquid from the reservoir 611 , decrease the volume of the printing liquid supply chamber 603 to thereby pressurise the received printing liquid for supply to the printhead 604.

[0032] it may be that the pumping action of the pump 602 is to increase, decrease or maintain (e.g. substantially maintain) the internal pressure of the printing liquid supply chamber 603, For example, to provide printing liquid (e.g. continuously) to the printhead 604, the pump 602 may be to increase or maintain a pressure of the printing liquid in the printing liquid chamber 603 as the printing liquid flows out of the printing liquid supply chamber 603 to be consumed by the printhead 604. it may be that during consumption of the printing liquid from the printing liquid supply chamber 603 by the printhead 604, the pump 602 (during fault-free operation) is to maintain the pressure of the printing liquid supplied to the printhead 604 from the printing liquid supply chamber 603 by decreasing (e.g. continuously decreasing) the internal volume of the printing liquid supply chamber 603. Thus, the pumping action of the pump 602 may be to decrease the internal volume of the printing liquid supply chamber 603.

[0033] It may be that to resupply (e.g. refill, for example fully or partially refill) the printing liquid supply chamber 603 with printing liquid (i.e. due to the consumption of the printing liquid by the printhead 804) the pump 602 may be to increase the infernal volume of ihe printing liquid supply chamber 603. For example, the pumping action may be to increase the internal volume of the printing liquid supply chamber 603. It may be that the increase in interna! volume of the printing liquid supply chamber 803 is to initiate receipt of printing liquid 612 in the printing liquid supply chamber 603 from the reservoir 611 connected to the printing liquid supply chamber 803, It may be that the increase in the internal volume of the printing liquid supply chamber 603 removes or reduces an obstruction to a flow of printing liquid to the printing liquid supply chamber 603 from the reservoir 611 . For example, the flow 612 of the printing liquid to the printing liquid supply chamber 603 from the reservoir 611 may be obstructed or opposed by the internal pressure of the printing liquid supply chamber 603 before the initiation of the pumping action (i.e. the pumping action to increase the internal volume/decrease the internal pressure of the printing liquid supply chamber 603). In some examples it may be that printing liquid from the reservoir 611 is to flow into the printing liquid supply chamber 603 (e.g. under gravity) when not opposed by pressure in the printing liquid supply chamber, it may be that a (e.g. non-return) valve is disposed between the reservoir 611 and the printing liquid supply chamber 603 and it may be that the valve is to inhibit or prevent backward flow of printing liquid from the printing liquid supply chamber 603 towards the reservoir 611 .

[0034] The printing liquid supply chamber 603 may comprise a housing (e.g. a cylinder) having an adjustable internal volume. For example, the housing may have at least one moveable wall or boundary, such as a bottom wail or floor, (e.g, which may be provided by or be moveable by a moveable piston of the pump 602), to be moved (e.g. by an eccentric cam in force communication with the movable wall or boundary or piston) to change or maintain (e.g. while printing liquid is consumed by the printhead 604, e.g. from the printing liquid supply chamber 603) the internal pressure of the printing liquid supply chamber 603 (and printing liquid therein) by (e.g. cyclically) changing the internal volume of the printing liquid supply chamber 603. It may be that the pumping action of the pump 602 corresponds to a movement of the at least one moveable wail or boundary to increase the volume of the printing liquid supply chamber 603 (e.g. to initiate receipt of printing liquid from the reservoir 611).

[0035] In another example, the printing liquid supply chamber 603 may comprise a compressible housing or body (e.g. a compressible bag) and the pump 602 (during normal operation) may be to change the internal volume of the printing liquid supply chamber 603 by e.g. compressing the housing, for example by way of moveable arms which may be to compress (substantially) opposing sides of the compressible housing or body, in this case, the moveable arms may be to separate (e.g. to reduce compression applied to the compressible housing or disengage from the compressible housing) to thereby allow the compressible housing or body to be refilled with printing liquid, e.g. from the reservoir. It may be that the pumping action of the pump is associated with the separation of the moveable arms (e.g. to initiate receipt of printing liquid from the reservoir 611).

[0036] Alternatively, the printing liquid supply chamber 603 may be any structure that may be acted on (e.g. by the pump 602) to change (i.e. directly, or by way of a change in internal volume) the internal pressure of the chamber 603.

[0037] in some examples, the sensor 609 may be to estimate a quantity of printing liquid consumed by the printhead 604 by monitoring a flow of printing liquid out of the printing liquid supply chamber 603, for example along path 607 between the printing liquid suppiy chamber 603 and the printhead 604. For example, the sensor 609 may be a flow rate sensor. In some examples, the apparatus 600 may comprise additional flow rate sensors, such that the consumption of printing liquid by the printhead 604 may be monitored by way of its flow along the path 607 by a plurality of flow rate sensors. The flow rate sensors may be used in combination to estimate a quantity of printing liquid consumed by the printhead 604.

[0038] It may be that the sensor data indicates a flow rate of printing liquid along the path 607 (or a part of the path 607) between the printing liquid supply chamber 603 and the printhead 604. In some examples, it may be that the sensor data is from at least one sensor disposed along the path 607. in some examples, it may be that the printing liquid consumption data is based on a cumulative analysis of the flow rate data. This is described in more detail below, in some examples, the cumulative analysis may be reset after each resupply of the printing liquid supply chamber 603 (i.e. each resupply of printing liquid to the printing liquid supply chamber 603 from ihe reservoir 611 for supply to the printhead 604 under pressure, for example in a pumping cycle).

[0039] As described above, the printing liquid consumption information may indicate a quantity of printing liquid consumed by the printhead 604 and/or may indicate a quantity of printing liquid available under pressure to the printhead 604 (e.g. a quantity of printing liquid remaining in the printing liquid supply chamber 603). For example, the estimate of the quantity of printing liquid consumed by the printhead 604 may be considered with an estimated or known quantity of printing liquid available to the printhead 604 before the estimated quantity of printing liquid was consumed to estimate a quantity of printing liquid (remaining) available under pressure to the printhead 604 (or vice versa).

[0040] in some examples, the printing liquid consumption information based on the monitored flow of printing liquid out of the printing liquid suppiy chamber 603 may be subject to error or uncertainty, it may be that the error is associated with at least one of: uncertainty associated with sensing the flow of printing liquid by the sensor(s) 609; uncertainty associated with a determination of actual flow rate of liquid based on the sensor data from sensor(s) 609 (e.g. approximations or assumptions); uncertainty associated with the actual consumption of printing liquid by the printhead 604 for the sensed flow rate.

[0041] The obtained printing liquid consumption information may alternatively be based on an estimate of a number of printing liquid drops that have been ejected by the printhead (e.g. via drop counting). For example, it may be that the number of printing liquid drops that have been ejected by the printhead may be based on e.g. information relating to a print job or data (e.g, stored data) relating to previous operation of the printhead. Alternatively, it may be that the estimate is based on a detected number of printing liquid drops that have been ejected by the printhead (e.g. based on sensor data from a drop counting sensor, e.g. at the printhead). For example, it may be that the estimated drop count is based on a number of detected firings of at least one nozzle of the printhead. The printing liquid consumption information may be further based on an estimated printing liquid volume per drop of printing liquid ejected. For example, the printing liquid consumption information may be based on the product of the drop count and the estimated printing liquid volume per drop of printing liquid ejected.

[0042] Fig. 7 illustrates an example 700 of apparatus 500 comprising processing circuitry 701 , printing liquid pump 702, printhead 704 and further comprising a plurality of nozzles 714 of printhead 704, controller 713 and sensor or counting unit 709. The pump 702, printhead 704, channels 705, 706, path 707 and processing circuity 701 may perform the same or similar functionality to pumps 502, 602 printheads 504, 604 channels 505, 605, 506, 606, paths 507, 607 and processing circuitry 501 , 601 of Figs. 5, 6 respectively. Path 712 may perform the same or similar functionality to path 612 in the example of Fig. 6. Similar to the example 600 of Fig. 6, during fault-free operation, the pump 702 may be to provide printing liquid under pressure to the printhead 704 by way of a printing liquid supply chamber 703. The printing liquid supply chamber 703 may be to receive printing liquid from a printing liquid reservoir 711. The pump 702 may be to pressurise printing liquid in the printing liquid supply chamber 703 for supply to the printhead 704 along channel 707. The printhead 604 may be to deposit printing liquid on print medium 708.

[0043] in a similar way to the example 600 of Fig. 6, it may be that the printing liquid supply chamber 703 is of variable volume. For example, it may be that the volume of the printing liquid supply chamber 703 is to be increased to reduce the pressure in the printing liquid supply chamber 703 and thereby receive printing liquid from the reservoir 711 , for example under gravity. It may be that the pump 702 is to, after the printing liquid supply chamber 703 has received printing liquid from the reservoir 711 , decrease the volume of the printing liquid supply chamber 703 to thereby pressurise the received printing liquid for supply to the printhead 704.

[0044] in some examples, the estimate of the quantity (or volume) of printing liquid consumed by the printhead 704 may be determined based on a number of firings of at least one nozzle 714 of printhead 704 and a known (or predetermined) volume of printing liquid associated with an ejected drop or with a plurality of ejected drops. It may be that flow rate sensors 609 described above with respect to the example 600 of Fig. 6 are omitted.

[0045] In some examples sensor 709 may be to detect or count the number of drops of printing liquid ejected by printhead 704 based on a detected number of firings of at least one nozzle 714 of printhead 704.

[0046] in some examples (not shown), the sensor 709 may be associated with the printhead 704, i.e. may be located at the printhead 704, and may be to detect/count the number of times the at least one nozzle 714 of the printhead 704 has been fired. For example, the sensor 709 may detect the activation of a component of the at least one nozzle 714 associated with nozzle-firing, such as an activation of a circuit etc.

[0047] In alternative examples, as shown In Fig. 7, the sensor 709 may comprise a counting unit 709 associated with a controller 713 of the apparatus 700. in some examples, it may be that controller 713 is to control the pump 702 and the printhead 704, for example responsive to receiving a print job, or associated data.

[0048] It may be that counting unit 709 is to estimate the count of the number of firings of at least one nozzle 714 of the printhead 704 based on e.g. a control signal from controller 713. Counting unit 709 may be to send the estimated count information to processing circuitry 701 (e.g. by way of communication channel 706), or otherwise enable processing circuitry 701 to obtain (e.g. retrieve) the count information.

[0049] it may be that the predetermined liquid drop volume is associated with each firing or with a given number of firings. For example, it may be that a liquid drop volume per nozzle firing is (pre-)determined during a calibration process, e.g. at the point of manufacture of the apparatus (e.g. the printing apparatus or printhead). For example, it may be that after manufacture a subset of similarly manufactured printheads (or each printhead) may be subjected to calibration in order to determine the liquid drop volume consumed (i.e. ejected) per nozzle firing. It may be that the calibration is performed as pari of a quality assurance process etc.

[0050] it may be that the predetermined liquid drop volume associated with each firing is different for different printing liquids (e.g. different types of printing liquids or different colours of the same type of printing liquid etc), it may be that the predetermined liquid drop volume associated with each firing is different for different types of print jobs or types of printing, for example text printing or fill printing etc. However, it may be that a single value of liquid drop volume is associated with each firing of the at least one nozzle of the printhead 704 for the estimation of the printing liquid consumption by the printhead 704.

[0051 ] it may be that the predetermined liquid drop volume associated with each firing has a degree of uncertainty, i.e. the predetermined liquid drop volume may be an approximation of a true printing liquid drop volume, in some examples, the uncertainty or approximation of the predetermined liquid drop volume associated with each firing of the nozzles of the printhead may be accounted for in the estimate of the quantity of printing liquid consumed by the printhead based on the drop count. In some examples, the detected number of firings of the at least one nozzle (or the detected number of printing liquid drops ejected by the printhead) may (also) include a degree of uncertainty, e.g. an error associated with the detection of the nozzle firing (i.e. the counting of drops). It may be that the estimate of the quantity of printing liquid consumed by the printhead may (also) include the error associated with the detection of the number of drops ejected by the printhead, it may be that the error in the estimate of the quantity of printing liquid consumed by the printhead is relatively high. For example, the error may be or order of 1 s or 10s of percent of the estimate. For example, the error may be 20 percent of the estimated quantity of consumed printing liquid.

[0052] Referring back to Fig. 5, the estimate of the quantity (or volume) of printing liquid consumed by the printhead 504 may alternatively be based on a sensed quantity or volume of printing liquid remaining in the (e.g. intermediate) printing liquid supply chamber (such as printing liquid supply chamber 603, 703 in the examples of Figs. 6, 7) which receives printing liquid from a reservoir and by way of which printing liquid is supplied (e.g. under pressure) to the printhead 502. The sensed quantity or volume of printing liquid remaining may be (e.g. indirectly) indicative of a quantity or volume of printing liquid which has been consumed by the printhead 504, for example by comparison with a known or predetermined prior volume of printing liquid in the printing liquid supply chamber or because, during normal operation, the quantity of printing liquid in the printing liquid supply chamber may cyclically vary between a predetermined minimum value and a predetermined maximum value, e.g. due to a cyclical operation of the printing liquid pump.

[0053] The printing liquid consumption information may (e.g. directly) indicate, or may be used to determine, whether (or when) the printing liquid consumption by the printhead has reached a predetermined printing liquid consumption threshold. It may be that the printing liquid consumption information may directly specify whether the printing liquid consumption by the printhead has reached (for example has been met, exceeded or fallen below) a printing liquid consumption threshold. For example, printing liquid consumption information may comprise a flag having a value set to indicate whether the printing liquid consumption by the printhead has reached the printing liquid consumption threshold.

[0054] For example, it may be that sensor 609, counting unit 709, or processing circuitry thereof, is to analyse the estimated quantity of printing liquid consumption by the printhead with respect to the printing liquid consumption threshold and, as above, to send or enable the processing circuitry 601 or 701 to obtain printing liquid consumption information (e.g. by way of a flag having a value set to indicate whether the printing liquid consumption by the printhead has reached the printing liquid consumption threshold) directly indicating whether a printing liquid consumption threshold has been reached,

[0055] Alternatively, the printing liquid consumption information may indirectly indicate whether the printing liquid consumption of printing liquid by the printhead 504 has reached the printing liquid consumption threshold. For example, as set out above, the printing liquid consumption information may comprise an indication of a volume (or quantity} of printing liquid consumed by the printhead. For example, as set out above, the printing liquid consumption information may comprise information (e.g. directly) indicating the quantity or volume of printing liquid consumed by the printhead or indicating the quantity or volume of printing liquid available under pressure to the printhead (e.g. the quantity or volume of printing liquid remaining in the printing liquid supply chamber). For example, the printing liquid consumption information may comprise information related to an absolute or relative (e.g. fractional) measure of printing liquid consumption by the printhead, it may be that the processing circuitry 501 is to compare the indication of the volume (or quantity) of printing liquid consumed by the printhead to the predetermined printing liquid consumption threshold to determine if the printing liquid consumption threshold has been reached.

[0056] It will be understood that, in any of the above examples, the processing of sensor data (e.g. to determine an estimated quantity or volume of printing liquid consumed by the printhead or to determine whether the printing liquid consumption of the printhead has reached the printing liquid consumption threshold) may be performed by the processing circuitry 501 , 601 , 701 or by processing circuitry of ihe respective sensor 609, 709 itself, in the former case, the sensor data may be obtained by the processing circuitry 501 , 601 , 701 for processing to determine the estimated quantity or volume of printing liquid consumed by the printhead (and in some examples to determine whether the quantity of printing liquid consumed by the printhead has reached the printing liquid consumption threshold), in the latter case, the respective sensor 609, 709 may determine the estimated quantity or volume of printing liquid consumed by the printhead (and in some examples to determine whether the quantity of printing liquid consumed by the printhead has reached the printing liquid consumption threshold) and provide the estimated quantity (or a (e.g. direct) indication as to whether the quantity of printing liquid consumed by the printhead has reached the threshold) to the processing circuitry.

[0057] For example, it may be that the processing circuitry 601 or 701 is to determine an estimated quantity or volume of printing liquid consumed by the printhead based on the count or flow rate information and the predetermined printing liquid drop volume (and in some examples to determine whether the quantity of printing liquid consumed by the printhead has reached the printing liquid consumption threshold by comparing the estimated quantity to the threshold). Alternatively, it may be that sensor 603, counting unit 709, or processing circuitry thereof, is to determine an estimated quantity or volume of liquid consumption of the printing liquid by the printhead based on the count or flow rate information and the predetermined printing liquid drop volume and to provide the estimated quantity or volume of liquid consumption of the printing liquid by the printhead to the processing circuitry 601 or 701 based thereon (and in some examples to determine whether the quantity of printing liquid consumed by the printhead has reached the printing liquid consumption threshold by comparing the estimated quantity to the threshold and to provide a (e.g. direct) indication as to whether the quantity of printing liquid consumed by the printhead has reached the threshold to the processing circuitry).

[0058] in some examples, the quantity (or volume) of printing liquid consumed by the printhead indicated by the printing liquid consumption information may be a quantity (or volume) of printing liquid consumed by the printhead since a previous or latest resupply of the printing liquid supply chamber 603, 703 from the printing liquid reservoir 611 , 711. [0059] in some examples (e.g. depending on the nature of the printing liquid consumption information, e.g. depending on whether the printing liquid consumption information indicates a quantity of printing liquid consumed by the printhead or whether the printing liquid consumption information indicates a quantity of printing liquid available under pressure to the printhead), the printing liquid consumption threshold may be e.g. an upper threshold of printing liquid consumed by the printhead, or may be a lower threshold of printing liquid in the printing liquid supply chamber 603, 703.

[0959] in examples where the printing liquid consumption threshold is an upper threshold (or limit) for printing liquid that has been consumed by the printhead, it may be that a quantity (or volume) of printing liquid that has been consumed by the printhead (based on the printing liquid consumption information) is compared to the printing liquid consumption threshold. [0081] Alternatively, in examples where the printing liquid consumption threshold is a lower threshold (or limit) for printing liquid available for consumption by the printhead (e.g. remains available for consumption by the printhead), it may be that a quantity (or volume) of printing liquid that is available for consumption by the printhead (e.g. under pressure, e.g. in the printing liquid supply chamber) is compared to the printing liquid consumption threshold.

[0062] in some cases, it may be that the printing liquid consumption information indicating the quantity (or volume) of printing liquid consumed by the printhead since a previous or latest resupply of the printing liquid supply chamber is compared to a known or predetermined volume of printing liquid supplied to the printing liquid supply chamber from the reservoir.

[0083] The comparison of the printing liquid consumed by the printhead since the previous or latest resupply of the printing liquid supply chamber from the reservoir to the known or predetermined volume of printing liquid supplied to the printing liquid supply chamber from the reservoir may indicate a volume of printing liquid that remains available (under pressure) to be consumed by the printhead. It may be that the quantity of printing liquid available for consumption by the printhead is determined based on subtracting the quantity of printing liquid consumed by the printhead (e.g. since the latest resupply of printing liquid to the printing liquid supply chamber from the reservoir) from the known or predetermined volume of printing liquid supplied to the printing liquid supply chamber from the reservoir in the previous or latest resupply of printing liquid to the printing liquid supply chamber from the reservoir,

[0064] The quantity of printing liquid available for consumption by the printhead, or the quantity of printing liquid consumed by the printhead, may be determined based on a cumulative analysis. For example, the cumulative analysis may be based on a monitored cumulative quantity of printing liquid consumed by the printhead and a cumulative quantify of printing liquid resupplied to the printing liquid supply chamber since a predefined starting point. In some examples, it may be that a number of resupplies (i.e. pumping action initiations) since a predefined starting point are counted to determine the total quantity of printing liquid supplied to the printing liquid supply chamber since the starting point. An indication of the volume of printing liquid consumed by the printhead (e.g. based on the detected number of printing liquid drops ejected by the printhead) since the starting point may also be estimated to determine the total quantity of printing liquid consumed by the printhead since the starting point. The total quantities of printing liquid consumed by the printhead and supplied to the printing liquid chamber may be compared to determine a quantity of printing liquid available in the printing liquid supply chamber for consumption by the printhead at a given time. For example, a quantity of printing liquid available for consumption by the printhead at a given time may be determined by subtracting the total quantity of printing liquid consumed by the printhead since the starting point from the total quantity of printing liquid supplied to the printing liquid supply chamber since the starting point,

[0065] The previous or latest resupply of the printing liquid supply chamber from the reservoir may have been initiated by a previous pumping action of the pump, such as a pumping action to increase the volume of the printing liquid supply chamber to initiate resupply of printing liquid to the printing liquid supply chamber from the reservoir (e.g. under gravity). As explained in more detail below, it may be this pumping action to which the pump initiation information relates. Thus, it may be that the printing liquid consumption information may indicate the quantity (or volume) of printing liquid consumed by the printhead since a previous or latest (e.g. detected) pumping action of the pump.

[0088] Referring back to Fig. 1 , the pump initiation information obtained in block 120 may indicate whether the pumping action of the pump is to be, is being, or has been initiated. The pumping action may be a depressurising action of the pump, for example to initiate receipt of printing liquid from a reservoir (e.g. under gravity). For example, the pumping action may be to increase a volume of the printing liquid supply chamber to initiate receipt of printing liquid therein from a reservoir (e.g. under gravity). Alternatively, the pumping action may be a pressurising pumping action of the pump, for example to pressurise printing liquid for providing to the printhead. For example, the pumping action may be to increase or maintain pressure of printing liquid within the printing liquid supply chamber. An increase in pressure applied by the pump to the liquid in the printing liquid supply chamber may be (indirectly) indicative of a corresponding prior decrease in pressure of the printing liquid supply chamber to initiate receipt of printing liquid therein from a reservoir.

[0067] it may be that the pump initiation information is based on sensor data. For example, it may be that the pump initiation information is based on sensor data from sensor 610 of Fig, 6 or sensor 710 of Fig.7 for sensing that the pumping action has been initiated. The pump initiation information may be obtained based on sensor data from (e.g. directly from) a pump initiation sensor. The pump initiation information may be sensed directly or indirectly.

[0088] It may be that the pump initiation information is based on (e.g. comprises) at least one of: a signal (e.g. from a sensor such as sensor 610 or sensor 710) to trigger initiation of the pumping action of the pump has been obtained; an absence of a signal (e.g. from a sensor such as sensor 610 or sensor 710} for triggering initiation of the pumping action of the pump; an indicator (e.g. based on sensor data, for example from sensor 610 or 710) of whether an initiation of a pumping action of the pump has occurred.

[0069] in some examples, a depressurising (or printing liquid supply chamber volume increasing) action of the pump is to be triggered when a volume of the printing liquid supply chamber reaches a predetermined (e.g. minimum) volume, e.g. based on sensor data indicative of the volume of the printing liquid supply chamber reaching the predetermined (e.g. minimum) volume.

[0070] Thus, it may be that the pump initiation information is based on at least one of: a signal to trigger initiation of a depressurising (or printing liquid supply chamber volume increasing) action of the pump (e.g. to initiate receipt of printing liquid into the printing liquid supply chamber from the reservoir, e.g. under gravity); an absence of a signal to trigger initiation of a depressurising (or printing liquid supply chamber volume increasing) action of the pump (e.g. to initiate receipt of printing liquid into the printing liquid supply chamber from the reservoir, e.g. under gravity).

[0071] In some examples, the pump initiation sensor may be associated with the pump or a component thereof, in some examples, the pump initiation sensor may be associated with the printing liquid supply chamber (e.g. printing liquid supply chamber 603, 703 of Figs. 6, 7). it may be that a sensor (e.g. sensor 610 or sensor 710) is provided for sensing a motion, a rotation, or position of a moveable component (e.g. a piston) of the pump to thereby determine that the pump action is to be, is being or has been initiated. It may be that the pump initiation information is based on an indication e.g. from sensor data that the pump action is to be, is being or has been initiated. For example, sensor 610 or sensor 710 may be an inertial sensor.

[0072] As the initiation of the pumping action may be associated with a change in an internal pressure of the printing liquid supply chamber, in some examples the initiation of the pumping action of the pump (and thus the determination of the fault) may be based on sensor data from a sensor (such as a pressure sensor) associated with (e.g. within) the printing liquid supply chamber (where provided, such as printing liquid supply chamber 603, 703 of Figs, 6, 7), where the sensor associated with the printing liquid supply chamber may sense a change in the internal pressure of the printing liquid supply chamber. The sensing of the change in the internal pressure of the printing liquid supply chamber may be based on direct pressure sensing (e.g. within the printing liquid supply chamber) or may be based on sensing an indicator associated with a change in pressure. [0073] Thus, the sensor data from the pump initiation sensor may indicate at least one of: a signal to trigger initiation of the pumping action; an absence of the signal to trigger initiation of the pumping action of the pump; an indication of whether an initiation of a pumping action of the pump has occurred,

[0074] in some examples, the pump initiation information may comprise or indicate the signal (or the absence of the signal) to trigger initiation of the pumping action of the pump. It may be that the signal (or the absence of the signal) to trigger initiation of the pumping action of the pump 602, 702 or the indication of whether initiation of the pumping action has occurred is based on data from the sensor 610, 710 indicative of whether the volume of the printing liquid supply chamber or the volume of printing liquid in the printing liquid supply chamber 603, 703 has reached a predetermined lower threshold. For example, it may be that the sensor 610, 710 is to detect a position or location in a pumping sequence of the pump 602, 702 (e.g, a position of a piston of the pump reciprocating within a cylinder of the pump).

[0075] it may be that the sensor 610, 710 is to detect or indicate that the volume of the printing liquid supply chamber or the volume of printing liquid in the printing liquid supply chamber 603, 703 has reached a predetermined lower threshold based on a detecting an internal pressure or an internal volume of the printing liquid supply chamber 603, 703, The predetermined lower threshold may relate to, for example, the volume of the printing liquid supply chamber 603, 703 when the pump 602, 702 has completed a pressurising pumping action on printing liquid within the printing liquid supply chamber 603, 703. For example, the predetermined lower threshold may relate to, for example, the volume of the printing liquid supply chamber 603, 703 when a piston (where provided) of the pump has reached the maximum extent of its pressurising stroke,

[0076] The sensor 610, 710 may be an optical sensor (or other light-based sensor), For example, the sensor 610, 710 may be a light-gate comprising a light source configured to direct light onto a light detector such that the absence of a signal detected by the light defector may indicate when light from the source is blocked (e.g. by a piston of the pump reaching the maximum extent of its pressurising stroke), or such that the detection of a signal by fhe light detector after a period of the absence of a signal indicates when a body (e.g. piston at or around the maximum extent of its pressurising stroke) blocking the source is removed, it may be that the body blocking the source may be part of the printing liquid supply chamber 603, 703 such as a moveable wall or floor thereof. It may be that the body blocking the source may be an element of the pump 602, 702 such as a piston. Alternatively, sensor 610, 710 may be any other light-based sensor, such as a camera to detect when a visual indicator (indicative of a volume of the printing liquid supply chamber 603) is displayed.

[0077] It may be that a change in pressure, an absolute pressure, or an indication of whether the interna! pressure in the printing liquid supply chamber has reached a pressure threshold may be determined (e.g. derived or inferred) based on sensor data obtained (e.g. received) from the optical sensor 610, 710. For example, changes in the internal volume of the printing liquid supply chamber 603, 703 defected by the optica! sensor may result in changes in internal pressure of the printing liquid supply chamber 603, 703 and the printing liquid therein, or vice versa.

[0078] in some examples, it may be that the sensor 610, 710 is to detect a change in a pumping state of the pump 602, 702 such as a change from a pressurising state to a depressurising state or vice versa (e.g. by way of detecting the position or motion of a moveable component, such as a piston, of the pump 602, 702).

[0079] For example, an optica! sensor 610, 710 may be to detect when a piston of the pump 602, 702 has reached a maximum extent of its pressurising stroke, which may indicate that the volume of the printing liquid supply chamber has reached the predetermined lower threshold or that the state of the pump 602, 702 is to change from the pressurising state to the depressurising state (e.g. to initiate receipt of printing liquid from the reservoir 611 , 711).

[0080] it may be that the sensor 610, 710 is to detect a motion, rotation, or a position of a (e.g. moveable) component of the pump 602, 702. For example, it may be that the pump 602, 702 comprises a moveable piston to be moved by a cam (e.g. an eccentric or elongated cam), for example to vary the volume of the printing liquid supply chamber 603, 703, and it may be that the sensor 610,710 is to detect a motion, rotation, or a position of the cam. For example, the sensor 610, 710 may comprise a cam encoder (e.g. to indicate a rotational position of the cam, and thus the position of the piston and the volume of the printing liquid supply chamber). It may be that the sensor data from a cam encoder may be indicative of a change in the pump state from a pressurising state to a depressurising state or vice versa. For example, it may be that the cam encoder data is indicative of the position of the piston of the pump 602, 702 along its pressurising or depressurising stroke (and thus the volume of the printing liquid supply chamber). For example, the cam encoder data may Indicate when the piston of the pump 602, 702 has reached a maximum extent of its pressurising stroke.

[0081] in some examples, the sensor 610, 710 may be a pressure sensor, for example within the printing liquid supply chamber 603, 703 to measure the pressure or detect changes in pressure therein. The pressure measured within the chamber 603, 703 may be indicative of the volume of the chamber 603, 703, and so may be used to determine when the volume of the chamber 603, 703 has reached the minimum volume. Additionally or alternatively, the sensor 610, 710 may be to indicate that the initiation of the pumping action of the pump 602, 702 has occurred based on indicating that a pressure of printing liquid in the printing liquid supply chamber 603, 703 has changed. As has been discussed herein, a change in pressure within the printing liquid supply chamber 603, 703 (either directly determined, or indirectly determined, such as through a volume determination) may indicate an initiation of a pumping action of pump 602, 702 has occurred.

[0082] Thus, it may be that sensor 610, 710 is to directly detect when the minimum threshold volume of the printing liquid supply chamber 603, 703 has been reached fie. met or fallen beiow) or it may be that sensor 610, 710 detects an internal pressure of the printing liquid supply chamber 603, 703 and the detected pressure (i.e. based on pressure sensor data) may be compared to a threshold (e.g. by the processing circuitry 601 , 703 or by additional processing circuitry of the sensor 610, 710, not shown) to determine when the minimum volume threshold has been reached.

[0083] Referring back to Fig. 1 , in some examples, it may be that the fault determined based on the printing liquid consumption information and pump initiation information indicating that the printing liquid consumption by the printhead has reached a printing liquid consumption threshold without a corresponding initiation of pumping action of the pump may be caused by a fault with sensor 610 or sensor 710. For example, it may be that sensor 610 or sensor 710 may not generate or issue a trigger signal in response to the minimum threshold volume of the printing liquid supply chamber 603, 703 having been reached, or sensor 610 or sensor 710 may not correctly (i.e may fail to) detect when the minimum threshold volume of the printing liquid supply chamber 603, 703 has been reached.

[0084] In other examples, it may be that the determination that the printing liquid consumption by the printhead has reached a printing liquid consumption threshold without a corresponding initiation of pumping action of the pump may be caused by a fault relating to pump 602 or pump 702. For example, it may be that pump 602 or pump 702 may not correctly initiate, perform or complete a pumping action (e.g. a pressurising or depressurising action), for example it may be that the pump may be jammed. In this example, it may be that the pumping action is not detected by sensor 610 or 710, (e.g. even if correctly triggered) as the pumping action may not be initiated, performed or completed due to a fault with the pump 602 or 702. [0085] Fig. 3 illustrates an example method for determining a fault relating to a printing liquid pump for a printhead based on the method of Fig. 1 , At block 310 printing liquid consumption information as described herein is obtained, and at block 311 the method 300 may comprise (e.g. by the processing circuitry 501 , 801 or 701 ) comparing the indication of the quantity (or volume) of printing liquid that has been consumed by the printhead based on the printing liquid consumption data to the predetermined printing liquid consumption threshold in order to determine if the printing liquid consumed by the printhead has reached the printing liquid consumption threshold.

[0086] At block 331 it may be determined, based on the output of the comparison of block 311 , whether the printing liquid consumption threshold has been reached. It may be that if it is determined at block 331 that the printing iiquid consumption threshold has not been reached (or that it is not determined that the threshold has been reached) the method may return to block 310 and repeat until it is determined at block 331 that printing Iiquid consumption threshold has been reached, at which point the method may proceed to block 332. The printing Iiquid consumption threshold may indicate that printing Iiquid available for consumption by (e.g. available under pressure to) the printhead may be likely to tall below a predetermined (e.g. safe i.e. safe for continued operation) quantity (or volume). For example, the printing iiquid consumption threshold may indicate that if the printhead continues to consume the printing Iiquid (e.g. without a corresponding pumping action of the pump), the printing Iiquid supply available under pressure to the printhead may run out, which may result in the printhead running dry (i.e. without sufficient printing liquid to allow normal operation of the printhead, resulting in damage, for example by overheating),

[0087] it may be that an additional supply of printing Iiquid may be available (e.g. to the printing apparatus), e.g. from a reservoir (e.g. as discussed above with respect to Figs. 8, 7), but it may be that (e.g. due to a fault relating to the printing liquid pump) this printing liquid is not being supplied under pressure to the printhead by the printing Iiquid pump. Thus, the fault determined based on the printing Iiquid consumption information may not relate to a lack of printing Iiquid available (e.g. to the printing apparatus from, for example, the reservoir) but rather to a lack of printing Iiquid supplied under pressure to the printhead by the printing Iiquid pump.

[0088] in some examples, as discussed, during normal operation, i.e. fault-free operation, the pump is to supply printing iiquid under pressure to the printhead. As also discussed, in some examples the pump may supply printing liquid to the printhead by way of a printing liquid supply chamber. It may be that, during fault-free operation, the pump is to pressurise printing liquid within the printing iiquid supply chamber in order to cause the pressurised printing liquid to be supplied to the printhead. In some examples, during fault-free operation the pump may be to act on printing liquid within the printing liquid supply chamber to change or maintain (e.g. substantially maintain) pressure applied to printing liquid within the printing liquid supply chamber, for example so as to provide or maintain (e.g. substantially maintain) a supply of pressurised printing liquid to the printhead, in some examples, it may be that the initiation of the pumping action of the pump relates to a decrease in an internal pressure within (or applied to) the printing liquid supply chamber. For example, it may be that the initiation of the pumping action of the pump relates to an increase in the volume of the printing liquid supply chamber. In these examples, the initiation of the pumping action may relate to initiating a receipt of printing liquid by the printing liquid supply chamber from a reservoir.

[0089] For example, as discussed with respect to Fig. 8 and Fig. 7, printing liquid reservoir 611 , 711 may be connectable to printing liquid supply chamber 603, 703 and may be to supply (e.g. resupply) printing liquid to printing liquid supply chamber 603, 703 via path 612, 712.

[0090] It may be that it it is determined that the printing liquid consumption threshold has been reached at block 331 then it is determined at block 332, based on pump initiation information obtained in block 320, whether a corresponding pumping action of the pump has been initiated.

[0091] in some examples, the initiation of the pumping action may relate to initiating the receipt of printing liquid by the printing liquid supply chamber from the reservoir as a result of (or at least by way of) a decrease in an internal pressure within or applied to (e.g. an increase in the volume of) the printing liquid supply chamber. For example, it may be that a decrease in an internal pressure of the printing liquid supply chamber (e.g. caused by an increase in the volume thereof) allows printing liquid to be received thereby from the reservoir, e.g. under gravity,

[0092] in some examples, it may be that if no corresponding pumping action of the pump has been initiated, a fault is detected. It may be that the fault results in the interruption of the printing liquid being supplied under pressure to the printhead. For example, the fault may be a fault of the pump itself, such as a fault (e.g. jamming) of at least one moving part of the pump inhibiting or preventing the pump from pressurising printing liquid for use by the printhead. Additionally or alternatively, the fault may be a fault of pump initiation sensor associated with the pump, which may be for triggering a pumping action of the pump such that a fault of the pump initiation sensor may (without intervention) result in a failure of the pump to perform a pumping action (e.g. to initiate receipt of pumping liquid from a reservoir to a printing liquid supply chamber). As a result, without intervention, it may be that the fault would result in, or increase a likelihood that, the printhead being damaged, such as by overheating.

[0093] It may be that, in order to determine whether a pumping action of the pump has been initiated which corresponds to the printing liquid consumption by the printhead reaching the printing liquid consumption threshoid, it may be determined at block 332 based on the pump initiation information and the printing liquid consumption information whether the pumping action was initiated when the printing liquid consumption of the printhead was within a predetermined tolerance or range of the predetermined printing liquid consumption threshold. In this case, the printing liquid consumption information may comprise a plurality of indications of quantities of printing liquid consumed or available to the printhead (e.g. at different times), based on obtained printing liquid consumption information corresponding to different times (e.g, a sequence of indications of estimated quantity or volume of printing liquid consumption of or available under pressure to the printhead). It may be that, based on the plurality of indications, it is determined whether a pump initiation is to be, is being, or has been initiated when the quantity of printing liquid consumed or available under pressure to the printhead is within the predetermined range of the printing liquid consumption threshold. If will be understood that a similar determination may be made in block 130 of Fig. 1 , block 230 of Fig. 2 and block 432 of Fig. 4.

[0094] In some examples, it may be that an initiation of a pumping action is determined or considered to correspond to the printing liquid consumption reaching the printing liquid consumption threshold if the initiation of the pumping action is determined to have occurred when the printing liquid consumption of the printhead is within a given (e.g. predetermined) range of printing liquid consumption values, e.g. 1 , 5, or 10 seconds or 1 , 2 or 5 cm ³ (cubic centimeters) around the printing liquid consumption threshoid. In some examples, it may be that range is symmetrically centred on the printing liquid consumption threshold. For example, e.g. the range may be 5 cm ³ in total and may extend to plus and minus 2.5 cm ³ about the printing liquid consumption threshoid.

[0095] Alternatively, the range may be asymmetric. In some examples, the asymmetric range may extend above, below, or above and below the printing liquid consumption threshold.

[0096] in some examples, the printing liquid consumption threshold may correspond to an upper or lower limit for determining a correspondence with an initiation of a pumping action of the pump and the tolerance (or range) may be zero. [0097] li may be that uncertainty on the estimate of the quantity of printing liquid consumed by the printhead (as discussed above) may be accounted for in setting the threshold, where, as described herein the threshold for the printing liquid consumption is to indicate that the printing liquid available to the printhead may be low and indicative that the printhead may be (about to be) run without sufficient printing liquid (i.e. the printhead may be run dry) if there is no corresponding pumping action,

[0098] in some examples, it may be that the printing liquid consumption threshold is based on a lower level of printing liquid available under pressure to the printhead with which the printhead may be operated (or may be to continue operation), for example without a corresponding pumping action. For example, it may be that below the printing liquid consumption threshold a pumping action of the pump is to be initiated, for example to resupply printing liquid of the printing liquid supply chamber, e.g. by causing de- pressurisation of the printing liquid supply chamber to allow resupply thereof with printing liquid. It may be that if the pumping action of the pump is not initiated when the printing liquid consumption threshold is reached, the continued operation of the printhead may result in damage to the printhead.

[0099] it may be that the threshold is set to a pre-determined value of printing liquid within (e.g. remaining within) the printing liquid supply chamber, e.g. 5cm ³ of printing liquid. If may be that the threshold takes into account the level of uncertainty (error) associated with the estimate of the printing liquid consumption by the printhead. For example, in order provide an indication of a possible operation that will result in damage to the printhead (e.g. without sufficient printing liquid) before the operation occurs, it may be that the threshold (e.g. a lower limit of available printing liquid) is set to the lower level of printing liquid within the printing liquid supply chamber, with an applied error correction.

[00100] For example, it may be that the lower level of printing liquid is set to Xcrrs ³ and the error associated with the printing liquid consumption may be Y percent, in this case, the printing liquid consumption threshold may be set at Y percent of Xcm ³ above Xcm ³ , For example, it may be that the lower level printing liquid which may indicate continued operation (without a corresponding pumping action of the pump) may lead fo damage to the printhead may be 5cm ³ and the error associated with the printing liquid consumption may be 20 percent, and the printing liquid consumption threshold may be set at 20 percent of 5cm ³ above 5cm ³ , i.e. 5cm ³ plus 1 cm ³ , i.e. 6cm ³ . The error correction term added to the printing liquid consumption threshold may be applied in respect of any estimation of the printing liquid consumption, including at least the drop count and flow rate printing liquid consumption estimation examples provided above. [00101] At block 341 of Fig, 3, an error signal may be generated based on (i.e. in response to) the determination that the printing liquid consumption threshold has been reached without a corresponding initiation of a pumping action of the pump. Alternatively, at block 342 of Fig. 3, it may be that no fault is detected based on the determination. Block 320, at which the pump initiation information is obtained, may be performed in any sequence (or in parallel) with respect to blocks 310, 311 and 331. For example it may be that block 320 is performed before or substantially simultaneously with block 310, may be performed responsive to the determination at block 331 that the printing liquid consumption threshold has been reached, or at any time and in any sequence between blocks 310 and 331 . [00102] Fig. 2 depicts flowchart 200 according to an example method for determining a fault in the printing liquid pump for the printhead, It may be that the determination of the fault illustrated in flowchart 200 is based on a comparison of the pumping action initiation information to the printing liquid consumption information. Similarly to block 110 of flowchart 100, at block 210 of flowchart 200 printing liquid consumption information may be obtained. The obtained printing liquid consumption information may be as described herein.

[00103] Similarly to block 120 of flowchart 100, at block 220 of flowchart 200 pump initiation information may be obtained. The obtained pump initiation information may be as described herein,

[00104] in a similar way to block 130 of Fig.1 , at block 230 of Fig, 2 if may be determined whether the printing liquid consumption has reached a predetermined printing liquid consumption threshold without a corresponding initiation of a pumping action of the pump having occurred. If at block 230 it is determined that the printing liquid consumption of the printhead reached the printing liquid consumption threshold with a corresponding initiation of a pumping action of the pump, the method may return to block 210 and repeat blocks 210-230. If at block 230 it is determined that the printing liquid consumption of the printhead reached the printing liquid consumption threshold without a corresponding initiation of a pumping action of the pump, an error signal (e.g. a signal to pause or terminate operation of the printhead and/or an error message) may be generated at block 240.

[00105] Fig, 4 depicts example flowchart 400 according to an example method for determining a fault relating to a printing liquid pump for a printhead where it may be that the printing liquid consumption information and the pump action initiation information are based on sensor data.

[00106] At block 410 the printing liquid consumption information may be obtained based on sensor data. [00107] At block 411 the printing liquid consumption information obtained from sensor data may be compared to the printing liquid consumption threshold.

[00108] At block 431 , it may be determined whether the printing liquid consumption threshold has been reached, if the printing iiquid consumption threshold has been reached, the method may progress to blocks 432 and 441 or 442: or if the printing liquid consumption threshold has not been reached, the method may repeat blocks 410, 411 and 431 until it is determined at block 431 that the printing Iiquid consumption threshold has been reached. Alternatively, it may be that the method proceeds from block 431 to block 432 without repeating blocks 410, 411 and 431 , and the method is instead repeated after block 442 for example if no fault is detected.

[00109] At block 432, it may be determined (similar to block 332 described above in respect of Fig. 3), based on pump initiation information obtained in block 420, whether a pumping action of the pump has been initiated which corresponds to the printing liquid consumption sensor data indicating that the printing Iiquid consumption of the printhead has reached the printing Iiquid consumption threshold.

[00110] in other examples, it may be that blocks 411 and 431 are omitted. For example, it may be that the printing liquid consumption information directly indicates whether the printing Iiquid consumption of the printhead has reached the printing iiquid consumption threshold, in these examples, the printing iiquid consumption threshold may still be determined taking into account an error associated with a printing Iiquid consumption estimate as discussed above.

[00111] Fig. 8 illustrates a schematic diagram of an apparatus 800 for determining a fault in the printing Iiquid pump for the printhead. The apparatus 800 may comprise processing circuitry 810 and memory 830. Memory 830 may comprise instructions 831 , such as machine or computer readable instructions, which when executed by the processing circuitry 810 may cause the circuitry 810 to perform the method of any of the blocks illustrated in Figs. 1 to 4.

[00112] Apparatus 800 may further comprise pump 820 for which the fault may be determined. Apparatus 800 may further comprise printhead 840 to which the pump 820 is to supply printing liquid during fault free operation thereof.

[00113] It is to be understood that although not shown, machine readable instructions 831 may be stored on any transitory or non-transitory medium, it is also to be understood that any of the blocks illustrated in Figs. 1 to 4 may be combined or omitted.

[00114] Within the scope of this application it is expressly intended that the various examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all examples and/or features of any example can be combined in any way and/or combination, for example it may be that apparatus features correspond to method features or vice versa, uniess such features are incompatible.

[00115] In this specification, the phrase “at least one of A or B” and the phrase “at least one of A and B” should be interpreted to mean any one or more of the plurality of listed items A, B, etc., taken jointly and severally in any and all permutations.

[00116] Where functional units are described as circuitry, such as the processing circuity 501 , 601 , 701 the circuitry may be general purpose processor circuitry configured by program code to perform specified processing functions. The circuitry may also be configured by modification to the processing hardware. The configuration of the circuitry to perform a specified function may be entirely in hardware, entirely software, or using a combination of hardware modification and software execution. Program instructions may be used to configure the logic gates of general purpose or special purpose processor circuitry to perform a processing function.

[00117] Circuitry may be implemented, for example, as a hardware circuit comprising processors, microprocessors, circuits, circuit elements (e.g., transistors, resistors, capacitors, inductors, and so forth), integrated circuits, application specific integrated circuits, programmable logic devices, digital signal processors, field programmable gate arrays, logic gates, registers, semiconductor devices, chips, microchips, chipsets, and the like,

[00118] Circuitry may be implemented, for example, as part of a computing device comprising single or multiple cores, or may be implemented as part of a distributed computing system. Alternatively, or additionally, the circuitry may be implemented by way of a virtual machine.

[00119] The processors may comprise general purpose processors, network processors that process data communicated over a computer network, processors of any distributed computing system, or other types of processor, including reduced instruction set computers or complex instruction set computers. Each processor may have a single or a multiple core design. Multiple core processors may integrate different processor core types on the same integrated circuit die.

[00120] The method described herein may be implemented in whole or in part by machine-readable program instructions. Machine-readable program instructions may be provided on a transitory medium, such as a transmission medium, or on a non-transitory medium, such as a storage medium. These machine-readable instructions (computer program code) may be implemented in a high level procedural or object oriented programming language. However, the program(s) may be implemented in assembly or machine language, if desired, in any case, the language may be a compiled or interpreted language, and combined with hardware implementations.

[00121] Examples of the present disclosure are applicable for use with all types of semiconductor integrated circuit (IC) chips. Examples of these IC chips include but are not limited to processors, controllers, chipset components, programmable logic arrays, memory chips, and network chips. One or more of the components described herein may be embodied as a System On Chip (SOC) device. A SOC may include, for example, one or more Central Processing Unit cores, one or more Graphics Processing Unit cores, an Input/Output interface, and a memory controller. In some examples, a SOG and its components may be provided on one or more integrated circuit die; for example, they may be packaged into a single semiconductor device.

[00122] The disclosure also extends to the following examples.

[00123] Example 1 : A method of determining (e.g. identifying) a fault relating to (e.g. a fault in or of) a printing liquid pump for a printhead, the method comprising: obtaining printing liquid consumption information relating to a consumption of printing liquid by the printhead; obtaining pump initiation information relating to initiation of a pumping action of the pump; determining the fault based on the printing liquid consumption information and the pump initiation information, the printing liquid consumption information and pump initiation information indicating that the printing liquid consumption by the printhead has reached a printing liquid consumption threshold without a corresponding initiation of pumping action of the pump; and generating an error signal (e.g. an error message or a signal to pause or terminate operation of the printhead) in response to determination of said fault.

[00124] Example 2: The method of Example 1 , wherein during fault-free operation the pump is to provide printing liquid under pressure to the printhead by way of a printing liquid supply chamber, and wherein the initiation of the pumping action relates to initiating the receipt of printing liquid by the printing supply chamber from a reservoir. [00125] Example 3: The method of Example 2, wherein the printing liquid supply chamber is to be resupplied with printing liquid from the printing supply reservoir,

[00126] Example 4: The method of Example 2 or Example 3, wherein the initiation of the pumping action is associated with a change in an internal pressure of the printing liquid supply chamber (and a change in the pressure of printing liquid therein) to initiate the receipt of printing liquid by the printing liquid supply chamber from the reservoir.

[00127] Example 5: The method of Example 4, wherein the change in pressure of the printing liquid supply chamber [and the change in the pressure of the printing liquid therein) is a decrease in pressure of the printing liquid supply chamber (and a decrease in the pressure of the printing liquid therein).

[00128] Example 6: The method of Example 4 or Example 5, wherein the change in pressure of the printing liquid supply chamber associated with the initiation of the pumping action of the pump is provided by way of a change in a volume of the printing liquid supply chamber (and the change in the pressure of the printing liquid in the printing liquid supply chamber is correspondingly provided by way of the change in the volume of the printing liquid supply chamber).

[00129] Example 7: The method of any of the preceding Examples, wherein the pump initiation information indicates whether the pumping action of the pump has been initiated.

[00130] Example 8: The method of any of the preceding Examples, wherein the printing liquid consumption information is indicative that the printing liquid consumption by the printhead has reached the printing liquid consumption threshold.

[00131] Example 9: The method of any of the preceding Examples, wherein determining the fault comprises: comparing the printing liquid consumption information and the pump initiation information.

[00132] Example 10: The method of Example 9, wherein comparing the printing liquid consumption information and the pump initiation information comprises determining whether an initiation of a pumping action of the pump has occurred (e.g. determining that an initiation of the pumping action of the pump has not occurred) when a consumption of printing liquid by the printhead is within a predetermined printing liquid consumption tolerance (e.g. a range) of the printing liquid consumption threshold.

[00133] Example 11 : The method of any of the preceding Examples, wherein the printing liquid consumption information is indicative of (e.g, based on or comprises an estimate of) a quantity of printing liquid consumed by the printhead.

[00134] Example 12: The method of Example 11 , wherein the printing liquid consumption information (e.g. the estimate of a quantity of printing liquid consumed by the printhead) is based on a monitored flow of printing liquid out of a printing liquid supply chamber by way of which, during fault-free operation, the pump is to supply printing liquid under pressure to the printhead.

[00135] Example 13: The method of Example 12. wherein the monitored flow of printing liquid out of the printing liquid supply chamber is based on a monitored flow of printing liquid along a path between the printing liquid supply chamber and the printhead.

[00136] Example 14: The method of Example 11 or Example 12, wherein the printing liquid consumption information (e.g. the estimated quantity of printing liquid consumed by the printhead) is based on a monitored quantity of printing liquid ejected from the printhead.

[00137] Example 15: The method of any of Example 14, wherein the printing liquid consumption information (e.g. the estimated quantity of printing liquid consumed by the printhead) is based on a (e.g, detected) number of printing liquid drops that have been ejected by the printhead.

[00138] Example 16: The method of any of the preceding Examples, wherein the printing liquid consumption information is based on sensor data (e.g. drop count sensor data from a drop count sensor or pressure sensor data from a pressure sensor).

[00139] Example 17: The method of any of the preceding Examples, wherein the pump initiation information is based on sensor data.

[00140] Example 18: The method of Example 17, wherein the sensor data is from a pump initiation sensor to sense a pumping action of the pump.

[00141] Example 19: The method of Example 17 or Example 18, wherein the sensor data is from a pump initiation sensor associated with the pump or a part thereof. [00142] Example 20: The method of any one of Examples 17 to 19, wherein the sensor data is from a pump initiation sensor associated with a printing liquid supply chamber by way of which, during fault-free operation, the pump is to provide printing liquid under pressure to the printhead,

[00143] Example 21 : The method of any of the preceding Examples, wherein the pump initiation information is based on at least one of: a signal to trigger initiation of the pumping action of the pump; an absence of a signal to trigger initiation of the pumping action of the pump; an indication of whether an initiation of a pumping action of the pump has occurred.

[00144] Example 22: The method of Example 21 , wherein at least one of the following is based on sensor data from a pump initiation sensor: the signal to trigger initiation of the pumping action; the absence of the signal to trigger initiation of the pumping action of the pump; the indication of whether an initiation of a pumping action of the pump has occurred.

[00145] Example 23: The method of Example 22, wherein the pump initiation sensor is associated with the pump,

[00146] Example 24: The method of Example 22, wherein the pump initiation sensor is associated with a printing liquid supply chamber by way of which, during fault-free operation, the pump is to supply printing liquid under pressure to the printhead.

[00147] Example 25: The method of any of Examples 22 to 24, wherein the signal to trigger initiation of the pumping action of the pump or the indication of whether an initiation of the pumping action of the pump has occurred is based on sensor data indicating that a volume of a printing liquid supply chamber or a volume of printing liquid in a printing liquid supply chamber has reached a predetermined lower threshold, wherein during fault-free operation the pump is to supply printing liquid under pressure to the printhead by way of the printing liquid supply chamber.

[00148] Example 26: The method of any of Examples 22 to 24, wherein the indication that the initiation of the pumping action of the pump has occurred is based on sensor data indicating that a pressure of printing liquid in the printing liquid supply chamber has changed,

[00149] Example 27: The method of Example 25 or Example 26, wherein the sensor data is from a sensor to detect an internal pressure of the printing liquid supply chamber. [00150] Example, 28: The method of Example 27, wherein the sensor is a pressure sensor.

[00151] Example 29: The method of Example 25 or Example 26, wherein the sensor data is from a sensor to detect (or determine) an internal volume of the printing liquid supply chamber.

[00152] Example, 30: The method of Example 29, wherein the sensor Is an optical sensor (e.g. a light-gate, e.g. to detect a position or a motion of a moveable part of the pump, such as a piston),

[00153] Example 31 : The method of Example 25 or Example 26, wherein the sensor data is from a sensor associated with the pump, the sensor to detect an action (or state, such as whether the pump is in a pressurising state or a depressurising state) of the pump.

[00154] Example 32: Machine readable instructions, which when executed by processing circuitry cause the processing circuitry to perform the method of any of Examples 1 to 31 .

[00155] Example 33: The machine readable instruction of Example 32 provided on a transitory or non-transitory medium.

[00156] Example 34: Apparatus for determining (e.g. identifying) a fault relating to (e.g. in or of) a printing liquid pump for a printhead, the apparatus comprising processing circuitry to: obtain printing liquid consumption information relating to a consumption of printing liquid by the printhead; obtain pump initiation information relating to initiation of a pumping action of the pump; determine the fault based on the printing liquid consumption information and the pump initiation information, the printing liquid consumption information and pump initiation information indicating that the printing liquid consumption by the printhead has reached a printing liquid consumption threshold without a corresponding initiation of pumping action of the pump; and generate an error signal (e.g. an error message or a signal to pause or terminate operation of the printhead) in response to determination of said fault.

[00157] Example 35: The apparatus of Example 35 further comprising: the printhead; the printing liquid pump,

[00158] Example 36: The apparatus of Example 34 or Example 35, further comprising a printing liquid supply chamber by way of which during fault-free operation the pump is to provide the pressurised printing liquid to the printhead, and wherein the initiation of the pumping action relates to initiating the receipt of printing liquid by the printing liquid supply chamber from a reservoir,

[00159] Example 37: The apparatus of Example 36, wherein the printing liquid supply chamber is to be resupplied with printing liquid from the reservoir,

[00160] Example 38: The apparatus of Example 37, wherein the initiation of the pumping action is associated with a change in an internal pressure of the printing liquid supply chamber to initiate the receipt of printing liquid by the printing liquid supply chamber from the reservoir.

[00161] Example 39: The apparatus of Example 38, wherein the change in pressure of printing liquid in the liquid supply chamber is a decrease in pressure of printing liquid in the printing liquid supply chamber.

[00162] Example 40: The apparatus of any of Examples 34 to 39, wherein the apparatus further comprises at least one of: at least one pump initiation sensor for detecting initiation of the pumping action; at least one printing liquid consumption sensor for detecting a printing liquid consumption of the printhead.

[00163] Example 41 : The apparatus of Example 40, wherein the printing liquid consumption sensor is to monitor the flow of printing liquid out of a printing liquid supply chamber by way of which, during fault-free operation, the pump is to provide printing liquid under pressure to the printhead.

[00164] Example 42: The apparatus of Example 41 , wherein the printing liquid consumption sensor is a flow rate sensor.

[00165] Example 43: The apparatus of Example 40 or Example 41 , wherein the printing liquid consumption sensor is a printing liquid drop count sensor.

[00166] Example 44: The apparatus of Example 40, wherein the pump initiation sensor is associated with the pump,

[00167] Example 45: The apparatus of Example 40, wherein the pump initiation sensor is associated with a printing liquid supply chamber by way of which, during fault-free operation, the pump is to provide printing liquid under pressure to the printhead. [00168] Example 46: The apparatus of Example 40, wherein the pump Initiation sensor is a pressure sensor.

[00169] Example 47: The apparatus of Example 40, wherein the pump initiation sensor is an optical sensor (e.g. a light-gate), for example to detect movement or a position of a moveable part (e.g. a piston) of the pump.

[00170] Example 48: The apparatus of Example 40, wherein the pump initiation sensor is an inertial sensor (e.g. motion or rotation sensor).

[00171] Example 43: The apparatus of Example 40, wherein the pump comprises a moveable piston to be moved by (e.g. an eccentric) cam and wherein the pump initiation sensor comprises a cam encoder.