BACKGROUND

[0001 ] The printhead of a printer is responsible for firing printing liquid at a medium. The printhead may be replaced, particularly if the print quality deteriorates. However, determining when to replace a printhead is not always straightforward.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figure 1 is a perspective view an example printer;

[0003] Figure 2 is a block diagram of the printer of Figure 1 ;

[0004] Figure 3 is a perspective view of an example printhead suitable for use with the printer of Figure 1 ;

[0005] Figure 4 is a graph illustrating the average printing time between successive thermal events for a sample number of printheads;

[0006] Figure 5 is a flowchart of an example method for determining the need to replace a printhead of the printer of Figure 1 ;

[0007] Figure 6 is a flowchart of an example method that may form part of the method of Figure 5;

[0008] Figure 7 is a flowchart of a further example method that may form part of the method of Figure 5;

[0009] Figure 8 is a flowchart of a still further example method that may form part of the method of Figure 5; [0010] Figure 9 illustrates a printer system; and

[0011] Figure 10 is a block diagram of a diagnostic server forming part of the printer system of Figure 9.

DETAILED DESCRIPTION

[0012] Figures 1 and 2 show an example printer 10 that comprises a carriage assembly 20 and a control unit 30.

[0013] The carriage assembly 20 comprises a plurality of printheads 21 carried by a carriage 22. A motor (not shown) moves the carriage 22 along a rail 23 of the printer 10 in response to signals received from the control unit 30. [0014] The control unit 30 comprises a controller 31 , a memory 32, a communications interface 33, and a user interface 34. The controller 31 is responsible for controlling the operation of the printer 10, and may execute an instruction set stored in the memory 32. in response to print data received via the communications interface 33, the controller 31 transmits control signals to the carriage assembly 20, and more particularly the printheads 21 .

[0015] Figure 3 shows an example printhead 21 suitable for use with the printer 10 of Figures 1 and 2. The printhead 21 comprises a reservoir 25, a plurality of nozzles 26, a drive circuit 27, and a temperature sensor 28. The nozzles 26 are supplied with printing liquid from the reservoir 25, which itself may be supplied from an external supply, such as a cartridge. The drive circuit 27 delivers firing pulses to the nozzles 26 in response to control signals received from the controller 31. In response to a firing signals, a nozzle 26 ejects or fires a drop of printing liquid. The temperature sensor 28 senses a temperature of the printhead 21.

[0016] When seated within the carriage 22, the drive circuit 27 and the temperature sensor 28 are eiectricaily connected to the control unit 30, and more particularly the controller 31 , via electrical contacts 29 on the printhead 21 , which mate with corresponding contacts on the carriage 22. An electrical connector (not shown) then extends between the carriage 22 and the controller unit 30. [0017] During use of the printer 10, the controller 31 may determine that an error or fault has occurred with one or more of the printheads 21. Depending on the nature of the error, printing may be suspended and reseating of a printhead 21 may be advised; this involves removing and then reinserting or reseating the printhead 21 within the carriage 22.

[0018] Reseating a printhead is disruptive and may result in significant downtime in printing. Advising the user to replace a printhead before the frequency of reseats becomes excessive may improve productivity as well as user satisfaction. However, these benefits have to be weighed against the cost of replacing the printhead. Identifying the optimal point at which the replacement cost offsets the drop in productivity associated with reseating has been difficult. [0019] The applicant has studied the occurrence of one particular type of fault or reseat event, called a thermal reseat. A thermal reseat occurs when a printhead overheats. The applicant has found that thermal reseats occur principally during the latter part of the life of a printhead. The applicant has also found that the printing time between thermal reseats decreases with each successive thermal reseat.

[0020] The results of the study are illustrated in Figure 4, which shows the average printing time between successive thermal reseats. It can be seen that the printing time between thermal reseats decreases markedly until the third thermal reseat, after which the decrease in printing time between thermal events is relatively small. There is a marked drop in the printing time between the sixth and seventh thermal reseats. However, this is unlikely to be statistically significant and is more likely due to a small sampling size. In this regard, the applicant found that, of the printheads that experienced thermal reseats, 4.5% of them experienced six of more thermal reseats. That is to say that, of those printheads that experienced a thermal reseat, most had reached end-of-life and had been removed from the printer before reaching a sixth thermal reseat.

[0021] The results of the study suggest a correlation between the occurrence of thermal reseats and the eventual end-of-life and removal of the printhead from the printer. The applicant has devised a method that exploits this finding in order to determine when to replace a printhead. [0022] Figure 5 shows an example method 100 for determining a replacement condition of a printhead. The method 100 comprises monitoring 110 thermal events associated with a printhead 21 of a printer 10, and then determining 120 that the printhead 21 merits replacing based on the thermal events. A thermal event is deemed to occur when the printhead 21 overheats. The thermal event may involve the physical reseating of the printhead 21. However, it is the overheating of the printhead 21 , rather than the subsequent reseating of the printhead 21 , that is an indicator of end-of-life.

[0023] Referring now to Figure 6, monitoring 110 thermal events may comprise sensing 111 the temperature of the printhead 21 , and determining 112 that a thermal event has occurred when the temperature of the printhead 21 is greater than a thermal threshold. Upon determining that a thermal event has occurred, the method may comprise recording 113 the occurrence of the thermal event.

[0024] Determining 120 that the printhead 21 merits replacing may be based on the total number of thermal events for that printhead 21 . For example, the method 100 may determine 121 that the printhead 21 merits replacing when the total number of thermal events is greater than a first threshold. In the example shown in Figure 4, the printing time between successive thermal events decreases markedly until the interval between third and fourth thermal events. Consequently, for this particular example, the method 100 may determine 121 that the printhead 21 merits replacing when the total of thermal events is three or more (i.e. when the total number of thermal events is greater than two).

[0025] Upon determining 120 that the printhead 21 merits replacing, the method may comprise generating 123 an indication that the printhead 21 merits replacing. The indication may take the form of, for example, an alert, which may be generated on the user interface 33 of the printer 10 or it may be transmitted to a device located remotely.

[0026] Referring now to Figure 7, determining 120 that the printhead 21 merits replacing may additionally or alternatively be based on a time interval between thermal events. For example, the method 100 may determine 122 that the printhead 21 merits replacing when the time interval is less than a second threshold. Again, using the example shown in Figure 4, the method may determine 122 that the printhead 21 merits replacing when the printing time between successive thermal events is less than, say, 20 hours.

[0027] The time interval may be that between two successive thermal events. However, a thermal event may arise for reasons other than an aging or defective printhead. By way of example, a thermal event may arise following a prolonged and continuous period of printing. A more reliable method may therefore be achieved by using the time interval between more than two thermal events.

[0028] The time interval may be the printing time between thermal events. Printing time provides a relatively direct measure of the efficacy or productivity of a printer. Nevertheless, an alternative metric may be used for the time interval between thermal events. For example, the time interval may be the actual elapsed time between thermal events. Although this may be a less reliable measure of the efficacy of the printer, there may nevertheless be a correlation between printing time and actual elapsed time for each particular user. For example, if a user typically prints for five hours each day, and the elapsed time between thermal events is four days, this may be said to translate to a printing time of around 20 hours between thermal events. Accordingly, for this particular user, the second threshold may be set to 20 hours (when using printing time as the time interval) or four days (when using elapsed time as the time interval). When the determination 120 is based on the elapsed time between thermal events, the second threshold may be unique to each user and may be based on printing behavior. Using elapsed time rather than printing time may provide a simpler method of determining the time interval between thermal events. For example, the method 100 may comprise recording 113 the date and time of each thermal event, without the need to continually monitor and record printing usage. [0029] The method 100 may use more than one type of time interval in order to determine 120 if the printhead 21 merits replacing. For example, the method may use both the printing time and the elapsed time between thermal events. The method may then determine that the printhead 21 merits replacing when one or both of these time intervals meets a criterion. By way of example, the method may determine that the printhead merits replacing when either the printing time is less than 20 hours or when the elapsed time is less than four days. Alternatively, the method may determine that printhead merits replacing when both the printing time is less than 20 hours and the elapsed time is less than four days.

[0030] In the examples described above, the method 100 employs a static rule when determining 120 if the printhead 21 merits replacing. For example, the method may determine 120 that the printhead 21 merits replacing when the total number of thermal events is greater than a first threshold and/or when the time interval between thermal events is less than a second threshold. In the examples described above, both the first threshold and the second threshold are fixed. The method 100 may, however, employ a dynamic rule when determining 120 if the printhead 21 merits replacing. In this instance, one or both of the thresholds would then vary according to some other parameter.

[0031] The occurrence of thermal events is likely to have a bigger impact on a user who operates the printer more frequently. For example, a thermal event every 20 hours is likely to have a bigger impact on a user that operates on a 24- hour basis versus a user who operates just one hour a day. Accordingly, the method 100 may determine 120 that the printhead merits replacing based additionally on past usage of the printhead and/or printer. Where the method 100 uses a threshold in order to determine 120 if the printhead merits replacing, the method may define the threshold based on the usage of the printhead. So, in the examples described above, the method 100 may define the first threshold and/or the second threshold based on past usage of the printhead and/or printer. More particularly, for a printhead or printer that has been used more frequently, a lower first threshold and/or a lower second threshold may be used.

[0032] The occurrence of thermal events and their correlation with the end- of-life of a printhead may differ for different types of printhead and/or different types of printer. Accordingly, the method 100 may determine 120 that the printhead merits replacing based additionally on the identity or the type of printhead and/or printer. [0033] As shown in Figure 8, the method 100 may use thermal event data from a further printer(s) in order to define the rules for determining if the printhead merits replacing. More particularly, the method 100 may comprise monitoring 130 thermal events associated with a printhead of a further printer, and determining 140 that the printhead 21 of the printer 10 merits replacing based on the thermal events of the printer 10 and also on the thermal events of the further printer. Thermal events that have already occurred with one printer may therefore be used to inform the rules for determining the printhead replacement of another printer. As a result, the method is able to adapt more quickly to change. The method may use thermal event data and/or usage data from a large number of printers. As a result, the rules for determining if a printhead merits replacing may be better optimized for each printer, printhead and/or user.

[0034] The example methods described above may be performed wholly or partly by the printer 10 of Figures 1 and 2. For example, the controller 31 may determine that a thermal event has occurred when the temperature of the printhead 21 , as sensed by the temperature sensor 28, is greater than a thermal threshold. Upon determining that a thermal event has occurred, the controller 31 may record data relating to the thermal event (e.g. date and time) to the memory 32. The controller 31 may then analyze the thermal event data in order to determine if the printhead 21 merits replacing. For example, the controller 31 may determine that a printhead merits replacing based on the time interval between thermal events and/or the total number of thermal events. Upon determining that a printhead 21 merits replacing, the controller 31 may generate an alert or other indication on the user interface 33, advising the user that a printhead merits replacing.

[0035] The example methods may in part be performed by a diagnostic system located remotely from the printer. Figure 9 shows an example printer system 40 that comprises a plurality of printers 10 connected remotely to a diagnostic system 50. The printers 10 send diagnostic data 60 to the diagnostic system 50 via the communications interfaces 33. The diagnostic data 60 comprises thermal event data 61 (i.e. data relating to thermal events associated with printheads of the printer), and may comprise additional data, such as usage data 62 (i.e. data relating to past printing usage of the printer) or identifier data 63 (i.e. data that identifies the type of printhead and/or printer). The diagnostic data 60 may be sent to the diagnostic system 50 at regular intervals or in response to a particular trigger, such as the occurrence of fault or error (e.g. a thermal event).

[0036] Figure 10 shows an example diagnostic system 50 suitable for use with the printer system 40 of Figure 9. The diagnostic system 50 comprises a processor 51 , a memory 52 and a communications interface 53. The processor 51 is responsible for controlling the operation of the diagnostic system 50 and may execute an instruction set stored in the memory 52.

[0037] During operation, the communications interface 53 receives diagnostic data 60 from the printers 10, which may then be stored in the memory 52. The processor 51 then analyzes the diagnostic data 60. More particularly, the processor 51 analyzes the thermal event data 61 within the diagnostic data 60 in order to determine if a printhead of a printer merits replacing. The processor 51 may additionally analyze the usage data 62 and/or the identifier data 63 in order to determine if a printhead merits replacing, as discussed above. Upon determining that a printhead merits replacing, the processor 51 may generate an indication that the printhead merits replacing. For example, the processor 51 may generate an alert that is displayed on a user interface (not shown) of the diagnostic system 50. A service engineer operating the diagnostic system 50 is then notified and is able to take appropriate action. The processor 51 may additionally or alternatively generate an indication 70 that is transmitted to the relevant printer via the communication interface 53. The controller 31 of the printer 10, in response to receiving the indication 70 from the diagnostic system 50, may generate an alert or other warning on the user display 30.

[0038] With the printer system of Figure 9, the printers 10 are responsible for monitoring 110 thermal events. Diagnostic data, which includes data relating to the thermal events, are then transmitted to the diagnostic system 50, which is then responsible for determining 120 the need to replace a printhead based on the diagnostic data. The division of responsibilities in this way enables a relatively simple or dumb controller 31 to be used in the printers 10. Additionally, for existing printers that already transmit diagnostic data, the methods described above may be employed without the need to modify the printers.

[0039] By employing a diagnostic system 50 that collates data from a number of printers, the rules for determining if a printhead merits replacing may be better optimized. For example, the diagnostic system 50 may employ rules that are unique to each printer, printhead and/or user. Additionally, the diagnostic system 50 may devise rules that are adjusted or refined based on the behavior (e.g. occurrence of the thermal events, print usage) of other printers. As a result, the diagnostic system may devise rules that are better able to adapt to change. [0040] In the example printer system 40 described above, the diagnostic system 50 is responsible for determining if a printhead merits replacing. In an alternative printer system 40, the printers 10 may be responsible for determining if the printhead merits replacing. That is to say that the printer 10 rather than the diagnostic system 50 is responsible for analyzing the thermal event data in order to determine if a printhead merits replacing. The printer 10 continues to send diagnostic data to the diagnostic system 50, which the diagnostic system 50 then analyzes in order to define the rules for determining if a printhead merits replacing. If the diagnostic system 50 determines that the rules employed by a particular printer need revising or updating, the diagnostic system 50 may send revised rules to the printer 10. The revised rules may be sent as rule data, and may comprise one or more criterion (e.g. the first threshold and/or the second threshold), which the printer 10 then uses to determine if a printhead merits replacing. The revised rules or rule data may be downloaded by the printer 10 as a firmware update. With this alternative printer system 40, the diagnostic system 50 continues to collate data in order to better optimize the rules. However, the printers 10 are no longer reliant on the diagnostic system 50 for determining if a printhead merits replacing. Accordingly, if the connection with the diagnostic system 50 is broken or otherwise unavailable, the printer 10 is nevertheless able to advise a user if a printhead merits replacing. Additionally, since the diagnostic system 50 is no longer responsible for determining if a printhead merits replacing, the diagnostic data may be sent from the printers 10 less frequently, thus reducing bandwidth use. [0041] As noted above, the applicant studied the occurrence of thermal reseats in a large number of printers, and observed a correlation between the occurrence or frequency of thermal reseats and the eventual end-of-life and removal of a printhead. The examples described above (i.e. the methods, printers and diagnostic systems) exploit the findings of the study in order to determine when a printhead merits replacing. The study was performed on a particular model of inkjet printer having thermal printheads. However, the examples described above may be used to determine the replacement need of a printhead in alternative models and/or types of printer, particularly but not exclusively those printers having thermal printheads.

[0042] The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with any features of any other of the examples, or any combination of any other of the examples.