Continuous inkjet printer and method of its operation

Abstract

A method of operating a continuous inkjet (CIJ) printer (100, Fig.1) comprises determining that a predetermined event has occurred S2. Following the determination of the predetermined event, displayin

Description

The present invention relates to inkjet printing and more particularly to a continuous ink jet printer and a method of operating the same. More particularly, but not exclusively, the present invention relates to the use of a backup battery to support the operation of continuous inkjet printer. In inkjet printing systems the print is made up of individual droplets of ink generated at a nozzle and propelled towards a substrate. There are two principal inkjet printing systems: drop on demand where ink droplets for printing are generated as and when required; and continuous inkjet printing in which droplets are continuously produced and only selected ones are directed towards the substrate, the others being recirculated to an ink supply. Continuous ink jet printers, such as electrostatic deflection continuous ink jet printers, are a form of industrial printer commonly used to apply markings to products passing along a production line. For example, packaged products may be marked with a batch code or a date indicating the date of manufacture, or a date of expiry. Such printers may be operated for batch production or in a continuously operating environment, where production continues at all times. Such printers may be required to run for extended periods of time with minimal interruption to printing. Continuous inkjet printers supply pressurised ink to a print head drop generator (or ink gun) where a continuous stream of ink emanating from a nozzle is broken up into individual regular drops by, for example, an oscillating piezoelectric element. The drops are directed past a charge electrode where they are selectively and separately given a predetermined charge before passing through a transverse electric field provided between a pair of deflection plates. Each charged drop is deflected by the field by an amount that is dependent on its charge magnitude before impinging on the substrate whereas the uncharged drops proceed without deflection and are collected at a gutter from where they are recirculated to the ink supply for reuse. The charged drops bypass the gutter and hit the substrate at a position determined by the charge on the drop and the position of the substrate relative to the print head. Typically the substrate is moved relative to the print head in one direction and the drops are deflected in a direction generally perpendicular thereto, although the deflection plates may be oriented at an inclination to the perpendicular to compensate for the speed of the substrate (the movement of the substrate relative to the print head between drops arriving means that a line of drops would otherwise not quite extend perpendicularly to the direction of movement of the substrate). In continuous inkjet printing a character is conventionally printed from a matrix comprising a regular array of potential drop positions. Each matrix comprises a plurality of columns (strokes), each being defined by a line comprising a plurality of potential drop positions (e.g. seven) determined by the charge applied to the drops. Thus each usable drop is charged according to its intended position in the stroke. If a particular drop is not to be used then the drop is not charged and it is captured at the gutter for recirculation. This cycle repeats for all strokes in a matrix and then starts again for the next character matrix. Ink is delivered under pressure to the print head by an ink supply system that is generally housed within a sealed compartment of a cabinet that includes a separate compartment for control circuitry and a user interface panel. The system includes a main pump that draws the ink from a tank of the ink supply system via a filter and delivers it under pressure to the print head. As ink is consumed the tank is refilled from a replaceable ink cartridge that is releasably connected to the tank by a supply conduit. The ink is fed from the tank via a flexible delivery conduit to the print head. The unused ink drops captured by the gutter are recirculated to the tank via a return conduit by a source of low pressure. The flow of ink in each of the conduits is generally controlled by solenoid valves and / or other like components. As the ink circulates through the system, there is a tendency for it to thicken as a result of solvent evaporation, particularly in relation to the recirculated ink that has been exposed to air in its passage between the nozzle and the gutter, and air that is vented from the ink system to maintain equilibrium pressure. In order to compensate for this, “make-up” solvent is added to the ink as required from a replaceable solvent cartridge so as to maintain the ink viscosity within desired limits. This solvent may also be used for flushing components of the print head, such as the nozzle and the gutter, in a cleaning cycle. Therefore, a typical continuous inkjet printer has both a replaceable ink cartridge and a replaceable solvent cartridge. Continuous inkjet printers are often configured to operate for extended periods of time. When operation is interrupted in an intentional manner (e.g. at the end of a shift) a jet shutdown process is preferably performed, so as to reduce the likelihood of ink clogging components of the printer upon resumption. However, when power is abruptly removed, it may not be possible to perform a proper jet shutdown process. It is an object of the present invention, among others, to provide a continuous ink jet printer which obviates or mitigates one or more problems associated with known continuous inkjet printers, whether described herein, or otherwise. According to a first aspect of the present disclosure there is provided a method of operating a continuous inkjet printer comprising: causing a jet of ink to be ejected from a nozzle of a printhead; and receiving at least a portion of the jet of ink in a gutter. The method further comprises: determining that a predetermined event has occurred; and following the determination of the predetermined event, generating a prompt to a user of the printer. The method further comprises, based on a first condition being satisfied following the prompt being generated, performing a first action; or based on a second condition being satisfied following the prompt being generated, performing a second action. According to a second aspect of the present disclosure there is provided a method of operating a continuous inkjet printer comprising: causing a jet of ink to be ejected from a nozzle of a printhead; and receiving at least a portion of the jet of ink in a gutter. The method further comprises: determining that a predetermined event has occurred; following the determination of the predetermined event, displaying a prompt to a user of the printer, the prompt including a countdown timer; and based upon a first user response to the prompt, performing a first action; or based upon the expiry of the countdown timer, performing a second action. The following explanations and optional features may apply equally to either of the first and second aspects described above. Certain events may occur during operation of a printer that could result in a safety issue, and could therefore require immediate action to cease printing, so as to prevent escalation. On the other hand, similar events may also be expected, and may not require such drastic action (i.e. immediate stopping of a jet). When such events are detected, rather than acting immediately (and risking interrupting production or possibly causing re-start difficulties) it may be advantageous to prompt a user to confirm which course of action should be followed, while also providing a default option in case a user is not able to respond. This permits flexible yet safety conscious operation and reduces the risk of unnecessary printing disruption. The method may further comprise determining whether or not a first user response has been received prior to the expiry of the countdown time. Performing the first action based upon a first user response to the prompt may comprise performing the first action based on a determination that the first user response has been received prior to the expiry of the countdown timer. Performing the second action based upon the expiry of the countdown timer may comprise performing the second action based on a determination that the first user response has not been received prior to the expiry of the countdown timer. The generation of a user prompt and associated countdown timer following the determination of the occurrence of the predetermined event (e.g. a loss of power) can be effective to guide a user to perform certain steps following the predetermined event, so as to enable operation of the printer to continue, to the extent possible, in a safe manner, while also minimising operational inconvenience (e.g. by avoiding an unnecessary shutdown and / or unnecessary immediate jet stop). Indeed, by displaying the user prompt, a user can be alerted to a technical status of the machine (e.g. an absence of mains power) that may otherwise have been unknown to the user, while also providing an indication of a technical status of the battery (e.g. a charge level, and / or associated timer duration). By providing this technical information regarding the operational status of the printer to a user, they can make time-critical decisions regarding the continued operation of the machine, and provide input in response to the technical information to control the printer, in a way that is safe and operationally efficient. The first action may comprise an immediate ink jet stop. The second action may not comprise an immediate inkjet stop. Performing an immediate ink jet stop may comprise immediately stopping a supply of power to an ink pump configured to deliver ink to a printhead, thereby causing the ink jet to stop abruptly. Performing an immediate ink jet stop may comprise immediately stopping a supply of power to a valve configured to allow ink to be delivered to a printhead. The second action may comprise performing a normal ink jet stop, the normal ink jet stop comprising stopping the inkjet and performing a printhead shutdown process. Performing the printhead shutdown process may comprise: causing a droplet generator of the printer to stop a jet of ink from being generated; and after causing the droplet generator to stop the jet of ink from being generated, causing solvent to flow to the droplet generator. Performing the printhead shutdown process may further comprise causing the solvent to flow through at least a portion of the droplet generator. The printhead shutdown process may further comprise causing the solvent to be ejected from a nozzle of the droplet generator and captured by a gutter of the printer and returned to an ink supply system of the printer via a gutter line. By ejecting a jet of solvent from the nozzle, it is possible to flush residual ink from the nozzle, and to reduce the risk that any residual ink will dry within the nozzle during a period of inactivity, which may hinder subsequent printing. The printhead shutdown process may further comprise causing the solvent to flow through the droplet generator and return to the ink supply system of the printer via a purge line. By causing solvent to flow through the droplet generator, it is possible to flush residual ink from the droplet generator, and to reduce the risk that any residual ink will dry within the droplet generator during a period of inactivity, which may hinder subsequent printing. One or more of the processes associated with the printhead shutdown process may be performed for a predetermined time period. The predetermined flushing period may be determined based upon one or more characteristics of the printer. The one or more characteristics of the printer may comprise an ink type. In general terms it will be understood that a printhead shutdown process refers to a sequence of steps or processes that are performed by a printer when it is intended to stop an ink jet in a controlled way, thereby minimising the risk of problems occurring when an ink jet is subsequently re-started at a future time. The printhead shutdown process may include causing a jet of solvent to be ejected from the droplet generator. The jet of solvent may be received in the gutter. The jet of solvent may be caused to run for a predetermined jetting period of time. Additionally, or alternatively, the printhead shutdown process may include a solvent flush process, which comprises causing a solvent to be supplied to the droplet generator and returned to the printer without having been ejected from the nozzle. The solvent may be returned to the ink system via the purge line. The solvent flush process may be performed for a predetermined flushing period of time. The countdown timer may be configured to countdown from an initial countdown timer value, and to display a remaining time during the countdown. The countdown timer may commence counting down from the initial countdown timer value when the prompt is displayed. The predetermined event may comprise a power supply disruption event. The power supply disruption event may comprise a loss of mains power to the continuous inkjet printer. The power supply disruption event may comprise a persistent loss of mains power to the continuous inkjet printer. In certain regions, brief interruptions to power supplies are a common occurrence. As such, responding to only those power supply disruptions that are persistent avoids user inconvenience by prompting a user to take action only when it is appropriate. The persistent loss of mains power may comprises a loss of mains power for longer than a minimum power loss period. The minimum power loss period may be configurable by a user. The minimum power loss period may be a period may be less than 10 seconds. Preferably the minimum power loss period may be around 5 seconds, or less. A relatively short minimum power loss period of around 5 seconds is intended to distinguish between temporary interruptions and persistent interruptions. Generating the prompt to a user of the printer may comprise displaying a screen on a display associated with the printer. The display associated with the printer comprises a printer user interface configure to allow a user to control operations of the printer. The printer may comprise a main body housing components of an ink supply system, and a printhead connected to the main body by an umbilical. The display associated with the printer may be provided on the main body of the printer. The screen may comprise a countdown timer. Generating the prompt may comprise generating a first display feature associated with the first action. The first display feature may comprise a first button. The display feature may indicate that a user should take a particular action (e.g. pressing the first button, or pressing a button that is not displayed on the screen) to cause the first action to be selected. The first condition being satisfied may comprise receiving a first user response. Receiving the first user response may comprise receiving a user response associated with the first display feature. To provide a user response associated with the first display feature a user may press a first button displayed on the screen. The first button may comprise the first display feature. The first condition being satisfied may comprise a user pressing a first button. The first button may be a physical button or a virtual button. The second condition being satisfied may comprise not receiving the first user response. The second condition being satisfied may comprise a user taking no action, or a user taking a different action. The second condition being satisfied may comprise not receiving the first user response within a predetermined time period. The predetermined time period may commence when the prompt is generated. The predetermined time period may correspond to an initial countdown timer value. The predetermined time period may comprise a time of greater than 60 seconds. The predetermined time period may comprise a time of less than 10 minutes. The predetermined time period may be around 3 minutes. The predetermined time period or initial countdown timer value, may be based upon one or more characteristics of the printer and / or one or more configuration settings. The one or more characteristics of the printer may comprise a charge level of the printer battery. The one or more characteristics of the printer may comprise a type of ink used by the printer for printing. The method may comprise determining that the first user response has not been received if no first user response has been received when the countdown timer reaches zero. By providing a countdown timer it is possible to allow a preferred course of action to be selected, while also ensuring that if a user does not respond a proper shutdown process is initiated while sufficient battery power is available. If the first user response is received before the countdown timer reaches zero, the first condition is satisfied, and the first action may be performed (e.g. an immediate jet stop may be performed). Generating the prompt may comprise generating a second display feature associated with the second action. The second display feature may comprise a second button. The second button may indicate that a user should take a particular action to select the second action. The second condition being satisfied may comprise receiving a second user response. Receiving the second user response may comprise receiving a user response associated with the second display feature. The second condition being satisfied may comprise receiving the second user response within a predetermined time period, or determining that the first user response has not been received within the predetermined time period. The method may further comprise performing the second action based upon a second user response to the prompt. Performing the second action based upon the second user response to the prompt may comprise performing the second action based on a determination that the second user response has been received prior to the expiry of the countdown timer. Generating the prompt may comprise generating a third display feature associated with a third action. The method may further comprise performing the third action based upon receiving a third user response to the prompt. Receiving the third user response may comprise receiving a user response associated with the third display feature. Performing the third action based upon receiving the third user response to the prompt may comprise performing the third action based on a determination that the third user response has been received prior to the expiry of the countdown timer. The third display feature may comprise a move printer button. The third action may comprise adjusting a value of the countdown timer. Adjusting a value of the countdown timer may comprise adjusting (e.g. increasing) a remaining time of the countdown timer. For example, by selecting a move printer action, the remaining value shown by the countdown timer can be increased so as to allow for a longer period during which to move the printer. The increased battery supported run-duration can be enabled by not preserving sufficient battery power to perform an extended controlled jet shutdown process. Such a course of action may be acceptable, since even if the battery does run out before the printer has been re-connected to mains power in a new location, it is expected that printing operations will resume shortly, rather than there being an extended shutdown period (during which ink could dry within the nozzle). Performing the third action may further comprise selecting an alternative printhead shutdown process. Selecting an alternative printhead shutdown process may comprise selecting a second printhead shutdown process having fewer steps, and / or a shorter duration than a first printhead shutdown process. The first printhead shutdown process may be a default or normal printhead shutdown process. The continuous inkjet printer may comprise a battery. The method may further comprise: responsive to determining that the predetermined event has occurred, supplying, by the battery, electrical power to components of the printer to cause the jet of ink to be ejected from the nozzle of the printhead. That is, when mains power is interrupted, printing operations can be continued by using battery power. Alternatively, if the printer is in a jet-running, but not printing, state, the printer can be maintained in the jet-running state for a period of time by relying on battery power. The battery may be configured to supply electrical power to components of the printer to cause the jet of ink to be ejected from the nozzle for the duration of the countdown timer. The battery may be configured to supply electrical power to an ink pump. The battery may be configured to supply electrical power to a controller of the printer, so as to allow the controller to control operations of the printer. The battery may be configured to supply electrical power to a display of the printer. Performing the first action may comprise causing the battery not to supply electrical power to components of the printer to cause a jet of ink to be ejected. That is, if it is determined that a power supply disruption event has occurred, and the first condition is satisfied (e.g. a first user response has been received), the printer can immediately enter a powered down state, with no jet running. Performing an immediate jet stop comprises causing the battery not to supply electrical power to components of the printer to perform a printhead shutdown process. Performing the second action may comprise causing the battery to supply electrical power to components of the printer to cause a printhead shutdown process to be performed. If it is determined that a predetermined event, such as a power supply disruption event, has occurred, and the second condition is satisfied (e.g. the time has expired, or the second user response has been received), the printer can perform the printhead shutdown process by using power supplied by the battery. Such operation can prevent a power disruption event from resulting in ink drying within the printing nozzle, and causing subsequent printing disruption upon resumption of normal power conditions. During the printhead shutdown process, the battery may be configured to supply electrical power to a pump configured to supply solvent to the printhead. The battery may be configured to supply electrical power to a controller of the printer, so as to allow the controller to control operations of the printer. The battery may be configured to supply electrical power to a display of the printer. If the printer is not configured to generate a jet of ink when it is determined that the predetermined event has occurred (e.g. not in a jet-running state), the battery may be caused not to supply electrical power to components of the printer. The predetermined event may comprise a user selection of a predetermined printer operating mode. The predetermined printer operating mode may comprise a move printer mode, which is configured to operate the printer in a jet-running state for a short period of time while the printer is moved between printing locations. By selecting such a mode, when power is subsequently lost (due to an intentional disconnection), the countdown timer may be initiated. According to a third aspect of the present disclosure there is provided a method of operating a continuous inkjet printer comprising: receiving power from an external power supply provided externally from the printer; initiating a software update process while operating components of the printer using power supplied by the external power supply; determining that a power supply disruption event has occurred, such that the printer is no longer receiving power from the external power supply; and continuing to perform the software update process while operating components of the printer using power supplied by an internal power supply provided within the printer. By providing a backup power supply that is configured to provide power in the event of a power supply disruption event it is possible to continue a software update that was initiated before the power supply disruption event, thereby reducing the risk of a malfunction caused by an incomplete software update. That is, if a power loss event occurred while the software update was being performed, critical software files may become corrupted, which can result in a loss of functionality. By using the back-up power supply (i.e. the internal power supply, or battery), the software update can be completed without issue, providing a more reliable system, even where power supply integrity cannot be guaranteed. Operating components of the printer using power supplied by an internal power supply provided within the printer may comprise: supplying power to at least a controller of the printer, so as to cause the controller to continue to perform the software update. Operating components of the printer using power supplied by an internal power supply provided within the printer may comprise supplying power to a display of the printer. The power supply disruption event may comprise a persistent loss of mains power to the continuous inkjet printer. The method may further comprise, prior to initiating the software update process, performing an inkjet stop process. It may be considered to be unsafe to perform a software update process on the printer while the inkjet is running. The method may further comprise: after determining that a power supply disruption event has occurred, activating the internal power supply provided within the printer. The method may further comprise, after determining that the software update has been completed, deactivating the internal power supply. The internal power supply may comprise a battery and a power convertor configured to convert a voltage received from the battery to a different voltage required for supply to the components of the printer. The features described in the context of the third aspect may apply equally to either of the first and second aspects described above. Similarly, the third aspect may be combined with either of the first and second aspects described above. The continuous inkjet printer may comprise: an ink supply system; a droplet generator configured to receive ink from the ink supply system and to generate a jet of ink for printing; a gutter configured to receive parts of the jet that are not required for printing; and a gutter line connected to the gutter and configured to return the parts of the jet that are not required for printing to the ink supply system. According to a fourth aspect of the present disclosure there is provided a continuous ink jet printer comprising: an ink supply system; a droplet generator configured to receive ink from the ink supply system and to generate a jet of ink for printing; a gutter configured to receive parts of the jet that are not required for printing; and a gutter line connected to the gutter and configured to return the parts of the jet that are not required for printing to the ink supply system; wherein the printer is configured to perform a method according to any of the first to third aspects. Optional features described above in the context of the first to third aspects may be combined with the fourth aspect. Similarly, features described below in the context of the fourth aspect, may be combined with the first to third aspects described above. The continuous inkjet printer may further comprise a controller and a user interface. The controller may be configured to: determine that the predetermined event has occurred; and cause the user interface to display a predetermined screen based upon the determination that the predetermined event has occurred. The user interface may comprise a touch-screen user interface. The continuous inkjet printer may further comprise a battery. The battery may be configured to supply electrical power to components of the printer in the event of disruption to a mains power supply. The battery may be part of an internal power supply, comprising the battery and a power convertor. The continuous inkjet printer may further comprise a battery system, the battery system comprising: the battery; a battery charger configured to charge the battery; a power convertor configured to receive power from the battery and provide power to components of the printer; and a battery controller. The battery controller may be configured to provide control signals to control the battery charger and the power convertor. The battery system may be provided within a housing of the continuous inkjet printer. The power convertor may be configured to provide a DC supply voltage of around 22 V to a printer power supply rail. The battery controller may be configured to control the battery charger to charge the battery when one or more battery charging conditions are satisfied. The one or more battery charging conditions may comprise a one or more temperature based charging conditions. For example, the battery controller may be configured to cause the battery charger to charge the battery when the temperature exceeds a minimum charging temperature, and / or is less than a maximum charging temperature. The battery controller may be configured to monitor a temperature of the printer and / or battery, and to control the battery system based upon the monitored temperature. The battery controller may be configured to monitor a voltage battery, and to control the battery system based upon the monitored voltage. The battery controller may be configured to monitor charge and discharge cycles of the battery, and to control the battery system based upon the monitored charge and discharge cycles. Monitoring in this way allows battery health to be monitored, and, if appropriate, alerts to be generated for a user, and / or operation of the battery disabled. The continuous inkjet printer may comprise a switch configured to allow the printer to disconnect components of the printer from the printer power supply rail. The switch may be configured to allow the printer to disconnect components of the ink supply system, and / or the printer controller, and / or the components printhead from the printer power supply rail. The continuous inkjet printer may further comprise a power supply unit, configured to receive mains power from an external power supply network, and to provide power to components of the printer via a printer power supply rail. The power supply unit may be configured to receive AC power from the external power supply network, and to provide a DC supply voltage to the printer power supply rail. The power supply unit may be configured to provide a DC supply voltage of around 24 V to the printer power supply rail. An output of the power supply unit and an output of the power convertor may be operably coupled to a shared capacitance. Each of the power supply unit and the power convertor may include a switched mode power supply. The output of each of these power supplies may be somewhat unstable and / or noisy in terms of voltage. Therefore, each of these power supplies may usually include a separate capacitor, or arrangement of capacitors, configured to smooth the output to meet a desired voltage ripple characteristic. By sharing a capacitance between these two power supplies, it is possible to reduce the overall number of components included in the system, thereby reducing cost and the space required for installation of the backup power supply. The shared capacitance may be provided in the power supply unit. By the output of the power supply unit and the output of the power convertor being operably coupled to the common capacitance, it is meant that both outputs are connected to the capacitance in such a way that the capacitance can effectively smooth the output voltage provided by each of the power supply unit and the power convertor. It will be understood, for example, that if each of the outputs was connected to the printer supply rail via a respective diode, a capacitance provided within the PSU would be effectively prevented from smoothing an output voltage of the power convertor, and vice versa. The output of the power supply unit and the output of the power convertor may be connected directly to the printer power supply rail. The output of the power supply unit and the output of the power convertor may be connected directly to the printer power supply rail without passing through a diode. The battery controller may comprise a comparator configured to compare a voltage of a printer power supply rail with a reference voltage. The battery controller may be configured to control the power convertor based upon the output of the comparator. The printer may be configured to determine that the predetermined event has occurred based upon the output of the comparator. The reference voltage may be lower than a normal output voltage of the power supply unit. For example, where a normal output voltage of the power supply unit is 24 V DC, the reference voltage may be 23 V DC. The battery controller may be configured to enable the power convertor when the voltage of the printer power supply rail drops below the reference voltage. As such, when the voltage of the printer power supply rail drops below the reference voltage this may be indicative of a power supply disruption event. The battery controller may be configured to control the battery charger based upon the output of the comparator. The battery controller may be configured to disable the battery charger when the voltage of the printer power supply rail drops below the reference voltage. Operating the charger in this way can prevent the charger attempting to charge the battery using power supplied by the battery itself. The battery controller may be connected to a controller of the ink jet printer by a communication interface. The battery controller may be configured to provide a power supply status signal to the controller of the inkjet printer. The battery controller may be configured to provide a power supply status signal to the controller of the ink jet printer based upon an output of the comparator. The continuous inkjet printer may further comprise a printhead operable to receive ink from the ink supply system for printing. The printhead may comprise the droplet generator and the gutter. The jet of ink may be a modulated jet of ink configured to form a stream of individual droplets. The continuous inkjet printer may be an electrostatic deflection continuous inkjet printer configured to selectively charge ink droplets within the ink jet and to deflect charged droplets in an electrostatic field. The continuous inkjet printer may further comprise at least one charge electrode configured to induce charge on ink droplets. The continuous inkjet printer may further comprise at least one deflection electrode configured to generate the electrostatic field. The printer may be configured to deactivate a high voltage supply to the deflection electrode in certain circumstances. For example, if a move printer button is pressed, the high voltage supply to the deflection electrode may be deactivated. It will be appreciated that while it may be advantageous to maintain a high voltage supply to the deflection electrode during printing operations powered by a battery, it is unlikely that printing operations will be performed during a printer move operation. As such, it may be preferred (and possible considered safer) to deactivate the high voltage supply during a printer movement. The ink supply system may comprise an ink feed tank configured to store ink for printing and an ink pump configured to pump ink from the ink feed tank to the printhead for printing. The ink supply system may further comprise a pump configured to pump solvent to the printhead during a printhead shutdown process. The battery may be configured to provide power to the pump to perform the printhead shutdown process in the event of a power supply disruption event. The ink supply system may further comprise a solvent supply configured to store solvent for cleaning the printhead and for maintaining a viscosity of the ink within the ink feed tank. The solvent supply may comprise a solvent supply cartridge, or may be provided by a separate solvent reservoir in addition to a solvent supply cartridge. The printer may further comprise one or more valves configured allow solvent to be supplied to the printhead during a printhead shutdown process. The battery may be configured to provide power to the one or more valves to perform the printhead shutdown process in the event of a power supply disruption event. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 schematically illustrates a continuous inkjet printer; Figure 2 schematically illustrates a fluid system of the continuous inkjet printer of Figure 1; Figure 3 schematically illustrates a control system of the continuous inkjet printer of Figure 1; Figure 4 schematically illustrates a power supply system of the continuous inkjet printer of Figure 1; Figure 5 illustrates a display screen of the continuous inkjet printer of Figure 1; Figure 6 schematically illustrates a method of operating continuous inkjet printer of Figure 1; and Figure 7 schematically illustrates an alternative method of operating continuous inkjet printer of Figure 1. In the figures, like parts are denoted by like reference numerals. It will be appreciated that the drawings are for illustration purposes only and may not be drawn to scale. Figure 1 schematically illustrates an inkjet printer 100. The printer 100 comprises a printer main body 103 connected to printhead 105 by an umbilical cable 107. The printer main body 103 may comprise the ink supply system and a printer controller, and the printer main body 103 may have an interface 109 (e.g. a touchscreen display) for use by an operator. The printhead 105 is arranged to print on a substrate, such as the surface of an item 111 moving along a production line 113. Referring now to figure 2, a simplified schematic diagram of a fluid system for the ink jet printer of Figure 1 is shown. The inkjet printer 100 comprises an ink supply system 115 which is contained within the main printer body 103. The ink supply system comprises an ink feed tank 117 (which may also be referred to as an ink supply tank) configured to store ink and supply ink along an ink pickup line 119. The ink is drawn from the ink feed tank 117 by a pump 121 with ink also passing through a filter 123 to remove any particles contained within the ink feed tank. A damper 125 is provided after the pump to reduce fluctuations in ink pressure within the ink supply. A valve 127 is provided after the damper 125. An ink supply line 128 is configured to carry ink from the ink supply system 115, along the umbilical 107, to the print head 105. The ink supply line 128 is connected to the ink pickup line 119 via the pump 121, damper 125 and valve 127. The ink supply line 128 and the ink pickup line 119 cooperate to transport ink from the ink feed tank 117 to the print head 105, and may collectively be referred to as the ink supply line 128. The valve 127 is configured to control the ink supply to the print head 105. A pressure sensor 129 is connected to the ink pickup line 119 and is configured to monitor the pressure at the outlet of the pump 121. The pump 121 may be operated as a constant pressure pump (i.e. the pump is controlled to maintain a constant output pressure). The ink supply system 115 also includes an ink cartridge connection 131 which may be connected to an associated ink cartridge 133 and a solvent cartridge connection 135 which may be connected to an associated solvent cartridge 137. The ink cartridge 133 and ink cartridge connection 131 are connected to an ink refill line 141, allowing ink to be drawn through a valve 143 by a pump 145 (e.g. a transfer pump), and fed to the ink feed tank 117. Similarly, the solvent cartridge 137 and the solvent cartridge connection 135 are connected to a solvent refill line 149, allowing solvent to be fed via a valve 151 to the ink feed tank 117 under the influence of the pump 145. Each of the valves 143, 151 can be operated independently allowing either ink or solvent to be supplied to the ink feed tank independently of one another under the control of the pump 145. In some configurations, an ink reservoir and / or a solvent reservoir (not shown) may be provided to temporarily store ink or solvent between the cartridge 133, 137 and respective refill line 141, 149. Where a separate ink reservoir and / or a solvent reservoir is included, one or more additional pumps (or pump connections) may be required to permit ink and / or solvent to be pumped from the respective reservoir to a destination. The solvent supply cartridge and / or any solvent reservoir may be referred to as a solvent supply. As described above, ink is fed along the ink pickup line 119 and ink supply line 128 to the print head 105 via the umbilical 107. Within the print head 105 the ink is provided to a droplet generator 155. The ink is provided to the droplet generator 155 under pressure (under the influence of the pump 121) and is forced through a nozzle of the droplet generator 155 forming an ink jet 157. The ink jet 157 begins as a constant stream of ink and, under the influence of surface tension and vibrations applied in the droplet generator 155 (e.g. by a piezoelectric oscillator), gradually separates into a series of ink droplets 159 which continue to travel in the direction of the inkjet 157. In some printers (such as that illustrated in Fig. 2) a purge line 158 is connected to the droplet generator. The purge line 158 may be connected to a purge port of the droplet generator 155. The droplet generator 155 may be provided as part of a droplet generator assembly, which includes a droplet generator body having known acoustic properties, and a piezoelectric oscillator. The purge port may be provided by the body, or by a separate part connected to the body. The purge line 158 allows ink to flow out of the droplet generator via a purge aperture without passing through the nozzle, and allows the droplet generator to be cleaned. The purge line 158 extends from the droplet generator 155, along the umbilical 107, and returns ink (or solvent), depending upon the phase of operation, to the ink feed tank 117. One or more valves (not shown) may be provided within the purge line 158. It will be understood that the purge line is not essential, and may be omitted in some printers. Shortly after emerging from the nozzle of the droplet generator 155, the ink jet 157 is passed through a charge electrode 161. The point at which the continuous inkjet 157 separates into droplets 159 is arranged to occur within the charge electrode 161. The ink is an electronically conductive liquid, and the droplet generator is conventionally held at a fixed (e.g. ground) potential. A variable voltage is applied to the charge electrode 161 causing charge to be induced on the continuous stream of ink extending from the ink droplet generator 155 towards the charge electrode 161. As the continuous stream of ink (i.e. ink jet 157) separates into droplets 159, any charge induced on the ink within the droplet becomes trapped at the moment the individual droplet “snaps” off from the main stream of ink 157. In this way, a variable charge can be applied to each of the ink droplets within in the stream of ink droplets 159. The stream of ink droplets 159 then continues to pass from the charge electrode 161 between deflection electrodes 163, 165. A first one of the deflection electrodes 163 is held at a first voltage, whereas the second one of the deflection electrodes 165 is held at second voltage, with a large potential difference (e.g. 8-10 kilovolts) established between the deflection electrodes 163, 165. That is, the deflection electrode 163 is configured to generate an electrostatic field. In some systems, one electrode may be maintained at a ground potential while the other electrode is held at a high (positive or negative) voltage (with respect to ground). In other systems, one electrode is held at a negative voltage (with respect to ground) and the other electrode is held at a positive voltage (with respect to ground). The field established between the deflection electrodes 163, 165 causes any charged droplets (i.e. those that have been charged by the charge electrode 161) to be deflected. In this way, based upon the variable charge applied by electrode 161, the droplets 159 can be selectively (and variably) steered from the path along which they are emitted from the nozzle of the droplet generator 155. The printer 100 may be referred to as an electrostatic deflection continuous inkjet printer. As described above, the printer 100 is configured to selectively charge ink droplets within the inkjet and to deflect charged droplets in an electrostatic field. Droplets which pass through the deflection field without being deflected travel to a gutter 167. The gutter 167 comprises an orifice into which the droplets enter. The gutter 167 is connected to a gutter line 169 which extends from the gutter back to the ink system 115. A valve 171 is optionally provided within the gutter line 169 enabling the line to be opened and closed. A suction force is applied to the gutter line 169 by a suction system so as to draw ink along the line from the gutter back towards the ink system 115. While the gutter valve 171 is shown within the ink system 115, it may alternatively be provided within the print head 105. The suction force is provided in many inkjet printers by the suction system which comprises a Venturi 173 (which may also be referred to as a jet pump). The Venturi 173 is provided within the ink system 115 and is configured to receive a pressurised flow of ink from the ink pump 121 from a Venturi supply line 175 which branches from the ink supply line 128 after the pump 121 (but before damper 125). The ink flowing through the Venturi 173 from the Venturi supply line 175 returns to the ink feed tank 117 via an ink return line 177 after it has passed through the Venturi 173. The Venturi supply line 175 could be controlled (e.g. restricted, or selectively blocked) by a valve (not shown). The ink pump may be operated as a pressure controlled pump, meaning that the ink flow rate through the pump will be adapted as appropriate to maintain a target pressure at the pump outlet (e.g. as monitored by pressure sensor 129). The ink pump 121 may be configured to supply ink to the printhead at a predetermined system operating pressure, which may be determined based upon the printer configuration (e.g. nozzle geometry). For example, a nozzle having a diameter of 75 pm may require a lower operating pressure than a nozzle having a diameter of 62 pm to achieve a similar jetting performance (e.g. ink droplet breakup location, or flight time to breakup). The system operating pressure may also be varied in dependence upon other system parameters (e.g. ink type, viscosity). Any ink flowing into gutter 167 will be caused to flow along the gutter line 169, and will eventually be sucked into the Venturi 173 (via suction port 178) and will exit the Venturi and will pass along the return line 177 before returning to the ink feed tank 117. By using a Venturi in this way (i.e. as a jet pump), a system can be designed in which the main system ink pump 121 can generate both positive pressures (e.g. to supply ink to the print head) and negative vacuum pressure (e.g. to provide gutter suction). It will be understood that the terms “negative vacuum pressure” and “negative pressure” are intended to refer to pressure which is lower than atmospheric pressure, with a negative differential pressure or gauge pressure being established between the region concerned and the ambient environment (which is at atmospheric pressure). In addition to unprinted droplets of ink being recirculated via the gutter 167, any air which is sucked into the gutter 167 will also be delivered to the Venturi 173 where it will become entrained with the ink flow and will then pass to the ink feed tank 117. The ink feed tank 117 is vented by a vent 179, preventing excess pressure building up within the ink tank 117. It will be understood, however, that venting air via the vent 179 may cause solvent vapour to be vented to the external environment, which may be undesirable (e.g. since the solvent will need to be replaced, and may be damaging to the environment). In some embodiments, a capture tank 180 may be connected to the vent 179 to capture solvent from the vented air. The capture tank 180 may comprise a condenser. Captured solvent may be returned to another location within the ink supply system 115, such as, for example, the ink feed tank 117, and may be connected to the pump 145. As described above, the valve 127 is configured to prevent the ink supply line 128 from being continuously open. However, since the valve 127 is provided downstream of the branch with Venturi supply line 175, even when the valve 127 is closed, when the pump 121 is operating, a flow of ink will flow along Venturi supply line 175 through the Venturi 173, resulting in suction being applied to the gutter line 169. In this way, the gutter line 169 suction can be applied even when ink is not being supplied to the ink print head 105. Of course, valve 171 may also be operated to block the gutter line, meaning that the gutter suction can be controlled independently of the Venturi 173. A solvent flush valve 181 is provided within the printer, providing a connection from the solvent refill line 149, via the pump 145, to the ink supply line 128. An additional valve 182 may also be provided between the pump 145 and the ink feed tank 117. By appropriate operation of the solvent flush valve 181, valve 182, and pump 145 it is possible to supply solvent directly from the solvent cartridge 137 to the printhead 105. This solvent can be jetted from the nozzle of the droplet generator 155 and captured by the gutter 167 and returned to the ink feed tank 117 via the gutter line 169. Alternatively, solvent can be supplied to the droplet generator 155 and returned to the ink feed tank 117 via the purge line 158. It will be appreciated, of course, that alternative ink supply system arrangements may be provided. Figure 3 shows schematically a control system for the printer 100. The main body 103 contains the ink supply system 115 described above with reference to Figure 2. The main body 103 also houses a controller 300 which is configured to provide control signals to control the various actuators (e.g. valves and pumps) of the ink supply system 115. The printer main body 103 may also be referred to as a printer housing. The controller 300 is also configured to control the electrical components of the print head, such as the droplet generator 155, charge electrode 161, and the deflection electrodes 163, 165. Control signals for the electrical components of the print head are carried by electrical wires 301 (which may comprise a plurality of wires carrying different types of electrical signal and or supply). The electrical wires 301 pass along the umbilical 107 from the controller 300 to the print head 105. The controller 300 may also be configured to receive one or more feedback signals from the print head 105. In particular, the controller may receive sensor signals from various sensors contained within the print head 105. The controller 300 is also configured to receive inputs from and to display information to the interface 109 as required. Of course, the controller may also be configured to interact with different I / O devices and may be additionally connected to a network via a network interface device 302 (e.g. a modem), allowing remote access to and / or control of the printer 100. A network interface also allows data to be provided from the controller 300 to external monitoring systems. It will be appreciated that the controller 300 may take any appropriate form. In particular, the controller 300 may comprise one or more processing components such as a microprocessor and other associated components such as memories and / or interface blocks. Moreover, different control functions of the printer 100 may be performed by different sub-controllers which may be provided on a single control board, or may be provided in different locations within the printer 100. The controller 300 may thus comprise a plurality of separate sub-controllers or processors. The controller 300 may also be configured to control and / or generate high voltage signals for the deflection electrodes via a voltage convertor provided within the printer housing 103 (also referred to as a printer main body 103) or the printhead 105. Such components are not described in detail herein, since they are common components of an industrial inkjet printer. The controller 300 may be referred to as a printer controller. One or more temperature sensors 303 may also be provided within the printer 100, and may be configured to provide as an output a temperature signal which is passed to the controller 300. The controller 300 may be configured to receive the temperature signal. The temperature sensor may generate data indicative of an ambient temperature. Alternatively, data indicative of an ambient temperature may be received by the controller 300 from an external source (e.g. a factory control system). A physical emergency stop button 310 may be provided on the printer housing. Alternatively, a physical emergency stop button may be provided externally to the printer 100, but connected to the controller 300 (either via a wired or wireless connection). The printer 100 further comprises an AC / DC power supply unit (PSU) 401 and a battery system 403, as described in more detail below with reference to Figure 4. The power supply 401 and battery system 403 are provided within the main printer body 103, and may collectively be referred to as a power supply system 400. Components of the printer 100 other than those of the power supply system 400 may be referred to as a printing system 405. The printing system 405 includes all components of the ink supply system 115 and printhead 105. During normal operations, the printer 100 is configured to print on items 111 on a production line 113 adjacent to the printer 100. In such a configuration, ink is provided to the droplet generator 155 under pressure and is forced through the nozzle of the droplet generator 155 generating an ink jet 157 within the printhead 105. The ink jet 157 passes through the charge electrode 161 shortly after emerging from the nozzle of the droplet generator 155. The ink jet 157 begins as a constant stream of ink and, under the influence of surface tension and vibrations applied in the droplet generator 155 (e.g. by a piezoelectric oscillator), gradually separates into a series of ink droplets 159 which continue to travel in the direction of the ink jet 157. Based upon the variable charge applied by electrode 161, the stream of droplets 159 can be selectively (and variably) steered from the path along which they are emitted from the nozzle of the droplet generator 155. In this way, a continuous stream of ink droplets 159 is emitted from the nozzle of the droplet generator 155 within the printhead 105 to be used to print on a substrate, such as the surface of the item 111 moving along the production line 113. The gutter 167 receives droplets which pass through the charge electrode 161 without being deflected. The configuration described above may be considered to be a normal or “jet running” configuration of the printer 100. That is, the inkjet 157 is running. Some of the droplets of ink may be used for printing, but most will be collected by the gutter and returned to the ink system 115. Even when the production line 113 is not operational, a printer may be left in a “jet running” state, so as to enable printing to begin immediately that the production line resumes. When it is intended to stop printing operations and / or to power-down a printer it is often preferred to perform a printhead shutdown process that involves a controlled stop of the inkjet. Typically, during a printhead shutdown process, solvent is jetted from the inkjet nozzle (e.g. supplied via the solvent refill line 149 under the influence of the pump 145, and via solvent flush valve 181), and into the gutter 167 so as to flush ink residue from the nozzle and associated pipework. The jetting of solvent may be performed for a predetermined solvent jetting period of time. Solvent is also typically caused to flow to the droplet generator 155 and return to the ink supply system 115 via the purge line 158. This solvent flushing may be performed for a predetermined solvent flushing period of time. This printhead shutdown process enables reliable shutdown and start-up operation of the printer. It will be appreciated that alternative printhead shutdown processes may be used (e.g. emitting either or both of the solvent jetting and solvent flushing processes described above). The preferred printhead shutdown process will depend upon various factors, including the particular ink system configuration. Different printhead shutdown processes may also be selected based upon operational characteristics (e.g. type of ink used, temperature, fault conditions, time since last cleaning process etc.). Different printhead shutdown processes may also be selected based upon expected next steps. For example, a more thorough (and therefore longer) cleaning process may be performed when entering a long (or unknown) duration shutdown (e.g. several days or weeks), than when it is expected that a shutdown may be very short (e.g. a few minutes). In general terms, it will be understood, however that a printhead shutdown process refers to a sequence of steps or processes that are performed by a printer when it is intended to stop an inkjet in a controlled way, thereby minimising the risk of problems occurring when an ink jet is subsequently re-started at a future time. The printhead shutdown process may include causing solvent to flow through at least a portion of the droplet generator and solvent to be ejected from the nozzle of the droplet generator 155. The ejected solvent may be received in the gutter 167 and returned to the ink supply system 115 via the gutter line 169. The jet of solvent may be caused to run for a predetermined period of time. Additionally, or alternatively, the printhead shutdown process may include a solvent flush process, which comprises causing a solvent to be supplied to the droplet generator 155, causing the solvent to flow through at least a portion of the droplet generator and be returned be to the ink system 115 without having been ejected from the nozzle. The solvent may be returned to the ink system via the purge line 158. The solvent flush process may be performed for a predetermined period of time. The predetermined period of time may be selected based upon a shutdown configuration setting. Figure 4 shows features of the power supply system 400 in more detail. The AC / DC power supply unit (PSU) 401 is connected, in use, to an external power supply network, which may be referred to as a mains power supply. The PSU 401 is configured to generate an output voltage to be supplied to the printing system 405 via a printer power supply rail 402. The PSU may be configured to receive AC power from the external power supply network, and to provide a DC supply voltage to the printer power supply rail 402. For example the PSU may be configured to receive an incoming mains AC voltage of 230 V, and generate a DC output voltage of 24 V. It will be appreciated, of course, that different input and / or output voltages may be provided in some systems, e.g. to comply with local power distribution networks. Further, it will be appreciated that components of the printer will be connected to a common ground connection (not shown). In normal use the PSU 401 is configured to supply power to the printing system 405, including the controller 300, as well as components of the ink system 115 (e.g. pumps 121, 145, valves 121, 127, 143, 151, 171, 181, 182 etc.). The power supplied by the PSU 401 may also be further converted by one or more additional power supply circuits within the printing system 405 to provide different (e.g. higher) voltages that may be required by components of the print head 105, such as the droplet generator 155, charge electrode 161, and the deflection electrodes 163, 165. Such additional power supply circuits are not described in detail herein, but may be considered to be part of the printing system 405, and may be configured to receive a power directly or indirectly from the printer power supply rail 402. The PSU 401 is a switched mode power supply, and comprises a capacitance 410, which is used to smooth the output voltage and filter out electrical noise. The capacitance 410 may comprise a capacitor 410 having, for example, a capacitance of around 1000 micro Farad. The capacitance 410 enables the PSU 401 to deliver a stable supply voltage to the components of the inkjet printer 100, in spite of a typically high internal switching frequency. The capacitance 410 further enables the PSU 401 to temporarily supply some power to the components of the inkjet printer 100 in the event of a power supply voltage fluctuation or temporary power loss (e.g. “brown-out”). That is, if the mains power supply is disrupted momentarily, the capacitance 410 will prevent the voltage of the printer power supply rail 402 from dropping immediately, and will instead cause the voltage of the printer power supply rail 402 to drop gradually, at a rate determined by the rate of power consumption the printer, and capacitance value. The PSU 401 is also connected to the battery system 403, via the printer power supply rail 402. As described in more detail below, the battery system 403 is configured to provide electrical power to the printing system 405 of the inkjet printer 100 in the event of power supply disruption. The power supply disruption may comprise a loss of mains power, such as a persistent loss of mains power. A persistent loss of mains power may comprise a loss of mains power for longer than a minimum power loss period. The minimum power loss period may be configurable by a user. The minimum power loss period may, for example, be less than 5 seconds. Power supply disruption of the sort described above (e.g. a loss of mains power) may be referred to as a predetermined event. The battery system 403 comprises a battery controller 420, a battery charger 421, a boost supply unit 422 and a battery 423. The battery controller 420 is configured to provide control signals to the battery charger 421 and the boost supply unit 422, respectively. The battery charger 421 is configured to charge the battery 423. The battery charger 421 is configured to charge the battery using power supplied by the PSU 401 via the printer power supply rail 402. The battery charger 421 may, for example, comprise a switched mode power supply configured to receive the 24 V input voltage and generate a different charging voltage VCharge (e.g. 14 V) for charging the battery 423. In some configurations, the battery charger 421 may follow a predetermined battery charging protocol. For example, a constant charging current may be provided for a period of time until a charge threshold is reached, after which a fixed voltage may be provided, to allow a final (i.e. full) charge level to be reached. It will be understood that an appropriate battery charging process (i.e. current, voltage, duration etc.) will depend upon the battery configuration and chemistry. The battery 423 is configured to store electrical power. The battery is configured to supply a battery output voltage Vbatt to the boost supply unit 422. The battery may also supply power directly to the battery controller 420. The battery 423 may be a Lithium-ion battery. As described in more detail below, the battery 423 may store enough energy to power the ink jet printer 100 for a fixed period of time. The fixed period of time may, for example, be around 10 minutes. Other durations are also possible. The boost supply unit 422 is configured to convert the battery voltage Vbatt to a voltage output by the boost supply unit Vb00St. The boost supply unit 422 may be referred to as a power convertor. The boost supply unit 422 may, for example, comprise a switched mode power supply configured to receive the battery voltage Vbatt (e.g. 12 V) and generate a different (e.g. higher) output voltage Vb00St (e.g. 22V). The output of the boost supply unit 422 is provided directly to the printer power supply rail 402. The boost supply unit 422 comprises a boost supply capacitance 412, which is used to smooth the output voltage. The boost supply capacitance 412 may comprise a capacitor having, for example, a capacitance of around 10-20 micro Farad. The boost supply capacitance 412 enables the boost supply unit 422 to deliver a stable supply voltage to the printer power supply rail 402, in spite of a typically high internal switching frequency. The battery controller 420 is connected to the printer controller 300 via a communication interface 404. The communication interface 404 is configured to transmit control and status signals between the battery controller 420 and the printer controller 300. The control signals may comprise a signal which indicates that the ink jet is currently running. The communication interface 404 may be an I2C communication interface. The battery controller 420 comprises a comparator 424 and a processor 425. A first input 424A of the comparator 424 is connected to the printer power supply rail 402 and a second input 424B of the comparator 424 is connected to a reference voltage Vref. The reference voltage Vref may be configured by the user. The reference voltage Vref may be 23 V. By comparing the voltage of the first input 424A and the second input 424B, the comparator 424 generates an output 424C, which is received by the processor 425 of the battery controller 420. The output 424C may indicate whether the voltage of the printer power supply rail 402 is above or below the reference voltage Vref. In this way, it is possible for the battery controller 420 to identify power supply disruption events. Based on the result of the output 424C and / or the control signals, the battery controller 420 can generate control signals to the battery charger 421 and / or the boost supply unit 422. The control signal for the battery charger 421 may comprise a signal to enable or disable the battery charger 421. The control signal for the boost supply unit 422 may comprise a signal to enable or disable the boost supply unit 422. The control signals may comprise signals to enable or disable both the battery charger 421 and the boost supply unit 422. That is, the battery controller 420 is configured to control the boost supply unit 422 based upon the output of the comparator 424. The battery controller 420 is also configured to control the battery charger 421 based upon the output of the comparator 424. In some embodiments the comparator 424 may comprise a differential amplifier. The differential amplifier may comprise an operational amplifier. It will be appreciated, however that different control and voltage detection arrangements may be provided. For example, an analog-to-digital convertor (ADC) may be configured to monitor a voltage of the printer power supply rail 402, and to provide a signal to the processor 425 indicating the monitored voltage. A comparison may be made by a software routine running on the processor 425, rather than by a hardware comparator. Based on the output 424C of the comparator 424, the battery controller 420 is further configured to inform the printer controller 300 when a power supply disruption event takes place, for example, by transmitting control signals via the communication interface 404. It will further be understood that the controller 420 may be configured to control the boost supply unit 422 based on control signals and conditions other than those generated by the comparator 424. For example, the controller 420 may be configured to receive signals from the controller 300, or via a remote connection (e.g. via network interface device), or to apply internal logic to determine a control output. The battery charger 421 may be enabled and disabled by the battery controller 420. For example, based on the output 424C of the comparator 424, the battery controller 420 may send a control signal to prevent the battery charger 421 from charging the battery 423 when the battery 423 is discharging. Therefore, issues such as energy loss, inefficiency, and potential damage of the battery system 403 can be mitigated. The boost supply unit 422 may be enabled and disabled by the battery controller 420. The voltage output by the boost supply unit Vboost is intended to provide power to the inkjet printer 100 when a power supply disruption event takes place. The voltage output by the boost supply unit Vboost may be configured at design time. In some embodiments, the boost supply unit Vboost may be capable of providing a different voltage depending on configuration settings (e.g. which could be adjusted by a service engineer). In many circumstances, the voltage output by the boost supply unit Vboost may be fixed during normal use of the printer 100. The voltage output by the boost supply unit Vboost may be 22 V. That is, while the printer is ordinarily configured to run based on a 24 V DC supply voltage, supplied by the PSU 401, the printer may also be configured to operate based on a 22 V DC supply voltage in certain circumstances. The printer 100 may comprise a voltage regulator (not shown) configured to ensure that components of the printer (e.g. pumps, valves, additional power supply circuits) are provided with a suitable voltage, regardless of whether the voltage received via the printer power supply rail 402 is 24 V or 22 V (or some other voltage). The capacitance 410, provided within the PSU, may be further configured to enable the boost supply unit to deliver a stable power to the ink jet printer 100. The output of the power supply unit 401 and the output of the boost supply unit 422 are both operably coupled to the capacitance 410, in addition to the smaller capacitance 412 provided within this boost supply. By the output of the power supply unit and the output of the boost supply unit being operably coupled to the capacitance 410, it is meant that both outputs are connected to the capacitance in such a way that the capacitance can effectively smooth the output voltage provided by each of the power supply unit 401 and the boost supply unit 422, and also prevent sudden changes in the voltage on the supply rail 402. It will be understood, for example, that if each of the outputs was connected to the printer supply rail via a respective diode, a capacitance provided within the PSU would be effectively prevented from smoothing an output voltage of the boost supply unit, and vice versa. The output of the power supply unit 401 and the output of the boost supply unit 422 may be connected directly to the printer power supply rail 402, without passing through a diode. It is described above that the capacitance 410 is provided within the PSU, and that the boost supply unit 422 includes a small output smoothing capacitance. However, in alternative configurations a shared capacitance may be provided within the boost supply unit 422. In further alternative configurations a shared capacitance may be provided in the printer system (e.g. the capacitance 428). It will be appreciated that where each of the PSU and the boost supply unit are provided with an output smoothing capacitance, a diode may be used to connect the PSU to the printer power supply rail 402. During normal operation, when the PSU 401 is receiving power from the mains supply, the battery 423 can be charged by the battery charger 421, with power being supplied to the battery charger 421 via the printer power supply rail 402. On the other hand, when the power supply has been disrupted (i.e. the mains supply disconnected, or interrupted), the battery 423 may provide electrical power to the inkjet printer 100, via the boost supply unit 422 (provided that it is enabled). The battery controller 420 may be further configured to monitor various operational parameters of the battery 423. The battery controller 420 may be further configured to control the charging (by battery charger 421) and / or discharging (by boost supply unit 422) of the battery 423 based on one or more monitored operational parameters, and / or one or more battery charging conditions. The operational parameters may comprise temperature of the battery 423. The battery controller 420 may monitor the temperature of the battery 423 and control charging of the battery 423 based upon the temperature. For example, the battery charger 421 may be controlled to charge the battery 423 only when one or more temperature conditions are satisfied. For example. The one or more temperature conditions may comprise a minimum charging temperature (below which the battery 423 is not charged). The one or more temperature conditions may comprise a maximum charging temperature (above which the battery 423 is not charged). That is, the battery controller 420 may be configured to ensure that the battery 423 is charged in a preferred temperature range. When the temperature of the battery 423 reaches the minimum or maximum charging temperature, the battery controller 420 may send control signals to disable the battery charger 421 from charging the battery 423. The one or more temperature conditions may be referred to as battery charging conditions. The operational parameters may also comprise voltage of the battery 423. For example, the battery charger 421 may be controlled to charge the battery 423 so as to ensure that one or more voltage conditions are satisfied. For example, battery controller 420 may monitor the voltage of the battery 423 to ensure that the battery 423 is charged to an acceptable level. The acceptable level may be set according to different shipping regulations in different countries / regions. For example, it may be necessary, for shipping, for a battery to have no more than a predetermined percentage charge (e.g. an upper charge limit). On the other hand, it may also be preferred, for a battery to be maintained with no less than a predetermined percentage charge (e.g. a lower charge limit). The one or more voltage conditions may be referred to as battery charging conditions. The operational parameters may also comprise a number of charge and discharge cycles of the battery 423. The battery controller 420 may monitor the number of charge and discharge cycles of the battery 423, and provide a warning to an operator, or even disable battery charging or operation when the number of charge cycles reaches a predetermined number of cycles. The number of charge cycles may be referred to as a battery charging condition. That is, the battery controller 420 is configured to control the battery charger 421 to charge the battery 423 when one or more battery charging conditions are satisfied. The ink jet printer 100 further comprises a switch 427, which is configured to control a power status of components of the ink jet printer 100 within the printing system 405. For example, switch 427 may be operated to cause the inkjet printer 100 to enter a low power or powered-off state. The switch 427 is thus configured to allow the printer 100 to disconnect components of the printer from the printer power supply rail 402. The switch 427 may be configured to allow the printer to disconnect components of the ink supply system 115, and / or the printer controller 300, and / or the components printhead 105 from the printer power supply rail 402. In the low power state, the components of the ink jet printer 100 associated with printing (e.g. ink system and printhead components) may be powered off, whereas the PSU 401 may still receive power, and the battery 423 may be charged by the battery charger 421. Once the battery has been fully charged (or if charging is disabled), the standby power of the printer, when in a low power state, may, for example, be less than 0.5 W. The printer 100 may further comprise a printing system capacitance 428. This capacitance may be operatively coupled to the printer power supply rail 402, and may be provided as part of the printing system 405. As with the capacitance 410 of the PSU 401, the printing system capacitance 428 may be operative to smooth the voltage experienced by the printing system 405. The printing system capacitance 428 may, for example, have a capacitance value of 1000 micro Farad. The capacitance 410 and the printing system capacitance 428 may act to reduce the impact of a transition between the printer 100 running on mains power (e.g. at 24 V), and battery power (e.g. at 22 V DC). As described above, the printer 100 is ordinarily configured to operate using mains power, as supplied via the PSU 401. However, the provision of the battery system 403 allows the printer 100 to perform limited operations even in the absence of mains power. That is, in the event of a power supply disruption, the boost supply unit 422 can be activated to provide power from the battery 423 to components of the printer 100, so as to allow the printer 100 to perform certain operations. The printer 100 may be configured to detect power supply disruption, and to enable the boost supply unit 422 immediately upon detection of a power disruption event. As discussed in more detail below, various conditions may be put in place to cause the backup battery to be enabled, or disabled. It will be understood that at the time of a power supply disruption event the printer 100 may be in a variety of different operational states. For example, the printer may be printing onto articles passing along production line 113. If power is promptly withdrawn from an operational printer 100, then the inkjet being ejected from the print head 105 will abruptly stop. In such circumstances ink within and around the inkjet nozzle of the droplet generator 155 may dry out, causing the nozzle to become blocked. Moreover, when printing is once again to be resumed, the blocked nozzle may prevent normal operation. As such, when a printer is stopped, as described above, it is often preferred to perform a flushing or cleaning process that involves a controlled stop of the inkjet. During such a controlled stop, solvent may be jetted from the inkjet nozzle and into the gutter so as to flush ink residue from the nozzle and associated pipework. Such a printhead shutdown process enables reliable shutdown and start-up operation of the printer. It will be understood however that where such a proper shutdown process cannot be performed a printer may become unreliable upon resumption of operations. It is therefore desirable to provide a backup battery (for example battery system 403) that is configured to provide power to the printer in the event of a power supply disruption so as to enable a proper printhead shutdown process to be completed. It will also be understood that in certain circumstances a power supply disruption event is either intentional, or that continued cooperation of a printer after the power supply disruption event would be undesirable. For example, in the event of a system malfunction, an operator may intentionally disconnect a printer from a power supply (or otherwise cut off a power supply) so as to stop printing operations. Similarly, in the event of a fire, or other safety critical event in the vicinity of a printer, power to the region of a production or packaging facility may be withdrawn so as to limit further damage. It will be appreciated that a continuous inkjet printer typically prints with ink which is based on volatile and combustible solvents. As such, to continue to eject jets of ink or solvent in the event of a fire, or other hazardous event, may be undesirable. In other circumstances it may be desirable for a printer to continue operating in one way or another in spite of a power supply disruption event. For example, as noted above a proper shutdown operation is desirable so as to ensure proper operation of the printer upon resumption of printing activities. Alternatively, in some circumstances it may be desirable to move a printer from one location to another, without undertaking a complete shutdown. For example, where the printer is required to be moved from a first printing location to a second printing location (e.g. between adjacent production lines), it may be possible or desirable for the printer to remain powered up and jetting ink while being relocated. It may not be possible, however, to maintain a continuous connection to a mains power supply during such a relocation. As such, it will be appreciated that a temporary disruption to the power supply may be expected, and that continued operation of a printer may be desirable during such a temporary power supply disruption event. During such a temporary power supply disruption event, it may be preferred to leave the inkjet running with ink droplets being ejected from the printhead and being captured by the gutter, so as to minimise disruption and to allow more rapid resumption of operations in the new location. Similarly, where it is intended to switch one printer on a production line for another, a spare printer may be brought into an online (i.e. inkjet running) state at a location away from the printing location and then switched with a malfunctioning printer at the printing location quickly, in order to minimise production disruption. Other circumstances may exist where it is desirable to temporarily maintain a printer in a powered-up state in spite of a loss of mains power. In view of these circumstances, when a power supply disruption event occurs, it may be preferred to continue normal operations, without initiating a shutdown sequence (whether immediate or controlled), since it may be expected that printing operations will resume shortly, and that battery power will not be needed for more than a limited period of time. It has been realised that it would be beneficial to provide an option for a user to control what action the printer takes upon detection of a power supply disruption event. That is, as described above, in certain circumstances a loss of power may be indicative of a safety critical issue, and immediate shutdown of the printer is preferred. On the other hand, in other circumstances a loss of power may be expected or intended, or otherwise non-critical, and it may be preferred to maintain the printer in an inkjet running condition (although not necessarily in a printing condition) until the power is reconnected. In yet other circumstances, a loss of power may indicate that an extended period of shutdown has commenced (e.g. at the end of a production shift). In such circumstances it may be preferred to perform a proper shutdown, under battery power, so as to improve the likelihood of smooth resumption of future printing operations. It will be appreciated therefore that there are several different actions that may be taken upon the detection of a power supply disruption event, and that providing a user with an interface to allow selection between these different actions may be desirable. Figure 5 shows an emergency stop screen 500 that can be displayed by the interface 109 of the printer 100 in the event of a power supply disruption event being detected. The emergency stop screen 500 includes an indication 501 of the nature of the trigger event (in this case a power supply disruption event). The emergency stop screen 500 also includes an emergency stop button 502. The emergency stop button 502 may be referred to as a first display feature associated with an immediate ink jet stop. The emergency stop button 502, if pressed, leads to immediate stop being of any running inkjet, along with the termination of any power supply to the operational components of the printer (save as for those components of the battery system 403). When a user presses the emergency stop button 502, the printer may be considered to have received a user response associated with the first display feature, or a first user response. Performing an immediate stop being of the running inkjet, along with the termination of any power supply to the operational components of the printer may be referred to as performing a first action. The emergency stop screen 500 also includes a stop jet button 504. The stop jet button 504 may be referred to as a second display feature associated with a normal ink jet stop. The stop jet button 504 allows a controlled stop of the inkjet to be performed. Performing a controlled stop may be referred to as performing a second action. When a user presses the stop jet button 504, the printer may be considered to have received a user response associated with the second display feature, or a second user response. A controlled stop of the inkjet includes a printhead shutdown process as described above. For example the printhead shutdown process may include causing the droplet generator 155 of the printer to stop a jet of ink from being generated, and then cleaning the droplet generator with solvent by causing solvent to flow to the droplet generator (e.g. and then jetting and / or flushing). The emergency stop screen 500 also includes a countdown 506. The countdown timer 506 indicates that once the timer has reached zero an automatic shutdown sequence will occur. The automatic shutdown sequence may, for example, comprise the same actions as the stop jet sequence (i.e. it may include the printhead shutdown process). The initial countdown timer value for the countdown timer may depend upon various configuration settings and printer characteristics. For example, the initial countdown timer value for the countdown timer 506 may be selected so as to enable the battery to supply power to the printer for long enough to continue operations for the duration of the countdown timer, and also to supply power to the printer for the duration of the printhead shutdown process. For example, the total duration of the countdown timer and the subsequent the printhead shutdown process may be around 10 minutes. The 10 minutes may include around 3 minutes of countdown timer operation, and 7 minutes of the printhead shutdown process. Of course different time periods may also be selected as appropriate. For example, the countdown timer may count down for a predetermined time period (or initial countdown timer value) which is greater than 60 seconds. Moreover, the particular configuration of countdown timer and printhead shutdown process may be selected based upon various operational characteristics of the printer. The operational characteristics may, for example, include the type of ink being used by the printer, the temperature, the extent of charge within the battery 403, among others. Further still, as described in more detail below, the countdown timer value may be adjusted even after it has started counting down, based on further user inputs. The emergency stop screen 500 may also include an indication 508 explaining the actions associated with various indicated options. The emergency stop screen 500 may also include an illustration indicating the nature of the power supply disruption 510. It will be appreciated, however, that these indications 508, 510 are optional, and may be omitted, or varied. The emergency stop screen 500 illustrated also includes a move printer button 512. The move printer button 512 may be referred to as a third display feature associated with an alternative action. When a user presses the move printer button 512, the printer may be considered to have received a user response associated with the third display feature, or a third user response. The move printer button 512 is an optional feature, and may be omitted from the emergency stop screen. The move printer button 512 is intended for use when a user intends to move the printer from a first printing location to a second printing location, with minimal disruption. It will be understood that during movement of a printer it may not be possible to maintain a connection to a mains power supply at all times (i.e. it may become necessary during a move to temporarily disconnect a printer from the mains power supply). When power is removed, the emergency stop screen can be triggered. Further, since the power loss is planned, but not expected to be for an extended period, it may be possible to use battery power to keep the printer running in an idle (e.g. jet-running) state for the duration of the move. As such, rather than shutting down the printer immediately upon detection of a power loss event, the printer may continue to generate the jet. In the event of a printer move, the emergency stop screen 500 may be generated, and the countdown timer initiated, as described further above. When it is intended to move the printer and quickly resume printing operations it may be that a full jet stop procedure is not required. That is, a full jet stop (which can take several minutes) may be preferred if it is likely that an extended period of inactivity will be experienced (e.g. at the end of a shift). On the other hand, where an extended period of inactivity is not expected, then a shorter jet-stop process may be performed. That is, rather than preserving sufficient battery power to power the printer during an extended (or full) shut-down process, in some circumstances, the controller may be configured to preserve only enough battery power to power the printer for a shorter (or quick) shutdown process, allowing more time for moving the printer. The move printer button may be provided to allow a user to increase the available time for moving the printer, when maintaining a running ink jet, and reduce the time associated with a controlled shut-down process. For example, assuming that a battery has sufficient energy stored to operate the printer for 10 minutes, this may be divided to include around 3 minutes of countdown timer operation, and 7 minutes of a printhead shutdown process. However, if during the 3 minutes of countdown timer operation (i.e. after a power loss event, but before commencing the shutdown process), the move printer button is pressed, the countdown timer value may be adjusted (e.g. increased) by 6 minutes, so as to provide only 1 minute to perform a more limited shut down process, if mains power has not been restored by that time. In this way, more time (i.e. 9 minutes, rather than 3 minutes, in this example) can be provided to move the printer. Further, if reconnection is not possible within these 9 minutes, the consequence will be that a short shut-down process will be performed. Nevertheless, since power is expected to be restored shortly, significant ink drying is unlikely to occur. It will be appreciated, of course, that the times provided above for the countdown timer and shut-down process duration are examples only, and can be configured as required by a particular use case. Moreover, in some circumstances, it may be preferred to provide an option for a user to select an immediate jet-stop once the countdown timer has expired, or even to continue to operate until the battery charge level has been depleted to a predetermined level, regardless of the countdown timer status (e.g. even if it has already expired). In general, it will be understood that the countdown timer may be triggered following a persistent power loss event, and may count down for a predetermined time-period, starting from an initial countdown timer value. Moreover, while the countdown timer may typically be displayed on the emergency stop screen 500, in some configurations the countdown timer may not be shown. Pressing the move printer button may be considered to be a user selection of a predetermined printer operating mode, such as a move printer mode. Alternatively, a user may select a move printer mode via a user interface before a power supply disruption event has even occurred. Selecting such a mode may cause the emergency stop screen, or a variant thereof, to be displayed to a user, with the countdown timer then being triggered when the power loss is detected. In some configurations, the printer may be configured to deactivate a high voltage supply to the deflection electrode when the move printer button is pressed. The emergency stop screen 500 may be referred to as a prompt to a user of the printer. The printer 100 is configured to respond to the selection of one or more of the emergency stop, stop jet, and move printer buttons 502, 504, 512 or to the expiry of the countdown timer 506. That is, based on various conditions being satisfied (e.g. selection of a button, or no action being taken) after the generation of the prompt, the printer may respond by taking a particular action. The emergency stop screen 500 described above is one example configuration. It will be understood, however, that alternative configurations exist. The above described example is displayed on a touchscreen, allowing user interaction and input via virtual buttons that are displayed on the screen. However, alternative input techniques may be possible. For example, physical buttons may be provided adjacent to a display, with a display indicating an action associated with the button. In a further alternative, dedicated buttons may be provided, either close to, or separated from, the display. Moreover, the button names provided above are examples only. In alternative configurations buttons having the same or different functions to those described herein may be included, possible with different text indicators. It has been described above that the printer 100 responds to a power supply disruption event by presenting a prompt to a user (i.e. the emergency stop screen 500). The power supply disruption event described above is a particular example of a predetermined event that is configured to trigger the emergency stop screen 500. It will be appreciated, however, that the emergency stop screen 500 may be triggered by different events. Where such an event does not rely upon the use of a backup battery, the battery system 403 may be omitted from the printer 100. For example, the printer 100 may be configurable by a user to present an emergency stop screen in response to any suitable trigger event, such as, for example an external trigger event, or a user selection of a predetermined printer operating mode. Figure 6 shows a control process performed by the printer 100 to generate the prompt to a user (i.e. emergency stop screen 500), and control actions of the printer 100 in response to any user response (or lack of response) following the generation of the prompt. The processing is generally performed by the controller 300. At step S1, the printer 100 is operating in a normal operating mode with the inkjet 157 running. Printing may or may not be occurring, but the printer is in a state in which printing could be carried out immediately upon receipt of a print trigger signal. At step S2, it is determined that a predetermined event has occurred. For example, the printer controller 300 or the battery controller 420 may detect the voltage of the power supply rail is below than a predetermined voltage (e.g. 23V). This voltage change may be detected by using the comparator 424 in the battery controller 420. A signal may be transmitted to the printer controller 300 via communication interface 404. Upon detection of the power loss event by the comparator 424, the battery controller 420 may be configured to enable the boost supply unit 422 (if not already enabled), such that the printing system 405 is supplied with power from the battery 423, rather than from the power supply unit (PSU) 401. The battery 423 may thus be configured to supply electrical power to components of the printer to cause the jet of ink to be generated in response to a determination that the predetermined event has occurred. Processing then passes to step S3. At step S3, a delay of a minimum power loss period (e.g. 1-5 seconds) is inserted before processing passes to step S4. The minimum power loss period may be referred to as an emergency stop screen delay. The emergency stop screen delay is a relatively short period of time, and is intended to avoid initiating the emergency stop screen operation following a transient power supply fluctuation. The minimum power loss period enables the printer to determine that the loss of mains power is a persistent loss of mains power. That is, where a power supply is not stable, and may experience transient or temporary interruptions, fluctuations or disruptions, the battery system 403, or even a system capacitance, may allow continued operation through the temporary interruption. If any power loss (or disruption) is only for a short period of time (i.e. less than the length of the emergency stop screen delay) then there is no need to continue the emergency stop screen operation, and normal printer operation can resume, with processing returning to step S1. The minimum power loss period may be a period of less than 10 seconds. Preferably, the minimum power loss period may be around 5 seconds, or less. At step S4, a prompt to a user of the printer is generated by the interface 109. The prompt may, for example, comprise displaying the emergency stop screen 500, in response to which the user of the printer can provide a plurality of different responses. The controller 300 may thus cause the user interface to display a predetermined screen (e.g. the emergency stop screen 500) based upon the determination that the predetermined event has occurred. It will, of course, be understood that the prompt to a user of the printer may take any suitable form, and may comprise icons, text or illustrations. Various aspects of the prompt screen may be varied based upon printer configuration settings (e.g. the length of any delay timers, available response options, and / or the language of displayed content). Processing then passes to step S5. At step S5, the printer controller 300 determines whether one or more conditions are satisfied, based upon user actions following the prompt being generated. For example, if it is determined that the user has provided a first user response to the generated prompt, a first condition may be considered to be satisfied. That is, if the user has responded to the generated prompt by pressing button 502, processing passes to step S6, where a first action is performed. Alternatively, if the user does not press the button 502 in response to the generated prompt processing passes to step S8, as described further below. At step S6, the boost supply unit 422 is disabled by the controller 420. This causes the power supplied to the printer system 405 to be stopped immediately. If the ink jet it running at this point, an immediate, or emergency, ink jet stop is performed. Performing an immediate jet stop thus comprises causing the battery 423 not to supply electrical power to components of the printer to cause a jet of ink to be generated. For example, by stopping a supply of power to the ink pump 121 configured to deliver ink to the printhead 105, the ink jet will be caused to stop abruptly. Alternatively, or additionally, where a valve is configured to close when it does not receive power, by stopping a supply of power to the valve (e.g. valve 127) configured to allow ink to be delivered to the printhead 105, the inkjet will be caused to stop abruptly. During such an emergency, or immediate, stop, no printhead shutdown process (e.g. nozzle flush) is performed. Processing then passes to step S12, which is described in more detail below. As noted above, if the button 502 is not selected in response to the generated prompt at step S4, processing passes to step S7. At step S7, it is determined if the user has provided a second user response. The second user response comprises selecting to stop the jet normally (e.g. by pressing button 504). If the user has provided the second user response, processing passes to step S11, where a second action is performed. Alternatively, if button 504 is not selected, processing passes to step S8. At step S8, it is determined if the user has provided a third user response. The third user response comprises selecting the move printer option (e.g. by pressing button 512). If the user has provided the third user response, processing passes to step S10, where a third action is performed. In the third action, the remaining value of the countdown timer is increased. Alternatively, if button 512 is not selected at step S8, processing passes to step S9. At step S9, the printer controller 300 determines if the countdown timer has reached zero (e.g. has 3 minutes elapsed since the countdown timer was initiated at step S4). If the countdown timer has reached zero, processing passes to step S11, where the second action is performed, as described in more detail below. If the countdown timer has not reached zero, processing continues to loop around steps S5, S7, S8 (and optionally S10), and S9 until a user response is received to either of steps S5 or S7, or the countdown timer has expired. That is, the processing performed may repeatedly determine whether or not a first user response has been received prior to the expiry of the countdown timer, and take appropriate action based upon the outcome of that determination (i.e. whether or not a particular user response has been received prior to the expiry of the countdown timer). It will be appreciated that steps S8 and S10 are optional (hence being shown in dashed lines), and may be omitted entirely (e.g. the move printer button 512 may be omitted). Moreover, in some configurations it may be possible to perform step S10 only once, since once the countdown timer has been increased to a maximum value, it may not be increased further. If it is no-longer possible to increase the countdown timer, the button 512 may be removed from the display, or changed in appearance (e.g. greyed-out) to indicate that it is no longer available for selection. In other configurations it may be possible to perform step S10 multiple times, with each pressing of button 512 causing a shorter “stop jet” sequence to be selected at the expiry of the countdown timer. Indeed, in one such configuration, it may be selected to perform an immediate jet stop once the countdown timer has reached zero (i.e. by passing directly to step S6 from step S9, rather than to step S11. At step S11 the second action is performed and the printer controller 300 causes the printer to perform an inkjet stop. Such an inkjet stop may also be referred to as normal ink jet stop process, and can be contrasted with an immediate, or emergency, ink jet stop process. The ink jet stop process comprises the printhead shutdown process. During the printhead shutdown process, various components of the printer 100 (e.g. pumps, valves, controllers) are powered by the battery system 403. That is, performing a normal ink jet stop comprises causing the battery 423 to supply electrical power to components of the printer to cause the printhead shutdown process to be performed. Once the normal ink jet stop process is finished (including the printhead shutdown process), processing passes to step S6. As explained above, at step S6, the boost supply unit 422 is disabled by the battery controller 420. This causes the power supplied to the printing system 405 to be stopped. Since the jet has already been stopped (at step S11) there is no effect on the ink jet. However, any other powered components of the printing system 405 are now disabled. Processing then passes to step S12. At step S12, processing concludes, with the printer being in a powered down state, with no power being supplied by the battery 423, and no inkjet running. It will be understood that power may be restored to the printer at any time during the processing described above. For example if power is resumed before the boost power supply is disabled (at step S6), or before jet stop is commences (at step S11) then there may be no need to continue the emergency stop screen operation, and normal printer operation can resume, with processing returning to step S1. It will be understood, however, that if a jet stop has commenced, it may be preferred to complete the jet stop process, since to terminate part-way through the process could result in unpredictable performance. Put another way, if power is restored before processing has passed line L1, then processing may pass back to step S1. On the other hand, if processing has passed the line L1, the jet may be stopped. Of course, if power is restored, the backup battery may resume charging, and may remain in an active state. Further, while not shown in Figure 6, it will be appreciated that the emergency stop button 502 may be displayed while the jet stop process is performed at step S11. Pressing the emergency stop button 502 during the jet stop process may cause the jet stop process to terminate immediately (i.e. regardless of whether or not it is complete) and processing to pass to step S6, where the boost power supply is disabled. In parallel to the processing of steps S1-S12, an alternative process exists if the ink jet is not running. The alternative process may start with the inkjet in a non-running state. In such a configuration, the boost supply unit 422 is typically disabled. That is, in some embodiments the backup battery operation is configured to be enabled only when the ink jet is running (or if enabled for other reasons, e.g. as described further below). Thus, if the printer is in a non-running state, the backup battery may be disabled. If it is determined that a predetermined event has occurred (e.g. the voltage of the power supply rail is below the predetermined voltage). Processing may pass immediately to step S6, with the printer 100 entering a powered down state. That is, if the printer is not configured to generate a jet of ink when it is determined that the predetermined event has occurred, the battery 423 may not be configured to supply electrical power to components of the printer. In an alternative configuration, the emergency stop screen operation may be disabled (e.g. via a user setting within the printer). If the emergency stop screen operation has been disabled, processing may pass directly from step S2 to step S6 (as shown by dashed line). It will be understood that a user may be able to enable or disable the emergency stop screen via a configuration interface of the printer 100. The configuration status of the emergency stop screen operation may be stored in a memory location or register associated with the controller 300. In some configurations, however, the emergency stop screen operation is enabled permanently. In some configurations, the printer may be configured to send signals or alerts to an external system (e.g. via network interface 302). For example at step S2, when it has been determined that a predetermined event has occurred, a signal may be sent to a remote server. The remote server may, for example, generate an alert to a user (e.g. an email alert), or add details of the power loss to a fault log. In alternative embodiments it may be possible for the battery system 403 to be operated even when the ink jet is not running. That is, the battery system 403 can provide some power to the printing system 405 even if the ink jet is not running. For example, the battery system 405 may provide power to the controller 300 of the printer 100 for an extended period of time. It will be understood that if the jet is not running, the most power consuming components of the printer (e.g. the main ink pump) may be deactivated, allowing the limited power stored by the battery 423 to last for an extended period of time. This configuration may, for example, allow configuration changes to be made to the printer (e.g. print message creation or modification, software updates, etc.) while the printer 100 is not connected to a mains power supply. In the processing described above, the first condition being satisfied is described as comprising a user selection of button 502 at step S5 (i.e. the first user response). The selection of the button 504 (stop jet) at step S7, or the expiry of the countdown time 506 at step S9 may each be considered to comprise a second condition being satisfied. That is, not receiving the first user response may be considered to be a second condition. Not receiving the first user response may comprise receiving an alternative user response (i.e. the second user response, e.g. button 504), or receiving no user response within the predetermined time period (i.e. before expiry of the countdown timer 506). The processing described above allows the immediate stop to be performed at step S6, following a user action to select a first user response. In addition, an emergency or immediate jet stop may be performed following receipt of an emergency stop signal received from the physical emergency stop button 310 (provided on the printer housing or elsewhere). It will be understood, however, that a physical emergency stop button is an optional feature. Further, a physical stop button may be provided which is configured to cause the PSU 401 to be disabled, while still allowing the battery system 403 to operate. As noted above, the battery system 403 may alternatively, or additionally, be configured to provide power in the event of a power loss event even when the inkjet is not running, such as during a software update process. Such processing is illustrated with reference to Figure 7, which shows a control process performed by the printer 100 to perform a software update. The processing is generally performed by the controller 300. At step S20, the printer 100 is operating in an idle state with the inkjet 157 not running. That is, it is conventional for software updates to be performed when printing is not occurring. In some embodiments, as a preliminary step, an inkjet may be stopped from running. At step S21, a software update is initiated. The software update may be initiated by a local user (e.g. via the interface 109), or via a remote connection (e.g. via network interface device 302). The software update may be performed using an update file downloaded via network interface device 302, or provided by a local user (e.g. via a physical data transfer device, such as a USB memory storage device). The software update may comprise updates to software running on the printer controller 300, and may comprise firmware updates. During step S21 a message to a user may be displayed on the interface 109, for example explaining that a software update is underway and that certain functionality is not available (e.g. printing, message creation, configuration changes). At step S22, while the software update is underway, it is determined that a power supply disruption event, or power loss event, has occurred. The power supply disruption may comprise a loss of power, such as a disruption to the supply of mains power to the printer. As described above in more detail with reference to Figure 4, the printer controller 300 or the battery controller 420 may detect the voltage of the power supply rail is below a predetermined voltage (e.g. 23V), as a result of a loss of mains power. At step S23, following detection of the power loss event, the battery controller 420 may be configured to activate the boost supply unit 422, such that the printing system 405 is supplied with power from the battery 423, rather than from the power supply unit (PSU) 401. It is noted, however, that step S23 may be omitted (hence being shown in dashed lines), since the boost supply unit 422 may be maintained in an active state prior to the detection of the power loss event. At step S24, the printer is configured to continue the software update using power supplied by the battery 423 (via boost supply unit 422). The battery 423 may thus be configured to supply electrical power to components of the printer, including the controller 300, to allow the software update to continue in spite of the power loss event. During step S24 a message to a user may be displayed on the interface 109, for example explaining that power has been lost. At step S25, it is determined that the software update has been completed (using battery power). At step S26, the battery controller 420 may be configured to de-activate the boost supply unit 422, such that power is no longer supplied to the printing system 405 from the battery 423. It is noted, however, that (as with step S23) step S26 may be omitted (hence being shown in dashed lines), since the boost supply unit 422 may be maintained in an active state after the completion of the software update. Finally, processing terminates at step S27, with the printer being in a powered down state (provided that step S26 has been performed), or returning to an idle state. If power resumes at any point during the process, the software update will continue (if initiated) until completion, but the components of the printer will operate using power supplied by the external power supply, rather than the backup battery 423. It will further be understood that certain functions of the printer may be disabled when a software update is performed. For example, printing, or even generating an inkjet, may be prevented during a software update. Moreover, access to configuration settings usually accessible via the interface 109 may be restricted during the software update process. It will be understood that the method described above with reference to Figure 7 may be performed by a printer which is also configured to perform the method of Figure 6, but may also be performed independently (i.e. either method may be performed independently of the other). In both methods (or at least in some configurations of each method), a backup battery is used to provide power to components of the printer when mains power is not available. It will be appreciated that while a particular form of ink system 115 and printer 100 is described above, the power supply configuration and / or emergency stop processes described herein can be applied to different printer and ink system configurations. Indeed, as noted above, the emergency stop screen is described above as being triggered by a power supply disruption event, but other events may also trigger the same (or similar) emergency stop screen. For example, a remote server or process (either initiated by an operator, or an automated process) may trigger the emergency stop screen. That is, the predetermined event may comprise a manual input, or a control signal. Where processes are described above as occurring in a particular order, this is not necessarily required. For example steps S5, S7 and S8 may occur effectively simultaneously, with the controller 300 monitoring for any of the first to third user responses at the same time. It will be appreciated that embodiments disclosed herein can be implemented in any convenient form. Embodiments of the subject matter and the operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices). The operations described in this specification can be implemented as operations performed by a processor on data stored on one or more computer-readable storage devices or received from other sources. The terms “processor” and “controller” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, or combinations, of the foregoing. The apparatus can include special purpose reprogrammable logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures. Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Devices suitable for storing computer program instructions and data include all forms of computer-readable media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry and fiber-optic platform for faster data transfer remotely. To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor including audio, for displaying information (e.g. an indication and / or alert) to the user. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback. Although the disclosure has been described in terms of preferred embodiments as set 5 forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. The skilled person will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the disclosure, whether 10 alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

1. A method of operating a continuous inkjet printer comprising: causing a jet of ink to be ejected from a nozzle of a printhead; receiving at least a portion of the jet of ink in a gutter;determining that a predetermined event has occurred;following the determination of the predetermined event, displaying a prompt to a user of the printer, the prompt including a countdown timer; andbased upon a first user response to the prompt, performing a first action; or based upon the expiry of the countdown timer, performing a second action.

2. The method of claim 1, wherein the first action comprises an immediate ink jet stop, and wherein the second action does not comprise an immediate inkjet stop.

3. The method of claim 1 or 2, wherein the second action comprises performing a normal ink jet stop, the normal ink jet stop comprising stopping the ink jet and performing a printhead shutdown process.

4. The method of claim 3, wherein performing the printhead shutdown process comprises:causing a droplet generator of the printer to stop a jet of ink from being generated; andafter causing the droplet generator to stop the jet of ink from being generated, causing solvent to flow to the droplet generator.

5. The method of any preceding claim, wherein the countdown timer is configured to countdown from an initial countdown timer value, and to display a remaining time during the countdown.

6. The method of any preceding claim, wherein the predetermined event comprises a power supply disruption event.

7. The method of any preceding claim, wherein generating the prompt to a user of the printer comprises displaying a screen on a display associated with the printer.

8. The method of any preceding claim, wherein generating the prompt comprises generating a first display feature associated with the first action.

9. The method of any preceding claim, wherein generating the prompt comprises generating a second display feature associated with the second action.

10. The method of any preceding claim, further comprising performing the second action based upon a second user response to the prompt.

11. The method of any preceding claim, wherein generating the prompt comprises generating a third display feature associated with a third action, the method further comprising performing the third action based upon receiving a third user response to the prompt.

12. The method of claim 11, wherein the third action comprises adjusting a value of the countdown timer.

13. The method of any preceding claim, wherein the continuous inkjet printer comprises a battery, wherein the method further comprises:responsive to determining that the predetermined event has occurred, supplying, by the battery, electrical power to components of the printer to cause the jet of ink to be ejected from the nozzle of the printhead.

14. The method of claim 13, wherein, performing the first action comprises causing the battery not to supply electrical power to components of the printer to cause a jet of ink to be ejected.

15. The method of claim 13 or 14, wherein, performing the second action comprises causing the battery to supply electrical power to components of the printer to cause a printhead shutdown process to be performed.

16. The method of any preceding claim, wherein the predetermined event comprises a user selection of a predetermined printer operating mode.

17. A method of operating a continuous inkjet printer comprising:receiving power from an external power supply provided externally from the printer;initiating a software update process while operating components of the printer using power supplied by the external power supply;determining that a power supply disruption event has occurred, such that the printer is no longer receiving power from the external power supply; andcontinuing to perform the software update process while operating components of the printer using power supplied by an internal power supply provided within the printer.

18. The method of claim 17, wherein operating components of the printer using power supplied by an internal power supply provided within the printer comprises: supplying power to at least a controller of the printer, so as to cause the controller to continue to perform the software update.

19. The method of claim 18, wherein the power supply disruption event comprises a persistent loss of mains power to the continuous inkjet printer.

20. The method of any one of claims 17 to 19, further comprising: prior to initiating the software update process, performing an inkjet stop process.

21. The method of any one of claims 17 to 20, further comprising: after determining that a power supply disruption event has occurred, activating the internal power supply provided within the printer.

22. A continuous ink jet printer comprising:an ink supply system;a droplet generator configured to receive ink from the ink supply system and to generate a jet of ink for printing;a gutter configured to receive parts of the jet that are not required for printing; anda gutter line connected to the gutter and configured to return the parts of the jet that are not required for printing to the ink supply system;wherein the printer is configured to perform a method according to any preceding claim.

23. The continuous inkjet printer according to claim 22, further comprising a controller and a user interface, wherein the controller is configured to: determine that the predetermined event has occurred; and cause the user interface to display a predetermined screen based upon the determination that the predetermined event has occurred.

24. The continuous inkjet printer according to claim 22 or 23, further comprising a battery, wherein the battery is configured to supply electrical power to components of the printer in the event of disruption to a mains power supply.

25. The continuous inkjet printer according to claim 24, further comprising a battery system, the battery system comprising:the battery;a battery charger configured to charge the battery;a power convertor configured to receive power from the battery and provide power to components of the printer; anda battery controller, the battery controller being configured to provide control signals to control the battery charger and the power convertor.

26. The continuous inkjet printer according to claim 25, wherein the battery controller is configured to control the battery charger to charge the battery when one or more battery charging conditions are satisfied.

27. The continuous inkjet printer according to any one of claims 22 to 26, further comprising a power supply unit, configured to receive mains power from an external power supply network, and to provide power to components of the printer via a printer power supply rail.

28. The continuous inkjet printer according to claim 27, wherein the power supply unit is configured to receive AC power from the external power supply network, and to provide a DC supply voltage to the printer power supply rail.

29. The continuous inkjet printer according to claim 27 or 28 and claim 25, wherein an output of the power supply unit and an output of the power convertor are operably coupled to a shared capacitance.

30. The continuous inkjet printer of claim 25, or any preceding claim dependent thereon, wherein the battery controller comprises a comparator configured to compare a voltage of a printer power supply rail with a reference voltage, and the battery controller is configured to control the power convertor based upon the output of the comparator.

31. The continuous inkjet printer according to any one of claims 22 to 30, further comprising a printhead operable to receive ink from the ink supply system for printing, wherein the printhead comprises the droplet generator and the gutter.

32. The continuous inkjet printer according to any one of claims 22 to 31, wherein the continuous inkjet printer is an electrostatic deflection continuous inkjet printer configured to selectively charge ink droplets within the ink jet and to deflect charged droplets in an electrostatic field.

33. The continuous inkjet printer according to any one of claims 22 to 33, wherein the ink supply system further comprises a pump configured to pump solvent to the printhead during a printhead shutdown process.

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