WO2025257562A1

WO2025257562A1 - Deflection electrode, printhead, printer and associated method

Info

Publication number: WO2025257562A1
Application number: PCT/GB2025/051298
Authority: WO
Inventors: David Andrew Horsnell; Michael Jeffrey Stamp; Nigel Edward Sherman; Salhadin Omer; Robert Smith
Original assignee: Videojet Technologies Ltd; Videojet Technologies Inc
Current assignee: Videojet Technologies Ltd; Videojet Technologies Inc
Priority date: 2024-06-14
Filing date: 2025-06-12
Publication date: 2025-12-18
Anticipated expiration: 2026-12-14
Also published as: GB202408533D0

Abstract

A deflection electrode for a continuous inkjet printer comprising an elongate body portion, the body portion having: a first dimension in an ink jetting direction; a second dimension in a second direction perpendicular to the ink jetting direction, the second direction being an ink deflection direction; and a third dimension in a third direction perpendicular to the ink jetting direction and the ink deflection direction; wherein the first dimension is at least 20 millimetres, and the third dimension is less than 5 millimetres.

Description

M&C PM364787GB 1 Deflection electrode, printhead, printer and associated method The present invention relates to a deflection electrode, a print head, a continuous inkjet printer and various associated methods. 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 systems: droplet on demand, where ink droplets for printing are generated as and when required; and continuous inkjet (CIJ) printing, in which droplets are continuously produced and only selected ones are directed towards the substrate, the others being recirculated to an ink system. CIJ printers supply pressurised ink to a print head droplet generator where a continuous stream of ink emanating from a nozzle is broken up into individual regular droplets by, for example, an oscillating piezoelectric element. The droplets are directed past a charge electrode, where they are selectively and separately given a predetermined charge, before passing through a transverse electric field provided across a pair of deflection plates, the pair typically comprising a high voltage (or extra high tension (EHT)) plate and a zero or negative voltage plate (the ‘ground’ plate). Each charged droplet is deflected by the field by an amount that is dependent on its charge magnitude before impinging on the substrate, whereas the uncharged droplets proceed without deflection and are collected at a gutter from where they are recirculated to the ink system. The charged droplets bypass the gutter and hit the substrate at a position determined by the charge on the droplet 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 droplets 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 droplets arriving means that a line of droplets would otherwise not quite extend perpendicularly to the direction of movement of the substrate). The various components of the print head are typically contained within a cover tube or print head casing. In CIJ printing, a character is printed from a matrix comprising a regular array of potential droplet positions. Each matrix comprises a plurality of columns (strokes), each 69420659-3 M&C PM364787GB 2 being defined by a line comprising a plurality of potential droplet positions (e.g. seven) determined by the charge applied to the droplets. Thus, each usable droplet is charged according to its intended position in the stroke. If a particular droplet is not to be used then the droplet 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 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 ink system includes a main pump that draws the ink from a reservoir or tank (often referred to as a mixing tank) via a filter and delivers it under pressure to the print head. As ink is consumed, the reservoir is refilled as necessary from a replaceable ink cartridge that is releasably connected to the reservoir by a supply conduit. The ink is fed from the reservoir via a flexible delivery conduit to the print head. The unused ink droplets captured by the gutter are recirculated to the reservoir via a return conduit by a pump. 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 because 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. In order to compensate for this, “make-up” solvent is added to the ink as required from a replaceable solvent cartridge to maintain the ink viscosity within desired limits. The ink and solvent cartridges are filled with a predetermined quantity of fluid and generally releasably connected to the reservoir, or mixing tank, of the ink supply system so that the reservoir can be intermittently topped-up by drawing ink and/or solvent from the cartridges as required. CIJ printers generally operate in high throughput environments for which the printers, and inks, need to be able to keep up with high production line speeds, fast drying time requirements and virtually non-stop production. A problem faced by operators of existing continuous inkjet printers is that of undesirable build-up of deposits within, and around, the print head. Deposits include 69420659-3 M&C PM364787GB 3 _{ink ‘fur’, created by non-volatile ink components which remain after the fluid component} of the ink (and solvent mixture) has evaporated. Such deposits risk the accuracy of printing, the operation of the print head, and, in extreme circumstances, may result in the blocking of an ink ejection aperture of the print head (e.g. rendering the print head non-operational for at least a period of time). Deposits can exist internally within the print head, but also externally. For example, an (external) end face of the print head (e.g. in which the ink aperture is located) may also be liable to the build-up of deposits due to ink ‘splash-back’ during printing. There exists a need to provide an alternative continuous inkjet (CIJ) printer that overcomes one or more of the disadvantages of known systems, whether mentioned in this document or otherwise. According to a first aspect of the present disclosure there is provided a deflection electrode for a continuous inkjet printer comprising an elongate body portion, the body _{portion having: a first dimension in an ink jetting direction; a second dimension in a} second direction perpendicular to the ink jetting direction, the second direction being an ink deflection direction; and a third dimension in a third direction perpendicular to the ink jetting direction and the ink deflection direction. The first dimension is at least 20 millimetres, and the third dimension is less than 5 millimetres. By providing a deflection electrode with a limited dimension in the third direction it is possible to reduce the volume of the printhead in which the electrode is installed, thereby allowing a more compact overall geometry, and reducing the area which must be cleaned. Such an arrangement may also permit a reduced cleaning volume, when the electrode is provided in a self-cleaning printhead, thereby reducing the volume of solvent required for cleaning. It will be understood, however, that reducing the third dimension has generally been avoided in prior art printers, since to do so can reduce the field uniformity. As such, it is generally preferred to provide a third dimension in excess of 5 millimetres. The first dimension may be referred to as a length. The second dimension may be referred to as a thickness. The third first dimension may be referred to as a width. 69420659-3 M&C PM364787GB 4 The third dimension may be less than 4 millimetres. The third dimension may be less _{than 3 millimetres. The third dimension may be around 2 millimetres or less. The third} dimension may be around 1 millimetre. _{The first dimension may be least 25 millimetres. The first dimension may be around 30} millimetres. Providing an elongate deflection electrode allows an extended deflection field to be provided, allowing ink droplets to be steered by the deflection field for an extended duration as they travel in the ink jetting direction. By providing a deflection electrode with a high aspect ratio (i.e. ratio of length in the first direction, to width in the third direction) it is possible to provide a stable field for guiding the ink droplets as they travel along the ink jetting direction, while avoiding taking up too much volume. The second dimension may be less than 2 millimetres. The thickness in the second direction (i.e. the second dimension) does not contribute significantly to the field created by the deflection electrode, since only the surface extending in the first and third directions is exposed to the ink droplets during use. As such, the second dimension may be selected so as to provide a robust physical structure, while not consuming excessive space. The second dimension may be less than the third dimension. The second and third dimensions may be similar, for example with a dimension of around 1.5 millimetres. Edges of the body portion of the deflection electrode may be rounded. Edges defined between adjacent surfaces of the body portion may have a radius of curvature of at least 0.5 millimetres. By providing a minimum radius of curvature of at least 0.5 millimetres, it is possible to reduce the likelihood of an electrostatic discharge, by avoiding sharp edges or points. 69420659-3 M&C PM364787GB 5 _{The deflection electrode may further comprise a support pillar extending from the body} portion in the second direction, the support pillar being configured to secure the deflection electrode to a printhead and to electrically connect the body portion to an energisation source. _{The body portion may define a deflection surface extending along the first direction, the} deflection surface having a first portion generally parallel to the first direction, and a second portion inclined at an acute angle to the first direction and being angled away from the ink jetting direction, the first portion being provided at a first end of the deflection electrode, and the second portion being provided at a second end of the deflection electrode, the first portion being an upstream end in the ink jetting direction. The acute angle may be less than 20 degrees. The deflection surface may comprise the surface extending along the first direction and the third direction. The support pillar may be provided on an opposite side of the deflection electrode from the deflection surface. _{The deflection electrode may further comprise an insulating coating.} By providing an insulating coating it is possible to reduce the risk of short circuits taking place. According to a second aspect of the present disclosure there is provided a printhead _{for a continuous inkjet printer comprising: a nozzle for generating and ejecting a stream} _{of ink droplets in the ink jetting direction; a charge electrode for selectively charging the} stream of ink droplets; a deflection electrode according to the first aspect. The deflection electrode is disposed downstream of the charge electrode nozzle in the ink jetting direction, and configured to cause charged ink droplets to deflect in the ink deflection direction. 69420659-3 M&C PM364787GB 6 The printhead may further comprise a gutter for receiving droplets of ink which are not used for printing. Those droplets that are charged by the charge electrode may be used for printing. The charge electrode may selectively charge the droplets by a variable amount. The amount of deflection of the droplets when passing the deflection electrode may correspond to the variable amount of charge applied by the charge electrode. _{The deflection electrode may comprise a first deflection electrode, the printhead further} comprising a second deflection electrode. In use, the first deflection electrode and the second deflection electrode may be energised to opposing voltages. For example, the first deflection electrode may be energised to +4kV, whereas the second deflection electrode may be energised to -4kV, providing a potential difference of 8kV between the first deflection electrode and the second deflection electrode. The second deflection electrode may be generally similar to the first deflection electrode. Each of the optional features described in the context of the first deflection electrode, and its configuration within the printhead may apply equally to the second deflection electrode. The second deflection electrode may be a ground electrode. For example, the first deflection electrode may be energised to +8kV, providing a potential difference of 8kV between the first deflection electrode and the second deflection electrode. Opposing surfaces of the first deflection electrode and the second deflection electrode may be separated by a deflection electrode separation of around 4 millimetres. Where the second deflection electrode is a ground electrode, a surface of the second deflection electrode may define part of the cleaning chamber wall. _{The second deflection electrode may be a ground electrode, and may define a} deflection surface opposing the first electrode. The second deflection electrode may _{have a greater dimension in the third direction than the deflection electrode. The} 69420659-3 M&C PM364787GB 7 _{second deflection electrode may extend further than the deflection electrode in both a} positive and negative direction along the third dimension. By providing a relatively narrow deflection electrode, a region of stable electric field strength may be relatively small. By providing a wider ground electrode than the deflection electrode, it is possible to reduce the extent of field strength variation. The deflection surface of the second deflection electrode may be curved around the first deflection electrode. The deflection surface may define a concave surface facing towards the first deflection electrode. In this way, a field strength can be maintained around the intended jet direction, even when a relatively narrow deflection electrode is provided. By curving around the first deflection electrode, it is meant that at least a portion of the deflection surface extends further in the ink deflection direction than a central portion of the deflection surface directly opposite the first deflection electrode. _{The printhead may comprise a cleaning chamber selectively sealable by a sealing} mechanism. The deflection electrode may be disposed within the cleaning chamber. _{The printhead may comprise a printhead body, the printhead body comprising walls} defining the cleaning chamber, wherein the walls are spaced apart from surfaces of the body portion of the deflection electrode by a minimum separation distance of at least 1 millimetre in each of the first, second and third directions. By providing a minimum separation distance it is possible to reduce the risk of short circuits from the deflection electrode to the cleaning chamber walls, or tracking, via the walls to other components (e.g. a ground electrode). The ground electrode may define a portion of the walls defining the cleaning chamber. 69420659-3 M&C PM364787GB 8 _{The cleaning chamber may have a height in the third direction of no more than 8} millimetres. At least a portion of the nozzle may be disposed within the cleaning chamber. The charge electrode may be disposed within the cleaning chamber. _{The deflection electrode may further comprise a support pillar extending from the body} portion in the second direction, the support pillar being configured to secure the deflection electrode to the printhead and to electrically connect the body portion to an energisation source. The support pillar may comprise the only part of the deflection electrode that is not spaced apart from the printhead body wall by at least the minimum separation distance. The support pillar may be enclosed in an insulating material. The insulating material may be the same material as is used to form the cleaning chamber walls. The insulating material may be any solvent resistant insulating material. The insulating material may be, for example, glass filled polyphenylene sulphide (PPS). The insulating material may surround the support pillar, such that no part of the support pillar is exposed within the cleaning chamber. By encasing the support pillar in an insulating material, it is possible to reduce the likelihood of short circuits from the support pillar to other components of the printhead when in use. According to a third aspect of the present disclosure there is provided a continuous inkjet printer comprising a print head according to the second aspect, an ink system for _{storing ink and supplying ink to a print head, and a high voltage source configured to} supply a voltage of at least 2000 volts in magnitude to the deflection electrode. The voltage may be around +8kV. 69420659-3 M&C PM364787GB 9 The continuous inkjet printer may further comprise an umbilical comprising a plurality of fluid tubes for delivering ink from the ink system to the print head and recycled fluid back to the ink system. The umbilical may further comprise a plurality of electrical wires configured to provide electrical signals to the printhead. Where the deflection electrode comprises a first deflection electrode, and the printhead further comprises a second deflection electrode, the power supply may be configured _{to supply first voltage of at least 2000 volts in magnitude to the deflection electrode,} and to supply second voltage of at least 2000 volts in magnitude to the second deflection electrode, the first and second voltages being of opposite polarities. The first and second voltages may be around +4kV, and -4kV. _{According to a fourth aspect of the present disclosure there is provided a method of} _{cleaning a printhead of a continuous inkjet printer. The printhead comprises a nozzle} _{for generating and ejecting a stream of ink droplets in the ink jetting direction; a charge} electrode for selectively charging the stream of ink droplets; a deflection electrode disposed downstream of the charge electrode nozzle in the ink jetting direction, and _{configured to cause charged ink droplets to deflect in an ink deflection direction, and a} cleaning chamber selectively sealable by a sealing mechanism. The deflection electrode comprises an elongate body portion, the body portion having a first dimension in an ink jetting direction, a second dimension in a second direction perpendicular to the ink jetting direction, the second direction being an ink deflection direction, and a third dimension in a third direction perpendicular to the ink jetting direction and the ink deflection direction, the first dimension being at least 20 millimetres, and the third dimension being less than 5 millimetres. The deflection electrode is disposed within the cleaning chamber. The method comprises sealing the cleaning chamber by the sealing mechanism; at least partially filling the cleaning _{chamber with cleaning fluid; and draining the cleaning fluid from the cleaning chamber.} By virtue of reduced electrode thickness, the volume of the cleaning chamber is reduced, allowing a smaller volume of cleaning fluid (e.g. solvent) to be used for cleaning. 69420659-3 M&C PM364787GB 10 The method may further comprise a soaking stage during which the cleaning fluid is held in the chamber. The method may further comprise a drying stage following the draining. _{Optional features described in the context of the first aspect (deflection electrode) may} be used with the second aspect (printhead), third aspect (printer) and fourth aspect (method) in any combination. According to a fifth aspect of the present disclosure there is provided a printhead for a _{continuous inkjet printer comprising: a printhead body; a nozzle for generating and} ejecting a stream of ink droplets in an ink jetting direction, the nozzle comprising a _{nozzle body defining a nozzle chamber, and an nozzle plate, defining an orifice; a} charge electrode for selectively charging the stream of ink droplets; a deflection electrode according disposed downstream of the charge electrode in the ink jetting _{direction, and configured to cause charged ink droplets to deflect in an ink deflection} _{direction; and a gutter for receiving droplets of ink which are not used for printing. The} _{printhead comprises a removable assembly comprising the nozzle plate and the gutter,} such that the removable assembly can be removed from the printhead while retaining a fixed positional relationship between the nozzle plate and the gutter. The nozzle plate may comprise a metal plate (e.g. a stainless steel nozzle plate), or a _{‘jewel’ (e.g. comprising a synthetic sapphire) or other orifice body, mounted in a} supporting plate. By providing a removable assembly that can be removed from the printhead while retaining a fixed positional relationship between the nozzle plate and the gutter it is possible to reduce the need for complex adjustments to be made within the printhead, thereby reducing the printhead complexity, while simultaneously allowing some adjustment to be made during a manufacturing setup, to accommodate small deviations in nozzle performance that arise through manufacturing processes. There is also provided a removable assembly for a continuous inkjet printhead comprising a nozzle plate and the gutter. The removable assembly is configured to be define a fixed positional relationship between the nozzle plate and the gutter when removed from the printhead. 69420659-3 M&C PM364787GB 11 The removable assembly comprises a frame configured to support the gutter and the nozzle plate. The frame may comprise a rigid frame. _{The removable assembly comprises a gutter mounting portion configured to support} the gutter and a nozzle mounting portion configured to support the nozzle plate, the frame comprising first and second elongate support elements connected between the first and second mounting portions, the first and second elongate support elements each extending along a respective side of the cleaning clamber. _{The printhead may comprise a cleaning chamber selectively sealable by a sealing} mechanism. The nozzle plate and the gutter may each be disposed within the cleaning chamber. The nozzle body may be disposed within the cleaning chamber. The charge electrode may be disposed within the cleaning chamber. The deflection electrode may be disposed within the cleaning chamber. By providing a cleaning chamber that encloses all of the components that interact with ink during operation of the printhead, it is possible to effectively clean each of those components. Opposite the nozzle plate, a wall of the nozzle chamber may be defined by an actuator (e.g. a PZT actuator) configured to impart an oscillation on fluid contained within the nozzle body. The actuator causes pressure fluctuations within ink contained within the chamber, leading to a controlled breakup of ink jetted through the nozzle orifice. The nozzle may comprise a piezo electric actuator. The piezo electric actuator may be secured to the opposite end of the nozzle body to the nozzle plate. The end of the nozzle body opposite to the nozzle plate may define part of a perimeter of the cleaning chamber. 69420659-3 M&C PM364787GB 12 The piezo electric actuator may be disposed outside the perimeter of the cleaning chamber. _{A seal may be formed between the nozzle body and the printhead body. A sealing} component (e.g. an O-ring) may be provided between the nozzle body and the printhead body to form the seal. _{The printhead may comprise a printhead body comprising walls defining the cleaning} _{chamber. The printhead may further comprise a removable closure portion, defining a} portion of a wall of the cleaning chamber. The printhead may be configured such that removal of the removable closure portion _{permits removal of the removable assembly comprising the nozzle plate and the gutter.} By providing a removable lid, it is possible to allow access to the internals of the printhead for service (e.g. replacement of the nozzle plate), while also allowing a sealed cleaning chamber to be defined. _{The printhead and the removable assembly comprising the nozzle plate and the gutter} may each comprise cooperating registration features, configured to provide a secure _{engagement and alignment of the removable assembly with the printhead body.} The printhead may be configured to clamp the removable assembly in a direction opposite to the nozzle jetting direction. By arranging both placement critical components in a removable assembly, and sealing both parts to corresponding parts of the printhead during assembly, it is possible to provide a quickly replaceable component which is pre-aligned, while also ensuring good seals are formed between the nozzle body and nozzle plate, and the gutter mount and gutter tube. _{The printhead body may comprise a gutter tube configured to engage with the gutter.} The nozzle plate may be mounted to the frame by an adjustable mounting, permitting adjustment of the nozzle jetting direction to be made. In this way, the nozzle jetting 69420659-3 M&C PM364787GB 13 direction can be aligned with the gutter during a manufacturing step. The nozzle-gutter alignment can then be fixed (e.g. by clamping the nozzle plate, or by potting the components together), such that, in use, the nozzle-gutter alignment is substantially guaranteed. _{The deflection electrode may comprise a deflection electrode according to the first} aspect. According to a sixth aspect of the present disclosure there is provided a continuous inkjet printer comprising a print head according to the fifth aspect, and an ink system for storing ink and supplying ink to the print head. According to a seventh aspect of the present disclosure there is provided a removable assembly for use with the printer according to the fifth aspect. The removable assembly comprises the nozzle plate and the gutter, such that the removable assembly can be removed from the printhead while retaining a fixed positional relationship between the nozzle plate and the gutter. The removable assembly may further comprise optional features as described in the context of the fifth aspect. _{According to an eighth aspect of the present disclosure there is provided a method of} _{assembling a printhead for a continuous inkjet printer. The printhead comprises: a} _{printhead body; a nozzle for generating and ejecting a stream of ink droplets in an ink} jetting direction, the nozzle comprising a nozzle body defining a nozzle chamber, and _{an nozzle plate, defining an orifice; a charge electrode for selectively charging the} stream of ink droplets; a deflection electrode according disposed downstream of the charge electrode in the ink jetting direction, and configured to cause charged ink _{droplets to deflect in an ink deflection direction; and a gutter for receiving droplets of ink} _{which are not used for printing. The method comprises inserting a removable assembly} _{within the printhead body, the removable assembly comprising the nozzle plate and the} gutter, such that when assembled a fixed positional relationship is established between the nozzle plate and the gutter. According to a ninth aspect of the present disclosure there is also provided a method of maintaining a printhead for a continuous inkjet printer. The printhead comprising: a printhead body; a nozzle for generating and ejecting a stream of ink droplets in an ink jetting direction, the nozzle comprising a nozzle body defining a nozzle chamber, and 69420659-3 M&C PM364787GB 14 an nozzle plate, defining an orifice; a charge electrode for selectively charging the stream of ink droplets; a deflection electrode according disposed downstream of the charge electrode in the ink jetting direction, and configured to cause charged ink droplets to deflect in an ink deflection direction, and a gutter for receiving droplets of ink which are not used for printing. The method comprises removing a first removable assembly from the printhead body, the removable assembly comprising the nozzle plate and the gutter, and inserting a second removable assembly into the printhead body, such that when assembled the fixed positional relationship is established between the nozzle plate and the gutter. In this way, it is possible to service a printer (e.g. replace a defective or blocked nozzle) without having to re-align the nozzle within the printhead. Features described in the context of the fifth to ninth aspects may be used in any combination. According to a tenth aspect of the present disclosure there is provided a self-cleaning _{printhead for a continuous inkjet printer comprising: a printhead body; a nozzle for} _{generating and ejecting a stream of ink droplets in an ink jetting direction; a charge} electrode for selectively charging the stream of ink droplets; a deflection electrode disposed downstream of the charge electrode in the ink jetting direction, and configured to cause charged ink droplets to deflect in an ink deflection direction, and a gutter for receiving droplets of ink which are not used for printing. The printhead body defines a cleaning chamber selectively sealable by a sealing mechanism; wherein the nozzle, the charge electrode, the deflection electrode and the gutter are disposed within the cleaning chamber. By providing a cleaning chamber that encloses all of the components that interact with ink during operation of the printhead, it is possible to effectively clean each of those components. The nozzle may comprise a nozzle body and a nozzle plate. The nozzle plate may be configured to engage, in use, with the nozzle body to form the nozzle. The nozzle body may define a nozzle chamber. The nozzle chamber may be supplied with ink from an ink supply line. The chamber may also be in fluid communication with 69420659-3 M&C PM364787GB 15 a bleed or purge line, allowing ink (or solvent) to be flushed through the nozzle body (and chamber) in order to clean the nozzle. The ink line and purge line may enter the nozzle body on a same side. Such an arrangement may permit a simplified fluid circuit arrangement, since only a single fluid feed through region into the cleaning chamber. The nozzle chamber may be closed at one end by the nozzle plate. Opposite the nozzle plate, a wall of the nozzle chamber may be defined by an actuator (e.g. a PZT actuator) configured to impart an oscillation on fluid contained within the nozzle body. The actuator causes pressure fluctuations within ink contained within the chamber, leading to a controlled breakup of ink jetted through the nozzle orifice. The nozzle may comprise a piezo electric actuator. The piezo electric actuator may be secured to the opposite end of the nozzle body to the nozzle plate. The end of the nozzle body opposite to the nozzle plate may define part of a perimeter of the cleaning chamber. The piezo electric actuator may be disposed outside the perimeter of the cleaning chamber. _{A seal may be formed between the nozzle body and the printhead body.} A sealing component (e.g. an O-ring) may be provided between the nozzle body and the printhead body to form the seal. Electrical wires supplying the piezo electric actuator may pass through the printhead wall from the inside of the cleaning chamber to the exterior of the cleaning chamber. According to an eleventh aspect described herein, there is provided a continuous inkjet printer comprising: a print head according to the tenth aspect; and an ink system for storing ink and supplying ink to the print head. 69420659-3 M&C PM364787GB 16 The continuous inkjet printer may further comprise an umbilical comprising a plurality of fluid tubes for delivering ink from the ink system to the print head and recycled fluid back to the ink system. The umbilical may further comprise a plurality of electrical wires configured to provide electrical signals to the printhead. According to a twelfth aspect of the present disclosure there is provided a method of cleaning a printhead of a continuous inkjet printer. The printhead is a self-cleaning printhead comprising: a printhead body; a nozzle for generating and ejecting a stream of ink droplets in an ink jetting direction; a charge electrode for selectively charging the stream of ink droplets; a deflection electrode according disposed downstream of the charge electrode nozzle in the ink jetting direction, and configured to cause charged ink droplets to deflect in an ink deflection direction, and a gutter for receiving droplets of ink which are not used for printing. The printhead body defines a cleaning chamber selectively sealable by a sealing mechanism; wherein the nozzle, the charge electrode, the deflection electrode and the gutter are disposed within the cleaning chamber. The method comprises sealing the cleaning chamber by the sealing mechanism; at least partially filling the cleaning chamber with cleaning fluid; and draining the cleaning fluid from the cleaning chamber. The method may further comprise a soaking stage during which the cleaning fluid is held in the chamber. The method may further comprise a drying stage following the draining. Features described in the context of the tenth and eleventh aspects may be combined with the twelfth aspects. According to a thirteenth aspect of the present disclosure there is also provided a method of operating a continuous inkjet printer according to any of the aspects described herein. The method comprises generating and ejecting, by a nozzle, a stream of ink droplets in an ink jetting direction, selectively charging, by a charge electrode, the stream of ink droplets; deflecting, by a deflection electrode disposed downstream of the charge electrode in the ink jetting direction, charged ink droplets in an ink deflection direction, and receiving, by a gutter, droplets of ink which are not used for printing. 69420659-3 M&C PM364787GB 17 The method may further comprise supplying ink to the printhead from an ink system. Supplying ink may comprise supplying ink along an umbilical connecting the ink system _{to the printhead. The method may further comprise supplying, by a high voltage} source, a voltage of at least 2000 volts in magnitude to the deflection electrode. Optional and/or preferred features as set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional and/or preferred features for each aspect of the disclosure set out herein are also applicable to any other aspects of the disclosure, where appropriate. For example, it will be appreciated that any of the first to _{fourth, may be combined with any of the fifth to ninth, and/or tenth to twelfth aspects of} the disclosure. Similarly, optional or preferred features of any of the first to twelfth _{aspects of the disclosure may be combined with the thirteenth aspect.} Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a continuous inkjet (CIJ) printer according to an embodiment of the invention; Figure 2 is a schematic illustration of a self-cleaning printhead for use with the printer shown in Figure 1; Figure 3 is a flow chart illustrated a method of cleaning the printhead of figure 2; F_{igure 4 is perspective view of a deflection electrode for use in the printhead of} figure 2; F_{igures 5a-5c are front, side and end views of deflection electrode of Figure 4;} _{Figures 6a and 6b are perspective views of alternative configurations of the} deflection electrode of Figure 4; Figure 7 is a schematic cross-section view of the printhead of Figure 2; Figure 8 is a schematic cross-section view of an alternative configuration of the printhead of Figure 2; Figure 9 is a schematic cross-section view of an alternative configuration of the printhead of Figure 2; Figure 10 is a schematic cross-section view of an alternative configuration of the printhead of Figure 2; Figure 11 is a schematic cross-section view of an alternative configuration of the printhead of Figure 2; 69420659-3 M&C PM364787GB 18 Figure 12 is a perspective view of an alternative printhead for use with the printer shown in Figure 1; Figure 13 is a perspective view of part of the printhead of Figure 12; Figure 14 is a schematic side view of the printhead of Figure 12; Figure 15 is a schematic top view of the printhead of Figure 12; and Figure 16 is a schematic top view of an alternative printhead for use with the printer shown in Figure 1. Figure 1 schematically illustrates a continuous inkjet (CIJ) printer 1 according to an embodiment of the invention. The printer 1 comprises a printer body 2 (which may be referred to as a cabinet) connected to a print head 3 by an umbilical cable 4. The _{printer body 2 houses an ink system 5, a high voltage source 11, and a printer} controller 6. The printer body 2 also has an interface 7 (e.g. a display, keypad, and/or touch screen) for use by an operator. Although the controller 6 is disposed in the printer body 2 in the illustrated embodiment, in other embodiments the controller 6 may be disposed in the print head 3. In either case, the controller 6 is provided in electrical communication with the print head 3, and preferably also the printer body 2. The print head 3 is arranged to print on a substrate provided adjacent to the print head 3. The printer 1 typically comprises two cartridge connections for engagement with respective fluid cartridges. In particular, the printer 1 comprises an ink cartridge connection for engagement with an ink cartridge 8 and a (separate) solvent cartridge connection for engagement with a solvent cartridge 10. The cartridge connections typically each comprise a fluid port arranged to connect to a fluid pathway within the printer 1 to allow fluid to flow between the cartridges 8, 10 and other parts of the inkjet printer 1, such as the ink system 5 and the print head 3 (via the umbilical 4). The solvent cartridge 10 comprises unused solvent. In operation, ink from the ink cartridge 8 and solvent from the solvent cartridge 10 can be mixed within the ink system 5 to generate printing ink of a desired viscosity that is suitable for use in printing. This ink is supplied to the print head 3 and unused ink is returned from the print head 3 to the ink system 5 (via the umbilical 4). When unused ink is returned to the ink system 5 from the print head 3, air may be drawn in with ink from a gutter of the print head 3. The air may then become saturated with solvent in the gutter line. 69420659-3 M&C PM364787GB 19 In operation, ink is delivered under pressure from the ink system 5 to the print head 3 _{and recycled back via flexible tubes (e.g. conduits) which are bundled together with} other fluid tubes and electrical wires (not shown) into the umbilical cable 4. In order to maintain correct consistency of the ink, the ink system 5 may be operable to mix ink _{removed from the cartridge 8 with solvent removed from the cartridge 10 and to mix} them together to obtain an ink having the correct viscosity and/or density for a particular printing application. In accordance with the invention, the print head 3 can be cleaned. In the illustrated example, the print head 3 is a self-cleaning print head. Without operator intervention, the print head 3 can be sealed, and a cleaning fluid (e.g. fresh and/or used solvent, or a fresh and/or used blend of solvents) be flushed through at least part of the print head 3, in order to clean the print head 3. The ink system 5 is also operable to store cleaning fluid and supply cleaning fluid to the print head 3 (e.g. in isolation of ink). This is particularly advantageous for a self- cleaning print head 3, in which cleaning fluid is circulated through the printer 1 to clean the printer 1 (e.g. specifically a chamber, and associated components, within the print head 3). Alternatively, a continuous inkjet printer may comprise an ink system for storing ink and supplying ink to the print head, and a separate system (e.g. cleaning fluid system) for storing cleaning fluid and supplying cleaning fluid to the print head. In other embodiments, the print head may not be a self-cleaning print head, but be cleaned using a wash station. Turning to Figure 2, a schematic cross-section side view through part of the self- _{cleaning print head 3, as shown in Figure 1, is provided. Figure 2 shows the print head} 3 comprising a nozzle body 20, charge electrode 24, chamber 26, low voltage electrode 28, deflection electrode 30, gutter 32 and sealing mechanism 34. An ink jet 36 (e.g. a stream of ink droplets), not deflected by deflection electrode 30, is also schematically indicated in Figure 2. Briefly stepping through each of the aforementioned components in turn: the nozzle body 20, as mentioned, defines the nozzle 22. The nozzle 22 is for generating and 69420659-3 M&C PM364787GB 20 ejecting a stream of ink droplets for printing. The ink jet 36 is shown being expelled by the nozzle 22, although these ink droplets would not be used for printing because they _{pass straight into the gutter 32. The ink jet 36 travels in an ink jetting direction, parallel} to an x-axis, which may also be referred to as a first direction. Downstream of the nozzle and nozzle body 20, 22, the charge electrode 24 is provided. As the stream of ink droplets 36 is directed past the charge electrode 24, they are selectively and separately given a pre-determined level of charge by the charge _{electrode 24. The pre-determined level of charge by vary in accordance with an} intended deflection amount. Downstream of the charge electrode 24, low voltage and deflection electrodes 28, 30 _{are provided. The deflection electrode 30 may be described as a high voltage} electrode, or a first deflection electrode. The low voltage electrode 28 may otherwise be described as a grounded, or negative potential, electrode, or alternatively as a second deflection electrode. The electrodes 28, 30 may collectively be described as a _{pair of deflection electrodes. An electric field, or deflection field, is selectively} generated between the low voltage and deflection electrodes 28, 30 for guiding the stream of ink droplets 36 away from the gutter 32 and towards an ink aperture for _{printing onto a substrate in use. Droplets that are charged by the charge electrode 24} _{may be deflected by the deflection field and may be used for printing. The amount of} deflection of the droplets when passing the deflection electrode may correspond to the variable amount of charge applied by the charge electrode. Droplets that are not charged by the charge electrode 24 are not deflected by the deflection field, and pass to the gutter 32. Deflection of the ink droplets 36 by the deflection field causes a component of movement in a deflection direction, or second direction, parallel with the y-axis shown in Figure 2, to be imparted on the selected droplets. The ink aperture is labelled 38. The ink aperture 38 may be described as being selectively opened and closed by the sealing mechanism 34. The electric field generated by the low voltage and deflection electrodes 28, 30 is generated by connecting the deflection electrode 30 to the high voltage source 11. In 69420659-3 M&C PM364787GB 21 some embodiments the deflection electrode may be connected to a voltage of +8 kV, with the low voltage electrode being connected to 0V (ground). In alternative arrangements both of the deflection electrode 30 and the low voltage electrode 28 may be connected to different voltages. For example the deflection electrode may be connected to a voltage of +4 kV, with the low voltage electrode being connected to a voltage of -4kV, providing a similar electric field to a single high voltage electrode arrangement, but with each electrode having a lower magnitude voltage. Different (e.g. lower) voltages may be used, with the required deflection field depending on the electrode separation and length, as well as the required extent of deflection, and charging voltages. Downstream of the electrodes 28, 30, the gutter 32 is provided. The gutter 32 comprises a gutter aperture through which droplets of ink not used for printing (e.g. of ink jet 36) are received and subsequently recirculated back into the ink system. _{Also shown in Figure 2 is a sealing mechanism 34. The purpose of the sealing} mechanism 34 is to selectively seal the chamber 26 within the print head 3. The chamber 26 is thus a selectively sealable volume which can be at least partly filled with cleaning fluid, and subsequently drained, in order to clean one or more components disposed within the chamber 26. As indicated in Figure 2, components disposed within the chamber 26 include the gutter 32 and electrodes 28, 30. Although the chamber 26 is schematically shown as not including the charge electrode 24, fluid within the chamber 26 can also enter the charge electrode 24. The charge electrode 24 can thus also be cleaned by filling the chamber 26 with cleaning fluid. In some interpretations a cavity defined by the charge electrode 24 may be considered to form part of the chamber 26. The chamber 26 may be described as a cleaning chamber, or a cleaning volume. The sealing mechanism 34 may otherwise be described as a closure. The sealing mechanism 34 may take one of a number of different forms. The sealing mechanism 34 may comprise: a rotatable sealing mechanism (e.g. a rotatable body that rotates about an axis to selectively open/seal chamber 26), a slidable sealing mechanism which selectively opens/seals the chamber 26, an inflatable balloon seal that selectively opens/seals the chamber 26, or slidable housing pieces which selectively change the volume of the chamber. 69420659-3 M&C PM364787GB 22 Although not illustrated in Figure 2, one or more ports, preferably a plurality of ports, may be disposed in fluid communication with the chamber 26. These ports may provide one or more of: a supply of cleaning fluid for cleaning the chamber, a supply of air for pressure balancing (e.g. during printing, to replenish fluid drawn out of the chamber by the gutter), drainage of used cleaning fluid from the chamber, and a supply of air for drying the chamber. One or more of the gutter 32 and the nozzle 22 may also provide the aforementioned port functionalities, although in preferred embodiments the gutter 32 and nozzle 22 are not used to provide the chamber with such filling, draining or drying functionalities (the chamber 26 instead comprising one or more ‘dedicated’ multifunction fill/drain/dry ports). Turning to Figure 3, steps of a method 50 are shown illustrating a cleaning cycle for the self-cleaning print head 3. The method 50 comprises a fill stage 52, soak stage 54, drain stage 56 and a dry stage 58. During the fill stage 52, the chamber 26 is at least partly filled with cleaning fluid. By virtue of the chamber 26 being partly filled with cleaning fluid, components within the chamber 26 which are reached by the liquid level of the cleaning fluid are contacted by the cleaning fluid. In the soaking stage 54, the cleaning fluid is held in the chamber. As suggested by the name, the soaking stage 54 provides a dwell period, (e.g. a period of time) in which the cleaning fluid acts to remove deposits/build-up from the components and the chamber 26 itself. The soaking stage 54 may comprise percolating air or otherwise disturbing the cleaning fluid in the chamber 26 to improve the clean. In the draining stage 56, the used cleaning fluid from within the chamber 26 is drained. The chamber 26 is thus emptied of used cleaning fluid (and any deposit/build-up entrained within the used cleaning fluid). In the drying stage 58, the chamber 26, and any components provided in fluid communication with the chamber 26, are dried. Although there are a number of different ways in which the drying can take place, one such example is that a supply of air be provided through one or more ports in communication with the chamber 26. 69420659-3 M&C PM364787GB 23 It will be appreciated that the method 50 may be modified in various different ways, and may be repeated in multiple cycles to provide a deeper clean. For example, the method 50 may run multiple times in succession for a deeper clean of the print head 3a. It will also be appreciated that a sealing step, in which the sealing mechanism sealing the chamber, precedes the fill stage 52. _{The deflection electrode 30 is illustrated schematically in Figure 2. A more detailed} _{drawing of a deflection electrode 30 is shown in Figures 4 and 5a-5c. Figure 4 shows a} perspective view of the deflection electrode 30. Figures 5a-5c shown views of the deflection electrode 30 from along the y-axis, z-axis, and x-axis, respectively. The deflection electrode 30 comprises an elongate body portion 40. The body portion has a first dimension in an ink jetting direction. The ink jetting direction is aligned with _{the x-axis as shown in Figures 2 and 4, and coincides with the direction of the jet of ink} 36 shown in Figure 2. The first dimension may be referred to as a length. The body portion has a second dimension in a second direction perpendicular to the ink jetting direction. The second direction is aligned with the y-axis shown in Figure 4 (as also shown in Figure 2). The second direction may be referred to as an ink deflection direction. The second dimension may be referred to as a thickness. The body portion has a third dimension in a third direction perpendicular to the ink jetting direction and the ink deflection direction. The third direction is aligned with the z-axis shown in Figure 4 (but not shown in Figure 2, since the z-dimension is the dimension out of the plane of the image). The third dimension may be referred to as a width. The third dimension _{(width) may be less than 5 millimetres. The first dimension (length) is at least 20} millimetres. Where it is desired to provide a sealable cleaning chamber 26, it will be understood that the volume of the chamber may dictate the volume of cleaning fluid (e.g. solvent) that is required to fill the chamber (e.g. during step 52). While it may not be required to completely fill the chamber during the fill step 52, it will nevertheless be appreciated that a cleaning efficacy may be improved by filling an increased proportion of the chamber volume. It may desirable to reduce the volume of the cleaning chamber, so as to enable a reduced volume of cleaning fluid to be used for cleaning. 69420659-3 M&C PM364787GB 24 By providing a deflection electrode with a limited (i.e. small) dimension in the third direction it is possible to reduce the volume of the printhead in which the deflection electrode 30 is installed, thereby allowing a more compact overall geometry, and reducing the area which must be cleaned. Such an arrangement may also permit a reduced cleaning volume, when the electrode is provided in a self-cleaning printhead, thereby reducing the volume of solvent required for cleaning. It will be understood, however, that reducing the third dimension may generally be avoided, since to do so can reduce the field uniformity. As such, it has previously been _{preferred to provide a third dimension in excess of 5 millimetres. In contrast, it has} been realised that by providing a deflection electrode having a third dimension less than 5 millimetres can enable a more efficient cleaning process to be performed. In order to further reduce the volume of the cleaning chamber, the third dimension may be less than 4 millimetres. Preferably, the third dimension may be less than 3 millimetres. Even more preferably the third dimension may be around 2 millimetres or _{less. In some embodiments, the third dimension may be around 1 millimetre, or 1.5} millimetres. Providing an elongate deflection electrode (i.e. relatively long in the first direction) allows an extended deflection field to be provided, allowing ink droplets to be steered by the deflection field for an extended duration as they travel in the ink jetting direction. By providing a deflection electrode with a high aspect ratio (i.e. ratio of length in the first direction, to width in the third direction) it is possible to provide a stable field for guiding the ink droplets as they travel along the ink jetting direction, while avoiding taking up too much volume. _{The first dimension (length) may preferably be at least 25 millimetres. The first} dimension may be around 30 millimetres. The thickness in the second direction (i.e. the second dimension) does not contribute _{significantly to the field created by the deflection electrode 30, since only a deflection} _{surface 42 extending in the first and third directions is exposed to the ink droplets} during use. As such, the second dimension may be selected so as to provide a robust 69420659-3 M&C PM364787GB 25 physical structure, while not consuming excessive space, or introducing other difficulties (e.g. sharp edges). The second dimension may be less than the third _{dimension. The second dimension may be is less than 2 millimetres. The second and} third dimensions may be similar, for example each having with a dimension of around 1.5 millimetres. _{The body portion 40 defines a deflection surface 42 extending along the first direction.} _{The deflection surface 42 has a first portion 43 generally parallel to the first direction,} _{and a second portion 44 inclined at an acute angle to the first direction, the first portion} _{43 being provided at a first end of the deflection electrode, and the second portion 44} being provided at a second end of the deflection electrode, the first portion being an upstream end in the ink jetting direction. The acute angle may be less than 20 degrees (e.g. around 12 degrees). _{The deflection surface 42 may comprise a surface extending along the first direction} and the third direction. As explained above, the deflection electrode 30 is connected to the high voltage source _{11 which provides a high voltage (e.g. 8kV), allowing the deflection field to be} established. It will be understood that any sharp edges or points on the deflection _{electrode may result in a field concentration, and an increased risk of electrostatic} discharge to a lower potential surface. As such, edges, and corners of the body portion of the deflection electrode may be rounded. For example, edges and corners of the body portion may have a minimum radius of curvature of 0.5 millimetres. Such edges _{are illustrated as edge 40b formed between the deflection surface 42 and a top surface} _{of the body portion (top surface as shown in Figure 5a), edge 40c formed between the} _{deflection surface 42 and a tip of the body portion, and edge 40d formed between the} tip of the body portion and a top surface of the body portion. In each case, the edges 40b, 40c, 40d have a minimum radius of curvature. The deflection electrode 30 further comprises a support pillar 41. The support pillar 41 _{extends from the body portion 40 in the second direction, and is configured to secure} the deflection electrode 30 to a printhead body. The support pillar 41 comprises an electrical connector 41a for connection to a corresponding connector provided within the printhead body, and an alignment protrusion 41b, for aligning the deflection 69420659-3 M&C PM364787GB 26 electrode within the printhead body 46. In the illustrated embodiment the electrical connector 41a and the alignment protrusion 41b are provided separately, but alternatively (e.g. combined) arrangements are possible. The support pillar 41 is provided on an opposite side of the deflection electrode from _{the deflection surface 42.} _{Parts of the deflection electrode may comprise a coating of an insulating material 45.} For example, as shown in Figure 6b, the support pillar 41 may be enclosed, or surrounded by the insulating material 45. For the purposes of comparison, Figure 6a shows the same arrangement of Figure 6b, with insulating material omitted. _{The insulating coating reduces the risk of short circuits taking place due to surface} tracking from the high voltage deflection electrode 30 to lower potential surfaces (e.g. a _{ground electrode, the nozzle etc.). The insulating material may surround the support} _{pillar, such that no part of the support pillar is exposed within the cleaning chamber 26.} By encasing the support pillar in an insulating material, it is possible to reduce the likelihood of short circuits from the support pillar to other components of the printhead when in use. In a further variant, other surfaces of the deflection electrode (even the entire surface) may be provided with a coating of insulating material, thereby reducing the discharge risk further still. The insulating material may be the same material as is used to form the cleaning chamber walls. The insulating material may be any solvent resistant insulating material. The insulating material may be, for example, glass filled polyphenylene sulphide (PPS). As described above with reference to Figure 2, the deflection electrode 30 is provided within a self-cleaning printhead 3, having a sealing mechanism for selectively sealing the cleaning chamber 26. The printhead 3 comprises a printhead body 46 which comprises walls that define the cleaning chamber 26. The deflection electrode 30 is _{disposed within the cleaning chamber 26, as shown in Figure 7, which shows a cross} 69420659-3 M&C PM364787GB 27 section in the y-z plane, looking from the gutter 32 towards the nozzle 22. The body 46 surrounds the deflection electrode 30. _{As described above, the printhead 3 further comprises a second deflection electrode} _{28. As shown in Figure 7, the second deflection electrode 28 may partly define an} internal surface of the cleaning chamber 26, or a part of a cleaning chamber wall. That is the second deflection electrode 28 defines a side wall of the cleaning chamber, with the remaining walls defined by the printhead body 46. The second deflection electrode 28 in such a configuration may be a ground electrode, with only the first deflection electrode 30 being provided with a high voltage (e.g. 8kV), so as to establish a potential difference of 8kV between the first deflection electrode and the second deflection electrode. Opposing surfaces of the first deflection electrode 30 and the second deflection _{electrode 28 are separated by a deflection electrode separation E_sep of around 4} millimetres. The deflection electrode separation 47 may be defined as a separation between the closest parts of the respective deflection electrodes along the second direction. _{It will be appreciated that the high voltage of the deflection electrode 30 may discharge} to a nearby ground, and that any surface provided close to the high voltage electrode can provide a source to ground (e.g. due to surface tracking, the likelihood of which is increased by surface contaminants, such as ink). In order to minimise the risk of unwanted discharge, the walls of the printhead body 46 are spaced apart from surfaces _{of the body portion of the deflection electrode by a separation distance 48. The} _{separation distance 48 may be at least a minimum separation distance. The minimum} separation distance may be at least 1 millimetre in each of the first, second and third directions. By providing a minimum separation distance it is possible to reduce the risk of short circuits from the deflection electrode to the cleaning chamber walls, or tracking, via the walls to other components (e.g. the ground electrode). It will further be understood that increasing the separation distance increases the volume of fluid (e.g. cleaning fluid) that will be required to fill the chamber 26 for cleaning. As such, while an increased separation distance is desirable for prevention of electric discharge, a reduced separation distance is desirable to reduce solvent use. 69420659-3 M&C PM364787GB 28 _{The support pillar 41 (not shown in Figure 7) may comprise the only part of the} deflection electrode 30 that is not spaced apart from the printhead body walls by at least the minimum separation distance. _{The cleaning chamber 26 has dimensions that are at least in part defined by the} _{dimensions of the deflection electrode 30, and separations to the walls. As can be seen} _{in Figure 7, the dimension of the cleaning chamber in the third direction comprises the} dimension of the deflection electrode 30 in the third direction, plus twice the separation _{distance. The cleaning chamber may, for example, have a height H in the third} _{direction of no more than 8 millimetres. Similarly, the dimension of the cleaning} chamber in the second direction comprises the dimension of the deflection electrode 30 in the second direction, plus the wall separation distance W_SEP, plus the electrode separation E_SEP. The cleaning chamber may, for example, have a width W in the second direction of no more than 10 millimetres. Such a geometry provides a relatively small cleaning chamber volume, allowing cleaning to be carried out with a relatively small volume of solvent. _{The dimension of the deflection electrode in the third direction may be reduced further} from that shown in Figure 7. For example the dimension of the deflection electrode 30 in the third direction may be around 1.5 mm. Various alternative electrode geometries are shown in Figures 8 to 11. In each case, a cross section through a cleaning chamber is shown, with the relative dimensions and positions of a deflection electrode, ground (or second deflection) electrode and nozzle _{shown. Each of the illustrated components generally perform the same functions as} described above with reference to the Figures 1-7. Moreover, many components are omitted in order to improve clarity. Different reference numerals are used in each of Figures 8-11 for components that are changed. As shown in Figure 8, a deflection electrode 60 may have a substantially circular cross section in the y-z plane, with the chamber height being reduced accordingly, thereby _{further reducing solvent use. As also shown in Figure 8, a second deflection electrode} 62, which in this configuration is a ground electrode, has a greater dimension in the 69420659-3 M&C PM364787GB 29 _{third direction (z-axis) than the deflection electrode 60, and extends further than the} deflection electrode 30 in both a positive and negative direction along the third _{direction. By providing a relatively narrow deflection electrode 30 (in the z-axis), with a} relatively wide ground electrode, a region of stable electric field strength may be _{increased. That is, by extending the ground electrode beyond the extent of the} deflection electrode in the third direction, it is possible to extend the region of stable _{deflection field, without also increasing the volume of the cleaning chamber.} _{In a further variation, as shown in Figure 9, a second deflection electrode 72 still has a} greater dimension in the third direction than a deflection electrode 70, and extends further than the deflection electrode 30 in both a positive and negative direction along _{the third dimension. However, rather than defining a planar form (as per the} _{configuration of Figure 8) the second deflection electrode 72 has a deflection surface} _{72a that is curved towards the first deflection electrode in the y-z plane. That is,} _{deflection surface 28a defines a concave surface facing towards the deflection} _{electrode 70, with top and bottom edges of the deflection surface 72a extending further} _{in the second direction (y-axis) than the centre portion of the deflection surface 72a. In} this way, the electric field strength can be maintained substantially constantly around the intended jet direction, even when a relatively narrow deflection electrode is provided. _{Whereas it is illustrated in Figures 7, 8 and 9 that the second deflection electrode is a} ground electrode, and defines a surface of the chamber wall, this is not necessarily the case in all configurations. For example, as shown in Figure 10, in some configurations, a second deflection electrode 82 may be generally similar to a first deflection electrode 80. For example the second deflection electrode 82 may be elongate, and have dimensions similar to the first deflection electrode 80, and also the deflection electrode 30. _{Unlike the first deflection electrode 30 described further above, the first deflection} _{electrode 80 and/or the second deflection electrode 82 may define a planar deflection} _{surface, without an angled portion (e.g. the second portion 44). In some configurations} the angled section may be provided only on a first deflection electrode, with the second deflection electrode remaining generally linear. 69420659-3 M&C PM364787GB 30 _{Where a second deflection electrode is generally similar to a first deflection electrode,} the first deflection electrode and the second deflection electrode may be energised to opposing voltages. For example, the first deflection electrode 80 may be energised to a first voltage of at least 2 kV in magnitude (e.g. +4kV), whereas the second deflection electrode 82 may also be energised to a second voltage of at least 2 kV in magnitude, but of an opposite polarity to the first voltage (e.g. -4kV), providing a potential difference of 8kV between the first deflection electrode 80 and the second deflection _{electrode 82.} _{In such an arrangement, a minimum clearance Cmin may be provided around each of} _{the surfaces of the first deflection electrode 80 and the second deflection electrode 82.} It will be appreciated, however, that where both electrodes are energised to a lower _{magnitude voltage (e.g. 4kV, rather than 8kV), a smaller minimum clearance may be} provided (e.g. around 1 mm). As shown in Figure 11, in a further alternative, first and second deflection electrodes _{90, 92 may each have a circular cross section of similar dimensions. In such an} _{arrangement, the diameter may be around 1.5 mm. The use of a reduced height and} width for the electrodes, and a split-voltage configuration (i.e. +4kV, -4kV) allows a _{reduced minimum clearance, and therefore an associated reduction in cleaning} chamber volume (and solvent usage). It will be understood that tolerances in manufacturing of the nozzle, and or other system components, may result in some deviation of the ink jet from the nominal ink jetting direction. Some adjustability may therefore be provided to ensure that the ink jet is incident upon the gutter opening when not deflected, and also so as to permit reliable _{charging and deflection of the ink droplets by the charge and deflection electrodes,} respectively. Alternatively, a degree of tolerance may be built into various system components, so as to provide a degree of insensitivity to small deviations in ink jetting direction. In some arrangements, the need to align the gutter and nozzle within a printhead may be avoided entirely. For example, by ensuring accurate control of the nozzle 69420659-3 M&C PM364787GB 31 _{manufacturing or assembly process, it may be possible to reduce the likelihood of jet} deviations. _{For example, if some adjustment is required, an assembly may be provided so as to} allow the nozzle and gutter to be aligned before assembly into a printhead. For example, a nozzle-gutter assembly may be provided, in which the nozzle and gutter are _{provided in a pre-aligned state. Alignment of the nozzle and gutter in such an assembly} may be performed in a manufacturing facility, with the nozzle permanently secured in place once aligned. The pre-aligned nozzle-gutter assembly may then be installed into _{a printhead body. In this way, it is possible to provide a replaceable component} (nozzle-gutter assembly) that does not require re-alignment if a nozzle (or gutter) should need to be replaced. _{Such an arrangement is shown in Figure 12, which shows an alternative printhead 100} for a continuous inkjet printer. The printhead 100 comprises a printhead body 102, a _{nozzle 104 for generating and ejecting a stream of ink droplets in an ink jetting direction} _{J (see Fig 13). The nozzle 104 comprises a nozzle body 105 defining a nozzle} _{chamber, and a nozzle plate 106, defining an orifice. The printhead further comprises a} _{charge electrode 107 for selectively charging the stream of ink droplets and at least} _{one deflection electrode 108, disposed downstream of the charge electrode nozzle in} the ink jetting direction, and configured to cause charged ink droplets to deflect in the ink deflection direction. The printhead further comprises a gutter 110 for receiving droplets of ink which are not used for printing. The charge electrode 107 and the deflection electrode(s) 108 are be supported by (e.g. fixedly mounted to) the printhead body 102. _{The printhead further comprises a removable assembly 112, which is shown separated} _{from the printhead in Figure 12, and separately in Figure 13. The removable assembly} _{112 comprises the nozzle plate 105 and the gutter 110. The removable assembly 112} can be removed from the printhead 100 while retaining a fixed positional relationship _{between the nozzle plate 106 and the gutter 110.} _{The nozzle plate 106 may comprise a metal plate (e.g. a stainless steel nozzle plate),} _{or a ‘jewel’ (e.g. comprising a synthetic sapphire) or other orifice body, mounted in a} 69420659-3 M&C PM364787GB 32 _{supporting plate. The nozzle plate 106 is configured to engage, in use, with the nozzle} body 105 to form the nozzle 104. The nozzle chamber (within nozzle body 105) is supplied with ink from an ink supply line (e.g. from ink system 5). The nozzle chamber may is also in fluid communication with a bleed or purge line (not shown), allowing ink (or solvent) to be flushed through the nozzle body 105 (and chamber) in order to clean the nozzle. The nozzle chamber may be closed at one end by the nozzle plate 106. Opposite the nozzle plate, a wall of the nozzle chamber may be defined by an actuator (e.g. a PZT actuator) configured to impart an oscillation on fluid contained within the nozzle body. The actuator causes pressure fluctuations within ink contained within the chamber, leading to a controlled breakup of ink jetted through the nozzle orifice. The removable assembly 112 comprises a frame 114 configured to support the gutter _{110 and the nozzle plate 106. The frame 114 is a rigid frame, for example formed from} _{glass fibre reinforced plastic (GFRP).} _{The removable assembly 112 comprises a gutter mounting portion 116 configured to} support the gutter 110 and a nozzle mounting portion 118 configured to support the _{nozzle plate 106. The frame 114 comprises first and second elongate support elements} _{120, 122 extending between the gutter mounting portion 116 and nozzle mounting} portion 118. _{The printhead body 102 and the removable assembly 112 comprising the nozzle plate} _{106 and the gutter 110 each comprise cooperating registration features. The} cooperating registration features are configured to provide a secure engagement and _{alignment of the removable assembly 112 with the printhead body 102.} The cooperating registration features comprise clamping surfaces 124 provided on the removable assembly 112, and pivoting clamps 126 provided on the printhead body 102. In use, the clamps 126 are configured to clamp the removable assembly in a direction opposite to the nozzle jetting direction J. That is, as the clamps 126 pivot downwards, as shown by arrow 126A, they exert a force 124F on the clamping portions _{124. It will be appreciated, however that a wide range of alternative cooperating} registration features may be used. 69420659-3 M&C PM364787GB 33 _{As the removable assembly 112 is clamped a sealing surface of the nozzle plate (or} _{the nozzle mounting portion 118) is pressed against the nozzle body 105, defining the} _{nozzle 104. A gasket 128 is provided between the nozzle components, the gasket 128} being compressed by the applied clamping force. _{The nozzle plate 106 is mounted to the frame 114 via the nozzle mounting portion 118.} _{As shown in Figure 11, the nozzle plate 106 is mounted to the nozzle mounting portion} _{118 by screws 130, with a further gasket 132 provided between the nozzle plate 106} and the nozzle mounting portion 118, allowing a seal to be created. Variable tightening _{of the screws 130, and compressibility of the gasket 132, provides an adjustable} mounting, permitting adjustment of the nozzle jetting direction to be made. In this way, the nozzle jetting direction can be aligned with the gutter 110 during a manufacturing step. The nozzle-gutter alignment can then be fixed (e.g. by clamping the nozzle plate, or by potting the components together), such that, in use, the nozzle-gutter alignment is substantially fixed. It will be appreciated that alternative fixing and adjustment systems _{can be used (e.g. a ball joint, adjustment screws, etc.)} _{As the removable assembly 112 is clamped in place a sealing surface of the gutter} _{mounting portion 134 is pressed against a corresponding gutter tube portion 136} _{provided on the printhead body 102. A further gasket (not shown) may be provided} between the gutter and the gutter tube portion to provide a seal. Such an arrangement allows gutter suction to be applied (e.g. by a gutter pump provided within the printer body 2) to the gutter 110 to recover unprinted droplets of ink. The gutter 110 is supported by the gutter mounting portion 116, which may, for example, be an injection moulded part attached to the frame 114. By providing a removable assembly 112 that can be removed from the printhead 100 while retaining a fixed positional relationship between the nozzle plate 106 and the gutter 110 it is possible to reduce the need for complex adjustments to be made within _{the printhead itself, thereby reducing the printhead complexity. The removable} _{assembly 112 may also allow some adjustment to be made during a manufacturing} setup, to accommodate small deviations in nozzle performance that arise through manufacturing processes. However, in some arrangements, sufficient manufacturing tolerances may be achieved to avoid the need for nozzle adjustment. 69420659-3 M&C PM364787GB 34 Further by arranging both alignment critical components (i.e. nozzle and gutter) in a first assembly, and sealing both parts to corresponding parts of the printhead during assembly, it is possible to provide a quickly replaceable component which is pre- aligned, while also ensuring good seals are formed between the nozzle body 105 and _{nozzle plate 106, and the gutter 110 and gutter tube portion 136.} _{As illustrated with reference to Figure 14 and Figure 15, which show schematic side} and top views of the printhead 100, respectively, the printhead 100 is a self-cleaning _{printhead comprising a cleaning chamber 140 which is selectively sealed by a sealing} _{mechanism 142. The sealing mechanism may be any convenient arrangement (e.g. a} sliding, rotating, or inflating sealing mechanism, of any of the sorts described above with reference to sealing mechanism 34). _{The first and second elongate support elements 120, 122 each extend along a} _{respective side of the cleaning clamber 140. The nozzle plate 106 and the gutter 110} are each disposed within the cleaning chamber 140. The additional components of the printhead (e.g. charge and deflection electrodes 107, 108) are also disposed within the cleaning chamber 140. _{The printhead body 102 comprises walls 144 defining the cleaning chamber 140. The} _{printhead 100 further comprise a removable closure portion 146, which may, for} _{example, define a lid of the cleaning chamber 140. The printhead is configured such} that removal of the removable closure portion 146 permits access to the interior of the _{cleaning chamber 140, and removal of the removable assembly 112. By providing a} _{removable lid (or other closure portion), it is possible to allow access to the internals of} the printhead for service (e.g. replacement of the nozzle plate), while also allowing a sealed cleaning chamber to be defined when required. Alternative access arrangements may be provided. For example, the printhead body _{102 may comprise separable components that cooperate to define a complete} printhead 102. 69420659-3 M&C PM364787GB 35 A cleaning cycle of the printhead 100 may be substantially as described above with _{reference to Figure 3. The printhead 100 may also comprise additional fill or drain} ports, allows cleaning fluid to be added or removed from the chamber as required. When servicing (or maintaining) a printer or printhead, it is possible to quickly remove a first removable assembly from the printhead body and insert a second removable assembly into the printhead body, such that when assembled the fixed positional relationship is established between the nozzle plate and the gutter. In this way, a rapid and adjustment free service operation can be performed. Prior to replacement of the removable assembly, a lid or closure portion of the printhead may be removed, to allow access. A further alternative arrangement is shown in Figure 16, in which an alternative _{printhead 200 for a continuous inkjet printer is shown. The printhead 200 comprises a} _{printhead body 202, a nozzle 204 for generating and ejecting a stream of ink droplets in} an ink jetting direction J. The nozzle 204 comprises a nozzle body 205 defining a _{nozzle chamber 212, and a nozzle plate 206, defining an orifice. The printhead further} comprises a charge electrode 207 for selectively charging the stream of ink droplets and at least one deflection electrode 208, disposed downstream of the charge electrode nozzle in the ink jetting direction, and configured to cause charged ink droplets to deflect in the ink deflection direction. The printhead further comprises a gutter 210 for receiving droplets of ink which are not used for printing. The charge electrode 207 and the deflection electrode(s) 208 are be supported by (e.g. fixedly mounted to) the printhead body 202. The nozzle chamber 212 (within nozzle body 205) is supplied with ink from an ink _{supply line 214 (e.g. from ink system 5). The nozzle chamber 212 may also be in fluid} communication with a bleed or purge line 216, allowing ink (or solvent) to be flushed through the nozzle chamber 212 in order to clean the nozzle. The nozzle chamber 212 may be closed at one end by the nozzle plate 206. Opposite the nozzle plate, a wall of the nozzle chamber may be defined by an actuator 218. The actuator 218 may be a piezo electric actuator. The piezo electric actuator may be secured to the opposite end _{of the nozzle body 205 to the nozzle plate 206. The actuator 218 is configured to impart} an oscillation on fluid contained within the nozzle body. The actuator 218 causes 69420659-3 M&C PM364787GB 36 pressure fluctuations within ink contained within the chamber, leading to a controlled breakup of ink jetted through the nozzle orifice. The printhead 200 is a self-cleaning printhead comprising a cleaning chamber 240 which is selectively sealed by a sealing mechanism 242. The sealing mechanism may be any convenient arrangement, for example as described above with reference to _{sealing mechanism 34 (e.g. a sliding, rotating, inflating, etc.).} _{The nozzle 204 and the gutter 210 are each disposed within the cleaning chamber 240.} The charge and deflection electrodes 207, 208 are also disposed within the cleaning chamber 240. The printhead body 202 comprises walls 244 defining the cleaning chamber 240. The printhead 200 may further comprise a removable closure portion (not shown), defining a lid of the cleaning chamber 240. Alternatively, the chamber may be sealed once manufactured, apart from a sealable ink aperture sealed by the sealing mechanism _{242, and fluid and electrical pass-through features to provide fluid or electrical signals} to and from the printhead. The ink line 214 and purge line 216 may enter the nozzle body 205 on a same side. Such an arrangement may permit a simplified fluid circuit arrangement, since only a single fluid feed through region into the cleaning chamber 240 is required. A cleaning cycle of the printhead 200 may be substantially as described above with _{reference to Figure 3. The printhead 200 may also comprise additional fill or drain} ports, allows cleaning fluid to be added or removed from the chamber as required. By providing a cleaning chamber that encloses all of the components that interact with _{ink during operation of the printhead 200 (e.g. nozzle 204, electrodes 207, 208, gutter} 210), it is possible to effectively clean each of those components, while also providing a simplified architecture, since no seals are needed between each of those components. In order to ensure accurate jet alignment, the nozzle 204 and/or printhead body 202 may provide an alignment mechanism, so as to allow the jet to be directed into the gutter 210. The nozzle 204 may be aligned with the gutter 210 during a setup or 69420659-3 M&C PM364787GB 37 assembly operation, and may then be permanently fixed in place for use. Alternatively, an adjustment mechanism may be provided, allowing post-manufacture alignment _{changes to be made. Alignment may be performed prior to final assembly of the} printhead. For example, alignment adjustments may be made before a closure is applied to the printhead body 202. Electrical wires supplying the piezo electric actuator may pass through the printhead wall 244 from an inside of the cleaning chamber 240 to the exterior of the cleaning _{chamber. Alternatively, the piezo electric actuator 218 may be provided at an exterior} of the cleaning chamber 240, with the nozzle body 205 being substantially within the cleaning chamber 240. Where the piezo electric actuator 218 is provided at an exterior of the cleaning chamber 240, a seal may be formed between the nozzle body 205 and the printhead _{body 202. For example, a compliant sealing component such as an O-ring (e.g. an} _{EPDM O-ring) may be provided between a face of the nozzle body opposite from the} _{nozzle orifice and the adjacent portion of the printhead body. Alternatively, a flexible} sealing component may be provided around an external surface of the nozzle body. _{The formation of such a seal may permit some flexibility in relative positioning of the} _{nozzle body 205 and printhead body 202, thereby permitting some jet alignment to be} made (e.g. with appropriately arranged clamping and adjustment mechanisms). _{Alternatively, where adjustability of the nozzle body is not required (e.g. due to} improved consistency of jet alignment, alignment insensitivity, or alternative alignment provision), the nozzle body may be securely engaged with the printhead body. The printhead 202 may comprise an electronics compartment 250 that is fluidically _{sealed from the cleaning chamber 240. In use, during cleaning the cleaning chamber} _{may be filled with solvent (as descried with reference to Figure 3). During cleaning, the} electronics compartment 250 may be maintained in a dry condition, allowing electronic _{components therein to be operated safely.} _{Electrical wires connected to the piezo electric actuator 218 that are exposed within the} _{cleaning chamber may be shielded from solvent, so as to minimise short circuit risk} _{and/or risk of degradation of the insulation due to solvent exposure. Alternatively, or in} 69420659-3 M&C PM364787GB 38 addition, where the piezo electric actuator 218 is provided within the cleaning chamber the piezo electric actuator 218 may be coated with a conformal insulating coating. Features described in the context of the printhead 200 (i.e. nozzle fully contained within a cleaning chamber) may be readily combined with features of the printhead 100 (i.e. removeable nozzle and gutter assembly) and vice versa. Similarly, features described in the context of the printheads 100, 200 may be combined with features of the _{deflection electrodes described in the context of Figures 4 to 11. Further still, the} printheads 100, 200, may each be used in place of printhead 3, shown in Figures 1 and 2. The terms “having”, “containing”, “including”, “comprising” and the like are open and the terms indicate the presence of stated structures, elements or features but not preclude the presence of additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art 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 alone or in any appropriate combination with any other feature disclosed or illustrated herein. 69420659-3

Claims

M&C PM364787GB 39 CLAIMS: _{1. A deflection electrode for a continuous inkjet printer comprising an elongate} _{body portion, the body portion having:} a first dimension in an ink jetting direction; a second dimension in a second direction perpendicular to the ink jetting _{direction, the second direction being an ink deflection direction; and} a third dimension in a third direction perpendicular to the ink jetting direction and the ink deflection direction; wherein the first dimension is at least 20 millimetres, and the third dimension is less than 5 millimetres. _{2. The deflection electrode according to claim 1, wherein:} _{the third dimension is less than 4 millimetres; and/or} the third dimension is less than 3 millimetres; and/or t_{he third dimension is around 2 millimetres or less.} _{3. The deflection electrode according to claim 1 or 2, wherein the first dimension} _{at least 25 millimetres.} _{4. The deflection electrode according to any one of claims 1 to 3, wherein edges} defined between adjacent surfaces of the body portion have a radius of curvature of at least 0.5 millimetres. _{5. The deflection electrode according to any one of claims 1 to 4, further} comprising a support pillar extending from the body portion in the second direction, the support pillar being configured to secure the deflection electrode to a printhead and to _{electrically connect the body portion to an energisation source.} _{6. The deflection electrode according to any one of claims 1 to 5, wherein the} body portion defines a deflection surface extending along the first direction, the deflection surface having a first portion generally parallel to the first direction, and a _{second portion inclined at an acute angle to the first direction and being angled away} from the ink jetting direction, the first portion being provided at a first end of the 69420659-3 M&C PM364787GB 40 deflection electrode, and the second portion being provided at a second end of the deflection electrode, the first portion being an upstream end in the ink jetting direction. _{7. The deflection electrode according to any one of claims 1 to 6, further} comprising an insulating coating. 8. A printhead for a continuous inkjet printer comprising: a nozzle for generating and ejecting a stream of ink droplets in the ink jetting direction; a charge electrode for selectively charging the stream of ink droplets; a_{deflection electrode according to any one of claims 1 to 7 disposed} downstream of the charge electrode nozzle in the ink jetting direction, and configured to cause charged ink droplets to deflect in the ink deflection direction. _{9. The printhead according to claim 8, wherein:} the deflection electrode comprises a first deflection electrode, the printhead further comprising a second deflection electrode. _{10. The printhead according to claim 9, wherein:} opposing surfaces of the first deflection electrode and the second deflection electrode are separated by a deflection electrode separation of around 4 millimetres. _{11. The printhead according to any one of claims 8 to 10, wherein:} _{the second deflection electrode is a ground electrode, and defines a deflection} _{surface opposing the first electrode; and} the second deflection electrode has a greater dimension in the third direction than the deflection electrode, and extends further than the deflection electrode in both _{a positive and negative direction along the third dimension.} _{12. The printhead according to claim 11, wherein:} the deflection surface of the second deflection electrode is curved around the first deflection electrode. _{13. The printhead according to any one of claims 8 to 12, wherein:} 69420659-3 M&C PM364787GB 41 t_{he printhead comprises a cleaning chamber selectively sealable by a sealing} mechanism, and the deflection electrode is disposed within the cleaning chamber. _{14. The printhead according to claim 13, wherein the printhead comprises a} printhead body, the printhead body comprising walls defining the cleaning chamber, wherein the walls are spaced apart from surfaces of the body portion of the deflection _{electrode by a minimum separation distance of at least 1 millimetre in each of the first,} second and third directions. _{15. The printhead according to claim 14, wherein the cleaning chamber has a} height in the third direction of no more than 8 millimetres. _{16. The printhead according to any one of claims 8 to 15, wherein the deflection} electrode further comprises a support pillar extending from the body portion in the second direction, the support pillar being configured to secure the deflection electrode to the printhead and to electrically connect the body portion to an energisation source. _{17. The printhead according to claim 16, wherein the support pillar is enclosed in an} insulating material. _{18. A continuous inkjet printer comprising:} a print head according to any one of claims 8 to 17; an ink system for storing ink and supplying ink to a print head; and a high voltage source configured to supply a voltage of at least 2000 volts in magnitude to the deflection electrode. _{19. The continuous inkjet printer according to claim 18, wherein the printhead is a} printhead according to claim 9, or any preceding claim dependent thereon, wherein the power supply is configured to supply first voltage of at least 2000 volts in magnitude to the deflection electrode, and to supply second voltage of at least 2000 volts in magnitude to the second deflection electrode, the first and second voltages being of opposite polarities. 69420659-3 M&C PM364787GB 42 20. A printhead for a continuous inkjet printer comprising: a printhead body; a_{nozzle for generating and ejecting a stream of ink droplets in an ink jetting} direction, the nozzle comprising a nozzle body defining a nozzle chamber, and an nozzle plate, defining an orifice; a charge electrode for selectively charging the stream of ink droplets; a deflection electrode according disposed downstream of the charge electrode in the ink jetting direction, and configured to cause charged ink droplets to deflect in an _{ink deflection direction; and} a gutter for receiving droplets of ink which are not used for printing; wherein: t_{he printhead comprises a removable assembly comprising the nozzle} _{plate and the gutter, such that the removable assembly can be removed from} the printhead while retaining a fixed positional relationship between the nozzle p_{late and the gutter.} _{21. The printhead according to claim 20, wherein the removable assembly} comprises a frame configured to support the gutter and the nozzle plate. _{22. The printhead according to claim 21, wherein the removable assembly} comprises a gutter mounting portion configured to support the gutter and a nozzle mounting portion configured to support the nozzle plate, the frame comprising first and second elongate support elements connected between the first and second mounting portions, the first and second elongate support elements each extending along a respective side of the cleaning clamber. _{23. The printhead according to any one of claims 20 to 22, wherein:} the printhead comprises a cleaning chamber selectively sealable by a sealing mechanism, and the nozzle plate and the gutter are each disposed within the cleaning chamber. _{24. The printhead according to claim 23, wherein, the printhead comprises a} printhead body comprising walls defining the cleaning chamber, the printhead further comprising a removable closure portion, defining a portion of a wall of the cleaning chamber. 69420659-3 M&C PM364787GB 43 25. The printhead according to claim 24, wherein the printhead is configured such that removal of the removable closure portion permits removal of the removable _{assembly comprising the nozzle plate and the gutter.} _{26. The printhead according to any one of claims 20 to 25, wherein the printhead} _{and the removable assembly comprising the nozzle plate and the gutter each comprise} cooperating registration features, configured to provide a secure engagement and _{alignment of the removable assembly with the printhead body.} _{27. The printhead according to any one of claims 20 to 26, wherein the printhead is} configured to clamp the removable assembly in a direction opposite to the nozzle jetting direction. _{28. The printhead according to any one of claims 20 to 27, wherein the printhead} body comprises a gutter tube configured to engage with the gutter. 29. The printhead according to any one of claims 20 to 28, wherein the deflection electrode comprises a deflection electrode according to any one of claim 1 to 7. 30. A method of assembling a printhead for a continuous inkjet printer, the printhead comprising: a printhead body; a nozzle for generating and ejecting a stream of ink droplets in an ink jetting direction, the nozzle comprising a nozzle body defining a nozzle chamber, and an nozzle plate, defining an orifice; a charge electrode for selectively charging the stream of ink droplets; a deflection electrode according disposed downstream of the charge electrode _{in the ink jetting direction, and configured to cause charged ink droplets to deflect in an} _{ink deflection direction; and} a gutter for receiving droplets of ink which are not used for printing; the method comprising inserting a removable assembly within the printhead _{body, the removable assembly comprising the nozzle plate and the gutter, such that} when assembled a fixed positional relationship is established between the nozzle plate and the gutter. 69420659-3 M&C PM364787GB 44 31. A self-cleaning printhead for a continuous inkjet printer comprising: a printhead body; a nozzle for generating and ejecting a stream of ink droplets in an ink jetting direction; a charge electrode for selectively charging the stream of ink droplets; a deflection electrode disposed downstream of the charge electrode in the ink jetting direction, and configured to cause charged ink droplets to deflect in an ink deflection direction, and a gutter for receiving droplets of ink which are not used for printing; wherein the printhead body defines a cleaning chamber selectively sealable by a sealing mechanism; wherein the nozzle, the charge electrode, the deflection electrode and the gutter are disposed within the cleaning chamber. 69420659-3