Printing assembly

Abstract

A printer comprises a frame and a printing assembly 100. The printing assembly comprises one or more stationary print heads 102a-c for dispensing material, and a movement mechanism 108 for moving a su

Description

Field of the invention The present invention relates to methods and systems for printing. In particular, the present invention relates to a printing assembly and a printer and to methods for operating the printing assembly and printer. Background to the Disclosure Inkjet printers work by spraying droplets of liquid ink onto paper through microscopic nozzles, forming images and text. Conventionally, these nozzles are located on a printhead that moves across the substrate, controlled by printer software to precisely place each ink droplet. In use, as the print head moves, it ejects microscopic droplets of ink through the nozzles onto precise locations on the substrate to recreate images or text. Inkjet heads and their associated electronics are typically high cost components in a printer. Inkjet printers are typically divided into two types: Type 1, Single pass, format machines and Type 2, multiple pass format machines. With single-pass machines, an array of printheads are located above a printing width of a web of a substrate so that these printheads are able to print a design onto a substrate in a single pass under the printheads. These machines are fast but expensive, requiring large numbers of printheads to provide a substantial printing width and hence requiring a large cost. Furthermore, these machines require high degrees of precision and sophistication. Automatic cleaning maybe required to mitigate the inherent problem of keeping a large number of nozzles working since trouble shooting blocked nozzles after the fact becomes increasingly different as the number of print heads increases. Wide-format machines scan across the web of the substrate at 90 degrees. These machines have a single set of printheads scanning across the web, where the web is then advanced between successive sweeps of print heads. These wide-format machines are typically slower than, but cheaper than, single pass machines. Furthermore, the higher printing width that is typical in wide-format machines can limit the uses of these machines. Systems and methods that provide more efficient, quicker, or lower cost, printers are generally desired. Summary of the Disclosure According to an aspect of the present disclosure, there is described: a printer, the printer comprising: a frame; and a printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame of the printer; and a movement mechanism for moving a substrate relative to the print heads; wherein the movement mechanism is arranged to move the substrate in a first direction so as to move the print heads relative to the substrate across the web of the substrate. According to an aspect of the present disclosure, there is described: a printer, the printer comprising: a frame; and a printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame; and a movement mechanism for moving a substrate relative to the print heads; wherein the movement mechanism is arranged to move the substrate in a first direction that has a component and / or is perpendicular to a feeding direction, wherein the feeding direction is a direction in which the substrate moves through the printing assembly between an inlet of the printing assembly and an outlet of the printing assembly. For example, wherein the feeding direction of a particular point of the substrate is the direction in which this point of the substrate moves in order to progress towards the outlet of the printing assembly. According to an aspect of the present disclosure, there is described: a printer, the printer comprising: a frame; and a printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame; and a movement mechanism for moving a substrate relative to the print heads; wherein the movement mechanism is arranged to move the substrate in a first direction that has a component and / or is parallel to a direction of a nozzle axis of the print heads. Preferably, the movement mechanism is arranged to also move the substrate: along the web of the substrate; and / or in a feeding direction; and / or perpendicular to a direction of a nozzle axis of the print heads. Preferably, the movement mechanism comprises: a first component mechanism that moves the substrate in the first direction; and a second component mechanism, e.g. a conveying mechanism, that moves the substrate in a second direction so as to advance the substrate in a feeding direction. Preferably, the movement mechanism is arranged to: in a first step, move the substrate in a feeding direction; in a second step, move the substrate perpendicular to the feeding direction so as to sweep the print head across the substrate; and in a third step, move the substrate in the feeding direction. Preferably, the movement mechanism is arranged to move the substrate in the feeding direction by a printing step. Preferably, the movement mechanism is arranged to, in a fourth step, move the substrate perpendicular to the feeding direction so as to sweep the substrate across the print head, preferably wherein the direction of movement of the fourth step is opposite the direction of movement of the second step. Preferably, the movement mechanism is arranged to move the substrate in an outward sweep and a reverse sweep, the outward sweep being opposite the reverse sweep, preferably wherein the movement mechanism and / or a conveying mechanism is arranged to advance the substrate between the reverse sweep and the outward sweep. Preferably, the movement mechanism is arranged to move the substrate perpendicular to a feeding direction between a first position and a second position so as to sweep the substrate across the print heads, wherein the movement mechanism is arranged to provide a plurality of printing sweeps between the first position and the second position, preferably wherein the movement mechanism is arranged to advance the substrate in the feeding direction between printing sweeps. Preferably, the movement mechanism is arranged to perform a plurality of sweeps of the substrate across the print heads between one or more advances in the feeding direction. Preferably, the movement mechanism is arranged to advance the substrate in the feeding direction between each sweep of the substrate across the print heads. Preferably, the movement mechanism is arranged to sweep the substrate across the print heads at an angle to a nozzle axis of the print heads, preferably at an angle of between 30 and 60 degrees, more preferably at an angle of between 40 and 50 degrees. Preferably, the movement mechanism is arranged to move the substrate at a constant speed and / or velocity during a working portion of a sweep, the working portion being a portion during which the print heads are able to, and / or arranged to, deposit material onto the substrate. Preferably, the movement mechanism is arranged to accelerate and / or decelerate the substrate during an acceleration and / or deceleration ramp of the sweep. Preferably, the movement mechanism is arranged to rotate a drum connected to the substrate in order to advance the substrate in a feeding direction. Preferably, a direction of a nozzle axis of the print heads is perpendicular to a feeding direction. Preferably, a direction of a nozzle axis of the print heads is at an angle of between 30 degrees and 60 degrees. More preferably, between 40 degrees and 50 degrees, to a feeding direction. Preferably, the feeding direction is along the web of the substrate. Preferably, the printer comprises a substrate holder for holding the substrate, wherein the motor is arranged to drive a movement of the substrate holder. Preferably, the substrate holder comprises one or more divert bars, preferably one or more divert bars arranged to alter a direction of a substrate passing over the divert bars. Preferably, the printer comprises a plurality of divert bars oriented at the same angle and / or oriented at 90 degree angles relative to each other, wherein the substrate is arranged to pass over a succession of divert bars. Preferably, the movement mechanism is arranged to move one or more of the divert bars so as to move the substrate perpendicular to the feeding direction. Preferably, the movement mechanism comprises a divert and turnover assembly, wherein the divert and turnover assembly comprises two elongate members positioned at 90 degrees to each other, wherein the elongate members are separated in a z-direction. Preferably, the printing assembly is arranged to print onto a substrate with a printing width of between 50mm and 1250mm, preferably a printing width between 150 and 650mm, more preferably a printing width between 250mm and 350mm. Preferably, the print heads are arranged to print with a print width of no more than 100mm, and / or no more than 55mm, and / or no more than 35mm. Preferably, the printing assembly is arranged to print onto a substrate with a printing width of at least 150mm. Preferably, the print heads are arranged to print with a print width of no more than 100mm preferably no more than 55mm. Preferably, the movement mechanism comprises a conveying mechanism, the conveying mechanism arranged to be driven by a motor to move the substrate in the feeding direction. Preferably, the conveying mechanism is arranged to move the substrate continuously in the first direction during printing. Preferably, the conveying mechanism is arranged to move the substrate in the feeding direction between sweeps of movement perpendicular to the feeding direction. Preferably, the conveying mechanism is arranged to advance the substrate by a printing step, preferably wherein the printing step is between 10 and 110mm, preferably between 50 and 70mm, more preferably 55mm. Preferably, the printing step is dependent on a printing width of the print heads, preferably wherein the printing step is: a distance at least 90% of the printing width of the print heads, at least 100% of the printing width, and / or at least 110% of the printing width; and / or a distance no more than 130% of the printing width of the print heads, no more than 130%ofthe printing width, and / or no more than 110% of the printing width. Preferably, the movement mechanism is arranged to move the substrate in the first direction at an angle to a nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to a nozzle axis of the print heads. Preferably, the feeding direction is at an angle to a nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to a nozzle axis of the print heads, more preferably at an angle of between 40 degrees and 50 degrees to a nozzle axis of the print heads. According to an aspect of the present disclosure, there is described a printing assembly, the printing assembly comprising: one or more print heads for dispensing material, each print head comprising a plurality of nozzles arranged along a nozzle axis; wherein the printing assembly is arranged to print onto a substrate using a relative direction of movement between the substrate and a nozzle axis of the print heads such that the substrate moves at an angle to the nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to the nozzle axis of the print heads, more preferably at an angle of between 40 degrees and 50 degrees to the nozzle axis of the print heads. Preferably, the printer is arranged to move the substrate relative to the print heads (and / or the print heads relative to the substrate) at an angle to a nozzle axis of a print head that is determined as 0P = arctanC^2), where n is an integer value, Sr is an intra-row spacing of nozzles in each row of the print dr head, and Dr is a distance between a first row of nozzles within the print head and a second row of nozzles within the print head. Preferably, each print head comprises a plurality of rows of nozzles, preferably a plurality of rows of nozzles of different widths. Preferably, a first row, or set of rows, of the print head has a different printing width to a second row, or set of rows of the print head. Preferably, wherein the second row is arranged to dispense material so as to merge successive strips of material dispensed by the first row. Preferably, the printer being arranged to move the substrate relative to the print heads (and / or the print heads relative to the substrate) at an angle to a nozzle axis of a print head so as to avoid overlap between material dispensed by different rows of print heads. Preferably, the print heads are arranged to print at a different resolution along the web of the substrate than across the web of the substrate, preferably a lower resolution. Preferably, the print heads are arranged to print at the different resolution so as to avoid the overlap between the material. Preferably, the printer comprises no more than 6 print heads. Preferably, the printing heads are arranged to print at least 80m / minute (e.g. at 10Om / minute) and / or at least 500 DPI (e.g. at 600DPI). Preferably, the printer further comprises a user interface. Preferably, the printer comprises a means (e.g. a communication interface) for receiving an input, preferably a design, from a further device. Preferably, the printer comprises a means for receiving a substrate (e.g. an input), preferably wherein the means for receiving the substrate is arranged to receive a substrate in the form of a roll. Preferably, the printer comprises one or more curing or drying mechanisms, e.g. ultraviolet (UV) curing or drying mechanisms, preferably wherein the curing mechanism is arranged adjacent the print heads so as to dry the material deposited by the print heads. Preferably, the printer comprises a plurality of curing or drying mechanism located at opposite sides of the print heads. Preferably, the printer being a roll-to-roll printer. A printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame of the printer; and a movement mechanism for moving a substrate relative to the print heads; wherein the movement mechanism is arranged to move the substrate in a first direction so as to move the print heads relative to the substrate across the web of the substrate. According to an aspect of the present disclosure, there is described: a printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame; and a movement mechanism for moving a substrate relative to the print heads; wherein the movement mechanism is arranged to move the substrate in a first direction that has a component and / or is perpendicular to a feeding direction; preferably, wherein the feeding direction is a direction in which the substrate moves through the printing assembly. According to an aspect of the present disclosure, there is described: a printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame; and a movement mechanism for moving a substrate relative to the print heads; wherein the movement mechanism is arranged to move the substrate in a first direction that has a component and / or is parallel to a direction of a nozzle axis of the print heads. According to an aspect of the present disclosure, there is described: a printing assembly, the printing assembly comprising: one or more print heads for dispensing material, each print head comprising a plurality of nozzles arranged along a nozzle axis; wherein the printing assembly is arranged to print using a feeding direction that is at an angle to the nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to the nozzle axis of the print heads, more preferably at an angle of between 40 degrees and 50 degrees to the nozzle axis of the print heads. Preferably, the dispensed material is a one of: an ink; a clear liquid; a suspension of chemicals; or a functional fluid. According to an aspect of the present disclosure, there is described: a method of printing using the printing assembly or printer of any preceding printer or printing assembly. According to an aspect of the present disclosure, there is described: a method of printing using the printer of any preceding claim, the method comprising: operating the movement mechanism to move the substrate in a direction of a nozzle axis of the print heads; and / or operating the print heads to dispense material from the print heads. Preferably, the method further comprises operating the print heads during a working portion of a sweep of the substrate relative to the print heads, preferably wherein the substrate moves at a constant speed during the working portion. Preferably, operating is controlled by a motion controller. Preferably, the method further comprising determining a printing angle based on the print heads, preferably based on a spacing between rows of nozzles in the print heads and an intra-row distance between nozzles in each row of the print heads. According to an aspect of the present disclosure, there is described: a method of operating a printer comprising a frame and one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame of the printer, the method comprising; moving the substrate in a first direction so as to move the substrate relative to the print heads across the web of the substrate. Preferably, the method comprises operating the print heads during a working portion of a sweep of the substrate relative to the print heads, preferably wherein the substrate moves at a constant speed during the working portion. Preferably the method comprises moving the substrate in the first direction so as to move the substrate at an angle to a nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to a nozzle axis of the print heads. According to an aspect of the present disclosure, there is described: a method of operating a printer, so as to print using a feeding direction that is at an angle to the nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to the nozzle axis of the print heads, more preferably at an angle of between 40 degrees and 50 degrees to the nozzle axis of the print heads. According to an aspect of the present disclosure, there is described: a method of operating a printing assembly, the printing assembly comprising: one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame; and a movement mechanism for moving a substrate relative to the print heads; wherein the method comprises operating the movement mechanism to move the substrate in a first direction that has a component and / or is parallel to a direction of a nozzle axis of the print heads. According to an aspect of the present disclosure, there is described: a method of operating a printing assembly, the printing assembly comprising: one or more print heads for dispensing material, each print head comprising a plurality of nozzles arranged along a nozzle axis; wherein the method comprises printing using a feeding direction that is at an angle to the nozzle axis of the print heads, preferably at an angle of between 30 degrees and 60 degrees to the nozzle axis of the print heads, more preferably at an angle of between 40 degrees and 50 degrees to the nozzle axis of the print heads. Preferably, the method comprises a computer-implemented method. According to an aspect of the present disclosure, there is described: a (e.g. non-transitory) computer readable medium comprising instructions for performing the aforesaid method. Any feature in one aspect of the disclosure may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, features implemented in hardware may be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly. Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory. It should also be appreciated that particular combinations of the various features described and defined in any aspects of the disclosure can be implemented and / or supplied and / or used independently. The disclosure extends to methods and / or apparatus substantially as herein described with reference to the accompanying drawings. The disclosure will now be described, by way of example, with reference to the accompanying drawings. Description of the Drawings Figures 1a-1f show various embodiments of printing assemblies according to the present disclosure. Figures 2a-2g show further embodiments of printing assemblies according to the present disclosure. Figure 3 shows a further embodiment of a printing assembly according to the present disclosure. Figures 4a and 4b show possible orientations of print heads. Figures 5a and 5b illustrate movements of a substrate of a printing assembly. Figures 6a and 6b show embodiments of computer devices that may be a part of a printing assembly. Figures 7 and 8 show methods of operating a printing assembly. Figures 9a and 9b illustrate movements of a substrate holder of a printing assembly. Figures 10a and 10b show velocity and acceleration profiles of a substrate holder of a printing assembly. Figures 11a, 11b, 12a, 12b, 13a-13d, 14a, and 14b illustrate the operation of a print head with a plurality of rows of nozzles. Description of the preferred embodiments Referring to Figure 1a, there is shown a printing assembly 100 viewed from above. This printing assembly may comprise a printer, or may comprise a part of a printer (e.g. the printing assembly may be arranged to be inserted into an existing printer that may comprise, e.g. a frame, a substrate inlet, a substrate storage (e.g. a drum of paper), etc. The printing assembly 100 comprises one or more printing heads 102a, 102b, 102c (these printing heads may also be called ‘print heads’ or ‘printheads’). Each of the print heads is arranged to deposit material onto a substrate. Typically, each of the print heads comprises one or more jets or nozzles, where the corresponding print head is able to dispense fluid (or another material) though these nozzles, e.g. in the form of droplets. The fluid dispensed by the print heads may be ink; however, it will be appreciated that the methods and systems described herein are more generally suitable for dispensing any fluid by a print head (such as clear liquids (varnish), suspensions of chemicals or functional fluids (e.g. the methods disclosed herein may be used to dispense precise amounts of pharmaceutical fluids)). This arrangement enables the printing assembly to dispense material onto a substrate 104 that is disposed upon a substrate holder 106 in order to print a design (e.g. text or images) onto the substrate. The substrate 104 may be any material (e.g. paper, card, fabric, etc.). Typically, the substrate holder 106 comprises a retaining structure that enables the substrate holder to secure the substrate on the substrate holder. For example, the retaining structure may comprise a moveable locking arm. Typically, the substrate 104 is provided as a web, where a web of the substrate is fed onto the substrate holder 106 to enable the print heads 102a, 102b, 102c to print material onto the web as the substrate passes beneath the print heads. The web may be formed from a part of a roll or body of material. For example, the printing assembly may comprise a roll-to-roll printer, where the web is formed of a portion of a roll of substrate (so that the substrate is unrolled to provide the substrate to the substrate holder). Specifically, the roll may be unrolled and then a portion of this roll may be cut prior to printing to provide the web. In such a printing assembly, movement along the substrate, e.g. in the direction in which the substrate moves between an inlet and an outlet of the printing assembly, can be considered to be movement along a web of the substrate. This is also referred to herein and in the figures as the ‘feeding direction’. Movement across the substrate, e.g. perpendicular to the direction in which the substrate moves between an inlet and an outlet of the printing assembly, can be considered to be movement across a web of the substrate. The feeding direction is the direction at which, for a given point, the substrate is fed in order to move the substrate from the inlet of the printing assembly towards the outlet of the printing assembly. Where the substrate is moved directly from the inlet to the outlet (along the shortest possible route), the feeding direction is typically a fixed direction. In some embodiments, the substrate may take a more convoluted route through the printing assembly and in such embodiments the feeding direction may change as the substrate moves through the printing assembly (e.g. if the substrate is diverted so as to change a direction of movement of the substrate). In a single-pass printer, print heads can be arranged across the entirety of the substrate so that the printheads can print across the substrate and the substrate can then be advanced (in the feeding direction) so as to enable these printheads to print along the substrate. In the printing assembly of the present disclosure, the substrate is typically advanced between printing steps so that print heads can move across the web of the substrate during a printing step so as to print a design. Typically, each print head 102a, 102b, 102c is disposed along an axis (e.g. in a line in the ‘x’ direction or the ‘y’ direction shown in Figure 1a), where the web of the substrate passes perpendicular to this axis, e.g. the print heads are arranged to print a string of droplets across a web of the substrate. The direction of feeding, e.g. the x-direction movement of the substrate through the printing assembly, is typically perpendicular to the axis of the print heads so that the print heads can print a string of droplets onto the substrate in a row as it passes beneath the print heads. As described below, the present disclosure considers a mechanism for moving the substrate relative to one or more print heads in order to print a design onto the substrate. To provide an example, Figure 1 a shows a printing assembly in which the substrate 104 is arranged to move in the y direction so that each print head is able to print a string of droplets of solvent in a printing angle across a (part of) the substrate as the substrate moves. This direction of movement of the substrate may be perpendicular to the feeding direction so that the printing assembly is arranged to print sweeps of material onto the substrate between advancements of the substrate in the feeding direction. In general, according to certain aspects of the present disclosure, the substrate holder 106 is arranged to move (or rotate) relative to a frame of the printing assembly. Typically, the print heads 102a, 102b, 102c are fixed to this frame of the printing assembly (that is, e.g., stationary during use of the printer). Therefore, the movement of the substrate holder results in the substrate moving relative to the print heads so that the print heads are able to print a design onto the substrate. To effect this movement, the printing assembly 100 may comprise an actuator or a motor 108 that is arranged to move the substrate holder in one or more (e.g. predefined) directions. To achieve a movement of the substrate 104 in the feeding direction, the motor 108 may be arranged to rotate one or more drums located at an inlet and an outlet of the printing assembly in order to advance the web forwards in between movements of the substrate holder 106. The substrate is then able to unwind from an input roll, and wrap round a first drum, pass through or over the substrate holder to pass the substrate by the print heads, then wrap round a second drum in order to pull the substrate through the printing assembly. Finally, the web may be rewound onto an output roll. In some examples, the drums may be motorised by respective motors. In some embodiments, the motor 108 operates the substrate holder 106 so as to move the substrate in one or more predefined directions defined by an x, y plane of the substrate holder. In some embodiments the motor may also move the substrate in a z direction. In this regard, the substrate holder typically lies on a plane that extends in an y direction and a x feeding direction, where the z direction extends perpendicularly out of this plane. The one or more printing heads are then located above or below the substrate holder in the z direction so that these heads pass above or below the substrate holder as the motor causes a movement of the substrate holder in the x, y plane. It will be appreciated that while the disclosure generally refers to ‘the motor 108’, in practice the printing assembly may comprise a variety of motors in order to achieve the various movements described herein. For example, a first motor may effect the rotation of the drums in order to advance the substrate in the feeding direction and a second motor may effect the movement of the substrate holder 106 that causes the substrate 104 to move within the x,y plane relative to the print heads 102a, 102b, 102c. Where the present disclosure refers to ‘the motor’, this should be interpreted as referring to a motor that is one of one or more motors of the printing assembly. The motor may also be arranged to cause the dispelling of ink from the nozzles of the print heads. More generally, according to the present disclosure, a movement mechanism (e.g. that comprises the motor) is typically arranged to move the substrate holder 106 in each of a first direction and a second direction perpendicular to the first direction, where the first direction is, for example, the y direction and the second direction is, for example, in the x direction. Therefore, the movement mechanism is able to move the substrate both along and across a direction of the print heads 102a, 102b, 102c. This arrangement provides a printer in which the print heads 102a, 102b, 102c can be held stationary (or near stationary), while the substrate 104 moves relative to the print heads to enable the print heads to print a design onto the substrate. The above-described arrangement in which a substrate moves relative to a fixed array of print heads is of particular benefit when the print heads comprise high frequency print heads, e.g. which can print at 100 m / min at 600 dpi (dots per inch). Such print heads enable rapid printing, but can be unsuitable in conventional printing machines where the print heads are arranged to move in between the printing of tracks. In this regard, the rapid accelerations that occur when moving the print heads can cause pressure changes in the ink within the print heads, resulting in jetting failure. This problem is avoided with the arrangement disclosed herein since the print heads and the ink supply can be kept stationary, with the substrate being moved instead to achieve printing. The resulting production speed enables a printing assembly with high printing speed without the need for a great number of printer heads (as would be needed for a single-pass machine that has print heads located across the entire width of the substrate holder 106. Therefore, this printing assembly bridges a gap between expensive and complex single-pass printing assemblies with numerous print heads and simpler, but slower, printing assemblies that have a printing speed limited by the accelerations and deceleration experienced by the print heads. Typically, the printing assembly 100 comprises four print heads. In some embodiments, each print head has a print width of 2 inches. By moving the substrate holder 106 in a direction that is perpendicular to a feeding direction (e.g. by moving the substrate holder in the x direction) a small number of print heads can still be used to print a high width, e.g. 330mm wide) design. It will be appreciated that the disclosures herein can be used with any number or configuration of print heads. In some examples, the one or more printing heads are arranged so that the rows of nozzles of these printing heads extend in a x direction on an x, y plane above or below the substrate holder 106 and the motor 108 drives the substrate 104 back and forth at an angle 110 less than 90 degrees from the y direction (e.g. the motor may drive the substrate back and forth in the y direction). In a specific embodiment, the print heads 102a, 102b, 102c comprise four rows of printer nozzles, e.g. a Row A, a Row B, a Row C, and a Row D with each row extending in a first direction (e.g. the x direction) and each row of nozzles being parallel to each other row (e.g. each with row being located parallel to each other row in the y-direction). The motor 108 drives the substrate 104 back and forth by a distance determined by a width of the substrate and / or by a printing width. Typically, the printing assembly 100 comprises a computer device, where a processor of this computer device is arranged to determine a buffer and to move the substrate holder back and forth a distance that is the width of the substrate minus the buffer. The buffer may be, for example, a percent of the width. For example, given a substrate width of 300 mm and a 10% buffer, the distance moved by the substrate holder (and hence the substrate) may be 270 mm, leaving a 15 mm border on either edge of the width of the substrate. In other examples, the buffer is determined based on a maximum achievable printing width, for example a maximum printing width of 330mm. In other examples, the buffer is set by a user of the printing assembly and hence the printing width is determined by subtracting the buffer from the substrate width. The motor 108 may be arranged to move the substrate holder 106 along sliders. For example, the sliders may comprise a stationary member attached to a frame of the printing assembly and a moving member attached to the substrate holder. The sliders may be fixed on the substrate holder at a predetermined angle to achieve a desired angle of printing. Alternatively, the substrate holder 106 may be arranged to move the substrate 104 relative to the print heads 102a, 102b, 102c using a ‘divert and turnover assembly’ that comprises two rigid members mounted in a cross with 90 degree quadrants sitting above a ball screw (as shown, for example in Figures 5a and 5b). The divert and turnover assembly is driven by the motor 108 to move the substrate during printing. This mechanism enables movement of the substrate in a range of directions. The divert and turnover assembly (or, more generally, the substrate holder and / or a movement mechanism associated with the substrate) may be arranged to provide compressed air to the substrate in order to produce an air bearing supporting the substrate so that the can move back and forth over the divert and turnover assembly with low friction. Typically, the substrate holder 106 comprises one or more divert bars, where the substrate is arranged to pass over these divert bars. The motor 108 may then be arranged to move the divert bars in order to move the substrate relative to the print heads 102a, 102b, 102c. In some examples, ink is dispensed by spraying ink from jets located in the print heads 102a, 102b, 102c. In other examples the jets dot ink onto the substrate. Each print head may contain one or more coloured inks; typically, each printing head contains cyan, magenta, black and yellow ink in separate channels. Typically, the printing heads are arranged to print 100m / minute at 600 dpi. Whilst in typical printing assemblies, scanning at this speed risks causing severe pressure changes in the ink, by keeping the print heads of the present printing assembly stationary, higher printing speeds can be achieved without jetting failure. While the print heads 102a, 102b, 102c are typically arranged to deposit ink onto the substrate 104, it will be appreciated that other materials may be printed (e.g. fabric, fluids, powders, etc.). Typically, the print heads are arranged to print a UV, pharmaceutical fluid, solvent, oil and / or water-based material. In some embodiments, the print heads 102a, 102b, 102c have a print width of 2 inches. In some embodiments, the substrate holder 106 is arranged to hold a substrate 104 with a web width of 330m. It will be appreciated that various types and dimensions may be used. By moving the print heads in the direction of the line of the print heads, higher printing widths may be achieved (with each printing stage providing printing on a web width of, e.g. 330mm). Typically, each print head 102a, 102b, 102c comprises a plurality of nozzles arranged along a nozzle axis (e.g. the nozzle axis may extend in the ‘y’ direction of Figure 1a). The printing assembly typically defines a feeding direction that is perpendicular to the nozzle axis (e.g. in the ‘x’ direction of Figure 1a), where the substrate moves in this feeding direction in order to move from an inlet of the printing assembly to an outlet of the printing assembly. The feeding direction may be defined such that the substrate moves in the feeding direction between sweeps of the substrate across the print heads. Typically, the print heads are arranged to deposit material in one or more strings of droplets of ink in the printing angle during one or more printing sweeps and then the motor 108 is arranged to advance the substrate 104 in the feeding direction in between printing sweeps. Typically, no material is deposited by the print heads while the substrate is advancing in the feeding direction. Each print head may be arranged to print a different colour of material, e.g. the print heads may comprise yellow, magenta, cyan, and black print heads so that the combination of print heads are able to print various colours of material onto the substrate by depositing a combination of material onto the substrate as it passes beneath the print heads. Typically, the print heads are arranged so that the nozzle axes of the plurality print heads are parallel to each other. Therefore, a feeding direction that is at a given angle to a nozzle axis of the print heads will be at this angle to each nozzle axis of the print heads. Referring to Figure 1 b, there is shown an embodiment of the printing assembly 100 viewed from above. As shown in Figure 1b, the print heads sit above the substrate 104 in a z-direction and the substrate is arranged to move across a plane in the x and y directions. As is also shown in Figure 1b, the printing assembly 100 comprises one or more printing heads 102a, 102b, 102c. Each printhead is arranged to deposit material onto the substrate 104. Typically, each printhead comprises one or more rows of jets or nozzles, enabling it to dispense ink (or another material) though these nozzles. With this example of Figure 1b, the substrate 104 comprises a roll of material that is provided on a drum. By rotating this drum (using a drum motor 108a), the substrate can be unrolled and passed through the printing assembly in the feeding direction shown in Figure 1b. The printheads 102a, 102b, 102c are then able to print in the printing angle onto the web of the substrate as the substrate passes through the printing assembly and beneath the printheads. Referring to Figure 1c, printheads 102 may be arranged across a substantial portion of the web of the substrate so that the printheads can print across an entire y direction of the substrate and the substrate can be advanced continuously, enabling these printheads to print continuously along the substrate in the x direction. However, typically, the printheads are arranged across only a portion of the web of the substrate and the printheads are arranged to move relative to the substrate in order to print across an entire printing width of the substrate. This relative movement may be achieved by moving the substrate while the print heads remain stationary. In this regard, Referring to Figure 1d. there is there is shown a printing assembly 100 viewed from above. The printing assembly 100 comprises one or more printing heads 102, disposed across the web of substrate 104, and mounted so that they can be moved across the web in the y direction by the motor 108. This enables the printing heads 102 to print a design onto the substrate. Referring to Figure 1 e, the substrate may be arranged to move at an angle (the printing angle) between the x and y directions as shown so as to print a path 112 of material. As described below, the present disclosure considers a mechanism for moving the substrate relative to the printheads so that the printing assembly of the present disclosure may not have a fixed direction of printing relative to the substrate. As is also shown in Figure 1e, the substrate holder 106 is arranged to move in the x direction relative to a frame of the printing assembly. Typically, the printheads 102a, 102b, 102c are fixed to the frame of the printing assembly (and are therefore stationary during use of the printing assembly). Therefore, the movement of the substrate holder results in the substrate moving relative to the printheads at a predetermined angle (the printing angle - both along and across a direction of the printheads) so that the printheads are able to print a design onto the substrate in the printing angle. To effect, this x direction movement of the substrate holder 106, the printing assembly 100 may comprise an actuator or a motor 108 arranged to move the substrate holder. The motor is typically arranged to drive the substrate holder back and forth a sufficient distance that the print heads can print across the entirety of a printing width of the substrate. Additional motors 108a and 108b may be arranged to rotate one or more drums or cylinders located at the inlet and the outlet of the printing assembly in order to advance the web forwards in between movements of the substrate holder 106. The substrate is then able to unwind from an input roll, and wrap round a first drum, pass through the substrate holder for printing, then wrap round a second drum in order to pull the substrate through the printing assembly. Finally the web may be rewound onto an output roll. This arrangement provides a printer in which the printheads and the printing assembly can be held stationary, while the substrate 104 moves relative to the printheads at a chosen predetermined angle to enable printing. The above-described arrangement in which a substrate moves relative to a fixed array of printheads is of particular benefit when high frequency printheads are used. Such printheads enable rapid printing, but in conventional scanning printing machines, where the printheads must reverse direction between scans, the rapid accelerations that occur can cause pressure changes in the ink within the printheads, resulting in jetting failure, unless the speed is restricted. This problem is avoided with the arrangement disclosed herein since the printheads and the ink supply can be kept stationary, with the substrate being moved instead to achieve printing. The resulting production speed enables a scanning printing assembly with high printing speed without the need for a great number of printer heads (as would be needed for a single-pass machine that has printheads located across the entire width of the substrate). Therefore, this printing assembly bridges a gap between expensive and complex singlepass printing assemblies with numerous printheads, and simpler, but slower printing assemblies whose printing speed may be limited by the accelerations and deceleration experienced by the printheads. Typically, the printing assembly 100 comprises four printheads. In some embodiments, each printhead has a print width of 2 inches (50.8mm). By moving the substrate holder 106 sufficiently far in a direction along the x axis as shown in Figure 1e, this small number of printheads can be used to print a wide design, e.g. 312mm wide. It will be appreciated that the disclosures herein can be used with any number or configuration of printheads, and arranged to print both narrower and wider webs of substrate. The motor 108 may be arranged to move the substrate holder 106 along sliders during printing. For example, the sliders may comprise stationary members attached to the frame of the printing assembly and moving members attached to the substrate holder. The substrate holder may comprise a ‘divert and turnover assembly’ that comprises two rigid members mounted in a cross with 90 degree quadrants sitting above a ball screw. The substrate holder may be fixed on the sliders at a predetermined angle to achieve a desired angle of printing. The divert and turnover assembly (or, more generally, the substrate holder) may be arranged to provide compressed air to the interior of the rigid members in order to produce an air bearing supporting the substrate. The substrate can then slide over the divert and turnover assembly in either direction with very low friction. Typically the printheads project small droplets of ink onto the substrate. Each printhead may contain one or more coloured inks in separate channels, typically either cyan, magenta, black or yellow ink. While the printheads 102a, 102b, 102c are typically arranged to deposit ink onto the substrate 104, it will be appreciated that other fluid materials may be printed. Typically, the printheads may be arranged to print either ultraviolet curing inks, solvent based, oil based or water based inks. In this regard the term “ink” may include colourless fluids, such as clear varnish, or other specialised fluids containing for example fluorescent pigments, or suspensions of pharmaceutical substances. Referring to Figure 1 f, in some embodiments, the substrate holder 106 comprises two divert bars providing a support for the substrate 104. Typically, the two bars are oriented one above the other at a 90 degree angle to each other, to form a “divert and turnover” assembly. The assembly diverts the substrate so as to change the feeding direction of the substrate, then return it to its original direction, but upside down. A relative orientation of 90 degrees provides a substrate holder that causes a substrate to exit the printing assembly in the same direction that it enters the printing assembly. As shown in Figure 1 f, further bars (e.g. a third bar or a fourth bar) may be arranged between the first and second divert bars to ensure that the substrate passes along a desired path. Such an arrangement enables the divert bars to be moved in the x direction without affecting the inlet or the outlet of the substrate, as shown in Figure 1f. This arrangement therefore enables the substrate holder 106 to move the substrate 104 about a working space of a printer while operating in a fixed frame with a fixed inlet and a fixed outlet - essentially, this printing mechanism can work within a black box formed by a printing frame, where the substrate is continuously being fed into a fixed inlet of the printer and out of a fixed outlet of the printer; the working of the printing mechanism does not affect the substrate beyond this inlet or outlet. This movement can be used during printing to move the substrate 104 backwards and forwards relative to the printheads 102, while the printheads are kept stationary. While printing a design onto a roll of substrate, the substrate holder 106 (e.g. the divert bars) may be moved forwards along the x direction from a first position to a second position (an outward printing sweep), then the substrate may be advanced through the printer (in the feeding direction) to present a new section of substrate to be printed, then the divert bars may be moved from the second position back to the first position (a return printing sweep). A plurality of such printing sweeps, with the substrate being advanced between each sweep so as to expose new portions of the substrate provides a method of continuous printing. In some embodiments, this arrangement is provided such that both divert bars are moved using a single motor; this can provide efficiency improvements over arrangements where the divert bars are separated so that they cannot be moved with a single motor. In operation, while the substrate holder (the divert and turnover assembly) is moving in the x direction, the printheads 102 are able to deposit droplets (e.g. to print) onto the substrate, Typically, the printheads are arranged to deposit droplets at an angle (the printing angle) to the web of the substrate. In particular, the substrate may move relative to the printheads at an angle of roughly 45 degrees to the line of the printheads and / or the nozzle axis. More generally, the substrate may be arranged to move relative to the printheads at a predetermined angle of between 35 degrees and 55 degrees to the line of the printheads and / or the nozzle axis, by changing the orientation of the divert and turnover from the orthogonal orientation shown in Figure 1f. As described below, a suitable printing angle typically depends on the implementation and in particular the arrangement of the printheads used in the printing assembly so that an angle of exactly 45 degrees may not be suitable for all printing assemblies. That being said, angles of between 35 and 55 degrees have been found to provide high efficiency and accuracy. The use of this specific angle range is desirable as it reduces a common defect found in single-pass machines known as “chaining” or “longitudinal scratches”. This defect is caused by adjacent droplets deposited close to each other merging longitudinally into a chain, attracted to each other by their surface tension. By providing a printing assembly that prints at roughly 45 degrees to the web, the droplets in each row are spaced out by factor of 1.414 further apart than occurs with a printing assembly that prints at zero degrees to the web, thus reducing the risk of chaining. A practical operation of the printing assembly of Figure 1 f is concisely described below: Two drums are provided at the inlet and outlet of the assembly. The substrate is wrapped around both of these drums so that the drums can be rotated to move the substrate through the printing assembly. The substrate is moved in the feeding direction through the printing assembly, either continuously or in discrete printing steps. Typically, discrete printing steps are used. Following each movement in the feeding direction, the divert bars are moved in order to move the paper relative to the print heads. During this movement, the print heads are operated to print strings of material onto the substrate. Referring to Figures 2a, 2b, and 2c, there is shown a divert bar as referred to with reference to Figure 1f. The divert bar provides a support for the substrate 106 and also diverts the substrate so as to change a direction of movement of the substrate. The divert bar may be arranged to rotate in order to move the substrate over the divert bar. Equally, the movement may be achieved using another mechanism (e.g. a drum that is attached to an end of the substrate and that rotates to push / pull the substrate). Such a divert bar may be used with a roll-to-roll printer, where one end of a roll of substrate is passed over the divert bar in order to unroll the substrate and pass the substrate by the print heads. In some embodiments, the substrate holder 106 comprises a plurality of divert bars. In particular, the substrate holder may comprise a plurality of divert bars oriented at the same angle and / or oriented at 90 degree angles. As described above, typically the substrate holder comprises two divert bars located on top of each other in a ‘z’ direction and angled at 90 degrees to each other. These divert bars may be moved simultaneously with a single motor, e.g. by rotating a ball that is attached to the divert bars. In one example, different to that shown in Figure 1e, Figure 2d shows a relative orientation of 90 degrees provides a substrate holder that causes a substrate to exit the printing assembly from the same side that it enters the printing assembly. In contrast, a relative orientation of 0 degrees provides a substrate holder that causes a substrate to exit the printing assembly from the opposite side to that at which enters the printing assembly. Referring to Figure 2b, the divert bar may be arranged to be perpendicular to the web of the substrate so as to cause the substrate to double back on itself as it passes over the divert bar. Equally, referring to Figure 2c, the divert bar may be angled to the web of the substrate 104 so as to alter a direction of the web of the substrate as the substrate passes over the divert bar. Referring to Figures 2d and 2e, an alternative use of divert bars is shown, different to that described with reference to Figure 1f. The use of divert bars as shown in figures 2d and 2e enables a printing assembly to be provided in which a substrate can be passed over a first angled divert bar to change a direction of the web of the substrate from a first direction to a second direction (e.g. from a x direction to an y direction), and the substrate can then move in this second direction over a second angled divert bar to change the direction of the web of the substrate from the second direction to a third direction (e.g. where the third direction is parallel to, e.g. the same as or opposite, the first direction). Such an arrangement enables the divert bars to be moved in the first direction (e.g. along a x axis) without affecting the inlet or the outlet of the substrate. This is shown in Figures 2d and 2e, which show such a movement of the divert bars in the x direction. This arrangement therefore enables the substrate holder 106 to move the substrate 104 about a working space while operating in a fixed frame with a fixed inlet and a fixed outlet. As shown in these Figures 2d and 2e, this movement can be used to move one or more print heads 102 relative to the substrate 104, where the print heads are kept stationary while the divert bars move so that the print heads move relative to the divert bars and to the print heads. The print heads are then able to print onto the substrate as the divert bars more relative to the print heads. The movement may, for example, be achieved using a ball screw attach to one or more divert bars so that a rotation of the ball screw causes the one or more divert bars to move relative to the print heads (and / or relative to a frame of the printing assembly). This arrangement can be used to provide the turnover and divert assembly described above). In order to print a design onto a roll of substrate, the substrate holder 106 (e.g. the divert bars) may be moved (e.g. along the x direction) from a first position to a second position, then the substrate may be advanced through the printer, e.g. to change the part of the substrate that is located between the two divert bars, and then the divert bars may be moved from the second position back to the first position. Such a method of operation provides a plurality of printing sweeps, where, for each sweep, the movement of the divert bars cause the substrate to move past the print heads so that the print heads can dispense material onto the substrate in the printing angle. Typically, between each printing sweep, the substrate is advanced in a feeding direction (e.g. the y direction) so as to expose a new portion of the substrate to the print heads 102a, 102b, 102c on a following sweep. As shown by Figures 2f and 2g, the divert bars may be arranged to move in each of the x direction and the y direction. Various movements of the divert bars and various angling of the print heads 102a, 102b, 102c may be performed to achieve a movement of the print heads across the web of the substrate at a desired angle. For example, a first directional component the movement mechanism may be arranged to move a divert bar in a direction that is aligned with a central axis of a divert bar and also in a second direction that is perpendicular to this central axis. Typically, the divert bars are limited to movement in a single plane (e.g. to a two-dimensional movement, where the location in a third plane is fixed - so that, referring to Figures 2f and 2g for the sake of an example, the divert bars can move across the page but not into or out of the page). It will be appreciated that arrangements with three-dimensional movement are also possible. The divert bars, and more generally the substrate holder 106, may be arranged to move between two or more fixed positions to provide a regular movement of the substrate. Equally, the substrate holder may be arranged to move freely to provide a range of possible patterns of movement. Referring to Figure 2g, there is shown a printing pattern that may be printed during the movement of the divert bars and the corresponding movement of the substrate 104 across the print heads 102a, 102b, 102c. In the embodiments shown in Figures 2d - 2g, the direction of printing is in the y axis, since the substrate 104 moves in this direction within the print space (where the print heads are located). The print heads 102a, 102b, 102c are then arranged to sweep across the substrate in the x-direction to print across the web of the substrate. Therefore, each printing sweep results in material being deposited in the y direction, but the overall operation results in a movement in the x direction along the web of the substrate. In some embodiments, the printer comprises a plurality of sets of print heads, where each print head may be associated with a different direction of printing. The feeding direction for a given print head is typically defined as a direction of movement that occurs between each printing sweep. For example, a further print head may be located prior to the first divert bar of the arrangement of Figures 2f and 2g, where this further print head may be associated with a feeding direction that is in the x direction. As described above, the divert bars may comprise a bearing mechanism, such as a compressed air bearing mechanism, that enables the substrate to move smoothly along the divert bars as this movement occurs. While these figures show a plurality of divert bars moving, it will be appreciated that a sweep of the substrate 104 across the print heads can also be achieved by moving only a single divert bar (e.g. so that the substrate moves along a second, stationary, divert bar). Equally arrangements with more than two moveable divert bars may be provided. More generally, it will be appreciated that various methods of moving the substrate relative to the print heads are possible. For example, the substrate may be secured to a moveable platform that is able to move the substrate relative to the print heads. Divert bars are a particularly useful implementation of the substrate holder 106 where the printing assembly is designed for roll-to-roll printing since they enable the movement of a continuous web of substrate without damaging the substrate. Referring to Figures 2 (and as shown in Figures 2d and 2e), in some embodiments the print heads 102a, 102b, 102c are arranged to deposit material (e.g. to print) at an angle to the web of the substrate, at an angle to a feeding direction, and / or in a direction that is (at least partly) in a direction of a line of print heads. This may comprise the printing assembly moving the substrate 104 at an angle to a nozzle axis of one or more of (or all of) the print heads. In particular, the substrate may be arranged to move relative to the print heads at an angle of roughly 45 degrees to the line of the print heads and / or the nozzle axis (the printing angle). More generally, the substrate may be arranged to move relative to the print heads at an angle of between 30 degrees and 60 degrees (or between 40 and 50 degrees) to the line of the print heads and / or the nozzle axis. As described below, a suitable angle typically depends on the implementation and in particular the arrangement of the print heads used in the printing assembly so that an angle of exactly 45 degrees may not be suitable for all printing assemblies. That being said, angles of between 30 and 60 degrees and in particular 40 and 50 degrees provide high efficiency and accuracy. Figure 3 also shows that, in some embodiments, the substrate holder 106 comprises (or is disposed on) a conveyor belt or mechanism 214. More generally, the substrate holder 106 may comprise, or be disposed on, a movement mechanism that is arranged to move the substrate holder and / or to advance the substrate in the feeding direction. A part of this movement mechanism may be a conveyor or conveying mechanism that is arranged to advance the substrate in a feeding direction, e.g. to advance the substrate from an inlet towards an exit of the printing assembly and / or of a workspace of the printing assembly. Typically, advancing the substrate this comprises moving the substrate over the divert bars (where the movement mechanism is also arranged to provide printing sweeps that move the substrate across the printing heads, e.g. along the divert bars). As described previously, the conveying mechanism typically comprises a drum that can be rotated to move the substrate 104. The embodiment of Figure 3 is provided to show that other conveying mechanisms are also possible and also that other types of substrate holder are possible. The conveyor mechanism 214 may move the substrate across of the web (e.g. in the y direction), perpendicular to the line of the print heads. As described above, the conveyor mechanism may move the substrate 104 at an angle to the feeding direction and / or a nozzle axis of a print head, e.g. at a 45 degree angle. In examples where the printing assembly is a roll to roll printer, the roll need not be cut prior to printing to provide the portion to enable a full range of movement of the substrate holder 106 (e.g. where the substrate holder comprises one or more divert bars). In other implementations, the substrate may be cut to size prior to the printing process and then placed on, or secured to, the substrate holder 106 while the printing process is performed. In some embodiments, the substrate holder 106 comprises the divert and turnover assembly described above. In some embodiments, the substrate holder sweeps (e.g. when driven by the movement mechanism) the substrate 104 in a first direction perpendicular to a nozzle axis of the print heads and / or in a second direction parallel a nozzle axis of the print heads. The substrate holder 106 may be used alongside a conveying mechanism 214 that advances the substrate in a fixed direction (e.g. a conveyor belt). The substrate holder may then move the substrate across the conveying mechanism in order to print a design. To achieve different printing angles such as the printing angle 212 shown in Figure 3, the movement mechanism may be operated at a suitable speed (e.g. to move at a suitable angle relative to the print heads). Typically, the movement in the x direction and y direction are adjusted so that the print heads 102a, 102b, 102c print material onto the substrate 104 at between a 30 and 60 degree angle, and / or between a 40 and 50 degree angle to a nozzle axis of the print heads (it will be appreciated that other angles are possible). The use of this specific angle range reduces common defects used in singlepass machines such as “chaining” or “longitudinal scratches”. These defects are caused by adjacent drops deposited by a print head merging into a chain. By providing a printing assembly that prints at 45 degrees to the web, the drops in each row can be spaced by factor of 1.414 further apart than occurs with a printing assembly that prints at zero degrees to a web so as to reduce the risk of chaining. Regarding the possibility of chaining, the print heads 102a, 102b, 102c typically comprise several rows of nozzles; e.g. two rows or four rows, where these nozzles are located on one or more nozzle axes Na. For example, a print head may comprise two offset rows of nozzles located on parallel nozzle axes. These nozzles are arranged to deposit drops of material in sequence, in long strings in order to print a design. Sometimes, undesirably, the drops of material in a first string can merge or chain together to form a channel that does not merge with an adjacent second string. By performing a scanning process at an angle (the printing angle) of 45 degrees to a nozzle axis of a print head (or to the nozzle axes of each print head) this problem can be reduced because adjacent drops from a printer nozzle are now spaced apart by a factor of 1.414 (square root of two) so that these drops are less likely to merge. In some embodiments the movement mechanism is arranged to move the substrate 104 in between movements of the conveyor mechanism. For example, the conveyor mechanism may advance the substrate holder 106 a predetermined distance in the y direction and then the movement mechanism may perform a sweep to move the substrate 104 in the x direction as the printheads deposit material. As used herein, a ‘sweep’ typically describes a back or forward movement of the substrate made by the divert and turnover assembly (e.g. a movement at some angle to the x axis and / or to the web of the substrate. Typically, the movement mechanism sweeps the substrate 104 at an angle to a nozzle axis of the print heads, preferably between 40 and 50 degrees from the nozzle angle. This may be achieved, e.g. by sweeping at an angle to the y direction or by angling the print heads relative to the y direction (as in Figures 2f and 2g). The sweeps may be provided by a single component of a movement mechanism, where this component may perform a series of sweeps with each sweep moving the substrate a certain amount in a feeding direction while also sweeping the substrate across the print heads. Typically, the movement mechanism comprises a plurality of component mechanisms, where a first mechanism provides movement in a feeding direction and a second component mechanism provides the sweeps across the print heads (at an angle to, e.g. perpendicular to, the feeding direction). It will be appreciated that the divert and turnover mechanism described herein is merely an optional implementation of the substrate holder 106 and that other mechanisms may be used to provide the substrate holder 106 and to move the substrate 104 in the feeding direction and / or perpendicular to the feeding direction. In general, the printing assembly comprises a movement mechanism for moving the substrate holder 106 in the direction of the line of print heads (e.g. perpendicular to a feeding direction) and / or for moving the substrate holder 106 in a direction perpendicular to the direction of movement of the conveying mechanism. More specifically, the movement mechanism may be arranged to move the substrate holder 106 in a direction that has a component that is perpendicular to the direction of movement of the conveying mechanism (this movement may also have a component that is parallel to the direction of movement of the conveying mechanism). Referring to Figures 4a and 4b, there are various ways to provide an angle between the substrate and the nozzle axis of a print head. Figure 4a shows an ‘across the web’ arrangement in which the nozzle axis is arranged to be perpendicular to a feeding direction, then the web of substrate is moved across under the printheads at an angle. Figure 4b shows an ‘along the web’ (also referred to in the art as ‘down the web’) arrangement in which the nozzle axis is arranged to be parallel to a feeding direction and then the web of substrate is moved across under the printheads at an angle as above. While either arrangement is useable, the present disclosure largely considers implementation examples in which an across the web arrangement is used. An across the web arrangement enables additional print heads to be added without needing an extra stroke to print and also enables rapid printing of designs of narrow width (e.g. if a design is narrower than a width of the print heads, then with an across the web arrangement no scanning of the print heads perpendicular to the feeding direction is needed). More generally, it will be appreciated that various orientations of print heads may be used with the printing assemblies disclosed herein. In either orientation, the movement of the actuator is typically enough that every nozzle of every printhead is able to apply droplets across the entire width of the substrate web. Furthermore, it will be appreciated that an angle between the print heads and substrate may be achieved by either angling the print heads (e.g. so that a nozzle axis of the print heads is at an angle to a feeding direction) or by moving the print heads across the substrate at an angle (e.g. so that a nozzle axis of the print heads is perpendicular to a feeding direction, but the print heads or the substrate moves at an angle to cause printing that is at an angle to the nozzle axis). In various embodiments, the operation of the movement mechanisms within the printing assembly can be provided as one or more of the following components, or axes of movement / operation: A first component of the operation comprises a backwards and forwards movement of the substrate holder 106 (e.g. the divert bars). The first component may move the substrate holder in the x direction by means of a ballscrew and servomotor operating in “step and direction mode”. Typically, the first component is arranged to move in steps that are the same distance as a pixel (to enable precise printing). A second component of the operation comprises a movement of the substrate in the feeding direction, in order to present a new unprinted area of substrate. For example, the second component may be achieved by input and output drums at either end of the printer, driven by two additional servomotors in “step and direction” mode so as to advance the substrate forwards rapidly in between printing sweeps. A third component of the operation comprises the use of lightweight compensation rollers to smooth out intermittent movements of the substrate in the feeding direction (e.g. to manage the rapid acceleration / deceleration of the substrate between printing sweeps). The third component of the operation may involve the operation of two compensating rollers in a frame, moved by a second ballscrew and a further servomotor in “step and direction” mode. The compensating movement of these rollers cancels out the rapid movements of the substrate, with the effect that the substrate may be unwound from a large roll at a continuous velocity (since inertia would prevent the periodic unrolling of the substrate in sudden lurches). Similarly the substrate can be rewound at constant velocity onto an output roll. A fourth component of the operation of the printer is the printing of material. In particular, the printer may be arranged to fire the nozzles of the print heads so as to deposit droplets of ink or other fluid material onto the substrate at a desired resolution. In some embodiments, the first component of the movements is continuous or near continuous. For example, the advance of the substrate 104 (the second component) may occur while the substrate holder 106 is accelerating and / or decelerating in between printing sweeps. In practice, the substrate holder 106 typically accelerates from rest at the end of a sweep up to a constant velocity during the working portion of a sweep, and then decelerates to rest before reversing at the other end of the printing sweep. While the substrate holder is accelerating or decelerating the printheads stop printing, since they can only lay droplets down in a precise rectangular array, at the required resolution, while the substrate moves at constant velocity. Figures 5a and 5b show an operation using a divert and turnover assembly with the arrangement described with reference to Figure 1 e. Figure 5a shows an operation of the first component mechanism where the substrate holder makes an ‘outward sweep’. More specifically, the movement mechanism moves the substrate in a direction that is typically at around 45 degrees to a nozzle axis of the printheads. Figure 5b shows an operation of the first component mechanism, where the substrate holder makes a 'return' sweep. More specifically, the movement mechanism moves the substrate in a direction opposite to that of the outward sweep, typically at around at around 135 degrees to a nozzle axis of the printheads. Typically, the movement mechanism is operated so that each part of the substrate 104 passes beneath the print heads a single time. However, the movement mechanism may instead be operated so that one or more sections and / or all of the substrate passes beneath the print heads twice or a plurality of times, which enables higher resolution printing, but at a lower overall printing speed In order to provide a consistent printing of a design, the substrate holder 106 is typically arranged to move the substrate at a constant velocity while the print head is triggered at a constant frequency. It will be appreciated that the printheads may be fired at various different but constant frequencies to enable different resolutions. In general, printheads 102 typically comprise several rows of nozzles; e.g. two rows or four rows, where these nozzles are located in straight lines along the nozzle plate. For example, a printhead may comprise two offset rows of nozzles (e.g. row A and row B) located on parallel nozzle axes. It is essential that the string of droplets from each nozzle of say row A of the printhead interlaces exactly halfway between the string of droplets from say row B nozzles, otherwise they may be attracted by their surface tension to join laterally, producing a severe longitudinal scratch (a white line) in the print. For this reason, as mentioned, an angle of exactly 45 degrees may not be suitable, and a different angle may be required for the droplets from each row of nozzles to interlace correctly, so as to form an exactly equally spaced array of droplets. Referring to Figure 6a, in order to achieve the movements described above the printing assembly 100 typically comprises a computer device 1000, where the computer device may comprise one or more of: a processor 1002 for executing instructions (e.g. so as to perform one or more of the steps of the various methods described below), a communication interface 1004 for facilitating communication between computer devices (e.g. an ethernet interface, a Bluetooth® interface, or a universal serial bus (UBS) interface), a memory 1006 and / or storage 1008 for storing information and instructions (e.g. a random access memory (RAM), a read only memory (ROM), a hard drive disk (HDD) a solid state drive (SSD), and / or a flash memory, and a user interface 1012 (e.g. a display, a mouse, a keyboard, and / or an emergency stop button) for enabling a user to interact with the computer device. These components may be coupled to one another by a bus 1012 of the computer device. In some embodiments, the printing assembly 100 comprises a computer device as shown in Figure 6b. The movement assembly shown in Figure 6b comprises a single variable frequency train of electronic pulses which may control the movement of any components within the printing assembly. In some embodiments, given four moving components, four components of movement may be operated at the same time, controlled by a motion controller. For example, the first component may achieve a continuous movement of the substrate holder backwards and forwards, while the second component may move to advance the substrate only during the acceleration and deceleration ramps of the first movement, remaining stationary while the printheads are operating. The third movement may operate continuously backwards and forwards a short distance such as to ensure the input and output velocity of the substrate remains constant, in order to allow smooth unwinding and rewinding of the input and output rolls of substrate. The fourth component controlling the triggering of the printheads, allows the image being printed to be released in slices to the printheads, timed exactly with the first movement during its constant velocity periods, so as to deposit droplets in the required rectangular array. The source of all the components of movement may be a single variable frequency train of electronic pulses. The frequency may be varied from a low frequency up to a maximum frequency in order to make all the movements move faster while remaining synchronised, hence to make the printer run faster. The lowest frequency provides a “slow “crawl” speed and the maximum frequency provides the maximum production speed of the printer. The “crawl” speed is necessary for safely setting up the printer for production, and for example feeding through a join or splice after the input roll of substrate is exhausted and a new one is loaded. This embodiment of Figure 6b enables a relatively simple (and cheap and robust) controller to be used to achieve the various movements required by the printing assembly where the timings of each movement are achieved using the motion controller. In particular, the printing assembly may be operated by a motion controller that comprises a printed circuit board, PCB, and / or an EEPROM component (Electrically Erasable Programmable Read-Only Memory). Referring to Figure 7, there is described a method of operating the printing assembly 100 described above. This method is typically carried out by a computer device, e.g. a control unit of the printing assembly. In a first step 11, the computer device identifies a design to be printed. This design typically comprises text and / or images. Identifying the design may comprise receiving the design, or receiving printing instructions to print the design, from a further computer device (e.g. via the communication interface 1004. In some embodiments, the design may comprise printing instructions that indicate a path of travel for a movement mechanism or a conveying mechanism. In a second step 12, the computer device initiates a printing process. In particular, the computer device may operate the movement mechanism so as to move the substrate in a direction that is (at least partly) perpendicular to a line of print heads. This can be considered moving the substrate along a web direction. In a third step 13, the computer device moves, e.g. using the movement mechanism and / or the substrate holder 106, the substrate 104 in a direction that is (at least partly) parallel to a line of print heads and / or parallel to a nozzle axis. This can be considered moving the substrate across a web and / or across a feeding direction. As described with reference to Figures 1e, 2a-2g and 5a and 5b, this may involve moving one or more divert bars in order to achieve the movement of the substrate across the feeding direction. Referring to Figure 8 there is shown a method of printing that may be implemented by a computer device (e.g. the control unit) of the control unit of the printing assembly to perform a plurality of printing stages. In a first step 21, the computer device initiates a printing process. In a second step 22, the computer device operates the movement mechanism (e.g. to move a divert bar of the substrate holder 106) to move the substrate in a direction of (e.g. at least partially parallel to) the line of print heads and / or the nozzle axis. In a third step 23, the computer device operates the movement mechanism (e.g. to operate a motor of a drum) to move the substrate in a feeding direction, e.g. at least partially perpendicular to the line of print heads and / or the nozzle axis. As described above, the movement of the substrate parallel to or perpendicular to the line of print heads may comprise moving the substrate at an angle (the printing angle) to the line of print heads (e.g. a 45 degree angle) so that the substrate moves with a component that is perpendicular to the line of print heads and a component that is parallel to the line of print heads. As described above with reference to Figures 4a and 4b, the movements and operation of the movement mechanism (and the printing assembly) can typically be provided as one or more of the following components or axes of movement / operations: The first component of the operation which, as described with reference to Figures 4a and 4b may comprise a movement of the substrate holder 106 (e.g. the divert bars). Preferably, the first component moves the substrate holder in a direction that is (at least in part) perpendicular to a feeding direction so as to move a substrate in a direction that is (at least in part) parallel to a nozzle axis of a print head. Typically, the first component of the operation moves the substrate at an angle that is between 40 and 50 degrees to the nozzle axis. Typically, the first component is arranged to move in steps that are the same distance as a pixel (to enable precise printing). For example, the movement mechanism may be able to move the substrate holder in a number of steps that is equal to a distance of a printing step divided by a number of nozzles of the print heads. For example, for a print head with 1200 nozzles that is used with a 55mm printing step, the movement mechanism may be arranged to move the substrate with a step of 55mm / 1200 = 45.8pm. In a specific embodiment, the first component may be achieved using a 40mm pitch ballscrew, geared 12:11 to a stepper motor set to have 800 steps per rev, where the ballscrew is attached to a divert bar so as to move this divert bar as the ballscrew rotates. The second component of the operation, which, as described above with reference to Figures 4a and 4b, comprises a movement of the substrate in a feeding direction. For example, the second component may be achieved by rolling and unrolling drums at either end of the printer so as to move the substrate forwards / backwards over one or more divert bars, e.g. to move the substrate forwards / backwards by 55mm in each printing step. The third component of the operation, which, as described above with reference to Figures 4a and 4b, comprises the use of compensation rollers to smooth out intermittent movements of the substrate (e.g. to manage the acceleration / deceleration between printing sweeps and / or between steps in a feeding direction). An aspect of the third component of the movements is described further below with reference to Figures 10a and 10b. The third component of the operation may involve the operation of a compensating movement that cancels out a movement of the substrate. In this regard, the substrate may be unrolled from a drum at a continuous velocity (since inertia can prevent the periodic unrolling of the substrate). In such an embodiment, the printing assembly can comprise a compensator that cancels out this unrolling within a workspace of the printing assembly. Therefore, the substrate may be continuously unrolled from a drum at a first velocity, where the compensating mechanism causes converts this continuous movement into a series of steps (where each step occurs at a second velocity that is greater than the first velocity in order to prevent any buildup of the substrate within the printing assembly). A fourth component of the operation of the printer is the printing of material. In particular, the printer is arranged to fire the nozzles of the print heads so as to deposit material onto the substrate at a desired resolution. This fourth operation is as described above with reference to Figures 4a and 4b. In some embodiments, the first component of the operation is continuous or near continuous. For example, the advance of the substrate 104 between sweeps of the substrate across the print heads may occur while the substrate holder 106 is accelerating and / or decelerating at the start of a printing sweep. In practice, the substrate holder 106 typically accelerates at the start of a sweep, moves at a constant velocity during a working portion of a sweep, and then decelerates as the substrate holder nears the end of a printing sweep. While the substrate holder is accelerating or decelerating the print heads may stop printing and the motor may advance the substrate by the printing step. In particular, this may occur as the substrate holder decelerates and then starts to accelerate in an opposite direction (e.g. to move from an outward sweep to a return sweep) so that by the time the substrate has advanced by the printing step the substrate holder is starting to accelerate for another sweep and the print heads can start printing shortly after the advance of the substrate. A detailed method of operating the movement mechanism and the conveying mechanism is described with reference to Figures 9a and 9b. Figure 9a shows an operation of the movement mechanism in a first stage where the movement mechanism makes an ‘outward sweep’ and moves in a path that includes a movement perpendicular to a direction of a line of print heads. More specifically, the movement mechanism moves the substrate in a direction that is (or has a component in) a first direction. This direction is typically at around 45 degrees to a nozzle axis of the print heads 102a, 102b, 102c. Figure 9b shows an operation of the movement mechanism in a second stage, where the movement mechanism makes a return sweep. More specifically, the movement mechanism moves the substrate in a direction that is (or has a component in) a second direction. This second direction is typically opposite the first direction and / or substantially opposite the first direction (e.g. at around 150 degrees from the nozzle axis). As shown in these figures, each of these sweeps results in the substrate 104 moving relative to the print heads 102a, 102b, 102c so that different portions of the substrate pass beneath the print heads. Between the outward sweep and the reverse sweep, the motor 108 may advance the substrate by a printing step so that the outward sweep and the reverse sweep deposit material onto different sections of the substrate. Typically, the movement mechanism is operated so that each part of the substrate 104 passes beneath the print heads 102a, 102b, 102c a single time. However, the movement mechanism may instead be operated so that one or more sections and / or all of the substrate passes beneath the print heads a plurality of time, where this enables higher resolution printing. For example, the substrate may only be advanced once every two steps or once every three steps. The substrate may be moved perpendicular to the feeding direction in between advances of the substrate, for example, the movement mechanism may shift the substrate by half a pixel perpendicular to the feeding direction in between an outward sweep and a return sweep and then advance the substrate by a printing step following the return sweep. In order to provide a consistent printing of a design, the substrate holder 106 is typically arranged to move the substrate at a constant (or near-constant) velocity while the print head is operating. It will be appreciated that a varying velocity may also be used (e.g. to provide areas of different resolution). Referring to Figures 10a and 10b, in order to provide this constant velocity of movement over a working portion of a sweep, the movement mechanism may be arranged to accelerate and decelerate the substrate holder 106 during an onset portion and an ending portion of a sweep. The substrate holder then moves at a constant velocity during a dwell portion (or the working portion) of the sweep In this regard, the substrate holder is at rest at the beginning and end of each sweep and typically needs to be accelerated up to a movement speed before the working portion and then decelerated from the movement speed after the working portion. This acceleration / deceleration may be performed using a linear acceleration. However, typically, the acceleration is performed using a sinusoidal ramp where this increases the number of cycles that may be performed in a given unit time and avoids placing high forces on the substrate holder. The sinusoidal ramps require a distance that is 0.3243*P*vmax (where P is the acceleration ramp time). Therefore, given a vmax of 75m / min and a P value of 0.0329 seconds, each ramp requires a distance of 13.34mm. Equally, given a vmax of 100m / min and a P value of 0.1072 seconds, each ramp requires a distance of 57.94mm. Table 1 shows printing widths vs average printing speeds for various printing widths as well as showing the torque required if the sweep (or ‘stroke’) is produced by a 40mm pitch ballscrew: Printing width versus maximum average web speed Printing Width" mm Remp Length ft mm Stroke Length L Dwelt Length Q mm Average speed” V m / wn Time for WB cyde sec Printing speed" wnsx mm / see Max rpm of motor Anting speed of heads m / min hemp time 0 sec Terete Ornes hm 312 91.6667 462.92 371.26 19,.73 0.615 1666.39 3727,15 190 9.035 4.09 293 91.6663 449.167 367.60 11.02 0.699 1865.73 2736.72 199 0.088 4.09 230 21,6067 436.417 343.75 11.34 0.582 1666,84 2727.58 300 0.088 4.90 240 91.666? 394.167 303. SO 12.39 0.833 1666,30 2 / 25.67 100 0.835 4,09 210 01.6667 362.067 270.42 13.36 0.494 1666.58 2727.62 100 0.088 4.09 175 91.666? 328.417 233.36 14.66 0,450 1666,17 2725,46 100 0.( / 35 4,09 140 91.6667 293.337 201.67 16.03 0,433 1666.05 3729,28 190 9,035 4,09 100 91.6667 '332.087 160,42 18.33 0.362 1666.83 2737.58 190 0.088 4.00 It will be appreciated that these values are purely exemplary and that various arrangements of componentry may be used to obtain, for example, different acceleration ramps and different printing speeds. To illustrate the benefits of printing at an angle, referring to Figure 11a, there is shown an exemplary print head that comprises a plurality of rows of nozzles arranged along parallel axes. Specifically, the print head comprises: a Row A arranged along a nozzle axis Na; a Row B arranged along a nozzle axis Nb; a Row C arranged along a nozzle axis Nc; and a Row D arranged along a nozzle axis Nd. Preferably, the distance between Rows A and B is equal to the distance between Rows C and D, but not equal to the distance between rows B and C. Such a (conventional) print head is generally intended to be used with a feeding direction that is perpendicular to the nozzle axes. The nozzles on each row are typically offset so that, when this printing is performed, the material deposited by each nozzle does not overlap. For example, as shown in Figure11b, each nozzle may dispense a plurality of strings of material, where the strings from separate nozzles are parallel to each other. These strings of drops of materials may then merge to form a single image using smooth areas of colour. When printing at an angle of roughly 45 degrees, as in the present disclosure, it is essential to achieve the same exact rectangular array of droplets, to avoid visible defects in the printed image. Referring to Figure 12a, there are shown exemplary dots printed by the nozzles of Row A and Row B. As shown in this Figure 12a, there is: a row distance DR between a first string of drops dispensed by a first row of nozzle axes and a first string of drops dispensed by a second row of nozzle axes so that the first rows printed by the nozzles of Row A begin a distance DR above the strings printed by the nozzles of Row B. Furthermore, for each row of nozzles (Row A and Row B), the nozzles of that row are spaced by an intra-row spacing of SR. The nozzles of Row B are offset from the nozzles of Row A by a row offset of Ro. It should be appreciated that the printhead manufacturers have arranged that distance Dr is an exact whole number multiple of the distance P, and that P is one pixel (eg 1 / 600th inch), and Dr is for example 26 pixels in the preferred embodiment. It will therefore be appreciated that a printer that uses a nonzero feeding direction as shown in Figure 12b has a limited choice of printing angle, given the relative distances Dr and P, in order to achieve a perfect rectangular array of droplets deposited. Referring to Figure 12b, the present disclosure considers a printer that uses a feeding direction that is at a non-zero printing angle (6P) to a nozzle axis of a print head (and since the nozzle axes for a given print head are typically parallel to each other, this leads to a printing angle that is at the same for each row of nozzles in a print head). The use of this non-zero printing angle reduces the possibility of chaining (where the drops printed by a single nozzle join together and form a channel that does not join to the dots printed by an adjacent nozzle (e.g. from a different row). In this regard, printing the material at an angle to a nozzle axis, the distance between the drops from a single nozzle are increased. A potential problem with this non-zero printing angle is that, depending on the values of DR, SR,dP, Ro and PD (the printing density) it is possible that the dots printed by separate rows of nozzles could overlap. Referring to Figure 13, the choice of possible angles is illustrated. An angle of exactly 45 degrees results in Row A droplets falling on top of Row B droplets (Figure 13a), and is therefore unsuitable. Three possible alternative angles are shown, which result in correct interlacing of Row A and Row B droplets. In the preferred embodiment, one particular angle is used (Figure 13d) which results in slightly higher production speed at the expense of slightly reduced resolution in the direction of the substrate. It will be appreciated that printing at an angle to the nozzle axis of the print head provides benefits even in a printer where the print heads move relative to the frame of the printer. Similarly, a printer that has stationary print heads and a movement mechanism for moving a substrate relative to these print heads provides benefits regardless of the angle of printing relative to the nozzle axis. We now consider a detailed practical implementation using four rows of 319 nozzles printing at 600DPI (droplets per inch) with a print width of 54mm. To avoid issues that may occur using nozzles at the end of the rows of nozzles, the number of nozzles used to print may be reduced to 1200 nozzles with a printing width of 50.8mm. If a printing angle of 42.709 degrees is used as in Figure 13d with a row distance of = 26 pixels, then one print sweep would cover a width of 55.03mm. Such a printing angle may be used with a printing step of 55mm, so a complete forwards and backwards cycle (two sweeps) is 110mm. To provide a printing speed of 10 metres / minute with this arrangement, a cycle time of 0.660s is needed between sweeps of the substrate holder. The selection of 1200 nozzles for printing and a 55mm printing step enables the required ratios of distances to be achieved simply by gearing, simplifying the electronics considerably. The aforementioned printing angle can be achieved using the divert and turnover assembly described above with the conveying mechanism (e.g. the two drum motors) that moves the substrate forward only needing to move enough to avoid gaps or overlaps between the sweeps. The distance of each printing step can typically be adjusted as needed to provide printing sweeps that fit together exactly. As described above, the movement mechanism is typically arranged to provide a printing angle such that the substrate moves relative to the print heads at an angle that is greater than zero (and less than ninety). In general, the printing angle is generally selected so as to be a value that is 0P = arctan¢7¾ where dr n is an integer number. Such a printing angle generally avoids overlaps. Typically the printing angle is selected to be between 30 and 60 degrees and / or between 40 and 50 degrees, where these ranges of printing angles are found to provide rapid printing. Typically, the row offset Ro is at least 1 pixel. Typically, the row offset is the same for each row of a print head (e.g. to provide a plurality of rows, where each row is spaced from each adjacent row by 1 pixel). Typically, the nozzles in each row are spaced regularly, but it will be appreciated that irregular spacing is also possible. It will be appreciated that the skilled person would have been able to identify printing angles that prevent overlap between adjacent rows of nozzles (e.g. using the equations above and / or using reasonable trial and error). It will be appreciated that printing at an angle to the nozzle axis of the print head provides benefits even in a printer where the print heads move relative to the frame of the printer. Similarly, a printer that has stationary print heads and a movement mechanism for moving a substrate relative to these print heads provides benefits regardless of the angle of printing relative to the nozzle axis. We now consider a detailed practical implementation using four rows of 319 nozzles printing at 600DPI with a print width of 54mm. To avoid issues that may occur using nozzles at the end of the rows of nozzles, the number of nozzles used to print may be reduced to 1200 nozzles with a printing width of 50.8mm. If a printing angle dP of 42.709 degrees is used with a row distance of DR = 26 pixels, then one print sweep would cover a width of 55.03mm. Such a printing angle may be used with a printing step that is a multiple of 55mm, e.g. that is 110mm. To provide a printing speed of 10 metres / minute with this arrangement, a cycle time of 0.660s is needed between sweeps of the substrate holder. The selection of 1200 nozzles for printing and a 55mm printing step enables the required ratios of distances to be achieved simply by gearing, simplifying the electronics considerably. The aforementioned printing angle 9P can be achieved using the divert and turnover assembly described above with the conveying mechanism (e.g. the motor) that moves the substrate forward only needing to move enough to avoid gaps or overlaps between the sweeps. The distance of each step can typically be adjusted as needed to provide printing sweeps that fit together exactly. Referring to Figure 14a, as described above, the movement mechanism is typically arranged to provide a printing angle such that the substrate moves relative to the print heads at an angle that is greater than zero (and less than ninety). Figure 14a shows an embodiment with a printing angle of 42.709 degrees printing at a printing width of 312mm wherein the strings of droplets extend in the y direction (i.e. located underneath each other in the x-direction). Typically however, the print heads comprise a plurality of rows of nozzles (e.g. a Row A, a Row B, a Row C, and a Row D) The unused rows B,C &D would produce parallel strings of droplets interlaced between the Row A strings. Typically, such an angle is used with a printing step (or a ‘sweep increment’) of between 50 and 60mm, e.g. 55mm, where the printing step is the movement of the web in the feeding direction between successive sweeps of the substrate across the print heads 102a, 102b, 102c (e.g. between the outward sweep and the return sweep). Figure 14b shows an embodiment with a printing angle of 42.709 degrees and a print width of 312mm, using all four rows of nozzles. It will be seen that the second two rows of nozzles print a half-density strip of droplets so as to provide an (e.g. 12mm) overlap zone between the adjacent strips of fulldensity droplets produced by all four rows of nozzles. The overlap zones of 12mm help to blend together successive sweeps without visible joints. More generally, the print heads 102a, 102b, 102c may comprise a plurality, e.g. four, rows of printer nozzles, e.g. a Row A, a Row B, a Row C, and a Row D. A third row and / or a fourth row, e.g. Row C and Row D, may have a smaller printing width than a first row and / or a second row, e.g. Row A and Row B. Such a print head can be used such that the third and fourth rows are used to blend drops from the first and second rows. Typically, the printing assembly (e.g. a controller of the printing assembly) is arranged to use a sweep increment that is dependent on a printing width of the print head, where the sweep increment may be similar to the printing width. Preferably, the sweep increment is a distance at least 90% of the printing width, at least 100% of the printing width, and / or at least 110% of the printing width. Preferably, the sweep increment is a distance no more than 130% of the printing width, no more than 130% of the printing width, and / or no more than 110% of the printing width. This ensures blending between strips of material printed by each print head during each printing sweep. Alternatives and modifications It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. For example, the printing assembly may be provided as part of a printer that may comprise a number of further features, e.g. a substrate input, an output, accessories such as a stapler, hole punch, roll cutter etc. The present disclosure extends to a printer comprising the printing assembly. Typically, the printer comprises an ultraviolet (UV) emitter for curing a material deposited onto the substrate 104. The printer may comprise a plurality of UV emitters, e.g. either side of the printheads, so that the UV emitters are able to cure material dispensed during each of an outward printing sweep and a return printing sweep (e.g. to cure the material immediately after it has been deposited onto the substrate). More generally, the printer may comprise one or more curing or drying mechanisms for curing or drying the material deposited onto the substrate. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

1. A printer, the printer comprising:a frame; and5 a printing assembly, the printing assembly comprising:one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame of the printer; anda movement mechanism for moving a web of a substrate relative to the print heads;wherein the movement mechanism is arranged to move the web of the substrate in a first 10 direction so as to sweep the web of the substrate back and forth across the print heads at anangle of between 30 and 60 degrees to a nozzle axis of the print heads.

2. The printer of any preceding claim, wherein the movement mechanism comprises:a first component mechanism that moves the web of the substrate in the first direction so as 15 to sweep the web of the substrate across the print heads; anda second component mechanism that moves the web of the substrate in a second direction so as to advance the web of the substrate in a feeding direction.

3. The printer of any preceding claim, wherein the movement mechanism is arranged to:20 in a first step, move the web of the substrate in a feeding direction;in a second step, move the web of the substrate perpendicular to the feeding direction so as to sweep the print head across the web of the substrate; andin a third step, move the web of the substrate in the feeding direction, preferably, wherein the movement mechanism is arranged to move the web of the substrate in the feeding direction by a 25 printing step.

4. The printer of claim 3, wherein the movement mechanism is arranged to, in a fourth step, move the web of the substrate perpendicular to the feeding direction so as to sweep the web of the substrate across the print head, preferably wherein:30 the direction of movement of the fourth step is opposite the direction of movement of thesecond step; and / orthe movement mechanism is arranged to move the web of the substrate in an outward sweep and a reverse sweep, the outward sweep being opposite the reverse sweep, more preferably wherein the movement mechanism and / or a conveying mechanism is arranged to advance the 35 web of the substrate between the reverse sweep and the outward sweep.

5. The printer of any preceding claim, wherein the movement mechanism is arranged to move the web of the substrate perpendicular to a feeding direction between a first position and a second position so as to sweep the web of the substrate across the print heads, wherein the movement mechanism is 40 arranged to provide a plurality of printing sweeps between the first position and the second position, wherein the movement mechanism is arranged to advance the web of the substrate in the feeding direction between printing sweeps.26 02 266. The printer of claim 4 or 5, wherein the movement mechanism is arranged to sweep the web of the substrate across the print heads at an angle to a nozzle axis of the print heads of between 40 and 50 degrees.5 7. The printer of any of claims 3 to 6, wherein the movement mechanism is arranged to move the webof the substrate at a constant speed and / or velocity during a working portion of a sweep, the working portion being a portion during which the print heads are able to, and / or arranged to, deposit material onto the web of the substrate.10 8. The printer of claim 7, wherein the movement mechanism is arranged to accelerate and / ordecelerate the web of the substrate during an acceleration and / or deceleration ramp at each end of the sweep where the print heads are arranged not to deposit material onto the web of the substrate.

9. The printer of any preceding claim, comprising a substrate holder for holding the web of the 15 substrate, wherein the motor is arranged to drive a movement of the substrate holder.

10. The printer of claim 9, wherein the substrate holder comprises one or more divert bars, preferably one or more divert bars arranged to alter a direction of a web of the substrate passing over the divert bars.2011. The printer of claim 10, comprising a plurality of divert bars oriented at the same angle and / or oriented at 90 degree angles relative to each other, wherein the web of the substrate is arranged to pass over a succession of divert bars.25 12. The printer of claim 10 or 11, wherein the movement mechanism is arranged to move one ormore of the divert bars so as to move the web of the substrate perpendicular to the feeding direction.

13. The printer of any preceding claim, wherein the movement mechanism comprises a divert and turnover assembly, wherein the divert and turnover assembly comprises two elongate members 30 positioned at 90 degrees to each other, wherein the elongate members are separated in a z-direction.

14. The printer of any preceding claim, wherein the printing assembly is arranged to print onto a web of the substrate with a printing width of at least 150mm; wherein the print heads are arranged to print with a print width of no more than 100mm.3515. The printer of any preceding claim, wherein the print heads are arranged to print with a print width of no more than 55mm.

16. The printer of any preceding claim, being arranged to move the web of the substrate relative to 40 the print heads (and / or the print heads relative to the web of the substrate) at an angle to a nozzle axis of a print head that is determined as 0P = arctan(3^) where n is an integer value, Sr is an intra-row drspacing of nozzles in each row of the print head, and Dr is a distance between a first row of nozzles within the print head and a second row of nozzles within the print head.26 02 2617. The printer of any preceding claim, wherein each print head comprises a plurality of rows of nozzles.

18. The printer of claim 17 comprising plurality of rows of nozzles of different widths.

519. The printer of any preceding claim, wherein the print heads are arranged to print at a different resolution along the web of the substrate than across the web of the substrate.10 20. A printing assembly, the printing assembly comprising:one or more stationary print heads for dispensing material, the stationary print heads being stationary relative to the frame of the printer; anda movement mechanism for moving a web of a substrate relative to the print heads; wherein the movement mechanism is arranged to move the web of the substrate in a first direction so as to15 sweep the web of the substrate back and forth across the print heads at an angle of between 30 and60 degrees to a nozzle axis of the print heads21. A method of printing using the printing assembly or printer of any preceding claim.20 22. A method of operating a printer comprising a frame and one or more stationary print heads fordispensing material, the stationary print heads being stationary relative to the frame of the printer, the method comprising:moving a web of a substrate in a first direction so as to sweep the web of the substrate back and forth across the print heads at an angle of between 30 and 60 degrees to a nozzle axis of the print 25 heads.

23. The method of claim 21 or 22, the method further comprising:operating the print heads during a working portion of a sweep of the web of substrate relative to the print heads wherein the substrate moves at a constant speed during the working portion.30IntellectualPropertyOfficeApplication GB2510658.4Search report under Section 17 of the Patents Act 1977Date search completed: 27 November 2025Claims searched: 1-25International classificationSubclass and subgroup Valid from B41J13 / 32 01 / 01 / 2006 B41J15 / 06 01 / 01 / 2006 B41J2 / 155 01 / 01 / 2006Field of searchWorldwide search of patent documents classified in the following areas of the IPC:B41JDatabases used in the preparation of this search report:SEARCH-PATENTDocuments considered to be relevantPatent literatureCategory Relevant Document of relevanceclaimsX 1-25 US 6113232 A (BELON et al.), See whole document especially abstract; claim 1 and figures. X 1-25 US 4219822 A (PARANJPE), See whole document especially column 5, lines 45-47 and figure 1.CategoriesLetter or symbol Description X Document indicating lack of novelty or inventive step. Y Document indicating lack of inventive step, if combined with another document of the same category. & Member of the same patent family. A Document indicating technological background. P Document published on or after the priority date but before the fling date of the present application. E Earlier application published on or after the filing date of the present application.

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