Patent Description:
Substrate support units are typically used for conveyor printers for supporting the conveyor belt, on which a substrate rests. The conveyor belt moves over a support surface of the support unit to feed a substrate to an array of printheads for printing. As the conveyor belt moves over the support surface, friction is generated resulting in heat, especially at high conveyor speeds. These high temperatures can cause wear to the conveyor belt, and may affect print quality.

Vacuum apertures are typically used for maintaining a substrate in a fixed position on printer tables, including for conveyor printers. The conveyor belt is typically perforated so that vacuum apertures in the support unit can apply a negative pressure to pull the substrate down onto the conveyor belt. This helps keep the substrate fixed in position, improving print quality. However, using a vacuum to pull down the substrate also inherently acts on the conveyor belt by creating a clamping force and making it more difficult for the belt to move over the support unit. This further exacerbates the problem of friction between the conveyor belt and the support unit. The friction force varies as the substrate comes into and out of contact with the vacuum section of the belt, which tends to alter the belt tracking. This causes alignment problems and thus affects print quality.

<CIT> discloses a transfer apparatus for transferring a substrate comprising: a supporting member, which has a supporting surface that supports one surface of the substrate, and which has a plurality of through holes formed therein, said through holes penetrating between the supporting surface and the surface on the reverse side of the supporting surface; and a holding mechanism, which is provided with a gas suction section disposed to face a first region of the rear surface of the supporting member, said first region including the holes, and a gas supply section disposed to face a second region of the rear surface of the supporting member, said second region being different from the first region, and which holds the rear surface of the supporting member in a non-contact state and sucks the substrate to the supporting surface via the through holes by supplying and sucking a gas with respect to the rear surface of the supporting member.

<CIT> discloses a pick-up device <NUM> that vacuum picks up a workpiece W to a pick-up face 1a by way of a plurality of vacuum pick-up units <NUM> having a pick-up hole <NUM> provided on the pick-up face 1a. An opening-closing valve <NUM> can open and close a suction opening 32a.

<CIT> discloses a media transport system utilizing a honeycomb core platen for transporting and maintaining the flatness of a sheet of media in an associated printing system. According to one exemplary embodiment, the honeycomb platen includes a plurality of laminated layers that include features configured to communicate vacuum throughout the entire thickness of the plate.

<CIT> discloses a printing module including a plurality of printheads, a transport belt located below the plurality of printheads to transport print media below the plurality of printheads, wherein the transport belt comprises a plurality of vacuum openings, and a positive pressure plenum system, wherein the positive pressure plenum system provides a positive air flow to create an air interface between a top surface of the positive pressure plenum system and a bottom surface of the transport belt, wherein the positive pressure plenum system provides a negative air flow to create a vacuum through the plurality of vacuum openings of the transport belt to hold the print media against the transport belt.

The present disclosure attempts to address one or more of the above mentioned problems.

According to a first aspect of the present disclosure, there is provided a substrate support system for a conveyor printer, comprising a support unit comprising: a plurality of vacuum apertures arranged for fluidic communication with a source of negative pressure; and at least one air bearing arranged for fluidic communication with a source of positive pressure, wherein the air bearing comprises porous media; and a conveyor belt arranged over the support unit for supporting a substrate to be printed on, the conveyor belt comprising a plurality of belt apertures; wherein the vacuum apertures are arranged to convey a negative pressure through the belt apertures for retaining the substrate on the conveyor belt; and wherein the at least one air bearing is arranged to convey a positive pressure to support the conveyor belt.

As used herein, a conveyor printer is preferably a printer which uses a conveyor belt for printing motion, for example by moving a substrate along a conveyor belt and past an array of printheads. Optionally, the conveyor printer comprises an ink-jet printer.

The substrate support system therefore supports a conveyor belt over the support unit by resting the conveyor belt on at least one air bearing. The positive pressure from the at least one air bearing spaces the air bearing away from an upper surface of the support unit. This avoids contact between an underside of the conveyor belt and the upper surface of the support unit. As a result, friction is reduced as the conveyor belt moves over the support unit. This removes heat and also prevents sticking and enables smooth movement of the conveyor belt. In turn, this can improve efficiency, avoid damage to the belt, and also improve print quality.

The vacuum apertures act to retain the substrate on the conveyor belt by applying a negative pressure through the belt apertures. This keeps the substrate fixed in the correct place, improving alignment and thus print quality.

As the at least one air bearing comprises porous media, the at least one bearing may be referred to as a porous media air bearing. The porous media means that a component of the air bearing is porous to air. When air is applied through the porous media, air can permeate through the porous media. This allows air to be supplied from underneath the air bearing, and the air to pass through the porous media to form an air cushion, or an air film, above an upper surface of the air bearing. The conveyor belt can then rest on the air cushion, spaced above the air bearing. In some examples, the porosity of the porous media is between <NUM> % and <NUM> %, measured by density. Porous media air bearings are advantage compared to aperture air bearing because the air consumption is much lower. Aperture air bearings require a high consumption of air and are much less stable. In contrast, the use of porous media air bearings decreases the air flow required, improving efficiency and stability, while reducing cost.

Preferably, the porous media comprise carbon. Carbon has been found to be particularly advantageous as it can provide the desired porosity while also providing stability. Carbon is tolerant and relatively soft, so that it can wear slightly in order to avoid damage to the belt in the event of misalignment. Carbon is also easy to machine and manufacture. In other examples, the porous media comprises a porous metal or plastic, or medium-density fibreboard (MDF). However, carbon is advantageous because other materials often are too porous, leading to a high flow rate which has a high air consumption which reduces efficiency, the high flow rate pushes the belt up too high, and leads to rapid wear and friction damage to the belt. Carbon also has the advantage that plastic often melts and seals the holes, whereas carbon does not.

Optionally, the porous media comprises a mixture including carbon. For example, the porous media may comprise a mixture of amorphous carbon and graphite. This may generally be referred to as carbon-graphite or graphite. In some examples, the porous media may comprise sintered carbon. The grade of carbon may be one or more selected from the list of: MCCA, Y460B, Y552, Y459, or Y464B (each commercially available from Olmec Advanced Materials), or EG-<NUM>, EDM-<NUM>, or EDM-<NUM> (each commercially available from Entegris POCO Materials).

Preferably, the at least one air bearing is configured to support the conveyor belt on a film of air having a thickness of between <NUM> and <NUM>. This means that the underside of the conveyor belt is supported at a position between <NUM> and <NUM> above an upper surface of the air bearing. More preferably, the film thickness is between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>. This ensures that contact is avoided between the air bearing and the conveyor belt. It is desirable to keep the film thickness greater than the surface roughness in order to avoid contact. Air consumption increases rapidly with film thickness, so it is desirable to keep the film thin. The upper limit avoids a large gap between the air bearing and the conveyor belt, which requires a large airflow to support. This improves efficiency and reduces air consumption.

Preferably, the source of negative pressure is configured to apply a negative pressure of -<NUM> mbarg to -<NUM> mbarg to the vacuum apertures. As such, in some examples the substrate support system comprises the source of negative pressure. As used herein, the term "mbarg" preferably refers to a pressure in units of mbar relative to atmospheric pressure (approximately <NUM> kPa). The applied negative pressure can be sufficient to act to retain a variety of substrates in position, such as paper or card of varying thicknesses and porosities. In some examples, there may be at least <NUM> vacuum apertures per m<NUM>. In some examples, each vacuum aperture may supply two belt apertures, but in other examples each vacuum aperture corresponds to each belt aperture.

Preferably, the source of positive pressure is configured to apply a positive pressure of <NUM> MPa to <NUM> MPa to the at least one air bearing. As such, in some examples the substrate support system comprises the source of positive pressure. The applied positive pressure can be sufficient to support a conveyor belt on a film of air to space the conveyor belt away from the at least one air bearing. In some examples, each air bearing having a diameter of <NUM> can support a load of <NUM> to <NUM> N with a positive pressure of <NUM> MPa to <NUM> MPa. Using an array of <NUM> air bearings per m<NUM> means that in some examples the total supported load can be <NUM> to <NUM> kN, where the minimum supported load is when the <NUM> MPa supply pressure is connected to <NUM> % of the bearings, and the maximum supported load is when the <NUM> MPa supply pressure is connected to <NUM> % of the bearings.

Preferably, a ratio of the flow rate of the negative pressure to the flow rate of the positive pressure is greater than <NUM> to <NUM>.

Preferably, the at least one air bearing is supported on a resilient member. For example, the resilient member may be in the form of an O-ring. The resilient member is made from a resilient material. The resilient member may be made from a deformable material. In some examples, the resilient member may be made from rubber. The resilient member can deform under the load of the air bearing so that the air bearing can self-align, improving alignment.

Preferably, the at least one air bearing has an upper surface arranged above an upper surface of the support unit. In other words, the air bearing protrudes above the upper surface of the support unit. As the conveyor belt is support on the air bearing, this provides a space between the upper surface of the support unit and the underside of the conveyor belt. The vacuum apertures can be in fluid communication with this space so that a negative pressure is applied in this space.

Preferably, the at least one air bearing is arranged to protrude above the upper surface of the support unit by between <NUM> and <NUM>. This ensures that a small gap is avoided. For example, if the air bearing is flush with the upper surface of the support unit, the gap between the underside of the conveyor belt and the upper surface of the support unit is only the height of the air film, which might typically be around <NUM> to <NUM>. As the at least one air bearing may not be continuous across the upper surface (e.g. in an array of air bearings), the supporting force is lower between air bearings, and therefore the belt can sag between air bearings. By providing the air bearing protruding from the upper surface in this manner, it is ensured that the conveyor belt will not touch the upper surface, even if the belt sags. Additionally, it is beneficial to avoid a large gap as this requires a larger space, requiring a stronger vacuum force to provide the desired effect on the substrate.

Preferably, the upper surface of the at least one air bearing is circular. In other examples, the upper surface has different shapes such as square or rectangular. For example, the air bearing may be shaped to fit between vacuum apertures.

Preferably, the upper surface of the at least one air bearing comprises a slit. The slit is provided to provide a connection to the space between the upper surface of the support unit and the underside of the conveyor belt which is at a negative pressure. This reduces the flow rate of air in the slit. As the slit may align with belt apertures as the conveyor belt passes over the support unit, the slit ensures that there is not a strong positive pressure applied in this region, which would otherwise provide an upward force on the substrate through the belt apertures, reducing the hold down force. As such, the retaining force on the substrate is improved. The slit may be arranged through the centre of the air bearing (i.e. across a width of the air bearing). In one example, the slit extends across a diameter of the air bearing where the air bearing is circular. For example, the slit may have a width of <NUM>. In some examples, the slit has a generally rectangular shape. The slit may have a depth of <NUM>. It is desirable for the depth of the slit to be significantly deeper than the air film thickness (which may be for example around <NUM> to <NUM>). Effectively, the slit allows for the reduction of the number of air bearings, because it splits the air bearing into two effective air bearings either side of the slit. This avoids the need for providing a larger number of smaller air bearings between rows of vacuum apertures.

Preferably, the at least one air bearing comprises a plurality of air bearings arranged in an array. In this way, the air bearings may be interspersed with the vacuum apertures in the upper surface of the support unit. By providing a plurality of discrete air bearings, the conveyor belt can be supported at multiple locations. This improves the uniformity of the supporting force and can reduce sagging of the belt. In some examples, the air bearings are arranged in an offset pattern. In other words, the air bearings are staggered over the upper surface. This avoids the air bearings being arranged in continuous strips along the belt axis. This allows the conveyor belt to be forced to deform into a complex curve over the air bearings, which makes the belt much stiffer than if a simple curve was permitted. In contrast, where air bearings are arranged in non-offset patterns (e.g. continuous strips), the belt may be easier to deform and is not as stiff, reducing printing accuracy. In some examples, the air bearings may be arranged in rows extending in a direction offset from the belt axis (the direction of movement of the conveyor belt). For example, the air bearings may be arranged in rows extending in a direction that forms an angle with the belt axis. For example, the air bearings may be arranged to extend in rows in a diagonal direction.

Preferably, each of the plurality of air bearings cover an area of an upper surface of the support unit of between <NUM><NUM> and <NUM><NUM>. More preferably, the area is between <NUM><NUM> and <NUM><NUM>. This provides an optimum surface area for supporting the conveyor belt, while fitting the air bearings between vacuum apertures. In one example, the air bearings are circular and have a diameter of between <NUM> and <NUM>, preferably around <NUM>. This provides an area of around <NUM><NUM>. In examples where a slit is provided, the effective surface area is reduced by the area of the slit because the positive pressure does not act effectively in this region. For a slit across the diameter having a width of <NUM>, the effective area is around <NUM><NUM>.

Preferably, the plurality of air bearings comprise at least <NUM> air bearings per m<NUM> of the area of an upper surface of the support unit. In one example, there are <NUM> air bearings per m<NUM>. This provides a uniform supporting force on the conveyor belt, avoiding sag of the belt between air bearings.

Preferably, the plurality of air bearings cover between <NUM> % and <NUM> % of the area of an upper surface of the support unit. More preferably, the total area is between <NUM> % and <NUM> %, even more preferably around <NUM> %. This provides the desired supporting force while minimising the number of air bearings.

Preferably, the support unit comprises at least one tile comprising porous media forming the at least one air bearing. In this way, the at least one air bearing is in the form of the at least one tile. In other words, there are no individual discrete air bearings in an array. Instead, the tile itself provides the air bearings. The tile comprises porous media so that the surface of the tile as a whole provides one effective air bearing. This provides a convenient solution as individual air bearings can be avoided, and the system can be manufactured cheaply and easily. The surface area of the porous media is also much larger than providing individual air bearings, which means a higher force can be generated for supporting the conveyor belt. The tile can also provide the vacuum apertures by providing holes in the tile. The upper surface of the tile can then act as the upper surface of the support unit. This results in higher performance and lower cost. This negates the need for close tolerance between the air bearing and the upper surface because the upper surface is defined by the porous media tile. This also allows for use of a thinner steel belt or a plastic belt due to uniform support and lower friction operation due to no velocity stability issues or premature stretch or wear, leading to significantly lower costs.

Preferably, the air bearing covers at least <NUM> % of the area of an upper surface of the support unit. Because the area of the tile comprises porous media, the area can be significantly higher than providing individual air bearings. This improves the uniformity of the supporting force on the belt.

Disclosed herein is a substrate support system for a conveyor printer, comprising a support unit comprising: a plurality of vacuum apertures arranged for fluidic communication with a source of negative pressure; wherein the support unit comprises porous media, wherein the porous media is configured as an air bearing arranged for fluidic communication with a source of positive pressure; and a conveyor belt arranged over the support unit for supporting a substrate to be printed on, the conveyor belt comprising a plurality of belt apertures; wherein the vacuum apertures are arranged to convey a negative pressure through the belt apertures for retaining the substrate on the conveyor belt; and wherein the air bearing is arranged to convey a positive pressure to support the conveyor belt.

In other words, the support unit may provide the functionality of an air bearing. The support unit may be formed of porous media. In some examples, the support unit comprises at least one tile. The porous media may be in the form of a tile. In this way, the porous media tile may act as an air bearing. The conveyor belt can be supported on the upper surface of the support unit, and the porous media can supply positive pressure to form an air cushion over the upper surface of the support unit to support the conveyor belt and provide an air bearing. This avoids the need for separate air bearings. The porous media may be arranged around the vacuum apertures such that the support unit is formed of porous media with vacuum apertures arranged through the porous media. Preferably, the porous media comprises holes which form the vacuum apertures (for example, the vacuum apertures may have slots), in contrast to applying negative pressure through the porous media, thereby improving the hold-down force on the substrate.

The support unit (e.g. the tile) may comprise a plurality of slots defining the vacuum apertures. In some examples, the slots may have a length which extends along the direction of movement of the conveyor belt (belt axis). In some examples, the vacuum apertures may be offset so that vacuum apertures in adjacent rows (where rows extend along the belt axis) are not aligned with each other. This improves the hold-down force on the substrate by forcing the conveyor belt to deform into a complex shape.

In some examples, the support unit comprises a tile as set out above, and a carrier for supporting the tile. The carrier may be arranged on an underside of the tile. The carrier may comprise a plurality of channels (or one continuous channel) for distributing air to the porous media (for example by distributing air over the underside surface of the tile). The porous media can be arranged over the channels so that air can pass along the channels and through the porous media. The channels may be connected to a source of positive pressure. The carrier may define an attachment surface between the channels, which may be configured to attach to the tile (e.g. to the porous media). The carrier may also comprise a plurality of vacuum openings, such as in the attachment surface, which may be configured to connect the vacuum apertures of the tile to a source of negative pressure. Thus, the vacuum openings of the carrier may be aligned with the vacuum apertures of the tile.

In some examples, the support unit comprises a plurality of tiles arranged together to form an air bearing surface.

Preferably, the plurality of vacuum apertures each comprise a slot in an upper surface of the support unit and a vacuum feed hole in the base of the slot, wherein the vacuum feed hole is connected to the source of negative pressure. The slots conveys the negative pressure to the belt apertures moving over the upper surface. The slots connect the vacuum feed hole to the space between the conveyor belt and the upper surface defined by the air bearings. In some examples, the slots can have a size and shape complementary to the belt apertures, but in some cases can be slightly wider to accommodate lateral movement of the belt. Because the slots are apertures rather than a porous material, the vacuum force applied can be greater. In other words, because the vacuum can be applied directly through the slots rather than through a porous material, the vacuum force can be stronger. This can increase the strength of the hold-down force for a given pressure, or can improve efficiency, complexity, and cost by reducing the magnitude of the negative pressure required. Instead, by passing a vacuum through a porous material, this would result in wastage and reduce the hold-down force. The volume of the aperture slots thus acts to permit a better vacuum. The combination of porous media air bearings for positive pressure with apertures for negative pressure optimises the supply of positive and negative pressures.

Preferably, the slots of the vacuum apertures extend in a direction parallel to a direction of movement of the conveyor belt.

Preferably, the slots have a width of between <NUM> and <NUM>. More preferably, the slots have a width of between <NUM> and <NUM>, even more preferably around <NUM>.

Preferably, a pitch between adjacent slots of the vacuum apertures in a direction perpendicular the direction of movement of the conveyor belt is between <NUM> and <NUM>. More preferably, the pitch is between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

Preferably, a land between adjacent slots of the vacuum apertures in a direction perpendicular to the direction of movement of the conveyor belt is between <NUM> and <NUM>. More preferably, the land is around <NUM>.

Preferably, the substrate support system further comprises a plurality of valves operable to open and close the plurality of vacuum apertures. For example, the valves may be ball valves using a spring to close and open the vacuum apertures due to a pressure differential based on whether a substrate covers the vacuum aperture. In this way, the vacuum apertures can self-seal to improve the efficiency of the vacuum hold down force.

Preferably, the substrate support system further comprises a sheet comprising: a plurality of valves formed into the sheet; wherein the sheet is made from a resilient material; and wherein each valve comprises a valve head for sealing a respective vacuum aperture in the substrate support unit, and a valve lever arm for permitting movement of the valve head towards and away from the vacuum aperture in order to open and close the valve.

This can provide a sheet of valves for use with the air bearings. The combination of vacuum apertures and air bearings can be supplemented with a convenient sheet of valves for operating the vacuum apertures. In this way, the valves can be operated to move to close the vacuum apertures. This can be effected automatically when a substrate covers the vacuum aperture by causing a pressure differential and the air drag force pulls the valve head down towards the vacuum aperture. The valve lever arm permits the movement of the valve head by bending due to the resilience of the sheet.

This allows a plurality of valves to be used for opening and closing an array of vacuum apertures in a substrate support unit of a printer. For example, the printer may be an ink-jet printer. The printer may be a flat-bed printer. In other examples, the printer may be a conveyor printer which uses a conveyor belt to move a substrate past a printhead in a printing motion. For example, the substrate may comprise paper or cardboard. The sheet provides a simple and cheap solution which avoids the need for ineffective masking. For conveyor printers, masking is not possible, so this avoids the need for complex ball valves. The sheet can be rapidly produced simply by forming the valves from the sheet, such as by cutting. This allows for rapid production and prototyping, and permits easy and fast replacement, limiting downtime of the printer.

Preferably, the resilient material comprises a plastic.

Preferably, the plastic comprises BoPET. In other examples, the resilient material comprises polyimide e.g. Kapton (RTM), styrene, polyvinyl chloride (PVC), or polycarbonate.

Preferably, the sheet has a thickness of between <NUM> and <NUM>. More preferably, the sheet has a thickness of between <NUM> and <NUM>. In one example, the sheet has a thickness of <NUM>. In a most preferred example, the sheet has a thickness of <NUM>. By providing a thickness of less than around <NUM>, preferably around <NUM>, the valve head is light enough that the time to open the valve is short, improving the efficiency.

Preferably, the valve lever arm has the same thickness as the remainder of the sheet. In other words, the thickness of the sheet is uniform. The valve head and the valve lever arm can have the same thickness. This makes it easier to manufacture because it is not necessary to reduce the thickness of the sheet in any region.

Preferably, the plurality of valves are defined by a plurality of cut-outs in the sheet. The cutout sections leave material which form the valve lever arm and the valve head. The cut-outs forms gaps in the sheet, which also permit airflow through the valve.

Preferably, the valve head is connected to the sheet by the valve lever arm. For example, the valve head may be connected to the sheet only by the valve lever arm. Otherwise, the valve head is free from the sheet. This allows the valve head to move to and from the vacuum aperture.

In some examples, when the valve is open, the valve head is arranged in the plane of the sheet, for example being in line with the rest of the sheet. In other words, the valve head is preferably not pre-bent into a different plane in the open configuration. This improves ease of manufacture because the valve head does not require pre-bending into another position. Instead, the flat sheet can simply be provided, and the valve head can simply be provided by cutting out a section of the sheet, for example.

Preferably, the valve lever arm is configured to permit the valve head to move out of the plane of the sheet. This allows the valve head to move towards the vacuum aperture to close the valve. To achieve this, the valve lever arm is bendable so that the valve lever arm can bend as the valve head is pulled down towards the vacuum aperture. As the sheet is resilient, the valve lever arm can be configured to return the valve head to the plane of the sheet when the force closing the valve is removed. In other words, tension due to the bending of the valve lever arm pulls the valve head and returns it to the equilibrium position in the plane of the sheet, thus opening the valve. Thus, the valve may be auto-resetting. This is particularly preferable for conveyor printers, where it is not convenient to require a separate opening mechanism, and this does not require shutting off the vacuum.

Preferably, the valve lever arm is configured to cause the valve head to remain parallel to the plane of the sheet when the valve head is arranged out of the plane of the sheet. This is achieved by the particular shape of the valve lever arm. For example, this can be provided by using a valve lever arm which is curved around the side of the valve head. In other examples, this can be provided by a valve lever arm which is straight and has a length greater than the width of the valve head.

In some examples, the valve head may be arranged parallel to the plane of the sheet when the valve is closed. In other words, when the valve head covers the vacuum aperture to close the valve, the valve head may be arranged parallel to the plane of the sheet. In some examples, the valve head may be arranged parallel to a plane defined by an upper surface of the substrate support unit when the valve is closed. The plane of the sheet may be parallel to the plane defined by the upper surface of the substrate support unit. Thus, the valve head may be arranged parallel to the plane of the sheet and parallel to the upper surface of the substrate support unit. This allows the valve head to lie flat against the vacuum aperture to provide an improved seal. The valve head may be arranged parallel to a plane of the vacuum aperture, for example when the valve head closes the valve. In other words, the valve head may lie flat (e.g. horizontal) on the substrate support unit to close the valve. This is in contrast to the valve head lying at an angle, where the substrate support unit is also at an angle. For instance, the substrate support unit may comprise a recess (e.g. cut into the substrate support unit) in which the vacuum aperture is arranged, and the valve head may be arranged to contact a base of the recess to seal the vacuum aperture to close the valve. In some cases, the base of the recess may be parallel to an upper surface of the substrate support unit (e.g. horizontal).

Preferably, the valve lever arm has a length equal to or greater than a width of the valve head. This enables the valve head to move generally parallel to the plane of the sheet so that the valve head can lie flat against the vacuum aperture. The valve lever arm may have a length which is longer than the width of the valve head, preferably at least twice as long, more preferably at least three times as long, even more preferably at least four times as long. Most preferably, the valve lever arm has a length between two and five times the width of the valve head, to provide desired flexibility for ensuring the valve head can lie flat against the vacuum aperture, whilst improving compactness and density of valves.

Preferably, the valve lever arm is configured to permit the valve head to lie flat against the vacuum aperture to seal the vacuum aperture. This allows for a more effective seal. For example, the valve lever arm may permit the valve head to close the vacuum aperture by arranging the valve head parallel to a plane of the vacuum aperture and in contact with the vacuum aperture.

Preferably, the valve lever arm extends from the sheet at a first side of the valve head around the side of the valve head and is connected to the valve head at a second side opposite the first side. This shape permits the valve head to lie flat against the vacuum aperture by being arranged in a plane parallel to the sheet, while also providing a compact arrangement because the valve lever arm is arranged in a small space surrounding the valve head. This allows the packing density to be increased relative to straight valve lever arms.

Preferably, the valve lever arm is curved around the side of the valve head between the first side and the second side. For example, the valve head may be circular. This further improves the compactness by following the curve of the circular valve head. In other examples, the valve lever arm may extend around the valve head in a U-shape.

Preferably, the plurality of valves comprises between <NUM> and <NUM> valves per m<NUM> of the sheet. This enables a large density of vacuum apertures to be controlled. Clearly, providing this density of ball valves would be complex and expensive, so using a simple sheet provides a much more useful solution.

Preferably, each valve comprises a bypass for equalising pressure. This aids the opening of the valve when the substrate no longer covers the opening. This allows the valve to be auto-resetting. This means that a separate mechanism is not required to open the valve. Instead, the valve automatically opens in response to the substrate no longer covering the opening. This simplifies construction and operation.

Preferably, the substrate support system further comprises a second sheet comprising a plurality of recesses formed into the second sheet, wherein each recess is configured to align with a vacuum aperture when arranged over the substrate support unit, and wherein each recess is configured to receive a valve of the first sheet when the first sheet is arranged over the second sheet.

Preferably, the recesses of the second sheet provide a space to permit movement of the valve head towards the vacuum aperture for closing the valve.

According to a second aspect of the present disclosure, there is provided a method for using the substrate support system as disclosed herein, the method comprising: providing the substrate support system as disclosed herein; placing a substrate on the conveyor belt; applying, by the source of negative pressure, a negative pressure to the plurality of vacuum apertures to retain the substrate on the conveyor belt; and applying, by the source of positive pressure, a positive pressure to the at least one air bearing to support the conveyor belt. The negative pressure can therefore act to retain the substrate on the conveyor belt, while the positive pressure can support the conveyor belt on the at least one air bearing.

Features of one aspect can be readily applied to the other aspect and vice versa. Apparatus features of the substrate support system can be applied to the method.

Disclosed herein is a support unit for a conveyor printer, comprising: a plurality of vacuum apertures arranged for fluidic communication with a source of negative pressure; and at least one air bearing arranged for fluidic communication with a source of positive pressure, wherein the air bearing comprises porous media; wherein the support unit is configured to receive a conveyor belt in use for supporting a substrate to be printed on; wherein the vacuum apertures are arranged to convey a negative pressure in use through belt apertures of the conveyor belt for retaining the substrate on the conveyor belt; and wherein the at least one air bearing is arranged to convey a positive pressure in use to support the conveyor belt. In this way, it will be appreciated that the support unit can be used together with a conveyor belt, a source of negative pressure, and a source of positive pressure to form a substrate system such as in the first aspect. Features of the first aspect may be applied to this disclosure.

Disclosed herein is a substrate support system for a printer, comprising: a support unit comprising: a plurality of vacuum apertures arranged for fluidic communication with a source of negative pressure; at least one air bearing arranged for fluidic communication with a source of positive pressure, wherein the air bearing comprises porous media; and a substrate support surface for supporting a substrate to be printed on; wherein the vacuum apertures are arranged to convey a negative pressure through the substrate support surface for retaining the substrate on the substrate support surface; and wherein the at least one air bearing is arranged to convey a positive pressure for releasing the substrate from the substrate support surface. In this way, the substrate support system may be used for a printer such as a flat-bed printer. The air bearings may be used for aiding release of the substrate, such as after a printing operation has been completed or for otherwise moving the substrate. Features of the first aspect may be applied to this disclosure.

Disclosed herein is a substrate support system for a conveyor printer, comprising: a support unit comprising: a plurality of vacuum apertures arranged for fluidic communication with a source of negative pressure; and at least one air bearing arranged for fluidic communication with a source of positive pressure; and a conveyor belt arranged over the support unit for supporting a substrate to be printed on, the conveyor belt comprising a plurality of belt apertures; wherein the vacuum apertures are arranged to convey a negative pressure through the belt apertures for retaining the substrate on the conveyor belt; and wherein the at least one air bearing is arranged to convey a positive pressure to support the conveyor belt. In this way, the at least one air bearing need not be a porous media air bearing. For example, the air bearing may be an aperture air bearing. In one example, the air bearing may be an aerostatic air bearing. For example, the air bearing may be a micro-nozzle air bearing, an orifice type air bearing, or an air caster air bearing. In another example, the air bearing may be an aerodynamic air bearing. Features of the first aspect may be applied to this disclosure.

Embodiments of the disclosure are described below, by way of example only, with reference to the accompanying Figures.

Referring to <FIG> and <FIG>, a substrate support unit <NUM> for a substrate support system according to a first embodiment of the present disclosure is provided. The substrate support unit <NUM> may otherwise be referred to as a support unit <NUM>. The support unit <NUM> is for a conveyor printer. A conveyor printer is a printer which uses a conveyor belt to provide the printing motion. In particular, the conveyor belt is provided to feed a substrate towards a printhead for printing, and printing can be performed by the conveyor belt moving the substrate under the printhead. The substrate support system comprises the support unit <NUM> and further comprises a conveyor belt (not shown in <FIG> and <FIG>).

In use, the conveyor belt is supported on the support unit <NUM>. In particular, the support unit <NUM> comprises an upper surface <NUM>. The conveyor belt is then arranged over the upper surface <NUM> so that the conveyor belt can move over the upper surface <NUM> to feed a substrate through a printer for printing. More precisely, as will be described below, the conveyor belt is supported at a position slightly above the upper surface <NUM>, by virtue of air bearings, rather than directly on the upper surface <NUM> itself.

The upper surface <NUM> is arranged in a plane which extends in the x direction and the y direction. The x direction is indicated by arrows in <FIG> and <FIG>, and the y direction is indicated by arrows in <FIG>. The y direction is the direction of movement of the conveyor belt, and hence the feed direction of the substrate. In other words, the y direction is parallel to the length of the conveyor belt. The x direction is perpendicular to the y direction. The x direction is perpendicular to the direction of movement of the conveyor belt, and hence is perpendicular to the feed direction of the substrate. In other words, the x direction is parallel to the width of the conveyor belt. The z direction is perpendicular to the x and y directions, and is arranged out of the page in <FIG>. The z direction corresponds to a height, for example above the upper surface <NUM>. The z direction is indicated by arrows in <FIG> and <FIG>. In the first embodiment, in use, the x and y directions are horizontal, and the z direction is vertical.

As shown in <FIG>, the upper surface <NUM> is at least partially defined by an upper surface of a plate <NUM>. In the first embodiment, the support unit <NUM> comprises the plate <NUM>. The plate <NUM> is attached to an upper surface of a mount <NUM>. The plate <NUM> extends in the x-y plane and has a thickness in the z direction. In other examples, the upper surface <NUM> may be defined by a plate <NUM> integral with the mount <NUM>.

The support unit <NUM> comprises a plurality of vacuum apertures <NUM>. In particular, the vacuum apertures <NUM> are arranged through the upper surface <NUM>. The vacuum apertures <NUM> are spaces in the upper surface <NUM> which provide communication with a negative pressure. The vacuum apertures <NUM> are arranged through the thickness of the plate <NUM>. In this way, the vacuum apertures <NUM> provide fluid communication between the upper surface <NUM> at the upper surface of the plate <NUM> and the underside of the plate <NUM>. This allows the vacuum apertures <NUM> to provide a connection between a negative pressure applied from below the upper surface <NUM> (i.e. from below the plate <NUM>) to the upper surface <NUM> (i.e. to above the plate <NUM>). To provide this, the vacuum apertures <NUM> are connected to a source of negative pressure.

In the first embodiment, the vacuum apertures <NUM> comprise a plurality of slots <NUM> in the plate <NUM>. Each vacuum aperture <NUM> is in the form of a slot <NUM>. In other words, the plate <NUM> comprises a plurality of slots <NUM>. The slots <NUM> form the vacuum apertures <NUM> in the upper surface <NUM>. The slots <NUM> are distributed over the upper surface <NUM> in the upper surface of the plate <NUM>. These slots <NUM> have an elongate shape which is longer in the y direction than the x direction. The slots <NUM> are formed from parallel sides along the length with rounded ends. The slots <NUM> have a shape which may be referred to as a stadium shape or a rounded rectangle. The slots <NUM> extend in the y direction so that a length of the slots <NUM> is in the y direction, and a width of the slots <NUM> is in the x direction. The slots <NUM> have a depth into the thickness of the plate <NUM> in the z direction. In the first embodiment, the slots <NUM> extend a depth less than the thickness of the plate <NUM>. Each slot <NUM> therefore forms a recess in the plate <NUM>. At the bottom of the recess, the vacuum aperture <NUM> comprises a hole through the remaining thickness of the plate <NUM>, wherein the hole is connected to the slot <NUM>. In other embodiments, the slot <NUM> extends through the entire thickness of the plate <NUM> so that the slot <NUM> is in the form of a through-hole through the plate <NUM>. Each slot <NUM> corresponds to a respective vacuum aperture <NUM>. Each slot <NUM> thus functions as a vacuum aperture <NUM> providing fluid communication through the plate <NUM>.

The support unit <NUM> also comprises a plurality of vacuum openings <NUM>. The vacuum openings <NUM> are arranged in the upper surface of the mount <NUM>. The vacuum openings <NUM> thus lie in the x-y plane which aligns with the lower surface of the plate <NUM>. The vacuum openings <NUM> are thus arranged in a plane which is parallel to the upper surface <NUM>. The vacuum openings <NUM> correspond to the slots <NUM>. In particular, each vacuum opening <NUM> is aligned with a respective slot <NUM> in the plate <NUM>. Thus, the vacuum openings <NUM> are arranged in the z direction at the base of each slot <NUM>. In the first embodiment, the vacuum openings <NUM> in the mount <NUM> are aligned and in fluid communication with the holes at the bottom of the slots <NUM>. In other embodiments where the slots <NUM> extend through the entire thickness of the plate <NUM>, the vacuum openings <NUM> are instead aligned generally with and are in fluid communication directly with the slots <NUM>. The vacuum openings <NUM> are arranged in the centre of the slots <NUM> in the x direction. Each vacuum opening <NUM> is connected through the mount <NUM> to the source of negative pressure. Therefore, the vacuum aperture <NUM> provides fluid communication between the upper surface <NUM> and the source of negative pressure through the slots <NUM>, and in turn through the vacuum openings <NUM>. In this way, the vacuum opening <NUM> at the base of the slot <NUM> can apply the negative pressure through the slot <NUM> to the upper surface <NUM>. In other words, the slot <NUM> becomes the effective vacuum aperture <NUM> arranged at the upper surface <NUM>. The uppermost point of the slots <NUM> at the upper surface of the plate <NUM> define the uppermost point of the vacuum apertures <NUM> at the upper surface <NUM>. In other words, the upper surface <NUM> comprises the upper surface of the plate <NUM> with a plurality of vacuum apertures <NUM> in the form of slots <NUM> in the plate <NUM>. Each vacuum opening <NUM> corresponds with a respective vacuum aperture <NUM>.

The function of the vacuum apertures <NUM> is to hold down a substrate which is placed onto the conveyor belt which runs over the upper surface <NUM>. In particular, the vacuum apertures <NUM> are connected to a source of negative pressure so that the vacuum apertures <NUM> are arranged to convey a negative pressure to the substrate arranged on the upper surface <NUM>. In the first embodiment, the source of negative pressure is a vacuum pump. The vacuum pump is connected to the vacuum apertures <NUM> underneath the upper surface <NUM> through conduits arranged through the mount <NUM>, through the vacuum openings <NUM>, and to the slots <NUM>. The slots <NUM> convey the negative pressure to the upper surface <NUM> above which the conveyor belt is supported by the air bearings. To convey the negative pressure from the vacuum apertures <NUM> to the substrate, the conveyor belt is perforated to permit fluid communication between the vacuum apertures <NUM> and the substrate. To achieve this the conveyor belt has belt apertures which are arranged in rows which generally align with the rows of slots <NUM> so that the vacuum apertures <NUM> can convey the negative pressure through the conveyor belt and to the substrate. By applying a negative pressure to the substrate, a suction force is applied to the substrate towards the upper surface <NUM> by virtue of the vacuum apertures <NUM>. This acts to hold the substrate down on the conveyor belt. This keeps the substrate retained in place during movement of the conveyor belt and during the printing process. This improves alignment and thus printing quality.

In the first embodiment, the vacuum apertures <NUM> are arranged in an array over the upper surface <NUM>. The vacuum apertures <NUM> are arranged in rows which each extend in the y direction. In particular, the slots <NUM> are arranged in rows each extending in the y direction. Each adjacent slot <NUM> in the y direction is adjacent but separated so that each slot <NUM> is isolated from each other. This permits the vacuum pressure to be more precise, as certain vacuum apertures <NUM> may be opened or closed in order to turn on or off the vacuum in each particular location. This can be used for precise control over retaining the substrate, for example at the edge of the substrate.

The vacuum openings <NUM> are also arranged in an array. In the first embodiment, the vacuum openings <NUM> are arranged in rows extending in the y direction. Precisely, each row of vacuum openings <NUM> extends in the y direction. The vacuum openings <NUM> align with the slots <NUM>, so thus correspond to the arrangement of the rows of the slots <NUM>. In the first embodiment, each alternate row of vacuum openings <NUM> in the x direction is offset in the y direction with a repeating period of two. In other words, each adjacent vacuum opening <NUM> in the x direction is not aligned at the same y position. The offset amount is equal to the pitch between adjacent rows, so that the vacuum openings <NUM> form a square array parallel to the upper surface <NUM>. Thus, every two rows in the x direction are aligned in position in the y direction. As such, the vacuum openings <NUM> are diagonally aligned in rows extending in the x = y direction i.e. the diagonal between the x and y directions. The skilled person will appreciate that other arrangements of vacuum openings <NUM> may be provided in other embodiments.

In the first embodiment, the vacuum apertures <NUM> have a pitch of <NUM>. The pitch is the distance between rows of adjacent vacuum apertures <NUM> in the x direction. In other words, the pitch is the separation between the centre line of a first row of slots <NUM> which extends in the y direction and the centre line of a second row of slots <NUM> immediately adjacent to the first row of slots in the x direction. In other examples, the pitch may be longer or shorter, and in one example is between <NUM> and <NUM>. The value is chosen to correspond to the pitch between belt apertures in the conveyor belt so that the apertures can align for application of the pressure to the substrate. In the first embodiment, the belt apertures of the conveyor belt also have a pitch of <NUM>. A smaller pitch improves hold down closer to the substrate edges, but requires smaller structure and more structures per m<NUM> of the belt, which is more difficult and expensive to manufacture. In some examples, the belt may comprise a structure on the upper surface of the belt to distribute vacuum.

In the first embodiment, the separation in the y direction between adjacent vacuum openings <NUM> in the same row along the y direction (i.e. at the same position in the x direction) is twice the pitch in the x direction. In other embodiments, this separation may be different, and may be different from the pitch, resulting in an array which is not square.

In the first embodiment, the width of the slots <NUM> is <NUM>. The width is the extent of the slot <NUM> in the x direction. More precisely, the width is the distance in the x direction between opposing edges of the same slot <NUM>. The width is the widest point in cases where the width is not constant. The width is perpendicular to the length of the slot <NUM> which extends in the y direction. In other examples, the width of the slots <NUM> has other values such as between <NUM> and <NUM>. In some embodiments, the width of the slot <NUM> corresponds to the width of the belt apertures. In other examples, the width of the slot <NUM> is slightly larger to give some tolerance in belt tracking.

The land between adjacent slots <NUM> in the x direction is <NUM>. The land is the distance between the closest edges of adjacent slots <NUM> in the x direction. In other examples, the land has other values. In one example, the land may be between <NUM> and <NUM>. The size of the land may be chosen to provide sufficient space for air bearings and to avoid reducing the positive pressure around the edges of the air bearing.

The length of the slots <NUM> is between <NUM> and <NUM>. The length is the extent of the slot <NUM> in the y direction. More precisely, the length is the distance in the y direction between opposing edges of the same slot <NUM>. The length is the longest point in cases where the length is not constant. In the first embodiment, the length is measured as the largest separation in the y direction between either (furthermost) end of the slot <NUM>. The length of the slots <NUM> is chosen to be not too long because then they will be vented by the edge of the substrate, and will not provide good hold down. The length of different slots <NUM> is varied to accommodate the air bearings mentioned below. As such, in some cases the vacuum opening <NUM> is not aligned in the centre of the slot <NUM> in the y direction for slots <NUM> which have a short length to accommodate an air bearing. In other examples, the length of the slots <NUM> has other values.

The bridge between adjacent slots <NUM> in the y direction is as short as possible. The bridge is the distance between the closest edges of adjacent slots <NUM> in the y direction. It is beneficial for the bridges to be short because they interrupt vacuum supply to the substrate.

The upper surface <NUM> comprises at least <NUM> vacuum apertures <NUM> per m<NUM> of the upper surface <NUM>. It is noted that <FIG> only show a portion of the upper surface <NUM> for illustrative purposes. As such, the plate <NUM> comprises at least <NUM> slots per m<NUM> of the upper surface of the plate <NUM>, and the mount <NUM> comprises at least <NUM> vacuum openings <NUM> per m<NUM> of the upper surface of the mount <NUM>. In the first embodiment, the number of slots is <NUM> per m<NUM>, but this may be varied in other embodiments.

In the first embodiment, the source of negative pressure is configured to apply a negative pressure of between -<NUM> mbarg to -<NUM> mbarg to the vacuum apertures <NUM>. For the avoidance of doubt, the unit mbarg refers to millibars of gauge pressure above atmospheric pressure, sometimes also represented as mbar(g). Therefore, the negative pressures above refer to a gauge pressure below atmospheric pressure (i.e. a vacuum pressure). In SI units, this provides a negative pressure of-<NUM> kPa to -<NUM> kPa relative to atmospheric pressure (being approximately <NUM> kPa).

The support unit <NUM> also comprises at least one air bearing <NUM>. The air bearing <NUM> provides fluid communication with a positive pressure. In the first embodiment, the support unit <NUM> comprises a plurality of air bearings <NUM>. These air bearings <NUM> are individual air bearings <NUM> which are arranged in an array over the upper surface <NUM>. In particular, the air bearings <NUM> are distributed throughout the plate <NUM>. The air bearings <NUM> are arranged through the thickness of the plate <NUM>. The plate <NUM> comprises holes for receiving the air bearings <NUM> and the air bearings <NUM> are arranged through holes in the plate <NUM>. As will be described in more detail below, the air bearings <NUM> have an upper surface <NUM> which is arranged to protrude above the plane of the upper surface <NUM>. In the first embodiment, the upper surface <NUM> is arranged at a height of <NUM> above the upper surface <NUM> of the support unit <NUM>. The air bearings <NUM> extend through the entire thickness of the plate <NUM> so that the air bearings <NUM> can be connected to a source of positive pressure below the plate <NUM>.

In this way, the air bearings <NUM> provide fluid communication between the upper surface <NUM> at the upper surface of the plate <NUM> and the underside of the plate <NUM>. This allows the air bearings <NUM> to provide a connection between a positive pressure applied from below the upper surface <NUM> (i.e. from below the plate <NUM>) to the underside of the conveyor belt above the upper surface <NUM> (i.e. to above the plate <NUM>).

The air bearings <NUM> are porous media air bearings <NUM> and comprise a porous media <NUM>. The porous media <NUM> is arranged at the upper part of the air bearing <NUM> in the z direction. The upper surface <NUM> of the porous media <NUM> is arranged to protrude above the plane of the upper surface <NUM>. The air bearings <NUM> deliver a positive pressure to the underside of the conveyor belt. As will be described in more detail with reference to <FIG>, the air bearing <NUM> is structured so that the air bearing <NUM> can convey an airflow to the conveyor belt. The air bearing <NUM> is in fluid communication with a source of positive pressure. The air applied by the source of positive pressure can diffuse through the porous media <NUM> to the upper surface <NUM> of the air bearing <NUM> to be released above the upper surface <NUM> for supporting the conveyor belt.

The function of the air bearings <NUM> is to support the conveyor belt which is placed onto the upper surface <NUM>. The air bearings <NUM> provide a cushion of air on which the conveyor belt rests. In particular, the air bearings <NUM> are connected to a source of positive pressure so that the air bearings <NUM> are arranged to supply a positive pressure to the conveyor belt arranged on the upper surface <NUM>. In the first embodiment, the source of positive pressure is an air pump. The air pump is connected to the air bearings <NUM> underneath the upper surface <NUM> through conduits arranged through the mount <NUM>. A flow of air is then provided to the air bearings <NUM> which is delivered to the upper surface <NUM> by diffusing through the porous media <NUM> to the upper surface <NUM> of the air bearing <NUM>. This positive pressure released at the upper surface <NUM> of the air bearing <NUM> forms a thin film of air over the upper surface <NUM> of the air bearing <NUM>. For example, this film of air may have a thickness of around <NUM> to <NUM>. The conveyor belt then rests on the cushion of air, suspending the conveyor belt away from (above) the upper surface <NUM>. As such, the conveyor belt does not rest in physical contact with elements of the upper surface <NUM> (i.e. it does not rest on the upper surface of the plate <NUM>). This reduces friction between the conveyor belt and the upper surface <NUM> because they are not in direct physical contact and the conveyor belt does not move over the upper surface <NUM> while being in contact. This prevents sticking of the conveyor belt on the upper surface <NUM> and enables smooth movement. Furthermore, heat dissipation due to high friction can be avoided, and the efficiency can be improved while avoiding damage to the conveyor belt via wear due to contact with the upper surface <NUM>.

Therefore, the support unit <NUM> provides an arrangement which permits a conveyor belt to be supported on an array of air bearings <NUM> to reduce friction, while permitting the substrate to be appropriately held down to the conveyor belt by the vacuum apertures <NUM>.

It will be appreciated that this describes an idealised embodiment of the system. In a practical implementation, the conveyor belt may touch areas of the support unit <NUM> due, for example to the belt or the upper surface of the plate <NUM> being slightly uneven.

The porous media <NUM> of the air bearings <NUM> is advantageous compared to traditional aperture-based air bearings because this requires a much lower air consumption to generate the required air cushion for supporting the conveyor belt. In contrast, aperture air bearings require a high consumption of air which is costly and complex to implement, and well as increasing noise of operation. The porous media <NUM> of the air bearings <NUM> is also much more stable. The leak path is also improved and the bleed at the edges is lower, so the balance of the positive and negative pressures is easier to manage. This is particularly important given the close proximity of the air bearings <NUM> and the vacuum apertures <NUM>.

The air bearings <NUM> are arranged interspersed between the vacuum apertures <NUM>. In the first embodiment, there are more vacuum apertures <NUM> than air bearings <NUM>. In particular, on average, there are around <NUM> vacuum apertures <NUM> for each air bearing <NUM>, and in one example there are on average <NUM> vacuum aperture <NUM> for each air bearing <NUM>.

In the first embodiment, the porous media <NUM> comprises carbon. Specifically, the carbon is in the form of sintered carbon. This carbon is porous so that when the positive air pressure is applied to the air bearing <NUM>, the air permeates through the carbon porous media <NUM> to the upper surface <NUM> to be released above the upper surface <NUM> to form the cushion of air. In some cases, the porosity of the porous media <NUM> can be controlled over a wide range during manufacture by varying the pressure during sintering, grain size of the powder before sintering, and then impregnating with resin and sintering again to reduce porosity.

In the first embodiment, the porous media <NUM> has a thickness of <NUM>. The thickness is selected to withstand the pressures, which in the first embodiment is around <NUM> bar pressure on most of the underside, and to avoid significant distortion. The thickness is also chosen to ensure the positive air can diffuse to be reasonably uniform by the time the air reaches the upper surface <NUM>. In other words, this avoids regions of significantly less airflow, such as above the attachment surface to the carrier described below.

In the first embodiment, the air bearings <NUM> are generally circular. More precisely, the upper surface <NUM> of each air bearing <NUM> exposed above the upper surface <NUM> is of a generally circular shape.

In the arrangement of the first embodiment, the air bearings <NUM> have a diameter larger than the pitch between the vacuum apertures <NUM>. The diameter of the air bearings <NUM> is also larger than the width of the slots <NUM>. In fact, in the first embodiment the air bearings <NUM> have a diameter approximately equal to twice the pitch between the vacuum apertures <NUM> in the x direction. Thus, the air bearings <NUM> have a diameter of <NUM>. This means that the air bearings <NUM> cannot be arranged in between adjacent rows of vacuum apertures <NUM> because there is not enough space between the slots <NUM>. To accommodate this, the air bearings <NUM> are placed in regions on the upper surface <NUM> where the vacuum apertures <NUM> are not arranged. In other words, gaps are formed in the array of the vacuum apertures <NUM> and vacuum apertures <NUM> are removed from the array so that the air bearing <NUM> can fit into the array. In other words, the rows of vacuum apertures <NUM> in the y direction are interrupted to fit the air bearings <NUM>. In the first embodiment, due to the offset pattern of the vacuum apertures <NUM> and the size of the air bearings <NUM>, on average only one vacuum aperture <NUM> is removed from the array for the positioning of each air bearing <NUM>. The lengths of the slots <NUM> immediately around the air bearing <NUM> are shortened in order to accommodate the size of the air bearing <NUM>.

In other examples, smaller air bearings <NUM> may be provided which can fit between adjacent slots <NUM>. To achieve this, the air bearings <NUM> have a diameter smaller than the land between adjacent slots <NUM>. This makes the air bearings <NUM> smaller, which means a larger number are required to generate the supporting force for the conveyor belt, leading to higher costs. As such, the first embodiment provides a particular optimum embodiment which balances costs and supporting force.

In the first embodiment, the air bearings <NUM> are arranged to align with some of the rows of vacuum apertures <NUM>. In particular, the centre line of each air bearing <NUM> in the y direction is aligned with a row of vacuum apertures <NUM> in the y direction. In this arrangement, because the air bearing <NUM> has a diameter larger than a width of the slot <NUM>, the air bearing <NUM> extends over the land between adjacent rows of vacuum apertures <NUM>. This means that a positive pressure is provided to the area of the air bearing <NUM> and thus to a point above this portion of the upper surface <NUM> including the land between adjacent rows of vacuum apertures <NUM> at which the air bearing <NUM> is located. Thus, the air bearing <NUM> forms a positive pressure region amongst the vacuum apertures <NUM>. The air bearings <NUM> are arranged in an array with rows in the x direction where each adjacent row in the y direction is offset with a repeating period of five. In other words, every five rows in the y direction are aligned in position in the x direction. The air bearings <NUM> are diagonally aligned at an angle. The skilled person will appreciate that, in other embodiments, different arrangements are possible. For example, the array of air bearings <NUM> may be a square array, or may have an offset with a different repeating period.

Each row of air bearings <NUM> in the x direction is separated from an adjacent row in the y direction by an amount from the centre of each row along the x direction equal to the diameter of the air bearings <NUM>. In other words, the pitch of the air bearings <NUM> in the y direction is equal to the diameter. In the first embodiment, the pitch of the air bearings <NUM> in the y direction is <NUM>. The edges of air bearings <NUM> of one row are thus aligned with the edges of air bearings <NUM> of an adjacent row. However, as the air bearings <NUM> of adjacent rows are offset in the x direction, air bearings <NUM> in adjacent rows do not touch. The air bearings <NUM> are arranged in columns in the y direction. Each column is separated from an adjacent column in the x direction by an amount from the centre of each column along the y direction equal to the diameter of the air bearings <NUM>. In other words, the pitch of the air bearings <NUM> in the x direction is equal to the diameter. In the first embodiment, the pitch of the air bearings <NUM> in the x direction is <NUM>. The edges of air bearings <NUM> of one column are thus aligned with the edges of air bearings <NUM> of an adjacent column. However, as the air bearings <NUM> of adjacent columns are offset in the y direction, air bearings <NUM> in adjacent columns do not touch.

Other arrangements of individual air bearings <NUM> and vacuum apertures <NUM> may be provided, and the arrangement may vary, for example, based on the thickness of the belt, the size of the air bearings <NUM> and the pressure of the positive pressure source.

In the first embodiment, the source of positive pressure is configured to apply a positive pressure of between <NUM> MPa to <NUM> MPa to the air bearings <NUM>. In one embodiment, the vacuum pressure can be around -<NUM> mbarg, and the positive pressure can be around <NUM> MPa, but the volume flow in the vacuum regions is much higher than the volume flow in the positive pressure region because the positive pressure air film is so thin. In one embodiment, with <NUM> MPa applied to the air bearings <NUM> having a diameter of <NUM> and a thickness of <NUM>, an airflow of around <NUM> litre per minute (Ipm) can be achieved.

In the first embodiment, each air bearing <NUM> also comprises a slit <NUM>. The slit <NUM> is arranged in the upper surface <NUM> of the porous media <NUM>. The slit <NUM> extends across a width of the air bearing <NUM> at the centre in the y direction. In other words, the slit <NUM> extends across a diameter of the porous media <NUM> of the air bearing <NUM>. The slit <NUM> is thus aligned with the respective row of vacuum apertures <NUM>. The slit <NUM> is a recess in the porous media <NUM> of the air bearing <NUM> so that the porous media <NUM> in the region of the slit <NUM> does not extend up to the upper surface <NUM>, creating a space. In the first embodiment, the slit <NUM> has a depth less than the height of the porous media <NUM> in the z direction, meaning the slit <NUM> does not extend through the full thickness of the porous media <NUM>. In the first embodiment, the slit <NUM> has a depth of <NUM>. The depth of the slit <NUM> is significantly deeper than the air film thickness (which may, for example, be around <NUM>). The slit <NUM> forms a region along the centre line which has a lower pressure than the air bearing <NUM> at either side of the slit <NUM>. This is because the vacuum pressure acts to evacuate the slit <NUM> and prevent positive pressure building up in this region. In particular, the slit <NUM> forms a gap at the side of the air bearing <NUM> away from the upper surface <NUM>, and so due to the height difference between the air bearing <NUM> and the upper surface <NUM> of the plate <NUM>, a connection is provided between the slit <NUM> and the gap between the upper surface <NUM> of the plate <NUM> and the underside of the conveyor belt. The gap between the upper surface <NUM> and the conveyor belt means that the vacuum apertures <NUM> evacuate this gap and a negative pressure is formed in this region. The slit <NUM> provides fluid communication between the slit <NUM> and this negative pressure region between the vacuum apertures <NUM> and the conveyer belt. The positive pressure generated at the location of the slit <NUM> is thus much lower than either side of the slit <NUM>. This effectively splits the air bearing <NUM> into two smaller effective air bearings either side of the slit <NUM>.

In use, a conveyor belt with belt apertures aligned with the rows of vacuum apertures <NUM> will pass over (and disposed away from) the upper surface <NUM> in the y direction. The belt apertures are arranged in rows extending in the y direction and aligned with the slots <NUM>. Because the centre of the air bearings <NUM> intersects this row, the belt apertures will pass over the centre line of the air bearings <NUM>. Without the slits <NUM>, the positive pressure from the air bearings <NUM> would pass through the belt apertures and act on the substrate. This would reduce the effectiveness of the vacuum hold-down force applied by the vacuum apertures <NUM> and pushing the substrate away from the conveyor belt. By providing the slits <NUM>, the air provided to the central region and thus released between the upper surface <NUM> and the conveyor belt is evacuated by the vacuum. This avoids a reduction in the effectiveness of the vacuum. In some examples, the slit <NUM> can be sealed, for example with varnish, to save air consumption. In other examples, the slit <NUM> is not hollow and may be filled with a non-porous or low porosity material in order to reduce air flow through the central region. In some examples, the slits <NUM> are not required. For example, in embodiments where the air bearings <NUM> are smaller than the lands, slits <NUM> are not required as the air bearing <NUM> can be located in regions which do not overlap with the rows of slots <NUM>.

Referring to <FIG>, a substrate support system <NUM> according to the first embodiment is provided. The substrate support system <NUM> comprises a support unit <NUM>. The support unit <NUM> is the same as the support unit <NUM> of the first embodiment shown in <FIG> and <FIG>, and is represented schematically.

The support unit <NUM> comprises an upper surface <NUM>. The upper surface <NUM> is arranged in the x-y plane, where the x direction is into the page in <FIG>. The support unit <NUM> has a plurality of vacuum apertures <NUM> and a plurality of air bearings <NUM>. As described above, the vacuum apertures <NUM> are connected to a source of negative pressure and are configured to provide a negative pressure at the upper surface <NUM>. The vacuum apertures <NUM> are represented by downward facing arrows in the negative z direction to indicate the downward force of the negative pressure. As described above, the air bearings <NUM> are connected to a source of positive pressure and are configured to provide a positive pressure above the upper surface <NUM>. The air bearings <NUM> are represented by upward facing arrows in the z direction to indicate the upward force of the positive pressure. It is noted that the number and spacing of the arrows is for illustrative purposes only.

The substrate support system <NUM> also comprises a conveyor belt <NUM>. The conveyor belt <NUM> is made from metal, in particular stainless steel. In other examples, the conveyor belt <NUM> may be made from other materials such as other metals including copper, or made from plastic. In the first embodiment, the conveyor belt has a length of <NUM>, a width of <NUM> and a thickness of <NUM>, but other dimensions are possible. The conveyor belt <NUM> can be chosen to be reasonably robust but not require large diameter drums or rollers. The drum diameter can be chosen as the minimum to avoid fatigue problems with the desired belt.

The conveyor belt <NUM> is supported over the upper surface <NUM>. The conveyor belt <NUM> is tensioned between two rollers <NUM> and can use conventional means for moving the conveyor belt <NUM>. In <FIG>, the rollers <NUM> are arranged to rotate about the x direction in a counter-clockwise direction as indicated by the arrows. This moves the conveyor belt <NUM> in a loop in the counter-clockwise direction around the support unit <NUM>, meaning that the conveyor belt <NUM> moves over the upper surface <NUM> in the positive y direction.

In use, a substrate <NUM> is arranged on the conveyor belt <NUM>. The substrate <NUM> may be any substrate to be printed on, such as paper or card. When the substrate <NUM> is placed on the conveyor belt <NUM>, the rollers <NUM> can be rotated to move the conveyor belt <NUM> which feeds the substrate <NUM> along the y direction. This can be used to move the substrate <NUM> to be printed. In this manner, the support unit <NUM> can be used alongside a printer (not shown). The printer can be a conveyor printer which uses the conveyor belt <NUM> to move a substrate <NUM> under an array of printheads to print onto the substrate <NUM>. For example, the conveyor printer may be an inkjet printer arranged on deposit ink onto the substrate <NUM> as it moves under the printhead.

The conveyor belt <NUM> comprises belt apertures through the thickness of the conveyor belt <NUM>. The belt apertures are configured to convey the negative pressure from the vacuum apertures <NUM> in the upper surface <NUM> to the substrate <NUM>. In the first embodiment, the belt apertures are arranged in rows which extend along the length of the conveyor belt <NUM>. The vacuum apertures <NUM> are arranged in rows corresponding to the rows of the belt apertures. These belt apertures align with the slots <NUM> of the plate <NUM>. In this arrangement, when the conveyor belt <NUM> is arranged over the upper surface <NUM> such that the belt apertures align with the vacuum apertures <NUM>, the vacuum apertures <NUM> are arranged to convey the negative pressure from the source of negative pressure through the belt apertures and to the substrate <NUM> which is arranged above the belt apertures. When a substrate <NUM> is placed over the belt apertures aligned with the vacuum apertures <NUM>, the substrate <NUM> can be held in place by the vacuum force. This is indicated by the downward facing arrows in the negative z direction above the substrate <NUM> due to atmospheric pressure acting on the substrate <NUM> towards the negative pressure from the vacuum apertures <NUM>. In this way, the substrate <NUM> is held down onto the conveyor belt <NUM> and can be securely retained, improving alignment for printing.

The air bearings <NUM> act on the conveyor belt <NUM> to provide a cushion of air between the upper surface <NUM> of the air bearings <NUM> and the underside of the conveyor belt <NUM>. The air bearings <NUM> protrude from the upper surface <NUM> so that the upper surface <NUM> of the air bearings <NUM> is arranged above the upper surface <NUM>. The cushion of air provided over the upper surface <NUM> of the air bearings <NUM> is arranged slightly above the upper surface <NUM> so that the conveyor belt <NUM> is supported slightly above the upper surface of the plate <NUM>. In this way, direct physical contact is avoided between the conveyor belt <NUM> and the plate <NUM> or other components of the upper surface <NUM>. Instead, the conveyor belt <NUM> is supported on the cushion of air provided by the air bearings <NUM>, reducing friction when the conveyor belt <NUM> is advanced.

Because the air bearings <NUM> are generally not aligned with the belt apertures (by virtue of the slits <NUM> preventing an air cushion forming in the region of the slits <NUM> aligned with the belt apertures), the air bearings <NUM> generally do not act on the substrate <NUM> and cause minimal interference with the vacuum hold-down force on the substrate <NUM> on the conveyor belt <NUM>. Instead, the air bearings <NUM> support the conveyor belt <NUM> at a position spaced away from the upper surface <NUM> so that the conveyor belt <NUM> can slide over the upper surface <NUM> with reduced friction.

In this manner, the support unit <NUM> can be used in a conveyor printer to retain the substrate <NUM> on the conveyor belt <NUM> by the vacuum apertures <NUM> for more precise printing, while the air bearings <NUM> act to support the conveyor belt <NUM> and reduce friction.

Referring to <FIG>, the structure of the air bearings <NUM> used in the support unit <NUM> of the first embodiment are shown in more detail. <FIG> shows an air bearing <NUM> without the porous media <NUM> attached, in order to show the structure underneath. The air bearing <NUM> comprises a carrier <NUM>. The carrier <NUM> is made of metal, but may be made of other materials in other examples. The carrier <NUM> has a circular shape complementary to the circular shape of the porous media <NUM>. The carrier <NUM> is shaped to support the porous media <NUM>. The carrier <NUM> comprises channels <NUM> for distributing the air over the lower surface of the porous media <NUM>. The carrier <NUM> also comprises an attachment surface <NUM> for attaching the porous media <NUM> to the carrier <NUM>. For example, the porous media <NUM> may be attached to the carrier <NUM> by adhesive. The channels <NUM> are arranged around the attachment surface <NUM>. The attachment surface <NUM> includes an outer rim around the circumference of the carrier <NUM> so that the air is sealed within the channels <NUM> and forced through the porous media <NUM>. The channels <NUM> are connected to the source of positive pressure through a central opening <NUM> which passes through the centre of the carrier <NUM>. The channels <NUM> are contiguous and form a single continuous channel <NUM> in fluid communication with the central opening <NUM> of the carrier <NUM>. The air bearing <NUM> also comprises a conduit <NUM> connected to the carrier <NUM> which houses a passageway for air to enter the central opening <NUM> of the carrier <NUM> and pass into the channels <NUM>. The conduit <NUM> has an outer surface with a hexagonal cross-sectional shape, but other shapes are possible.

<FIG> shows the air bearing <NUM> of <FIG> with the porous media <NUM> applied. In the first embodiment, the porous media <NUM> is formed of carbon, in particular sintered carbon. The porous media <NUM> is applied over the carrier <NUM>. The porous media <NUM> is applied to the attachment surface <NUM> via adhesive so that a space is formed by the channels <NUM> for distribution of air from the central opening <NUM> across the porous media <NUM>. To provide this, the lower surface of the porous media <NUM> is planar so that the channels <NUM> form spaces between the lower surface of the porous media <NUM> and the surface of the carrier <NUM>. The porous media <NUM> has the same diameter as the diameter of the carrier <NUM>.

As described above, the air bearing <NUM> has an upper surface <NUM>. In particular, the upper surface <NUM> is the uppermost surface of the porous media <NUM>. The upper surface <NUM> is the surface exposed at the upper surface <NUM>. As the porous media <NUM> is porous to air, the air in the channels <NUM> permeates through the porous media <NUM> to the upper surface <NUM>. This then generates an air cushion between the upper surface <NUM> of the porous media <NUM> at the upper surface <NUM> and the underside of the conveyor belt.

As described above, the air bearing <NUM> has a slit <NUM>. The slit <NUM> is arranged in the upper surface <NUM> of the porous media <NUM>. The slit <NUM> extends through the centre of the porous media <NUM> across the diameter. The slit <NUM> has a depth less than the thickness of the porous media <NUM>. The slit <NUM> reduces the pressure at the central location.

Referring to <FIG>, the air bearing <NUM> of <FIG> is shown applied to the support unit <NUM> according to the first embodiment. The support unit <NUM> comprises an upper surface <NUM> which comprises the upper surface of a plate <NUM> arranged on a mount <NUM>. The upper surface <NUM> contains slots <NUM> which define vacuum apertures <NUM> provided to supply a negative pressure to a substrate mounted on a conveyor belt arranged above the upper surface <NUM>. The support unit <NUM> also comprises an air bearing <NUM>. The air bearing <NUM> is arranged through a recess in the plate <NUM>. As described above, the air bearing <NUM> has a porous media <NUM> with an upper surface <NUM>. The upper surface <NUM> of the porous media <NUM> is arranged above the upper surface <NUM> and thus the upper surface of the plate <NUM>. In the first embodiment, the upper surface <NUM> of the air bearing <NUM> is arranged <NUM> above the upper surface <NUM>. This spaces the underside of the conveyor belt from the upper surface <NUM> to avoid contact in the event of slight sagging of the belt. This means the air cushion is provided at the upper surface <NUM> of the air bearing <NUM> spaced above the upper surface <NUM> of the support unit <NUM>. In this way, the conveyor belt is supported above the upper surface <NUM> to avoid contact. In the first embodiment, with a belt thickness of <NUM> and a pitch of <NUM> to <NUM> between air bearings <NUM>, the belt does not sag enough to touch the upper surface <NUM> when the spacing between the upper surface <NUM> of the air bearings <NUM> and the upper surface <NUM> of the support unit <NUM> is <NUM>.

The air bearing <NUM> has a slit <NUM> in the upper surface <NUM> of the porous media <NUM>. The slit <NUM> is shown aligned with the slots <NUM> of the vacuum apertures <NUM>, which reduces the positive pressure in the region aligned with the row of vacuum apertures <NUM>.

The air bearing <NUM> has a carrier <NUM>, which defines channels <NUM> for distributing air to the porous media <NUM>, and an attachment surface <NUM> for attaching the porous media <NUM> to the carrier <NUM>. The carrier <NUM> has a central opening <NUM> which connects the channels <NUM> to a passageway passing through a conduit <NUM> which extends down from the carrier <NUM>. The conduit <NUM> has a connection opening <NUM> at the base, which is at the opposing end of the conduit <NUM> to the carrier <NUM>. The connection opening <NUM> is connected to the central opening <NUM> by the passageway. The connection opening <NUM> is connectable to a source of positive pressure, such as an air pump, and may be connected by further conduits or pipes and connectors as necessary.

In use, the source of positive pressure can apply a positive pressure in the form of an airflow, which can pass through the connection opening <NUM>, through the passageway of the conduit <NUM>, through the central opening <NUM>, through the channels <NUM>, and through the porous media <NUM> to the upper surface <NUM> of the air bearing <NUM> in order to provide a cushion of air above the upper surface <NUM>, between the upper surface <NUM> of the air bearing <NUM> and the underside of the conveyor belt.

The air bearing <NUM> is arranged through a recess in the plate <NUM>, and the carrier <NUM> is mounted on a shoulder defined by the mount <NUM>. The conduit <NUM> of the air bearing <NUM> is arranged through a hole in the mount <NUM> which is connected to the recess in the plate <NUM> so that the air bearing <NUM> can be mounted within the plate <NUM> and the mount <NUM>.

The upper surface <NUM> of the air bearing <NUM> is arranged above the upper surface of the plate <NUM>. This means that the air cushion is provided at a position in the z direction that means the conveyor belt is supported at a position slightly above the upper surface <NUM>. In the first embodiment, the height of the air cushion in the z direction is around <NUM> to <NUM>, and the height of the upper surface <NUM> of the air bearing <NUM> above the upper surface <NUM> of the support unit <NUM> is <NUM>. This disposes the conveyor belt slightly away from the elements of the upper surface <NUM> such as the upper surface of plate <NUM> and the upper surface <NUM> of the porous media <NUM>.

If the air bearing <NUM> is not properly aligned with the upper surface <NUM>, and for example is at a slight angle with respect to the x-y plane, then the air cushion will not be parallel to the upper surface <NUM>. This means that the conveyor belt would not actually be supported on the air cushion, but instead will be supported by the surface of the air bearing <NUM> itself, for example by contacting and resting on an edge part of the porous media <NUM>. This can lead to wear between the air bearing <NUM> and the conveyor belt. Especially where the porous media <NUM> is particularly hard this can damage the conveyor belt or melt the air bearing.

To mitigate this problem with aligning the air bearings <NUM>, a resilient member <NUM> is provided. In the first embodiment, the resilient member <NUM> is an O-ring. The resilient member <NUM> is made from a material which is deformable. For example, the resilient member <NUM> may be made from an elastic material such as rubber. The resilient member <NUM> is arranged between the air bearing <NUM> and the mount <NUM>. In particular, the resilient member <NUM> is arranged between an underside of the carrier <NUM> and the shoulder of the mount <NUM> on which the carrier <NUM> rests. In this way, the carrier <NUM> is supported on the mount <NUM> by the resilient member <NUM>. Under the weight of the air bearing <NUM>, the resilient member <NUM> can deform. This provides a mechanism for automatically self-aligning the air bearing <NUM>. This can be used to conform the array of air bearings <NUM> to the topology of the conveyor belt. In other examples, the resilient member <NUM> is not required. In some cases, if the air bearing <NUM> is made from a relatively soft material, for example graphite, then if the air bearing <NUM> is not properly aligned, the raised portions of the air bearing <NUM> can wear down so that it then becomes aligned over time after movement of the conveyor belt. Such air bearings <NUM> can be provided with or without the resilient member <NUM>.

Referring to <FIG>, a tile <NUM> is provided for a substrate support system <NUM> according to a second embodiment of the present disclosure. Referring to <FIG>, the tile <NUM> defines the upper surface <NUM>. In particular, an upper surface of the tile <NUM> defines the upper surface <NUM>. In this manner, the tile <NUM> replaces the plate <NUM> of the first embodiment. The tile <NUM> forms the support unit <NUM> for supporting the conveyor belt.

The tile <NUM> comprises a plurality of vacuum apertures <NUM>. The vacuum apertures <NUM> are in the upper surface <NUM> because they are arranged in the upper surface of the tile <NUM>. The vacuum apertures <NUM> of the second embodiment may be similar to the vacuum apertures <NUM> of the first embodiment. In a similar manner to the first embodiment, the vacuum apertures <NUM> are provided in the form of a plurality of slots <NUM>. The slots <NUM> extend through the thickness of the tile <NUM> so that fluid communication between the upper surface of the tile <NUM> defining the upper surface <NUM> and the underside of the tile <NUM> can be established. The slots <NUM> are elongate and in a stadium shape and are arranged in rows extending in they direction. In other examples, the slots <NUM> can extend through part of the thickness of the tile <NUM> and comprise a hole at the base of the slot <NUM> in a similar manner to the first embodiment. The slots <NUM> may extend in the direction of movement of the conveyor belt, so that belt apertures will sequentially align with slots <NUM> along the row. The vacuum apertures <NUM> are offset which can help maintain tension in the belt by forcing the belt to deform into a complex shape, as adjacent vacuum apertures <NUM> in adjacent rows are not aligned, so the hold-down force is not applied along a continuous line across the belt.

The tile <NUM> itself acts as an air bearing <NUM>. As such, the tile <NUM> does not comprise the individual air bearings <NUM> of the first embodiment. The tile <NUM> is the air bearing <NUM> because the tile <NUM> comprises porous media <NUM>. In particular, the tile <NUM> is formed from porous media <NUM> so that the regions of the tile <NUM> around the slots <NUM> are formed of porous media <NUM>. In the second embodiment, the porous media <NUM> is formed of carbon, in the form of sintered carbon. The porous media <NUM> may be the same as the porous media <NUM> of the air bearing <NUM> of the first embodiment. Because the whole tile <NUM> is porous, the tile <NUM> as a whole can then diffuse air from below the tile <NUM> to the upper surface and provide an air cushion for supporting the conveyor belt. The upper surface of the porous media <NUM> is therefore inherently arranged at the upper surface <NUM> because this defines the upper surface of the tile <NUM>. In the second embodiment, the upper surface <NUM> consists of the upper surface of the porous media <NUM> of the air bearing <NUM>. In this way, there are no other elements of the upper surface <NUM> on which the conveyor belt can rest, so that the conveyor belt is supported on the air bearing <NUM> to reduce friction.

Because there are no individual air bearings <NUM> through the tile <NUM> (unlike the plate <NUM> of the first embodiment), there is no need to interrupt the rows of slots <NUM>. As such, the slots <NUM> can be uniformly and evenly distributed over the upper surface of the tile <NUM>, which further improves the uniformity of the vacuum force delivered.

In this way, the tile <NUM> forms a single large air bearing <NUM>. In other words, the tile <NUM> provides the at least one air bearing <NUM> of the support unit <NUM>. Instead of providing an array of individual air bearings <NUM> over the upper surface <NUM> in the first embodiment, the entire tile <NUM> of the second embodiment is formed of porous media <NUM> so that the tile <NUM> acts as a continuous air bearing <NUM> over the upper surface <NUM>. This removes the need for a plate <NUM> with recesses and individual air bearings <NUM> to be mounted therein. This makes the assembly much cheaper and simpler. The area of porous media <NUM> is also much larger than is possible with individual air bearings <NUM>, meaning that the pressure can be much lower and the force can be much higher. This also reduces cost and provides a simpler arrangement because a plurality of individual air bearings <NUM> are not required.

Referring to <FIG>, a carrier <NUM> is provided for use with the tile <NUM> of <FIG>. In particular, the carrier <NUM> is for supporting the tile <NUM>. The carrier <NUM> replaces the carrier <NUM> of the first embodiment. Specifically, the carrier <NUM> is provided to support an underneath of the tile <NUM> and arranged to provide the air to the porous media <NUM> of the tile <NUM>. Thus, in use, the tile <NUM> is arranged over the carrier <NUM>.

The carrier <NUM> has generally the same shape as the tile <NUM>. In the second embodiment, the carrier <NUM> and the tile are both square. The tile <NUM> has a surface area of around <NUM><NUM>. The tile <NUM> is arranged to be placed on the carrier <NUM>. In the first embodiment, the carrier <NUM> is made from metal, in particular aluminium, but may be made from other materials in other examples.

The carrier <NUM> has channels <NUM> having a similar function to the channels <NUM> of the first embodiment. The carrier <NUM> comprises an attachment surface <NUM> having a similar function to the attachment surface <NUM> of the first embodiment. The carrier <NUM> has vacuum openings <NUM> similar to the vacuum openings <NUM> of the first embodiment.

The channels <NUM> comprise a central channel <NUM> through the centre of the carrier <NUM> extending in the x direction. The central channel <NUM> is connected to a plurality of channels <NUM> which extend in the y direction between adjacent rows of vacuum openings <NUM>. The channels <NUM> are provided to distribute the air from a source of positive pressure over the underside of the tile <NUM> so that is diffuses through the porous media <NUM> to form an air cushion on the upper surface <NUM>.

The attachment surface <NUM> is for supporting the underside of the tile <NUM>. The underside of the tile <NUM> is attached to the carrier <NUM> at the attachment surface <NUM>, for example by adhesive. The attachment surface <NUM> is arranged between the channels <NUM> and around the vacuum openings <NUM>.

The vacuum openings <NUM> are arranged to couple the slots <NUM> of the tile <NUM> to a source of negative pressure for providing the vacuum force of the vacuum apertures <NUM>. When the tile <NUM> is arranged on the carrier <NUM>, the slots <NUM> align with the vacuum openings <NUM> so that the vacuum openings <NUM> are arranged at the base of the slots <NUM> in a similar manner to the vacuum openings <NUM> of the first embodiment. When the tile <NUM> is arranged on the carrier <NUM>, the slots <NUM> do not align with or overlap the channels <NUM>. In other words, the slots <NUM> of the tile <NUM> are arranged between, and offset from, adjacent channels <NUM>. In this way, the positive pressure from the channels <NUM> is provided to the porous media <NUM>, while the negative pressure from the vacuum openings <NUM> acts on the slots <NUM>.

In the same manner as the first embodiment, the slots <NUM> form the upper part of the vacuum apertures <NUM>. The opening of the slots <NUM> in the upper surface of the tile <NUM> are thus aligned in the upper surface <NUM>. The slots <NUM> thus convey the negative pressure from the vacuum openings <NUM> to the upper surface <NUM> and thus to the substrate through belt apertures in the conveyor belt. In other embodiments, to further avoid the vacuum reducing the efficiency of the positive pressure through the porous media <NUM> around the slots <NUM>, the internal surface of the slots <NUM> may be coated with a non-porous material to avoid air diffusing from the porous media <NUM>, through the sides of the slots <NUM>, and into the slots <NUM>. In other examples, the tile <NUM> may be made entirely of porous media <NUM> to reduce manufacturing costs and complexity.

The tile <NUM> also increases the effective area of the air bearings <NUM> in the upper surface <NUM>. Over <NUM>% of the area of the upper surface <NUM> may be covered in porous media <NUM> by using the tile <NUM>. This is much higher than the <NUM> to <NUM> % of the first embodiment. This increases the potential force, and enables a more precise air cushion to be provided to the conveyor belt, achieving the desired lift. Due to the increase in coverage, spots of high positive pressure due to individual air bearings <NUM> are eliminated. This can otherwise cause the conveyor belt to lift up at these regions and mean the conveyor belt does not run flat, causing issues with alignment and thus printing. As such, the second embodiment provides a further improvement in supporting the conveyor belt on an air bearing <NUM>.

The tile <NUM> can then be used in the same arrangement as the first embodiment in place of the air bearings <NUM>. In some embodiments, a plurality of tiles <NUM> may be provided joined together to form a surface on which the conveyor belt can be supported. An array of tiles <NUM> and the carriers <NUM> can be used to provide the support unit <NUM>. The slots <NUM> and the vacuum openings <NUM> can then be aligned with a connection to the source of negative pressure for applying the negative pressure to the substrate through the slots <NUM>. The channels <NUM> of the carrier <NUM> can then be connected to a source of positive pressure to apply the positive pressure to the porous media <NUM> of the tile <NUM> to form the air cushion on the upper surface <NUM>. The tile <NUM> can then be used as part of the substrate support system <NUM> for a conveyor printer in the same way as described above in relation to the first embodiment.

Features of the first embodiment may be readily applied to the second embodiment. For example, one or more resilient members <NUM> may be used to support the tile <NUM> or the carrier <NUM> and align the upper surface of the tile <NUM> correctly. In another example, slits <NUM> may be provided in the air bearing <NUM> aligned with the rows of slots <NUM>. In another example, the vacuum openings <NUM> may have a similar arrangement to the vacuum openings <NUM> of the first embodiment.

In one embodiment, the support unit <NUM>, <NUM> may provide a plurality of vacuum apertures <NUM>, <NUM> and at least one air bearing <NUM>, <NUM> as part of a substrate support system <NUM>, <NUM> which is used for a printer other than a conveyor printer. For example, the printer may be a flat-bed printer. A flat-bed printer may have a printer table on which a substrate is to be printed by moving a printhead over the substrate. In this case, the upper surface <NUM> is for supporting the substrate directly, rather than supporting the conveyor belt. The air bearings <NUM>, <NUM> provide a positive pressure which can be used, for example, to release the substrate after printing. The vacuum apertures <NUM>, <NUM> provide a negative pressure to hold down the substrate onto the upper surface <NUM>, <NUM> in a similar way as the first and second embodiments, except that the vacuum apertures <NUM>, <NUM> apply the pressure directly to the substrate rather than through belt apertures in a conveyor belt. In such cases, as the air bearings <NUM>, <NUM> are not used to reduce friction, the air bearings <NUM>, <NUM> need not be arranged to protrude from the upper surface <NUM>, and instead may be flush with the upper surface <NUM> to avoid wear with the substrate when the air bearings <NUM>, <NUM> are not in use.

Referring to <FIG> and <FIG>, a support unit <NUM> for use in a substrate support system <NUM> according to a third embodiment is provided. The support unit <NUM> of the third embodiment is identical to the support unit <NUM> of the first embodiment, except where provided below. Specifically, the support unit <NUM> differs from the support unit <NUM> of the first embodiment in that the support unit <NUM> comprises a sheet <NUM>. <FIG> shows the support unit <NUM> without the sheet, and <FIG> shows the sheet <NUM> applied. Corresponding reference numerals are used to indicate identical features of the first embodiment, unless explained otherwise.

In <FIG>, the plate <NUM> is also removed, exposing the upper surface of the mount <NUM>. The support unit <NUM> comprises a plurality of vacuum openings <NUM> arranged in the surface of the mount <NUM> for connection to the vacuum apertures <NUM> as described above. The vacuum opening <NUM> are identical to the vacuum openings <NUM> described in relation to the first embodiment. The vacuum apertures <NUM> are arranged in an array in rows across the surface. The particular arrangement of the array of vacuum apertures <NUM> is not essential, and may be varied in different embodiments.

The support unit <NUM> also comprises a plurality of air bearings <NUM> made of porous media <NUM> and having an upper surface <NUM> arranged above the upper surface <NUM>. The air bearings <NUM> are identical to the air bearings <NUM> of the first embodiment. The particular arrangement of the array of air bearings <NUM> is not essential, and may be varied in different embodiments.

The support unit <NUM> also comprises a plurality of pockets <NUM>. The pockets <NUM> are in the form of recesses in the upper surface of the mount <NUM>. In particular, the pockets <NUM> extend into the thickness of the mount <NUM>. In the third embodiment, the pockets <NUM> are milled into the mount <NUM>. In other examples, the pocket <NUM> may be drilled or otherwise machined. In an alternative embodiment, the pockets <NUM> can be provided in a separate sheet in addition to the sheet <NUM>. Forming the counterbore of the pocket <NUM> and controlling the depth of cut is difficult compared to simply drilling a through-hole such as the vacuum opening <NUM>. Instead, by using a sheet containing these pockets <NUM>, the milling step can be avoided.

Forming the pocket <NUM> in a sheet increases the ease of manufacture and reduces cost. The flexibility is also increased as different shaped pockets <NUM> can easily, cheaply, and quickly be produced. The sheet of the pockets <NUM> can then be used alongside the sheet <NUM> of valves to form a stack of sheets. The pockets <NUM> may be cut into the sheet, such as by laser cutting.

In the third embodiment, the pockets <NUM> are aligned with the vacuum openings <NUM>. Each vacuum opening <NUM> has a corresponding pocket <NUM>. The pockets <NUM> are provided around the vacuum openings <NUM> so that the vacuum opening <NUM> is arranged within the pocket <NUM> and at the base of the pocket <NUM>. The pocket <NUM> therefore provides a recessed volume between the vacuum opening <NUM> and the upper surface of the mount <NUM>. The pocket <NUM> is connected to a source of negative pressure through the vacuum opening <NUM>. Thus, the vacuum openings <NUM> are arranged in a plane below and parallel to the upper surface.

Referring to <FIG>, a sheet <NUM> is provided over the upper surface of the mount <NUM>. The sheet <NUM> is made from a resilient material. In the third embodiment, the sheet <NUM> is made from biaxially-oriented polyethylene terephthalate (BoPET), also known by the trade name Mylar (RTM). In other examples, other materials may be used, such as polyimide e.g. Kapton (RTM), styrene, polyvinyl chloride (PVC), or polycarbonate. The sheet <NUM> has a plurality of valves <NUM> formed in the sheet <NUM>. The valves <NUM> are cut into the sheet <NUM>, such as by laser cutting. The process forms cut-outs which define the valves <NUM>. Thus, the valves <NUM> are integral with the sheet <NUM> and form part of the sheet <NUM>. Thus, the sheet <NUM> provides an array of valves <NUM>.

The sheet <NUM> lies over the pockets <NUM>. The pockets <NUM> are configured to receive valves <NUM> of the sheet <NUM>. The valves <NUM> are provided for opening and closing the vacuum openings <NUM>. The valves <NUM> each comprise a valve head <NUM> which is configured to seal the vacuum opening <NUM>. In the third embodiment, the valve head <NUM> is circular. The valves <NUM> also each comprise a valve lever arm <NUM> attached to the valve head <NUM>. The valve lever arm <NUM> is configured to permit the valve head <NUM> to move to open and close the vacuum opening <NUM>. In particular, the valve lever arm <NUM> permits the valve head <NUM> to move out of the plane of the sheet <NUM> and towards the vacuum opening <NUM> arranged below the sheet <NUM>. This is achieved by the valve lever arm <NUM> bending to permit the movement. The valve lever arm <NUM> has a curved shape around the side of the valve head <NUM> which provides a length in a compact space. This allows the packing density of the valves <NUM> to be increased. The length permits the valve head <NUM> to be arranged in a plane parallel to the plane of the sheet <NUM> so that the valve head <NUM> can lie flat against the vacuum opening <NUM> to form a tight seal. In other examples, the valves <NUM> have a different shape. For example, the valves <NUM> may have a straight valve lever arm <NUM>, but this would be less compact than the third embodiment.

<FIG> shows that each pocket <NUM> has a particular shape for receiving the shape of the valve <NUM>. In particular, the pocket <NUM> has a first portion having a generally semi-circular shape for receiving the valve head <NUM>. The first portion is arranged at one side of the pocket <NUM>. The pocket <NUM> also has a second portion having a generally semi-circular shape which has a diameter larger than the first portion. The second portion is for receiving the valve lever arm <NUM>. The second portion is arranged at the opposite side of the pocket <NUM> to the first portion. In this way, the pocket <NUM> provides a shape complementary to the shape of the valve <NUM>. The pocket <NUM> provides a space for the valve <NUM> to be arranged, in particular so that the valve lever arm <NUM> can bend and the valve head <NUM> can extend into the pocket <NUM> to seal against the vacuum opening <NUM>. In other examples, the shape of the pocket <NUM> can be different to accommodate the shape of different valves <NUM>.

<FIG> shows an array of pockets <NUM> with some pockets <NUM> arranged at different orientations. This is provided to further increase the packing density. The particular arrangement can depend on the shape of the valves <NUM>. In the arrangement of <FIG>, the array of vacuum openings <NUM> is positioned around the air bearings <NUM> to accommodate the air bearings <NUM>. The orientation of the pockets <NUM> is also selected to improve compactness by arranging the pockets <NUM> around the air bearings <NUM>. In other examples, the arrangement may be changed, and for example the orientation may be uniform with each pocket <NUM> oriented in the same direction.

In the third embodiment, the sheet <NUM> has holes for receiving the air bearings <NUM>, so that the air bearings <NUM> can act through the sheet <NUM>. In embodiments where the pockets <NUM> are formed in a sheet, that sheet may also comprise holes for the air bearings <NUM> to pass through.

In use, when the negative pressure is applied to the vacuum openings <NUM> in the same way as the first embodiment when no substrate is present over the vacuum openings <NUM>, the valve head <NUM> is pulled downwards into the pocket <NUM> and into contact with the vacuum opening <NUM> to close the valve <NUM>. In particular, a pressure differential is generated between the atmospheric pressure due to the open valve <NUM> between a region above the sheet <NUM> and the vacuum opening <NUM> through the cut-outs in the valve <NUM>. This causes an air drag force on the valve head <NUM>, pulling the valve head <NUM> downwards to the vacuum opening <NUM> due to the negative pressure. The valve head <NUM> and the valve lever arm <NUM> are located in the pocket <NUM> so that they have space to move out of the plane of the sheet <NUM>. The valve head <NUM> contacts the vacuum opening <NUM> and forms a seal, closing the valve <NUM>. This allows vacuum openings <NUM> that are not covered by a substrate to be closed, improving the effectiveness of the vacuum. This avoids the need for masking. This also provides a simple array of valves, which simple, fast, and cheap to manufacture and apply.

When a substrate is present over the vacuum openings <NUM>, the pressure equalizes and the valve <NUM> opens as the valve head <NUM> returns to the plane of the sheet <NUM> due to the tension in the bent valve lever arm <NUM>. This allows the negative pressure at the vacuum openings <NUM> to act on the substrate to retain it in place on the upper surface <NUM>.

Once the sheet <NUM> is applied to the mount <NUM>, the plate <NUM> can then be applied. The plate <NUM> is identical to the plate <NUM> of the first embodiment. Thus, the plate <NUM> can be applied and provides the upper surface <NUM>. The support unit <NUM> then appears similar to as shown in <FIG>. The plate <NUM> is arranged over the sheet <NUM> and thus over the upper surface of the mount <NUM>. The plate <NUM> defines a plurality of vacuum apertures <NUM> in the form of a plurality of slots <NUM>. The slots <NUM> are connected, via the valves <NUM>, to the vacuum openings <NUM>. As such, when the valves <NUM> are open, the vacuum openings <NUM> are in fluid communication with the vacuum apertures <NUM>. Thus, when the valves <NUM> are open, the negative pressure applied to the vacuum openings <NUM> is transmitted through the valves <NUM> to the vacuum apertures <NUM>.

A substrate placed over the conveyor belt can then be held down by the vacuum pressure. As mentioned above, when a substrate passes over a vacuum opening <NUM>, the valve <NUM> opens to allow the negative pressure to act on the substrate through the slots <NUM> and through the belt apertures. After the substrate passes further along the conveyor belt and no longer covers the vacuum opening <NUM>, the valve <NUM> automatically closes due to the pressure differential. This improves the vacuum force across the array as a whole without requiring masking. This makes it particularly useful for a conveyor belt system as the substrate continually moves over different vacuum openings <NUM>, and thus it is not possible to mask uncovered vacuum openings <NUM>.

As such, the third embodiment provides a particularly preferred arrangement for a conveyor printer. The air bearings <NUM> provide a cushion of air for supporting the conveyor belt above the upper surface <NUM>, while the vacuum apertures <NUM> and the valves <NUM> in the sheet <NUM> retain the substrate in position while improving the vacuum effectiveness. Together, these features synergistically contribute to providing an improved vacuum conveyor which improves alignment and thus print quality.

In another embodiment, the substrate support system <NUM> of the first embodiment or the substrate support system <NUM> of the second embodiment may be provided with a set of valves for sealing the vacuum openings <NUM>, <NUM> in a different manner than the sheet <NUM> of the third embodiment. For example, the valves may comprise ball valves in each vacuum aperture <NUM>, <NUM> for self-sealing the vacuum aperture <NUM>, <NUM> when no substrate is placed over the vacuum aperture <NUM>, <NUM>. However, the valves of the third embodiment are advantageous as the sheet <NUM> is simple, cheap, and fast to produce, prototype, and replace, and avoids complexity of having individual valves such as ball and springs for each vacuum aperture <NUM>, <NUM>.

Claim 1:
A substrate support system for a conveyor printer, comprising:
a support unit (<NUM>) comprising:
a plurality of vacuum apertures (<NUM>) arranged for fluidic communication with
a source of negative pressure, wherein the plurality of vacuum apertures comprises a plurality of slots (<NUM>) in an upper surface of the support unit; and
a plurality of air bearings (<NUM>) arranged in an array and arranged for fluidic communication with a source of positive pressure, wherein each air bearing comprises porous media, wherein the porous media comprises carbon, and wherein each air bearing comprises an upper surface of the porous media arranged above the upper surface of the support unit; and
a conveyor belt (<NUM>) arranged over the upper surface of the support unit for supporting a substrate to be printed on, the conveyor belt comprising a plurality of belt apertures;
wherein the vacuum apertures are arranged to convey a negative pressure through the belt apertures for retaining the substrate on the conveyor belt; and
wherein the plurality of air bearings is arranged to convey a positive pressure to support the conveyor belt.