Patent Description:
Document <CIT> discloses a printing system comprising means to keep the distance between the printhead and the print medium.

Various example features will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, wherein:.

A printing system comprises a printhead which may deliver print agent onto a print medium, e.g. a paper sheet. The printhead may be provided with a plurality of nozzles to deliver print agent, e.g. ink, onto the print medium so as to print an image. During printing, dots of print agent may be precisely delivered onto the print medium at a specific printhead - to - print medium spacing or distance. Increasing the printhead - to - print medium spacing (PPS) may reduce the precision of the position of the print agent dots. Consequently, print quality may be reduced. Decreasing the printhead - to - print medium spacing (PPS) may increase the probabilities of crashes between the print medium and the printhead.

Printing systems may comprise print medium advance systems, e.g. hold down systems and/or print medium feed mechanisms, to transport a print medium. These print medium advance systems may additionally flatten the print medium.

In some examples, print media may comprise unflattened regions such as bent or bowed edges, warpages or wrinkles. In some examples, a print medium may bend or buckle upwardly towards the printhead and may unintentionally contact the printhead. Such a contact may damage the printhead.

<FIG> illustrates a cross-sectional view of a printing system according to an example of the present disclosure. The printing system <NUM> comprises a printhead <NUM> to deliver a print agent on a print medium <NUM>, a print platen surface <NUM> to support the print medium <NUM> advancing in a print medium advance direction <NUM> and a hold down system <NUM> to hold down the print medium <NUM> on the print platen surface <NUM>. The printing system <NUM> further comprises a safety assembly <NUM> associated with the printhead <NUM>. The safety assembly <NUM> comprises a rolling element <NUM> upstream of the printhead <NUM> in the print medium advance direction <NUM> to prevent the print medium <NUM> from contacting the printhead <NUM>.

The safety assembly <NUM> may prevent the print medium <NUM> from contacting the printhead <NUM> when the print medium <NUM> bends upwards towards the printhead <NUM>. As the safety assembly <NUM> is upstream of the printhead <NUM> in the print medium advance direction <NUM>, the rolling element <NUM> contacts a portion of the print medium bending upwards before reaching the printhead position. The rolling element <NUM> forces the upwards portion of the print medium to bend downwards. Damages caused on the printhead <NUM> by an undesirable contact with the print medium <NUM> may thus be reduced. In addition, a predetermined printhead - to - print medium spacing (PPS) may be maintained. The print agent may thus be delivered at a predetermined position or distance with respect to the print medium. Quality and reliability of the printing process may thus be improved.

The print platen surface <NUM> supports the print medium <NUM> to receive the print agent delivered by the printhead <NUM>. The printhead is above the print platen surface and a print zone may be defined therebetween. The print platen surface may guide and support the print medium in the print zone during printing. A lower side of the print medium may lie on the print platen surface.

The print medium is a material capable of receiving print agent, e.g. ink. The print medium may comprise paper, cardboard, cardstock, textile material or plastic material. The print medium may be a sheet, e.g. a sheet of paper or a sheet of cardboard.

The print medium may comprise a substantially planar substrate to receive print agent delivered by the printhead. The print medium may extend from a leading edge to a trailing edge in the print medium advance direction along a width. In some examples, the print medium may comprise an average thickness greater than <NUM>. In some examples, the average thickness of the print medium may be between <NUM> and <NUM>.

A print medium having a thickness greater than <NUM> may involve a relatively high structural rigidity which may imply greater forces to flatten the print medium. Print media having an average thickness between <NUM> and <NUM> may be called rigid print media. Manufacturing a rigid print medium may generate a curvature on the print medium in a direction between the leading edge and the trailing edge. This curvature may cause the trailing edge and the leading edge of the print medium to bend upwards.

The hold down system <NUM> may apply a holding force on the print medium <NUM> to hold down the print medium <NUM> on the print platen surface <NUM>. The hold down system may thus help to flatten the print medium when passes over the print zone. In some examples, hold down system may comprise a vacuum assembly to apply vacuum under the print platen surface for flattening the print medium onto the print platen surface. The print platen surface may be permeable, so as to allow the vacuum through the print platen surface to pull the print medium against the print platen surface. For example, the print platen surface may comprise a plurality of through-holes in fluid communication with a vacuum source. The vacuum assembly may suck the print medium towards the print platen surface.

In some examples, a holding force applied on the print medium by the hold down system may be lower than a force for flattening the print medium. For example, the holding force applied by the hold down system may be lower than a force for flattening the upwards edges of a rigid print medium, e.g. a print medium with an average thickness between <NUM> and <NUM>. Accordingly, in some examples, the print medium may comprise unflattened or lifted regions, e.g. bent or bowed edges. In some examples, the upwards edges of a rigid print medium, e.g. the leading edge, may remain lifted when the print medium advances towards the print zone. Accordingly, a leading edge of a rigid print medium may remain upwards and may impact against the printhead. Thicker print media may increase a risk of failure of the printhead in case of a crash.

According to the invention, the rolling element contacts an upwards region of the print medium, e.g. a leading edge of a print medium with an average thickness between <NUM> and <NUM>, when a height of this upwards region is greater than a height between the rolling element and the print platen surface. The rolling element may guide the upwards region, e.g. an upwards leading edge, towards the print platen surface. The rolling element applies a force against the upwards region, e.g. the leading edge, greater than a force for flattening a given print medium. The rolling element may thus counteract a rigidity of the print medium and the flatness of the print medium in the print zone may be improved. The rolling element may thus flatten the print medium downstream of the rolling element. The safety assembly may thus prevent the print medium from contacting the printhead when the hold down system is not capable of maintaining the print medium, e.g. a leading edge of the print medium, on the print platen surface. Accordingly, printing defects may be reduced.

The print platen surface of this figure extends from an upstream region <NUM> to a downstream region <NUM>. In <FIG>, the printhead <NUM> is above the downstream region <NUM> of the print platen surface <NUM>. In some examples, the printhead may be above a central region of the print platen surface, e.g. between the upstream region <NUM> and the downstream region <NUM> of the print platen surface <NUM>.

In some examples, the printing system may comprise a print medium feed mechanism for feeding print medium to a print zone. The print medium feed mechanism may make the print medium advance in the print medium advance direction. The print medium feed mechanism may be away from the printhead. In some examples, the print medium feed mechanism may be adjacent to the upstream region of the print platen surface. For example, the print medium feed mechanism may be prior of the upstream region of the print platen surface in the print medium advance direction.

The print medium feed mechanism may comprise a drive roller engaging the print medium. The print medium feed mechanism may further comprise a pinch wheel or roller above the drive roller in contact with print medium. The print medium may be gripped between the drive roller and the pinch wheel. The driver roller may rotate causing the print medium to advance in the print medium advance direction. As the pinch roller is in contact with the print medium, moving the print medium in the print medium advance direction may cause the rotation of the pinch roller.

In some examples, the printing system may comprise a print medium advance system comprising a print platen surface, a hold down system and a print medium feed mechanism according to any of the examples herein disclosed.

The safety assembly <NUM> of this figure is associated with the printhead <NUM>. In this disclosure, a safety assembly associated with a printhead means that a height of the safety assembly with respect to the print platen surface is related to a height of the printhead. A difference between the height of the safety assembly and the height of the printhead with respect to the print platen surface is maintained substantially constant during printing.

In this disclosure, a height means a distance in a direction perpendicular to the print platen surface or in a direction perpendicular to the print medium. Therefore, during printing, a height of a component of a printing system may substantially correspond to a vertical direction.

In some examples, a safety assembly associated with a printhead may comprise connecting the safety assembly to the printhead. In some examples, a safety assembly associated with a printhead may comprise connecting the safety assembly with a print bar which may support a printhead.

The printing system of <FIG> comprises a printhead which may deliver print agent onto a print medium advancing along a print medium advance direction. The printhead may be provided with a plurality of nozzles to deliver print agent, e.g. ink, onto the print medium to form an image. In this disclosure, depositing print agent on a print medium includes firing, ejecting, spitting or otherwise delivering print agent onto the print medium. The printhead may comprise a print agent chamber containing print agent to be delivered onto the print medium.

In some examples, a heating element may cause a rapid vaporization of print agent in a print agent chamber, increasing an internal pressure inside this print agent chamber. This increase in pressure makes a drop of print agent exit from the print agent chamber to the print medium through a nozzle. These printing systems may be called as thermal inkjet printing systems.

In some examples, a piezo electric may be used to force a drop of print agent to be delivered from a print agent chamber onto the print medium through a nozzle. A voltage may be applied to the piezo electric, which may change its shape. This change of shape may force a drop of print agent to exit through the nozzle. These printing systems may be called as piezo electric printing systems.

In some examples, the printhead may be static. The printhead or a plurality of printheads may extend along a width of a print medium, i.e. in a print medium width direction. The plurality of nozzles may be distributed within the printhead or a plurality of printheads along the width of the print medium. The width of the print medium extends in a print medium width direction. The print medium width direction may be substantially perpendicular to the print medium advance direction. Such an arrangement may allow most of the width of the print medium to be printed simultaneously. These printing systems may be called as page-wide array (PWA) printing systems.

The printing system of <FIG> is a page-wide array printing system. The printhead <NUM> or a plurality of printheads may statically span substantially the whole width of print medium along the print medium width direction. In some examples, printheads may be provided in printhead modules comprising several printheads.

In <FIG> the printing system <NUM> comprises a print bar <NUM> spanning a width of the print medium <NUM> along the print medium width direction. The printhead <NUM> of this figure is mounted on the print bar <NUM>. In this figure the print bar <NUM> comprise a print bar structure <NUM> spanning a width of the print medium <NUM> in the print medium width direction. The printhead <NUM> may be connected to the print bar structure <NUM>. In some examples a plurality of printheads may be mounted on the print bar to cover the width of the print medium. For example, a plurality of printhead modules may be mounted on the print bar.

The safety assembly <NUM> may be connected to the print bar <NUM>. In this figure, the safety assembly <NUM> is connected to the print bar structure <NUM>. The safety assembly <NUM> of this figure is thus connected to the printhead <NUM> through the print bar structure <NUM>. Consequently, the safety assembly <NUM> is associated with the printhead <NUM>.

In some examples, the safety assembly may be connected to the printhead or to a printhead module. For example, the safety assembly may be screwed to the printhead.

In some examples, the printhead may travel repeatedly across a scan axis for delivering print agent onto a print medium which may advance along a print medium advance direction. The scan axis may be substantially perpendicular to the print medium advance direction. The scan axis may be substantially parallel to print medium width direction. A printhead height, i.e. a distance between the printhead and the print platen surface, may thus be maintained substantially constant when the print medium travels across the scan axis. The printhead may be mounted on a carriage for moving across the scan axis. In some examples, several printheads may be mounted on a carriage. In some examples, four printheads may be mounted on a single carriage. In some examples, eight printheads may be mounted on a single carriage.

Printing systems having a printhead travelling across a scan axis may comprise a fixed structure spanning a width of a print medium along the scan axis which is parallel to the print medium width direction. The fixed structure may be mounted at a height with respect to print platen surface and may extend along a direction parallel to the print medium width direction. The printhead may thus slide along the fixed structure in a direction parallel the print medium width direction. The fixed structure may comprise a beam extending between lateral sides of the printing system.

A safety assembly may be connected to the fixed structure of a scan axis printing system. A difference between the height of the rolling element and the height of the printhead may be maintained substantially constant. Accordingly, a safety assembly may be associated with a scan axis printhead.

In some examples, the rolling element may continuously contact the print medium. Flattening the print medium may be enhanced. Consequently, a predetermined printhead - to - print medium may be precisely maintained.

In some examples, the rolling element may occasionally contact the print medium, e.g. when the upwards regions of the print medium are greater than a predetermined height. Marks on the print medium may thus be reduced. A print medium contacting the rolling element may induce a rotation of the rolling element. In some examples, the safety assembly may comprise a plurality of rolling elements. In some examples, the roller element may be a roller to rotate about an axis parallel to a print medium width direction. An upwards region of the print medium may contact the roller and may induce the roller to rotate. The roller may be a cylinder. In some examples, the roller element may be a sphere that may rotate after contacting an upward region of the print medium.

In some examples, the rolling element may rotate about a spindle extending in a print medium width direction. For example, when the rolling element comprises a sphere, the spindle may extend through a diameter of the sphere.

In some examples, the printing system may comprise a sensor to sense a force exerted by the print medium against the rolling element when the rolling element contacts the print medium. The sensor may thus detect if a force exerted by the print medium against the rolling element is greater than a predetermined force. In some examples, the sensor may be an optical sensor. In some examples, the sensor may be a contact sensor.

Greater contacting forces may imply higher upwards regions of the print medium upstream of the rolling element. For example, a leading edge of the print medium may crash against an upper half part of the rolling element. In some examples, a force exerted by the leading edge of the print medium contacting an upper half part of the rolling element may be greater than the predetermined force. In some examples, a leading edge of the print medium may crash against a lower half part of the rolling element exerting a force greater than a predetermined force. The sensor system may send a safety signal if a force greater than the predetermined is detected.

In some examples, the sensor system may comprise a detector to detect a movement or a deflection of a component of the safety assembly. The detector may detect a change of a height of the rolling element. For example, the detector may detect a deflection of a spindle supporting the rolling element of the safety assembly. In some examples, the detector may directly measure a deflection of the spindle. In some examples, the detector may detect a movement of a component, e.g. a bar or an encoder, connected to the spindle. In some examples, the detector may be contacted by the spindle or by an element connected to the spindle after deflecting.

The printing system may comprise a controller. The controller may receive a safety signal if the sensor system detects a force greater than the predetermined force. The controller may further stop the operation of the printing system if a safety signal is received. For example, the controller may prevent the print medium from advancing. The protection of the printhead may thus be improved.

In some examples, a printing system may comprise a plurality of safety assemblies. The safety assemblies may be distributed along a print medium width direction.

<FIG> schematically illustrates a zoom-in view of a part of the printing system of <FIG>. Heights, distances and/or dimensions of <FIG> are not in scale. The printhead <NUM> of this figure comprises a printhead lower portion <NUM>. During printing, the printhead lower portion <NUM> faces the print medium (not illustrated in <FIG>). The printhead lower portion <NUM> of this figure is the portion of the printhead <NUM> closest to the print platen surface <NUM>. i.e. the lowest portion of the printhead <NUM>. A distance <NUM> between the printhead lower portion <NUM> and the print platen surface <NUM> defines a height of the printhead. In this disclosure, height of the printhead <NUM>, printhead height <NUM>, height of the printhead lower portion <NUM> and distance <NUM> between the printhead lower portion and the print platen surface are used interchangeable to denote the minimum distance between any portion of the printhead <NUM> and the print platen surface <NUM>. In some examples, the printhead lower portion <NUM> may correspond to a printhead die.

The rolling element <NUM> of <FIG> comprises a rolling element lower portion <NUM> facing the print medium (not shown in <FIG>) and the print platen surface <NUM>. The rolling element lower portion <NUM> is a point, a line or a surface of the rolling element <NUM> closest to the print platen surface <NUM>. Accordingly, a distance <NUM> between the rolling element lower portion <NUM> and the print platen surface <NUM> may thus be defined. In this disclosure, height <NUM> of the rolling element, rolling element height <NUM>, height of the rolling element lower portion <NUM> and distance <NUM> between the rolling element lower portion and the print platen surface are used to denote the minimum distance between any point of the rolling element <NUM> and the print platen surface <NUM>.

A tangential line or a tangential surface from the rolling element lower portion <NUM> may be parallel to the print medium advance direction and/or to the print platen surface <NUM>. A distance <NUM> between the rolling element lower surface <NUM> and the print platen surface <NUM> may be independent from the rotation of the rolling element. For example, the rolling element <NUM> may comprise a cylinder rotatably about a rotation axis perpendicular to the print medium advance direction. The rolling element lower portion <NUM> of the cylinder may be the lowest line or surface of the cylinder when the cylinder rotates.

The rolling element lower portion <NUM> may extend a length <NUM> from the printhead lower portion <NUM> in a direction towards the print medium. The printhead height <NUM> may thus be the sum of the rolling element height <NUM> and the length <NUM>.

In some examples, the length <NUM> extending between the print height <NUM> and the rolling element height <NUM> may be greater than <NUM>. An upwards region of the print medium may occasionally contact the rolling element of the safety assembly to flatten or direct this upwards region towards the print platen surface. The printhead may thus be protected against crashes. Furthermore, an optimum printhead - to - print medium spacing (PPS) may be maintained. In some examples, the length <NUM> may be between <NUM> and <NUM>. In some examples, the length <NUM> may be between <NUM> and <NUM>.

In some examples, the rolling element height <NUM>, i.e. a height of rolling lower portion <NUM> from the print platen surface <NUM>, may greater than <NUM> plus a thickness of the print medium. Accordingly, there may be a gap or a distance between the rolling element lower portion <NUM> and a flatten print medium greater than <NUM>. This gap may be defined as a rolling element - to - print medium spacing. This may prevent the print medium from being continuously contacted by the rolling elements. Marks on the print medium may thus be reduced.

For example, for a given print medium having a thickness of <NUM>, the rolling element height <NUM> may be greater than <NUM>. Accordingly, upwards regions of a print medium with a height greater than <NUM> may contact the rolling element. Then, the rolling element may reduce the height of this upwards regions. Crashes of the print medium with the printhead may thus be prevented.

In this disclosure, a print medium height may be defined as a distance between the uppermost regions of the print medium and the print platen surface. The print medium height may be equal to the thickness of the print medium (when the print medium is flat) or greater than the thickness of the print medium (when the print medium comprises unflattened regions).

In some examples, the rolling element height <NUM> may between <NUM> and <NUM> plus a thickness of the print medium. For example, the rolling element height <NUM> may be <NUM> plus a thickness of the print medium. In this example, a gap or a distance between the rolling element lower portion <NUM> and a flatten print medium may be <NUM>, i.e. the rolling element height. Following with this example, if the thickness of the print medium is <NUM>, then, the rolling element height <NUM> is <NUM>.

In some examples, the rolling element height <NUM> may be between <NUM> and <NUM>. For example, the rolling element height may be <NUM>. The rolling element height may thus correspond with the thickness of the print media. The rolling element may thus continuously contact the print medium. Flattening the print medium may be enhanced. Consequently, a predetermined printhead - to - print medium may be precisely maintained.

In some examples, the rolling element height <NUM> may be adjusted as a function of the thickness of the print medium. For example, the rolling element height <NUM> may be adjusted to set a distance between the rolling element lower portion <NUM> and the print platen surface <NUM> greater than a <NUM> plus the thickness of the print medium. In some examples, the rolling element height may be adjusted to continuously contact the print medium. Accordingly, the safety assembly may be adjusted for several the print medium thicknesses. The printing system may thus be compatible with several print media.

<FIG> respectively illustrate an upwards region of a print medium before and after being contacted by a rolling element of a safety assembly according to an example of the present disclosure. Heights, distances and/or dimensions of <FIG> are not in scale. In these figures, the safety assembly <NUM> comprises a rolling element <NUM> at a height <NUM>.

In <FIG>, a print medium <NUM> is advancing in a print medium advance direction <NUM>. The print medium <NUM> of these figures comprises a leading edge <NUM>.

In <FIG>, the leading edge <NUM> of the print medium comprises an upwards region having a print medium height <NUM> greater than the thickness of the print medium. Throughout this region, the print medium <NUM> does not contact the print platen surface <NUM>. The leading edge <NUM> of the print medium <NUM> of <FIG> is unflattened, i.e. the leading edge bends upwards.

In <FIG>, the print medium height <NUM> is greater than the rolling element height <NUM>, so as the print medium will contact the rolling element when continues advancing in the print medium advance direction.

<FIG> schematically represents the print medium <NUM> after being contacted by the rolling element <NUM>. An advance of the print medium of <FIG> (represented with dotted lines referenced as 100a in <FIG>) in the print medium advance direction <NUM> makes the rolling element <NUM> rotate in a counterclockwise rotation <NUM> after being contacted by the leading edge <NUM>. The rolling element may lower the leading edge <NUM> of the print medium <NUM>. The rolling element may thus pull the print medium <NUM> against the print platen surface <NUM>.

In <FIG>, a print medium height <NUM> after being contacted by the rolling element <NUM> is lower than the print medium height 105a before being contacted by the rolling element (corresponding the print medium of <FIG>). The action of the rolling element <NUM> of this figure flattens the print medium <NUM>, so that the print medium height <NUM> is lower than the rolling element height <NUM>. Accordingly, the print medium height <NUM> is lower than a printhead height. In addition, the print medium is pulled against the print platen surface <NUM>. The rolling element may thus collaborate to hold down the print medium on the print platen surface. The rolling element may thus help a hold down system to pull the print medium against the print platen surface.

<FIG> illustrates a cross-sectional view of a printing system according to an example of the present disclosure. The printing system <NUM> comprises a print medium advance system <NUM> to transport the print medium <NUM> in a print medium advance direction <NUM>. The print medium advance system <NUM> comprises a print platen surface <NUM> to support the print medium <NUM>. The printing system <NUM> further comprises a printhead <NUM> to deliver print agent on the print medium <NUM> supported by the print platen surface <NUM>, wherein the printhead comprises a printhead lower portion <NUM> to face the print medium. In addition, the printing system <NUM> comprises a safety assembly <NUM> having a rolling element <NUM> above the print platen surface <NUM> to maintain a distance <NUM> between a leading edge <NUM> of the print medium and the printhead lower portion <NUM>, i.e. a printhead to - print medium spacing (PPS), greater than a predetermined safety distance.

In this figure, the printhead height is higher than the rolling element height. A printhead - to - print medium spacing (PPS) <NUM> greater than a predetermined safety distance may thus be maintained. Quality and reliability of the printing process may be improved. In addition, the leading edge of the print medium is prevented from crashing against the printhead.

In some examples, the predetermined distance may be <NUM>. Consequently, a printhead - to - print medium spacing (PPS) greater than <NUM> may be maintained. For example, the printhead - to - print medium spacing (PPS) may be about <NUM>.

The predetermined safety distance may be set as a function of the type and/or thickness of the print medium. The print medium may be according to any of the examples herein disclosed. For example, the print medium may comprise a thickness between <NUM> and <NUM>.

For example, for a given PPS about <NUM> and a given thickness of <NUM> of the leading edge of the print medium, the printhead height may be about <NUM>.

The safety assembly of <FIG> may be according to any of the examples herein disclosed. The printing system may comprise a plurality of safety assemblies.

In the example of this figure, the print medium advance system <NUM> comprises a print medium feed mechanism <NUM> for feeding print medium to a print zone. In this example, the print medium feed mechanism <NUM> is upstream of an upstream region <NUM> of the print platen surface <NUM> and the printhead <NUM> is above a downstream region <NUM> of the print platen surface <NUM>. The print medium feed mechanism <NUM> may thus be away from the printhead <NUM>.

The print medium feed mechanism <NUM> of this figure comprises a drive roller <NUM> and a pinch roller <NUM> above the drive roller <NUM>. The print medium may be continuously gripped between the drive roller <NUM> and the pinch roller <NUM>. The rotation of the drive roller <NUM> makes the print medium advance towards the print zone.

In some examples, the print medium advance system may comprise a hold down system according to any of the examples herein disclosed.

In <FIG>, the safety assembly <NUM> is directly connected to the printhead <NUM>. Accordingly, the safety assembly may be closer to the printhead <NUM>. Precision of the printhead - to - print medium spacing (PPS) may thus be improved.

In some examples, the safety assembly <NUM> may be connected to a print bar structure extending along print medium width direction. The print bar structure may be connected to the printhead.

The printhead of <FIG> may be according to any of the examples herein disclosed. In some examples, the printing system may comprise a plurality of printheads.

The printing system of <FIG> is a page-wide array printing system. The printing system may comprise a plurality of printheads. The printhead or the plurality of printheads may span the whole width of the print medium.

The printing system may comprise a sensor system to detect a force exerted by the leading edge of the print medium against the rolling element greater than a predetermined force. Safety of the printhead may thus be improved.

In some examples, the sensor may be according to any of the examples herein disclosed. For example, the rolling element may be mounted about a spindle extending in a print medium width direction and the sensor may comprise a detector to detect a deflection of the spindle. A force exerted by the leading edge of the print medium greater than a predetermined may thus be detected.

The printing system may comprise a controller according to any of the examples herein disclosed. In some examples, the controller may control the operation of the printing system. In some examples, the controller may be a dedicated controller. The controller may receive a safety signal if the sensor system detects a force greater than the predetermined force and may stop the print medium advance system if the controller receives the safety signal. For example, the controller may send a signal to the print medium advance system to stop the movement of the print medium advancing towards the printhead.

<FIG> and <FIG> respectively illustrate a top view of print bar for a page-wide array printing system and a cross-sectional view along A - A' according to an example of the present disclosure. The print bar <NUM> comprises a printhead <NUM> having a plurality of nozzles to deliver a print agent on a print medium <NUM>. The printhead <NUM> comprises a printhead lower portion <NUM> to face the print medium <NUM>. The print bar <NUM> comprises a print bar structure <NUM> spanning a width <NUM> of the print medium <NUM>. The print bar structure <NUM> supports the printhead <NUM>. The print bar <NUM> further comprises a safety assembly <NUM> comprising a rolling element <NUM> upstream of the printhead <NUM> in a print medium advance direction <NUM> to prevent the print medium <NUM> from contacting the printhead <NUM>. The rolling element <NUM> comprises a rolling element lower portion <NUM> to face the print medium <NUM>. The rolling element lower portion <NUM> extends a length <NUM> in a direction perpendicular to the print medium advance direction <NUM>, so that a distance <NUM> between the printhead lower portion and the print medium is greater than a distance <NUM> between the rolling element lower portion and the print medium.

When the print bar <NUM> is mounted in a printing system, the printhead - to - print medium spacing (PPS) <NUM> is greater than the rolling element - to - print medium spacing <NUM>. Accordingly, a printhead height is greater than a rolling element height. The safety assembly <NUM> may thus prevent the print medium from contacting the printhead <NUM>.

The print bar <NUM> of these figures may be mounted in a page-wide array printing system according to any of the examples herein disclosed.

The print bar may extend substantially the whole width <NUM> of the print medium in the print medium width direction <NUM>. A printhead or a plurality of printheads may statically span substantially the whole width <NUM> of the print medium.

In these figures, the print bar <NUM> comprises a plurality of printhead modules <NUM>. The printhead modules <NUM> may comprise a plurality of printheads <NUM>. The printheads may comprise a plurality of nozzles (not illustrated in these figures) to deliver a print agent to the print medium. The Printheads of these figures may be according to any of the examples herein disclosed.

In these figures, the printhead modules <NUM> are connected to the print bar structure <NUM>. For example, the printhead modules may be fitted in receivers formed in the print bar structure. In some examples, the printheads may be directly connected to the print bar structure.

The print bar of these figures comprises a connecting structure <NUM> adjustably connected to the print bar structure <NUM>. A safety assembly <NUM> may be connected to the connecting structure <NUM>, so that the length <NUM> between the rolling element lower portion <NUM> and the printhead lower portion <NUM> in the direction perpendicular to the print medium advance direction <NUM> is adjustable. The height of the rolling element may thus be adjusted.

In these figures, a plurality of safety assemblies <NUM> is connected to the connecting structure <NUM>. Accordingly, the height of the plurality of the safety assemblies may be precisely adjusted. Mounting tolerances may thus be reduced.

The safety assemblies <NUM> of these figures comprise a bracket. The bracket or brackets <NUM> may be connected to the connecting structure <NUM>. The rolling element <NUM> is rotatably mounted about the bracket <NUM>. For example, the rolling element may be supported by a spindle rotatably connected to the bracket. The rolling element <NUM> may thus rotate about the bracket <NUM>. The spindle may extend in a direction parallel to the print medium width direction <NUM>.

In some examples, the safety assembly may be adjustably connected to the printhead, so that the length between the rolling element lower portion and the printhead lower portion in the direction perpendicular to the print medium advance direction may be adjustable. A bracket of the safety assembly may be fastened to the printhead and/or to the printhead modules.

<FIG> schematically illustrates a plurality of safety assemblies according to an example of the present disclosure. In this figure, four safety assemblies <NUM> are connected to a connecting structure <NUM>. The connecting structure <NUM> may be to connect to a print bar structure or to a printhead according to any of the examples herein disclosed.

The safety assemblies of this figure may be mounted in any of the printing systems and/or on the print bars herein disclosed. The safety assemblies <NUM> of this figure comprises a rolling element <NUM> mounted on a spindle <NUM>. The rolling element <NUM> of this figure is a cylinder extending in a direction parallel to the print medium width direction <NUM>. The roller or cylinder may rotate about a direction parallel to print medium width direction <NUM>.

The rolling element <NUM> comprises a rolling element lower portion <NUM> as described with respect to other examples of the present disclosure.

In some examples, a plurality of rolling elements may be mounted on a spindle. For example, two or three rolling elements may be mounted on a spindle.

In some examples, the rolling element, e.g. a roller, may comprise a material having a high stiffness and a low friction coefficient. One example of a material with a high stiffness and a low friction coefficient may be polyoxymethylene (POM), also known as acetal, polyacetal and polyformaldehyde. The rolling element may made from an injection-molded polyoxymethylene. A low friction material may reduce marks on the print medium when the print medium contacts the rolling element.

In this figure, the roller <NUM> comprises a through hole and the spindle <NUM> is inserted in this through hole. The spindle may engage the through hole of the roller. Accordingly, the roller and the spindle may rotate together. The spindle may extend in a direction parallel to the print medium width direction <NUM>. In some examples, the spindle may comprise steel. The spindle may deflect or bend if a print medium contacts the rolling element, e.g. roller. The spindle may thus act as spring-like element. Such a deflection may be used to determine a force of the print medium against the rolling element.

In some examples, the roller may extend between <NUM> and <NUM>. The roller may comprise a diameter between <NUM> and <NUM>. The spindle may extend between <NUM> and <NUM>. The spindle may comprise a diameter between <NUM> and <NUM>.

The safety assemblies of this figure comprise a bracket <NUM> having a first leg <NUM> and a second leg <NUM>. A central portion <NUM> connects the first leg <NUM> to the second leg <NUM>. A first end of the spindle may be rotatably connected to the first leg <NUM> and a second end of the spindle may be rotatably connected to the second leg <NUM>. In this figure, the central portion <NUM> comprises holes through which fasteners <NUM> may be inserted to connect the bracket to the connecting structure <NUM>. The connecting structure may comprise a plurality of holes to receive the fasteners <NUM> inserted in the holes of the brackets.

In <FIG>, the plurality of brackets <NUM> is connected at a predetermined position of the connecting structure <NUM>. Distance between each of the rolling elements and the connecting structure <NUM> may be substantially constant along the print medium width direction <NUM>.

The connecting structure <NUM> of this figure comprise a plurality, e.g. two, elongated holes or slots <NUM>. A fastener may be inserted in an elongated hole to fasten the connecting structure to a component of the printing system, e.g. a print bar structure or printhead or a printhead module. The height of the connecting structure may thus be adjusted with respect to the printhead height. In this way, the rolling height may be adjusted for a given thickness of a print medium.

In some examples, the brackets may be fastened to a printhead and/or to a printhead module. In these examples, the bracket may comprise elongated holes or slots to adjust the height of the bracket with respect to the printhead height.

<FIG> schematically illustrates a cross-sectional view of a safety assembly according to an example of the present disclosure. The safety assembly comprises a plurality of rolling elements <NUM> along a print medium width direction <NUM>.

The rolling elements <NUM> of this figure are spheres. The spheres may comprise a material having a high stiffness and a low friction coefficient. The spheres may comprise polyoxymethylene.

The rolling elements <NUM> of this figure are partially fitted in holes <NUM> of a bracket <NUM>. The bracket <NUM> may comprise supporting surfaces <NUM> around the holes <NUM> facing the rolling elements <NUM>. The hole may comprise a variable diameter along its height to substantially correspond to a partial shape of the spheres. In this example, the lower diameter of the hole is smaller than a diameter of the sphere so as to prevent the spheres from falling. The spheres may be partially embedded between two opposite supporting surfaces <NUM> in such a way that the spheres may rotate inside the holes. The bracket <NUM> may thus support the rolling elements <NUM>.

In <FIG>, the safety assembly <NUM> comprises cup-shaped members <NUM> engaging a shape of an upper portion of the spheres. The cup-shaped members <NUM> are connected to the bracket <NUM> through spring-like elements <NUM>. A force applied on a rolling element <NUM> may compress the spring-like element <NUM>.

When the safety assembly is mounted in a printing system, a print medium may contact the rolling element. This may generate a compression of the spring-like element. In some examples, the compression of the spring-like element may be used by a sensor system to determine the force applied on the rolling element.

The bracket <NUM> of <FIG> comprises a pair of elongated holes <NUM> to adjustably connect the safety assembly <NUM> to a print bar structure or to a printhead. A height with respect to the print medium may thus be adjusted.

In some examples, the bracket may be connected to print bar structure through a connecting structure. The connecting structure may be adjustable connected to the print bar.

Claim 1:
A printing system (<NUM>) comprising:
a printhead (<NUM>) configured to deliver a print agent on a print medium (<NUM>);
a print platen surface (<NUM>) configured to support a print medium (<NUM>) advancing in a print medium advance direction (<NUM>);
a hold down system (<NUM>) configured to hold down the print medium on the print platen surface (<NUM>);
a safety assembly (<NUM>) associated with the printhead (<NUM>), wherein the printhead (<NUM>) comprises a printhead lower portion (<NUM>) to face the print medium;
wherein the safety assembly (<NUM>) comprises a rolling element (<NUM>) upstream of the printhead (<NUM>) in the print medium advance direction (<NUM>) configured to prevent the print medium (<NUM>) from contacting the printhead (<NUM>); and wherein the rolling element (<NUM>) is above the print platen surface (<NUM>) to maintain a distance (<NUM>) between a leading edge (<NUM>) of the print medium (<NUM>) and the printhead lower portion (<NUM>) greater than a predetermined safety distance by forcing the leading edge (<NUM>) of the print medium to bend downwards when a height of the leading edge is greater than a height between the rolling element (<NUM>) and the print platen surface (<NUM>).