BACKGROUND

Printing systems comprise printing fluid ejection assemblies to provide drop- on-demand ejection of printing fluid droplets. In general printing systems print images by ejecting printing fluid droplets through a plurality of nozzles onto a printing medium (for instance, a sheet of paper or a layer of build material)

BRIEF DESCRIPTION OF DRAWINGS

Features of the present disclosure are illustrated by way of example and are not limited in the following figure(s), in which like numerals indicate like elements, in which:

FIG. 1 shows a side view of a printing fluid ejection assembly, according to an example of the present disclosure;

FIG. 2A shows a top view of a printing fluid ejection assembly comprising a first printing fluid channel and a second printing fluid channel, according to an example of the present disclosure;

FIG. 2B shows a top view of a printing fluid ejection assembly comprising a second printing fluid channel substantially orthogonal to a first printing fluid channel, according to an example of the present disclosure;

FIG. 2C shows a top view of a printing fluid ejection assembly comprising a first printing fluid channel in fluidic communication with a second printing fluid channel via an inlet region and an outlet region, according to an example of the present disclosure;

FIG 2D shows a top view of a printing fluid ejection assembly comprising a first printing fluid channel, a second printing fluid channel, and a third printing fluid channel, according to an example of the present disclosure: FIG. 2E shows a top view of a printing fluid ejection assembly comprising a first printing fluid channel a second printing fluid channel having a closed-end, and a third printing fluid channel, according to an example of the present disclosure;

FIG. 2F shows a top view of a printing fluid ejection assembly comprising a first printing fluid channel and a third printing fluid channel in fluidic communication with a second printing fluid channel via parallel channels, according to an example of the present disclosure:

FIG 2G shows a top view of a printing fluid ejection assembly comprising a first printing fluid channel and a third printing fluid channel in fluidic communication with a second printing fluid channel via a series of channels, according to an example of the present disclosure;

FIG. 3 shows a method for refreshing a nozzle meniscus region of a printing fluid ejection assembly, according to an example of the present disclosure;

FIG. 4 shows a method for refreshing a nozzle meniscus region in response to exceeding a threshold idle time, according to an example of the present disciosure;

FIG. 5 shows a printing fluid ejection assembly comprising a series of layers stacked on each other, according to an example of the present disclosure.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent, however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure

Throughout the present disciosure, the terms "a" and "an" are intended to denote at least one of a particular element. Unless otherwise indicated, in the to be used or printing fluid may be wasted, thereby increasing the cost and/or the size of the printing system. In some examples, servicing operations may comprise at least one of spitting printing fluid and wiping the printing fluid ejection elements.

In the following, printing fluid ejection elements with improved decap performance will be described. Accordingly, printing systems and methods are also described.

Printing fluid ejection devices such as printheads may comprise nozzles in fluidic communication with printing fluid chambers in which printing fluid is stored. To expel printing fluid from a printing fluid chamber through at least a nozzle of a printing fluid ejection device, the printing fluid chamber may comprise a printing fluid ejection element. Examples of printing fluid ejection elements comprise thermalbased ejection elements (for instance, a heat transducer to selectively heat printing fluid in the printing fluid chamber) or piezo-based ejection elements (for instance, a mechanical actuator to transmit a force to printing fluid). Subsequently, the printing fluid chamber is refilled via an inlet of the printing fluid chamber with printing fluid such that the previously expelled printing fluid is replenished. In some examples, the printing fluid chamber may further comprise an outlet to provide a fluid path from the inlet of the printing fluid chamber to the outlet of the printing fluid chamber.

In an example, a printing fluid chamber may comprise a plurality of printing fluid channels. For example, a printing fluid chamber may comprise a first printing fluid channel and a second printing fluid channel arranged to be in fluidic communication with the first printing fluid channel. In an example, the first printing fluid channel may comprise an inlet to receive printing fluid, an outlet to output printing fluid, and a printing fluid ejection element between the inlet and the outlet. In some examples, the second printing fluid channel may comprise an actuator to improve the decap performance of the printing fluid election device. Examples of actuators comprise thermal-based actuators (for instance, a heat transducer to selectively heat printing fluid in a region associated with the actuator) or piezo-based actuators (for instance, a mechanical actuator that selectively pushes printing fluid). In some examples, the actuator is arranged with respect to the printing fluid ejection element such that, in response to a trigger signal, the actuator is fired and printing fluid within the first printing fluid channel and the second printing fluid channel is disrupted. As previously explained, the firing of the actuator results in a pressure differential within the printing fluid chamber. In particular, the pressure differential is generated within the second printing fluid channel Because of the fluidic communication between printing fluid channels, the pressure differential moves through the printing fluid channels until reaching a nozzle meniscus region associated with the nozzle. If the pressure differential that reaches the nozzle meniscus region is greater than a minimum pressure differential value, the printing fluid located at the nozzle meniscus region is refreshed. On the other hand, if the pressure differential is greater than a maximum pressure differential value, the pressure differential may result in a printing fluid ejection through the nozzle corresponding to the printing fluid ejection element, in some examples, the actuator is arranged with respect to the printing fluid ejection such that the firing of the actuator refreshes the printing fluid in the nozzle meniscus region while not ejecting printing fluid droplets through the nozzle (i.e. , the pressure differential gsnsrated by the actuator over a period of time results in a zero-growth of the printing fluid within the printing fluid chamber). In this way, printing fluid waste associated with spitting operations is reduced while improving the decap performance. In some examples, the position of the actuator with respect to the printing fluid ejection element may be associated with a pressure differential value that will reach the printing fluid ejection element. In particular, in some examples, the minimum pressure differential value and the maximum pressure differential value may be associated with a range of admissible distances between the actuator and the printing fluid ejection member.

According to an example, the refreshing operation may be performed while the printing fluid ejection member of the printing fluid ejection assembly is idle (e.g., is not ejecting printing fluid out of the nozzle). In some other examples, the refreshing operation may be performed In parallel to other operations, such as microrecirculation or macro-recirculation operations. refresh printing fluid in the meniscus region 113a. In some exampies, the firing of the actuator 123 refreshes the meniscus associated with the nozzle 131 when the actuator 123 is positioned at a distance within a range of admissible distances with respect to the printing fluid ejection element 113.

In some examples, the actuator 123 may be arranged with respect to the printing fluid ejection element 113 based on a geometry of a fluid path defined from the actuator 123 to the printing fluid ejection element 113. in other examples, the actuator 123 may be in fluidic communication with the printing fluid ejection element 113 via a series of fluid paths, wherein the actuator 123 may be arranged with respect to the printing fluid ejection element 113 based on geometries of the series of fluid paths. In some other examples, to effectively refresh the meniscus region 113a associated with the nozzle 131 , the actuator 123 may be positioned at a distance within a range of admissible distances with respect to the printing fluid ejection element 113. Therefore, if the actuator 123 is positioned within the range of admissible distances, the firing of the actuator 123 results in an effective printing fluid refreshing operation at the meniscus region. On the other hand, if the actuator 123 is positioned at a distance outside the range of admissible distances, the firing of the actuator 123 may result in a faulty refreshing operation. In an example, if the actuator 123 is located at a shorter distance than the lower limit of the admissible range, the firing of the actuator 123 may result in a printing fluid droplet being ejected out of the nozzle 131 . On the other hand, if the actuator 123 is located at a distance greater than the upper limit of the admissible range, the firing of the actuator 123 may not effectively refresh the printing fluid at the meniscus region 113a

Referring now to FIG. 2A, a top view of a printing fluid ejection assembly 200A is shown. The printing fluid election assembly 200A comprises a first printing fluid channel 210 and a second printing fluid channel 220 (represented in hatched lines) arranged with respect to the first printing fluid channel 210. The first printing fluid channel 210 comprises an inlet 211 to receive printing fluid, an outlet 212 to output printing fluid, and a printing fluid ejection element 213 between the inlet 211 and the (Le. , the sum of the length 210a plus the length 220a) has to be within the range of admissible distance in order to obtain an effective refreshing operation when firing the actuator 223.

Referring now to FIG. 2B, a top view of a printing fluid ejection assembly 200B comprising a first printing fluid channel 210 in fluidic communication with a second printing fluid channel 220 is shown. The first printing fluid channel 210 has a first width 210b and the second printing fluid channel 220 has a second width 220b, the first width 210b being greater than the second width 220b. As previously explained, the distances at which the actuator effectively refreshes the nozzle meniscus region depend on the geometry of the fluid path from the actuator 223 to the printing fluid ejection element 213 For example, in FIG. 2B, the fluid path from the actuator 223 to the printing fluid ejection element 213 comprises a first section and a second section, wherein the first section is defined from the center of the actuator 223 to the center of the elbowed connection and the second section is defined from the center of the elbowed connection to the center of the printing fluid ejection element 213. Hence, as previously described, if any of the dimensions defining the geometry of the first section or the second section is modified, the range of admissible distances is modified accordingly.

In some examples, the range of admissible distances may be adjusted by modifying the geometry of at least one section forming the fluid path from the actuator 223 to the printing fluid ejection element 213. In this way, more compact printing fluid ejection assemblies may be obtained. In an example, the width of a section of the fluid path may be modified. In other examples, the height of a section of a fluid path may be modified.

Although in FIG. 2B the second printing fluid channel 220 is oriented substantially perpendicular with respect to the first printing fluid channel 210, in other examples the second printing fluid channel 220 may be aligned with respect to the first printing fluid channel 210 However, it should be noted that when having a second printing fluid channel 220 perpendicular to a first printing fluid channel 210, the overall length, from left to right (on the page in the case of the drawings), of the printing fluid ejection assembly 2008 is reduced compared to printing fluid assemblies in which the first printing fluid channel 210 and the second printing fluid channel 220 are aligned (e.g., the printing fluid ejection assembly 200A).

According to an example, each of the printing fluid ejection assemblies 200A and 2008 may comprise a first section and a second section having geometries within a range of geometries. For instance, the first section along the first printing fluid channel 210 may have a length (e.g., 210a) within a range from 60 to 100 pm, a width (e.g., 210b) within a range from 30 to 40 pm, and a height within a range from 12 to 21 pm. On the other hand, the second section along the second printing fluid channel 220 may have a length (e.g.. 220a) within a range from 20 to 30 pm, a width (e.g., 220b) within a range from 15 to 30 pm, and a height within a range from 15 to 25 pm. As a result, a range of admissible distances in which the firing of the actuator 223 effectively refreshes the meniscus region is a range from 80 to 130 pm (i.e., the sum of the length of the first portion plus the length of the second portion). In some examples, at least one dimension (e.g., the width or the height) of the second section may be modified such that a range of admissible distances is reduced (i e., the length along the second section decreases).

Referring now to FIG. 2C, a top view of a printing fluid ejection assembly 200C comprising a first printing fluid channel 210 in fluidic communication with a second printing fluid channel 220 via an inlet region 211a and an outlet region 212a is shown. As previously explained, the inlet region 21 la is associated with the inlet 211 of the first printing fluid channel 210 and the outlet region 212a is associated with the outlet 212 of the first printing fluid channel 210. Thus, instead of having a single fluid path from the actuator 223 to the printing fluid ejection element 213, multiple fluid paths are defined.

In FIG. 2C. the actuator 223 is at an intermediate position with respect to the inlet 211 and the outlet 212 of the first printing fluid channel 210. in this way, the pressure differential created by the actuator 223 along the channels does not result in a net flow through the first printing fluid channel 210. Similarly, the printing fluid ejection element 213 is at an intermediate position with respect to the inlet 211 and the outlet 212. Since the second printing fluid channel 220 is in fluidic communication with the first printing fluid channel 210 via the inlet region 211a and the outlet region 212a. a first fluid path 214a and a second fluid path 214b from the actuator 223 to the printing fluid ejection member 213 are established. In addition, each of the fluid paths includes a first section along the first printing fluid channel 210 and a second section along the second printing fluid channel 220. Along the first section, the fluid paths 214a and 214b have a first width 210b corresponding to the width of the first printing fluid channel 210. Along the second section, the fluid paths 214a and 214b have a second width 220b corresponding to the width of the second printing fluid channel 220. Due to the symmetry of the embodiment, in FIG 2C, the length of the first fluid path 214a is equal to the length of the second fluid path 214b.

As previously explained, the range of admissible distances in which the actuator 223 effectively refreshes the printing fluid is based on the geometries of the fluid paths from the actuator 223 to the printing fluid ejection element 213. When having more than a fluid path available from the actuator 223 to the printing fluid ejection element 213, arranging the actuator 223 at a different location will impact each of the first fluid path 214a and the second fluid path 214b. For instance, in FIG. 2C, positioning the actuator 223 closer to the inlet 211 will result in a decrease in the length of the first fluid path 214a and an increase in the length of the second fluid path 214b. To effectively improve the decap performance while not ejecting printing fluid through the nozzles, each of the length of the first fluid path 214a and the length of the second fluid path 214b have to be within the range of admissible distances.

In some examples, the addition of fluid paths from an actuator to a printing fluid ejection further reduces the range of admissible distances thereby providing more compact printing fluid ejection assemblies. Similarly, the use of different geometries may reduce the overall size of the printing fluid ejection assembly. However, in some examples, the dimensions of the first printing fluid channel including a printing fluid ejection element may have to meet other criteria associated with at least one of an effective fluid dispensing operation, an effective refilling operation of the printing fluid channel, or an effective recirculation operation. fluid channel 210. The second printing fluid channel 220, contrary to the printing fluid ejection assemblies explained in reference to FIG. 20, D and F, is not fluidly connected to the first printing fluid channel 210 via the inlet region and the outlet region. Instead, the second printing fluid channel 220 is in fluidic communication with the first printing fluid channel 210 via a series of parallel channels comprising a first parallel channel 221 , a second parallel channels 226a, a third parallel channel 226b, and fourth parallel channel 226c. in this way, the pressure differentials generated by the actuator 223 effectively reach each of the first printing fluid ejection member 213 and the second printing fluid ejection member 228.

Although in FIG. 2G the fluid paths from the actuator 223 to the first printing fluid ejection element 213 and the second printing fluid ejection element 228 have been omitted, it should be noted that the actuator 223 is arranged with respect to the printing fluid ejection elements 213 and 228 based on the respective fluid paths and their geometries. For instance, in FIG. 2G, the actuator 223 is in fluidic communication with the first printing fluid ejection element 213 via the first parallel channel 221 , the second parallel channel 226a, and the fourth parallel channel 226c. On the other hand, the actuator 223 is in fluidic communication with the second printing fluid ejection element 228 via the second parallel channel 226a, the third parallel channel 226b, and the fourth parallel channel 226c.

According to an example, a range of admissible distances from an actuator to a printing fluid ejection member of a printing fluid ejection assembly may be determined based on a printing fluid ejection assembly lumped parameter (PFEALP). In an example, the PFEALP may be determined based on a lumped parameter equation, being the lumped parameter equation a function of iength(s) of the fluid path(s) from the actuator to the printing fluid ejection member, height(s) of the fluid path(s) from the actuator to the printing fluid ejection members, width(s) of the fluid path(s) from the actuator to the printing fluid ejection members, and a number of singular fluid paths (i.e., non-overlapping fluid paths) from the actuator to the printing fluid ejection members. In an example, a PFEALP may be defined by the following equation: nce According to an exampie. the PFEALP and the AR of the printing fluid ejection assemblies 200A to 200E may be obtained based on the geometries of the printing fluid channels and the area of the actuator 223. in an exampie. the parameters associated with the first printing fluid ejection element 213 may be determined as follows:

[Table 1

Where the first column contains a reference to the figures representing the assemblies 200A to 200E, T corresponds to the number of fluid paths from the actuator 223 to the first printing fluid ejection element 213, "Li, n=1” corresponds to the length of the fluid path T along a long axis of the first printing fluid channel 210, “Wi, n~1” corresponds to the width of the fluid path “i" in a first short axis of the first printing fluid channel 210 (i.e., the width 210b), “Hi, n=1 ” corresponds to the height of the fluid path “i" in a second short axis of the first printing fluid channel 210, “Li, n=2'-’ corresponds to the length of the fluid path “i" along a long axis of the second printing fluid channel 220, “Wi, n=2” corresponds to the width of the fluid path “I" in a first short axis of the second printing fluid channel 220 (i.e., the width 220b), "Hi, n=2” corresponds to the height of the fluid path T in a second short axis of the second printing fluid channel 220, and “Aact” corresponds to the area of the actuator 223. Based on these values, the “PFEALP” and the “AR” corresponding to the first printing fluid ejection element 213 are calculated using the equations previously fluid ejection or the last refreshing operation. Then, at block 440, method 400 comprises performing a subsequent refreshing operation upon the ejection idie time exceeds a threshold idle time. In some examples, to perform the subsequent refreshing operation, the actuator may generate a subsequent non-ejecting impulse.

As previously explained, excessive ejection idle times associated with printing fluid ejection element(s) may result in faulty subsequent printing fluid ejection(s). Hence, by performing refreshing operations based on refresh signals and the ejection idle times, the printing fluid at the meniscus region(s) is effectively refreshed thereby improving the decap performance of the printing fluid ejection assembly.

In some examples, methods 300 and 400 may be performed to effectively refresh the printing fluid at the meniscus regions of an array of printing fluid assemblies.

According to an example, a printing system may comprise a controller and a plurality of printing fluid ejection assemblies, wherein each of the printing fluid ejection assemblies may correspond to any of the assemblies previously explained in FIGs. 1 to 2G. The plurality of printing fluid ejection assemblies comprises a plurality of nozzles to dispense printing fluid on a media. As previously explained, to dispense printing fluid out of the nozzles, printing fluid ejection elements are arranged to correspond with the nozzles. To effectively refresh the printing fluid at the meniscus regions, the controller may selectively control an actuator of each of the printing fluid ejection assembly. In particular, the controller may control the actuator to fire such that a pressure differential is generated within the printing fluid channels of the respective printing fluid ejection assembly. If the actuator is arranged with respect to the printing fluid ejection element within a range of admissible distances, the firing of the actuator will result in a refreshing operation that refreshes the printing fluid in the meniscus region, in some other examples, as previously explained in reference to FIGs. 3 and 4, refreshing operations may be performed in response to refresh signals and in response to ejection idle times exceeding a threshold idle time. supplied by the first printing fluid line to the first channel 510 via the printing fluid inlet 511 .

In some examples, the actuator 523 may be positioned with respect to the printing fluid ejection element 513 at a distance within a range of admissible distances. In some examples, the range of admissible distances may be based on geometries of fluid path 514 defined from the actuator 523 to the printing fluid ejection element 513. In some examples, the range of admissible distances at which the actuator 523 has to be positioned with respect to the printing fluid ejection element 513 to effectively refresh the nozzle meniscus region(s) may be associated with a printing fluid ejection assembly lumped parameter, in other examples, the range of admissible distance may be associated with a printing fluid ejection assembly lumped parameter and an actuator ratio.

What has been described and illustrated herein are examples of the disclosure along with some variations. The terms, descriptions, and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims (and their equivalents) in which all terms are meant in their broadest reasonable sense unless otherwise indicated