BACKGROUND

[0001] Printing mechanisms for printing content on a substrate are determined based on the type of content to be printed. For instance, for applications that entail delivery of small amounts of fluids to a specific location on the substrate, drop impact printing mechanisms may be utilized. Examples of such applications may include printing electronic devices such as, circuit boards, solar cells, and RFIDs; and delivering accurate quantities of drugs in pharmaceutical industry.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Figure 1 illustrates schematics of a printer for printing high viscosity fluids, in accordance with an example of the present subject matter,

[0003] Figure 2 illustrates schematics of the printer for printing high viscosity fluids, in accordance with another example of the present subject matter, and

[0004] Figure 3 illustrates a method for printing high viscosity fluids, in accordance with an example of the present subject matter.

DETAILED DESCRIPTION

[0005] In drop-impact printing mechanisms, for printing content on a substrate, a drop is impacted on a mesh. Upon impact of the drop on the mesh, capillary waves are created at the interface of the droplet during retraction, which leads to formation of a cylindrical air cavity within retracting interface of the drop. The interface retraction refers to the drop’s recoil phase after collision with the mesh. The air cavity subsequently collapses due to the motion of the interface and the kinetic energy of the fluid converges along the axis of collapse. When the cavity collapses, the resulting hydrodynamic singularity causes ejection of a narrow high-speed jet of the fluid. For meshes, a pore limits the lateral extent of the collapsing cavity. Specifically, the pore sets the lateral boundary for the interface motion resulting from the cavity collapse, thereby changing the collapse dynamics of the air cavity and ejection of a single microdroplet.

[0006] However, the drop-impact printing mechanism allows to print fluids having viscosities less than about 33 millipascal second (mPas). The inability of the drop-impact printing mechanism to print fluids with higher viscosities may be attributed to the fact that the viscous time scales of high viscous liquids are usually higher than that of droplet recoil time scales. Specifically, due to higher viscosity, the cylindrical air cavity is not formed within retracting interface of the droplet upon impact of the droplet on the mesh.

[0007] According to examples of the present subject matter, techniques for printing high viscosity fluids are disclosed.

[0008] In an example, the techniques involve arranging a mesh and a substrate included in a printer in a manner, such that, a distance between the mesh and the substrate is less than a predetermined value, where the predetermined value is determined based on a viscosity of the fluid. In the example, the predetermined value may indicate a maximum distance traversed by a fluid jet from amongst multiple fluid jets ejected upon impact of a droplet of the fluid on the mesh. Arranging the mesh and the substrate based on the predetermined value facilitates at least one fluid jet to contact the substrate upon impact of the droplet on the mesh, thereby printing a microdroplet on the substrate.

[0009] In an example of the present subject matter, a printer for printing high viscosity fluids is disclosed. The printer may include a fluid dispensing mechanism to generate a droplet of a fluid. The printer may further include a mesh arranged beneath the fluid dispensing mechanism, such that, when the droplet is generated by the fluid dispensing mechanism, the droplet impacts upon the mesh. Further, the printer may include a substrate arranged beneath the mesh. In an example, the mesh and the substrate may be arranged in a manner, such that, a distance between the mesh and the substrate is less than a predetermined value, where the predetermined value is determined based on a viscosity of the fluid In the example, the predetermined value may indicate a maximum distance traversed by a fluid jet from amongst multiple fluid jets ejected upon impact of a droplet of the fluid on the mesh.

[0010] The above aspects are further described in conjunction with the figures, and in associated description below. It should be noted that the description and figures merely illustrate principles of the present subject matter. Therefore, various arrangements that encompass the principles of the present subject matter, although not explicitly described or shown herein, may be devised from the description and are included within its scope.

[0011] Figure 1 illustrates schematics of a printer 100 for printing high viscosity fluids, in accordance with an example of the present subject matter. In an example, the printer 100 may be a bioprinter.

[0012] The printer 100 may include a fluid dispensing mechanism for generating droplets of a fluid to be printed. The fluid dispensing mechanism may include a fluid reservoir 102 and a fluid dispenser 104 coupled to the fluid reservoir 102. Examples of fluid dispenser 104 may include, but are not limited to, printhead nozzles and syringes.

[0013] In operation, the fluid may be fetched from the fluid reservoir 102 and supplied to the fluid dispenser 104 for generating the droplets. The fluid may be fetched from the fluid reservoir 102 and supplied to the fluid dispenser 104 in different ways.

[0014] In an example, a fluid pump (not shown) may be utilized for fetching the fluid from the fluid reservoir 102 and supplying the fluid to the fluid dispenser 104.

[0015] In another example, the fluid reservoir 102 may be a pressurized reservoir. In the example, a pressure driven flow controller coupled to the fluid reservoir 102 may be utilized for enabling flow of liquid from the fluid reservoir 102 to the fluid dispenser 104. In operation, the pressure driven flow controller may apply a gas input pressure within the fluid reservoir 102. The application of the gas input pressure within the fluid reservoir 102 may push the fluid into the fluid dispenser 104 from the fluid reservoir 102. In the example, the amount of fluid to be transferred from the fluid reservoir 102 to the fluid dispenser 104 may be controlled by altering the gas input pressure being applied within the fluid reservoir 102.

[0016] Further, the fluid dispenser 104 may generate the droplets in different ways. In an example, the manner in which the fluid dispenser 104 generates the droplet may vary based on a type of the fluid dispenser 104 being utilized for generation of the droplets. For instance, when the fluid dispenser is a printhead nozzle, different excitation mechanisms may be utilized within the printhead nozzle for ejecting droplets from the printhead nozzle. Examples of such excitation mechanisms may include, but are not limited to, acoustic excitation mechanism which involves usage of acoustic waves onto the liquid surface for ejecting drops from the printhead nozzle, Electrohydrodynamic (EHD) excitation mechanism that involves usage of electrostatic forces onto the liquid surface for ejecting drops from the printhead nozzle, and laser excitation mechanism that involves usage of lasers onto the liquid surface for ejecting drops from the printhead nozzle. In an example, utilization of different fluid dispensing mechanisms within the printhead nozzle may allow alteration in size of the droplet being generated from the printhead nozzle.

[0017] Further, when the fluid dispenser 104 is a syringe, a syringe pump (not shown) may be utilized to control the flow of the fluid from the syringe for generation of the droplets. In an example, the utilization of the syringe pump may allow alteration in the size of the droplet being generated from the syringe by controlling the pressure being applied to the fluid present within the syringe. [0018] In an example, the fluid reservoir 102 may further include a rheometer (not shown) for determining a viscosity of the fluid stored in the fluid reservoir 102.

[0019] In another example, the rheometer may be included in the fluid dispenser 104. In the example, the rheometer may determine the viscosity of fluid when the fluid reaches the fluid dispenser from the fluid dispenser 104. Although the printer 100 has been described to include a single fluid reservoir 102, it would be noted that the printer 100 can include multiple fluid reservoirs containing different fluids. In such a situation, inclusion of the rheometer in the fluid dispenser 104 may allow determination of viscosity of different fluids stored in multiple fluid reservoirs by a single rheometer, thereby reducing the bulkiness of the printer 100.

[0020] The printer 100 may further include a mesh 106 arranged beneath the fluid dispenser 104. . The mesh 106 may be arranged beneath the fluid dispenser 104 in a manner, such that, droplets generated by the fluid dispenser 104 are impacted on the mesh 106 upon generation. The mesh 106 may further have pores (not shown) that may allow the fluid to pass through the mesh 106 upon impact. In an example, the mesh 106 may be a superhydrophobic sieve. In the example, the superhydrophobic sieve ensures that residue drops are repelled and transferred to fluid reservoir 102, the residue drops being drops that do not pass through the mesh upon impact.

[0021] In an example, the fluid dispenser 104 may be mounted on a fluid dispenser holder 108. In the example, the fluid dispenser holder 108 may further be moveably coupled to a height adjuster 110. As illustrated, the height adjuster 110 may allow movement of the fluid dispenser holder 108 along x-y direction to facilitate adjustment of a distance between the fluid dispenser 104 and the mesh 106. In an example, the height adjuster 110 may utilize electric motors (not shown) for movement of the fluid dispenser holder 108 along the x-y direction. [0022] A mesh holder 112 may further be included in the printer 100 for holding the mesh 106 beneath the fluid dispenser 104. In an example, the mesh holder 112 may be moveably coupled to the to a height adjuster 110. In the example, the height adjuster 110 may allow movement of the mesh holder 112 along the x-y direction to facilitate adjustment of the distance between the fluid dispenser 104 and the mesh 106. In an example, the height adjuster 110 may utilize electric motors (not shown) for movement of the mesh holder 112 along the x-y direction.

[0023] The printer 100 may further include a substrate 114 placed beneath the mesh holder 112. In an example, the distance between the mesh 106 and the substrate 114 may be varied by moving the mesh holder 112 along the x-y direction. In the example, the mesh 106 and the substrate 114 may be arranged in a manner, such that, a distance between the mesh and the substrate is less than a predetermined value. In the example, the predetermined value may be determined based on a viscosity of the fluid and may indicate a maximum distance traversed by a fluid jet from amongst multiple fluid jets ejected upon impact of the droplet on the mesh. Arranging the mesh and the substrate based on the predetermined value facilitates at least one fluid jet to contact the substrate upon impact of the droplet on the mesh, thereby printing a microdroplet on the substrate.

[0024] A heating unit 116 may further be included in the printer 100, where the heating unit 116 may be placed beneath the substrate 114. In operation, the heating unit 116 may keep the substrate heated during the operation of the printer 100, thereby facilitating faster evaporation of the fluid on the substrate.

[0025] The heating unit 116 may further be arranged on a substrate mover 118. The substrate mover 118 may allow movement of the substrate 114 along x-y direction, y-z direction, and x-z direction .

[0026] Although the fluid dispensing mechanism has been explained to include one fluid dispenser 104, it would be noted that the fluid dispensing mechanism can include more than one fluid dispenser 104 for dispensing droplets of fluid of either same or different viscosities, simultaneously. Such a setup of multiple fluid dispensers and the mesh having multiple pores at different locations enables multi-material printing. Further, utilizing the multiple fluid dispensers to simultaneously generate droplets of same fluid at different locations on the mesh allows achieving higher printing throughput.

[0027] The printer 100 may further include a printer controller 120 for controlling operations of various components of the printer 100, such as the fluid reservoir 104, the fluid dispenser 104, the mesh holder 112, and the substrate mover 118. A detailed explanation on the operation of the printer controller 120 for controlling operations of the components of the printer 100 for performing printing operations is provided with reference to Figure 2.

[0028] Figure 2 illustrates the schematics of the printer 100, in accordance with another example of the present subject matter.

[0029] The printer 100 includes a printer controller 120. The printer controller 120 may include a processor 202 and a memory 204 coupled to the processor 202. The functions of functional block labelled as “processor(s)”, may be provided through the use of dedicated hardware as well as hardware capable of executing instructions. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” would not be construed to refer exclusively to hardware capable of executing instructions, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing instructions, random access memory (RAM), non-volatile storage. Other hardware, standard and/or custom, may also be included. [0030] The memory 204 may include any computer-readable medium including, for example, volatile memory (e.g., RAM), and/or non-volatile memory (e.g., EPROM, flash memory, etc.).

[0031] The printer controller 120 may further include engines 206, where the engines 206 may include a communication engine 208, a fluid fetching engine 210 coupled to the communication engine 208, a droplet generation engine 212 coupled to the fluid fetching engine 210, and a control engine 214 coupled to the fluid fetching engine 210. In an example, the engines 206 may be implemented as a combination of hardware and firmware or software. In examples described herein, such combinations of hardware and firmware may be implemented in several different ways. For example, the firmware for the engine may be processor executable instructions stored on a non-transitory machine-readable storage medium and the hardware for the engine may include a processing resource (for example, implemented as either a single processor or a combination of multiple processors), to execute such instructions.

[0032] In the present examples, the machine-readable storage medium may store instructions that, when executed by the processing resource, implement the functionalities of the engine. In such examples, the printer controller 120 may include the machine-readable storage medium storing the instructions and the processing resource to execute the instructions. In other examples of the present subject matter, the machine-readable storage medium may be located at a different location but accessible to the printer controller 120 and the processor 202.

[0033] The printer controller 120 may further include data 216, that serves, amongst other things, as a repository for storing data that may be fetched, processed, received, or generated by the engines 206.

[0034] In operation, the communication engine 208 may receive one or more print commands from a computing device coupled to the printer 100. Based on the one or more print commands received from the computing device, the fluid fetching engine 210 may cause fetching of the fluid from the fluid reservoir 102 and supply the fluid to the fluid dispenser 104. In an example, when the fluid reservoir 102 is the pressurized reservoir, the fluid fetching engine 210 may transmit an indication to the pressure driven flow controller to cause flow of liquid from the fluid reservoir 102 to the fluid dispenser 104. In other examples, the fluid fetching engine 210 may transmit the indication to the fluid pump to fetch the fluid from the fluid reservoir 102 and supply the fluid to the fluid dispenser 104.

[0035] The droplet generation engine 212 may then cause the fluid dispenser 104 to generate the droplets. The droplet generation engine 212 may cause the fluid dispenser 104 to generate the droplets in different ways. For instance, in an example, when the fluid dispenser 104 is the printhead nozzle, the droplet generation engine 212 may control various excitation mechanisms being utilized within the printhead nozzle for generation of droplets. In another example, when the when the fluid dispenser 104 is a syringe, the droplet generation engine 212 may control the syringe pump for generation of the droplets.

[0036] The droplets generated by the fluid dispenser 104 may then impact on the mesh 106. As illustrated in figure 2a, upon the impact of a droplet D on the mesh 106, multiple fluid jets, such as fluid jet J1 , fluid jet J2, and fluid jet J3,may be ejected from the mesh 106. In such a situation, the control engine 214 may control the mesh holder 112 to ensure that a distance between the mesh 106 and the substrate 114 placed beneath the mesh holder 112 is less than a predetermined value. The predetermined value may indicate maximum distance traversed by a fluid jet, such as fluid jet J2, from amongst the multiple fluid jets ejected upon impact of the droplet of the fluid on the mesh 106. In an example, the control engine 214 may determine the predetermined value based on a viscosity of the fluid.

[0037] The control engine 214 may determine the predetermined value based on the viscosity of the fluid received from the rheometer. In an example, the control engine 214 may determine the predetermined value based on the viscosity of the fluid based on a mapping table included in the data. In an example, the mapping table may include mappings of different viscosities and predetermined values of distance between the mesh 106 and the substrate 114 corresponding to such viscosities. In another example, the control engine 214 may predict the predetermined value based on the viscosity of the fluid by utilizing a machine learning model, where the machine learning model may be trained based on the different viscosities and the predetermined values of distance between the mesh 106 and the substrate 114 corresponding to such viscosities. Examples of various machine learning models that the control engine 214 may utilize for prediction of the predetermined value include, but are not limited to, Linear Regression, Logistic Regression, Linear Discriminant Analysis, Classification and Regression Trees, Naive Bayes, K-Nearest Neighbors (KNN), Learning Vector Quantization (LVQ), Support Vector Machines (SVM), and Random Forest.

[0038] The control engine 214 may further monitor the viscosity of the fluid. On detecting a change in the viscosity of the fluid, the control engine 214 may modify the predetermined value. The control engine 214 may modify the predetermined value either by utilizing the mapping table or the machine learning model in the manner described above. In such a situation, the control engine 214 may control the mesh holder 112 to change the distance between the mesh 106 and the substrate 114 placed beneath the mesh holder 112 as per modified predetermined value.

[0039] In an example, the control engine 214 may also consider a distance between the fluid dispensing mechanism and the mesh while determining the predetermined value. In the example, when the distance between the fluid dispensing mechanism and the mesh is higher than a threshold value, the control engine 214 may increase the predetermined value. In operation, the control engine 214 may determine a change factor by which the distance between the fluid dispensing mechanism and the mesh has changed over the threshold value. The control engine 214 may accordingly change the predetermined value based on the change factor. [0040] In an example, the droplet generation engine 212 or the control engine 214 may also change the velocity of impact of the droplet on the mesh 106 . In the example, the droplet generation engine 212 or the control engine 214 may control the velocity on detecting a change in viscosity of the fluid. For instance, the droplet generation engine 212 or the control engine 214 may increase the velocity on detecting an increase in the viscosity of the fluid. On the other hand, the droplet generation engine 212 or the control engine 214 may decrease the velocity on detecting a decrease in the viscosity of the fluid. Changing the velocity of impact of droplets on the mesh with the change in the viscosity of the fluid compensates for the variations that may arise in the maximum distance traversed by a fluid jet from amongst the multiple fluid jets ejected upon impact of the droplet of the fluid on the mesh due to the change in the viscosity of the fluid. Accordingly, microdroplets may be printed on the substrate without changing the predetermined value on every change in the viscosity of fluid.

[0041] The droplet generation engine 212 or the control engine 214 may change the velocity of impact of the droplets on the mesh 106 in several ways. In an example, the droplet generation engine 212 may control a velocity of impact of the droplets on the mesh 106. In the example, when the fluid dispenser 104 is the printhead nozzle, the droplet generation engine 212 may control the various excitation mechanisms being utilized within the printhead nozzle for controlling a force being applied on the fluid for generation of droplets. On the other hand, when the fluid dispenser 104 is the syringe, the droplet generation engine 212 may control the syringe pump for for controlling the force being applied on the fluid for generation of droplets.

[0042] In another example, the control engine 214 may control the velocity of impact of the droplets on the mesh 106. In the example, the control engine 214 may send an indication to the height adjuster 110 to control the movement of the fluid dispenser holder 108 along x-y direction to change the distance between the fluid dispenser 104 and the mesh 106. Thus, in the example, the control engine 214 may increase the velocity by increasing the distance between the fluid dispenser 104 and the mesh 106. Alternatively, the control engine 214 may decrease the velocity by decreasing the distance between the fluid dispenser 104 and the mesh 106. [0043] The control engine 214 may further control the movement of the substrate mover 118 to print the microdroplets on different portions of the substrate 114. The control engine 214 may send indications to the substrate mover 118 to move the substrate 114 along x-y-z directions to ensure printing of microdroplets at designated locations on the substrate 114.

[0044] In an example, the control engine 214 may also control the heating unit 116 placed beneath the substrate 114. In the example, the control unit may turn on the heating unit 116 on detecting the generation of droplets by the fluid dispenser 104. The control engine 214 may detect the generation of droplets by the fluid dispenser 104 based on an indication received from the droplet generation engine 212. It would be noted that turning on the heating unit 116 on detecting the generation of droplets by the fluid dispenser 104 may reduce the power consumption of the printer 100, thereby facilitating overall improvement in printing efficiency of the printer 100.

[0045] Figure 3 illustrates a method 300 for printing high viscosity fluids, in accordance with an example of the present subject matter. Although the method 300 may be implemented in a variety of systems, but for the ease of explanation, the description of the method 300 is provided in reference to the above-described printer 100. The order in which the method 300 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 300, or an alternative method.

[0046] It may be understood that blocks of the method 300 may be performed in the printer 100. The blocks of the methods 300 may be executed based on instructions stored in a non-transitory computer- readable medium, as will be readily understood. The non-transitory computer-readable medium may include, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media.

[0047] At block 302, a droplet of a fluid may be generated by a fluid dispensing mechanism, where the droplet is to impact on a mesh 106 arranged beneath the fluid dispensing mechanism upon generation. In an example, the droplet may be generated by the fluid dispenser in response to an indication received from a droplet generation engine 212 of a printer controller 120 of the printer 100. In the example, the droplet generation engine 212 may transmit the indication upon reception of a print command by a communication engine 208 of a printer controller 120.

[0048] At block 304, multiple fluid jets may be generated from the mesh 106 upon impact of the droplet on the mesh 106. In an example, the multiple jets may traverse different distances. The distances traversed by the multiple jets may depend on alignment of pores of the mesh 106 with the fluid dispenser. For instance, the distance travelled by a jet generated from a pore aligned directly below the fluid dispenser may be longer than the distance travelled by other jets.

[0049] At block 306, a microdroplet may be received on a substrate 114 arranged beneath the mesh 106, where a distance between the mesh 106 and the substrate 114 may be less than a predetermined value. In an example, the predetermined value may be determined based on a viscosity of the fluid and may indicate a maximum distance traversed by a fluid jet from amongst the multiple fluid jets. The predetermined value may be the distance travelled by the jet generated from the pore aligned directly below the fluid dispenser. In another example, the predetermined value may be determined based on a combination of the viscosity of the fluid and a distance between the fluid dispensing mechanism and the mesh. In the example, at a particular viscosity, when the distance between the fluid dispensing mechanism and the mesh is higher than a threshold value, the predetermined value may be increased. In operation, a change factor by which the distance between the fluid dispensing mechanism and the mesh has changed over the threshold value may be determined. Accordingly, the predetermined value may be changed based on the change factor.

[0050] In the example, the predetermined value may be determined by a control engine 214 of the printer controller 120.

[0051] In an example, the predetermined value may be modified based on a change in viscosity of the fluid. The modified predetermined value may be set in a manner, such that, the modified predetermined value is less than the maximum distance traversed by a fluid jet from amongst the multiple fluid jets ejected on impact of a droplet of new fluid on the mesh. In an example, the the predetermined value may be varied by the control engine 214.

[0052] In an example, the method may also include changing a velocity of impact of the droplets on the mesh for ensuring printing of microdroplets on the substrate. The velocity may be changed based on detecting a change in the viscosity of the fluid. For instance, the velocity may be increased on detecting an increase in the viscosity of the fluid. On the other hand, the velocity may be decreased on detecting a decrease in the viscosity of the fluid. Changing the velocity of impact of the droplets on the mesh with the change in the viscosity of the fluid compensates for the variations that may arise in the maximum distance traversed by a fluid jet from amongst the multiple fluid jets ejected upon impact of the droplet of the fluid on the mesh due to the change in the viscosity of the fluid. Accordingly, microdroplets may be printed on the substrate without changing the predetermined value on every change in the viscosity of fluid.

[0053] Although examples of the present subject matter have been described in language specific to methods and/or structural features, it is to be understood that the present subject matter is not limited to the specific methods or features described. Rather, the methods and specific features are disclosed and explained as examples of the present subject matter.