Method and system for delivering build material to a print head - Patents.com

Abstract

A system for supplying liquid material to a nozzle array of a printing system includes a cartridge and a vented subtank. The cartridge has a cartridge outlet and contains the liquid material. The subtank has a subtank inlet configured to receive the cartridge outlet to allow the liquid material to flow through the cartridge outlet by gravity, two inlet ports in the subtank inlet at different heights relative to a liquid level in the subtank, and a subtank outlet. The subtank outlet is sealably connectable to the nozzle array by a tube and has an outlet port below the inlet port.

Description

[Technical field]

[0001] (Related Applications) This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 294,961, filed December 30, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention, in some embodiments thereof, relates to additive manufacturing, and more particularly, but not exclusively, to methods and systems for supplying build material to a print head. [Background technology]

[0003] Additive manufacturing (AM) is generally a process of producing three-dimensional (3D) objects using a computer model of the object. Such processes are used in various fields, such as design-related fields for visualization, demonstration, and mechanical prototyping purposes, and in the field of rapid manufacturing (RM). The basic operation of any AM system consists of slicing a three-dimensional computer model into thin cross sections, converting the results into two-dimensional positional data, and providing that data to a controller to create the three-dimensional structure layer by layer.

[0004] One type of AM is three-dimensional (3D) inkjet printing, a process in which a build material is ejected from a dispensing head with a set of nozzles to deposit a layer onto a support structure. Depending on the build material, the layer can then be cured or solidified.

[0005] Various 3D inkjet printing techniques exist and are disclosed, for example, in U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,479,510, 7,500,846, 7,962,237, and WO 2020 / 194318, the contents of which are incorporated herein by reference. Summary of the Invention

[0006] According to an aspect of some embodiments of the present invention, there is provided a system for supplying liquid material to a nozzle array of a printing system. The system includes a cartridge and a vented subtank. The cartridge has a cartridge outlet and contains the liquid material. The subtank has a subtank inlet configured to receive the cartridge outlet to allow the liquid material to flow through the cartridge outlet by gravity, two inlet ports in the subtank inlet at different heights relative to a liquid level in the subtank, and a subtank outlet. The subtank outlet is sealably connectable to the nozzle array by a tube and has an outlet port below the inlet port.

[0007] According to some embodiments of the present invention, the subtank includes a filter having a base below the inlet port and a top above the inlet port.

[0008] According to some embodiments of the present invention, the cartridge outlet comprises a valve.

[0009] According to some embodiments of the present invention, the sub-tank inlet comprises a valve actuation member for opening the valve upon engagement of the sub-tank inlet with the cartridge outlet.

[0010] According to some embodiments of the invention, the sub-tank comprises a neck below the inlet port, According to some embodiments of the invention, the sub-tank comprises an additional neck above the inlet port.

[0011] According to some embodiments of the present invention, the system comprises a manifold, the sub-tank outlet being sealingly connectable to the nozzle array via the manifold.

[0012] According to an aspect of some embodiments of the present invention, there is provided a system for three-dimensional printing comprising a plurality of liquid material supply systems, each of which comprises a supply system as identified above and optionally, preferably further detailed below, the supply systems sharing a manifold, with a sub-tank outlet of each supply system being connected to a separate manifold inlet. The three-dimensional printing system also comprises a plurality of nozzle arrays, each connected to a separate manifold outlet and configured to eject liquid material received via the manifold, and a computer controller having circuitry configured to operate the nozzle arrays to sequentially eject a plurality of layers in a configuration pattern corresponding to a shape of a three-dimensional object.

[0013] According to some embodiments of the present invention, the manifold is elevated relative to the subtank outlet.

[0014] According to some embodiments of the present invention, the manifold includes a plurality of pressure sensing ports, each in fluid communication with a separate sub-tank outlet, and the system includes a plurality of pressure sensors for sensing pressure at the pressure sensing ports.

[0015] According to some embodiments of the present invention, the computer controller is configured to receive signals from the sensors and calculate the amount of liquid material in each sub-tank based on the signals received from the respective pressure sensors.

[0016] According to some embodiments of the present invention, the computer controller is configured to receive signals from the sensors and calculate a flow rate of liquid material through each nozzle array based on the signals received from the respective pressure sensors.

[0017] According to some embodiments of the invention, the computer controller is configured to identify when the cartridge is empty and, in response to the identification, automatically recalibrate the sensor data corresponding to the signals received from each pressure sensor.

[0018] According to some embodiments of the present invention, the computer controller is configured to determine when a cartridge is empty and, in response to that determination, automatically recalibrate the voltages applied to the respective nozzle arrays.

[0019] According to some embodiments of the present invention, each of the multiple nozzle arrays is connected to a respective manifold outlet by a tube, and the controller is configured to analyze signals received from the respective sensors to identify the presence of air pockets in the tube.

[0020] According to some embodiments of the invention, the system includes a service station controllable by a computer controller and configured to engage the nozzle array and apply a suction force to the nozzle array in response to control signals from the computer controller.

[0021] According to some embodiments of the invention, the controller is configured to operate the service station to perform a priming protocol on each of the nozzle arrays in response to determining the presence of an air pocket.

[0022] According to some embodiments of the invention, the system includes a service station controllable by a computer controller and configured to engage the nozzle array and apply a suction force to the nozzle array in response to control signals from the computer controller.

[0023] According to an aspect of some embodiments of the present invention there is provided a system for three dimensional printing comprising a computerized controller having a plurality of nozzle arrays each configured to dispense liquid material, circuitry configured to operate the nozzle arrays to sequentially dispense a plurality of layers in a configuration pattern corresponding to a shape of a three dimensional object, and a service station controllable by the computerized controller and configured to engage and apply a suction force to the nozzle array in response to control signals from the computerized controller.

[0024] According to some embodiments of the invention, the system comprises a tray, the layers are dispensed onto the tray, and the computer controller is configured to control the vertical position of the tray.

[0025] According to some embodiments of the invention, the computer controller is configured to control the vertical position of the service station to engage the nozzle array, and the tray moves along the vertical direction together with the service station.

[0026] According to some embodiments of the invention, the system comprises a levelling device for levelling the dispensed layer, and during engagement the vertical position of the tray is above the vertical position of the levelling device.

[0027] According to an aspect of some embodiments of the present invention, there is provided a method of priming, comprising providing a system for three-dimensional printing having a liquid material supply system as identified above and optionally, preferably as further detailed below, a manifold formed with a sensing port, sealingly connected to the nozzle array by a first tube and sealingly connected to the sub-tank by a second tube, and a pressure sensor for sensing pressure at the pressure sensing port, comprising: analyzing a signal generated by the pressure sensor to identify an air pocket in the first tube, and priming the system by removing the air pocket in response to the identification.

[0028] According to some embodiments of the present invention, air pockets are removed by applying a suction force to the nozzle array.

[0029] According to some embodiments of the present invention, the method includes positioning the nozzle array above the manifold prior to applying the suction force.

[0030] According to some embodiments of the present invention, the air pockets are removed by squeezing the first tube.

[0031] According to an aspect of some embodiments of the present invention there is provided a print head for three dimensional printing comprising a chamber vertically bounded by a partition having an inlet port and an outlet port, an array of nozzles in fluid communication with the chamber, and a pressure sensor configured to measure pressure below the partition.

[0032] According to some embodiments of the invention, the print head partition has a first surface that engages the first horizontal surface and a second surface that engages the second horizontal surface, the inlet port is in the lowest of the first and second surfaces and the outlet port is in the highest of the first and second surfaces. According to some embodiments of the invention, the height difference between the first and second surfaces is about 5 mm to about 10 mm.

[0033] According to some embodiments of the present invention, the inlet and outlet ports are approximately the same diameter.

[0034] According to some embodiments of the invention, the diameter of each of the inlet and outlet ports is less than 1 mm.

[0035] According to an aspect of some embodiments of the present invention there is provided a system for three dimensional printing comprising a print head having a vertically partitioned chamber, and a computerized controller configured to operate the print head to sequentially eject a plurality of layers in a configuration pattern corresponding to a shape of a three dimensional object, the computerized controller having circuitry configured to estimate a number of operational nozzles in the print head based on signals received from a pressure sensor during ejection.

[0036] According to some embodiments of the invention, the controller is configured to determine an amount of pressure drop below the partition based on the signal, and estimate the number of operational nozzles based on the determined amount of pressure drop.

[0037] According to some embodiments of the invention, the control device is configured to control the supply of liquid material to the chamber to fill at least a volume of the chamber below the partition with liquid material, and to perform the estimation immediately after the supply.

[0038] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0039] Implementation of the method and / or system of the present invention may include performing or completing selected tasks manually, automatically, or a combination thereof. Further, depending on the actual instrumentation and equipment of the method and / or system of the present invention, some selected tasks may be performed by hardware, software, or firmware, or a combination thereof, using an operating system.

[0040] For example, hardware for performing selected tasks according to embodiments of the present invention may be implemented as a chip or circuit. As software, selected tasks according to embodiments of the present invention may be implemented as a number of software instructions executed by a computer using any suitable operating system. In an exemplary embodiment of the present invention, one or more tasks according to exemplary embodiments of the methods and / or systems described herein are performed by a data processor, such as a computing platform for executing a number of instructions. Optionally, the data processor includes volatile memory for storing instructions and / or data, and / or non-volatile storage, such as a magnetic hard disk, and / or removable media for storing instructions and / or data. Optionally, a network connection is also provided. A display and / or a user device, such as a keyboard or mouse, are also optionally provided.

[0041] Some embodiments of the present invention are described herein, by way of example only, with reference to the accompanying drawings. With particular reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for illustrative purposes of embodiments of the invention. In this regard, the description made with the aid of the drawings will make apparent to those skilled in the art how embodiments of the present invention may be practiced. [Brief description of the drawings]

[0042] [Figure 1A] FIG. 1 is a schematic diagram of an additive manufacturing system according to some embodiments of the present invention. [Figure 1B] FIG. 2 is another schematic diagram of an additive manufacturing system according to some embodiments of the present invention. [Figure 1C] FIG. 2 is another schematic diagram of an additive manufacturing system according to some embodiments of the present invention. [Figure 1D] FIG. 2 is another schematic diagram of an additive manufacturing system according to some embodiments of the present invention. [Figure 2A]FIG. 2 is a schematic diagram of a print head according to some embodiments of the present invention. [Figure 2B] FIG. 2 is another schematic diagram of a printhead according to some embodiments of the present invention. [Figure 2C] FIG. 2 is another schematic diagram of a printhead according to some embodiments of the present invention. [Figure 3A] 1 is a schematic diagram demonstrating coordinate transformation according to some embodiments of the present invention. [Figure 3B] FIG. 13 is another schematic diagram demonstrating coordinate transformation according to some embodiments of the present invention. [Figure 4A] FIG. 1 is a schematic diagram of a system for supplying liquid material to a nozzle array of a printing system, according to some embodiments of the present invention. [Figure 4B] FIG. 2 is another schematic diagram of a system for supplying liquid material to a nozzle array of a printing system, according to some embodiments of the present invention. [Figure 4C] FIG. 2 is another schematic diagram of a system for supplying liquid material to a nozzle array of a printing system, according to some embodiments of the present invention. [Figure 4D] FIG. 2 is another schematic diagram of a system for supplying liquid material to a nozzle array of a printing system, according to some embodiments of the present invention. [Figure 4E] FIG. 2 is another schematic diagram of a system for supplying liquid material to a nozzle array of a printing system, according to some embodiments of the present invention. [Figure 5A] FIG. 4C is a schematic diagram of an exemplary three-dimensional printing system in which the system shown in FIGS. 4A-4E may be used, according to some embodiments of the present invention. [Figure 5B] FIG. 4C is another schematic diagram of an exemplary three dimensional printing system in which the system shown in FIGS. 4A-4E can be used, according to some embodiments of the present invention. [Figure 5C] FIG. 4C is a schematic diagram of an exemplary three dimensional printing system in which the system shown in FIGS. 4A-4E may be used, according to some embodiments of the present invention. [Figure 6]13A and 13B show the results of an experiment carried out by the inventors in which the pressure and amount of liquid material aspirated from the sub-tank outlet were monitored. [Figure 7A] FIG. 1 is a schematic diagram illustrating a priming protocol according to some embodiments of the present invention. [Figure 7B] FIG. 13 is another schematic diagram illustrating a priming protocol according to some embodiments of the present invention. [Figure 7C] FIG. 13 is another schematic diagram illustrating a priming protocol according to some embodiments of the present invention. [Figure 7D] FIG. 13 is another schematic diagram illustrating a priming protocol according to some embodiments of the present invention. [Figure 7E] FIG. 13 is another schematic diagram illustrating a priming protocol according to some embodiments of the present invention. [Figure 7F] FIG. 13 is another schematic diagram illustrating a priming protocol according to some embodiments of the present invention. [Figure 8A] FIG. 1 is a schematic diagram illustrating a head exchange protocol according to some embodiments of the present invention. [Figure 8B] FIG. 13 is another schematic diagram illustrating a head exchange protocol according to some embodiments of the present invention. [Figure 8C] FIG. 13 is another schematic diagram illustrating a head exchange protocol according to some embodiments of the present invention. [Figure 9A] FIG. 2 is a schematic diagram illustrating a print head having vertically partitioned chambers according to some embodiments of the present invention. [Figure 9B] FIG. 2 is another schematic diagram illustrating a print head having vertically partitioned chambers according to some embodiments of the present invention. [Figure 9C] FIG. 2 is another schematic diagram illustrating a print head having vertically partitioned chambers according to some embodiments of the present invention. [Figure 10] 1 is a graph of pressure measured by a sensor in mmH2O as a function of time from experiments performed in accordance with certain embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The present invention, in some embodiments thereof, relates to additive manufacturing, and more particularly, but not exclusively, to methods and systems for supplying build material to a print head.

[0044] Before describing at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details set forth in the following description or illustrated by way of examples, as the invention is capable of other embodiments or of being practiced or carried out in various ways.

[0045] The method and system of the present embodiment manufactures a three-dimensional object layer by layer by forming multiple layers in a configured pattern corresponding to the shape of the object based on computer object data. The forming of the layers is optionally and preferably performed by printing, more preferably by inkjet printing. The computer object data can be in any known format, including but not limited to Standard Tessellation Language (STL) or Stereo Lithography Contour (SLC) format, Virtual Reality Modeling Language (VRML), Additive Manufacturing File (AMF) format, Drawing Exchange Format (DXF), Polygon File Format (PLY), 3D Modeling Format (3MF), Object File Format (OBJ), or any other format suitable for Computer Aided Design (CAD).

[0046] As used herein, the term "object" refers to all or a portion of a three-dimensional object.

[0047] Each layer can be formed by an AM device that scans a two-dimensional surface to pattern it. During scanning, the device goes to multiple target locations on the two-dimensional layer, i.e., the surface, and determines for each target location or group of target locations whether the target location or group of target locations should be occupied by a build material formulation and what type of build material formulation should be dispensed thereto. The determination is made according to a computer image of the surface.

[0048] In preferred embodiments of the invention, AM includes three-dimensional printing, more preferably three-dimensional inkjet printing. In these embodiments, the build material is ejected from a print head having one or more nozzle arrays to deposit the build material in layers onto a support structure. In this manner, the AM device ejects the build material at target locations to be occupied, leaving other target locations empty. The device typically includes multiple nozzle arrays, each of which can be configured to eject a different build material. This is typically achieved by providing the print head with multiple fluid channels, separated from one another, each channel receiving a different build material via a separate inlet and conveying it to a different nozzle array.

[0049] Thus, different target locations can be occupied by different build material formulations. Build material formulation types can be divided into two main categories: modeling material formulations and support material formulations. Support material formulations function as a support matrix or support structure to support the object or part of the object during the manufacturing process and / or other purposes, such as providing a hollow or porous object. The support structure can further include modeling material formulation elements, for example to increase support strength.

[0050] Modeling material formulations are compositions that are typically formulated for use in additive manufacturing and that can form three-dimensional objects by themselves, i.e., without the need to mix or combine with any other substances.

[0051] The final three-dimensional object is made from the modeling material formulation, a combination of modeling material formulations, or a combination of modeling and support material formulations, or modifications thereof (e.g., after curing), all of which are well known to those skilled in the art of solid freeform fabrication.

[0052] In some exemplary embodiments of the invention, an object is manufactured by dispensing two or more different modeling material formulations, each material formulation being dispensed from a different nozzle array (belonging to the same or different print head) of the AM device. In some embodiments, two or more such nozzle arrays dispensing different modeling material formulations are both located in the same print head of the AM device. In some embodiments, the nozzle arrays dispensing the different modeling material formulations are located in separate print heads, e.g., a first nozzle array dispensing a first modeling material formulation is located in a first print head and a second nozzle array dispensing a second modeling material formulation is located in a second print head.

[0053] In some embodiments, the nozzle array that ejects the modeling material formulation and the nozzle array that ejects the support material formulation are both located in the same print head, in some embodiments, the nozzle array that ejects the modeling material formulation and the nozzle array that ejects the support material formulation are located in separate print heads.

[0054] A representative, non-limiting example of a system 110 suitable for AM of an object 112 according to some embodiments of the present invention is shown in Figure 1A. The system 110 includes an additive manufacturing apparatus 114 having a dispensing unit 16 that includes multiple print heads. Each head preferably includes one or more arrays 122 of nozzles typically attached to an orifice plate 121 through which a liquid build material formulation 124 is dispensed, as shown in Figures 2A-2C described below.

[0055] Preferably, but not necessarily, the device 114 is a three-dimensional printing device, in which case the print head is a print head and the build material formulation is dispensed via inkjet technology. This is not necessarily the case, as in some applications the additive manufacturing device may not need to use three-dimensional printing technology. Representative examples of additive manufacturing devices contemplated in accordance with various exemplary embodiments of the present invention include, but are not limited to, fused deposition modeling devices and molten material formulation deposition devices.

[0056] Each print head is optionally, but preferably, supplied with material via one or more build material formulation reservoirs, which may optionally include a temperature control unit (e.g., temperature sensor and / or heating device) and a material formulation level sensor. To eject the build material formulation, a voltage signal is applied to the print head, which selectively deposits droplets of the material formulation through the print head nozzles, similar to, for example, piezoelectric inkjet printing technology. Another example is a thermal inkjet print head. This type of head has a heater element in thermal contact with the build material formulation, and the voltage signal activates the heater element to heat the build material formulation and form a gas bubble therein. The gas bubble creates pressure in the build material formulation, causing a droplet of the build material formulation to be ejected from the nozzle. Piezoelectric and thermal print heads are known to those skilled in the art of solid freeform fabrication. For either type of inkjet print head, the ejection speed of the head depends on the number of nozzles, the type of nozzle, and the applied voltage signal speed (frequency).

[0057] Optionally, the total number of ejection nozzles or nozzle arrays is selected such that half of the ejection nozzles are designated to eject the support material formulation and half of the ejection nozzles are designated to eject the modeling material formulation. That is, the number of nozzles ejecting the modeling material formulation is the same as the number of nozzles ejecting the support material formulation. In the representative example of FIG. 1A, four print heads 16a, 16b, 16c, and 16d are shown. Each head 16a, 16b, 16c, and 16d has a nozzle array. In this example, heads 16a and 16b may be designated for modeling material formulation(s) and heads 16c and 16d may be designated for support material formulations. Thus, head 16a can eject one modeling material formulation, head 16b can eject another modeling material formulation, and both heads 16c and 16d can eject support material formulations. In alternative embodiments, for example, heads 16c and 16d may be combined into a single head having two nozzle arrays for depositing the support material formulation. In further alternative embodiments, any one or more print heads may have two or more nozzle arrays for depositing two or more material formulations, for example two nozzle arrays for depositing two different modeling material formulations, or two nozzle arrays for depositing one modeling material formulation and one support material formulation, with each formulation deposited through a different array or different number of nozzles.

[0058] However, this is not intended to limit the scope of the invention, and it should be understood that the number of modeling material formulation print heads (modeling heads) and the number of support material formulation print heads (support heads) may be different. Typically, the number of nozzle arrays discharging modeling material formulations, the number of nozzle arrays discharging support material formulations, and the number of nozzles in each array are selected to provide a predetermined ratio a between the maximum discharging speed of the support material formulation and the maximum discharging speed of the modeling material formulation. The value of the predetermined ratio a is preferably selected such that in each layer formed, the height of the modeling material formulation is equal to the height of the support material formulation. A typical value of a is about 0.6 to about 1.5.

[0059] As used herein, the term "about" refers to ±10%.

[0060] For example, when a=1, the overall dispensing rate of the support material formulation is typically the same as the overall dispensing rate of the modeling material formulation when all nozzle arrays are operational.

[0061] The apparatus 114 may, for example, comprise M modeling heads, each having m arrays of p nozzles, and S support heads, each having s arrays of q nozzles, such that M×m×p=S×s×q. Each of the M×m modeling arrays and the S×s support arrays may be fabricated as separate physical units, and may be assembled and disassembled from the group of arrays. In this embodiment, each such array may optionally, but preferably, comprise its own temperature control unit and material formulation level sensor, and receive an individually controlled voltage for its operation.

[0062] The apparatus 114 can further include a solidification device 324, which can include any device configured to emit light, heat, etc., that can harden the deposited material formulation. For example, the solidification device 324 can include one or more radiation sources, which can be, for example, ultraviolet, visible, or infrared lamps, or other electromagnetic radiation sources, or electron beam sources, depending on the modeling material formulation used. In some embodiments of the invention, the solidification device 324 serves to cure or solidify the modeling material formulation.

[0063] In addition to the solidification device 324, the device 114 optionally, but preferably, includes an additional radiation source 328 for solvent evaporation. The radiation source 328 optionally, but preferably, generates infrared light. In various exemplary embodiments of the invention, the solidification device 324 includes a radiation source that generates ultraviolet light, and the radiation source 328 generates infrared light.

[0064] In some embodiments of the invention, the device 114 includes a cooling system 134, such as one or more fans.

[0065] The print head(s) and radiation source are preferably mounted in a frame or block 128, which is preferably operable to move back and forth over a tray 360, which serves as a working surface. In some embodiments of the invention, the radiation source is mounted in the block and configured to follow the print head and at least partially cure or solidify the material formulation just dispensed by the print head. The tray 360 is arranged horizontally. According to common convention, an XYZ Cartesian coordinate system (i.e., a Cartesian coordinate system) is selected such that the XY plane is parallel to the tray 360. The tray 360 is preferably configured to move vertically (along the Z direction), typically downwards. In various exemplary embodiments of the invention, the device 114 further comprises one or more leveling devices 32, such as, for example, rollers 326. The leveling devices 326 serve to regulate, flatten and / or establish the thickness of a newly formed layer before forming a successive layer thereon. The leveling device 32 preferably includes a waste collector 136 for collecting excess material mix generated during leveling. The waste collector 136 may include any mechanism for delivering the material mix to a waste tank or waste cartridge.

[0066] In use, the print heads of the units 16 move in a scanning direction, referred to herein as the X-direction, and selectively dispense build material formulations in a predetermined configuration as they pass over the tray 360. The build material formulations typically include one or more support material formulations and one or more modeling material formulations. The pass of the print heads of the units 16 is followed by curing of the modeling material formulations by the radiation source 126. A reverse pass of the head back to the starting point of the just deposited layer may result in additional dispensing of the build material formulations according to a predetermined configuration. During the forward and / or reverse passes of the print heads, the layers thus formed may be leveled by a leveling device 32, which preferably follows the path of the forward and / or reverse movement of the print heads. When the print heads return to their starting points along the X-direction, they may move to another position along an indexing direction, referred to herein as the Y-direction, and continue to build the same layer by reciprocating movements along the X-direction. Alternatively, the print head may move in the Y direction between forward and reverse moves, or after two or more forward-reverse moves. The series of scans performed by the print head to complete a single layer is referred to herein as a single scan cycle.

[0067] Once a layer is completed, the tray 360 is lowered in the Z direction to a predetermined Z level depending on the desired thickness of the next layer to be printed. This procedure is repeated to build up the three-dimensional object 112 layer by layer.

[0068] In another embodiment, the tray 360 may be displaced in the Z direction within the layer between forward and reverse passes of the print head of unit 16. Such Z displacement is performed to allow the leveling device to contact the surface in one direction and prevent contact in the other direction.

[0069] This embodiment contemplates the use of a liquid material formulation supply system 330, which includes one or more liquid material reservoirs or cartridges 430, to supply liquid material to the print head. The supply system 330 can be used in an AM system such as system 110, where the liquid material in each reservoir is a build material.

[0070] The controller 20 controls the manufacturing equipment 114 and, optionally, preferably also the supply system 330. The controller 20 typically includes electronic circuitry configured to perform control operations. The controller 20 preferably communicates with a computer 24, which transmits digital data regarding manufacturing instructions based on computer object data, such as CAD configurations represented on a computer-readable medium in a format such as Standard Tessellation Language (STL) format. Typically, the controller 20 controls the voltage applied to each print head or each nozzle array and the temperature of the build material formulation at each print head or each nozzle array.

[0071] Once the manufacturing data is loaded into the control unit 20, the controller can operate without user intervention. In some embodiments, the controller 20 receives additional input from an operator, for example using the computer 24 or using a user interface 116 in communication with the controller 20. The user interface 116 can be of any type known in the art, such as, but not limited to, a keyboard, a touch screen, etc. For example, the controller 20 can receive one or more build material formulation types and / or attributes as additional inputs. Attributes include, but are not limited to, color, characteristic distortion and / or transition temperature, viscosity, electrical properties, magnetic properties, etc. Other attributes and groups of attributes are also contemplated.

[0072] Another representative, non-limiting example of a system 10 suitable for AM of an object according to some embodiments of the present invention is shown in Figures 1B-1D, which show a top view (Figure 1B), a side view (Figure 1C), and an isometric view (Figure 1D) of the system 10.

[0073] In this embodiment, the system 10 includes a tray 12 and a plurality of inkjet print heads 16, each having one or more nozzle arrays, each having one or more isolated nozzles. Material used for three-dimensional printing is supplied to the heads 16 by a build material supply system 330 having one or more liquid material reservoirs or cartridges 430, as described in further detail herein. The tray 12 may have the shape of a disk or may be annular. Non-circular shapes are contemplated, as long as they are rotatable about a vertical axis.

[0074] The tray 12 and head 16 are optionally, but preferably, mounted to allow relative rotational movement between the tray 12 and head 16. This can be accomplished by (i) configuring the tray 12 to rotate about a vertical axis 14 relative to the head 16, (ii) configuring the head 16 to rotate about a vertical axis 14 relative to the tray 12, or (iii) configuring both the tray 12 and the head 16 to rotate at different rotational speeds (e.g., rotation in opposite directions) about the vertical axis 14. Some embodiments of the system 10 below are described with particular emphasis on configuration (i), in which the tray is a rotating tray configured to rotate about a vertical axis 14 relative to the head 16, but it should be understood that configurations (ii) and (iii) of the system 10 are also contemplated by the present application. Any of the embodiments of the system 10 described herein can be adjusted to be applicable to either configuration (ii) or configuration (iii), and one of ordinary skill in the art would know how to make such adjustments given the details provided herein.

[0075] In the following description, the direction parallel to the tray 12 and pointing outward from the axis 14 will be referred to as the radial direction r, the direction parallel to the tray 12 and perpendicular to the radial direction r will be referred to herein as the azimuthal direction φ, and the direction perpendicular to the tray 12 will be referred to herein as the vertical direction z.

[0076] The radial direction r in system 10 defines an index direction y in system 110, and the azimuthal direction φ defines a scan direction x in system 110. Thus, in this specification, the radial direction is interchangeably referred to as the index direction, and the azimuthal direction is interchangeably referred to as the scan direction.

[0077] As used herein, the term "radial position" refers to a position on or above tray 12 that is a particular distance from axis 14. When the term is used in relation to a print head, the term refers to a position of the head that is a particular distance from axis 14. When the term is used in relation to a point on tray 12, the term corresponds to any point belonging to a locus of points that defines a circle whose radius is a particular distance from axis 14 and whose center is on axis 14.

[0078] As used herein, the term "azimuth position" refers to a position on or above tray 12 that is at a particular azimuthal angle relative to a given reference point. A radial position thus refers to any point belonging to a locus of linear points that form a particular azimuthal angle relative to a reference point.

[0079] As used herein, the term "vertical position" refers to a position on a plane that intersects the vertical axis 14 at a particular point.

[0080] The tray 12 serves as a build platform for three-dimensional printing. The working area on which one or more objects are printed is typically, but not necessarily, smaller than the total area of ​​the tray 12. In some embodiments of the invention, the working area is annular. The working area is indicated by the reference numeral 26. In some embodiments of the invention, the tray 12 rotates continuously in the same direction throughout the formation of the object, and in some embodiments of the invention, the tray 12 reverses its direction of rotation (e.g., to oscillate) at least once during the formation of the object. The tray 12 is optionally, but preferably, removable. Removal of the tray 12 can be performed for maintenance of the system 10, or to replace the tray before printing a new object, as desired. In some embodiments of the invention, the system 10 includes one or more different replacement trays (e.g., a kit of replacement trays), with two or more trays designated for different types of objects (e.g., different weights), different modes of operation (e.g., different rotation speeds), etc. Replacement of the tray 12 can be performed manually or automatically, as desired. When automated exchange is used, the system 10 includes a tray exchanger 36 configured to remove the tray 12 from its position beneath the head 16 and replace it with a replacement tray (not shown). In the representative diagram of Figure 1B, the tray exchanger 36 is shown as a drive 38 having a movable arm 40 configured to pull the tray 12, although other types of tray exchangers are contemplated.

[0081] Exemplary embodiments of print head 16 are illustrated in Figures 2A-2C. These embodiments may be employed in any of the AM systems described above, including, but not limited to, system 110 and system 10.

[0082] 2A-2B show a print head 16 having one nozzle array 22 (FIG. 2A) and two nozzle arrays 22 (FIG. 2B). The nozzles in the arrays are preferably arranged linearly along a straight line. The print head 16 is supplied with liquid material, which it ejects through the nozzle array 22 in response to voltage signals applied by a controller for the printing system. The head 16 is supplied with liquid material, which is the build material formulation.

[0083] In embodiments where a particular print head has two or more linear nozzle arrays, the nozzle arrays may optionally, and preferably, be parallel to one another. When a print head has two or more nozzle arrays (e.g., FIG. 2B), all arrays on the head can be supplied with the same build material formulation, or at least two arrays on the same head can be supplied with different build material formulations.

[0084] If a system similar to system 110 is employed, all print heads 16 are optionally, but preferably, oriented along an index direction with their positions along the scan direction offset from one another.

[0085] When a system similar to system 10 is employed, all print heads 16 are optionally, but preferably, oriented radially (parallel to the radial direction) with their azimuthal positions offset from one another. Thus, in these embodiments, the nozzle arrays of the different print heads are not parallel to one another, but rather at an angle to one another, the angle being approximately equal to the azimuthal offset between the respective heads. For example, one head may be oriented radially and located at an azimuthal position φ1, while another head may be oriented radially and located at an azimuthal position φ2. In this example, the azimuthal offset between the two heads is φ1-φ2, and the angle between the linear nozzle arrays of the two heads is also φ1-φ2.

[0086] In some embodiments, two or more print heads can be assembled into a block of print heads, where the print heads in the block are generally parallel to one another. A block including several inkjet print heads 16a, 16b, 16c is shown in FIG. 2C.

[0087] In some embodiments, the system 10 includes a stabilizing structure 30 positioned below the head 16, such that the tray 12 is between the stabilizing structure 30 and the head 16. The stabilizing structure 30 can serve to prevent or reduce vibrations of the tray 12 that may occur while the inkjet print head 16 is in operation. In configurations in which the print head 16 rotates about axis 14, the stabilizing structure 30 also preferably rotates so that the stabilizing structure 30 is always directly below the head 16 (with the tray 12 between the head 16 and the tray 12).

[0088] The tray 12 and / or print head 16 are optionally configured to move, preferably parallel to the vertical axis 14, along a vertical direction z to vary the vertical distance between the tray 12 and the print head 16. In configurations in which the vertical distance is varied by moving the tray 12 along the vertical direction, the stabilizing structure 30 also preferably moves vertically with the tray 12. In configurations in which the vertical position of the tray 12 remains fixed and the vertical distance is changed by the head 16 along the vertical direction, the stabilizing structure 30 is also maintained in a fixed vertical position.

[0089] Vertical motion can be established by vertical drive 28. Once a layer is completed, the vertical distance between tray 12 and head 16 can be increased by a predetermined vertical interval (e.g., tray 12 is lowered relative to head 16) depending on the desired thickness of the next layer to be printed. This procedure is repeated to build the three-dimensional object layer by layer.

[0090] The operation of inkjet print head 16, and optionally, and preferably, the operation of one or more other components of system 10, such as tray 12, is controlled by a controller 20. The controller may include electronic circuitry and a non-volatile storage medium readable by the circuitry that stores program instructions that, when read by the circuitry, cause the circuitry to perform control operations, as described in more detail below.

[0091] The control device 20 can also communicate with a host computer 24, which transmits digital data related to manufacturing instructions based on the computer object data. The computer object data is in the form of, for example, Standard Tessellation Language (STL) or Stereolithography Contour (SLC) format, Virtual Reality Modeling Language (VRML), Additive Manufacturing File (AMF) format, Drawing Exchange Format (DXF), Polygon File Format (PLY), or any other format suitable for computer-aided design (CAD). The object data format is usually structured according to a Cartesian coordinate system. In these cases, the computer 24 preferably performs a procedure to convert the coordinates of each slice in the computer object data from a Cartesian coordinate system to a polar coordinate system. The computer 24 optionally transmits manufacturing instructions using the converted coordinate system. Alternatively, the computer 24 can transmit manufacturing instructions using the original coordinate system provided by the computer object data, in which case the conversion of coordinates is performed by the circuitry of the control device 20.

[0092] The transformation of coordinates allows three-dimensional printing on a rotating tray. In a non-rotating system with a stationary tray, the print head typically moves back and forth along a straight line, usually above the stationary tray. In such a system, if the head has a uniform ejection speed, the print resolution is the same at any point on the tray. In the system 10, unlike a non-rotating system, not all nozzles of the head point cover the same distance on the tray 12 at the same time. The transformation of coordinates is optionally, but preferably, performed to ensure equal amounts of excess material mix at different radial positions. A representative example of the transformation of coordinates according to some embodiments of the present invention is shown in Figures 3A-3B, which show three slices of an object, each slice corresponding to a manufacturing instruction for a different layer of the object. Figure 3A shows the slices in a Cartesian coordinate system, and Figure 3B shows the same slices after applying a coordinate procedure transformation to each slice.

[0093] Typically, controller 20 controls the voltages applied to each component of system 10 based on manufacturing instructions and based on stored program instructions as described below.

[0094] Typically, controller 20 controls print head 16 while tray 12 rotates to eject droplets of the build material formulation layer by layer onto tray 12 to print a three-dimensional object, etc.

[0095] The system 10 optionally, but preferably, includes one or more radiation sources 18, which may be, for example, ultraviolet lamps, visible light lamps, infrared lamps, or other electromagnetic radiation sources, or electron beam sources, depending on the modeling material formulation used. The radiation sources may include any type of radiation emitting device, including, but not limited to, light emitting diodes (LEDs), digital light processing (DLP) systems, resistive lamps, and the like. The radiation sources 18 serve to cure or solidify the modeling material formulation. In various exemplary embodiments of the invention, the operation of the radiation sources 18 is controlled by a controller 20, which may activate and deactivate the radiation sources 18, and may optionally also control the amount of radiation generated by the radiation sources 18.

[0096] In some embodiments of the invention, the system 10 further comprises one or more leveling devices 32, which can be manufactured as rollers 326 or blades. The leveling devices 32 serve to prepare the newly formed layer before forming a successive layer thereon. In some embodiments, the leveling devices 32 have the shape of a conical roller arranged with its axis of symmetry 34 inclined with respect to the surface of the tray 12 and with its surface parallel to the surface of the tray. This embodiment is shown in a side view of the system 10 (FIG. 1C).

[0097] The conical roller may have the shape of a cone or a frustum of a cone.

[0098] The opening angle of the conical roller is preferably selected such that the ratio between the radius of the cone at any position along its axis 34 and the distance between that position and the axis 14 is constant. This embodiment allows the roller 32 to efficiently flatten the layer, since any point p on the surface of the roller while it rotates has a linear velocity that is proportional (e.g., the same) as the linear velocity of the tray at a point located directly below point p. In some embodiments, the roller has the shape of a truncated cone with height h and radius R1 at its closest distance from the axis 14 and radius R2 at its furthest distance from the axis 14. The parameters h, R1, and R2 satisfy the relationship R1 / R2=(Rh) / h, where R is the furthest distance of the roller from the axis 14 (e.g., R can be the radius of the tray 12).

[0099] The operation of the leveling device 32 is optionally, but preferably, controlled by the controller 20. The controller can activate and deactivate the leveling device 32 and, optionally, control its position along a vertical direction (parallel to the axis 14) and / or along a radial direction (parallel to the tray 12, toward or away from the axis 14).

[0100] In some embodiments of the invention, the print head 16 is configured to move back and forth relative to the tray along a radial direction r. These embodiments are useful when the length of the nozzle array 22 of the head 16 is less than the radial width of a working area 26 on the tray 12. The movement of the head 16 along the radial direction is optionally, but preferably, controlled by the controller 20.

[0101] Some embodiments contemplate the manufacture of objects by ejecting different material formulations from different nozzle arrays (belonging to the same or different printheads). These embodiments provide, among other things, the ability to select material formulations from a given number of material formulations and to define the desired combination of selected material formulations and their properties. According to the present embodiment, the spatial location of deposition of each material formulation comprising a layer is defined to allow the occupation of different three-dimensional spatial locations by different material formulations, or to allow the occupation of substantially the same three-dimensional location or adjacent three-dimensional locations by two or more different material formulations, allowing a spatial combination after deposition of the material formulations within the layer, thereby forming a composite material formulation at each location or locations.

[0102] Any post-deposition combination or mixing of modeling material formulations is contemplated. For example, when a particular material formulation is dispensed, it may maintain its original properties. However, when dispensed simultaneously with other modeling material formulations dispensed in the same or nearby location, a composite material formulation may be formed that has a different property or properties than the dispensed material formulation.

[0103] In some embodiments of the present invention, the system dispenses a digital material formulation for at least one of the layers.

[0104] The term "digital material blend" as used herein and in the art refers to the combination of two or more material blends at the pixel or voxel level, such that pixels or voxels of different material blends intersect with each other across an area. Such digital material blends may exhibit new properties that are influenced by the selection of material blend types and / or the selection of the ratios and relative spatial distribution of the two or more material blends.

[0105] As used herein, a "voxel" of a layer refers to a physical three-dimensional elementary volume within the layer that corresponds to a single pixel in a bitmap that describes the layer. The size of a voxel is approximately equal to the size of the area that would be formed by the build material if the build material were dispensed at a location corresponding to the respective pixel, flattened, and solidified.

[0106] Thus, the present embodiments allow for the deposition of a wide range of combinations of material formulations at various portions of the object, depending on the properties desired to characterize each portion of the object, and allow for the production of objects that may be composed of multiple different combinations of material formulations.

[0107] Further details of the principles and operation of an AM system suitable for this embodiment are described in U.S. Pat. No. 9,031,680, the contents of which are incorporated herein by reference.

[0108] Conventional printing systems, particularly three-dimensional printing systems, employ build material supply systems to supply build material to the nozzle array. Such conventional material supply systems typically employ a controllable pump that pumps build material from a cartridge of build material to the nozzle array. The inventors have found that build material can be supplied to the nozzle array without the use of a pump, with material flow being established by a combination of gravity and under-pressure in the print head to which the nozzle array is attached. The inventors have found that such a pump-less supply simplifies the printing system, thus significantly reducing the manufacturing costs of the system.

[0109] 4A-4E are schematic diagrams of a system 400 for supplying a liquid material to a nozzle array of a printing system, according to some embodiments of the present invention. The system 400 can be incorporated into a two-dimensional printing system in which the liquid material can be a printing ink. The system 400 can also be incorporated into a three-dimensional printing system in which the liquid material can be a build material. For example, the system 400 can be incorporated into the system 10 or system 110 described above. Additional exemplary three-dimensional printing systems in which the system 400 can be employed are described below with reference to FIGS. 5A-5C.

[0110] Referring to Figure 4A, the system 400 comprises a cartridge 402, which contains a liquid material to be dispensed (not shown, see Figure 5A), and comprises a cartridge outlet 404. Except for the cartridge outlet 404, the cartridge 402 is preferably completely sealed from all sides. An exploded view of a cross section of the cartridge 402 along a vertical axis according to some embodiments of the invention is shown diagrammatically in Figure 4B. In the illustrated embodiment, the cartridge outlet 404 comprises a valve 410, which is configured to prevent liquid material from exiting the cartridge 402 through the cartridge outlet 404 when the cartridge outlet 404 faces downwards. FIG. 4B illustrates the valve 410 as a ball valve that is restricted to move only along its central axis within the cartridge outlet 404, such that when the ball is at its lowest position within the cartridge outlet 404, the outlet port 412 of the cartridge outlet 404 is closed, and when the ball is not at its lowest position within the cartridge outlet 404, the outlet port 412 of the cartridge outlet 404 is open, allowing liquid to drip out of or into the cartridge 402. Because the ball is heavier than the liquid, when the cartridge outlet 404 is facing downward, the ball is at its lowest position, preventing liquid from dripping out of the cartridge outlet 404. However, the valve 410 need not be a ball valve. This embodiment contemplates any type of valve at the cartridge outlet 404. Additionally, in some embodiments of the present invention, the cartridge outlet 404 is provided without a valve.

[0111] Referring back to FIG. 4A, the system 400 further comprises a subtank 406 having a subtank inlet 408. As shown in the exploded view of FIG. 4A, the subtank inlet 408 is configured to receive the cartridge outlet 404 to allow the liquid material to flow through the cartridge outlet 404 by gravity. In an embodiment in which the cartridge outlet 404 comprises a valve 410 (FIG. 4B), the subtank inlet 408 comprises a valve actuating member 414 for opening the valve 410 upon engagement between the subtank inlet 408 and the cartridge outlet 404. For example, if the valve 410 is a ball movable along a central axis of the cartridge outlet 404, the valve actuating member 414 can be provided as a protrusion above the inlet port of the subtank inlet 408 such that upon engagement between the subtank inlet 408 and the cartridge outlet 404, the protrusion enters the cartridge outlet 404 and displaces the ball from the outlet port 412 of the cartridge outlet 404, thus opening a flow passage from the cartridge 402 into the subtank 406.

[0112] Reference is now made to FIG. 4C, which shows a close-up exploded view of the cross section of the subtank 406 along its vertical axis, according to some embodiments. The subtank 406 also comprises a subtank outlet 428, which is sealably connectable to the nozzle array by a tube (not shown, see FIG. 5A), and has an outlet port 430 at the bottom of the internal cavity of the subtank 406. Preferably, the subtank 406 is vented to the atmosphere by a non-sealed inlet cover 432 or a dedicated vent 434 (see FIG. 5A), so that the pressure above the liquid level in the subtank 406 is always atmospheric pressure. As shown in FIG. 4C, the two inlet ports 416 and 418 are provided in the subtank inlet 408 at different heights, either with respect to the liquid level in the subtank 406 (if the subtank 406 contains a liquid material) or with respect to the base 420 of the subtank 406. The outlet port 430 is below both the inlet ports 416 and 418.

[0113] Typically, the inlet ports 416 and 418 are provided at the ends of two lumens 422, 424 of different lengths that lead into the subtank inlet 404. Preferably, the two lumens 422, 424 are embodied as a double lumen conduit 426, as shown in Figure 4C, although embodiments in which the lumens 422 and 424 are separate from one another are also contemplated.

[0114] Configuring the two inlet ports at different heights of the subtank inlet 408 is advantageous because it ensures that the cartridge 402 supplies liquid material to the subtank 406 without the need to use an electronic control mechanism, as described below. Initially, when the subtank 406 is empty and the cartridge 402 is attached to the subtank inlet 408 with the outlet port 412 of the cartridge outlet 404 facing downwards, liquid material enters the subtank inlet 418 from the cartridge outlet 404. At this stage, material can enter the cavity of the subtank 406 through either or both of the ports 416 and 418. As liquid enters through these ports, air is drawn upwards into the cartridge 402 through the ports 416 and 418 to replace the empty volume in the cartridge 402. When the liquid level passes the lower port 418, material can still enter the cavity of the subtank 406 through the ports 416 and 418. However, at this stage, air is drawn upward only through the upper port 416 because port 418 is submerged below the liquid level and there is no air path to port 418. Once the liquid level reaches the upper port 416, the flow of material into the subtank 406 is interrupted because there is no air path to the cartridge 402. From this stage onwards, whenever an air gap forms between the liquid level and the upper port 416, additional liquid immediately enters the subtank 406 without intervention by the electronic controller.

[0115] 4D and 4E are schematic diagrams showing an exploded view (FIG. 4D) and a cross section along a vertical axis of the subtank 406 after assembly (FIG. 4E) in an embodiment in which a filter assembly 436 is disposed within a cavity of the subtank 406. The filter assembly 436 serves to filter the liquid material before it leaves the subtank 406 through a port 430 at the outlet 428 (not shown in FIGS. 4D and 4E, see FIG. 4C). The filter assembly 436 comprises a filter holder 437 having a base 438 and a top 440, and a filter 439 within the filter holder 437. Although not to be considered limiting, in the configuration shown in FIG. 4D, the filter 439 is disposed on the inner surface of the holder 437, such that material entering the subtank 406 through the subtank inlet 408 passes through the filter 439 and then exits the filter holder 437 from a side opening formed on the holder 437, since the base 438 is typically closed. The top 440 is preferably, but not necessarily, an open top. When the filter assembly 436 is in the internal cavity of the subtank 406, the base 438 is below the inlet ports 416 and 418, and the top 440 is above the inlet ports 416 and 418. In conventional printing systems, a filter is provided on a tube that provides a sealed connection to the nozzle array of the printing system. The inventors have found that such a configuration can affect the pressure in the nozzle array. Disposing the filter assembly 436 in the cavity of the subtank 406 according to some embodiments of the present invention is advantageous because such a configuration does not require a filter to be disposed on a tube that connects to the nozzle array. Since the pressure above the liquid level in the sub-tank 406 is atmospheric pressure, the filter assembly 436 does not affect the pressure in the nozzle array.

[0116] In some embodiments of the invention, the subtank 406 is provided with a neck 442 below the inlet ports 416, 418. In the region of the neck 442, the horizontal cross-sectional area of ​​the cavity of the subtank 406 is smaller than in the regions directly below and above the neck 442. The horizontal cross-section of the subtank 406 preferably has an additional constriction, e.g. in the form of an additional neck 443, e.g. typically at the top of the subtank 406, preferably above the inlet port 416. The inventors have found that providing the subtank 406 with necks 442 and 443 is advantageous as it allows for extracting various types of information regarding the state of the system, as will be further detailed in the Examples section below.

[0117] Reference is now made to Figures 5A-5C, which are schematic illustrations of a three dimensional printing system 500 employing material supply system 400, according to some embodiments of the present invention.

[0118] Apart from material supply system 400, system 500 includes tray 12, one or more nozzle arrays formed on an orifice plate of print head 16, and leveling device 32, as described in further detail herein. In the illustration of FIG. 5A, it is noted that leveling device 32 is behind print head 16. System 500 also includes a computer controller 20 configured to perform at least some of the operations described above with respect to systems 10 and 110.

[0119] The subtank 406 of the material supply system 400 is supplied with the liquid material 502 from the cartridge 402, as further detailed herein, and a sealed fluid communication 504 between the subtank outlet 428 and the head 16 ensures that the liquid material 502 is supplied to one or more of the nozzle arrays of the head 16 by the negative pressure of the head 16. Preferably, the fluid communication 504 includes a manifold 506 that establishes fluid communication with the nozzle array of the head 16 by a first tube 508 and with the subtank outlet 428 by a second tube 510. The manifold 506 can be part of the supply system 400 or the printing system 500. Preferably, but not necessarily, at least the first tube 508 has a flexible wall. The manifold 502 is preferably elevated with respect to the subtank 406 and with respect to the head 16.

[0120] Although FIG. 5A illustrates a printing system 500 employing only one material supply system 400, the system 500 does not necessarily have to employ one material supply system 400, since typically the system 500 will have multiple liquid material supply systems 400, each supplying liquid material to a different nozzle array of the print head 16. Furthermore, all nozzle arrays can be on the same print head, or more than one nozzle array can be attached to different print heads. However, in any of these embodiments, it is sufficient to have a single manifold 506 having multiple manifold inlet ports 510a, 510b for connecting to the respective multiple sub-tank outlets 428, and multiple manifold outlet ports 508a, 508b for connecting to the respective multiple nozzle arrays. In some embodiments of the invention, the outlet ports of the manifold 506 are controllable so that fluid communication between the manifold 506 and the nozzle array can be disconnected and re-established as needed. These embodiments are particularly useful for priming the system, as described in more detail in the Examples section below. Control can be manual or by the control device 20, as desired.

[0121] In some embodiments of the invention, the manifold 506 includes one or more pressure detection ports 512, each in fluid communication with a separate subtank outlet 428, and the system 500 includes one or more pressure sensors 514 for detecting the pressure at the pressure detection ports 512.

[0122] The computerized controller 20 receives signals from the sensors 514 and analyzes these signals to extract one or more parameters indicative of the state of the system 500. For example, in some embodiments of the present invention, the controller 20 calculates the amount of liquid material in each sub-tank based on the signals received from the respective pressure sensors. In some embodiments of the present invention, the controller 20 calculates the flow rate of liquid material through each nozzle array based on the signals received from the respective pressure sensors. In some embodiments of the present invention, the controller 20 identifies when each cartridge is empty. In some embodiments of the present invention, the controller 20 automatically recalibrates the sensor data corresponding to the signals received from the respective pressure sensors in response to identifying that a cartridge is empty. In some embodiments of the present invention, the controller 20 automatically recalibrates the voltage applied to each nozzle array in response to identifying that a cartridge is empty. In some embodiments of the present invention, the controller 20 analyzes the signals received from the respective sensors to identify the presence of an air pocket in the tube 508 connecting to the respective nozzle array. A preferred protocol for extracting such parameters is described in the Examples section below.

[0123] In three-dimensional inkjet printing, it is customary to periodically perform a procedure known as purging. Purging procedures are typically performed when changing the build material cartridge supplying the head to remove previous build material from the channels of the head or other fluid paths in the system. Purging procedures are also often performed during the printing process to ensure that the nozzle array of the head 16 remains functional and to prevent clogging. Traditionally, purging procedures involve moving the head to a service station and increasing pressure in the head with a pump to force all excess build material through the nozzle array.

[0124] The inventors have discovered a technique that allows purging to be performed without increasing the pressure in the head. In some embodiments, the system 500 includes a service station 516 that is controllable by the controller 20 and configured to engage the nozzle array of the head 16 and apply suction to the nozzle array in response to a control signal from the controller 20. Preferably, the suction is applied by a dedicated pump 518 that is decoupled from the system 400 and the fluid communication 504. For clarity of presentation, the piping between the pump 518 and the service station 516 is not shown, but one of ordinary skill in the art provided with the details described herein would know how to connect a suction line between the pump 518 and the service station 516. Thus, in this embodiment, purging is achieved by reducing the pressure outside the head (when engaged with the suction service station) rather than by increasing the pressure in the head.

[0125] In the system shown in Figures 5A and 5B, the tray 12 and service station 516 are mounted on a support platform 520 configured to move vertically by a vertical drive mechanism 522 actuated by a motor 524. Thus, in these embodiments, both the tray 12 and the service station move vertically together. Preferably, the service station 516 is mounted at a height relative to the platform 520 that is lower than the height of the tray 12. The tray 12 is slidably mounted to the platform 520 by tracks 526 that allow the tray 12 to move along a scanning direction x. The head 16 is slidably connected to a horizontal chassis portion 528 (not shown in Figure 5A, see Figure 5B) that allows the head 16 to move along an indexing direction y. It will be appreciated that the tray 12 may alternatively move along the indexing direction y and the head 16 may alternatively move along the scanning direction x.

[0126] Thus, an aspiration procedure according to some embodiments of the present invention includes moving the head 16 (e.g., along an index direction) until it is directly above the service station 516, moving the tray 12 (e.g., along a scan direction) until the service station is within the field of view of the head 16, raising the platform 520 together with the tray 12 and service station 516 by a vertical drive mechanism 522 until the service station 516 engages the nozzle array(s) of the head 16, and activating suction (e.g., by powering a pump 518) to extract liquid material from the nozzle array(s). Because the tray 12 is at a higher level than the service station 516, the vertical position of the tray 12 during aspiration is above the vertical position of the nozzle array(s), and optionally, preferably above the vertical position of the leveling device 32.

[0127] The aspiration procedure of this embodiment can be used, for example, to perform the purging procedure described above when changing the build material cartridge supplying the head and before placing a new cartridge. The aspiration procedure of this embodiment can also be used to perform a priming protocol on each nozzle array in response to identifying the presence of an air pocket in the tube 508 connecting to the respective nozzle array.

[0128] An alternative suction procedure can be performed that is particularly useful for removing air pockets from the tubes 508 while the nozzle array(s) are in a vertical position above the manifold 506. Thus, in some embodiments of the present invention, the system 500 includes an additional service station 530 configured to receive the print head 16 at a vertical position above the position of the manifold 506. For example, the additional service station 530 can be disposed at a vertical position above the manifold 506 and can include a platform 532 for receiving the head 16 at that vertical position. The additional service station 530 can also include a suction device 534 configured to engage the nozzle array(s) of the head 16 upon receipt by the platform 532. Referring to FIG. 5C, in use of the additional service station 530, the print head 16 is disengaged from the horizontal housing portion 528 while maintaining the head 16 in fluid communication with the manifold 506 by the tubes 508. When disengaged from the housing, the head 16 is preferably placed on the platform 532 such that the nozzle array of the head 16 faces upward. The suction device 534 is then engaged, preferably from above, with the nozzle array(s) of the head 16 and activated to apply a suction force to the nozzle array(s).

[0129] 9A-9C are schematic diagrams of the print head 16 in an embodiment in which the print head 16 is vertically partitioned. The inventors have found that such partitioning allows for a convenient and simple way to estimate the amount of operational and defective nozzles in the nozzle array.

[0130] Traditionally, operational and defective nozzles have been detected by performing a nozzle test procedure in which the ejection head ejects test droplets into a waste container. The container is weighed and the weight is analyzed to determine if the nozzle array has defective nozzles based on the difference in the weight of the container before and after ejection. The inventors have found that the amount of operational and defective nozzles can be estimated without the need to weigh the waste container in the manner described below.

[0131] The print head 16 shown in Figures 9A-9C includes a chamber 600 vertically partitioned by a partition 606 having an inlet port 602 and an outlet port 604. The chamber 600 is designed to contain a liquid material, such as a build material in liquid form. In use, the chamber 600 is typically at a negative pressure so that it can receive liquid material from a supply system (e.g., system 400 or 330) via a material supply port 622 at the top 620 of the chamber 600. During purging or after the chamber is emptied, the pressure increases as air enters the chamber. The negative pressure can be maintained by a pump (not shown) in fluid communication with a vacuum port 624 and, optionally, controlled by a controller of the printing system (e.g., controller 20 of systems 10 or 110 or 500), preferably.

[0132] The head 16 also includes a nozzle array 122 in fluid communication with the chamber 600, and a pressure sensor 608 configured to measure pressure in a lower portion 610 of the chamber 600 below the partition 606. In Figures 9A-9C, the sensor 608 is illustrated as an elongated rod whose lower portion functions as a pressure sensing element.

[0133] Three exemplary configurations of the divider 606 are shown in Figures 9A-9C. Figure 9B shows a configuration in which the divider 606 is planar and engages with the same plane it intersects. Figures 9A and 9C show an alternative configuration in which the divider 606 has a first surface 612 that engages with a first horizontal surface 614 and a second surface 616 that engages with a second horizontal surface 618. The inlet port 602 is preferably in the lowest of these two surfaces (surface 616 in this example) and the outlet port 604 is in the highest of these two surfaces (surface 612 in this example). In Figure 9A, the inlet 602 and outlet 604 are provided in the form of gaps between their respective surfaces and the sidewall of the chamber 600. In Figure 9C, the inlet 602 and outlet 604 are formed in the respective surfaces of the divider 606. When the partition 606 comprises a surface 616 and a surface 612 which engage the flat surfaces 618 and 614, the height difference between the surfaces 616 and 612 is preferably between about 5 mm and about 10 mm, for example 7 mm.

[0134] The inlet 602 serves to allow liquid material to enter the lower portion 610 of the chamber 600 after entering the upper portion 620 via the feed port 622. Air in the lower portion 610 is exhausted upwards through the outlet port 604. Because air is lighter than the liquid material, it is advantageous to use a divider with two surfaces as illustrated in Figures 9A and 9C, so that the air will accumulate on the top surface of the divider and be more likely to be exhausted through the outlet port. However, the inventors have found that air can also be exhausted using a flat divider as illustrated in Figure 9B.

[0135] The inlet port 602 and the outlet port 604 are preferably of approximately the same diameter. A typical diameter for these ports is less than 1 mm, such as about 0.2 mm to about 1 mm, such as about 0.7 mm. The advantage of ports 602 and 604 having such a diameter is that it amplifies the relationship between the pressure in the lower portion 610 of the chamber 600 and the amount of build material ejected from the nozzles in the array 122. The inventors have found that by carefully selecting the diameter of ports 602 and 604, changes in pressure in the lower portion 610 are detectable even when only a few nozzles, or even a single nozzle, ejects a single drop of material.

[0136] If the viscosity of the liquid in the upper portion 620 is too high to allow the liquid to pass through the inlet port 602, a purge operation can be performed as described in further detail herein to reduce the pressure in the lower portion 610 and facilitate filling of the lower portion 610 with the liquid material.

[0137] As demonstrated in the Examples section below, the inventors have found that the pressure below the partition during ejection of liquid material through the nozzles in the array 122 is indicative of the number of operational nozzles in the array (as well as the number of non-operating or defective nozzles, since the total number of nozzles in the array 122 is generally known). Thus, according to some embodiments of the present invention, a controller of the printing system (e.g., controller 20 of systems 10 or 110 or 500) estimates the number of operational nozzles in the print head 16 based on a signal received from the pressure sensor 608 during ejection. For example, the controller 20 can determine an amount of pressure drop dP below the partition 606 based on the signal from the sensor 608, and estimate the number of operational nozzles based on the determined amount of pressure drop dP. For example, the controller can access a computer-readable medium that stores a look-up table whose entries relate pressure drop to the number of operational or non-operating nozzles.

[0138] In some embodiments of the invention, the estimation of the number of working nozzles (or equivalently the number of non-working or defective nozzles) is performed during a test procedure of the print head, which is performed when the lower part 610 of the chamber 600 is filled with liquid material. In these embodiments, liquid material is supplied to the chamber 600 to fill the lower part 610 before the test procedure. However, this does not necessarily have to be the case, since the inventors have found that the number of working nozzles can also be estimated during the printing process of the three-dimensional object by monitoring the signal from the sensor 608. In this case, it is not necessary to interrupt the printing process of the object to estimate the number of working or defective nozzles.

[0139] The terms "comprises," "comprising," "includes," "including," "having" and their conjugations mean "including, but not limited to."

[0140] The term "consisting of" means "including and limited to."

[0141] The term "consisting essentially of" means that a composition, method, or structure may include additional components, steps, and / or moieties, but only if the additional components, steps, and / or moieties do not materially alter the basic and novel characteristics of the claimed composition, method, or structure.

[0142] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" can include a plurality of compounds, including mixtures thereof.

[0143] Throughout this application, various embodiments of the invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Thus, the description of a range should be considered to have specifically disclosed all possible subranges and individual numerical values ​​within that range. For example, description of a range such as 1-6 should be considered to have specifically disclosed subranges such as 1-3, 1-4, 1-5, 2-4, 2-6, 3-6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0144] Whenever a numerical range is given herein, it is meant to include any recited numbers (fractional or integer) within the given range. The phrases "ranging / ranges between" a first designated number and a second designated number, and "ranging / ranges from" a first designated number "to" a second designated number, are used interchangeably herein and are meant to include the first and second designated numbers and all fractional and integer numbers therebetween.

[0145] It will be understood that certain features of the invention are described for clarity in the context of separate embodiments, but may also be provided in combination in a single embodiment. Conversely, various features of the invention that are described for brevity in the context of a single embodiment may also be provided separately or in any suitable subcombination, or as appropriate to any other described embodiment of the invention. Certain features described in the context of various embodiments should not be considered essential features of those embodiments, unless the embodiment is inoperable without those elements.

[0146] Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples. EXAMPLES

[0147] Reference is now made to the following examples which, together with the above descriptions, illustrate certain non-limiting embodiments of the invention.

[0148] [Protocol for calculating the volume of liquid ingredients]

[0149] Since the horizontal cross-sectional area of ​​the cavity is smaller at the vertical positions of the necks 442 and 443 of the sub-tank 406, it is possible to identify the time when the liquid level passes these vertical positions by monitoring the pressure measured by the sensor 514 over time and identifying an abrupt change in the monitored pressure. Figure 6 shows the results of an experiment performed by the inventors in which the pressure measured by the sensor 514 and the amount of liquid aspirated through the sub-tank outlet 428 were monitored over time. The two arrows in Figure 6 indicate the identified time points where there was an abrupt change in the monitored pressure. Arrow 1 corresponds to the time when the liquid level was at neck 443 and arrow 2 corresponds to the time when the liquid level was at neck 442.

[0150] Absolute vertical position H of neck 442 n and the absolute vertical position H of the neck 443 in Given, the pressure sensor reading P when the liquid level is at neck 442 n and the pressure sensor reading P when the liquid level is at neck 443. in Using the difference between these values, the liquid level H(P) in the subtank 406 at any time can be obtained as a linear function of the pressure sensor reading P according to the following equation:

[0151] H(P)=[(H in -H n ) / (P in -P n )]((PP n )+H n

[0152] Preferably, the measurement of P is carried out while the nozzle array is not operating.

[0153] [Protocol for calculating flow rate]

[0154] If we denote by ΔP the difference in pressure reading between when the nozzle array is discharging a constant flow of material and when the nozzle array is not operating, we get:

[0155] ΔP=a×dw / dt

[0156] where dw / dt is the flow rate to be determined and a is the slope parameter. The slope parameter can be calculated by operating the nozzle array at a constant flow between times corresponding to arrows 1 and 2 in FIG. 6 and measuring the time difference between these times. This measured time difference is called T 1,2 Then, the gradient parameter a can be calculated as follows:

[0157] a=(P in -P n ) / [W / T]

[0158] where W is the volume of liquid between neck 442 and neck 443. Once the gradient parameters have been calculated, the flow rate can be determined as a function of the aforementioned pressure difference ΔP according to the following equation:

[0159] dw / dt=ΔP / a

[0160] The flow rate per nozzle can be calculated as (dw / dt) / N, where N is the number of nozzles in the array.

[0161] [Protocol for recalibrating the nozzle array voltage]

[0162] To recalibrate the nozzle array voltage, the nozzle array is operated at different voltages and the flow rate dw / dt is measured for each voltage. This provides a look-up table of flow rate as a function of voltage applied to the nozzle array. The voltage used to fabricate the three-dimensional object can then be selected based on the desired flow rate.

[0163] Preferably, the cartridge 402 is removed from the subtank 406 before running this protocol to reduce the amount of noise.

[0164] [Protocol for detecting defective nozzles by monitoring flow rate]

[0165] To detect defective nozzles, the flow rate dw / dt is periodically monitored. Deviations in the flow rate from values ​​dictated by the recalibration protocol described above indicate the presence of one or more defective nozzles in the nozzle array. To identify defective nozzles in the array, the nozzles of the array are operated in series and the flow rate per nozzle is monitored. Nozzles whose flow rate per nozzle deviates from values ​​dictated by the recalibration protocol described above can be defined as defective nozzles.

[0166] [Protocol for identifying air pockets in tube 508]

[0167] An air pocket within the tube 508 can be identified whenever operation of the nozzle array does not cause any change in the pressure reading of the sensor 514 .

[0168] [Priming Protocol]

[0169] The priming protocol is preferably performed when an air pocket in the tube 508 is identified. The priming protocol is preferably performed automatically, but can be performed manually in some embodiments of the invention. The priming protocol is described with reference to Figures 7A-7F. The protocol begins by engaging the service station 516 with the nozzle array(s) of the head 16 (Figure 7A). The protocol continues by applying suction to the nozzle array(s) while monitoring the pressure with the sensor 514. This action continues until there is no change in the pressure reading. After this action, the tube 510 is filled with liquid (Figure 7B). The protocol continues by controlling the manifold outlet 508a connected to the tube 508 to block flow through the manifold outlet 508a (Figure 7C). The protocol continues by continuing the suction to the nozzle array. This action continues until the tube 508 collapses (Figure 7D). The protocol continues by controlling the manifold outlet 508a connected to the tube 508 to allow flow through the manifold outlet 508a, and then continuing the suction to the nozzle array(s). This action continues until the tube 508 is filled with liquid (FIG. 7E). The protocol continues by disengaging the service station 516 with the nozzle array(s) from the head 16 (FIG. 7F).

[0170] [Head replacement protocol]

[0171] A first head replacement protocol will be described with reference to Figures 8A-8C. The protocol begins by controlling the manifold outlet 508a connected to tube 508 to block flow through manifold outlet 508a. At this stage, both tube 510 and tube 508 are filled with liquid (Figure 8A). The protocol continues by removing the print head from the system (Figure 8B) and then installing a replacement print head (Figure 8C).

[0172] In a second head replacement protocol, the head is disengaged from the housing portion while maintaining the head 16 in fluid communication with the manifold 506 via the tubes 508. Once disengaged from the housing, the head 16 is placed on the platform 532. The head is replaced while on the platform 532 and the replacement head is installed on the housing. If there are air pockets in the tubes 508, suction is applied to the nozzle array(s) of the replacement head before the replacement head is installed on the housing (see FIG. 5C). Once the replacement head is installed on the housing, suction is terminated.

[0173] [Protocol for detecting defective nozzles by monitoring the pressure in the head]

[0174] 9A-9C, as the nozzles in the array 122 dispense liquid material, the amount of liquid material in the lower portion 610 of the chamber 600 decreases and the liquid in the upper portion 620 flows downward through the inlet port 602. At the same time, air is expelled upward through the outlet port 604. Contributions to the pressure in the lower portion 610 include contributions from the viscosity of the liquid, contributions from the density of the liquid, and contributions from the surface tension of the liquid. Thus, changes in the rate at which the liquid flows into the lower portion 610 of the chamber 600 affect the pressure in the lower portion 610.

[0175] Experiments were conducted using the print head shown in Figure 9C, dispensing liquid material with a viscosity of about 6.5 cps at a dispensing rate of about 15 cc / min (192 nozzles). The signal from the pressure sensor 608 was monitored during dispensing and while filling the lower portion 610 between dispensing batches, with a different number of nozzles activated in each batch. The sampling rate was 3.17 Hz, which corresponds to a period of about 315 ms per sample.

[0176] 10 is a graph of pressure (in mmH2O) measured by sensor 608 as a function of time. The number of active nozzles for each batch is indicated on the graph ("noz." is an abbreviation for "nozzle"). As shown, the amount of pressure drop dP measured by the pressure sensor in the lower part of the chamber below the partition is indicative of the number of operating nozzles. In particular, the absolute value of dP decreases as a function of the number of operating nozzles.

[0177] While the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.

[0178] It is the intention of the applicants that all publications, patents, and patent applications mentioned herein are incorporated herein by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated herein by reference. Furthermore, citation or identification of any reference in this application should not be construed as an admission that such reference is available as prior art to the present invention. To the extent section headings are used, they should not be construed as necessarily limiting. Additionally, any priority documents of this application are incorporated herein by reference in their entirety.

Claims

1. 1. A system for supplying liquid material to a nozzle array of a printing system, comprising: a cartridge having a cartridge outlet and containing the liquid material; a vented subtank having a subtank inlet configured to receive the cartridge outlet to allow the liquid material to flow through the cartridge outlet by gravity, two inlet ports in the subtank inlet at different heights relative to a liquid level in the subtank, and a subtank outlet sealably connectable to the nozzle array by a tube and having an outlet port below the inlet port; A system comprising:

2. 2. The system of claim 1, wherein the subtank comprises a filter having a base below the inlet port and a top above the inlet port.

3. The system of claim 1 or claim 2, wherein the cartridge outlet comprises a valve.

4. 4. The system of claim 3, wherein the subtank inlet includes a valve actuation member for opening the valve upon engagement of the subtank inlet with the cartridge outlet.

5. The system of any one of claims 1 to 4, wherein the sub-tank comprises a neck below the inlet port.

6. A system according to any preceding claim, comprising a manifold, the sub-tank outlet being sealingly connectable to the nozzle array via the manifold.

7. The system of claim 6 , wherein the manifold is elevated relative to the subtank outlet.

8. 1. A system for three dimensional printing, comprising: a plurality of liquid material supply systems each comprising the system of claim 6, the liquid material supply systems sharing the manifold, the sub-tank outlet of each liquid material supply system being connected to a separate manifold inlet; a plurality of nozzle arrays, each connected to a separate manifold outlet and configured to eject the liquid material received through the manifold; a computer controlled device having circuitry configured to operate the nozzle array to sequentially eject a plurality of layers in a configuration pattern corresponding to a shape of a three-dimensional object; A system comprising:

9. The system of claim 8 , wherein the manifold is elevated relative to the subtank outlet.

10. 10. The system of claim 9, wherein the manifold comprises a plurality of pressure sensing ports, each in fluid communication with a separate subtank outlet, and the system comprises a plurality of pressure sensors for sensing pressure at the pressure sensing ports.

11. 11. The system of claim 10, wherein the computer controller is configured to receive signals from the pressure sensors and calculate an amount of liquid material in each sub-tank based on the signal received from each pressure sensor.

12. 12. The system of claim 10 or claim 11, wherein the computer controller is configured to receive signals from the pressure sensors and calculate a flow rate of liquid material through each nozzle array based on the signals received from the respective pressure sensors.

13. A system according to any one of claims 10 to 12, wherein the computer controller is configured to identify when the cartridge is empty and, in response to said identifying, automatically recalibrate sensor data corresponding to signals received from each pressure sensor.

14. A system according to any one of claims 10 to 13, wherein the computer controller is configured to identify when the cartridge is empty and, in response to said identifying, automatically recalibrate the voltages applied to the respective nozzle arrays.

15. 15. The system of claim 10, wherein each of the plurality of nozzle arrays is connected to a respective manifold outlet by a tube, and the computer controller is configured to analyze signals received from respective sensors to identify the presence of air pockets in the tubes.

16. 16. The system of claim 15, comprising a service station controllable by the computer controller and configured to engage the nozzle array and apply a suction force to the nozzle array in response to a control signal from the computer controller.

17. 17. The system of claim 16, wherein the computer controller is configured to operate the service station to perform a priming protocol on each nozzle array in response to the identifying the presence of the air pocket.

18. 15. A system according to any one of claims 8 to 14, comprising a service station controllable by the computer controller and configured to engage the nozzle array and apply a suction force to the nozzle array in response to a control signal from the computer controller.

19. A system according to any one of claims 16 to 18, comprising a tray onto which the plurality of layers are dispensed, and wherein the computer controller is configured to control the vertical position of the tray.

20. 20. The system of claim 19, wherein the computer controller is configured to control a vertical position of the service station to engage the nozzle array, and the tray moves along a vertical direction with the service station.

21. 21. The system of claim 20, further comprising a leveling device for leveling the dispensed layer, and wherein during said engagement, a vertical position of said tray is above a vertical position of said leveling device.

22. 1. A system for three dimensional printing, comprising: an array of nozzles, each configured to eject a liquid material; a computer controlled device having circuitry configured to operate the nozzle array to sequentially eject a plurality of layers in a configuration pattern corresponding to a shape of a three-dimensional object; a service station controllable by the computer controller and configured to engage the nozzle array and apply a suction force to the nozzle array in response to a control signal from the computer controller; A system for three dimensional printing comprising:

23. 23. The system of claim 22, comprising a tray onto which the layers are dispensed, and wherein the computer controller is configured to control a vertical position of the tray.

24. 24. The system of claim 23, wherein the computer controller is configured to control a vertical position of the service station to engage the nozzle array, and the tray moves along a vertical direction with the service station.

25. 25. The system of claim 24, further comprising a leveling device for leveling the dispensed layer, and wherein during said engagement, a vertical position of said tray is above a vertical position of said leveling device.

26. 1. A method of priming comprising: Provide a system for three-dimensional printing having a liquid material supply system, the liquid material supply system comprising: the system of claim 1; a manifold formed with a pressure detection port, the manifold being sealingly connected to the nozzle array by a first tube and to a sub-tank by a second tube; and a pressure sensor for detecting a pressure at the pressure detection port; analyzing a signal generated by the pressure sensor to identify air pockets within the first tube; priming the system by removing the air pocket in response to said identifying; A method comprising:

27. 27. The method of claim 26, wherein removing the air pockets comprises applying a suction force to the nozzle array.

28. 28. The method of claim 27, comprising positioning the nozzle array above the manifold prior to applying the suction force.

29. 27. The method of claim 26, wherein removing the air pocket comprises compressing the first tube.

30. 1. A print head for three dimensional printing, comprising: a chamber vertically bounded by a partition having an inlet port and an outlet port; a nozzle array in fluid communication with the chamber; a pressure sensor configured to measure a pressure below the partition; A print head comprising:

31. 31. The printhead of claim 30, wherein the partition has a first surface that engages a first horizontal surface and a second surface that engages a second horizontal surface, the inlet port being in a lowermost one of the first and second surfaces and the outlet port being in a highermost one of the first and second surfaces.

32. 32. The print head of claim 31, wherein the height difference between the first surface and the second surface is from about 5 mm to about 10 mm.

33. A printhead according to any one of claims 30 to 32, wherein the inlet port and the outlet port are of substantially the same diameter.

34. A print head according to any one of claims 30 to 33, wherein the inlet and outlet ports each have a diameter of less than 1 mm.

35. 1. A system for three dimensional printing, comprising: A print head according to any one of claims 30 to 34, a computer controller configured to operate the print head to sequentially eject a plurality of layers in a configuration pattern corresponding to a shape of a three-dimensional object, the computer controller having circuitry configured to estimate a number of operational nozzles in the print head based on signals received from the pressure sensor during the ejection; A system comprising:

36. 36. The system of claim 35, wherein the computer controller is configured to determine an amount of pressure drop across the partition based on the signal, and estimate the number of operational nozzles based on the determined amount of pressure drop.

37. 36. The system of claim 35, wherein the computer controller is configured to control the supply of liquid material to the chamber to fill at least a certain volume of the chamber below the partition with liquid material, and to perform the estimation immediately after the supply.

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