Fluid system and method for supplying a fluid to a print head in a 3D printer

Abstract

The invention, which relates to a fluid system (13) and a method for supplying a fluid (5) to a printhead (1) in a 3D printer, is based on the objective of providing a solution that ensures a reliable supply of fluid (5) to the printheads (1) of the 3D printer via the fluid system (13) and reliably prevents leakage from the printheads (1) of the 3D printer. This objective is achieved by the arrangement of a first pressure regulating unit (24) in the fluid line (22), wherein the first pressure regulating unit (24) comprises a first throttle valve (25) and a first pump (26) arranged parallel to the first throttle valve (25), bypassing the first throttle valve (25).

Description

[0001] The invention relates to a fluid system for supplying a fluid to a printhead in a 3D printer, wherein a distribution element for storing and distributing the fluid is connected to a printhead tank via a fluid line and wherein the printhead is arranged to be connected to a printhead tank via a fluid inlet channel.

[0002] The invention also relates to a method for supplying a fluid to a printhead in a 3D printer, in which the fluid is first supplied to a printhead tank from a distributor element via a fluid line and in which the fluid is subsequently supplied to the printhead from the printhead tank.

[0003] In particular, the invention relates to a fluid system and a method for supplying a fluid to a print head in a 3D printer, wherein a fluid such as a binder is applied through nozzles of the metering units arranged in a print head to a layer of a particulate building material produced on a build area of ​​the 3D printer in order to achieve selective solidification during the production of a 3D structure in the 3D printer.

[0004] It is well known that 3D printing, or a 3D printing process, is used to manufacture individual or serial components, workpieces, or molds. In such printing processes, three-dimensional components or workpieces are built up layer by layer.

[0005] The assembly process is computer-controlled and uses one or more liquid or solid materials according to predefined dimensions and shapes. Specifications for the components or workpieces to be printed can be provided, for example, by computer-aided design (CAD) systems.

[0006] The printing of 3D structures or 3D components involves physical or chemical hardening processes or a melting process within a particulate building material. Materials used for such 3D printing processes include plastics, synthetic resins, ceramics, unconsolidated sediments such as minerals or sands, and metals.

[0007] Various manufacturing process sequences are known for the implementation of 3D printing processes.

[0008] However, several of these processes include the following exemplary process steps: • Partial or full-surface application of particulate building material, also referred to as particle material or powdered building material, onto a so-called building site to form a layer of unsolidified particle material, wherein the partial or full-surface application of particulate building material includes spreading and smoothing the particulate building material; • Selective solidification of the applied layer of unsolidified particulate building material in predetermined areas, for example by selective compaction, printing or application of treatment agents, such as a fluid or binder, using a print head or the use of a laser or electron beams; • Repeating the preceding process steps in another layer level to build up the component or workpiece layer by layer. For this purpose, it is intended that the component or workpiece, which is built up or printed layer by layer on the build area, is lowered by one layer level or layer thickness at a time, or that the 3D printing device is raised by one layer level or layer thickness relative to the build area before a new layer is applied partially or completely; • Subsequent removal of loose, unsolidified particulate building material surrounding the manufactured component or workpiece.

[0009] Particulate building materials are generally understood to be an accumulation of individual particles of a substance or mixture, each particle having a three-dimensional shape. Since these particles are predominantly round, oval, or elongated, it is possible to specify an average diameter for such a particle, which is usually in the range of 0.01 mm to 0.4 mm. Such particulate building materials can exhibit fluid properties.

[0010] Various methods for producing a 3D structure, in particular for selectively solidifying the applied layer of non-solidified particulate building material in predetermined sub-areas, are known from the prior art.

[0011] For example, after applying particulate building material to a build platform to create a 3D structure, a binder or fluid is selectively applied, metered, or printed onto the applied and solidified particulate building material using a suitable device, such as a print head. This binder or fluid, in contact with the particulate building material, causes selective solidification and thus the formation of the 3D structure. From this point forward, only the term "fluid" will be used.

[0012] Such suitable devices for selectively applying or metering the fluid onto the particulate building material typically comprise several individual metering units or individual dispensers, each with at least one corresponding nozzle, the metering units usually being arranged in a common assembly, such as a print head.

[0013] Multiple dosing units can be arranged, for example, in a row or a matrix. In the matrix arrangement, multiple dosing units are positioned in each row and multiple dosing units in each column of the printhead matrix.

[0014] The individual metering units have channels for guiding or supplying the fluid, through which the fluid is transported in only one direction to the respective nozzle of the metering unit. Such a channel for supplying the fluid is also referred to as a supply channel.

[0015] Since the nozzles typically lack a seal for secure closure, it is designed to prevent unintentional leakage of the fluid supplied via the feed channel from the nozzle of the metering unit by creating at least no overpressure, or preferably a vacuum, relative to atmospheric pressure. This vacuum, acting on the liquid fluid at least in the area of ​​the metering units, retains the fluid at the nozzle outlet and prevents unintentional leakage through the printhead nozzles.

[0016] When a dosing process is carried out in a dosing unit, in which a droplet of fluid is dispensed from the nozzle of the dosing unit towards the particulate building material, the fluid outlet area outside the nozzle essentially forms the beginning of the droplet to be dispensed. Such a dosing process is effected by a means that generates a mechanical force, which can be located inside the dosing unit in the immediate vicinity of the nozzle. Such a means could, for example, be a piezoelectric element, which operates according to the piezoelectric effect and deforms when an electrical voltage is applied. A pneumatically operated element, a diaphragm, or a cam could also be used to generate such a mechanical force.The agent thus generates a mechanical force which is transferred to the fluid resting above the nozzle and forces a portion of the fluid through the nozzle, creating a metered droplet which is then applied to the particulate building material.

[0017] It is known from the prior art that the formation of the fluid exit area outside the nozzle cannot be prevented. Consequently, a portion of the fluid in the nozzle area is exposed to the ambient atmosphere. This leads to chemical reactions with the ambient atmosphere in this area and to changes in the fluid's properties.

[0018] Such changes in properties can include alterations in the fluid's composition, moisture loss, density, viscosity, surface tension, oxidation, and other factors. These changes can lead to hardening or adhesion in the fluid exit area at the nozzle and outside the nozzle, which is difficult to remove. Consequences include nozzle narrowing, inaccurate dispensing, and changes in the shape of the dispensed droplet. These effects negatively impact the printed image and, consequently, the shape, accuracy, and physical properties of the 3D-printed component.

[0019] German patent DE 10 2019 008 328 A1 discloses a dosing unit in a print head of a 3D printer and a method for dosing a fluid in a 3D printer. The problem to be solved is to specify a dosing unit in a print head of a 3D printer and a method for dosing a fluid in a 3D printer, thereby achieving improved quality and reliability in the dosing of a fluid by means of a dosing unit.

[0020] The solution involves a metering unit that has both a supply channel and a discharge channel. This allows the fluid to be kept in motion within the metering unit and to flow through it. This flow also encompasses the fluid outlet area that forms at the nozzle. Thus, the fluid is kept in constant motion both within the metering unit and at the outlet, preventing changes in the fluid's properties known from the prior art, such as moisture loss, changes in density, changes in viscosity, changes in surface tension, oxidation, and others, since the fluid is continuously renewed or replaced.

[0021] To supply the dispensing units arranged in a series or matrix within the printhead with the binding agent, the printhead, within a so-called printhead unit, is connected to a printhead tank via a supply channel and a discharge channel, thus ensuring the circulation of the fluid within the printhead. It is also known that several printheads within a printhead unit are connected to the printhead tank in a parallel circuit via the supply channel and the discharge channel.

[0022] It is also known that the printhead tank is connected to a reservoir tank via a fluid line. This reservoir tank holds the fluid for the 3D printer, which is then supplied to the printhead tank.

[0023] In 3D printer systems with multiple printhead units, it is common practice to install a distribution element between the reservoir and the printhead reservoirs. Such a distribution element has at least one inlet that connects it to the reservoir, through which the fluid is drawn from the reservoir to the distribution element. The distribution element typically has several outlets, each with a fluid line connecting it to different printhead reservoirs in different printhead units.

[0024] In this description, a fluid system is understood to be the entire area in which the fluid is stored and transported until it leaves the system via a nozzle of a metering unit. Thus, the fluid system includes, for example, the storage tank, the distribution element, several printhead tanks, several printheads, and all lines arranged between these components for transporting the fluid. It is clear to a person skilled in the art that the fluid system may include further components, such as pumps, valves, and others, to enable the process of supplying a fluid to a printhead in a 3D printer.

[0025] For example, EP 3 177 453 B1 discloses a printhead, its use, and a 3D printing method. The problem to be solved is to provide a printhead that avoids the stated disadvantages of the prior art.

[0026] The solution involves a printhead particularly suited for the selective application of printing fluid to a particle material during the fabrication of three-dimensional models using layer-by-layer technology. A printhead reservoir for holding the printing fluid is connected to printhead modules, through which the printing fluid is pumped into chambers and directed to the nozzles of a printhead. To fill the printhead reservoir, it is connected via tubing to an intermediate tank, which can be connected via a valve block to one of several reservoirs for the printing fluid.

[0027] Furthermore, a metallic support is provided to which the printhead modules are attached. Plastic fluid guides are also provided to direct the printing fluid through the metallic support; these guides are positioned by the metallic support. Thus, the metallic components for positioning are omitted in such a way that plastic components can be used for fluid guidance, which do not directly affect the positioning of the printhead.

[0028] Thus, EP 3 177 453 B1 describes a system which has at least one reservoir, one distribution element and several printhead units, wherein each printhead unit contains a printhead tank and a printhead module with several nozzles.

[0029] Since the printheads used in 3D printers are open systems, also known as thermodynamically open systems, a problem according to the state of the art is to precisely adjust the pressure of the fluid in the fluid system.

[0030] Such open systems are characterized by the fact that the system can exchange fluids with its environment. Using the example of a printhead in a fluid system for supplying fluid to a printhead in a 3D printer, this means that the fluid in the fluid system, especially the fluid in the area of ​​the nozzles of the printhead's metering units, can escape into the environment via the nozzles, or that ambient air can enter the fluid system via the nozzles.

[0031] If the fluid pressure in the fluid system exceeds the pressure of the surrounding air (atmosphere) around the print head, the fluid will unintentionally escape from the nozzles. This leads to defects in the 3D structure buildup, as the unintentionally escaping fluid causes selective and faulty solidification of the particulate building material. Furthermore, fluid is lost from the fluid system.

[0032] If the fluid pressure in the fluid system is lower than the pressure of the ambient air (atmosphere) surrounding the printhead, ambient air, along with any contaminants or other materials contained therein, can unintentionally enter the fluid system through the nozzles. This leads to contamination of the fluid within the system and to errors in the build-up of the 3D structure due to the contaminated fluid, which prevents proper selective solidification of the particulate building material.

[0033] The ambient air surrounding the printhead is also referred to as the atmosphere. In this description, the term atmosphere refers to a gaseous layer containing various gases, located above the Earth's surface, which envelops the planet Earth.

[0034] It is known that the average atmospheric pressure at sea level is 101,325 Pa (Pascals), which is approximately 1.013 bar or 1013 mbar. A 3D printer located at sea level is therefore exposed to an atmospheric pressure of 1013 mbar, which acts on the printer from all sides, including the nozzles in the print head.

[0035] This means that for a 3D printer operating at sea level, the fluid pressure in the fluid system at the nozzles of the print head must not exceed 1013 mbar at the interface between the fluid and the ambient air or atmosphere to prevent unwanted fluid leakage from the nozzles. In other words, the pressure at the interface must be nearly equal to the pressure of the fluid and the atmospheric pressure. Alternatively, the fluid pressure at the interface can be less than 1013 mbar within a certain tolerance, which is also referred to as negative pressure, and reliably prevent unwanted fluid leakage. The fluid pressure at the interface can also be greater than 1013 mbar if this value is also within the tolerance.

[0036] Such a tolerance, which ensures that no ambient air, contaminants contained in that ambient air, or other materials unintentionally enter the fluid system through the nozzles, is, for example, in the range of less than 3 mbar, and particularly less than 1 mbar. This value depends, for example, on capillary forces (adhesion), the static pressure of the fluid, the dynamic pressure of the fluid in both the lines and the printhead, movement of the entire printhead unit, and the surface tension of the fluid.

[0037] To supply the distributor element from the reservoir tank, as well as the printhead tanks within the printhead units, it is necessary to pressurize the fluid, at least in these internal areas of the fluid system. This overpressure can range from 0.5 bar to 3.0 bar, relative to the atmospheric pressure surrounding the 3D printer. For example, assuming an atmospheric pressure of 1013 mbar around the printhead, the overpressure in the area between the reservoir tank and the printhead tank would have an absolute value between 1513 mbar and 4013 mbar.

[0038] This overpressure is necessary, for example, to supply the distributor element from the storage tank, since the storage tank does not necessarily have to be located at a height sufficiently above the distributor element. The height difference between the storage tank and the distributor element would have to be large enough to allow the fluid to be pumped from the upper storage tank to the lower distributor element solely by the force of gravity acting on the fluid.

[0039] This overpressure is also necessary, for example, to supply the printhead tanks of the printhead units from the distributor element, since the distributor element cannot always be positioned at a sufficient height above the printhead tanks in the 3D printer to convey the fluid in sufficient quantity and speed using only the force of gravity acting on the fluid.

[0040] Since it is necessary to pump predetermined quantities of fluid through the small-diameter connecting pipes within a given time frame, appropriate means of generating overpressure in the fluid system are required. This is because if the height difference is too small to ensure sufficient gravity-driven fluid transport from top to bottom, an adequate flow rate cannot be achieved.

[0041] Additionally, filters, sensors, or friction losses in the lines lead to a pressure drop in the fluid system, which can only be compensated for by a corresponding overpressure. Pressure fluctuations requiring compensation also arise from movements of the entire print head unit in the 3D printer above the build area during the printing process.

[0042] Therefore, within the fluid system, it is necessary in some areas to pressurize the fluid, while at the interface between the fluid and the ambient air or atmosphere, at the nozzles of the fluid system's printheads, the fluid pressure must be adjusted to the current atmospheric pressure. The fluid pressure set in this way can have a tolerance of, for example, ±0.5 mbar.

[0043] Another problem stemming from the current state of the art is that 3D printers are not only operated at sea level with an atmospheric pressure of 1013 mbar. If the 3D printer is operated in an area significantly above sea level, it is surrounded by a different atmospheric pressure, as atmospheric pressure is known to decrease with increasing altitude.

[0044] While in the example the atmospheric pressure at sea level is expected to be 1013 mbar, the atmospheric pressure at an altitude of about 2000 m is about 800 mbar and at about 4000 m it is only about 600 mbar.

[0045] In the case described above, where the pressure of the fluid in the fluid system at the interface between the fluid and the ambient air or atmosphere at the nozzles is set to a value of 0.5 mbar, below the atmospheric pressure of 1013 mbar, at sea level, i.e., to a value of approximately 1012.5 mbar, when operating this 3D printer with this setting at an altitude of 2000 m at approximately 800 mbar, there would no longer be pressure equality or negative pressure in the area of ​​the nozzles of the fluid system, and the fluid would leak or escape uncontrollably from the nozzles of the print heads.

[0046] This means that it is necessary to adjust the pressure of the fluid, especially in the area of ​​the nozzles of the print heads of a 3D printer, i.e. at the interface, to the installation location of the 3D printer in order to ensure maximum accuracy in the production of the 3D structures in the 3D printer.

[0047] Another problem is that the weather at the 3D printer's location can change, affecting the local atmospheric pressure. If adequate measures aren't taken to prevent weather-related pressure changes from reaching the area around the 3D printer's print head, these changes will also impact the quality of the 3D structures being produced. One such measure could be a chamber surrounding the entire 3D printer, in which the pressure is kept constant.

[0048] Such weather-related air pressure differences, for example, range from 970 mbar to 1030 mbar. An air pressure difference of 60 mbar between these exemplary values ​​can therefore also affect the fluid system with its set negative pressure at the nozzle boundary of the printheads.

[0049] Therefore, there is a need for an improved fluid system and an improved method for supplying fluid to a print head in a 3D printer.

[0050] The object of the invention is to provide a fluid system and a method for supplying a fluid to a printhead in a 3D printer, thereby ensuring a reliable supply of fluid to the printheads of the 3D printer and reliably preventing leakage from the printheads. Furthermore, the solution should allow for adaptation to changing atmospheric pressure in the vicinity of the 3D printer.

[0051] The problem is solved by a fluid system with the features according to claim 1 of the independent patent claims. Further developments are specified in the dependent patent claims.

[0052] A known fluid system for supplying a fluid to a printhead in a 3D printer typically includes a distribution element for storing and distributing the fluid. The distribution element is connected to a printhead reservoir via a fluid line. The fluid is conveyed from the distribution element to the printhead reservoir via this fluid line.

[0053] The printhead is connected to the printhead tank via a fluid supply channel. In this way, the fluid is conveyed from the printhead tank to the printhead.

[0054] In an advantageous embodiment of the invention, the printhead is connected to a printhead tank via a fluid supply channel and a fluid discharge channel. This allows the fluid to circulate, flowing from the printhead tank to the printhead (also referred to as a recirculating printhead) via the fluid supply channel and from the recirculating printhead back to the printhead tank via the fluid discharge channel. Only this embodiment will be described in more detail below, without limiting the present invention to this embodiment.

[0055] According to the invention, a first pressure regulating unit is arranged in the fluid line, wherein the first pressure regulating unit comprises a first throttle valve and a first pump arranged parallel to the first throttle valve, bypassing the first throttle valve.

[0056] Within a printhead unit of a 3D printer, the printhead reservoir and at least one printhead are arranged. The printhead is connected to the printhead reservoir in a known manner via the fluid supply channel for supplying fluid to the printhead and via the fluid discharge channel for draining fluid from the printhead.

[0057] The printhead tank is connected via a fluid line to a distribution element for supplying the fluid from the distribution element to the printhead tank.

[0058] According to the invention, a first pressure regulating unit is arranged in the fluid line. This first pressure regulating unit reduces the inlet pressure of the fluid flowing from the distributor element through a first section of the fluid line to the first pressure regulating unit. As a result of this pressure reduction, the fluid exits the first pressure regulating unit at a reduced outlet pressure and is conveyed to the pressure head tank via a second section of the fluid line. This outlet pressure of the fluid at the outlet of the first pressure regulating unit is lower than the inlet pressure of the fluid at the inlet of the first pressure regulating unit.

[0059] In one example, the inlet pressure of the fluid is a gauge pressure of 1500 mbar, which means that the inlet pressure of the fluid has an absolute pressure of 2500 mbar at a current atmospheric pressure of 1000 mbar. In this example, the outlet pressure of the fluid is a gauge pressure of 100 mbar, or 1100 mbar absolute pressure, which means that the first pressure regulating unit with an active pump reduces the fluid pressure by 1400 mbar.

[0060] For example, a reduction in the inlet pressure of a pressure regulating unit with the pump inactive, achieved solely through the action of the throttle valve, is 1350 mbar. In the previous example, this meant that the inlet pressure of the fluid, at a gauge pressure of 1500 mbar (i.e., 2500 mbar absolute pressure), was reduced to an outlet pressure of 150 mbar (i.e., 1150 mbar absolute pressure) solely through the action of the throttle valve with the pump inactive.

[0061] Under normal operating conditions of the pressure regulating unit with an active pump and the action of the throttle valve of the first pressure regulating unit, it is possible to reduce the fluid pressure by 1600 mbar. In this configuration, the gauge pressure of 1500 mbar, i.e., 2500 mbar absolute pressure, would be reduced by 1600 mbar according to the example above, with the outlet pressure of the fluid being at a vacuum of -100 mbar, i.e., 900 mbar absolute pressure.

[0062] To achieve this reduction in fluid pressure between the distributor element and the pressure head tank, the first pressure regulating unit comprises a first throttle valve and a first pump. The first throttle valve is located within the fluid line, forming the first and second sections of the fluid line. The first pump is arranged parallel to the first throttle valve. Fluidically speaking, the first pump acts as a bypass to the first throttle valve. The general function of a throttle valve is twofold: first, to reduce pressure by decreasing the fluid flow rate, and second, to set the operating point of the associated pump, which returns a portion of the fluid from the outlet side of the throttle valve to the inlet side.

[0063] According to the invention, the fluid flows through the first throttle valve in a first flow direction on its transport path from the distributor element to the pressure head tank. Furthermore, the first pump delivers the fluid in a first operating mode in a second flow direction opposite to the first flow direction.

[0064] The first throttle valve and / or the first pump are controllable or adjustable. These components are connected to a central control unit for control or regulation. This central control unit also controls, for example, the generation of the 3D structure in the 3D printer, i.e., the entire manufacturing process. This central control unit also controls the method for supplying fluid to a print head in a 3D printer, and thus the units or assemblies of the fluid system. It is clear to a person skilled in the art that the central control unit is also connected to other elements such as sensors, pumps, and valves, which are not mentioned in this description.

[0065] For example, pressure sensors measure the inlet and outlet pressures of the fluid relative to the first pressure regulating unit. These sensor readings are transmitted to the central control unit. The central control unit processes these readings and generates at least one control signal, which activates the first pump. This influences the flow rate of the first pump. The first pump delivers the fluid in the opposite direction to the initial flow direction, thus creating a counter-pressure to the inlet pressure of the fluid acting on the first pressure regulating unit. The use of the first pressure regulating unit reduces the pressure of the fluid as it travels through the fluid line to the pressure head tank.The first pressure regulating unit thus makes it possible to precisely set and keep constant the pressure of the fluid required, for example, in the area of ​​the surface of the fluid in the printhead tank, according to a specified value.

[0066] Referring to the example above, with an inlet pressure of 1500 mbar and an outlet pressure of -100 mbar, the first pump generates a back pressure of 1600 mbar in the second flow direction. Thus, the first pressure regulating unit, which is connected to the pressure head tank via the second part of the fluid line, sets the outlet pressure of the fluid to -100 mbar, resulting in an absolute pressure of 900 mbar at a specific point on the surface of the pressure head tank. This example simplifies the calculation by assuming that the outlet pressure of the fluid is not affected by the second part of the fluid line or by the fluid level in the pressure head tank. In the practical implementation of this method, such influences are taken into account and compensated for according to the procedure.

[0067] It is further stipulated that the first pump, or the first pump and the first throttle valve, can be controlled by means of a control signal.

[0068] To reduce the outlet pressure and the fluid flow rate through the first pressure regulating unit, a first version of the control system provides for the first throttle valve to be factory-set to a predetermined value, thus creating flow resistance to the fluid flowing through the fluid line in the first direction. This flow resistance reduces the fluid flow rate through the first pressure regulating unit by 50% to 95%. The first throttle valve ensures at least a reduced fluid flow rate from the distributor element to the pressure head tank at all times.

[0069] To reduce or decrease the inlet pressure of the fluid by the first pressure regulating unit to a first setpoint value, which in this description is referred to as pressure p FT , which is referred to as the pressure of the fluid at the surface of the fluid in the pressure head tank, in the first variant of the control of the first pressure regulating unit it is still provided that the central control unit generates a first control signal for the first pump such that the pressure p FT in an area on the surface of the fluid in the printhead tank. A suitable pressure sensor is used to measure the pressure p. FT located in the area of ​​the fluid surface in the printhead tank, which is connected to the central control unit that generates the first control signal for transmitting its measured values.

[0070] According to the invention, the pressure p FTThe fluid level is generated or reached in a specific area on the surface of the fluid within the printhead tank. A point or position on the surface of the fluid in the printhead tank corresponds to the highest point the fluid reaches in the fluid system. This point or position essentially corresponds to the maximum fluid level in the printhead tank. In practical implementations, fluctuations in the fluid level within the printhead tank occur. Such fluctuations, for example, due to changing fluid demand at the printheads, can briefly range from +10% to -20% of the specified level and are compensated for as quickly as possible within the fluid system. An example of a specified printhead tank level is 80% of its capacity.

[0071] To reduce the outlet pressure and decrease the fluid flow rate through the first pressure regulating unit, a second control variant of the pressure regulating unit provides for the controllability of both the first throttle valve and the first pump. In this case, the central control unit generates the first control signal for the first pump and a second control signal for the first throttle valve. Again, the central control unit generates the control signals in such a way that the first setpoint value, i.e., the pressure p, is set to a specific value. FT , located in an area on the surface of the fluid in the printhead tank. In both variants, the central control unit uses the pressure sensor readings to measure the pressure p. FTIn the area of ​​the fluid surface in the printhead tank, further measured values ​​from additional pressure sensors, which measure current pressure values ​​of the fluid at various points in the fluid system, are required and processed for the generation of the control signal.

[0072] In one example, the first target value, or pressure p, is FT in an area on the surface of the fluid in the pressure head tank, the pressure was set to a value of 900 mbar absolute pressure according to the procedure.

[0073] Additionally, a second pressure regulating unit is provided in the fluid supply channel, which includes a second throttle valve and a second pump.

[0074] According to the invention, a second pressure regulating unit is arranged in the fluid supply channel. By means of the second throttle valve of the second pressure regulating unit, the inlet pressure of the fluid flowing from the printhead tank via the first part of the fluid supply channel to the second throttle valve of the second pressure regulating unit is reduced. As a result of this pressure reduction, or rather the reduction in the fluid flow rate by the second throttle valve, the fluid is discharged at the outlet of the second throttle valve at a reduced pressure and conveyed to the printhead via a second part of the supply channel.

[0075] This reduced pressure, and therefore the fluid flow rate at the outlet of the second throttle valve of the second pressure regulating unit, is smaller than the fluid pressure and flow rate at the inlet of the second pressure regulating unit, and therefore smaller than the pressure and flow rate of the fluid with which the fluid leaves the pressure head tank.

[0076] According to the invention, this generation of a pressure difference or differential pressure Δp2 of the fluid in the fluid supply channel between an outlet on the printhead tank and an inlet on the printhead is used for fine-tuning the pressure or volume flow of the fluid in the fluid system according to the invention, in order to effectively prevent the fluid from escaping from the nozzles of the printheads at the interface.

[0077] The second pressure regulating unit is designed such that the second throttle valve is arranged in the fluid supply channel with a throttle valve inlet connected via the first part of the fluid supply channel to an outlet of the pressure head tank. A throttle valve outlet of the second throttle valve is connected via the second part of the fluid supply channel to an inlet of the pressure head.

[0078] The second pump is arranged in the second pressure regulating unit in such a way that it is connected with a pump inlet to a further outlet of the pressure head tank and with a pump outlet to the throttle valve outlet of the second throttle valve and thus also to the inlet of the pressure head.

[0079] This allows the second pump to bypass the second throttle valve and pump fluid from the printhead tank to the printhead, bypassing the second throttle valve. The fluid flow direction through the second pump and the fluid flow direction through the second throttle valve are the same and directed towards the printhead.

[0080] This bypass function is required in case a corresponding or increased demand for fluid occurs during the generation of a 3D structure in the printhead, which cannot be met by the continuously reduced fluid flow rate of the second throttle valve. Even when ensuring this at least temporary increase in fluid demand, the procedure prevents fluid from leaking from the nozzles of the printhead or multiple printheads by maintaining equal pressure between the fluid pressure and atmospheric pressure at the interface.

[0081] Thus, the second pressure regulating unit, and in particular the second pump of the second pressure regulating unit, achieves a targeted control of the differential pressure Δp2 of the fluid in the fluid supply channel. In this way, the volumetric flow rate of the fluid is influenced, which flows from the printhead tank to the printhead via the fluid supply channel, while simultaneously effectively preventing fluid from leaking out of the printhead nozzles at the interface.

[0082] The problem is also solved by a method with the features according to claim 4 of the independent patent claims. Further developments are specified in the dependent patent claims.

[0083] Typically, in a 3D printer, the fluid is first supplied to a printhead tank from a distribution element via a fluid line, and subsequently the fluid is supplied to the printhead from the printhead tank via a fluid inlet channel.

[0084] According to the invention, it is provided that - that in a fluid system of the 3D printer, a first pressure regulating unit is provided in the fluid line between the distributor element and the print head tank, - that a differential pressure Δp1 of the fluid in the fluid system is determined, which results from a height difference Δh1 between the print head provided in the 3D printer at a height h2 and a surface of the fluid in the print head tank connected to the print head at a height h1, - that in the area of ​​the fluid surface in the pressure head tank, a pressure p is exerted by the first pressure regulating unit FT is generated, which according to p FT = p B - Δ p1 - Δ p SI results where p B corresponds to a base pressure of the air in the vicinity of the print head of the 3D printer, an atmospheric pressure, where Δp SIa security value is and - that the fluid from the printhead tank is conveyed through the fluid supply channel over the height difference Δh1 to the printhead, whereby a pressure p is present in the printhead FD sets which is equal to or less than the base pressure p B is.

[0085] According to the invention, the pressure in the area of ​​the surface of the fluid in the printhead tank is regulated such that a pressure p is maintained at the lowest point on the printhead of the 3D printer. FD a pressure is generated that corresponds to the current atmospheric pressure. Alternatively, as a precaution, a pressure p is used. FD generated, which is, for example, smaller or larger than atmospheric pressure by a tolerance of less than 3 mbar, in particular less than 1 bar.

[0086] According to the invention, the pressure p FDThe pressure is generated on the surface of the fluid in the printhead tank. Since the surface area or the fill level of the fluid in the printhead tank can change slightly dynamically, the pressure p is... FD in a region on the surface of the fluid in the printhead tank. The term region thus refers to a target fill level of the fluid in the printhead tank or minor permissible deviations from this target fill level of the fluid above and below. According to the procedure, a pressure p is generated in this region. FD A pressure sensor is arranged in an area on the surface of the fluid, which is connected to the central control unit to transmit its measured values.

[0087] The regulation of pressure p according to the invention FD In an area on the surface of the fluid in the pressure head tank, the known formula for hydrostatic pressure is taken into account: p = Rho*g*h.

[0088] For example, with a height difference of 20 cm between a viewing point in the fluid system at the surface of the fluid in the printhead tank and the lowest point at the printhead of the 3D printer, and an exemplary density of the fluid used, such as a binder, of 1200 kg / m³ 3 At an atmospheric pressure of 1013 mbar, a pressure or pressure difference Δp results. This pressure difference Δp between the point of observation in the fluid system at the surface of the fluid in the printhead tank and the lowest point at the printhead is 23.54 mbar in this example.

[0089] This pressure difference is subtracted from the atmospheric pressure: 1013 mbar - 23.54 mbar = 989.46 mbar.

[0090] This results in the target value for the pressure p. FDof the fluid in the area of ​​the surface of the fluid in the printhead tank, which according to the invention is set to a value of a maximum of 989 mbar using the first pressure regulating unit, so that in the area of ​​the interfaces of the nozzles of the printhead there is pressure equality between the pressure of the fluid p FD and atmospheric pressure p B exists and no fluid can leak from the printhead.

[0091] In this example calculation, capillary forces, surface tensions, and pressure drops due to friction losses that occur in practice were not explicitly taken into account.

[0092] The highest point of the fluid, or rather the surface of the fluid in the printhead tank, is located at height h1 in the 3D printer, which is above the printhead, which is located at height h2 in the 3D printer. Thus, there is a height difference Δh1 between the printhead at height h2 and the printhead tank at height h1, according to... ∑ h1=h1−h2.

[0093] The printhead tank is connected to the printhead via the fluid supply channel and the fluid discharge channel. This forms a fluid system comprising the printhead tank, the fluid supply channel, the fluid discharge channel, and the printhead, which is designed as a recirculating printhead. Within this fluid system, there is hydrostatic pressure in the fluid, which, when considering a point at height h1, depends on the height difference Δh1. As is known from the prior art, the hydrostatic pressure p is the product of the fluid's specific density, height, and gravitational acceleration, and is therefore particularly dependent on the height.

[0094] The height difference Δh1 corresponds to a pressure difference Δp1. This pressure difference Δp1 corresponds to a difference of pressure p. FTof the fluid in the area of ​​the surface of the fluid in the pressure head tank at a highest point in the fluid system to a pressure p FD of the fluid at the lowest point in the fluid system at the print head.

[0095] In a subsequent process step, a base pressure p is applied. B specified or determined. The base pressure p B This corresponds to the atmospheric pressure in the vicinity of the 3D printer's print head, or more precisely, in the area of ​​the nozzles of the 3D printer's print head. Such a base pressure p B for example, it lies at a height of the sea surface at p B = 1000 mbar. In an optional version, where a suction system in the 3D printer creates a vacuum in the area of ​​the print heads, the base pressure p is B at a value smaller than atmospheric pressure. In this example, the base pressure p Bat a value of, for example, only 900 mbar.

[0096] The base pressure p B For example, according to the invention, a fixed value of, for example, 1000 mbar is stored or can be read from a table. This table contains information on various base pressures p. B , which are assigned to different installation locations of the 3D printer or different 3D printer designs with and without extraction. In such a table, the base pressures p can be listed. B can also be assigned to different altitudes above sea level. In a further embodiment, the base pressure p B The pressure is currently determined by means of a sensor located in the 3D printer. During the process, the corresponding base pressure p is adjusted. B for example, taken from the table used and used in the calculation according to the procedure.

[0097] Based on this base pressure p BA value for a pressure p to be set is determined according to procedure. FT The pressure p of the fluid in the area of ​​the fluid's surface in the printhead tank is determined. FT of the fluid in the area of ​​the surface of the fluid in the pressure head tank results according to pFT=pB−Δ p1−Δ pSI.

[0098] Here, p B the base pressure or atmospheric pressure, Δp1 the differential pressure determined above and Δp SI a safety value. This safety value Δp SI Depending on the desired design, the pressure can be in a range between 0 bar and 80 mbar, especially at 25 mbar.

[0099] The pressure p determined in this way, which is to be set FT The pressure of the fluid in the area of ​​the surface of the fluid in the pressure head tank is generated by means of the first pressure regulating unit.

[0100] For this purpose, the central control unit generates a control signal for the first pump of the first pressure regulating unit such that the determined pressure p FT The pressure is set in the area of ​​the fluid surface in the printhead tank. A pressure sensor located in the area of ​​the fluid surface in the printhead tank detects when the preset pressure p value has been reached. FT checked.

[0101] Alternatively, the central control unit generates the control signal for the first pump and a control signal for the first throttle valve of the first pressure regulating unit in such a way that the determined pressure p FT in the area of ​​the fluid's surface in the printhead tank.

[0102] The fluid flows from the printhead tank through the fluid supply channel, overcoming the height difference Δh1 to the printhead. Thus, the required pressure p is established in the printhead according to the procedure. FDone which is equal to or less than the base pressure p B is. For example, if the safety value Δp SI Assuming 0 bar in the above calculation, the pressure p corresponds to... FD in the printhead the specified or determined base pressure p B In the event that the base pressure p B If it has a value of 1000 mbar, the pressure p is FD The fluid pressure in the print head is also 1000 mbar.

[0103] For example, is the safety value Δp used as an alternative? SI Assuming 25 mbar in the above calculation, the pressure p FD in the printhead a value 25 mbar lower than the specified or determined base pressure p B up. In the event that the base pressure p B If it has a value of 1000 mbar, the pressure p is FD The fluid pressure in the printhead is 975 mbar in this case.

[0104] In both cases, the procedure prevents unwanted fluid leakage from the printhead nozzles at the interfaces. If multiple printheads are supplied with fluid from the printhead tank, all located at height h2 in the 3D printer, fluid leakage from the nozzles of all printheads is prevented.

[0105] Furthermore, it is planned that the base pressure p B is predetermined or is currently determined by means of a sensor.

[0106] The base pressure p B The atmospheric pressure in the vicinity of the 3D printer's print head is specified as a value or a value readable from a table, since this is known, at least as an average value, relative to the 3D printer's location. This allows for flexibility in the 3D printer's location and compensates for weather-related fluctuations in the base pressure. BTo eliminate the effects in the vicinity of the 3D printer, an alternative version of the base print p B The current pressure is determined by a sensor on the 3D printer. These current measurements are transmitted to the central control unit and used in the process of calculating the pressure p. FT The fluid level in the printhead tank is taken into account. This further improves safety by preventing the unintentional leakage of fluid from the printhead nozzles.

[0107] It has also proven advantageous that a differential pressure Δp2 of the fluid in the fluid supply channel is generated between an outlet-side connection of the fluid supply channel at the printhead tank and an inlet-side connection of the fluid supply channel at the printhead.

[0108] To achieve the differential pressure Δp2 of the fluid in the fluid supply channel, a second pressure regulating unit is arranged, dividing the fluid supply channel. This second pressure regulating unit comprises a second throttle valve and a second pump. The second throttle valve is positioned to divide the fluid supply channel, creating a first section of the fluid supply channel and a second section of the supply channel. While the first section of the fluid supply channel connects an inlet of the second throttle valve to the printhead tank, the second section of the fluid supply channel connects an outlet of the second throttle valve to the printhead.

[0109] According to the invention, in this embodiment, the fluid flows through the second throttle valve on its transport path from the printhead tank to the printhead, the second throttle valve reducing the pressure and volume flow of the fluid. This creates the differential pressure Δp2 of the fluid in the fluid supply channel between the outlet of the printhead tank and the inlet of the printhead.

[0110] In a particular embodiment of the invention, it is provided that the differential pressure Δ p2 of the fluid is regulated by means of a second pump provided in a second pressure regulating unit, wherein the control of the differential pressure Δ p2 regulates a volume flow of the fluid (5) from the printhead tank (15) to the printhead (1).

[0111] The second pressure regulating unit provided includes a second pump in addition to the second throttle valve already described above.

[0112] The second throttle valve, as described above, is connected to the pressure head tank via the throttle valve inlet and to the pressure head via the throttle valve outlet, and is located in the fluid supply channel.

[0113] The second pump is arranged in the second pressure regulating unit in such a way that it is connected with a pump inlet to a further outlet of the pressure head tank and with a pump outlet to the throttle valve outlet of the second throttle valve and thus also to the inlet of the pressure head.

[0114] In this way, the second pump can act as a bypass to the second throttle valve, pumping fluid from the printhead tank to the printhead past the second throttle valve. The flow direction of the fluid through the second pump and the flow direction of the fluid through the second throttle valve are the same and directed towards the printhead.

[0115] Thus, a control signal generated by the central control unit for the second pump of the second pressure regulation unit allows the flow rate through the second pump to be continuously regulated between a minimum, where no fluid is pumped through the second pump, and a maximum, where the second pump operates at a predetermined or full delivery rate.

[0116] This bypass function is required in case a corresponding or increased demand for fluid occurs during the generation of a 3D structure in the printhead, which cannot be met by the continuously reduced fluid flow rate of the second throttle valve. Even when ensuring this at least temporary increase in fluid demand, the procedure prevents fluid from leaking from the nozzles of the printhead or multiple printheads by maintaining equal pressure between the fluid pressure and atmospheric pressure at the interface.

[0117] Thus, the second pressure regulating unit, and in particular the second pump of the second pressure regulating unit, achieves targeted control of the differential pressure Δp2 of the fluid in the fluid supply channel, i.e., between the outlet connection of the printhead tank and the inlet connection on the printhead. In this way, the differential pressure Δp2 of the fluid, and therefore the volumetric flow rate of the fluid, is influenced as it flows from the printhead tank to the printhead via the fluid supply channel, while simultaneously preventing fluid from leaking out of the printhead nozzles at the interface.

[0118] According to the invention, it is further provided that a first pump and a first throttle valve are provided in the first pressure regulating unit, that the first pump delivers the fluid in a first operating mode in a second flow direction opposite to a first flow direction of the fluid through the first throttle valve, and that the first pump delivers the fluid in a second operating mode in the first flow direction, wherein the first pump is controlled in both operating modes by a control signal from a central control unit.

[0119] To generate the pressure p FTIn the area of ​​the fluid surface in the pressure head tank, the fluid is designed to flow through the first throttle valve of the first pressure regulating unit in a first flow direction on its transport path from the distributor element to the pressure head tank, thereby reducing the fluid's volumetric flow rate. Furthermore, the first pump of the first pressure regulating unit is designed to deliver the fluid in a second flow direction, opposite to the first flow direction, towards the distributor element in a first operating mode. The predetermined pressure p is thus achieved by controlling the first pump via the control signal from the central control unit. FT generated in the area of ​​the fluid's surface in the printhead tank.

[0120] Additionally, the first pump of the first pressure regulating unit is designed to deliver the fluid in a second operating mode, in the first flow direction, towards the printhead tank. This ensures that, for example, during maintenance work, fluid changes in the fluid system, or for quickly filling the printhead tank, the fluid is delivered to the tank at an increased pressure and flow rate. Without this additional delivery capacity of the first pump in the second operating mode, in the first flow direction, the fluid reaches the printhead tank only at the reduced pressure and flow rate determined by the first throttle valve, which significantly increases the time required, for example, when filling the printhead tank.

[0121] In a further embodiment of the invention, it is provided that a current value for the generated pressure p is displayed. FTThe pressure is measured in the area of ​​a surface of the fluid in the printhead tank by means of a pressure sensor arranged above the surface of the fluid in the printhead tank without contact with the fluid.

[0122] The pressure sensor measures a current value for the generated pressure p FT It is positioned without contact with the fluid in the printhead tank. This prevents the fluid from wetting the pressure sensor, drying on the pressure sensor, and thus preventing it from distorting the measured values.

[0123] It is known that when the pressure sensor is arranged in the gas at a small distance above the surface of the fluid in the pressure head tank, the measured values ​​supplied by the pressure sensor correspond with sufficient accuracy to the pressure p. FTof the fluid. This fact applies assuming a pressure-tight system, in particular a pressure-tight pressure head tank. The low hydrostatic pressure of the gas surrounding the pressure sensor above the surface of the fluid can be neglected.

[0124] The pressure sensor is positioned between 10 mm and 100 mm above the surface of the fluid in the printhead tank at the tank's maximum fill level. This reliably prevents the fluid from wetting the pressure sensor.

[0125] The features and advantages of this invention explained above can be better understood and evaluated after careful study of the following detailed description of the preferred, non-restrictive exemplary embodiments of the invention with the accompanying drawings, which show: Fig. 1: a print head with multiple dosing units in a state-of-the-art 3D printer, Fig. 2: a state-of-the-art fluid system, Fig. 3: a first embodiment of the fluid system according to the invention, Fig. 4: an extract from the fluid system according to the invention to explain the method according to the invention and Fig. 5: a second embodiment of the fluid system according to the invention.

[0126] The Fig. Figure 1 shows a print head 1 with several dosing units 2 in a state-of-the-art 3D printer in a sectional view, using an example with three dosing units 2 in the print head 1. Such dosing units 2 can be arranged in the print head 2, for example, in the form of a matrix with several rows and several columns.

[0127] Each metering unit 2 of the printhead 1 has a nozzle 3 which is aligned in one direction of a build area 4. The metering units 2 are at least partially separated from each other, for example by corresponding chamber walls, without impeding the supply of a fluid 5. On this build area 4, a fluid is extruded in the Fig. 1. A particulate building material (not explicitly shown) is applied, smoothed, and solidified for the layer-by-layer construction of a 3D structure. For this purpose, methods known according to the state of the art are used for applying, smoothing, and solidifying the particulate building material.

[0128] The illustrated printhead 1 has a fluid supply channel 6 and a fluid discharge channel 7. The fluid 5, a binding agent, is supplied to the printhead 1 via the fluid supply channel 6 and discharged from the printhead 1 via the fluid discharge channel 7. Thus, the printhead 1, which is also referred to as a recirculating printhead, and its metering units 2 are circulated by the fluid 5. This circulation 8 of the fluid 5 through the printhead 1 is indicated by several small arrows.

[0129] The two large arrows above the fluid supply channel 6 and above the fluid discharge channel 7 in the Fig. The flow direction of the fluid 5 in the circulation 8 is indicated by 1. The fluid 5 located in the metering units 2 of the printhead 1 is prevented from exiting through the nozzle 3 by a vacuum. The printhead 1 can be supplied, for example, with fluid via the fluid supply channel 6 and the fluid discharge channel 7. Fig. 1 printhead tank not shown, connected.

[0130] To meter the fluid 5 via the nozzles 3 of the metering units 2 onto the particulate building material located on the build platform 4, a means 10 for generating a mechanical force is arranged in each metering unit 2. This means 10 generates a mechanical force in the form of a pressure wave, which propagates from the means 10 itself through the fluid 5 in the associated metering unit 2 towards the associated nozzle 3, thus metering a droplet 11 via the corresponding nozzle 3. Such a means 10 could, for example, be a piezoelectric element operating according to the piezoelectric effect.

[0131] The droplet 11 reaches the surface of the particulate building material located on the building site 4 and causes a selective solidification of the building material at the point of impact, creating a partial area of ​​the 3D structure to be produced.

[0132] The illustrated print head 1, with its chambered metering units 2, is moved across the build area 4 in the usual manner. In this way, the fluid 5 is metered precisely at the points necessary for the formation of a 3D structure or a 3D component.

[0133] In the example of the Fig. 1. A filter element 12 is provided in the fluid supply channel 6 and a filter element 12 in the fluid discharge channel 7. Alternatively, only one filter element 12 in the fluid supply channel 6 or one filter element 12 in the fluid discharge channel 7 can be provided. These filter elements 12 serve to protect against blockages or contamination. In this way, for example, blockage of the nozzles 3 can be prevented.

[0134] This printhead 1, known from the prior art, enables the fluid 5 to be kept in motion within the metering units 2 of the printhead 1 and to flow through the printhead 1 in a continuous circulating motion 8. This prevents moisture loss, changes in the viscosity of the fluid 5, oxidation, and narrowing of the nozzle 3 due to drying, thus preventing metering errors and defects in the printed image. In the area of ​​the nozzles 3, an interface forms between the fluid 5 in the printhead 1 and the surrounding ambient air or atmosphere, in which atmospheric pressure prevails. This atmospheric pressure acts uniformly on the printhead 1 from all sides. Therefore, the atmospheric pressure also acts uniformly on all interfaces at all nozzles 3 of the printhead 1.

[0135] The Fig. Figure 2 shows a prior art fluid system 13'. In a printhead unit 14 of the fluid system 13', a printhead tank 15 and at least one printhead 1 having several metering units 2 are arranged. The printhead 1 is connected to the printhead tank 15 via a fluid supply channel 6, for supplying the fluid 5, such as a binder, from the printhead tank 15 to the metering units 2 of the printhead 1, and a fluid discharge channel 7, for draining the fluid 5 from the metering units 2 of the printhead 1 into the printhead tank 15. By means not shown, such as pumps, the fluid 5 is moved from the printhead tank 15 to the printhead 1 and back again in a cycle 8. An arrangement of several printheads 1 in one printhead unit 14 is possible, which is shown in the Fig. 2 is not shown.

[0136] A distributor element 17 is typically arranged between a storage tank 16 and the printhead tank 15. The distributor element 17 has a distributor inlet 18, which is connected to the storage tank 16 via a fluid supply line 19. The distributor element 17 also has an outlet 20, which is connected to the storage tank 16 via a fluid return line 21. In this way, the fluid 5 can be circulated between the storage tank 16 and the distributor element 17 and back again to prevent flocculation or agglomeration in the fluid 5 or to dissolve any flocculation or agglomeration that has already formed.

[0137] The distributor element 17 and several printhead units 14, each having a printhead tank 15 and at least one printhead 1 connected to the printhead tank 15, are arranged in a print unit 23 which can be moved over a build area of ​​the 3D printer (not shown).

[0138] The distributor element 17 is connected to the first printhead tank 15 of the first printhead unit 14 via a first fluid line 22. The first fluid line 22 is connected to the printhead tank 15 at a printhead tank inlet 9, the printhead tank inlet 9 being located in the lower region of the printhead tank 15.

[0139] To supply the additional printhead tanks 15 in the additional printhead units 14, the distributor element 17 is connected to the associated printhead tanks 15 via additional fluid lines 22.

[0140] In the example of the Fig. 2 The distributor element 17 has four connected fluid lines 22. The connections of the further fluid lines 22 with the associated printhead tanks 15 in the further printhead units 14 are shown in the Fig. 2 not shown. The other printhead units 14 are shown only schematically.

[0141] The Fig. Figure 3 shows a first embodiment of the fluid system 13 according to the invention.

[0142] To describe the invention, see in the Fig. Figure 3 shows only a printhead unit 14 and the distributor element 17 of the fluid system 13. The printhead tank 15 and the printhead 1 are visible within the printhead unit 14. The printhead 1 is connected to the printhead tank 15 in a known manner via the fluid supply channel 6 for supplying the fluid 5 to the printhead 1 and via the fluid discharge channel 7 for discharging the fluid 5 from the printhead 1.

[0143] The printhead tank 15 is connected via fluid line 22 to the distributor element 17 for the supply of fluid 5 from the distributor element 17 to the printhead tank 15. The fluid line 22 opens into the printhead tank 15 at the printhead tank inlet 9.

[0144] According to the invention, a first pressure regulating unit 24 is arranged in the fluid line 22. By means of this first pressure regulating unit 24, the inlet pressure of the fluid 5 flowing from the distributor element 17 via a first section of the fluid line 22a to the first pressure regulating unit 24 is reduced in the first pressure regulating unit 24. As a result of this pressure reduction of the fluid 5, the fluid 5 is discharged from the first pressure regulating unit 24 at a reduced pressure and conveyed via a second section of the fluid line 22b to the pressure head tank 15. This reduced pressure of the fluid 5 at the outlet of the first pressure regulating unit 24 is lower than the pressure of the fluid 5 at the inlet of the first pressure regulating unit 24.In one example, the inlet pressure of fluid 5 is a gauge pressure of 1500 mbar, i.e., an absolute pressure of 2500 mbar, assuming a current atmospheric pressure of 1000 mbar, while the outlet pressure of fluid 5 in fluid line 22 at the outlet of the first pressure regulating unit 24 is a gauge pressure of -100 mbar, i.e., an absolute pressure of 900 mbar. In this example, the pressure regulating unit 24 reduces the pressure of fluid 5 by 1600 mbar.

[0145] To achieve this reduction of the pressure and volume flow rate of the fluid 5 in the area between the distributor element 17 and the pressure head tank 15, the first pressure regulating unit 24 comprises a first throttle valve 25 and a first pump 26. While the first throttle valve 25 is arranged in the fluid line 22, forming the first part of fluid line 22a and the second part of fluid line 22b, the first pump 26 is arranged parallel to the first throttle valve 25. The first pump 26 provides a bypass to the first throttle valve 25.

[0146] According to the invention, the fluid 5, on its transport path from the distributor element 17 to the pressure head tank 15, flows through the first throttle valve 25 in a first flow direction 27 towards the pressure head tank 15. Furthermore, the first pump 26 delivers the fluid 5 in a second flow direction 28, opposite to the first flow direction 27, towards the distributor element 17.

[0147] The first throttle valve 25 and the first pump 26 are designed to be controllable or adjustable. For control or adjustment of the first throttle valve 25 and the first pump 26, they are connected to a central control unit (not shown). This central control unit also controls, for example, the generation of the 3D structure in the 3D printer, i.e., the entire manufacturing process. This central control unit also controls the process for supplying fluid to a print head in a 3D printer and thus the units or assemblies of the fluid system.

[0148] For example, the inlet and outlet pressures of the fluid 5 are measured by means of corresponding sensors (not shown) with respect to the first pressure regulating unit 24. The measured values ​​from these sensors are transmitted to the central control unit. The central control unit processes these measured values ​​and generates at least one control signal, which is used to control the first pump 26. In this way, the power or flow rate of the first pump 26 is influenced. The first pump 26 pumps the fluid 5 in the opposite direction to the first flow direction 27 and thus generates a back pressure against the pressure of the fluid 5 acting on the inlet side of the first pressure regulating unit 24. This results in a reduction of the pressure and volume flow rate of the fluid 5 as it travels through the fluid line 22 to the pressure head tank 15.

[0149] Referring to the example with an inlet overpressure of fluid 5 of 1500 mbar (2500 mbar absolute pressure) and an outlet overpressure of fluid 5 of -100 mbar (900 mbar absolute pressure), the first pump 26 in the second flow direction 28 generates a pressure of fluid 5 with a value of 1600 mbar. Thus, the first pressure regulating unit 24, which is connected to the pressure head tank 15 via the second part of the fluid line 22b, outputs fluid 5 at an absolute pressure of 900 mbar.

[0150] To reduce the pressure and flow rate of the fluid 5 through the first pressure regulating unit 24, a first variant of the control system for the first pressure regulating unit 24 provides that the first throttle valve 25 is factory-set to a predetermined value and presents a constant flow resistance to the fluid 5 flowing through the fluid line 22 in the first flow direction 27. This flow resistance reduces the flow rate of the fluid 5 through the fluid line 22 by a range of 50% to 95%, particularly 75%. The first throttle valve 25 ensures at least a reduced flow of the fluid 5 from the distributor element 17 to the pressure head tank 15 at all times.

[0151] To reduce or decrease the pressure or volume flow of the fluid 5 by the first pressure regulating unit 24 to a first setpoint value, which in this description is referred to as pressure p FT , pressure of the fluid 5 at the surface 30 of the fluid 5 in the pressure head tank 15, it is in the first variant of the control of the first pressure regulating unit 24 further provided that the central control unit generates the first control signal for the first pump 26 such that the pressure p FT in an area on the surface 30 of the fluid 5 in the printhead tank 15, which is generated or present. The current value of the pressure p FT The pressure is determined by means of a pressure sensor 41, which is arranged inside the printhead tank 15 at a small distance above the surface 30 of the fluid 5 in the printhead tank 15. Thus, measured values ​​for the current pressure p can be obtained according to the procedure. FTThe pressure p is determined in a region 30 on the surface of the fluid 5 in the printhead tank 15 and transmitted to the central control unit. The central control unit compares this to the target value for the pressure p. FT with a current measured value for the pressure p FT and, depending on this comparison, generates the first control signal for the first pump 26 to maintain the specified pressure p FT to generate in the area on the surface 30 of the fluid 5 in the printhead tank 15 or in the area of ​​the pressure sensor 41.

[0152] To reduce the pressure and flow rate of the fluid 5 by the first pressure regulating unit 24, a second variant of the control system for the first pressure regulating unit 24 provides that both the first throttle valve 25 and the first pump 26 are controllable. In this case, the central control unit generates the first control signal for the first pump 26 and a second control signal for the first throttle valve 25. Again, the central control unit generates the control signals in such a way that the target value for the pressure p is set. FT in the area on the surface 30 of the fluid 5 in the printhead tank 15. In both variants, the central control unit receives measured values ​​from the pressure sensor 41 to measure the current pressure p. FTin the area of ​​the surface 30 of the fluid 5 in the printhead tank 15 as well as other sensors at various points in the fluid system, processed and used in the generation of the control signals.

[0153] According to the procedure, the first pressure regulating unit 24 is controlled by the control signals of the central control unit in such a way that the setpoint value for the pressure p is set. FT The pressure sensor 41 in the area of ​​the surface 30 of the fluid 5 in the printhead tank 15, for example, is set to a value of 900 mbar absolute pressure, which in the Fig. 3 is not shown.

[0154] In the Fig. Figure 3 shows, as an example, a degassing filter 29 with a line for removing the gas extracted from the fluid 5 in the fluid supply channel 6. This degassing filter 29 extracts gas from the fluid 5 that has entered the fluid 5 either via the nozzles 3 of the print head 1 or through leaks in the fluid system 13 and can affect the proper functioning of the 3D printer. This degassing filter 29 can also be installed at other locations in the fluid system 13. Furthermore, several degassing filters 29 can be arranged at different locations in the fluid system, which is advantageous in the Fig. 3 is not shown.

[0155] In the Fig. Figure 3 shows further fluid lines 22 on the distributor element 17, which are provided for supplying the fluid 5 from the distributor element 17 to further pressure head tanks 15. The fluid supply line 19 and the fluid return line 12, which are connected to the storage tank 16 (not shown), are also visible.

[0156] The Fig. Figure 4 shows an excerpt from the fluid system 13 according to the invention, limited to a selected area, which is used to explain the inventive method for supplying a fluid to a print head in a 3D printer. The method is particularly concerned with reliably preventing the unintentional escape of the fluid 5 at an interface on the nozzles 3 of the print head 1.

[0157] The depicted elements or assemblies have already been used for Fig. Section 3 has been described in detail, therefore a repetition is omitted.

[0158] The values ​​used in this example for different pressures (p B , Δ p Si , P FD , p FT , P F1 , P F2 , P F3 The values ​​shown are chosen as examples for this explanation and are intended to aid in understanding the invention. In practical application of the method according to the invention, the values ​​for the various pressures will deviate from the example values ​​without affecting the functionality of the present method.

[0159] To carry out the method according to the invention, it is provided, in order to prevent an unintentional escape of the fluid 5 from the printhead 1, that a pressure of p is maintained at ambient pressure. B of the printhead 1 matching pressure p FD to generate fluid 5 in the area of ​​the nozzles 3 of the printhead 1 at the interface between fluid and ambient air.

[0160] In an alternative implementation of the procedure, a safety value Δp is added.Si compared to ambient pressure p B of the printhead 1 lower pressure p FD generated in fluid 5 in the area of ​​the nozzles 3 of the printhead 1 at the interface between fluid and ambient air.

[0161] The ambient pressure p B is the current atmospheric pressure surrounding the printhead 1. This ambient pressure p B The pressure at sea level is approximately 1000 mbar, as stated in the Fig. The cloud shown in section 4 is located in the area of ​​the printhead 1.

[0162] As it is in the Fig. As can be seen in Figure 4, the printhead tank 15, specifically the surface 30 of the fluid 5 within the printhead tank 15 of the fluid system 13, is located at a first height h1. The printhead 1, specifically the lowest points of the nozzles 3 of the printhead 1, is located at a second height h2 within the fluid system 13 of the 3D printer. Thus, a height difference Δh1 exists between the surface 30 of the fluid 5 in the printhead tank 15 and the lowest point of the nozzles 3 in the printhead 1. Due to this height difference Δh1, a pressure differential Δp1 exists between the surface 30 of the fluid 5 in the printhead tank 15 and the fluid at the lowest point of the nozzles 3 in the printhead 1, corresponding to the height difference Δh1.

[0163] In this example, the pressure p to be generated in the area of ​​the surface 30 of the fluid 5 in the pressure head tank 15 at height h1 by the first pressure regulating unit 24 is FD 900 mbar absolute pressure. In the example of the Fig. Figure 4 further explains a first value for a location-specific pressure p. F1 of fluid 5 in an area in the pressure head tank 15 below the surface 30 of approximately 910 mbar, a second value for a local pressure p F2 of fluid 5 in a region of the supply channel 6 at approximately 950 mbar and a third value for a local pressure p F3 The pressure of fluid 5 in the supply channel 6 at a point on the printhead 1 is approximately 990 mbar. The pressure of fluid 5 at the interface of the nozzles 3 at height h2 is 1000 mbar to prevent fluid 5 from escaping the nozzles 3. These exemplary values ​​demonstrate a general increase in the hydrostatic pressure of fluid 5 from top to bottom, i.e., from the printhead tank 15 to the printhead 1.

[0164] Given a value for pressure p based on atmospheric pressure FDIn printhead 1, for example, the absolute pressure must be set to 1000 mbar, which is the value for the pressure p. FT The pressure at surface 30 in the printhead tank 15 at 900 mbar will be lower by the differential pressure Δ p1 at 100 mbar.

[0165] According to the invention, the base pressure p B predefined or currently determined by means of appropriate sensors near printhead 1. Such sensors are located in the Fig. 4 not shown.

[0166] After the target value for the pressure p has been determined according to the procedure FT according to p FT = p B - Δ p - Δ p SI The central control unit (not shown) controls the first pressure regulating unit 24 such that the determined value for the pressure p is reached in the area of ​​the surface 30 in the printhead tank 15. FT This is achieved, thus preventing the unwanted escape of fluid 5 from the printhead 1. To regulate the generation of the specified pressure p FDA pressure sensor 41 for measuring the current pressure p is located in an area directly above the surface 30 of the fluid 5 in the printhead tank 15. FT This pressure sensor 41 is arranged. It is connected to the central control unit for transmitting its measured values. The central control unit can thus determine the specified target value for the pressure p. FT with the measured current pressure p FT compare and generate corresponding control signals for the first pressure regulating unit 24 in order to minimize a deviation between the setpoint and the actual value in the usual way.

[0167] The Fig. Figure 5 shows a second embodiment of the fluid system 13 according to the invention.

[0168] The representation or the assemblies in the Fig. 6 are largely from the one already described above Fig. 3 known. Therefore, only the differences between the embodiments of the fluid system 13 according to the invention are described below.

[0169] In the second embodiment of the Fig. 5 A second pressure regulating unit 31 is arranged in the fluid supply channel 6. This second pressure regulating unit 31 has a second throttle valve 32 and a second pump 33.

[0170] The second embodiment makes it possible, in addition to the above-described method of generating the pressure p, to FT in the area on the surface 30 of the fluid 5 in the printhead tank 15, a fine adjustment of the pressure conditions in the fluid supply channel 6 between the printhead tank 15 and the printhead 1 is to be carried out.

[0171] In particular, a differential pressure Δp2 of the fluid 5 in the supply channel 6 can be generated in this way between an outlet-side connection of the fluid supply channel 6 at the printhead tank 15 and an inlet-side connection of the fluid supply channel 6 at the printhead 1.

[0172] To achieve the differential pressure Δp2 of the fluid 5 in the fluid supply channel 6, the second pressure regulating unit 31 comprises the second throttle valve 32 and the second pump 33. The second throttle valve 32 is arranged in the fluid supply channel 6, forming a first part of the fluid supply channel 6a and a second part of the supply channel 6b. The second throttle valve 32 is connected via a throttle valve inlet in the first part of the fluid supply channel 6a to an outlet of the printhead tank 15 and via a throttle valve outlet in the second part of the fluid supply channel 6b to an inlet of the printhead 1.

[0173] The second pump 33 is arranged in the second pressure regulating unit 31 such that it is connected with one pump inlet to a further outlet 35 of the printhead tank 15 and with one pump outlet to the throttle valve outlet of the second throttle valve 32, and thus also to the inlet of the printhead 1. This allows the second pump 33 to pump fluid 5 from the printhead tank 15 to the printhead 1 by way of a bypass to the second throttle valve 32.

[0174] According to the invention, in this embodiment, the fluid 5 flows through the second throttle valve 32 in a third flow direction 34 on its transport path from the printhead tank 15 to the printhead 1. Furthermore, the second pump 33 also delivers the fluid 5 in the third flow direction 34, parallel to and past the second throttle valve 32.

[0175] The second pump 33 is designed to be controllable or adjustable. For the control or regulation of the second throttle valve 32 and the second pump 33, these are connected to the central control unit (not shown).

[0176] By means of the adjustable differential pressure Δp2 of the fluid 5 generated in this way within the split supply channel 6, a fine adjustment of the pressure conditions in the fluid supply channel 6 between the printhead tank 15 and the printhead 1 is ensured, for example, in the event that a corresponding demand or additional demand for fluid 5 occurs in certain phases of the generation of a 3D structure in the printhead 1, which cannot be met by the continuously reduced volume flow of the fluid 5 through the fluid supply channel 6 by the second throttle valve 32. This additional demand is covered by the controllable second pump 33, whereby it is ensured by the procedure that the escape of fluid 5 from the nozzles 3 of the printhead 1 or several printheads 1 is prevented by maintaining the pressure of the fluid 5 and the atmospheric pressure at the interface equal.

[0177] Thus, the second pressure regulating unit 31, in particular the second pump 33 of the second pressure regulating unit 31, achieves a targeted influence on the differential pressure Δ p2 of the fluid 5 in the fluid supply channel 6. List of reference symbols 1 printhead 2 dosing units 3 nozzles 4 Building plot 5 Fluid 6, 6a, 6b fluid supply channel 7 Fluid drainage channel 8 cycles 9 Printhead tank inlet 10 Means of generating a mechanical force 11 drops 12 filter elements 13', 13 Fluid system 14 Printhead unit 15 printhead tank 16 storage tank 17 Distributor element 18 Distributor inlet 19 Fluid supply line 20 Procedure 21 Fluid return line 22, 22a, 22b Fluid line 23 printing units 24 first pressure regulating unit 25 first throttle valve 26 first pump 27 first flow direction 28 second flow direction 29 Degassing filters 30 Surface area of ​​the fluid in the printhead tank 31 second pressure regulating unit 32 second throttle valve 33 second pump 34 third flow direction 35 additional outlet of the printhead tank 36 third pressure regulating unit 37 third throttle valve 38 third pump 39 fifth flow direction 40 sixth flow direction 41 Pressure sensor for measuring the pressure p FT QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 008 328 A1

[0019] EP 3 177 453 B1 [0025, 0028]

Claims

Fluid system (13) for supplying a fluid (5) to a printhead (1) in a 3D printer, wherein a distributor element (17) for storing and distributing the fluid (5) is connected to a printhead tank (15) via a fluid line (22) and wherein the printhead (1) is arranged to be connected to a printhead tank (15) via a fluid supply channel (6), characterized in that a first pressure regulating unit (24) is arranged in the fluid line (22), wherein the first pressure regulating unit (24) comprises a first throttle valve (25) and a first pump (26) arranged parallel to the first throttle valve (25) that bypasses the first throttle valve (25). Fluid system (13) according to claim 1, characterized in that the first pump (26) or the first pump (26) and the first throttle valve (25) are connected to a central control unit which controls the first pump (26) or the first pump (26) and the first throttle valve (25) by means of a control signal. Fluid system (13) according to claim 1 or 2, characterized in that a second pressure regulating unit (31) is arranged in the fluid supply channel (6), which comprises a second throttle valve (32) and a second pump (33). A method for supplying a fluid (5) to a printhead (1) in a 3D printer, in which the fluid (5) is first supplied to a printhead tank (15) from a distributor element (17) via a fluid line (22), and in which the fluid (5) is subsequently supplied to the printhead (1) from the printhead tank (15) via a fluid supply channel (6), characterized in that: - a first pressure regulating unit (24) is provided in a fluid system (13) of the 3D printer in the fluid line (22) between the distributor element (17) and the printhead tank (15); - a differential pressure Δp1 of the fluid (5) in the fluid system (13) is determined, which is determined by a height difference Δh1 between the printhead (1) provided in the 3D printer at a height h2 and a surface (30) of the fluid (5) in the printhead tank connected to the printhead (1). (15) at a height h1 yields,- that in the area of ​​the surface (30) of the fluid (5) in the printhead tank (15) a pressure pFT is generated by the first pressure regulating unit (24), which results according to pFT = pB - Δp1 - ΔpSI, where pB corresponds to the base pressure of the air in the vicinity of the printhead (1) of the 3D printer, an atmospheric pressure, where ΔpSI is a safety value, and - that the fluid (5) is conveyed from the printhead tank (15) through the fluid supply channel (6) over the height difference Δh1 to the printhead (1), whereby a pressure pFD is established in the printhead (1), which is equal to or less than the base pressure pB. Method according to claim 4, characterized in that the base pressure pB is predetermined or is currently determined by means of a sensor. Method according to one of claims 4 or 5, characterized in that a differential pressure Δp2 of the fluid (5) is generated in the fluid supply channel (6) between an outlet-side connection of the fluid supply channel (6) on the printhead tank (15) and an inlet-side connection of the fluid supply channel (6) on the printhead (1). Method according to one of claims 4 to 6, characterized in that the differential pressure Δ p2 of the fluid (5) is controlled by means of a second pump (33) provided in a second pressure regulating unit (31), wherein the control of the differential pressure Δ p2 regulates a volume flow of the fluid (5) from the printhead tank (15) to the printhead (1). Method according to one of claims 4 to 7, characterized in that a first pump (26) and a first throttle valve (25) are provided in the first pressure regulating unit (24), that the first pump (26) delivers the fluid (5) in a first operating mode in a second flow direction (28) opposite to a first flow direction (27) of the fluid (5) through the first throttle valve (25) in the direction of a distributor element (17), wherein the first pump (26) is controlled by a control signal from a central control unit. Method according to one of claims 4 to 8, characterized in that a current value for the generated pressure pFT in the area of ​​a surface (30) of the fluid (5) in the printhead tank (15) is measured by means of a pressure sensor (41) arranged above the surface (30) without contact with the fluid (5). Method according to one of claims 4 to 9, characterized in that the first pump (26) conveys the fluid (5) in a second operating mode in the first flow direction (27), in the direction of the printhead tank (15), wherein the first pump (26) is controlled by the control signal of the central control unit.

Images