WO2021196850A1 - 螺杆式送料装置、用于3d打印的物料挤出系统和方法 - Google Patents

螺杆式送料装置、用于3d打印的物料挤出系统和方法 Download PDF

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Publication number
WO2021196850A1
WO2021196850A1 PCT/CN2021/073976 CN2021073976W WO2021196850A1 WO 2021196850 A1 WO2021196850 A1 WO 2021196850A1 CN 2021073976 W CN2021073976 W CN 2021073976W WO 2021196850 A1 WO2021196850 A1 WO 2021196850A1
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Prior art keywords
screw
feeding device
extrusion
extrusion port
viscosity
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PCT/CN2021/073976
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English (en)
French (fr)
Inventor
黄卫东
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苏州美梦机器有限公司
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Publication of WO2021196850A1 publication Critical patent/WO2021196850A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/30—Auxiliary operations or equipment
    • B29C64/307—Handling of material to be used in additive manufacturing
    • B29C64/321—Feeding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
    • B29C48/395—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using screws surrounded by a cooperating barrel, e.g. single screw extruders
    • B29C48/397—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using screws surrounded by a cooperating barrel, e.g. single screw extruders using a single screw
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
    • B29C48/50—Details of extruders
    • B29C48/505—Screws
    • B29C48/59—Screws characterised by details of the thread, i.e. the shape of a single thread of the material-feeding screw
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/78—Thermal treatment of the extrusion moulding material or of preformed parts or layers, e.g. by heating or cooling
    • B29C48/80—Thermal treatment of the extrusion moulding material or of preformed parts or layers, e.g. by heating or cooling at the plasticising zone, e.g. by heating cylinders
    • B29C48/802—Heating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/78—Thermal treatment of the extrusion moulding material or of preformed parts or layers, e.g. by heating or cooling
    • B29C48/86—Thermal treatment of the extrusion moulding material or of preformed parts or layers, e.g. by heating or cooling at the nozzle zone
    • B29C48/865—Heating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/92—Measuring, controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/106—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
    • B29C64/118—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using filamentary material being melted, e.g. fused deposition modelling [FDM]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/20—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/20—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B29C64/295—Heating elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/30—Auxiliary operations or equipment
    • B29C64/307—Handling of material to be used in additive manufacturing
    • B29C64/314—Preparation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/30—Auxiliary operations or equipment
    • B29C64/386—Data acquisition or data processing for additive manufacturing
    • B29C64/393—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y30/00—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y50/00—Data acquisition or data processing for additive manufacturing
    • B33Y50/02—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes

Definitions

  • This application relates to the field of material extrusion, in particular to a screw-type feeding device, a material extrusion system and method for 3D printing.
  • Materials Extrusion-based 3D printing technology such as fused deposition molding (FDM) technology, usually uses a material conveying system to transport materials, and the materials are deposited layer by layer on a working platform to form 3D objects.
  • FDM fused deposition molding
  • the application provides a screw-type feeding device, a material extrusion system and method for 3D printing.
  • a screw-type feeding device is provided.
  • the screw-type feeding device is used to convey a flowable material to an extrusion port, and the width of the extrusion port continuously changes during the material extrusion process.
  • the screw-type feeding device includes: a screw; a rotation controller configured to drive the screw to rotate; wherein the screw-type feeding device is configured to satisfy Q max /D 2 ⁇ 5cm/min, L/D ⁇ 5, where Q max It represents the maximum flow rate of the flowable material conveyed by the screw-type feeding device, D represents the diameter of the screw, and L represents the length of the screw.
  • a material conveying system for 3D printing including: an extrusion head; the screw-type feeding device according to the first aspect; and a first control system configured to control the The width of the extrusion port of the extrusion head continuously changes within a preset range.
  • a material conveying method for 3D printing including: during the 3D printing process, the screw-type feeding device as described in the first aspect is used to convey the flowable material to the extrusion head; The width of the extrusion port of the extrusion head continuously changes within a preset range.
  • Fig. 1 is a schematic structural diagram of a material conveying system provided by the first embodiment of the present application.
  • Fig. 2 is a schematic structural diagram of a material conveying system provided by a second embodiment of the present application.
  • Fig. 3 is a schematic diagram of the structure of the first feeding device in the second embodiment.
  • Fig. 4 is a schematic diagram of the structure of the buffer container in the second embodiment.
  • Fig. 5 is a schematic diagram of the corresponding relationship between the liquid level of the buffer container and the motor load in the second embodiment.
  • Fig. 6 is a flow chart of the calibration method of the corresponding relationship between the liquid level of the buffer container and the motor load in the second embodiment.
  • Fig. 7 is a schematic structural diagram of a buffer container with pressure or liquid level feedback function in the second embodiment.
  • Fig. 8 is a schematic diagram of the structure of the second feeding device in the second embodiment.
  • Fig. 9 is a schematic flowchart of a material conveying method provided by a third embodiment of the present application.
  • the material conveying system 10 for 3D printing includes a screw-type feeding device 40, an extrusion head 50 and a first control system 60.
  • the screw feeding device 40 is configured to receive the flowable material and convey the flowable material to the extrusion head 50.
  • the extrusion head 50 has an extrusion port 51 with a continuously adjustable width.
  • the first control system 60 may be configured to control the width of the extrusion port 51 to continuously change within a preset range during the 3D printing process.
  • the width of the extrusion port is required to vary with the cross-sectional contour line of the material filling area (or, the width of the extrusion port and the length of the cross-sectional contour line of the material filling area Match), so as to achieve ultra-high efficiency printing.
  • the system shown in FIG. 1 requires that the width of the extrusion port 51 be continuously changed within a preset range, which means that the material flow rate conveyed by the material conveying system 10 needs to dynamically change within a certain range.
  • the effects of countercurrent, leakage and shear thinning are particularly prominent.
  • the screw-type feeding device 40 includes a screw 41 and a rotation controller 42 (the rotation controller may include, for example, a motor 421 or a speed reducer 422).
  • the screw-type feeding device 40 is configured to satisfy Q max /D 2 ⁇ 5cm/min, L/D ⁇ 5, where Q max represents the maximum flow rate of the flowable material conveyed by the screw-type feeding device, and D represents the screw’s Diameter, L represents the length of the screw.
  • the screw diameter D has a strong positive correlation with the flow rate of the material, that is, the smaller the material flow rate, the smaller the corresponding screw diameter D will be designed. Therefore, in common screw designs, the screw length L is usually greater than 20D, and common screws are generally elongated rods.
  • the embodiment of the present application hopes to use the screw to accurately control the flow rate of the material in a relatively large range, it is necessary to suppress the leakage flow.
  • the screw-type feeding device needs to be processed with high precision, so that the gap between the screw and the barrel sleeved on the screw is very small.
  • This design requirement is very difficult to realize on a slender screw. Yes, the reason is that the rigidity of the slender screw is very poor, and a too small gap can easily cause friction between the screw and the barrel or even jam. Therefore, the embodiment of this application uses a screw with a very small L/D (L/D ⁇ 5).
  • This type of screw is characterized by a large screw diameter D relative to the length of the screw, and its rigidity is sufficient to satisfy the gap between the screw and the barrel. The gap is smaller in the design requirements.
  • the ultra-low screw speed will significantly reduce the shear rate of the material in the screw.
  • the material Under the condition of ultra-low shear rate, the material can be regarded as a Newtonian fluid (the material in the traditional material extrusion process is generally a non-Newtonian fluid), which brings the following advantages: (1) The flow caused by shear thinning can be ignored The complexity of the law controls the material conveying flow according to precise mathematical equations; (2) The viscous flow resistance in the screw is significantly greater than that of the non-Newtonian fluid, which has a significant effect on significantly reducing leakage and reverse flow; (3) In the same screw Under the condition of rotating speed, it has greater extrusion force, which is conducive to the extrusion of materials from extremely small extrusion ports during high-precision extrusion.
  • the super-large screw diameter D and super-low screw speed help reduce screw leakage and shear thinning effects, thereby helping to accurately control the material flow rate when the extrusion port width changes dynamically in a large range.
  • L/D ⁇ 5 provides a large screw diameter design relative to the screw length.
  • the gap ⁇ between the screw 41 and the barrel 43 can be designed as ⁇ ⁇ 0.001D.
  • this kind of clearance design is difficult to realize on a common slender screw, while it is relatively easy to realize on the super-large diameter screw in the embodiment of the present application. Therefore, the ultra-large screw diameter design relative to the screw length and the ultra-small gap design between the screw and the barrel can effectively reduce leakage, which helps to accurately control the material flow rate when the width of the extrusion port changes dynamically in a large range .
  • the helix angle of the screw Set in a smaller range (for example, you can set the helix angle Designed as ) To increase the extrusion pressure of the screw, which can further reduce the backflow.
  • you can set the helix angle Designed as to increase the extrusion pressure of the screw, which can further reduce the backflow.
  • the extrusion flow rate of the screw feeding device can be calculated by the following formula:
  • Q represents the extrusion flow rate (or flow rate) of the material
  • D represents the outer diameter of the screw 41
  • H represents the depth of the screw groove
  • n represents the screw speed
  • P represents the extrusion pressure of the extrusion port 51
  • P max represents the maximum extrusion pressure of the screw 41
  • L represents the screw length
  • ⁇ represents the gap between the screw and the barrel
  • e represents the method of screw edge Width
  • ⁇ represents the viscosity of the material in the groove
  • ⁇ 1 represents the viscosity of the material in the gap ⁇ .
  • the screw ridge width e is appropriately increased to prevent leakage.
  • the thread edge width e of the screw can be designed to satisfy: It can be seen from formula (3) that the larger the value of e, the smaller the ratio of leakage current to positive current, and the less obvious the phenomenon of leakage current.
  • the shear rate ⁇ of the screw to the flowable material in the groove of the screw can be controlled so that ⁇ 500/s.
  • the lower the shear rate the less obvious the shear thinning effect.
  • Materials with low shear thinning effect can be regarded as Newtonian fluids.
  • the flow rate of this fluid is easier to model and control accurately.
  • the units of D, H, e, L, and ⁇ in Table 1 are cm, and rpm represents the rotation speed per minute.
  • the first embodiment does not specifically limit the flowable material source of the screw feeding device 40.
  • a feeding port 45 may be provided for the screw-type feeding device 40, and the screw-type feeding device 40 may obtain a flowable material from the outside through the feeding port 45.
  • the screw-type feeding device 40 can be added with other types of material processing devices to convert solid materials into flowable materials.
  • the material conveying system 10 may also include a second control system 44, 52 configured to control the viscosity of the material in the screw 41 and/or the material at the extrusion port 51.
  • the viscosity is controlled so that the viscosity of the material in the screw 41 is greater than the viscosity of the material at the extrusion port 51.
  • the above-mentioned difference in material viscosity can greatly reduce the backflow and leakage problems of the screw-type feeding device 40, and even reduce the backflow and leakage to a negligible level compared with the forward flow, which is beneficial to the screw-type feeding device. 40. Precisely control the metering output of materials.
  • the inventor also found that reducing the extrusion pressure P of the extrusion port 51 can significantly reduce the power consumption of the screw-type feeding device 40, thereby reducing the cost of the material conveying system.
  • the second control system 44, 52 may include a first heater 44 and a second heater 52.
  • the first heater 44 is configured to heat the screw 41.
  • the second heater 52 is configured to heat the extrusion port 51.
  • the heating temperature of the second heater 52 is higher than the heating temperature of the first heater 44.
  • the above heating temperature setting method can widen the temperature difference between the extrusion port 51 and the screw 41. Setting a lower temperature at the screw 41 can increase the viscosity of the material, and setting a higher temperature at the extrusion port 51 can reduce the viscosity of the material at the extrusion port 51.
  • the temperature of the screw 41 can be controlled by the first heater 44 so that the temperature of the screw 41 is close to the melting temperature of the material.
  • the heating temperature T1 of the first heater 44 can be controlled within the range of T f to T f +30° C., where T f represents the melting temperature of the material.
  • the temperature at the extrusion port 51 can also be controlled by the second heater 52 so that the temperature at the extrusion port 51 is close to the decomposition temperature of the material.
  • the heating temperature T2 of the second heater 52 can be controlled within the range of (T f +50°C) to (T d -30°C), where T f represents the melting temperature of the material, and T d represents the decomposition of the material temperature.
  • the materials of different types of materials are different, and the corresponding temperature control range will have certain differences.
  • the temperature T1 of the first heater is greater than 155°C and less than 185°C; and/or the temperature T2 of the second heater is greater than 205°C and less than 310°C; or the material is acrylonitrile-butadiene -Styrene copolymer
  • the temperature T1 of the first heater is greater than 170°C and less than 200°C
  • the temperature T2 of the second heater is greater than 220°C and less than 250°C
  • the material is polycarbonate
  • the temperature T1 of the heater is greater than 220°C and less than 250°C; and/or the temperature T2 of the second heater is greater than 270°C and less than 320°C; or, the material is nylon-6, and the temperature T1 of the first heater is greater than 215°C and less than 245°C; and/or the temperature
  • the foregoing has introduced the ultra-low-speed screw-type feeding device with the characteristics of low shear thinning effect, so that the material can be regarded as a Newtonian fluid.
  • the viscosity of Newtonian fluids has the characteristics of obvious temperature effect, that is, the viscosity reduction effect caused by increasing the temperature at the extrusion port 51 is obvious, thereby significantly reducing the head pressure. It can be seen that the ultra-low speed The screw-type feeding device and the temperature difference method can help to significantly reduce the backflow and leakage phenomenon in the system.
  • PLA polylactic acid
  • PVA polylactic acid
  • it is a typical non-Newtonian fluid under high shear conditions in a conventional screw. Its viscosity has a low temperature dependence, but the shear rate is lower than 100s. Under the condition of -1 , when its viscosity increases from 170°C to 240°C, the viscosity can be reduced by more than 200 times.
  • the working temperature of the screw is set to 170°C
  • the temperature of the extrusion port is 240°C
  • the thickness of the extrusion port is 0.1mm
  • the backflow of the material conveying system 10 is less than 6% of the minimum positive flow, and leakage The flow is less than 1% of the minimum forward flow.
  • the leakage and reverse flow have a very weak effect on the material conveying in the screw and can be almost ignored.
  • the flow rate of the material conveying system is basically determined by the screw speed.
  • the leakage flow and the reverse flow are much smaller than the minimum positive flow, which are only 0.42 and 0.59% or less of the positive flow, and the impact on material transportation can be completely ignored. It can be seen that the above scheme suppresses leakage and reverse flow to the greatest extent, and there is a good linear relationship between the material conveying flow rate and the screw speed.
  • the second embodiment is similar to the first embodiment, and the main difference between the two is: the second embodiment has a screw feeder 40 (it should be noted that in the second embodiment, the screw feeder 40 is called the first
  • the second feeding device defines the source of the flowable materials provided to the extrusion head 50, and is provided by the buffer container. The following mainly describes in detail the differences between the second embodiment and the first embodiment, and the same parts can be referred to the first embodiment.
  • the material conveying system conveys materials at a fixed flow rate, it may be appropriate to continuously complete the conversion of the material from solid state to flowable state by a feeding device, and the metering output of flowable dynamic materials to the extrusion head may be appropriate of.
  • a feeding device is used to continuously complete the conversion of the material state and the metering output of the material to the extrusion head, the two processes will be difficult to coordinate. problem.
  • a screw feeder it usually includes a feeding section, a melting section (or compression section), and a metering section.
  • the feeding section is used to receive solid materials
  • the melting section is used to convert solid materials into a flowable state
  • the metering section is used to quantitatively output flowable materials to the extrusion head. If the flow rate of the material changes dynamically, the speed of the screw feeder will also change dynamically. In this way, the pressure, flow and temperature of the flowable material output from the melting section will fluctuate. Affected by the fluctuation of the flowable materials output from the melting section, it is difficult for the metering section to accurately and quantitatively transport the materials to the extrusion head.
  • this application assigns the two tasks of material state conversion and material metering output to two different feeding devices, and buffers the materials between the two feeding devices to shield the output of the first feeding device The impact of fluctuations on the second feeding device.
  • the detailed description will be given below in conjunction with FIG. 2.
  • Fig. 2 is a material conveying system 10 provided by some embodiments of the present application.
  • the material conveying system 10 can be applied to the field of plastic extrusion, and can also be applied to the field of 3D printing, such as a 3D printing technology based on materials extrusion.
  • the material conveying system 10 can be used to convey plastics and any paste-like materials that can be flowed and extruded.
  • the material delivery system 10 can be used to transport metal paste materials (metal paste materials can be formed by adding a liquid binder to metal powder), and ceramic paste materials (ceramic paste materials can be formed by adding a liquid binder to metal powder). Add liquid binder to form), organic polymer materials, inorganic paste materials (such as cement, gypsum slurry, mud slurry, etc.).
  • the material conveyed by the material conveying system 10 may also be a creamy food such as cream and chocolate.
  • the material conveying system 10 can be used to convey materials formed of the following materials: polylactic acid (PLA), acrylonitrile-butadiene-styrene copolymer (ABS), polycarbonate ( PC), nylon-6 (PA6), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA) and polyether ether ketone (PEEK).
  • PLA polylactic acid
  • ABS acrylonitrile-butadiene-styrene copolymer
  • PC polycarbonate
  • PA6 nylon-6
  • PPS polyphenylene sulfide
  • PMMA polymethyl methacrylate
  • PEEK polyether ether ketone
  • the material conveying system 10 includes a first feeding device 20, a buffer container 30, a second feeding device 40 and an extrusion head 50.
  • the broad arrow in Figure 2 represents the direction of material flow (or material conveying). It can be seen from the direction of the broad arrow that in the material conveying system 10, the material can pass through the first feeding device 20, the buffer container 30, the second feeding device 40, and the extrusion head 50 in sequence.
  • the first feeding device 20 is configured to convert solid materials into flowable materials (also referred to as molten materials).
  • the buffer container 30 is configured to store the flowable material output by the first feeding device 20.
  • the second feeding device 40 is configured to convey the flowable material in the buffer container 30 to the extrusion head 50 of the material conveying system 10.
  • the buffer container 30 Due to the existence of the buffer container 30, the difficulty of coordinating the two stages of material state conversion and metering output is reduced, thereby facilitating the realization of stable metering and output of materials.
  • the first feeding device 20 provides a source of materials. Therefore, the first feeding device 20 can be referred to as a material supply section of the material conveying system 10. Since the first feeding device 20 can melt solid materials into flowable materials, the first feeding device 20 can also be regarded as the melting section of the material conveying system 10.
  • the first feeding device 20 can also provide preliminary flow control of the flowable material, and deliver the flowable material to the buffer container 30 according to a given flow requirement.
  • the application does not specifically limit the flow rate adjustment range of the first feeding device 20, and can be set according to actual needs.
  • the first feeding device 20 may be configured with a flow rate adjustable range of 5 to 20 times.
  • the flow rate delivered by the first feeding device 20 can be adjusted according to a certain rule, for example, can be adjusted according to the volume of the material in the buffer container 30 or the height of the liquid level.
  • the first feeding device 20 may also provide preliminary temperature control, so as to deliver a flowable material at a given temperature to the buffer container 30.
  • the first feeding device 20 may be a screw feeding device (or a screw pump, or a screw extruder), or a pneumatic feeding device or a piston feeding device.
  • the discharge port of the first feeding device 20 may be provided with a filter element (such as a sieve plate), so that the material can filter out possible solid substances before entering the buffer container 30.
  • a filter element such as a sieve plate
  • the first feeding device 20 may include a feeding port 21, a screw 22, a discharging port 23 and a heater 26.
  • the feed port 21 can be used to receive solid materials.
  • the feed port 21 may be a hopper.
  • the screw 22 can be divided into three sections: a feeding section 221, a melting section (or compression section) 222, and a metering section 223.
  • the feeding section 221 can convey the solid material received by the feeding port 21 to the melting section 222.
  • the melting section 222 can convert solid materials into flowable materials, and then convey the flowable materials to the metering section 223.
  • the metering section 223 can perform rough metering and output of materials.
  • the heater 26 can control the working temperature of the screw, so as to maintain the state of the material in a flowable state.
  • the heater 26 may be disposed in the area corresponding to the melting section 222 and the metering section 223 of the screw 22.
  • the screw 22 can be rotated by the drive of the motor 27 to transport the material.
  • a reducer 28 can be provided between the motor 27 and the screw device 22 to match the rotation speed between the motor 27 and the screw 22.
  • the sieve plate 29 is located at the discharge port 23 to filter out solid substances that may be contained in the material.
  • the buffer container 30 can be regarded as a transition device between the first feeding device 20 and the second feeding device 40.
  • the buffer container 30 can receive the flowable material from the first feeding device 20 and serve as the feeding tank of the second feeding device 40 to meet the dynamic flow supply of the material required by the second feeding device 40.
  • the buffer container 30 can isolate the possible adverse effects of the fluctuation of the output of the first feeding device 20 on the second feeding device 40.
  • the fluctuations output by the first feeding device 20 include at least one of the following fluctuations: pressure fluctuations, flow fluctuations, and temperature fluctuations.
  • the isolation of the buffer container 30 from the fluctuation of the output of the first feeding device 20 facilitates the second feeding device 40 to precisely control the flow rate of the material.
  • the first feeding device 20 and the second feeding device 40 are directly connected, in order to achieve high-precision flow rate control at the extrusion port, it is necessary to perform a process between the first feeding device 20 and the second feeding device 40.
  • High-precision collaborative flow rate control when the material extrusion flow rate of the extrusion head 50 needs to be dynamically changed, the state of the material output by the first feeding device 20 is very unstable. In this case, it is very difficult to achieve high-precision coordination between the first feeding device 20 and the second feeding device 40.
  • the addition of the buffer container 30 between the first feeding device 20 and the second feeding device 40 can reduce the requirement for coordinated control between the first feeding device 20 and the second feeding device 40.
  • the buffer container 30 serves as a buffer component, which can smooth the fluctuation of the output of the first feeding device 20 and ensure that the material is supplied to the subsequent second feeding device 40 in a stable state.
  • a stirring device 32 may be provided for the buffer container 30.
  • the structure of the stirring device 32 can be various.
  • a blade mixer can be used, or a drum mixer can be used.
  • a blade mixer is taken as an example to illustrate the structure and working mode of the mixing device 32.
  • the stirring device 32 may include a stirring blade 322 and a servo motor 324.
  • the motor 324 drives the stirring blade 322 to stir the flowable materials stored in the buffer container 30, thereby stabilizing the fluctuations in the state (such as temperature or composition) of the materials conveyed by the first feeding device 20 to the buffer container 30, and ensuring buffering
  • the uniformity of the state of the material in the container 30 speeds up the overflow of residual gas in the material.
  • the shape of the stirring blade 322 and the inlet 34 (which can be connected to the first feeding device 20) and the outlet 36 (which can be connected to the second feeding device 40) of the buffer container 30 can adopt a specific structural design, so that The material entering the buffer container 30 from the inlet 34 is discharged from the outlet 36 after a sufficiently long flow in the buffer container 30. In this way, the flowable dynamic material passes through enough processes to better ensure the uniformity of the material state.
  • the mixing blade 322 can be designed with a certain shape, so that the flowable material enters the buffer container 30 from the inlet 34, spirals up, and then flows downward from the center to the outlet 36.
  • the buffer container 30 may also be provided with a temperature control device 38 to control the temperature of the flowable material stored in the buffer container 30.
  • the temperature control device 38 may include a heating component, a temperature sensor, and a temperature controller (not shown in FIG. 4).
  • the heating component may be a metal sleeve containing a heating rod/flexible heating sheet, which is sleeved outside the shell 37 of the buffer container 30.
  • the temperature sensor may be a high-precision thermocouple to measure the temperature of the housing 37 and feed back the temperature measurement result to the thermostat.
  • the thermostat can adopt a high-precision PID controller.
  • the controller can control the output power of the heating component according to the temperature fed back by the temperature sensor, thereby controlling the temperature of the housing 37 at a set target value.
  • the material conveying system 10 may also include a feedback control device.
  • the feedback control device can adjust the amount of flowable material output by the first feeding device 20 (or the rate of the flowable material output by the first feeding device 20) according to the amount of flowable material stored in the buffer container 30.
  • the volume of the buffer container 30 can be set according to actual material transportation requirements.
  • the buffer container 30 can be configured with an appropriate volume to keep the liquid level in the buffer container 30 within a reasonable range, and reduce the influence of the pressure generated by the liquid level difference on the subsequent material transportation.
  • the height of the liquid level in the buffer container 30 can be maintained at: when the extrusion port is extruding the material at the maximum flow rate, the amount of material in the buffer container 30 is sufficient to supply the demand of the extrusion port, and when the extrusion port is at the minimum flow rate When the material is extruded, the height of the liquid level of the buffer container 30 will not cause the material in the buffer container 30 to overflow.
  • the buffer container 30 meets the above two conditions at the same time, the pressure difference caused by the difference in the liquid level of the material stored in the buffer container 30 is very small, almost negligible, and will not affect the pressure of the extrusion port.
  • the extrusion head 50 may be an extrusion port 51 with a continuously adjustable width.
  • the control of the feedback control device can make the amount of flowable material stored in the buffer container 30 not less than the amount of material required when the extrusion port 51 adopts the maximum width for material extrusion.
  • Feedback control scheme 1 Feedback control based on the load/torque of the stirring motor
  • the viscosity of the flowable materials (especially high polymer materials) conveyed by the material conveying system is generally relatively large. Therefore, as the liquid level increases, the stirring resistance of the stirring device 32 will correspondingly increase, resulting in an increase in the load/torque of the motor 324. Therefore, the feedback control device can adjust the amount of material output by the first feeding device 40 according to the load or torque of the motor 324.
  • the load signal representing the load of the motor or the torque signal representing the torque of the motor (the torque signal can be collected by a torque sensor) can be obtained first, and then the signal can be fed back to the first feeding device 20 to control the first feeding device 20. Feed rate.
  • the load signal or torque signal of the motor is a continuously changing electrical signal.
  • the feeding rate of the first feeding device 20 can be controlled by the PID algorithm.
  • This control method has better control accuracy than a simple on-off control method. high.
  • the advantage of this solution is that feedback control can be realized by using the stirring device 32, and no additional feedback control device is required, thereby reducing the complexity of the system.
  • the corresponding relationship between the height of the liquid level in the buffer container 30 and the load/torque of the motor can be established first. Since the corresponding relationship between the height of the liquid level in the buffer container 30 and the load/torque of the motor will vary with temperature and the material/quality of the material, the height of the liquid level in the buffer container 30 and the load/torque of the motor can be adjusted in advance. The corresponding relationship between torque and torque is calibrated. A possible calibration method is given below.
  • the stirring blade 322 may be structurally designed so that the blade width of the stirring blade 322 increases suddenly at H3.
  • the load of the motor 324 will increase rapidly.
  • the program can be used to automatically identify the load size at H3, and then, according to the load size at H3, determine the target value of feedback control (the target value can be set according to actual needs, for example, it can be set to H3 80% of the load), so as to achieve the height control of the liquid level.
  • the load safety threshold can also be set according to the size of the load of the motor at H3. When the height of the liquid level causes the load of the motor to exceed the safety threshold, the load is rapidly increased to the safety threshold to control the first feeding device 20 to stop feeding. .
  • the slope of the liquid level-load curve will be determined by the shape of the stirring blade 322.
  • the stirring blade 322 may adopt a structure that gradually changes from wide to narrow. As shown in Figure 5, below H3, the width of the stirring blade 322 can be designed with an "inverted triangle" (or, in other embodiments, an "inverted trapezoid” design can also be adopted), which can increase the height of the liquid level. -The slope of the load curve improves the control accuracy.
  • the calibration process may include step S610 to step S660.
  • step S610 the temperature of the buffer container is increased to the target temperature, and the temperature is controlled.
  • the target temperature can be the temperature of the buffer container when it is actually working.
  • the value of the target temperature can be set according to actual needs, as long as it can ensure that the material is in a flowable state.
  • step S620 the rotation speed of the stirring motor is increased to the target rotation speed, and the stirring motor is operated at a constant speed, and the load of the motor is measured.
  • the measured load of the motor is the load when the motor is idling.
  • step S630 the first feeding device is controlled to start feeding the buffer container.
  • the outlet of the buffer container needs to be closed, and the buffer container is prohibited from outputting materials to the second feeder.
  • step S640 as the liquid level of the material rises, a P(t) curve representing the change of the load of the motor over time is recorded.
  • step S650 the first feeding device is controlled to stop feeding, and the P(t) curve is automatically analyzed.
  • the second derivative dP 2 /dt 2 of the P(t) curve can be calculated.
  • the P value corresponding to the maximum value of the second derivative is the motor load at H3. Assuming that the material of the system is material 1, the maximum value of the second derivative corresponds to As shown in Figure 5, the load P1 of material 1.
  • step S660 the target value and safety threshold of the feedback control are set according to the motor load at H3.
  • the motor load P1 at H3 can be multiplied by the height factor of the liquid level to obtain the target value of the feedback control.
  • the height factor can be set according to actual needs.
  • the height factor of the liquid level can be set to 80% of the total height from H1 to H3 (ie at H2 in Figure 5), 0.8*P1 can be set as the target value of the feedback control, and the liquid level can be controlled Below H2.
  • a safety threshold for the load can also be set.
  • the safety threshold can be set according to actual needs.
  • the safety threshold can be designed to be 120% of the P1 load, that is, 1.2*P1 is set as the safety threshold.
  • the motor load exceeds this threshold, the first feeding device 20 is controlled to stop feeding.
  • the above operation can be repeated to re-obtain the load P2 of material 2 at H3, and use 0.8*P2 as the target value of feedback control and 1.2*P2 as the safety threshold.
  • the material conveying system can be put into working state, the first feeding device and the second feeding device can be turned on, and the feeding rate of the first feeding device 20 can be controlled by real-time feedback according to the motor load, so as to buffer the liquid in the container.
  • the surface height is controlled below H2.
  • a pressure sensor 33 can be installed at the bottom of the buffer container 30, and the pressure value fed back by the pressure sensor 33 is used as a basis for controlling the feeding rate of the first feeding device 20.
  • the pressure sensor 33 can be a pressure sensor of a relative pressure measurement type.
  • a pressure sensor 33 with a range of kilopascals can be selected.
  • the pressure resolution of the pressure sensor 33 can be selected at ten Pascals, which is 1% of the range.
  • the pressure change rate with the height of the liquid level is 12.25. Pa/mm to achieve millimeter-level height control. If the feedback control scheme is adopted, the corresponding relationship between pressure and liquid level can be established in advance, and this relationship can be determined according to the density (or melt density) of the material in the flowable state.
  • Feedback control scheme 3 Feedback control based on liquid level buoy
  • the float 39 can be floated on the liquid surface of the material, and the float 39 will rise as the liquid level rises.
  • the float 39 has a floating rod, which rises out of the upper cover of the buffer container 30.
  • An electronic ruler 37 can be installed on the upper cover of the buffer container 30. By detecting the up and down movement of the floating rod, the liquid level is converted into an electrical signal, and the electrical signal is used as a feedback signal to control the feeding rate of the first feeding device 20.
  • the buffer container 30 can be designed as a cylindrical container or as a container of other shapes.
  • the inner surface with high smoothness can reduce the adhesion of materials, and prevent it from polluting other materials in the buffer container 30 after high-temperature decomposition.
  • the lower end of the buffer container 30 may be funnel-shaped to avoid dead corners in the container and cause material residue.
  • Both the inlet 34 and the outlet 36 can adopt standard interfaces (such as buckles or flanges), which are connected to the first feeding device 20 and the second feeding device 40, respectively.
  • the inlet 34 can be arranged at a position where the side wall of the buffer container 30 is biased toward the bottom, so as to prevent materials from flowing down from a high place and entrapped in gas.
  • the outlet 36 can be arranged on the bottom surface of the buffer container 30 to ensure that all the materials can flow out without any dead ends.
  • a filter member 35 (such as a filter screen) may be provided at the outlet 36 to prevent impurities from entering the second feeding device 40.
  • the second feeding device 40 can directly convey the flowable material in the buffer container 30 to the extrusion head 50 without the need to switch the material state, which is beneficial to realize the high-precision metering of the material Output. Therefore, the second feeding device 40 can also be referred to as a precision metering feeding device. Alternatively, the second feeding device 40 can be regarded as a precision feeding section of the material conveying system 10. In some embodiments, the second feeding device 40 can perform accurate real-time control of the material in a large flow rate range during the process of conveying the material. For example, the second feeding device 40 can accurately control the flow rate, temperature and other parameters of the material.
  • the first feeding device 20, the buffer container 30, the second feeding device 40 and the extrusion head 50 can be regarded as the four functional sections of the entire material conveying system 10. Each functional section can be based on its own The need for precise temperature control.
  • the first feeding device 20 can control the temperature to be suitable for converting the material from a solid state to a flowable state (or a molten state).
  • the buffer container 30 can control the temperature at a target value, and the target value can be determined according to the operating temperature of the second feeding device 40, for example, it can be slightly higher than the operating temperature of the second feeding device 40.
  • the second feeding device 40 and the extruding head 50 can be temperature controlled by the aforementioned temperature difference control method.
  • the second feeding device 40 may adopt the screw feeding device in the first embodiment. In order to avoid repetition, it will not be described in detail here.
  • the first embodiment to the second embodiment are device embodiments, and the third embodiment is a method embodiment.
  • the description on the device side and the description on the method side correspond to each other, and repeated descriptions are appropriately omitted for brevity.
  • Fig. 9 is a schematic flow chart of the material conveying method provided by the third embodiment.
  • the method S900 in FIG. 9 may be executed by the material conveying system 10 mentioned above.
  • the method S900 includes step S910 to step S920.
  • a screw-type feeding device is used to convey the flowable material to the extrusion head.
  • the screw-type feeding device may adopt the screw-type feeding device 40 provided in the first to third embodiments.
  • step S920 during the 3D printing process, the width of the extrusion port of the extrusion head is controlled to continuously change within a preset range.
  • the method S900 further includes: controlling the viscosity of the material in the screw and/or the viscosity of the material at the extrusion port, so that the viscosity of the material in the screw is greater than the viscosity of the material at the extrusion port .
  • the above-mentioned controlling the viscosity of the material in the screw and/or the viscosity of the material at the extrusion port so that the viscosity of the material in the screw is greater than the viscosity of the material at the extrusion port may include: The screw is heated; the extrusion port is heated; the heating temperature of the extrusion port is higher than the heating temperature of the screw.
  • the heating temperature of the screw T1 ⁇ (T f , T f +30° C.), where T f represents the melting temperature of the material.
  • the heating temperature of the extrusion port is T2 ⁇ (T f +50° C., T d -30° C.), where T f represents the melting temperature of the material, and T d represents the decomposition temperature of the material.
  • method S900 before step S910, further includes: converting solid materials into flowable materials; using a buffer container to store the flowable materials output by the first feeding device; The stored flowable materials are transported to the screw-type feeding device.
  • step S920 includes: controlling the width of the extrusion port to change with the change of the cross-sectional contour line of the material filling area.
  • the computer program product includes one or more computer instructions.
  • the computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices.
  • the computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium.
  • the computer instructions may be transmitted from a website, computer, server, or data center.
  • the computer-readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server or data center integrated with one or more available media.
  • the usable medium may be a magnetic medium (for example, a floppy disk, a hard disk, a tape), an optical medium (for example, a digital video disc (DVD)), or a semiconductor medium (for example, a solid state disk (SSD)), etc.
  • the disclosed system, device, and method can be implemented in other ways.
  • the device embodiments described above are only illustrative.
  • the division of the units is only a logical function division, and there may be other divisions in actual implementation, for example, multiple units or components may be combined or It can be integrated into another system, or some features can be ignored or not implemented.
  • the displayed or discussed mutual coupling or direct coupling or communication connection may be indirect coupling or communication connection through some interfaces, devices or units, and may be in electrical, mechanical or other forms.
  • the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.
  • the functional units in the various embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units may be integrated into one unit.

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Abstract

一种螺杆式送料装置、用于3D打印的物料挤出系统和方法。该螺杆式送料装置（40）用于为挤出口（51）输送可流动的物料，且在物料挤出过程中挤出口（51）的宽度连续变化，螺杆式送料装置（40）包括：螺杆（41）；转动控制器（42），被配置为驱动螺杆（41）转动；其中，螺杆式送料装置（40）被配置为满足Q max/D 2＜5cm/min，L/D≤5，Q max表示螺杆式送料装置（40）输送的可流动的物料的最大流率，D表示螺杆的直径，L表示螺杆的长度。上述技术方案有利于在物料流率大范围动态变化时，提高螺杆式送料装置（40）对物料流率的控制精度。

Description

螺杆式送料装置、用于3D打印的物料挤出系统和方法 技术领域
本申请涉及物料挤出领域，具体涉及一种螺杆式送料装置、用于3D打印的物料挤出系统和方法。
背景技术
基于材料挤出(Materials Extrusion)的3D打印技术，如熔融沉积成型(fused deposition molding，FDM)技术，通常利用物料输送系统输送物料，物料在工作平台上逐层沉积，从而形成3D物品。
发明内容
本申请提供一种螺杆式送料装置、用于3D打印的物料挤出系统和方法。
第一方面，提供一种螺杆式送料装置，所述螺杆式送料装置用于为挤出口输送可流动的物料，且在物料挤出过程中所述挤出口的宽度连续变化，所述螺杆式送料装置包括：螺杆；转动控制器，被配置为驱动所述螺杆转动；其中，所述螺杆式送料装置被配置为满足Q max/D 2＜5cm/min，L/D≤5，其中，Q max表示所述螺杆式送料装置输送的可流动的物料的最大流率，D表示所述螺杆的直径，L表示所述螺杆的长度。
第二方面，提供一种用于3D打印的物料输送系统，包括：挤出头；根据第一方面所述的螺杆式送料装置；第一控制系统，被配置为在3D打印过程中，控制所述挤出头的挤出口的宽度在预设范围内连续变化。
第三方面，提供一种用于3D打印的物料输送方法，包括：在3D打印过程中，利用如第一方面所述的螺杆式送料装置将可流动的物料输送至挤出头；控制所述挤出头的挤出口的宽度在预设范围内连续变化。
附图说明
图1是本申请第一实施例提供的物料输送系统的结构示意图。
图2是本申请第二实施例提供的物料输送系统的结构示意图。
图3是第二实施例中的第一送料装置的结构示意图。
图4是第二实施例中的缓冲容器的结构示意图。
图5是第二实施例中的缓冲容器的液面高度与电机负载的对应关系的示意图。
图6是第二实施例中的缓冲容器的液面高度与电机负载对应关系的标定方式的流程图。
图7是第二实施例中的具有压力或液面高度反馈功能的缓冲容器的结构示意图。
图8是第二实施例中的第二送料装置的结构示意图。
图9是本申请第三实施例提供的物料输送方法的示意性流程图。
具体实施方式
第一实施例：
如图1所示，用于3D打印的物料输送系统10包括螺杆式送料装置40、挤出头50 和第一控制系统60。
螺杆式送料装置40被配置为接收可流动态的物料，并将可流动态的物料输送至挤出头50。
挤出头50具有宽度连续可调的挤出口51。第一控制系统60可以被配置为在3D打印过程中，控制挤出口51的宽度在预设范围内连续变化。例如，在一些先进的3D打印系统中，要求挤出口的宽度随着物料填充区域的截面轮廓线的变化而变化(或者，使得挤出口的宽度与物料填充区域的截面轮廓线的截线段的长度相匹配)，从而实现超高效率的打印。此类挤出口的设计方案和控制方法可以参见WO2018/205149A1(需要说明的是，本申请中的挤出口的宽度相当于在该专利申请中的出料口的长度，物料填充区域相当于该专利申请中的目标填充区域，该物料填充区域可以是待打印层的部分或全部区域)。
螺杆式送料装置40将物料输送至挤出口时，会在挤出口处产生压力。由于该压力的存在，会存在逆流或漏流的问题(逆流指的是物料会沿螺杆的螺槽反向流动；漏流指的是物料会在螺杆与机筒间隙内朝着与螺杆挤出方向相反的方向流动)。进一步地，物料(尤其是高分子材料)普遍存在剪切稀化效应，即物料粘度随剪切速率的变化而变化，使得基于螺杆的送料系统的流率与螺杆转速之间呈现非线性的关系。由于逆流、漏流和剪切稀化效应的存在导致物料流率与螺杆转速之间的关系变得非常难以度量。
虽然逆流、漏流和剪切稀化效应在普通的塑料挤出系统和3D打印系统中就存在，但由于此类系统普遍采用宽度固定的挤出口、以恒定流率进行物料挤出，因此，逆流、漏流和剪切稀化效应对此类系统的影响并不明显。
与上述系统不同的是，图1所示的系统要求挤出口51的宽度在预设范围内连续变化，这意味着物料输送系统10输送的物料流率需要在一定的范围内动态变化。在该系统中，要想对物料流率进行精确控制，逆流、漏流和剪切稀化效应的影响就显得尤为突出。发明人发现，采用传统的螺杆式送料装置很难满足此类系统的需求，因此，本申请实施例首先提供一种螺杆式送料装置。
如图1所示，螺杆式送料装置40包括螺杆41和转动控制器42(转动控制器例如可以包括电机421，还可以包括减速器422)。该螺杆式送料装置40被配置为满足Q max/D 2＜5cm/min，L/D≤5，其中，Q max表示螺杆式送料装置输送的可流动的物料的最大流率，D表示螺杆的直径，L表示螺杆的长度。
在通常的螺杆设计中，螺杆直径D与物料的流率有很强的正相关性，即物料流率越小，对应的螺杆直径D就会设计得越小。因此，在常见的螺杆设计中，螺杆长度L通常大于20D，常见的螺杆一般均为细长杆。
由于本申请实施例希望利用螺杆在较大范围内精确控制物料的流率，因此，需要抑制漏流。要想有效抑制漏流，需要对螺杆式送料装置进行高精度的加工，使得螺杆与套接在螺杆上的机筒间的间隙非常小，这种设计要求在细长螺杆上实现起来是非常困难的，原因在于细长螺杆的刚度很差，过小的间隙很容易造成螺杆与机筒摩擦甚至卡死。因此，本申请实施例采用了L/D很小的螺杆(L/D≤5)，这种螺杆的特点是相对于螺杆长度具有超大的螺杆直径D，其刚度足以满足螺杆和机筒之间的间隙较小的设计要求。
在大螺杆直径D的基础上，如果螺杆的转速太快，螺槽中的物料的剪切稀化效应会非常明显，为了避免这一问题，本申请实施例控制螺杆式送料装置40输送的物料的最大流率，使其满足：Q max/D 2＜5cm/min。通过该参数设计可以看出，本申请实际上采用了超 低的螺杆转速，以解决在大螺杆直径下螺槽中物料流速太快而增大剪切稀化效应的问题。
超低的螺杆转速会显著降低物料在螺杆中的剪切率。在超低的剪切率条件下，物料可以视作牛顿流体(传统物料挤出工艺中的物料一般是非牛顿流体)，这带来以下优点：(1)可以忽略剪切稀化带来的流动规律的复杂性，按照精确的数学方程控制物料输送流量；(2)螺杆中的粘流阻力比非牛顿流体显著更大，对显著减小漏流和逆流有明显作用；(3)在相同螺杆转速条件下，具有更大的挤出力，有利于高精度挤出时物料从极小尺寸的挤出口挤出。
综上，超大的螺杆直径D和超低的螺杆转速有助于降低螺杆的漏流和剪切稀化效应，从而有助于挤出口宽度在较大范围动态变化时物料流率的精确控制。
前文指出，L/D≤5提供的是一种相对于螺杆长度的大螺杆直径设计，在此基础上，在一些实施例中，可以将螺杆41和机筒43之间的间隙δ设计成δ＜0.001D。如前文所述，这种间隙设计在普通的细长螺杆上是难以实现的，而在本申请实施例中的超大直径的螺杆上是比较容易实现的。因此，通过相对螺杆长度的超大螺杆直径设计以及螺杆和机筒之间的超小间隙设计，可以有效降低漏流，从而有助于挤出口宽度在较大范围动态变化时物料流率的精确控制。
可选地，在某些实施例中，可以将螺杆的螺旋角
Figure PCTCN2021073976-appb-000001
设置在较小的范围(例如，可以将螺旋角
Figure PCTCN2021073976-appb-000002
设计为
Figure PCTCN2021073976-appb-000003
)，以增大螺杆的挤出压力，这样可以进一步降低逆流。具体原因分析如下。
螺杆式送料装置的挤出流量可以通过下式计算：
Figure PCTCN2021073976-appb-000004
Figure PCTCN2021073976-appb-000005
Figure PCTCN2021073976-appb-000006
式中：Q表示物料的挤出流量(或流率)，D表示螺杆41的外径，H表示螺槽深度，
Figure PCTCN2021073976-appb-000007
表示螺旋角，n表示螺杆转速，P表示挤出口51的挤出压力，P max表示螺杆41的最大挤出压力，L表示螺杆长度，δ表示螺杆与机筒的间隙，e表示螺棱的法向宽度，η表示螺槽中的物料的粘度，η 1表示间隙δ中的物料的粘度。
通过式(2)可以看出，螺杆挤出压力的最大值P max越大，逆流与正流的比值就越小，逆流现象就越不明显。P max与螺旋角
Figure PCTCN2021073976-appb-000008
反相关，即螺旋角
Figure PCTCN2021073976-appb-000009
越小，P max越大。因此，可以通过控制螺旋角
Figure PCTCN2021073976-appb-000010
提升螺杆的挤出压力，降低逆流的影响。降低螺杆的逆流有助于为挤出口宽度在较大范围动态变化时物料流率的精确控制。
可选地，在某些实施例中，适当增加螺棱宽度e，可以抑制漏流。例如，可以将螺杆的螺棱宽度e设计成满足：
Figure PCTCN2021073976-appb-000011
从公式(3)可以看出，e的取值越大，漏流与正流的比例越小，漏流的现象越不明显。
可选地，在某些实施例中，可以控制螺杆对螺杆的螺槽内的可流动的物料的剪切速率γ，使得γ≤500/s。前文已经指出，剪切速率越低，剪切稀化效应越不明显。剪切稀化效应较低的物料可以视为牛顿流体，与非线性的非牛顿流体相比，这种流体的流率更容易进行精确的建模和控制。详细描述参见前文，此处不再详述。
综合前文描述的各种因素，下面结合表一，给出几种螺杆式送料装置的具体参数的示例。
表一
Figure PCTCN2021073976-appb-000012
表一中的D、H、e、L、δ的单位为cm，rpm代表每分钟转速。
第一实施例对螺杆式送料装置40的可流动态的物料来源不做具体限定。例如，参见图1，可以为螺杆式送料装置40设置送料口45，螺杆式送料装置40可以通过送料口45从外部获得可流动态的物料。又如，螺杆式送料装置40可以增设其他类型的物料加工装置，将固态的物料转化成可流动态的物料。
可选地，在一些实施例中，如图1所示，物料输送系统10还可以包括第二控制系统44,52被配置为对螺杆41中的物料的粘度和/或挤出口51处的物料的粘度进行控制，使得螺杆41中的物料的粘度大于挤出口51处的物料的粘度。
参见公式(1)-(3)，螺杆中的物料粘度越高，η和η 1的取值就越高。根据公式(1)-(3)可以看出，η和η 1的取值越高，逆流和漏流相对于正流的比例就越低，则逆流和漏流现象就越不明显。此外，逆流和漏流是由于物料在挤出口51处存在挤出压力P而产生的，挤出压力P越大，则逆流和漏流就越明显。因此，可以控制挤出口51处的物料具有与螺杆41中的物料相比更低的粘度，挤出口51处的物料的粘度越低，该物料在挤出口51处产生的挤出压力就越小，这样也可以减少逆流和漏流现象。上述物料粘度的差异设置可以很大程度上降低螺杆式送料装置40的逆流和漏流问题，甚至将逆流和漏流减少到与正流相比可以忽略不计的程度，这样有利于螺杆式送料装置40对物料的计量输出进行精确的控制。此外，发明人还发现，降低挤出口51的挤出压力P能够显著降低螺杆式送料装置40的功耗，从而降低物料输送系统的成本。
物料粘度的控制方式可以有多种，本申请实施例对此并不限定。例如，可以通过搅拌的方式控制物料的粘度，也可以通过温度控制物料的粘度。如图1所示，第二控制系统44,52可以包括第一加热器44和第二加热器52。第一加热器44被配置成对螺杆41进行加热。第二加热器52被配置成对挤出口51进行加热。第二加热器52的加热温度高于第一加热器44的加热温度。
上述加热温度设置方式可以拉开挤出口51和螺杆41之间的温差。在螺杆41处设置较低的温度可以增大物料的粘度，在挤出口51处设置较高的温度可以降低挤出口51处的物料的粘度。
在一些实施例中，可以通过第一加热器44控制螺杆41的温度，使得螺杆41的温度接近物料的熔融温度。例如，可以将第一加热器44的加热温度T1控制在T f到T f+30℃的范围内，其中，T f表示物料的熔融温度。此外，还可以通过第二加热器52控制挤出口51处的温度，使得挤出口51处的温度接近物料的分解温度。例如，可以将第二加热器52的加热温度T2控制在(T f+50℃)到(T d-30℃)的范围内，其中，T f表示物料的熔融温度， T d表示物料的分解温度。
当然，不同种类的物料的材质不同，相应的温控范围会存在一定的差异。例如，物料为聚乳酸，第一加热器的温度T1大于155℃，小于185℃；和/或第二加热器的温度T2大于205℃，小于310℃；或者，物料为丙烯腈-丁二烯-苯乙烯共聚物，第一加热器的温度T1大于170℃，小于200℃；和/或第二加热器的温度T2大于220℃，小于250℃；或者，物料为聚碳酸酯，第一加热器的温度T1大于220℃，小于250℃；和/或第二加热器的温度T2大于270℃，小于320℃；或者，物料为尼龙-6，第一加热器的温度T1大于215℃，小于245℃；和/或第二加热器的温度T2大于265℃，小于280℃；或者，物料为聚苯硫醚，第一加热器的温度T1大于280℃，小于310℃；和/或第二加热器的温度T2大于330℃，小于470℃；或者，物料为聚甲基丙烯酸甲酯，第一加热器的温度T1大于160℃，小于190℃；和/或第二加热器的温度T2大于210℃，小于240℃；或者，物料为聚醚醚酮，第一加热器的温度T1大于334℃，小于364℃；和/或第二加热器的温度T2大于384℃，小于490℃。
前文已经介绍了超低速的螺杆式送料装置具有剪切稀化效应低的特点，使得物料可以看成牛顿流体。与非牛顿流体相比，牛顿流体的粘度具有温度效应明显的特点，即在挤出口51处因提高温度而带来的粘度降低效果明显，从而显著降低机头压力，由此可见，超低速的螺杆式送料装置与温差方式配合起来，可以有助于显著减小系统中的逆流和漏流现象。
例如，对于3D打印常用的聚乳酸(PLA)材料，在常规螺杆中的高剪切条件下是一种典型的非牛顿流体，其粘度的温度依赖性很低，但在剪切速率低于100s -1条件下，其粘度从170℃升高到240℃时，粘度降低可达200倍以上。如果设置螺杆的工作温度为170℃，挤出口温度为240℃，挤出口厚度0.1mm，则如果按照表一中参数打印小型件，物料输送系统10的逆流低于最小正流的6％，漏流则低于最小正流的1％，此时漏流和逆流对于螺杆中的物料输送的影响非常微弱，几乎可以忽略不计，此时，物料输送系统的流率基本上由螺杆转速精确确定。对于如果照表一中参数打印大型件，漏流和逆流比最小正流小得更多，仅分别为正流的0.42和0.59％以下，对物料输送的影响可以完全忽略不计。由此可见，上述方案最大限度抑制了漏流和逆流，物料输送流率同螺杆转速之间有很好的线性关系。
第二实施例：
第二实施例与第一实施例类似，二者的主要不同在于：第二实施例对螺杆式送料装置40(需要说明的是，在第二实施例中，螺杆式送料装置40被称为第二送料装置)向挤出头50提供的可流动态的物料的来源进行了限定，由缓冲容器提供。下文主要对第二实施例与第一实施例的不同之处进行详细描述，相同的部分可以参见第一实施例。
在物料挤出领域中，如果物料输送系统以固定流率输送物料，则由一个送料装置连续完成物料从固态到可流动态的转换，以及可流动态物料向挤出头的计量输出可能是合适的。但是，随着物料挤出技术的发展，尤其是3D打印技术的发展，越来越多的物料输送系统需要能够满足物料输送流率动态变化的需求。发明人发现，在这种系统中，如果仍然沿用传统的物料输送方式，即采用一个送料装置连续完成物料状态转换，以及物料向挤出头的计量输出，则这两个过程会出现难以协调的问题。以螺杆式送料装置为例，其通常包括加料段、熔融段(或称压缩段)和计量段。加料段用于接收固态的物料，熔 融段用于将固态的物料转换成可流动态，计量段用于定量地向挤出头输出可流动的物料。如果物料的流率是动态变化的，那么螺杆式送料装置的转速也会是动态变化的。这样一来，熔融段输出的可流动态的物料的压力、流量和温度都会出现波动。受到熔融段输出的可流动物料的波动的影响，计量段很难精确、定量地将物料输送至挤出头。
为了解决上述问题，本申请将物料的状态转换和物料的计量输出两个任务分配给两个不同的送料装置，并在两个送料装置之间对物料进行缓冲，以屏蔽第一送料装置的输出的波动对第二送料装置的影响。下面结合图2进行详细说明。
图2是本申请某些实施例提供的物料输送系统10。该物料输送系统10可以应用于塑料挤出领域，也可应用于3D打印领域，如应用于基于材料挤出(Materials Extrsion)的3D打印技术。
本申请实施例对物料输送系统10所输送的物料的材质不做具体限定。在一些实施例中，物料输送系统10可用于输送塑料和任何膏状的可以流动和挤出的材料。在一些实施例中，物料输送系统10可用于输送金属膏状材料(金属膏状材料可以通过在金属粉末中添加液态粘结剂形成)，陶瓷膏状材料(陶瓷膏状材料可以通过在陶瓷粉末中添加液态粘结剂形成)，有机高分子聚合物材料，无机膏状材料(如水泥，石膏浆料、泥浆料等)。在某些实施例中，物料输送系统10输送的物料也可以是奶油、巧克力之类膏状的食品。更为具体地，在某些实施例中，物料输送系统10可用于输送如下材料形成的物料：聚乳酸(PLA)，丙烯腈-丁二烯-苯乙烯共聚物(ABS)，聚碳酸酯(PC)，尼龙-6(PA6)，聚苯硫醚(PPS)，聚甲基丙烯酸甲酯(PMMA)以及聚醚醚酮(PEEK)。
如图2所示，物料输送系统10包括第一送料装置20、缓冲容器30、第二送料装置40以及挤出头50。图2中的宽箭头代表的是物料流动(或物料输送)的方向。从该宽箭头方向可以看出，在该物料输送系统10中，物料可以依次经过第一送料装置20、缓冲容器30、第二送料装置40以及挤出头50。
第一送料装置20被配置成将固态的物料转化成可流动的物料(也可称为熔融态的物料)。缓冲容器30被配置成存储第一送料装置20输出的可流动的物料。第二送料装置40被配置成将缓冲容器30中的可流动的物料输送至物料输送系统10的挤出头50。
由于缓冲容器30的存在，降低了物料状态转化和计量输出两个阶段协调的难度，从而有利于实现物料的稳定地计量输出。
第一送料装置20提供物料的来源，因此，第一送料装置20可以称为物料输送系统10的物料供给段。由于第一送料装置20可以将固态物料熔解成可流动态物料，因此，第一送料装置20也可看成是物料输送系统10的熔融段。
在一些实施例中，第一送料装置20还可以提供可流动的物料的初步的流量调控，并按照给定的流量要求将可流动的物料输送至缓冲容器30中。本申请对第一送料装置20的流量调节范围不做具体限定，可以根据实际需求设定。例如，可以为第一送料装置20配置5至20倍的流量可调范围。第一送料装置20输送的流量可以按照一定规则调节，例如，可以按照缓冲容器30中的物料的容积或液面高度调节。
在一些实施例中，第一送料装置20还可以提供初步的温度控制，从而将给定温度的可流动的物料输送至缓冲容器30中。
第一送料装置20的实现方式可以有多种，本申请实施例对此并不限定。例如，第一送料装置20可以是螺杆式送料装置(或称螺杆泵，或螺杆挤出机)，也可以是气压式送 料装置或活塞式送料装置。
在一些实施例中，第一送料装置20的出料口可以设置过滤件(如筛板)，使得物料在进入缓冲容器30前，滤除可能存在的固态物质。
以螺杆式送料装置为例，如图3所示，第一送料装置20可以包括进料口21、螺杆22、出料口23以及加热器26。
进料口21可用于接收固态的物料。在一些实施例中，进料口21可以为料斗。
螺杆22可以分为三段：进料段221、熔融段(或称压缩段)222以及计量段223。进料段221可以将进料口21接收到的固态的物料输送至熔融段222。熔融段222可以将固态的物料转换成可流动的物料，然后将可流动的物料输送至计量段223。计量段223可以对物料进行粗略的计量输出。
加热器26可以对螺杆的工作温度进行控制，从而将物料的状态维持在可流动态。加热器26可以设置在螺杆22的熔融段222和计量段223对应的区域。
螺杆22可以在电机27的驱动下转动，从而对物料进行输送。电机27和螺杆装置22之间可以设置减速器28，以匹配电机27和螺杆22之间的转速。
筛板29位于出料口23处，以滤除物料中可能含有的固态物质。
重新参见图2，缓冲容器30可以视为第一送料装置20和第二送料装置40之间的过渡器件。缓冲容器30可以接收来自第一送料装置20的可流动的物料，并作为第二送料装置40的进料池，以满足第二送料装置40所需要的物料的动态流量供应。
缓冲容器30可以隔离第一送料装置20输出的波动对第二送料装置40可能产生的不利影响。第一送料装置20输出的波动包括以下波动中的至少一种：压力波动、流量波动和温度波动。缓冲容器30对第一送料装置20输出的波动的隔离有利于第二送料装置40可以精密地对物料进行流率控制。
具体而言，假如第一送料装置20与第二送料装置40直接连接，要想实现挤出口处的高精度的流率控制，就需要在第一送料装置20和第二送料装置40之间进行高精度的协同流率控制。但是，当挤出头50的物料挤出流率需要动态变化时，第一送料装置20输出的物料的状态是很不稳定的。在这种情况下，要想实现第一送料装置20和第二送料装置40的高精度协调的难度是很大的。在第一送料装置20和第二送料装置40之间加入缓冲容器30可以降低第一送料装置20和第二送料装置40之间的协同控制的要求。缓冲容器30作为缓冲部件，可以平抑第一送料装置20输出的波动，保证物料以稳定的状态供给后续的第二送料装置40。
为了使缓冲容器30内的可流动的物料的温度和混合状态尽可能均匀，并使物料中夹带的气体在此处释放排出，如图4所示，可以为缓冲容器30设置搅拌装置32。
搅拌装置32的结构可以有多种。例如，可以采用叶片搅拌机，也可以采用滚筒搅拌机。下面以叶片搅拌机为例，对搅拌装置32的结构和工作方式进行举例说明。
如图4所示，搅拌装置32可以包括搅拌叶片322和伺服电机324。电机324驱动搅拌叶片322，以对缓冲容器30中存储的可流动的物料进行搅拌，从而平抑第一送料装置20向缓冲容器30输送的物料的状态(如温度或组分)的波动，保证缓冲容器30中的物料状态的均匀性，并加快物料中残余气体的溢出。
在某些实施例中，搅拌叶片322的形状以及缓冲容器30的入口34(可以与第一送料装置20相连)和出口36(可以与第二送料装置40相连)可以采用特定的结构设计，使 得从入口34进入缓冲容器30中的物料在缓冲容器30内部经过足够长的流程之后，再从出口36排除。这样，可流动态的物料经过足够的流程，能够更好地保证物料状态的均匀。例如，搅拌叶片322可以采用一定的形状设计，使可流动的物料从入口34进入缓冲容器30后，螺旋上升，再从中心向下流至出口36。
在某些实施例中，如图4所示，缓冲容器30还可以设置温度控制装置38，以控制缓冲容器30中存储的可流动的物料的温度。温度控制装置38可以包括加热部件、温度传感器和温控器(图4中未示出)。加热部件可以是内含加热棒/柔性加热片的金属套筒，套在缓冲容器30的壳体37外部。温度传感器可以为高精度热电偶，以测量壳体37的温度，并将温度测量结果反馈给温控器。温控器可以采用高精度PID控制器。该控制器可以根据温度传感器反馈的温度控制加热部件的输出功率，从而将壳体37的温度控制在设定的目标值。
在某些实施例中，物料输送系统10还可以包括反馈控制装置。反馈控制装置可以根据缓冲容器30中存储的可流动的物料的量，调整第一送料装置20输出的可流动的物料的量(或第一送料装置20输出的可流动的物料的速率)。
缓冲容器30的容积可以根据实际的物料输送需求设定。例如，缓冲容器30可以配置适当的容积，使缓冲容器30内的液面高度保持在合理的范围，降低液面高度差产生的压力对后续的物料输送的影响。例如，可以将缓冲容器30内的液面高度保持在：当挤出口以最大流率进行物料挤出时，缓冲容器30内的物料的量足以供应挤出口的需求，当挤出口以最小流率进行物料挤出时，缓冲容器30的液面高度不至于导致缓冲容器30内的物料溢出。当缓冲容器30同时满足上述两个条件时，其内部存储的物料的液面高度差所产生的压力差是很小的，几乎可以忽略不计，不会对挤出口的压力产生影响。
作为一个示例，挤出头50可以是具有宽度连续可调的挤出口51。反馈控制装置的控制可以使得缓冲容器30中存储的可流动的物料的量不小于挤出口51采用最大宽度进行物料挤出时所需的物料的量。
下面给出三种可选的反馈控制方案。
反馈控制方案1：基于搅拌电机负载/扭矩的反馈控制
下面对这种反馈控制方案进行详细说明。
物料输送系统输送的可流动的物料(尤其是高分子材料的物料)的粘度一般较大。因此，随着液面的升高，搅拌装置32的搅拌阻力会相应增加，导致电机324的负载/扭矩也随之增加。因此，反馈控制装置可以根据电机324的负载或扭矩调整第一送料装置40输出的物料的量。例如，可以先获取表征电机的负载的负载信号或表征电机的扭矩的扭矩信号(扭矩信号可以通过扭矩传感器采集)，然后将该信号反馈至第一送料装置20，以控制第一送料装置20的送料速率。该电机的负载信号或扭矩信号为连续变化的电信号，因此，可以通过PID算法控制第一送料装置20的送料速率，这种控制方式与简单的通断式的控制方式相比，控制精度更高。此外，这种方案的优点还在于利用搅拌装置32即可实现反馈控制，不需设置额外的反馈控制装置，从而降低系统的复杂度。
为了根据电机的负载/扭矩实现反馈控制，可以先建立缓冲容器30内的液面高度和电机的负载/扭矩之间的对应关系。由于缓冲容器30内的液面高度与电机的负载/扭矩对应关系会随着温度、物料的材质/品质的不同而发生变化，因此，可以预先对缓冲容器30内的液面高度与电机的负载/扭矩的对应关系进行标定。下面给出一种可能的标定方式。
如图5所示，可以对搅拌叶片322进行结构设计，使得搅拌叶片322的叶片宽度在H3处突增。当缓冲容器30内的液面高度升高至H3处时，电机324的负载会急速增加。在标定过程中，可以采用程序自动识别出H3处的负载大小，然后，根据H3处的负载大小，确定反馈控制的目标值(该目标值可以根据实际需要设定，例如可以设置成H3处的负载的80％)，从而实现液面的高度控制。此外，还可以根据电机在H3处的负载大小设置负载的安全阈值，当液面的高度使得电机的负载超过该安全阈值时，负载急速增加至该安全阈值，以控制第一送料装置20停止送料。
可以理解的是，液面高度-负载曲线的斜率越大，则液面高度的控制精度越高。此外，当物料的成分、温度和搅拌转速都确定情况下，液面高度-负载曲线的斜率会由搅拌叶片322的形状决定。为了能够增大液面高度-负载曲线的斜率，搅拌叶片322可以采用由宽到窄逐渐变化的结构。如图5所示，在H3处以下，搅拌叶片322的幅宽可以采用“倒三角形”设计(或者，在其他实施例中，也可以采用“倒梯形”设计)，这样能增大液面高度-负载曲线的斜率，提高控制精度。
下面结合图6，详细描述上述标定流程的实施例。如图6所示，该标定流程可以包括步骤S610至步骤S660。
在步骤S610，将缓冲容器的温度升至目标温度，并对其进行恒温控制。
目标温度可以选择缓冲容器在实际工作时的温度。目标温度的取值可以根据实际需要设定，只要能够保证物料处于可流动态即可。
在步骤S620，将搅拌电机的转速升至目标转速，并使其恒速运转，并开始测量电机的负载。
此时，由于缓冲容器中还没有可流动的物料进入，测量出的电机的负载为电机在空转时的负载。
在步骤S630，控制第一送料装置开始向缓冲容器送料。
此时，需要关闭缓冲容器的出口，禁止缓冲容器向第二送料装输出物料。
在步骤S640，随着物料的液面升高，记录表征电机的负载随时间变化情况的P(t)曲线。
例如，当物料的液面高度达到H1时，电机的负载P随时间t开始逐渐增加，当液面高度达到H3时，因搅拌叶片的宽度突然增大，电机的负载P随时间t急速增加。可以将上述信息记录下来，供后续分析使用。
在步骤S650，控制第一送料装置停止送料，自动分析P(t)曲线。
例如，可以计算P(t)曲线的二次导数dP 2/dt 2，二次导数最大值对应的P值为H3处的电机负载，假设系统的物料为物料1，则二次导数最大值对应如图5中物料1的负载P1。
在步骤S660，根据H3处的电机负载，设定反馈控制的目标值和安全阈值。
例如，可以将H3处的电机负载P1乘以液面的高度因子，从而得到反馈控制的目标值。该高度因子可以根据实际需要设定。例如，可以将液面的高度因子设定成H1至H3的总高度的80％(即图5中的H2处)，将0.8*P1设定为反馈控制的目标值，可以将液面高度控制在H2以下。
此外，在某些实施例中，还可以设置负载的安全阈值。该安全阈值可以根据实际需要设定，例如，可以将安全阈值设计成P1负载的120％，即将1.2*P1设定为安全阈值。当电机负载超过此阈值时，控制第一送料装置20停止送料。
如果物料从物料1更换成物料2，则可以重复上述操作，重新获取物料2在H3处的负载P2，并将0.8*P2作为反馈控制的目标值，将1.2*P2作为安全阈值。
在完成上述标定流程后，可以让物料输送系统进入工作状态，开启第一送料装置和第二送料装置，并根据电机负载实时反馈控制第一送料装置20的送料速率，从而将缓冲容器内的液面高度控制在H2以下。
反馈控制方案2：基于压力的反馈控制
如图7中的左图所示，可以在缓冲容器30底部安装压力传感器33，以压力传感器33反馈的压力值作为控制第一送料装置20的送料速率的依据。由于缓冲容器30为开放容器，因此，压力传感器33可以选择相对压力测量型的压力传感器。压力传感器的量程可以根据物料的材质、缓冲容器30的容积等因素确定。例如，假设物料为PLA，密度ρ＝1.25×10 3kg/m 3，当液面高度h需要控制在0.1m左右时，压力传感器33承受的最大压强为P＝ρg h＝1.25×10 3×9.8×0.1＝1225Pa。在这种情况下，可以选择量程为千帕级的压力传感器33，该压力传感器33的压强分辨率可以选择十帕级，即为量程的1％，其压强随液面高度的变化率为12.25Pa/mm，从而实现毫米级的高度控制。如果采用该反馈控制方案，可以预先建立压力和液面高度的对应关系，而此关系可以根据物料在可流动态时的密度(或称熔体密度)确定。
反馈控制方案3：基于液面浮标的反馈控制
如图7中的右图所示，可以将浮子39浮在物料液面上，该浮子39会随着液面的升高而升高。浮子39带有一根浮杆，升出缓冲容器30的上盖。在缓冲容器30的上盖可以安装电子尺37，通过探测浮杆的上下移动，将液面高度转为电信号，并将该电信号作为反馈信号，控制第一送料装置20的送料速率。
重新参见图4，缓冲容器30可以设计成圆柱形容器，也可以设计成其他形状的容器。缓冲容器30的壳体37的内表面可以采用高光洁度的材质，如光洁度Ra＝0.4～0.8um的金属材质(如不锈钢或铜)。高光洁度的内表面可以降低物料的粘结，防止其高温分解后污染缓冲容器30中的其他物料。在某些实施例中，缓冲容器30的下端可以呈漏斗状，避免容器内出现死角，造成物料残留。
入口34和出口36均可采用标准接口(如卡扣或法兰)，分别与第一送料装置20和第二送料装置40连接。入口34可以设置在缓冲容器30的侧壁偏向底部的位置，避免物料从高处流下裹入气体。出口36可以设置在缓冲容器30的底面，保证物料能够全部流尽，无死角残余。
在一些实施例中，可以在出口36处设置过滤部件35(如过滤网)，避免杂质进入第二送料装置40。
由于缓冲容器30的存在，第二送料装置40可以直接将缓冲容器30中的可流动态的物料输送至挤出头50，而无需进行物料状态的转换，这样有利于实现物料的高精度的计量输出。因此，第二送料装置40也可称为精密计量供料装置。或者，第二送料装置40可以看成是物料输送系统10的精密供料段。在一些实施例中，第二送料装置40可以在输送物料的过程中，对物料在很大的流率范围内进行精确的实时调控。例如，第二送料装置40可以对物料的流率、温度等参数进行精确调控。
在上述物料输送系统10中，第一送料装置20、缓冲容器30、第二送料装置40和挤出头50可以看成是整个物料输送系统10的四个功能段，每个功能段可以根据自身的需 要进行精确的温度控制。例如，第一送料装置20可以将温度控制在适于物料从固态转换成可流动态(或熔融态)。缓冲容器30可以将温度控制在目标值，该目标值可以根据第二送料装置40的工作温度而定，例如，可以略高于第二送料装置40的工作温度。第二送料装置40和挤出头50可以采用前文所述的温差控制方式进行温度控制。
第二送料装置40(参见图8)可以采用第一实施例中的螺杆式送料装置，为了避免重复，此处不再详述。
第三实施例：
第一实施例至第二实施例为装置实施例，第三实施例为方法实施例。装置侧的描述和方法侧的描述相互对应，为了简洁，适当省略重复的描述。
图9是第三实施例提供的物料输送方法的示意性流程图。图9的方法S900可以由前文提及的物料输送系统10执行。方法S900包括步骤S910至步骤S920。
在步骤S910，在3D打印过程中，利用螺杆式送料装置将可流动的物料输送至挤出头。该螺杆式送料装置可以采用第一至第三实施例提供的螺杆式送料装置40。
在步骤S920，在3D打印过程中，控制挤出头的挤出口的宽度在预设范围内连续变化。
可选地，在一些实施例中，方法S900还包括：对螺杆中的物料的粘度和/或挤出口处的物料的粘度进行控制，使得螺杆中的物料的粘度大于挤出口处的物料的粘度。
可选地，在一些实施例中，上述对螺杆中的物料的粘度和/或挤出口处的物料的粘度进行控制，使得螺杆中的物料的粘度大于挤出口处的物料的粘度可以包括：对螺杆进行加热；对挤出口进行加热；其中挤出口的加热温度高于螺杆的加热温度。
可选地，在一些实施例中，螺杆的加热温度T1∈(T f,T f+30℃)，其中，T f表示物料的熔融温度。
可选地，在一些实施例中，挤出口的加热温度T2∈(T f+50℃,T d-30℃)，其中，T f表示物料的熔融温度，T d表示物料的分解温度。
可选地，在一些实施例中，在步骤S910之前，方法S900还包括：将固态的物料转换成可流动的物料；利用缓冲容器存储第一送料装置输出的可流动的物料；将缓冲容器中存储的可流动的物料输送至螺杆式送料装置。
可选地，在一些实施例中，步骤S920包括：控制挤出口的宽度随着物料填充区域的截面轮廓线的变化而变化。
在上述实施例中，可以全部或部分地通过软件、硬件、固件或者其他任意组合来实现。当使用软件实现时，可以全部或部分地以计算机程序产品的形式实现。所述计算机程序产品包括一个或多个计算机指令。在计算机上加载和执行所述计算机程序指令时，全部或部分地产生按照本发明实施例所述的流程或功能。所述计算机可以是通用计算机、专用计算机、计算机网络、或者其他可编程装置。所述计算机指令可以存储在计算机可读存储介质中，或者从一个计算机可读存储介质向另一个计算机可读存储介质传输，例如，所述计算机指令可以从一个网站站点、计算机、服务器或数据中心通过有线(例如同轴电缆、光纤、数字用户线(digital subscriber line，DSL))或无线(例如红外、无线、微波等)方式向另一个网站站点、计算机、服务器或数据中心进行传输。所述计算机可读存储介质可以是计算机能够存取的任何可用介质或者是包含一个或多个可用介质集成的服务器、数据中心等数据存储设备。所述可用介质可以是磁性介质(例如，软盘、硬 盘、磁带)、光介质(例如数字视频光盘(digital video disc，DVD))、或者半导体介质(例如固态硬盘(solid state disk，SSD))等。
本领域普通技术人员可以意识到，结合本文中所公开的实施例描述的各示例的单元及算法步骤，能够以电子硬件、或者计算机软件和电子硬件的结合来实现。这些功能究竟以硬件还是软件方式来执行，取决于技术方案的特定应用和设计约束条件。专业技术人员可以对每个特定的应用来使用不同方法来实现所描述的功能，但是这种实现不应认为超出本申请的范围。
在本申请所提供的几个实施例中，应该理解到，所揭露的系统、装置和方法，可以通过其它的方式实现。例如，以上所描述的装置实施例仅仅是示意性的，例如，所述单元的划分，仅仅为一种逻辑功能划分，实际实现时可以有另外的划分方式，例如多个单元或组件可以结合或者可以集成到另一个系统，或一些特征可以忽略，或不执行。另一点，所显示或讨论的相互之间的耦合或直接耦合或通信连接可以是通过一些接口，装置或单元的间接耦合或通信连接，可以是电性，机械或其它的形式。
所述作为分离部件说明的单元可以是或者也可以不是物理上分开的，作为单元显示的部件可以是或者也可以不是物理单元，即可以位于一个地方，或者也可以分布到多个网络单元上。可以根据实际的需要选择其中的部分或者全部单元来实现本实施例方案的目的。
另外，在本申请各个实施例中的各功能单元可以集成在一个处理单元中，也可以是各个单元单独物理存在，也可以两个或两个以上单元集成在一个单元中。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以所述权利要求的保护范围为准。

Claims (19)

  1. 一种螺杆式送料装置，其特征在于，所述螺杆式送料装置用于为挤出口输送可流动的物料，且在物料挤出过程中所述挤出口的宽度连续变化，所述螺杆式送料装置包括：
    螺杆；
    转动控制器，被配置为驱动所述螺杆转动；
    其中，所述螺杆式送料装置被配置为满足Q max/D 2＜5cm/min，L/D≤5，Q max表示所述螺杆式送料装置输送的可流动的物料的最大流率，D表示所述螺杆的直径，L表示所述螺杆的长度。
  2. 根据权利要求1所述的螺杆式送料装置，其特征在于，所述螺杆式送料装置还包括：
    机筒，所述螺杆位于所述机筒内，所述螺杆和所述机筒之间的间隙δ＜0.001D。
  3. 根据权利要求1或2所述的螺杆式送料装置，其特征在于，所述螺杆的螺旋角
    Figure PCTCN2021073976-appb-100001
    Figure PCTCN2021073976-appb-100002
  4. 根据权利要求1或2所述的螺杆式送料装置，其特征在于，所述螺杆的螺棱宽度e满足：
    Figure PCTCN2021073976-appb-100003
    其中，
    Figure PCTCN2021073976-appb-100004
    表示所述螺杆的螺旋角。
  5. 根据权利要求1或2所述的螺杆式送料装置，其特征在于，所述螺杆对所述螺杆的螺槽内的可流动的物料的剪切速率γ≤500/s。
  6. 一种用于3D打印的物料输送系统，其特征在于，包括：
    挤出头；
    根据权利要求1-5中任一项所述的螺杆式送料装置；
    第一控制系统，被配置为在3D打印过程中，控制所述挤出头的挤出口的宽度在预设范围内连续变化。
  7. 根据权利要求6所述的物料输送系统，其特征在于，所述物料输送系统还包括：
    第二控制系统，被配置为对所述螺杆中的物料的粘度和/或所述挤出口处的物料的粘度进行控制，使得所述螺杆中的物料的粘度大于所述挤出口处的物料的粘度。
  8. 根据权利要求7所述的物料输送系统，其特征在于，所述第二控制系统包括第一加热器和第二加热器，所述第一加热器被配置成对所述螺杆进行加热，所述第二加热器被配置成对所述挤出口进行加热，其中所述第二加热器的加热温度高于所述第一加热器的加热温度。
  9. 根据权利要求8所述的物料输送系统，其特征在于，所述第一加热器的加热温度T1∈(T f,T f+30℃)，其中，T f表示所述物料的熔融温度。
  10. 根据权利要求8或9所述的物料输送系统，其特征在于，所述第二加热器的加热温度T2∈(T f+50℃,T d-30℃)，其中，T f表示所述物料的熔融温度，T d表示所述物料的分解温度。
  11. 根据权利要求6-9中任一项所述的物料输送系统，其特征在于，所述物料输送系统还包括：
    第一送料装置，被配置成将固态的物料转换成所述可流动的物料，所述螺杆式送料装置为所述物料输送系统的第二送料装置；
    缓冲容器，与所述第一送料装置相连，被配置成存储所述第一送料装置输出的可流动的物料，并将所述可流动的物料输送至所述第二送料装置。
  12. 根据权利要求6-9中任一项所述的物料输送系统，其特征在于，所述第一控制系统被配置为控制所述挤出口的宽度随着物料填充区域的截面轮廓线的变化而变化。
  13. 一种用于3D打印的物料输送方法，其特征在于，包括：
    在3D打印过程中，利用如权利要求1-5中任一项所述的螺杆式送料装置将可流动的物料输送至挤出头；
    控制所述挤出头的挤出口的宽度在预设范围内连续变化。
  14. 根据权利要求13所述的物料输送方法，其特征在于，所述物料输送方法还包括：
    对所述螺杆中的物料的粘度和/或所述挤出口处的物料的粘度进行控制，使得所述螺杆中的物料的粘度大于所述挤出口处的物料的粘度。
  15. 根据权利要求14所述的物料输送方法，其特征在于，所述对所述螺杆中的物料的粘度和/或所述挤出口处的物料的粘度进行控制，使得所述螺杆中的物料的粘度大于所述挤出口处的物料的粘度，包括：
    对所述螺杆进行加热；
    对所述挤出口进行加热；
    其中所述挤出口的加热温度高于所述螺杆的加热温度。
  16. 根据权利要求15所述的物料输送方法，其特征在于，所述螺杆的加热温度T1∈(T f,T f+30℃)，其中，T f表示所述物料的熔融温度。
  17. 根据权利要求15或16所述的物料输送方法，其特征在于，所述挤出口的加热温度T2∈(T f+50℃,T d-30℃)，其中，T f表示所述物料的熔融温度，T d表示所述物料的分解温度。
  18. 根据权利要求13-16中任一项所述的物料输送方法，其特征在于，在所述利用螺杆式送料装置将可流动的物料输送至挤出头之前，所述物料输送方法还包括：
    将固态的物料转换成所述可流动的物料；
    利用缓冲容器存储所述第一送料装置输出的可流动的物料；
    将所述缓冲容器中存储的可流动的物料输送至所述螺杆式送料装置。
  19. 根据权利要求13-16中任一项所述的物料输送方法，其特征在于，所述控制所述挤出头的挤出口的宽度在预设范围内连续变化，包括：
    控制所述挤出口的宽度随着物料填充区域的截面轮廓线的变化而变化。
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