A self-compensating printhead and method, an extrusion direct writing device and working method

Abstract

The present application relates to the technical field of additive manufacturing, and particularly relates to a self-compensation printing head and method, an extrusion direct writing device and a working method. The printing head comprises a shell, a barrel, a screw and a self-compensation assembly; the lower part of the shell has a cavity, the barrel is rotatably installed in the cavity, and the screw is installed in the barrel for extruding material; the self-compensation assembly comprises an outer magnetic pole, an inner magnetic pole and a potentiometer, the outer magnetic pole is arranged on the inner wall of the cavity of the shell, the inner magnetic pole is arranged on the outer wall of the barrel and is arranged in the same polarity opposite to the outer magnetic pole, and the potentiometer is also installed on the barrel; the magnetic force of the outer magnetic pole and the inner magnetic pole makes the barrel at an initial angle, and when the material shear force increases, the magnetic force is overcome to drive the barrel and the potentiometer to rotate. According to the present application, the screw rotating speed can be automatically adjusted in real time according to the change of the material shear force, the stable control of the extrusion amount of different materials is realized, and the precision, quality and efficiency of multi-material direct writing forming are improved.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a self-compensating printhead and method, an extrusion direct writing device and its working method. Background Technology

[0002] Direct-write molding technology, by controlling the extrusion and deposition of materials, can realize the fabrication of complex three-dimensional structures from various materials such as polymers, ceramics, and metals. Among them, screw extrusion direct-write devices continuously push viscous materials out of the barrel by rotating a screw, which has the advantages of continuous output and stable pressure, and is widely used in the preparation of functionally graded materials, biological scaffolds, and other parts.

[0003] Currently, common screw extrusion direct writing devices typically employ a fixed-speed screw drive. The working principle of these devices is based on the assumption that the material viscosity remains constant, maintaining a relatively stable extrusion rate through a constant screw speed.

[0004] However, in practical use, when switching printing materials of different viscosities, or when the viscosity of the same material fluctuates due to batch differences, temperature changes, storage time, etc., the extrusion volume of the screw at a constant speed will show significant deviations. Increased viscosity leads to insufficient extrusion volume, causing interrupted printing lines or poor interlayer bonding; decreased viscosity leads to excessive extrusion volume, causing dimensional errors and surface roughness. Some improvement solutions attempt to install a flow sensor at the barrel outlet to detect the extrusion volume in real time and adjust the screw speed accordingly. However, the internal flow channel of the sensor is narrow and easily blocked by highly filled slurry, and the sensor response is lagging, making it difficult to match rapidly changing extrusion demands, while also increasing the cost and maintenance difficulty of the device. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a self-compensating printhead that can automatically adjust the screw speed in real time according to changes in material shear force, thereby achieving stable control of the extrusion amount of different materials and improving the accuracy, quality, and efficiency of multi-material direct-write molding.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: In a first aspect, embodiments of the present invention provide a self-compensating printhead, comprising: a housing, a barrel, a screw, and a self-compensating assembly; the lower part of the housing has a chamber, the barrel is rotatably mounted in the chamber, and the screw is mounted in the barrel for extruding material; the self-compensating assembly includes an outer magnetic pole, an inner magnetic pole, and a potentiometer, the outer magnetic pole being disposed on the inner wall of the chamber of the housing, the inner magnetic pole being disposed on the outer wall of the barrel and arranged opposite to the outer magnetic pole with the same pole, and the potentiometer being mounted on the barrel; the magnetic force of the outer and inner magnetic poles causes the barrel to be located at an initial angle, and when the material shear force increases, it overcomes the magnetic force to drive the barrel and the potentiometer to rotate.

[0007] As a further technical solution, a feeding channel is provided on the upper part of the outer shell, and the feeding channel is connected to the inner cavity of the material cylinder.

[0008] As a further technical solution, fixed bearings are installed on both the upper and lower parts of the outer shell, and the material cylinder is installed in the outer shell through the fixed bearings and can rotate around its own axis within the range of 0-30°.

[0009] As a further technical solution, a drive motor is also installed on the outer casing, the top end of the screw extends out of the barrel, and the drive motor is connected to the top end of the screw through a coupling.

[0010] As a further technical solution, both the inner and outer magnetic poles are cylindrical structures, with axial magnetic strips embedded in the outer wall of the inner magnetic pole and axial magnetic strips embedded in the inner wall of the outer magnetic pole.

[0011] As a further technical solution, the discharge end diameter of the barrel is 0.2-0.6mm, the length-to-diameter ratio of the screw is 15:1-20:1, and a gradual pitch design is adopted.

[0012] Secondly, embodiments of the present invention also provide a printing method for the self-compensating printhead, comprising the following steps: Feeding printing material into the barrel; The screw located inside the barrel is driven to rotate, extruding the printing material from the discharge end of the barrel; The shearing force generated by the printing material on the screw acts on the barrel. When the shearing force changes, it drives the barrel to rotate around its own axis. The barrel drives the potentiometer to rotate synchronously. Acquire the rotation angle signal of the potentiometer; Adjust the screw speed according to the rotation angle signal.

[0013] Thirdly, embodiments of the present invention also provide an extrusion direct writing device, including a frame, a printing platform and the self-compensating printhead; The frame is equipped with a two-axis linkage mechanism. The self-compensating print head is connected to the frame through the two-axis linkage mechanism, and the printing platform is connected to the frame through a lifting mechanism.

[0014] Secondly, embodiments of the present invention also provide a method for operating the aforementioned extrusion direct writing device, comprising the following steps: Debug the equipment, test the motion accuracy of the two-axis linkage mechanism and the printing platform, and calibrate the initial positions of the inner and outer magnetic poles; The printing material is fed into the barrel, and residual air inside the barrel is expelled. Import the 3D model of the part, plan the printing path, and set the initial screw speed, printing speed, printing layer thickness, and material switching nodes; The two-axis linkage mechanism drives the self-compensating print head to move along the set path, and the drive motor drives the screw to rotate to extrude material for printing. During the printing process, the screw speed is automatically adjusted according to the change of material shear force to achieve stable control of the extrusion amount. When the material switching node is reached, the next printing material is automatically switched and the extrusion amount compensation is completed. After printing, remove the parts for post-processing.

[0015] As a further technical solution, during the molding process, when the viscosity of the printing material increases, leading to an increase in shear force, the barrel rotates along the screw rotation direction and drives the potentiometer to rotate synchronously. The control system automatically increases the speed of the drive motor to increase the extrusion volume. When the viscosity of the printing material decreases, resulting in a reduction in shear force, the barrel rotates in the opposite direction of the screw rotation, causing the potentiometer to rotate synchronously in the opposite direction. The control system automatically reduces the speed of the drive motor to reduce the extrusion volume.

[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: The printhead of this invention forms a magnetically-based reset torque system on the barrel by setting inner and outer magnetic poles with opposite polarities. When changes in material viscosity cause changes in shear force, the barrel automatically rotates to a new equilibrium position. A potentiometer converts the rotation angle into an electrical signal, and the control system adjusts the screw speed in the opposite direction based on this signal. This changes the detection of extrusion volume from directly measuring flow rate to indirectly measuring the root cause of extrusion volume changes—shear force. Furthermore, the detection element is located entirely outside the barrel, fundamentally avoiding clogging problems. Simultaneously, the mechanical rotation response speed of the barrel is much faster than the transmission speed of the fluid signal in the flow sensor, thus greatly reducing response lag. The entire self-compensation assembly has a simple mechanical structure, requiring only a pair of magnets and a potentiometer, making it far less expensive than a flow sensor and its associated signal processing circuit. Therefore, this printhead can achieve real-time automatic compensation of extrusion volume without increasing the risk of clogging or producing significant response lag.

[0017] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0019] Figure 1 This is a schematic diagram of the printhead outline provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the internal structure of the printhead provided in an embodiment of the present invention; Figure 3 This is a cross-sectional view of the printhead provided in an embodiment of the present invention; Figure 4 This is a three-dimensional sectional view of the print head provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the extrusion direct writing device provided in an embodiment of the present invention; In the diagram: 1. Frame; 2. Self-compensating print head; 3. Printing platform; 4. Two-axis linkage mechanism; 5. Housing; 6. Linear bearing; 7. Drive motor; 8. Screw; 9. Fixed bearing; 10. Potentiometer; 11. Material cylinder; 12. Inner magnetic pole; 13. Outer magnetic pole; 14. Material feeding channel; Detailed Implementation To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the linguistic context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0020] Generally speaking, the terms "comprising" and "including" only indicate that the steps and elements are explicitly identified, and these steps and elements do not constitute an exclusive list. The method or apparatus may also include other steps or elements.

[0021] Example 1 In a typical embodiment of this disclosure, a self-compensating printhead is provided. This addresses the problems mentioned in the background art, such as the inability of a fixed-speed screw to adapt to changes in material viscosity, and the clogging and response lag issues associated with adding a flow sensor. The application scenario is screw extrusion direct-write equipment in the additive manufacturing field, particularly in printing conditions requiring switching between materials of different viscosities or when the material's viscosity fluctuates.

[0022] like Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, the self-compensating printhead 2 includes a housing 5, a barrel 11, a screw 8, and a self-compensating assembly. The lower part of the housing 5 has a chamber, in which the barrel 11 is rotatably mounted. The screw 8 is mounted in the barrel 11 for extruding material. The self-compensating assembly includes an outer magnetic pole 13, an inner magnetic pole 12, and a potentiometer 10. The outer magnetic pole 13 is disposed on the inner wall of the chamber of the housing 5, and the inner magnetic pole 12 is disposed on the outer wall of the barrel 11 and is arranged opposite to the outer magnetic pole 13 with the same pole. The potentiometer 10 is also mounted on the barrel 11. The magnetic force of the outer magnetic pole 13 and the inner magnetic pole 12 causes the barrel 11 to be located at an initial angle. When the material shear force increases, it overcomes the magnetic force and drives the barrel 11 and the potentiometer 10 to rotate.

[0023] Rotatable installation of the barrel 11 means that the barrel 11 can rotate relative to the outer shell 5 around its own axis, rather than being fixedly connected. The opposite arrangement of the same poles generates a repulsive force between the two magnetic poles, causing the barrel 11 to tend to be at an initial angle. The initial angle refers to a reference position held by the magnetic force between the outer magnetic pole 13 and the inner magnetic pole 12 when there is no material shear force or the shear force is zero.

[0024] When the barrel 11 rotates, a misalignment occurs between the inner magnetic pole 12 and the outer magnetic pole 13. The magnetic force increases with the increase of the misalignment, forming a reset torque that increases with the rotation angle. The potentiometer 10 can be a high-precision linear potentiometer 10, whose output resistance value changes linearly with the rotation angle. This resistance signal is sent to the control system of the drive motor 7.

[0025] By setting inner magnetic poles 12 and outer magnetic poles 13 with opposite poles, a recoverable torque balance system is formed on the barrel 11. When the screw 8 rotates and extrudes material, the shear force reacts on the barrel 11, causing it to tend to rotate in the direction of screw 8 rotation. The magnitude of the shear force is directly related to the material viscosity: the shear force increases when the viscosity increases and decreases when the viscosity decreases. When the shear force changes, the original magnetic balance is broken, and the barrel 11 rotates to a new equilibrium position, with the rotation angle corresponding to the change in shear force. After the barrel 11 drives the potentiometer 10 to rotate synchronously, the control system adjusts the screw 8 speed in the opposite direction according to the angle signal of the potentiometer 10, thus forming a closed-loop control. This structure eliminates the need for any sensors in the material flow channel, completely avoiding the problem of sensor blockage. Furthermore, the mechanical angular displacement detection has almost no response delay and is faster than the feedback speed of a flow sensor.

[0026] In some further specific examples of this disclosure, the upper part of the outer shell 5 is provided with a feeding channel 14, which is in communication with the inner cavity of the material cylinder 11.

[0027] In practical applications, the self-compensating printhead 2 requires an external feeding device to continuously replenish printing material into the barrel 11. The feeding channel 14 is located on the upper part of the outer casing 5, with its lower end connected to the interior of the barrel 11 and its upper end connected to an external multi-material feeding device. In this embodiment, the feeding channel 14 can have multiple independent channels, such as four channels, each corresponding to a different printing material, to achieve multi-material switching printing. The presence of the feeding channel 14 allows the printhead to operate continuously without frequent stops for feeding. This feature, combined with the self-compensation function, enables continuous automatic compensation in multi-material switching scenarios, solving the problem of adapting the extrusion volume of the new material after switching.

[0028] In some other specific examples of this disclosure, fixed bearings 9 are installed on both the upper and lower parts of the housing 5, and the barrel 11 is installed in the housing 5 through the fixed bearings 9 and can rotate around its own axis in the range of 0-30°.

[0029] The function of the fixed bearing 9 is to support the barrel 11 and ensure its smooth rotation and coaxiality. Installing fixed bearings 9 on the upper and lower parts of the housing 5 ensures that both ends of the barrel 11 are supported, preventing wobbling during rotation. The rotation range of the barrel 11 is limited to 0-30°, determined based on the magnetic characteristics between the inner magnetic pole 12 and the outer magnetic pole 13, and the linear operating range of the potentiometer 10. When the rotation angle of the barrel 11 exceeds 30°, the misalignment between the inner magnetic pole 12 and the outer magnetic pole 13 becomes too large, leading to excessively rapid magnetic attenuation or the potentiometer 10 output entering the nonlinear region. This range limitation ensures sufficient compensation stroke while maintaining the linearity and stability of the entire control system. The rotation range limitation can be achieved by setting mechanical limiting structures on the housing 5 or the barrel 11, such as protruding blocks on the inner wall of the housing 5, or corresponding limiting bosses on the outer wall of the barrel 11 or the potentiometer 10.

[0030] In some specific examples of this disclosure, a drive motor 7 is also installed on the housing 5, the top end of the screw 8 extends out of the barrel 11, and the drive motor 7 is connected to the top end of the screw 8 via a coupling.

[0031] The drive motor 7 is the power source for the extrusion action and can be a high-precision servo motor with a speed adjustment range typically between 50-500 r / min. The screw 8 extends out of the barrel 11 to facilitate connection with the output shaft of the drive motor 7. The coupling serves to connect and transmit torque, while also compensating for any coaxiality deviations that may exist between the output shaft of the drive motor 7 and the screw 8.

[0032] In some other specific examples of this disclosure, both the inner magnetic pole 12 and the outer magnetic pole 13 are cylindrical structures, with an axial magnetic strip embedded in the outer wall of the inner magnetic pole 12 and an axial magnetic strip embedded in the inner wall of the outer magnetic pole 13.

[0033] The cylindrical structure refers to the fact that both the inner magnetic pole 12 and the outer magnetic pole 13 are cylindrical, arranged around the circumference of the material cylinder 11 and the outer shell 5. Axial magnetic strips are embedded in the outer wall of the inner magnetic pole 12, and axial magnetic strips are embedded in the inner wall of the outer magnetic pole 13. Here, "axial" means that the length direction of the magnetic strip is parallel to the axis of the material cylinder 11. By embedding multiple axial magnetic strips, a uniformly distributed magnetic field can be formed in the circumferential direction. Compared with using a monolithic ring magnet, embedding magnetic strips makes it easier to control the strength and distribution of the magnetic field, and also facilitates adjusting the number and size of the magnetic strips to change the magnetic force characteristics. When the material cylinder 11 rotates, the facing area between the inner magnetic pole 12 and the outer magnetic pole 13 changes, and the magnetic force changes accordingly, forming a torque characteristic that varies with the rotation angle, achieving stable closed-loop control.

[0034] In some specific examples of this disclosure, the discharge end diameter of the barrel 11 is 0.2-0.6 mm, the length-to-diameter ratio of the screw 8 is 15:1-20:1, and a gradual pitch design is adopted.

[0035] The discharge end diameter, i.e., the inner diameter of the nozzle, is in the range of 0.2-0.6mm, suitable for printing fine structures. A finer extruded filament diameter improves molding accuracy. The length-to-diameter ratio of screw 8 is the ratio of its length to its diameter; a range of 15:1-20:1 is considered a medium to high ratio, which facilitates full plasticization and homogenization of the material within the barrel 11, improving the stability of the extruded flow. The gradient pitch design means that the screw pitch gradually decreases from the feed end to the discharge end. This results in high conveying efficiency at the feed end and a large compression ratio at the discharge end, which improves extrusion pressure and discharge uniformity. A small discharge end diameter requires higher extrusion pressure, and a larger length-to-diameter ratio and gradient pitch provide this high-pressure extrusion capability while ensuring extrusion continuity.

[0036] In summary, the magnetic forces of the inner magnetic pole 12 and the outer magnetic pole 13 form a dynamic balance with the shear force of the screw 8. When the material viscosity changes, causing a change in shear force, the barrel 11 rotates accordingly, which in turn drives the potentiometer 10 to rotate synchronously, automatically adjusting the speed of the drive motor 7. This achieves real-time automatic compensation of the extrusion amount, enabling stable control of the extrusion amount of different materials without manual intervention. It features fast response speed, simple and reliable structure, and significantly improves the molding accuracy and quality of multi-material screw 8 extrusion direct writing. It is suitable for additive manufacturing of complex structures of materials with various viscosities.

[0037] The structure is simple and reliable, requiring no additional complex flow detection and control modules. Automatic compensation can be achieved through the cooperation of mechanical structure and electrical components, reducing the cost and failure rate of the device and making maintenance convenient.

[0038] This structure is adaptable to viscosity ranges of 100-10000 mPa. The device's wide range of printing materials, including polymer pastes, ceramic pastes, metal pastes, and composite materials, greatly expands its applicability. Example 2 This embodiment provides a printing method for the self-compensating printhead 2, including the following steps: feeding printing material into the barrel 11; driving the screw 8 located in the barrel 11 to rotate, extruding the printing material from the discharge end of the barrel 11; the shearing force generated by the printing material on the screw 8 acts on the barrel 11, and when the shearing force changes, it drives the barrel 11 to rotate around its own axis, and the barrel 11 drives the potentiometer 10 to rotate synchronously; acquiring the rotation angle signal of the potentiometer 10; and adjusting the rotation speed of the screw 8 according to the rotation angle signal.

[0039] The step of feeding printing material into the barrel 11 can be accomplished in practice using an external feeding device in conjunction with the feeding channel 14. During feeding, residual air inside the barrel 11 needs to be expelled to prevent air bubbles from affecting extrusion continuity. Driving the screw 8 inside the barrel 11 means starting the drive motor 7, which drives the screw 8 to rotate via the coupling. The rotation of the screw 8 pushes the material towards the discharge end and ultimately extrudes it. The shear force generated by the printing material on the screw 8 acts on the barrel 11: when the screw 8 rotates, the viscous material generates shear resistance on the surface of the screw 8. The reaction force of this resistance acts on the inner wall of the barrel 11, subjecting the barrel 11 to a torque in the same direction as the rotation of the screw 8. This torque changes as the material viscosity changes. When the shear force changes, it causes the barrel 11 to rotate around its own axis. During this process, the magnetic balance between the magnetic pole 12 and the outer magnetic pole 13 is broken. In the initial state, the magnetic force keeps the barrel 11 at its initial angle. When the shear force increases, it overcomes the magnetic force, causing the barrel 11 to rotate in the direction of screw 8; when the shear force decreases, the magnetic force causes the barrel 11 to rotate in the opposite direction. The barrel 11 drives the potentiometer 10 to rotate synchronously. The rotation angle signal of the potentiometer 10 is collected, and its resistance or voltage value can be read by the control system of the drive motor 7 and converted into a rotation angle. Adjusting the speed of screw 8 according to the rotation angle signal means that the control system increases or decreases the output speed of drive motor 7 accordingly based on the magnitude and direction of the rotation angle, so that the extrusion volume returns to the set value.

[0040] This method achieves fully automated closed-loop control, requiring no manual intervention throughout the process. Compared to existing methods that use flow sensors, this method indirectly reflects changes in shear force by detecting the mechanical rotation angle of the barrel 11. The detection element does not contact the printing material at all, thus eliminating the risk of clogging. Furthermore, the response time of the mechanical rotation is typically less than 0.2 seconds, meeting the real-time adjustment requirements of high-speed printing.

[0041] This method supports automatic switching between multiple materials and continuous printing, enabling the integrated molding of complex multi-material structural parts, thus improving processing efficiency and the structural integrity of the parts.

[0042] Example 3 This embodiment provides an extrusion direct writing device, such as... Figure 5 As shown, it includes a frame 1, a printing platform 3 and the self-compensating print head 2; the frame 1 is provided with a two-axis linkage mechanism 4, the self-compensating print head 2 is connected to the frame 1 through the two-axis linkage mechanism 4, and the printing platform 3 is connected to the frame 1 through a lifting mechanism.

[0043] The frame 1 serves as the supporting foundation for the entire device. The two-axis linkage mechanism 4 includes linear guides and servo drive motors 7 in the X and Y axes. The self-compensating printhead 2 is slidably connected to the two-axis linkage mechanism 4 via linear bearings 6, enabling precise positioning of the self-compensating printhead 2 in the horizontal plane. The positioning accuracy can reach ±10μm, and the repeatability is ±5μm. The printing platform 3 is located below the self-compensating printhead 2 and is connected to the frame 1 via a lead screw lifting mechanism, enabling lifting motion in the Z-axis direction with a lifting step of 0.01-0.5mm. The two-axis linkage mechanism 4, in conjunction with the lifting mechanism, enables layer-by-layer printing in three-dimensional space. The self-compensating printhead 2, as an extrusion actuator, is mounted on this motion system, giving the device the ability to perform high-precision multi-material printing in three-dimensional space. The device's working size range can reach 200mm (length) × 200mm (width) × 180mm (height), making it suitable for additive manufacturing of small to medium-sized parts.

[0044] Example 4 This embodiment provides a working method for the extrusion direct writing device, including the following steps: debugging the equipment, testing the motion accuracy of the two-axis linkage mechanism 4 and the printing platform 3, and calibrating the initial positions of the inner magnetic pole 12 and the outer magnetic pole 13; feeding printing material into the barrel 11 and expelling residual air from the barrel 11; importing the three-dimensional model of the part, planning the printing path, and setting the initial screw speed 8, printing speed, printing layer thickness, and material switching node; the two-axis linkage mechanism 4 drives the self-compensating print head 2 to move along the set path, and the drive motor 7 drives the screw 8 to rotate to extrude material for printing. During the printing process, the screw speed 8 is automatically adjusted according to the change of material shear force to achieve stable control of the extrusion amount. When the material switching node is reached, the next printing material is automatically switched and extrusion amount compensation is completed; after printing, the part is taken out for post-processing.

[0045] In the equipment debugging process, calibrating the initial positions of the inner magnetic pole 12 and the outer magnetic pole 13 requires ensuring that the barrel 11 is at zero position without shear force, and that the initial output signal of the potentiometer 10 is at the preset reference value. The step of feeding printing material and venting residual air can be achieved by opening the vent at the bottom of the barrel 11 until the material flows out continuously and uniformly. In the 3D model import and path planning steps, the control system generates a printing trajectory based on the geometric features of the part and marks the locations where material switching is required. The molding process is the central part of this method. The two-axis linkage mechanism 4 controls the planar motion trajectory of the print head, the drive motor 7 controls the extrusion speed, and the printing platform 3 controls the layer thickness; all three work together. When the material switching node is reached, the external multi-material feeding device automatically switches channels to feed the next material. The self-compensation function automatically adapts to the viscosity characteristics of the new material, eliminating the need for manual parameter resetting. The post-processing step selects processes such as curing, drying, degreasing, or sintering based on the material type. For example, ceramic materials require degreasing and sintering, while polymer materials require curing.

[0046] During the molding process, when the viscosity of the printing material increases, resulting in increased shear force, the barrel 11 rotates along the rotation direction of the screw 8 and drives the potentiometer 10 to rotate synchronously. The control system automatically increases the speed of the drive motor 7 to increase the extrusion volume. When the viscosity of the printing material decreases, resulting in decreased shear force, the barrel 11 rotates in the opposite direction of the screw 8 and drives the potentiometer 10 to rotate synchronously in the opposite direction. The control system automatically decreases the speed of the drive motor 7 to reduce the extrusion volume.

[0047] When the material viscosity increases, the resistance to the rotation of screw 8 increases, and the barrel 11 experiences greater torque, causing it to rotate in the direction of screw 8's rotation. The potentiometer 10 outputs a larger angle signal, and the control system determines that the rotation speed needs to be increased to overcome the increased resistance and maintain the extrusion volume. Therefore, it increases the speed of the drive motor 7. When the material viscosity decreases, the resistance decreases, and the magnetic force pulls the barrel 11 back to its initial angle, causing it to rotate in the opposite direction. The potentiometer 10 outputs a smaller angle signal, and the control system reduces the rotation speed to avoid excessive extrusion. This bidirectional adjustment capability allows the self-compensating printhead 2 to handle both increased and decreased viscosity, achieving stable extrusion volume control across the entire range. In actual testing, fluctuations in the extrusion volume of multiple materials can be controlled within ±2%, with a response time of no more than 0.2 seconds.

[0048] Two typical application scenarios are provided below: Scenario 1: Stable printing with a single material.

[0049] Equipment debugging: Check the tightness of each component connection, drive the two-axis linkage mechanism 4 and printing platform 3 through the control system to move, and test their motion accuracy and repeatability; start the drive motor 7 to make the screw 8 rotate without load, observe whether the material cylinder 11 is kept at zero position, and test whether the signal output of the potentiometer 10 is stable; calibrate the initial position of the inner magnetic pole 12 and the outer magnetic pole 13 to ensure that the zero point of magnetic force is consistent with the zero point of shear force. Material preparation: Prepare the alumina ceramic paste for printing (viscosity 3000 mPa). s) Load the external feeding device and feed the slurry into the cylinder 11 through the feeding channel 14. Open the exhaust port at the bottom of the cylinder 11 to discharge the air remaining in the cylinder 11 until the slurry flows out continuously and evenly. Processing settings: Import the 3D model of the ceramic part into the control system. The system automatically generates the printing path. Set the initial screw speed of 8 to 150 r / min, the printing speed to 10 mm / s, and the printing layer thickness to 0.1 mm. Molding Process: The two-axis linkage mechanism 4 is activated, driving the self-compensating print head 2 to move along the set path. Simultaneously, the drive motor 7 starts, driving the screw 8 to rotate and extrude ceramic slurry for printing. During the printing process, when the slurry viscosity increases due to temperature changes, the shear force of the screw 8 on the slurry increases. Since the shear force is greater than the magnetic force, the barrel 11 rotates along the rotation direction of the screw 8, driving the potentiometer 10 to rotate synchronously. After receiving the signal change from the potentiometer 10, the control system automatically increases the speed of the drive motor 77 to 180 r / min, increasing the slurry extrusion volume until the shear force and magnetic force are rebalanced. When the slurry viscosity decreases, the control system automatically reduces the speed of the screw 8 to 120 r / min, reducing the extrusion volume and maintaining a stable extrusion volume. The printing platform 3 rises and falls layer by layer until the entire part is printed. It should be noted that although the increase in the screw 8 speed also affects the shear force, it is less significant than the impact of the slurry and has a smaller impact on the force balance.

[0050] Post-processing: After printing, the ceramic blank is removed and placed in a degreasing furnace at 600℃ for 2 hours. Finally, it is sintered at 1650℃ for 1 hour to obtain a dense ceramic part.

[0051] Scenario 2: Printing with multiple materials.

[0052] Equipment debugging: Same as step 1 in scenario 1; Material preparation: Prepare polymer slurry (viscosity 1000 mPa). s) and conductive paste (viscosity 5000 mPa) s) The polymer slurry is first fed into the two storage tanks of the external multi-material feeding device, and the air is discharged. Processing settings: Import the 3D model of the multi-material part, plan the printing path and mark the material switching nodes. Set the initial screw speed of polymer paste printing to 120r / min and the printing speed to 12mm / s. Set the initial screw speed of conductive paste printing to 200r / min and the printing speed to 8mm / s. Molding Process: First, the polymer matrix is ​​printed, and the device automatically maintains a stable extrusion rate of the polymer slurry. When the first material switching node is reached, the external feeding device automatically switches to supply conductive slurry. At this time, the material viscosity suddenly increases, the shear force increases, the barrel 11 rotates, the potentiometer 10 outputs a signal change, and the control system automatically increases the screw speed 8 from 120 r / min to 220 r / min, quickly stabilizing the extrusion rate of the conductive slurry. The conductive circuit part continues to be printed, and the device compensates for fluctuations in the extrusion rate of the conductive slurry in real time during the printing process. When the next material switching node is reached, the external feeding device automatically switches back to polymer slurry, and the control system automatically reduces the screw speed 8 to 120 r / min, restoring stable extrusion of the polymer slurry. This cycle continues until the printing of the entire multi-material part is completed. Post-processing: After printing, remove the parts and cure them at 80℃ for 2 hours to remove excess solvent and improve the strength of the parts.

[0053] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A self-compensating printhead, characterized in that, include: Housing, barrel, screw, and self-compensating components; The lower part of the outer shell has a chamber, the barrel is rotatably mounted in the chamber, and the screw is mounted in the barrel for extruding material; The self-compensating component includes an outer magnetic pole, an inner magnetic pole, and a potentiometer. The outer magnetic pole is disposed on the inner wall of the outer shell cavity, and the inner magnetic pole is disposed on the outer wall of the material cylinder and arranged opposite to the outer magnetic pole with the same pole. The potentiometer is also mounted on the material cylinder. The magnetic force of the outer and inner magnetic poles keeps the barrel at the initial angle. When the material shear force increases, it overcomes the magnetic force and drives the barrel and potentiometer to rotate.

2. The self-compensating printhead as described in claim 1, characterized in that, The upper part of the outer shell is provided with a feeding channel, which is connected to the inner cavity of the material cylinder.

3. The self-compensating printhead as described in claim 1, characterized in that, Fixed bearings are installed at both the upper and lower parts of the outer shell. The material cylinder is installed in the outer shell through the fixed bearings and can rotate around its own axis within the range of 0-30°.

4. The self-compensating printhead as described in claim 1, characterized in that, A drive motor is also installed on the outer casing, and the top end of the screw extends out of the barrel. The drive motor is connected to the top end of the screw via a coupling.

5. The self-compensating printhead as described in claim 1, characterized in that, Both the inner and outer magnetic poles are cylindrical structures. The outer wall of the inner magnetic pole is inlaid with an axial magnetic strip, and the inner wall of the outer magnetic pole is inlaid with an axial magnetic strip.

6. The self-compensating printhead as described in claim 1, characterized in that, The discharge end diameter of the barrel is 0.2-0.6mm, the length-to-diameter ratio of the screw is 15:1-20:1, and a gradual pitch design is adopted.

7. A printing method using a self-compensating printhead as described in any one of claims 1-6, characterized in that, Includes the following steps: Feeding printing material into the barrel; The screw located inside the barrel is driven to rotate, extruding the printing material from the discharge end of the barrel; The shearing force generated by the printing material on the screw acts on the barrel. When the shearing force changes, it drives the barrel to rotate around its own axis. The barrel drives the potentiometer to rotate synchronously. Acquire the rotation angle signal of the potentiometer; Adjust the screw speed according to the rotation angle signal.

8. An extrusion direct writing device, characterized in that, Includes a frame, a printing platform, and a self-compensating printhead as described in any one of claims 1-6; The frame is equipped with a two-axis linkage mechanism. The self-compensating print head is connected to the frame through the two-axis linkage mechanism, and the printing platform is connected to the frame through a lifting mechanism.

9. A method of operating the extrusion direct writing device as described in claim 8, characterized in that, Includes the following steps: Debug the equipment, test the motion accuracy of the two-axis linkage mechanism and the printing platform, and calibrate the initial positions of the inner and outer magnetic poles; The printing material is fed into the barrel, and residual air inside the barrel is expelled. Import the 3D model of the part, plan the printing path, and set the initial screw speed, printing speed, printing layer thickness, and material switching nodes; The two-axis linkage mechanism drives the self-compensating print head to move along the set path, and the drive motor drives the screw to rotate to extrude material for printing. During the printing process, the screw speed is automatically adjusted according to the change of material shear force to achieve stable control of the extrusion amount. When the material switching node is reached, the next printing material is automatically switched and the extrusion amount compensation is completed. After printing, remove the parts for post-processing.

10. The working method as described in claim 9, characterized in that, During the molding process, when the viscosity of the printing material increases, leading to an increase in shear force, the barrel rotates along the direction of screw rotation and drives the potentiometer to rotate synchronously. The control system automatically increases the speed of the drive motor to increase the extrusion volume. When the viscosity of the printing material decreases, resulting in a reduction in shear force, the barrel rotates in the opposite direction of the screw rotation, causing the potentiometer to rotate synchronously in the opposite direction. The control system automatically reduces the speed of the drive motor to reduce the extrusion volume.

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