3D printing device and printing method for plant fiber reinforced composite material

Abstract

The invention relates to a 3D printing device and method for a plant fiber reinforced composite material. The method comprises the steps of configuring printing nozzle parameters; zero calibration is carried out on the force sensor; the 3D printing device is started, a force sensor monitors a contact pressure measured value of a printing nozzle in the Z-axis direction in real time, and a control unit generates a Z-direction pose compensation instruction in real time according to deviation polarity and amplitude characteristics of the measured contact pressure value and a target value; and the controller of the mechanical arm adjusts the position of the mechanical arm to keep the contact pressure measured value within the contact pressure target value range. Compared with the prior art, the method has the advantages that according to the deviation polarity and amplitude characteristics of the actually measured contact pressure value and the target value, the position of the mechanical arm keeps the contact pressure actually measured value within the contact pressure target value range, and yarn diameter fluctuation of plant fiber yarn can be adapted; and the problems of overlarge local pressure and deformation accumulation caused by a traditional position control method are effectively solved, and the dimensional precision of products is improved.

Description

Technical Field

[0001] This invention relates to additive manufacturing of composite materials, and more particularly to a 3D printing apparatus and method for plant fiber reinforced composite materials. Background Technology

[0002] Fiber-reinforced composites, with their excellent specific strength, specific modulus, and good corrosion resistance and fatigue resistance, have become indispensable key materials in the aerospace field. However, traditional synthetic fibers such as carbon fiber and glass fiber face two major challenges in production: high energy consumption during the manufacturing process and difficulty in achieving environmentally friendly recycling after the products are discarded. Under the global sustainable development strategy, developing new green and environmentally friendly composite materials has become an important research direction in materials science. Plant fiber-reinforced composites, as an emerging sustainable material, have the following significant advantages: renewable and biodegradable raw materials; low density and high cost-effectiveness; unique microstructure endowing them with excellent damping properties; and good acoustic properties, making them particularly suitable for vibration reduction and noise reduction applications.

[0003] Currently, the main preparation processes for plant fiber reinforced composites include hot pressing, compression molding, and resin transfer molding. Hot pressing involves thoroughly impregnating pretreated plant fibers with a resin matrix and curing them under specific temperature, pressure, and time conditions. This method is mature, requires simple equipment, produces high-density products with stable mechanical properties, and is particularly suitable for producing structural components such as panels. However, hot pressing also has limitations: the high-pressure, high-temperature environment can easily damage heat-sensitive natural fibers, leading to a decrease in mechanical properties; and the production cycle is relatively long, making it unsuitable for manufacturing complex three-dimensional components. Compression molding has high production efficiency, but controlling the uniformity of fiber distribution is difficult. Although existing preparation methods can fully utilize the lightweight characteristics and renewable advantages of plant fibers, significant challenges remain in the synergistic optimization of the following key performance indicators: balancing processing efficiency with fiber structural integrity, adaptability to molding complex geometric components, and effective control of production costs. There is a particular need to develop novel preparation processes that highly match the intrinsic properties of plant fibers to maximize the comprehensive performance advantages of this material.

[0004] In the field of additive manufacturing, 3D printing technology for continuous fiber reinforced composite materials (represented by carbon fiber reinforced systems) has achieved a major breakthrough. This technology achieves integrated molding of high-strength, lightweight, and complex structures by simultaneously processing continuous fibers with thermoplastic resin matrices (including but not limited to polylactic acid, polyamide, and polyetheretherketone). Fused deposition modeling (FDM) is currently the most commonly used 3D printing process for continuous fiber reinforced composite materials. Core 3D printing process parameters include layer height, linewidth, printing temperature, and printing speed, which have a decisive impact on the performance, dimensional accuracy, and surface quality of the product. However, plant fiber yarns have uneven filament diameters and are prone to cross-sectional deformation under stress. Traditional 3D printing processes based on fixed layer height parameters can lead to uneven pressure distribution along the printing path when implementing interlayer stacking, making it difficult to guarantee consistent product quality.

[0005] Application publication number CN116638758A discloses a printhead with continuous fiber feeding and direct pressure tension online control, and its printing method. Specifically, the printhead structure utilizes a flexible pressure feedback fixing mechanism for the extruder, composed of components such as an optical axis, support springs, a spring fixing platform, and pressure sensors. This mechanism tolerates drag damage to the continuous fiber prepreg caused by mismatches between the extruder's filament feeding speed and the printhead's movement speed. Simultaneously, it quantifies the matching degree between the extruder's filament feeding speed and the printhead's movement speed based on pressure sensor values ​​influenced by extruder displacement changes, and then adjusts the extruder's filament feeding speed accordingly to achieve adaptive matching with the printhead's movement speed. While this prior art primarily focuses on the tension of the filament during manufacturing to prevent filament damage, it still cannot guarantee the consistency of printed product quality.

[0006] In summary, the technical problem that needs to be solved is how to design a printing device and method that can improve the quality of 3D printed products made from plant fiber reinforced composite materials. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of poor quality consistency of 3D printed products made of plant fiber reinforced composite materials in the prior art, and to provide a 3D printing device and printing method for plant fiber reinforced composite materials.

[0008] The objective of this invention can be achieved through the following technical solutions.

[0009] According to one aspect of the present invention, a 3D printing apparatus for plant fiber reinforced composite materials is provided, comprising a robotic arm, a force sensor, a 3D printing module, a printing table, and a control unit. The 3D printing module includes a printing nozzle, a heating module, and a feeding mechanism. The force sensor is fixedly mounted on the end effector of the robotic arm, and the 3D printing module is fixedly mounted on the measuring end of the force sensor. The printing nozzle includes a heat dissipation pipe, and a cooling fan is provided on one side of the heat dissipation pipe. The printing table is fixed on a vibration isolation platform, and the 3D printing module is located on one side of the printing table. The control unit is electrically connected to the robotic arm, the force sensor, and the cooling fan.

[0010] As a preferred technical solution, the plant fiber reinforced composite material includes plant fibers and resin materials.

[0011] According to another aspect of the present invention, a printing method using a 3D printing apparatus employing plant fiber reinforced composite materials is provided, specifically comprising the following steps: Step S1: Configure the target range of contact pressure of the print head in the Z-axis direction; Step S2: With the robotic arm and 3D printing module in the initial standby position, perform zero-point calibration on the force sensor; Step S3: Start the 3D printing device. The force sensor monitors the measured contact pressure of the printing nozzle in the Z-axis direction in real time. The control unit generates a Z-axis pose compensation command in real time based on the polarity and amplitude characteristics of the deviation between the measured contact pressure value and the target value. The controller of the robotic arm adjusts the position of the robotic arm to keep the measured contact pressure value within the range of the contact pressure target value.

[0012] As a preferred technical solution, step S1 also includes a printing line width and a printing speed; the printing line width is positively correlated with the material extrusion width.

[0013] As a preferred technical solution, the minimum value of the printed line width is 0.1 mm, and the printing speed is set in the range of 1~10 mm / s.

[0014] As a preferred technical solution, the target value of the contact pressure of the print head in the Z-axis direction is in the range of 0.1~10N.

[0015] As a preferred technical solution, step S1 further includes configuring a force sensor detection threshold range and a signal filter cutoff frequency; the signal filter is integrated inside the force sensor.

[0016] As a preferred technical solution, in step S2, after the force sensor is zero-point calibrated, a unique coordinate transformation relationship is established between the force sensor coordinate system and the end-effector coordinate system of the robotic arm.

[0017] As a preferred technical solution, step S1 further configures the contact pressure limit value; in step S3, when the measured contact pressure value suddenly changes to be greater than the contact pressure limit value, the 3D printing module stops abruptly, and the control unit controls the robotic arm to lift to the set height.

[0018] As a preferred technical solution, in step S3, the extrusion direction of the printing nozzle is kept parallel to the force sensor measurement axis.

[0019] Compared with the prior art, the present invention has the following beneficial effects.

[0020] 1) The force sensor of this invention is fixedly installed on the end effector of the robotic arm, and the 3D printing module is fixedly installed on the measuring end of the force sensor. This enables real-time detection of the contact pressure of the printing nozzle in the Z-axis direction, providing the possibility for local pressure control and improving manufacturing flexibility. The control unit keeps the position of the robotic arm within the range of the measured contact pressure value based on the polarity and amplitude characteristics of the deviation between the measured contact pressure value and the target value. This can adapt to the fluctuation of the filament diameter of plant fiber yarn. Real-time pressure adjustment effectively solves the problems of excessive local pressure and deformation accumulation caused by traditional position control methods, improving the dimensional accuracy of the product. This invention eliminates the mechanical platform leveling process required for traditional 3D printing, significantly simplifies the preliminary preparation work, and greatly improves the preparation efficiency of 3D printed products of plant fiber reinforced composite materials.

[0021] 2) A cooling fan is installed on one side of the heat dissipation pipe in this invention, which can effectively force-cool the extruded molten material and promote rapid solidification and molding. The printing worktable is fixed on a vibration isolation platform, which ensures the stability of the worktable.

[0022] 3) In this invention, the printing pressure serves as the target reference value for force feedback control; the printing line width determines the extrusion width of a single layer of material; and the speed parameter controls the movement speed of the extrusion nozzle along the printing path. By setting the cutoff frequency of the signal filter, the system response speed and noise resistance stability can be balanced.

[0023] 4) This invention ensures precise spatial alignment between the force sensor coordinate system and the end-effector coordinate system (TCP) of the robotic arm, or establishes an accurate and reliable coordinate transformation relationship.

[0024] 5) The present invention adopts an emergency stop control scheme. When the contact force value monitored in real time during system operation exceeds the limit value, the safety protection will be automatically triggered, the 3D printing module will stop suddenly, and the control unit will control the robotic arm to lift to the set height, which effectively ensures the overall safety of the device. Attached Figure Description

[0025] Figure 1This is a schematic diagram of the structure of a 3D printing device for plant fiber reinforced composite materials according to the present invention.

[0026] Figure 2 This is a flowchart of a 3D printing method for a plant fiber reinforced composite material according to the present invention.

[0027] Figure 3 This is a 3D printing path trajectory diagram of the present invention.

[0028] Figure 4 The graphs show the sound absorption coefficient test results of Examples 2 to 5 of the present invention.

[0029] The numbers in the diagram are as follows: 1. End effector, 2. Force sensor, 3. Feed inlet, 4. Heat pipe, 5. Cooling fan, 6. Print head. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0031] To address the bottlenecks in existing technologies, this invention innovatively proposes a method for preparing 3D printed plant fiber reinforced composite materials based on robotic arm pressure control. This method introduces a robotic arm force control system for real-time pressure feedback adjustment and precise control, overcoming the limitations of traditional layer height control. It effectively solves the problem of thickness direction pressure control in traditional processes, adapts to the deformation characteristics of plant fibers, ensures pressure uniformity during printing, improves the dimensional accuracy and performance consistency of the finished product, and contributes to achieving high-quality molding of plant fiber reinforced composite materials.

[0032] Example 1 like Figure 1 As shown, this embodiment provides a 3D printing device for plant fiber reinforced composite materials, including a robotic arm, a force sensor, a 3D printing module, a printing table, and a control unit. The 3D printing module includes a printing nozzle, a heating module, and a feeding mechanism. The force sensor is fixedly installed on the end effector of the robotic arm, and the 3D printing module is fixedly installed on the measuring end of the force sensor. The printing nozzle includes a heat dissipation pipe, and a cooling fan is provided on one side of the heat dissipation pipe. The printing table is fixed on a vibration isolation platform, and the 3D printing module is located on one side of the printing table. The control unit is electrically connected to the robotic arm, the force sensor, and the cooling fan.

[0033] Plant fiber reinforced composite materials include plant fibers and resin materials; the plant fibers are selected from natural plant fibers including but not limited to flax fiber, ramie fiber, sisal fiber, etc.; the resin materials are selected from thermoplastic resin materials including but not limited to polylactic acid, polypropylene, polyamide, etc.

[0034] Example 2 like Figure 2 As shown, a method for preparing 3D-printed plant fiber reinforced composite materials based on robotic arm pressure control specifically includes the following steps: S1. Material preparation: Based on the material performance requirements of the target printed component, select thermoplastic composite filaments (such as flax fiber prepreg) that are suitable for the fused deposition modeling (FDM) process, and accurately load the prepared flax fiber prepreg into the feeding mechanism of the 3D printing module.

[0035] S2. Force Sensor and Printing Module Installation: The high-precision force / torque sensor (hereinafter referred to as the "force sensor") is fixedly installed on the flange of the robotic arm's end effector. The 3D printing module, including the printing nozzle, heating module, and feeding mechanism, is then securely installed on the workpiece end (i.e., measuring end) mounting surface of the force sensor, ensuring a stable connection of all components. The core equipment used in this embodiment includes the IRB1200 5kg 0.9 / Type B industrial robotic arm, the ABB ForceControl 165 force / torque sensor, and a self-developed temperature-controlled extrusion module (flat-nozzle diameter of 0.8mm). The force sensor integrates a signal filter, sensor amplification / conditioning circuit, and analog-to-digital converter. After installation, the force sensor's detection threshold range and the signal filter's cutoff frequency parameters need to be configured. The signal filter can filter out high-frequency noise (such as electromagnetic interference and vibration noise) in the force signal, providing a clean and stable feedback signal and preventing noise interference from causing control malfunctions or system oscillations. By setting the cutoff frequency of the signal filter, the system response speed and noise immunity stability can be balanced.

[0036] During installation, the force sensor coordinate system must be precisely spatially aligned with the end-effector coordinate system (TCP) of the robotic arm, or an accurate and reliable coordinate transformation relationship must be established to ensure that the sensor can correctly identify the original load and calibrate to zero. The 3D printing module needs to determine the appropriate extrusion technology and nozzle diameter parameters based on the characteristics of the selected raw materials: pre-impregnated filaments use pre-impregnated filament extrusion technology, while non-pre-impregnated fibers or pre-impregnated filaments that need to be mixed with other resin matrices for extrusion use co-extrusion technology. The nozzle diameter is determined by the linear density and average diameter of the filaments; simultaneously, it must be ensured that the printing module is fixed in place relative to the force sensor without any looseness, and that the extrusion direction of the extrusion nozzle is strictly parallel to the force sensor's measurement axis (Z-axis) to monitor the forces acting on the nozzle during printing.

[0037] S3. Cooling system installation: The cooling fan is precisely installed on the heat dissipation tube spindle near the print head, configured to effectively force-cool the extruded molten material and promote rapid solidification.

[0038] S4. Printing Table Installation: The printing table, which carries the printing substrate, is installed on a dedicated platform with vibration isolation function using a fixing device to ensure the stability of the table. The installation position of the printing table must be completely within the effective working space of the robotic arm to ensure that all motion axes of the robotic arm can meet the accessibility requirements of all positions on the table.

[0039] S5. Process Parameter Settings: Based on the characteristics of the printing material and the target printing quality requirements, configure key process parameters: target contact pressure of the print head in the Z-axis direction, print linewidth, and printing speed, etc.; printing pressure serves as the target reference value for force feedback control, mainly depending on the requirements of finished product strength and interlayer performance; print linewidth determines the extrusion width of a single layer of material, mainly depending on the fiber volume content requirements (fiber filament diameter and prepreg diameter), and the print linewidth should be greater than the material extrusion width. Printing speed is the speed of the extrusion print head along the printing path, mainly depending on the material's physicochemical properties and finished product quality requirements. The printing pressure should be in the range of 0.1~10N, the printing speed should be set in the range of 1~10mm / s, and the minimum setting value for print linewidth is 0.1mm. The printing temperature setting needs to comprehensively consider the physicochemical properties such as the melting point and thermal decomposition temperature of the raw material: the printing temperature must be higher than the melting point of the raw material, but not higher than the thermal decomposition temperature of the material; the heating block is connected to the computer terminal through a microcontroller to achieve precise temperature setting and real-time control.

[0040] The optimized process parameters determined in this embodiment are as follows: the sample is a square thin plate with a length of 100 mm and a width of 100 mm, and the layup scheme is [0 / 90 / 0] ([0 / 90 / 0] is a general representation of fiber-reinforced composite laminates. The numbers represent the angles between the principal directions of the single-layer material of each layer of the laminate and the natural axis. In this example, it indicates that the laminate has a total of 3 layers and adopts orthogonal layup.); the printing speed is 5 mm / s, the printing line width is 0.7 mm, the printing temperature is 210℃, and the printing pressure of each layer is 3 N, 6 N, and 9 N respectively.

[0041] S6. Path Planning: Based on the 3D digital model of the component to be printed, Ultimaker Cura software is used for layer slicing to generate a printing path with a [0 / 90 / 0] layup scheme, such as... Figure 3 As shown; according to the planned printing path, a motion control program is programmed in the robotic arm control unit and debugged under no-load conditions.

[0042] S7. Sensor parameter settings: According to the control accuracy requirements, set the key parameters of the force sensor: the contact force range that the force sensor can measure is 0.5-100N, and the filter cutoff frequency is 3dB.

[0043] S8. System Calibration: With the robotic arm and printing system in the initial standby position, first perform the zero-point calibration operation of the force sensor, and then reset the force sensor reading to zero.

[0044] S9. Preheating treatment: Start the heating device to preheat the system to 210℃.

[0045] S10. Printing execution: Using the printing raw materials prepared in step S1, start the robotic arm motion control program; After the robotic arm motion program is initiated, the 3D printing filament moves synchronously with the robotic arm and adheres to and compacts on the printing table under pressure. Force sensors precisely monitor the pressure on the print head in the Z-axis direction in real time. The control unit generates Z-axis pose compensation commands in real time based on the polarity and amplitude characteristics of the deviation between the measured pressure value and the target value. The robotic arm controller converts the received displacement commands into coordinated movements of each joint, ultimately achieving millimeter-level high-precision adjustment of the print head pose. After dynamically adjusting the Z-axis height for pose compensation based on the pressure deviation, the actual pressure stabilizes within the 3±0.2N range, achieving real-time pressure feedback control. After the motion program ends, the continuous flax fiber bundle is cut, and after natural cooling to below the glass transition temperature, the printed component is removed from the substrate. The actual thickness of the printed component is measured to be 1.59mm. The deviation polarity index value indicates the direction of deviation (greater than / less than the target value), and the amplitude characteristic indicates the magnitude of the deviation value. Knowing the deviation polarity and amplitude characteristics, commands can be generated to fine-tune the position of the robotic arm's end effector in the Z-axis direction (upward / downward movement).

[0046] The process parameter settings also include the contact pressure limit value; when the contact force value monitored in real time during the operation of the device exceeds 5 times the preset limit value, the safety protection will be automatically triggered, that is, the execution of the force control program will be stopped immediately, the robotic arm will be controlled to slowly raise the height by 10~20mm at a speed of less than 10mm / s, and then an emergency stop operation will be performed.

[0047] The method for preparing flax fiber prepreg is as follows: French dew-covered flax fiber yarn (linear density of 139 Tex, count of 7.2 Nm) and polylactic acid granules (PLA, density of 1.24 g / cm³) are used. 3 As raw material, PLA particles were melted at 210℃ before the experiment and then fully penetrated into continuous flax fiber yarn through an impregnation process. The yarn was then pultruded into prepreg yarn (diameter 0.55±0.05mm) through a diameter control die. The prepreg yarn was stored in a dry environment at room temperature (relative humidity <70%) to prevent moisture absorption.

[0048] Example 3 This embodiment provides a method for preparing 3D printed plant fiber reinforced composite materials based on robotic arm pressure control. The difference from Embodiment 2 is that the printing pressure of each layer in this embodiment is 3N.

[0049] Example 4 This embodiment provides a method for preparing 3D printed plant fiber reinforced composite materials based on robotic arm pressure control. The difference from Embodiment 2 is that the printing pressure of each layer in this embodiment is 6N.

[0050] Example 5 This embodiment provides a method for preparing 3D printed plant fiber reinforced composite materials based on robotic arm pressure control. The difference from Embodiment 2 is that the printing pressure of each layer in this embodiment is 9N.

[0051] The plant fiber composite materials prepared in Examples 1-4 were cut into circular samples with a diameter of 100 mm, and their sound absorption performance was tested according to the national standard GB / T18696.2-2004. The test results are as follows. Figure 4 As shown in the figure, the results indicate that the frequency corresponding to the maximum sound absorption coefficient of the material varies with different printing pressures. This is because applying pressure during 3D printing disrupts the internal cavity structure of the plant fiber material, altering its shape and size, thus leading to differences in the frequency corresponding to the maximum sound absorption coefficient. Different arrangements of the gradient structure of the sound-absorbing panels also exhibited distinctions in the frequency corresponding to the maximum sound absorption coefficient. This suggests that adjusting the printing pressure can directionally improve sound absorption performance within a specific frequency range.

[0052] The present invention has the following advantages: Low-pressure molding protects the fiber structure: 3D printing low-pressure molding technology is used, and the molding pressure is significantly lower than that of traditional preparation methods. This fully preserves the multi-level cavity structure and twisting characteristics of plant fibers, ensuring that their unique structural features and the acoustic performance advantages they bring can be fully utilized.

[0053] Intelligent leveling improves efficiency: This invention achieves real-time dynamic compensation of nozzle height through a force feedback closed-loop control system, completely eliminating the mechanical platform leveling process required for traditional 3D printing, significantly simplifying the preliminary preparation work, and greatly improving the preparation efficiency of 3D printed plant fiber reinforced composite materials.

[0054] Adaptive compensation ensures quality: The robotic arm-based pressure control mechanism proposed in this invention can intelligently adapt to the diameter fluctuations of plant fiber yarns. Through real-time pressure adjustment, it effectively solves the problems of excessive local pressure and deformation accumulation caused by traditional position control methods, thereby improving the dimensional accuracy of the products.

[0055] Small-scale control improves manufacturing flexibility: The robotic arm-based pressure control device proposed in this invention has a simple configuration and can achieve pressure control and real-time monitoring down to the fiber scale during the manufacturing process, providing the possibility for local pressure control and improving manufacturing flexibility.

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A 3D printing device for plant fiber reinforced composite materials, characterized in that, The system includes a robotic arm, a force sensor, a 3D printing module, a printing table, and a control unit. The 3D printing module includes a printing nozzle, a heating module, and a feeding mechanism. The force sensor is fixedly mounted on the end effector of the robotic arm, and the 3D printing module is fixedly mounted on the measuring end of the force sensor. The printing nozzle includes a heat dissipation pipe, and a cooling fan is provided on one side of the heat dissipation pipe. The printing table is fixed on a vibration isolation platform, and the 3D printing module is located on one side of the printing table. The control unit is electrically connected to the robotic arm, the force sensor, and the cooling fan.

2. A 3D printing apparatus for plant fiber reinforced composite materials according to any one of claims 1 to 2, characterized in that, The plant fiber reinforced composite material includes plant fibers and resin materials.

3. A printing method using the 3D printing apparatus for plant fiber reinforced composite materials as described in claim 1, characterized in that, Specifically, the following steps are included: Step S1: Configure the target range of contact pressure of the print head in the Z-axis direction; Step S2: With the robotic arm and 3D printing module in the initial standby position, perform zero-point calibration on the force sensor; Step S3: Start the 3D printing device. The force sensor monitors the measured contact pressure of the printing nozzle in the Z-axis direction in real time. The control unit generates a Z-axis pose compensation command in real time based on the polarity and amplitude characteristics of the deviation between the measured contact pressure value and the target value. The controller of the robotic arm adjusts the position of the robotic arm to keep the measured contact pressure value within the range of the contact pressure target value.

4. The printing method according to claim 3, characterized in that, The step S1 also includes the configuration of printing line width and printing speed; the printing line width is positively correlated with the material extrusion width.

5. The printing method according to claim 4, characterized in that, The minimum print line width is 0.1 mm, and the print speed is set in the range of 1 to 10 mm / s.

6. The printing method according to claim 3, characterized in that, The target contact pressure of the printhead in the Z-axis direction is in the range of 0.1~10N.

7. The printing method according to claim 3, characterized in that, The step S1 also includes configuring the force sensor detection threshold range and the cutoff frequency of the signal filter; the signal filter is integrated inside the force sensor.

8. The printing method according to claim 3, characterized in that, In step S2, after the force sensor is zero-point calibrated, a unique coordinate transformation relationship is established between the force sensor coordinate system and the end-effector coordinate system of the robotic arm.

9. The printing method according to claim 3, characterized in that, In step S1, the contact pressure limit value is also configured; in step S3, when the measured contact pressure value suddenly increases to a value greater than the contact pressure limit value, the 3D printing module stops abruptly, and the control unit controls the robotic arm to rise to the set height.

10. The printing method according to claim 3, characterized in that, In step S3, the extrusion direction of the print head is kept parallel to the force sensor measurement axis.

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