PLA material pre-stretching and humidity self-adaptive calibration system

Abstract

The invention discloses a PLA material pre-stretching and humidity self-adaption calibration system which comprises a pre-stretching module, a humidity self-adaption module and a printing control module. The pre-stretching module adopts a double-roller tension control mechanism; a detection unit of the humidity self-adaptive module is a microwave moisture sensor; the execution unit is a micro hot air channel; the printing control module carries out dynamic parameter adjustment on the extrusion speed according to the adjustment formula V = 1.2 V0 # imgabs0 # 0.05 delta d, V is the adjusted extrusion speed, V0 is the basic extrusion speed, and delta d is the wire diameter deviation; when delta dgt; when 0, V is reduced to avoid material accumulation; when delta dlt; when 0, V compensation material insufficiency is improved, the core moisture content of the wire rod is controlled in real time, and bubble defects and interlayer strength reduction caused by moisture absorption are avoided; and a stress-humidity-printing parameter cooperative control model is established, and the printing precision and the material utilization rate are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing, and in particular to a PLA material pre-stretching and humidity adaptive calibration system. Background Art

[0002] In the field of 3D printing, PLA (polylactic acid) filament is a commonly used printing material. Currently, the pre-processing and control technology of PLA filament in 3D printing has many shortcomings: Limitations of Single Stress Control Technology: Traditional dual-roller tension mechanisms apply static tension through a fixed tension wheel, which can only partially mitigate wire diameter fluctuations (±0.05mm). Because they lack the integration of temperature softening and dynamic stretch rate regulation, residual stress is not fully released, leading to extrusion flow deviations exceeding 15%, seriously affecting printing accuracy and quality.

[0003] Limitations of single humidity control technology: Existing passive drying methods (such as silica gel desiccant cartridges) and surface detection methods (such as capacitive sensors) have extremely low drying efficiency. Reducing the moisture content from 0.35% to 0.2% requires >2 hours, and the core moisture content of the filament cannot be detected (with an accuracy of <±0.1%). During high-temperature extrusion, microbubbles are easily generated, reducing interlayer bond strength by >40%, resulting in insufficient strength and easy damage to the finished product.

[0004] Lack of a coordinated control mechanism: Existing technologies often address either stress or humidity issues individually, failing to establish a closed-loop linkage of "stress relief-humidity compensation-printing parameter adjustment," resulting in a high overall printing defect rate. Furthermore, traditional humidity detection is limited to the surface, and the drying method is static and constant temperature, which cannot respond to dynamic changes in the core moisture content of the filament in real time. This leads to poor material adaptability, poor extrusion stability during high-speed printing, and a low success rate for printing thin-walled structures. Summary of the Invention

[0005] The present invention aims to eliminate diameter fluctuations caused by residual stress in PLA filament production and stabilize the extrusion flow rate; control the core moisture content of the filament in real time to avoid bubble defects and decreased interlayer strength caused by moisture absorption; and establish a coordinated control model of stress, humidity, and printing parameters to improve printing accuracy and material utilization.

[0006] To achieve the above object, the present invention provides the following technical solutions: A PLA material pre-stretching and humidity adaptive calibration system includes a pre-stretching module, a humidity adaptive module, and a printing control module; the pre-stretching module adopts a dual-roller tension control mechanism; the detection unit of the humidity adaptive module is a microwave moisture sensor; the execution unit is a micro hot air channel; the printing control module dynamically adjusts the extrusion speed parameters, and the adjustment formula is V=1.2V0 0.05Δd, where V is the adjusted extrusion speed, V0 is the basic extrusion speed, and Δd is the wire diameter deviation; when Δd>0, reduce V to avoid material accumulation; when Δd<0, increase V to compensate for insufficient material.

[0007] As a further solution of the present invention, the active wheel of the pre-stretching module is driven by a servo motor, the driven wheel is integrated with a torque sensor, the wire wrap angle is 150°, and it is equipped with a temperature-controlled roller. The temperature-controlled roller has a built-in 40-80°C adjustable PTC heating plate, which is optimized based on the PLA glass transition temperature of 60°C.

[0008] Further preferably, the microwave moisture sensor adopts a ring waveguide structure, is suitable for 1.75 / 2.85mm wire diameter, has a penetration depth of 0.5-1mm, and a detection accuracy of ±0.02%. The micro hot air channel uses 60°C dry nitrogen with a flow rate of 0.5-2L / min. When the moisture content H is greater than 0.25%, the purge is triggered until H is less than 0.2%.

[0009] As a further solution of the present invention, in the pre-stretching stage, the temperature-controlled roller is heated to 60°C, PLA enters a highly elastic state, and a dynamic stretching rate of 1%-3% is applied. The residual stress is released through elastic deformation and viscous flow mechanisms. The elastic deformation follows Hooke's law σ=Eε, and the viscous flow conforms to the Maxwell model. The dynamic tension adjustment formula , dynamically adjust the tension, Δd is the wire diameter deviation, k1 and k2 are material coefficients, T represents dynamic tension, and dΔd / dt represents the displacement change rate.

[0010] Furthermore, during the moisture absorption process of PLA, the water diffusion conforms to Fick's second law. When the moisture content H>0.25%, the nozzle temperature compensation formula Increase nozzle temperature to compensate for the drop in viscosity caused by moisture absorption.

[0011] As a further solution of the present invention, by establishing a linear relationship between tension and wire diameter deviation T=n1 Δd n2 dn is used to perform mechanical modeling on the dynamic tension adjustment formula, where n1 is the proportional coefficient, n2 is the differential coefficient, Δd represents the wire diameter deviation, and dn represents the wire diameter.

[0012] As a further embodiment of the present invention, the melt viscosity of PLA after moisture absorption is or The relationship with temperature T conforms to the Arrhenius equation , by increasing the temperature to avoid extrusion instability caused by reduced viscosity.

[0013] Furthermore, the system established a collaborative control model of stress, humidity and printing parameters to achieve comprehensive and precise control of PLA filament during the 3D printing process.

[0014] The pre-stretching module's mechanical structure utilizes a dual-roller tension control mechanism, with the active roller driven by a servo motor and the passive roller integrated with a torque sensor. The wire wrap angle is 150°. The rollers are equipped with a temperature-controlled, built-in PTC heater with an adjustable temperature of 40-80°C, optimized for PLA's glass transition temperature of 60°C.

[0015] Humidity Adaptive Module: The detection unit is a 10-20 GHz microwave moisture sensor with a ring waveguide structure. It is compatible with 1.75 / 2.85 mm wire diameters, has a penetration depth of 0.5-1 mm, and a detection accuracy of ±0.02%, directly measuring the moisture content of the wire core. The actuator is a micro hot air channel that uses 60°C dry nitrogen at a flow rate of 0.5-2 L / min. When the moisture content H exceeds 0.25%, a purge is triggered (1-10 seconds) until H falls below 0.2%.

[0016] Print control module: Dynamically adjust the extrusion speed parameters and correct the tension fluctuation formula V=1.2V0 0.05Δd (where V is the adjusted extrusion speed (unit: mm / s), V0 is the base extrusion speed (i.e., the preset or nominal extrusion speed), and Δd is the wire diameter deviation). When Δd > 0 (thickening wire diameter), V is lowered to prevent material accumulation; when Δd < 0 (thinning wire diameter), V is increased to compensate for material shortage. Combined with a 1.2x base speed amplification, this ensures a stable extrusion flow rate during dynamic adjustments, ultimately keeping flow rate deviation within ±3%.

[0017] Analysis of the Mechanisms of Physical and Chemical Changes in PLA Materials: Viscoelastic Behavior During Stress Relief: PLA is a typical semi-crystalline thermoplastic polymer, and its mechanical behavior is significantly affected by temperature. During the pre-stretching stage, the temperature-controlled roller is heated to 60°C (close to the glass transition temperature of PLA), at which point PLA enters a highly elastic state and the mobility of the molecular segments increases. According to viscoelastic theory, when a dynamic stretch rate of 1%-3% is applied, residual stress is released through the following mechanisms: Elastic deformation: The initial stage is caused by changes in molecular chain bond length and bond angle, following Hooke's law σ=Eε, where the elastic modulus E decreases with increasing temperature (about 1.2GPa at 60℃). Viscous flow: As time goes on, the molecular chain segments overcome internal friction and slip, which conforms to the Maxwell model (relaxation time ( , viscosity ( ) decreases with increasing temperature. The dynamic tension adjustment formula , Δd is the wire diameter deviation, k1 and k2 are material coefficients, and T represents dynamic tension). The tension is dynamically adjusted to reduce the wire diameter fluctuation from ±0.05mm to ±0.01mm, corresponding to an 80% increase in the residual stress release rate.

[0018] Water diffusion and viscosity change during moisture absorption: PLA molecular chains contain polar ester groups, which are prone to moisture absorption, resulting in an increase in moisture content. The diffusion of water within PLA conforms to Fick's second law. , where the diffusion coefficient D is approximately ( m 2 / s), the core moisture content detection depth must reach 0.5-1mm (matching the penetration capability of the microwave sensor). When the moisture content H>0.25%, the plasticization effect of water causes the PLA melt viscosity η to decrease (according to the Carreau-Yasuda model), but during high-temperature extrusion, water vaporizes to form microbubbles. Nozzle temperature compensation formula , T0 is the nominal temperature, T is the nozzle temperature after compensation. The theoretical basis is: after moisture absorption, the viscosity activation energy Ec of PLA decreases, and the temperature needs to be increased to compensate for the viscosity drop and ensure stable melt fluidity (viscosity fluctuation <5%).

[0019] Flow stress coordinated control during printing: The relationship between extrusion flow Q, wire diameter d, and extrusion speed v is: In traditional technology, the wire diameter fluctuation of ±0.05mm leads to flow deviation of more than 15% ( ). The present invention dynamically corrects the extrusion speed ( ), establish flow closed-loop control: when ( ) (wire diameter becomes thicker), reduce ( ) Avoid excessive extrusion; when ( ) (wire diameter becomes thinner), improve ( ) compensates for insufficient flow. Combined with the wire diameter stabilization effect (±0.01mm) of the pre-stretching module, the flow deviation is ultimately achieved to be less than 5%, meeting the stability requirements during high-speed printing (>100mm / s). The present invention establishes a closed-loop flow control by dynamically correcting the extrusion speed. Combined with the wire diameter stabilization effect (±0.01mm) of the pre-stretching module, the flow deviation is ultimately achieved to be less than 5%, meeting the stability requirements during high-speed printing (>100mm / s).

[0020] Formula derivation and verification: Mechanical modeling of dynamic tension adjustment formula: Assume that the tension of the wire is T, and the wire diameter deviation Δd=d d0 (d0 is the nominal diameter), the torque M=T measured by the driven wheel torque sensor r μ θ (r is the roller radius, μ is the friction coefficient, and the wrap angle θ = 150° = 2.618 rad). According to the force balance and material elongation ( ), establish the linear relationship between tension and wire diameter deviation: , where k1 is the proportional coefficient (related to the PLA elastic modulus) and k2 is the differential coefficient (suppresses dynamic fluctuations). Experimental verification: When Δd = +0.05 mm, T increases by 15%, the elongation increases to 3%, and the wire diameter returns to the nominal value.

[0021] Viscosity correction for nozzle temperature compensation: PLA melt viscosity after moisture absorption ( ) and temperature( ) is the Arrhenius equation: , when the moisture content increases by 0.1%, the activation energy ( ) drops by 5%. Assume the nominal temperature ( ),when( ), the temperature needs to be raised to ( ),make( ) to 95% of the dry state, avoiding extrusion instability caused by reduced viscosity.

[0022] This invention eliminates diameter fluctuations caused by residual stress during PLA filament production, stabilizing extrusion flow. It also controls the core moisture content of the filament in real time, preventing moisture-induced bubble defects and decreased interlayer strength. It also establishes a coordinated control model for stress, humidity, and printing parameters, improving printing accuracy and material utilization.

[0023] The present invention has the following beneficial effects: Improved precision: effectively reduces wire diameter fluctuations, reduces extrusion flow deviation, and improves interlayer shear strength, significantly improving printing precision.

[0024] Defect suppression: Reduces bubble defect rates and significantly improves the success rate of printing thin-walled structures in high humidity environments (RH=80%).

[0025] Efficiency and energy consumption: Dynamic nitrogen purge consumes less energy than traditional constant temperature drying, reduces response time, is suitable for high-speed printing, and improves printing efficiency.

[0026] Compatibility: The modular design is compatible with mainstream printers and can be expanded to hygroscopic materials such as PETG and ABS by adjusting control parameters, with a wide range of applications. DETAILED DESCRIPTION

[0027] Example 1: A PLA material pre-stretching and humidity adaptive calibration system, comprising: System Architecture Pre-stretching module mechanical structure: dual-roller tension control mechanism (active roller driven by servo motor, driven roller integrated with torque sensor, wire wrap angle 150°) and temperature-controlled roller (with built-in 40-80°C adjustable PTC heating plate, optimized based on PLA glass transition temperature of 60°C).

[0028] Analysis of the mechanism of physical and chemical changes in PLA materials: viscoelastic behavior during stress relief. PLA (polylactic acid) is a typical semi-crystalline thermoplastic polymer, and its mechanical behavior is significantly affected by temperature. During the pre-stretching stage, the temperature-controlled roller is heated to 60°C (close to the glass transition temperature of PLA). )), at this time PLA enters a highly elastic state and the activity of the molecular chain segments increases. According to viscoelasticity theory, when a dynamic stretch rate of 1%-3% is applied, the residual stress is released through the following mechanisms: Elastic deformation: The initial stage is caused by changes in the molecular chain bond length and bond angle, following Hooke's law ( ), where the elastic modulus ( ) decreases with increasing temperature (about 1.2 GPa at 60°C). Viscous flow :As time goes by, the molecular chain segments overcome the internal friction and slip, which is consistent with the Maxwell model (relaxation time ( , viscosity ( ) decreases with increasing temperature). Dynamic tension adjustment formula ( ), wire diameter deviation ( ) reflects the real-time stress state, through proportional differential control ( ) is the material coefficient) and dynamically adjusts the tension to reduce the wire diameter fluctuation from ±0.05mm to ±0.01mm, corresponding to an 80% increase in the residual stress release rate.

[0029] The diffusion of water and the change of viscosity during the moisture absorption process. PLA molecular chains contain polar ester groups, which are easy to absorb moisture, resulting in an increase in moisture content. The diffusion of water in PLA conforms to Fick's second law: , where the diffusion coefficient ( ) is about ( ), the core moisture content detection depth must reach 0.51mm (microwave sensor penetration capability matches). When the moisture content ( ), the plasticizing effect of water makes the PLA melt viscosity ( ) decreases (according to the CarreauYasuda model), but when extruding at high temperature, water vaporizes and forms micro bubbles. Nozzle temperature compensation formula ( ) is based on the following theoretical basis: the viscous flow activation energy of PLA after moisture absorption ( ) decreases, the temperature needs to be increased to compensate for the viscosity drop and ensure stable melt fluidity (viscosity fluctuation <5%).

[0030] Flow stress coordinated control during printing process, extrusion flow ( ) and wire diameter ( )、Extrusion speed( ) is related to ( In traditional technology, the wire diameter fluctuation of ±0.05mm results in flow deviation of >15% ( ). The present invention dynamically corrects the extrusion speed ( ), establish flow closed-loop control: when ( ) (wire diameter becomes thicker), reduce ( ) Avoid excessive extrusion; when ( ) (wire diameter becomes thinner), improve ( ) to compensate for insufficient flow. Combined with the wire diameter stabilization effect of the pre-stretching module (±0.01mm), the ultimate flow deviation is less than 5%, meeting the stability requirements of high-speed printing (>100mm / s).

[0031] Formula derivation and verification, mechanical modeling of dynamic tension adjustment formula, assuming the tension of the wire is ( ), wire diameter deviation( )(( ) is the nominal diameter), the torque is measured by the driven wheel torque sensor ( )(( ) is the roller radius, ( ) is the friction coefficient, the wrap angle ( )). According to the force balance and material stretch rate ( ), by establishing the linear relationship between tension and wire diameter deviation T=n1 Δd n2 dn is used to conduct mechanical modeling of the dynamic tension adjustment formula, where n1 is the proportional coefficient (related to the elastic modulus of PLA), n2 is the differential coefficient (suppressing dynamic fluctuations), Δd represents the wire diameter deviation, and dn represents the wire diameter. Experimental verification: when (Δd=+0.05mm), ( ) increased by 15%, the elongation increased to 3%, and the wire diameter returned to the nominal value.

[0032] Viscosity correction for nozzle temperature compensation, PLA melt viscosity after moisture absorption ( ) and temperature( ) is the Arrhenius equation: , when the moisture content increases by 0.1%, the activation energy ( ) drops by 5%. Assume the nominal temperature ( ),when( ), the temperature needs to be raised to ( ),make( ) to 95% of the dry state, avoiding extrusion instability caused by reduced viscosity.

[0033] Control logic: dynamic tension adjustment formula (Δd is the wire diameter deviation, (k1, k2) are material coefficients, and T represents dynamic tension.) Applying a 1%-3% stretching rate reduces the wire diameter fluctuation to ±0.01mm.

[0034] Humidity Adaptive Module Detection Unit: 10-20GHz microwave moisture sensor (ring waveguide structure, suitable for 1.75 / 2.85mm wire diameter, penetration depth 0.5-1mm, detection accuracy ±0.02%), directly measures the moisture content of the wire core. Execution Unit: Micro hot air channel (60℃ dry nitrogen, flow rate 0.5-2L / min), when the moisture content H>0.25%, trigger purge (1-10 seconds) until H<0.2%; nozzle temperature compensation formula (T0 is the nominal temperature, T: the compensated nozzle temperature, the actual operating temperature adjusted according to humidity changes, Q: humidity-related parameter, indicating the deviation of the filament core moisture content. This formula indicates that when the filament core moisture content H exceeds the set threshold (such as 0.2%), the deviation is quantified and the nozzle temperature is increased proportionally (15°C / unit Q) to compensate for the viscosity drop caused by moisture absorption, thereby avoiding bubble defects and maintaining interlayer bonding strength. Print control module dynamic parameter adjustment: extrusion speed is corrected according to tension fluctuations , (V: adjusted extrusion speed (unit: mm / s), actual extrusion speed after dynamic correction based on wire diameter deviation, V0: basic extrusion speed, i.e. preset or nominal extrusion speed, Δd: wire diameter deviation;) Formula: When the actual wire diameter is greater than the target value (Δd > 0), the extrusion speed V is reduced to prevent material accumulation. When the wire diameter is smaller (Δd < 0), the extrusion speed V is increased to compensate for insufficient material. Combined with a 1.2x base speed amplification, this ensures a stable extrusion flow rate during dynamic adjustments, ultimately keeping flow rate deviation within ±3%.

[0035] The workflow of the present invention is as follows: Pre-stretching stage: The wire is stretched by 1%-3% by a double roller mechanism, and the temperature-controlled roller is heated to 60℃ to soften the PLA and eliminate the residual stress of winding. Humidity detection and treatment stage: The microwave sensor scans the core moisture content in real time, and the nitrogen purge is started when the limit is exceeded. Adjust the nozzle temperature. Printing stage: Dynamically correct the extrusion speed based on the wire diameter deviation Δd to form a "detection-processing-printing" closed-loop control.

[0036] Experimental data is shown in Table 1: Ambient humidity conditions: Low (30% RH), medium (50% RH), and high (80% RH) humidity levels were set. PLA filaments with low (<0.5 MPa), medium (0.5-1.0 MPa), and high (>1.0 MPa) initial residual stresses were tested under each humidity level. Printing parameters: A uniform layer thickness of 0.2 mm, a print speed of 50 mm / s, and a nozzle temperature of 200°C were used. Test indicators included wire diameter fluctuation (μm), extrusion flow rate deviation (%), bubble defect rate (%), interlaminar shear strength (MPa), thin-walled structures (wall thickness 0.4 mm), and print success rate (%). Table 1

[0037] The results show that the system can still maintain a line diameter wave of ±22μm, an extrusion flow deviation of ≤5.8%, and a thin-wall printing success rate of ≥90% under high humidity (80%RH) and high initial stress conditions, which is significantly better than traditional technology.

[0038] As shown in Table 1 above, under the conditions of an ambient humidity of 30% RH and a low initial residual stress (<0.5 MPa): During the pre-stretching phase, the PLA filament is mounted on a dual-roller tension control mechanism. The active roller is driven by a servo motor, while a torque sensor on the driven roller monitors the tension in real time. The temperature-controlled roller is heated to 60°C, applying a 1% dynamic stretch to the PLA filament. At this point, according to Hooke's law (σ = Eε), the elastic modulus (E) is approximately 1.2 GPa. Changes in the molecular chain bond lengths and angles result in elastic deformation. Over time, the molecular chains overcome internal friction and undergo viscous flow, conforming to the Maxwell model. The tension is adjusted using the dynamic tension control formula, gradually stabilizing the wire diameter fluctuation from its initial state.

[0039] Humidity detection and processing stage: A 10-20GHz microwave moisture sensor scanned the moisture content of the PLA filament core in real time. The detection found that the moisture content was at a normal low level, and the nitrogen purge of the micro hot air channel was not triggered.

[0040] Printing stage: According to the preset printing parameters, layer thickness 0.2mm, printing speed 50mm / s, nozzle temperature 200℃, combined with the wire diameter deviation Δd, through the formula V=1.2V0 0.05Δd.

[0041] Dynamically correct the extrusion speed. During this process, wire diameter fluctuations were controlled within ±10μm, extrusion flow deviation was 2.5%, bubble defect rate was 0.1%, interlayer shear strength reached 45.3MPa, and the printing success rate for thin-walled structures (wall thickness 0.4mm) was 98%.

[0042] Under conditions of 50% humidity and a moderate initial residual stress (0.5-1.0 MPa), during the pre-stretching phase, PLA filament passes through a dual-roller mechanism, with a servo motor operating the active roller and a torque sensor providing feedback from the passive roller. The temperature-controlled rollers are maintained at a constant 60°C, applying a 2% dynamic stretch rate to the filament. Elastic deformation and viscous flow work together to release residual stress, while a dynamic tension adjustment formula adjusts the tension in real time, gradually reducing wire diameter fluctuations.

[0043] Humidity detection and treatment phase: The microwave moisture sensor detects that the moisture content of the PLA filament core is close to 0.25%. This triggers the micro-hot air channel, which blows dry nitrogen at 60°C at a flow rate of 1 L / min for 3 seconds, reducing the moisture content to a safe range. Simultaneously, the nozzle temperature is fine-tuned according to the nozzle temperature compensation formula.

[0044] Printing stage: Printing is carried out according to the printing parameters, combined with the real-time wire diameter deviation Δd, through V=1.2V0 The extrusion speed was corrected by 0.05Δd. The final wire diameter fluctuation was ±18μm, the extrusion flow rate deviation was 4.5%, the bubble defect rate was 0.4%, the interlayer shear strength was 40.8MPa, and the thin-wall structure printing success rate was 93%.

[0045] For environments with an ambient humidity of 80% RH and high initial residual stress (>1.0 MPa): During the pre-stretching phase, the PLA filament enters a dual-roller tension control mechanism. A servo motor drives the active roller, while a torque sensor precisely monitors the driven roller. The temperature-controlled roller rapidly heats to 60°C, applying a 3% dynamic stretch rate to the filament. During elastic deformation and viscous flow, a dynamic tension adjustment formula is used to effectively control tension, significantly reducing wire diameter fluctuations. During the humidity detection and processing phase, a microwave moisture sensor detects that the core moisture content of the PLA filament exceeds 0.25%. The micro-hot air channel immediately activates, blowing dry nitrogen at 60°C for 5 seconds at a flow rate of 2 L / min, reducing the moisture content to below 0.2%. Simultaneously, the nozzle temperature is increased accordingly according to the nozzle temperature compensation formula to ensure stable melt viscosity.

[0046] Printing stage: Carry out printing according to the established printing parameters, and according to the wire diameter deviation Δd, pass V=1.2V0 The extrusion speed is dynamically adjusted by 0.05Δd. In this example, the wire diameter fluctuation is maintained at ±22μm, the extrusion flow deviation is 5.8%, the bubble defect rate is 0.6%, the interlayer shear strength is 39.5MPa, and the thin-wall structure printing success rate is 90%.

[0047] This invention achieves improved precision: reduced wire diameter fluctuation, reduced extrusion flow deviation, and enhanced interlayer shear strength. Defect suppression: reduced bubble defect rates and improved printing success rates for thin-walled structures in high humidity environments (RH = 80%). Efficiency and energy consumption: Dynamic nitrogen purge consumes only slightly less energy than traditional constant temperature drying, shortening response time and making it suitable for high-speed printing. Compatibility: The modular design is compatible with mainstream printers and can be expanded to handle hygroscopic materials such as PETG and ABS by adjusting control parameters.

[0048] In this invention, the collaborative control mechanism: the linkage architecture of the pre-stretching module and the humidity adaptive module, achieves the coordinated regulation of stress and humidity through a tension-temperature-speed closed-loop algorithm. Core detection technology: the ring waveguide structure design of the microwave moisture sensor (adaptive to 1.75 / 2.85mm wire diameter, penetration depth 0.5-1mm) and the non-contact core moisture content detection method. Dynamic control algorithm: proportional-differential tension adjustment formula based on wire diameter deviation And the linear temperature compensation formula of moisture content System integration: The combined structure of the dual-roller tension mechanism and the temperature-controlled roller, as well as the integration of the microwave sensor and the wire feeding path.

[0049] This invention addresses the shortcomings of existing PLA filament pretreatment and control technologies for 3D printing, such as single stress and humidity control, and the lack of a coordinated control mechanism. It aims to eliminate diameter fluctuations caused by residual stress during PLA filament production and stabilize extrusion flow. It also controls the core moisture content of the filament in real time to avoid bubble defects and interlayer strength loss caused by moisture absorption. Furthermore, it establishes a coordinated control model for stress, humidity, and printing parameters to improve printing accuracy and material utilization. This invention proposes a pre-stretching and humidity adaptive calibration system that combines temperature softening, dynamic stretch rate adjustment, and real-time core moisture content detection and processing to address the shortcomings of existing single stress and humidity control technologies. A microwave moisture sensor with a ring waveguide structure enables non-contact core moisture content detection with high accuracy. A micro-hot air channel dynamic purge drying system is designed, which is more efficient and less energy-intensive than traditional drying methods. A linear relationship between tension and wire diameter deviation is established for mechanical modeling. Dynamic control algorithms based on wire diameter deviation and moisture content, such as a proportional-differential tension adjustment formula and a linear moisture content temperature compensation formula, achieve precise control.

[0050] In this invention, a dual-roller tension control mechanism is employed. The active roller is driven by a servo motor, and the driven roller integrates a torque sensor to monitor tension. The wire wrap angle is 150°. A temperature-controlled roller is used to heat the PLA to 60°C (near the glass transition temperature) to induce a highly elastic state. A dynamic stretch rate of 1%-3% is then applied to release residual stress through elastic deformation (following Hooke's law) and viscous flow (conforming to the Maxwell model). A dynamic tension adjustment formula is used to dynamically adjust the tension based on wire diameter deviation, minimizing wire diameter fluctuations. The detection unit is a microwave moisture sensor, employing a ring waveguide structure to directly measure the core moisture content of the wire. When the moisture content H exceeds 0.25%, the micro-hot air channel of the actuator unit is activated, purging with 60°C dry nitrogen until H is less than 0.2%. Simultaneously, based on the relationship between moisture content and viscosity (consistent with the relevant model) and the change in viscous flow activation energy after moisture absorption, the nozzle temperature is increased using the nozzle temperature compensation formula to compensate for the viscosity drop caused by moisture absorption. Dynamic parameter adjustment of the extrusion speed is performed based on the wire diameter deviation Δd, using the formula V=1.2V0. 0.05Δd. When Δd>0, V is lowered to avoid material accumulation. When Δd<0, V is increased to compensate for material shortage. Combined with a 1.2x baseline speed amplification, a stable extrusion flow rate is maintained, achieving closed-loop flow control. This enables the establishment of a coordinated control model for stress, humidity, and printing parameters. Through the linkage architecture of the pre-stretching module and the humidity adaptive module, a closed-loop algorithm based on tension, temperature, and speed is used to achieve coordinated regulation of stress and humidity, forming a "detection-processing-printing" closed-loop control.

[0051] In summary, in terms of precision, the present invention effectively reduces wire diameter fluctuations (from ±0.05mm to approximately ±0.01mm), reduces extrusion flow deviation (controlled within ±3%, traditionally >15%), enhances interlayer shear strength, and significantly improves printing precision. In terms of defect suppression, the bubble defect rate is reduced, and the success rate of printing thin-walled structures in a high humidity environment (RH=80%) is greatly improved (≥90%, which is lower with traditional technologies). In terms of efficiency and energy consumption, dynamic nitrogen purge energy consumption is reduced, response time is shortened, and high-speed printing is compatible, improving printing efficiency. In terms of compatibility, the modular design is compatible with mainstream printers and can be expanded to hygroscopic materials such as PETG and ABS, with a wide range of applications.

[0052] The technical principles of the present invention have been described above in conjunction with specific embodiments, which are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention fall within the scope of protection of the present invention. Those skilled in the art will be able to conceive of other specific embodiments of the present invention without inventive effort, and such methods will fall within the scope of protection of the present invention.

Claims

1. A PLA material pre-stretching and humidity adaptive calibration system, characterized in that: It includes a pre-stretching module, a humidity adaptive module, a printing control module and an execution unit; the pre-stretching module adopts a double-roller tension control mechanism; the detection unit of the humidity adaptive module is a microwave moisture sensor; the execution unit is a micro hot air channel; the printing control module dynamically adjusts the extrusion speed parameters, and the adjustment formula is V=1.2V0 0.05Δd, where V is the adjusted extrusion speed, V0 is the basic extrusion speed, and Δd is the wire diameter deviation; when Δd>0, reduce V to avoid material accumulation; when Δd<0, increase V to compensate for insufficient material.

2. A PLA material pre-stretching and humidity adaptive calibration system according to claim 1, characterized in that: The active wheel of the pre-stretching module is driven by a servo motor, and the driven wheel is integrated with a torque sensor. The wire wrap angle is 150° and it is equipped with a temperature-controlled roller. The temperature-controlled roller has a built-in PTC heating plate adjustable from 40 to 80°C, which is optimized based on the PLA glass transition temperature of 60°C.

3. A PLA material pre-stretching and humidity adaptive calibration system according to claim 1, characterized in that: The microwave moisture sensor adopts a ring waveguide structure, is suitable for 1.75 / 2.85mm wire diameter, has a penetration depth of 0.5-1mm, and a detection accuracy of ±0.02%. The micro hot air channel uses 60°C dry nitrogen with a flow rate of 0.5-2L / min. When the moisture content H is greater than 0.25%, the purge is triggered until H is less than 0.2%.

4. A PLA material pre-stretching and humidity adaptive calibration system according to claim 3, characterized in that: In the pre-stretching stage, the temperature-controlled roller is heated to 60°C, PLA enters a highly elastic state, and a dynamic stretching rate of 1%-3% is applied. The residual stress is released through elastic deformation and viscous flow mechanisms. The elastic deformation follows Hooke's law σ=Eε, and the viscous flow conforms to the Maxwell model. The dynamic tension adjustment formula , dynamically adjust the tension, where Δd is the wire diameter deviation, k1 and k2 are material coefficients, T represents dynamic tension, and dΔd / dt represents the displacement change rate.

5. A PLA material pre-stretching and humidity adaptive calibration system according to claim 4, characterized in that: During the moisture absorption process of PLA, the water diffusion conforms to Fick's second law When the moisture content H>0.25%, the nozzle temperature compensation formula Increase nozzle temperature to compensate for the drop in viscosity caused by moisture absorption.

6. A PLA material pre-stretching and humidity adaptive calibration system according to claim 1, characterized in that: By establishing the linear relationship between tension and wire diameter deviation T=n1 Δd n2 dn is used to perform mechanical modeling on the dynamic tension adjustment formula, where n1 is the proportional coefficient, n2 is the differential coefficient, Δd represents the wire diameter deviation, and dn represents the wire diameter.

7. A PLA material pre-stretching and humidity adaptive calibration system according to claim 1, characterized in that: PLA melt viscosity after moisture absorption η The relationship with temperature T conforms to the Arrhenius equation , by increasing the temperature to avoid extrusion instability caused by reduced viscosity.

8. A PLA material pre-stretching and humidity adaptive calibration system according to claim 1, characterized in that: The system establishes a coordinated control model of stress, humidity and printing parameters to achieve comprehensive and precise control of PLA filament during the 3D printing process.

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