An online monitoring method for jet hysteresis of melt electrowriting curve printing and a method for improving the accuracy of melt electrowriting curve printing

Abstract

The present invention belongs to the technical field of polymer additive manufacturing, and discloses an online monitoring method for jet hysteresis of melt electrowriting curve printing and a method for improving the accuracy of melt electrowriting curve printing. The specific process is: firstly, the fiber deposition rate is calculated according to the diameter of the required printed fiber and the melt volume flow rate, and the position radius vector of the deposited fiber is determined according to the curve shape of the required printed fiber, and then the local curvature and the unit tangent vector are calculated, and then the jet hysteresis length is continuously adjusted during the curve printing process by using an online monitoring device for melt electrowriting jet hysteresis to monitor the jet hysteresis in real time (the online monitoring device for melt electrowriting jet hysteresis includes a servo motor, an industrial camera, a circular guide rail and a load-bearing bracket), and finally the jet hysteresis length is made less than 3mm by adjusting the voltage during printing, and the curve printing process is performed according to the adjusted jet hysteresis length. The present invention can monitor and accurately adjust the jet hysteresis length in real time, thereby effectively improving the accuracy of the printed pattern.

Description

Technical Field

[0001] The present invention belongs to the field of polymer additive manufacturing devices and methods, and relates to an online monitoring method for jet hysteresis of melt electrowriting curve printing and a method for improving the accuracy of melt electrowriting curve printing. Background Art

[0002] Melt electrostatic direct writing technology, as a solvent-free, high-resolution additive manufacturing technology that combines the advantages of melt electrospinning and 3D printing, has shown great potential in research fields such as tissue regeneration and soft robotics. This technology provides rich possibilities for scientific research and industrial applications with its wide material adaptability, high-precision printing capability, adjustable fiber diameter range and customizable microstructure.

[0003] However, in the practice of melt electrostatic direct writing, there are also a series of challenges. Especially during fiber deposition, if the platform movement rate does not reach the critical value, the jet is easily distorted due to the platform squeezing. When the platform movement rate exceeds the critical value, the jet will deviate from the vertical direction under the drag of the platform, forming a jet lag phenomenon. This phenomenon causes the actual fiber pattern to not coincide with the designed path, especially when printing complex patterns composed of curves, the printing accuracy is significantly reduced, and the fiber deposition accuracy and resolution are limited.

[0004] As the number of printing layers increases, especially when printing to high layers, the positive charge injected into the polymer during the melt electrostatic direct writing process gradually accumulates on the collection plate, repelling the jet with the same positive charge, weakening the acceleration of the jet by the electric field, and thus the jet lag length increases with the number of printing layers without changing the process parameters. Therefore, without changing the design path of each layer, the difference between the actual fiber pattern and the design path also increases with the number of printing layers, that is, there is an interlayer offset in the structure of the actual support. When the pattern always deposits fibers of the same fineness, the printing accuracy will be affected by the above two factors. The problem is more complicated when the printing pattern has different requirements for fiber diameter at different positions. Because at this time, the speed of the collection plate needs to be adjusted according to the change in fiber diameter, which further aggravates the change in jet lag length, making precision control during printing more difficult.

[0005] To address the above problems, researchers have explored a variety of solutions.

[0006] The first method is to adjust the process parameters to make the jet lag length approach zero as much as possible, that is, to make the jet print almost perpendicular to the collection plate to improve the accuracy of low-level curve printing. For example, in Reference 1 (Designing with CircularArc Toolpaths to Increase the Complexity of Melt Electrowriting[J]. Advanced Materials Technologies, 2022, 7(10).), when printing circular arc-shaped patterns, the collection plate movement speed is changed multiple times, and the printing results are compared to select the optimal collection plate movement speed to make the jet print almost perpendicular to the collection plate to improve the printing accuracy. As the number of printed layers increases, when the paths between layers shift, although the offset distance of each layer is uneven, this tilt can be corrected by compensating a certain empirical value on the printing path for each layer. However, this method requires multiple trial and error to succeed, is inefficient, and has limited applicability.

[0007] The second method is to set a dwell point at the turning point of the path to alleviate the impact of jet lag on printing accuracy. For example, in Reference 2 (Fiber Bridging during Melt Electrowriting of Poly(ε-Caprolactone)and the Influence of Fiber Diameter and Wall Height[J]. MacromolecularMaterials and Engineering, 2021, 306(3).), a dwell point is set at the turning point of the printing straight path, and the dwell time is set to allow the jet deposition point to catch up with the nozzle position before continuing printing. This method is only applicable to the turning point of the straight path and cannot be applied to curve printing.

[0008] The third is to fundamentally solve the influence of the jet lag length on the accuracy of the printing path by adjusting the printing method. For example, the curve printing theory is proposed in reference 3 (Analytical interpretation of microscale fiber deviation indesigning for polymer melt electrohydrodynamic-based additive manufacturing [J]. Additive Manufacturing, 2022.). When the fiber morphology and diameter to be printed are known and the jet lag length is assumed to be constant, the deviation caused by the jet lag length to the printing path and speed is calculated before printing, and the printing path is corrected accordingly to compensate for the influence of this part and avoid the process of selecting the best printing conditions through multiple experiments. However, this method still has limitations, that is, the motion trajectory and speed of the platform cannot be dynamically adjusted during the printing process, and cannot adapt to the dynamic changes of the jet lag length caused by other factors such as residual charge during the printing process, and the printing accuracy cannot be further improved.

[0009] Therefore, it is of great significance to provide an online monitoring method for the jet hysteresis of melt electrowriting curve printing and a method for improving the accuracy of melt electrowriting curve printing to solve the above problems. Summary of the invention

[0010] The purpose of the present invention is to solve the problems existing in the prior art and to provide an online monitoring method for jet hysteresis in melt electrowriting curve printing and a method for improving the accuracy of melt electrowriting curve printing.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] An online monitoring method for jet hysteresis in melt electrowriting curve printing, using an online monitoring device for jet hysteresis in melt electrowriting to monitor the jet hysteresis length in real time during the curve printing process; the online monitoring device for jet hysteresis in melt electrowriting comprises a servo motor, an industrial camera, an annular guide rail and a load-bearing bracket, the servo motor and the industrial camera are both fixed on a slider of the annular guide rail, the servo motor drives the industrial camera to move along the annular guide rail, the annular guide rail is fixed to a gantry of the melt electrowriting equipment through the load-bearing bracket, and the annular guide rail is coaxial with the center line of the melt electrowriting nozzle;

[0013] The servo motor drives the industrial camera to move on the circular guide rail at a certain speed. During the movement, real-time photos are taken and the jet lag length in the curve printing process is obtained. The speed at which the servo motor drives the industrial camera to move on the circular guide rail is shown in formula (1);

[0014] (1);

[0015] Wherein, R is the radius of the circular guide rail, in mm; , and are the local curvature of the deposition trajectory, the unit tangent vector and the deposition rate at the real-time deposition point of the fiber, respectively. The unit of the local curvature of the deposition trajectory is mm -1 , the unit of the unit tangent vector is 1, and the unit of the deposition rate is mm / s;

[0016] The derivation process of formula (1) is as follows:

[0017] The movement of industrial cameras is determined by their movement speed Uniquely determined, including the direction and speed of movement. The direction of movement of the camera lens is tangent to the fiber trajectory unit vector Keep consistent in real time. The rotation angular rate of the camera lens The angular velocity of the jet plane is consistent with the jet plane in real time, depending on the curvature of the fiber morphology and jet deposition rate : ,in is the arc length parameter of the fiber morphology. Therefore, the motion expression of the industrial camera is .

[0018] As the preferred technical solution:

[0019] In the above-mentioned online monitoring method for jet hysteresis of melt electrowriting curve printing, the height of the industrial camera is set to ensure that the jet profile is located in the center of the field of view, and the distance from the industrial camera to the center of the annular guide rail is set to ensure that the jet can be clearly imaged after focusing.

[0020] As described above, in the on-line monitoring method for jet hysteresis of melt electrowriting curve printing, the industrial camera model is TD-2000U3.

[0021] As described above, an online monitoring method for jet hysteresis in melt electrowriting curve printing, the image obtained by real-time photography by an industrial camera contains a needle, a jet and a collecting plate (the collecting plate is fixed on the curve printing platform), and the process of obtaining the jet hysteresis length during the curve printing process from the image is: after binarization of the image, each row of pixels is scanned from top to bottom (the needle is on top and the collecting plate is on the bottom), and when a row of pixels decreases by more than 30% for the first time (because the needle diameter is larger than the jet diameter, a large number of experiments have shown that the number of pixels from the needle to the part where the jet just flows out is reduced by more than 30%), the midpoint of the previous row of the two changed rows is extracted and a perpendicular line is drawn downward to obtain the straight line where the needle center is located, and then the scanning is continued downward until a row with a pixel increase of more than 100% appears, that is, the point where the jet reaches the collecting plate, the midpoint of the previous row is extracted and a perpendicular line is drawn to the straight line where the needle center is located, and the length of the perpendicular line is the jet hysteresis length.

[0022] The present invention also provides a method for improving the accuracy of melt electrowriting curve printing by using the on-line monitoring method of jet hysteresis in melt electrowriting curve printing as described in any one of the above items, comprising the following steps:

[0023] Step 1: According to the diameter of the required printed fiber The fiber deposition rate is calculated using the melt volume flow rate Q, as shown in formula (2);

[0024] (2);

[0025] Step 2: The positional radius of the deposited fiber can be determined based on the curve shape of the desired printed fiber. , expressed as an ordered series of points , where x is the horizontal coordinate, the unit is mm; y is the vertical coordinate, the unit is mm; i is the point number, no unit;

[0026] Step 3: Basis Calculate local curvature With unit tangent vector , as shown in formulas (3) and (4);

[0027] (3);

[0028] (4);

[0029] in, represents the difference;

[0030] Step 4: Continuously adjust the printing path according to the monitored jet lag length l, and calculate the real-time trajectory of the curved printing platform according to formulas (5) and (6): With speed ;

[0031] (5);

[0032] (6);

[0033] Wherein, l is the jet lag length obtained by real-time monitoring;

[0034] Step 5: According to the monitored jet lag length l, the voltage during printing is continuously adjusted to make the jet lag length l less than 3 mm. When the jet lag length l is less than 3 mm, the stability of the printing process will not be affected. When l ≥ 3 mm, the jet lag length can be reduced by increasing the voltage.

[0035] Step 6: Perform the curve printing process according to the jet lag length l obtained in step 5 to improve the accuracy of melt electrowriting curve printing.

[0036] As the preferred technical solution:

[0037] As described above, in a method for improving the accuracy of melt electrowriting curve printing, the fiber diameter in step 1 It should not exceed the fiber diameter range that can be printed by the melt electrowriting device in the conventional linear printing mode, which is 5~50μm; if the user requires If changes occur during the printing process, the ordered point sequence corresponding to step 2 is provided sequence;

[0038] The melt volume flow rate Q in step 1 is related to the polymer type, temperature, nozzle inner diameter, etc. For the same polymer, the melt volume flow rate increases with increasing temperature and nozzle inner diameter, and decreases conversely. If the feeding method is pneumatic, the volume flow rate can be adjusted by changing the air pressure.

[0039] In the method for improving the printing accuracy of the melt electrowriting curve as described above, the distance between two adjacent ordered dot columns in step 2 does not exceed 1 mm, otherwise the printing accuracy will be affected.

[0040] Beneficial effects:

[0041] (1) The online monitoring method for the jet hysteresis of melt electrowriting curve printing of the present invention adopts a simple detection device, which only adds a circular guide rail and an industrial camera to the original melt electrostatic direct writing printing device, so that the change of the jet hysteresis length can be monitored online in real time to dynamically calculate the curve printing path and the platform movement rate.

[0042] (2) The present invention adjusts the voltage to maintain the jet lag length at a constant length, which is simple to operate and has a quick response.

[0043] (3) The present invention uses a device and a method in combination. Compared with the previous method of improving printing accuracy by repeated trial and error, this method can provide more accurate and consistent adjustment results, reduce errors caused by subjective judgment differences, and improve efficiency. At the same time, the fineness of the printed fiber can be controlled, and the printing pattern path of different fiber finenesses can be optimized to improve printing accuracy, which has strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is an overall schematic diagram of the on-line monitoring device for melt electrowriting jet hysteresis of the present invention;

[0045] Figure 2 It is an operating principle diagram of the on-line monitoring device for melt electrowriting jet hysteresis of the present invention;

[0046] Figure 3 1 is a printing comparison diagram before and after adjusting the printing path in an embodiment of the present invention; in the figure, a is a pattern to be printed in the embodiment, b is a pattern printed before adjusting the printing path in the embodiment, and c is a pattern printed after adjusting the printing path in the embodiment;

[0047] Among them, 1-collecting plate, 2-annular guide rail, 3-servo motor, 4-load-bearing bracket, 5-slider, 6-industrial camera, 7-high voltage generator, 8-nozzle, 9-jet, 10-plane A, 11-plane a, 12-plane B, 13-plane b, 14-plane C, 15-plane c, 16-plane D, 17-plane E, 18-plane F. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0049] An online monitoring method for jet hysteresis in melt electrowriting curve printing, using an online monitoring device for jet hysteresis in melt electrowriting to monitor the jet hysteresis length in real time during the curve printing process;

[0050] like Figure 1 As shown, the on-line monitoring device for melt electrowriting jet hysteresis includes a servo motor 3, an industrial camera 6, a ring guide rail 2 and a load-bearing bracket 4;

[0051] The servo motor 3 and the industrial camera 6 are both fixed on the slider 5 of the annular guide rail 2. The servo motor 3 drives the industrial camera 6 to move along the annular guide rail 2. The annular guide rail 2 is fixed to the gantry of the melt electrowriting equipment through the load-bearing bracket 4. The annular guide rail 2 is coaxial with the center line of the melt electrowriting nozzle.

[0052] The model of industrial camera 6 is TD-2000U3. The height of industrial camera 6 is set to make the jet profile in the center of the field of view. The distance from industrial camera 6 to the center of the circular guide rail 2 is set to make the jet image clear after focusing.

[0053] The servo motor 3 drives the industrial camera 6 to move at a certain speed on the circular guide rail 2. During the movement, the camera takes pictures in real time to obtain images. The obtained image contains the needle, the jet and the collecting plate 1. Then, the obtained image is binarized and each row of pixels is scanned from top to bottom. When a row of pixels decreases by more than 30% for the first time, the midpoint of the previous row of the two changed rows is extracted and a vertical line is drawn downward to obtain the straight line where the needle center is located. Then, the scanning is continued downward until a row with a pixel increase of more than 100% appears. The midpoint of the previous row is extracted and a vertical line is drawn downward to the straight line where the needle center is located. The length of the vertical line is the jet lag length. The speed at which the servo motor 3 drives the industrial camera 6 to move on the circular guide rail 2 is shown in formula (1).

[0054] (1);

[0055] Where R is the radius of the circular guide rail, in mm. , and are the local curvature of the deposition trajectory, the unit tangent vector and the deposition rate at the real-time deposition point of the fiber, respectively. The unit of the local curvature of the deposition trajectory is mm -1 , the unit of the unit tangent vector is 1, and the unit of the deposition rate is mm / s;

[0056] Since the curve is printed, the plane where the jet is located is constantly changing. Therefore, the camera lens plane must be parallel to it to ensure that the jet lag length monitored in real time is accurate (e.g. Figure 2 As shown, with the continuous movement of the jet ejected from the nozzle 8, the industrial camera will also move continuously on the circular track. In order to ensure that the jet lag length monitored in real time is accurate, the camera lens plane and the jet plane need to be parallel to each other. When the industrial camera moves with the jet to the following positions in sequence: Figure 2When the camera lens is at the positions shown in the figure, the camera lens planes are respectively recorded as plane A 10, plane B 12, plane C 14, plane D 16, plane E 17, and plane F 18, and the corresponding jet planes are respectively recorded as plane a 11, plane b 13, and plane c 15, where plane A 10, plane D 16 and plane a 11 are parallel to each other, plane B 12, plane E 17 and plane b 13 are parallel to each other, and plane C 14, plane F 18 and plane c 15 are parallel to each other). Formula (1) links the camera speed and direction with the speed and direction of the printed pattern, and the corresponding camera speed and direction are designed according to the printed pattern and speed, so that the flow lag length can be reversed in real time.

[0057] A method for improving the accuracy of melt electrowriting curve printing by using an online monitoring method for jet hysteresis in melt electrowriting curve printing, the steps are as follows:

[0058] Step 1: According to the diameter of the required printed fiber The fiber deposition rate is calculated by the melt volume flow rate Q, as shown in formula (2); where the diameter of the desired printed fiber is 5~50μm;

[0059] (2);

[0060] Step 2: The positional radius of the deposited fiber can be determined based on the curve shape of the desired printed fiber. , expressed as an ordered series of points , where x is the horizontal coordinate, in mm; y is the vertical coordinate, in mm; i is the point number; the distance between two adjacent ordered point columns does not exceed 1 mm;

[0061] Step 3: Basis Calculate local curvature With unit tangent vector , as shown in formulas (3) and (4);

[0062] (3);

[0063] (4);

[0064] in, represents the difference;

[0065] Step 4: According to the jet lag length l monitored by the above melt electrowriting curve printing online monitoring method, the printing path is continuously adjusted, and the real-time trajectory of the curve printing platform movement is calculated according to formulas (5) and (6). With speed ;

[0066] (5);

[0067] (6);

[0068] Wherein, l is the jet lag length obtained by real-time monitoring;

[0069] Step 5: Adjust the voltage during printing so that the jet hysteresis length l is less than 3 mm, and adjust the printing path according to the jet hysteresis length l;

[0070] Step 6: Perform the curve printing process according to the jet lag length l obtained in step 5.

[0071] The above technical solution of the present invention is described below through specific embodiments:

[0072] This embodiment is to print Figure 3 Taking the four-leaf clover pattern shown in a as an example, a method for improving the accuracy of melt electrowriting curve printing by using an online monitoring method of jet hysteresis in melt electrowriting curve printing is as follows:

[0073] Step 1: According to the diameter of the required printed fiber =20μm and melt volume flow rate Q=0.25μL / h, the fiber deposition rate is calculated by formula (2): 4.43mm / s;

[0074] Step 2: The positional radius of the deposited fiber can be determined based on the curve shape of the desired printed fiber. , expressed as an ordered series of points , where x is the horizontal coordinate, in mm; y is the vertical coordinate, in mm; i is the point number; the distance between two adjacent ordered point columns is 0.05 mm;

[0075] Step 3: Basis The local curvature of each ordered point sequence is calculated by formulas (3) and (4) respectively: With unit tangent vector Taking the nth point (0,1) as an example, the fiber deposition rate is obtained through steps 1 and 2. 4.43mm / s, orderly point array is (0,1), and then the local curvature of the ordered point sequence is calculated by formulas (3) and (4): 1mm -1 , the unit tangent vector (-1,0);

[0076] Step 4: Figure 1As shown, on the collecting plate 1, the printing path is continuously adjusted according to the jet lag length l monitored by the above-mentioned online monitoring method for jet lag of melt electrowriting curve printing (wherein the radius R of the annular guide rail is 200 mm, and the distance from the camera lens plane to the center of the annular guide rail is 105 mm), and the real-time trajectory of the curve printing platform movement is calculated according to formulas (5) and (6). With speed , taking the nth point (0,1) in step (3) as an example, when the jet lag length l is maintained at 1 mm, the real-time trajectory is ,rate 4.95mm / s;

[0077] Step 5: Figure 1 As shown, by adjusting the voltage of the high-voltage generator 7 between [2.8kV, 3.5kV], and calculating the movement speed of the industrial camera on the circular guide rail according to the movement trajectory and speed of the collection plate after adjustment, the jet lag length l is maintained in the range of 0.5~1.5mm; taking the nth point (0,1) as an example, (-886,0);

[0078] Step 6: Print the curve according to the jet lag length l in step 5 until it is completed. Figure 3 As shown in c; if steps 4 and 5 are not performed, the final printed pattern will be as follows Figure 3 As shown in b.

[0079] By comparison Figure 3 From a, b and c in FIG. 1 , it can be seen that the method of the present invention significantly improves the printing accuracy.

Claims

1. An online monitoring method for jet hysteresis of melt electrowriting curve printing, characterized in that: The on-line monitoring device for jet hysteresis of melt electrowriting is used to monitor the jet hysteresis length in real time during the curve printing process; The online monitoring device for melt electrowriting jet hysteresis includes a servo motor, an industrial camera, an annular guide rail and a load-bearing bracket. The servo motor and the industrial camera are both fixed on a slider of the annular guide rail. The servo motor drives the industrial camera to move along the annular guide rail. The annular guide rail is fixed on the gantry of the melt electrowriting equipment through the load-bearing bracket. The annular guide rail is coaxial with the center line of the melt electrowriting nozzle. The servo motor drives the industrial camera to move on the circular guide rail at a certain speed. During the movement, real-time photos are taken and the jet lag length in the curve printing process is obtained. The speed at which the servo motor drives the industrial camera to move on the circular guide rail is shown in formula (1); （1）； Wherein, R is the radius of the circular guide rail, in mm; , and are the local curvature of the deposition trajectory, the unit tangent vector and the deposition rate at the real-time deposition point of the fiber, respectively. The unit of the local curvature of the deposition trajectory is mm -1 , the unit of the unit tangent vector is 1, and the unit of the deposition rate is mm / s.

2. The method for online monitoring of jet hysteresis in melt electrowriting curve printing according to claim 1, characterized in that: The height of the industrial camera is set so that the jet profile is located in the center of the field of view, and the distance from the industrial camera to the center of the circular guide rail is set so that the jet can be clearly imaged after focusing.

3. The method for online monitoring of jet hysteresis in melt electrowriting curve printing according to claim 2, characterized in that: The industrial camera model is TD-2000U3.

4. The method for online monitoring of jet hysteresis in melt electrowriting curve printing according to claim 1, characterized in that: The image obtained by the real-time photography of the industrial camera contains the needle, jet and collecting plate. The process of obtaining the jet lag length from the image during the curve printing process is as follows: after binarizing the image, scan each row of pixels from top to bottom. When a row of pixels decreases by more than 30% for the first time, extract the midpoint of the previous row of the two changed rows and draw a perpendicular line downward to obtain the straight line where the needle center is located. Then continue to scan downward until a row with an increase of more than 100% of pixels appears. Extract the midpoint of the previous row and draw a perpendicular line to the straight line where the needle center is located. The length of the perpendicular line is the jet lag length.

5. A method for improving the accuracy of melt electrowriting curve printing by using the on-line monitoring method for jet hysteresis of melt electrowriting curve printing as described in any one of claims 1 to 4, characterized in that: The steps include: Step 1: According to the diameter of the required printed fiber The fiber deposition rate is calculated by the melt volume flow rate Q, as shown in formula (2); （2）； Step 2: The positional radius of the deposited fiber can be determined based on the curve shape of the desired printed fiber. , expressed as an ordered series of points , where x is the horizontal coordinate, the unit is mm; y is the vertical coordinate, the unit is mm; i is the point number; Step 3: Basis Calculate local curvature With unit tangent vector , as shown in formulas (3) and (4); （3）； （4）； in, represents the difference; Step 4: Continuously adjust the printing path according to the monitored jet lag length l, and calculate the real-time trajectory of the curved printing platform according to formulas (5) and (6): With speed ; （5）； （6）； Wherein, l is the jet lag length obtained by real-time monitoring; Step 5: Adjust the voltage during printing to make the jet lag length l less than 3 mm; Step 6: Perform the curve printing process according to the jet lag length l obtained in step 5.

6. The method for improving the printing accuracy of melt electrowriting curve according to claim 5, characterized in that: Fiber diameter in step 1 5~50μm.

7. The method for improving the printing accuracy of melt electrowriting curve according to claim 5, characterized in that: In step 2, the distance between two adjacent ordered point columns shall not exceed 1 mm.

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