Curved surface conformal sensor direct writing printing method based on five-axis motion platform

Abstract

The present application discloses a method for direct-writing printing of curved surface conformal sensors based on a five-axis motion platform, which relates to the field of direct-writing printing technology. The method performs grid discretization processing on the printed curved surface in a three-dimensional digital model of a three-dimensional structural part and then designs a target printing trajectory, thereby simplifying the process of complex curved surface trajectory design and avoiding trajectory distortion caused by existing two-dimensional to three-dimensional projection methods; then, a two-axis rotation mechanism is used in a direct-writing printing system based on a five-axis motion platform to perform posture adjustment, and a three-axis motion mechanism is used to perform position adjustment and printing. Direct manufacturing on a three-dimensional structural part can be performed when the printing nozzle extrudes ink vertically downward along the normal direction of the contact surface, thereby improving the manufacturing efficiency of curved surface conformal sensors, avoiding pattern distortion caused by transfer, and improving the accuracy and conformality of the manufactured curved surface conformal sensors. The method is suitable for promotion and application in the preparation of curved surface electronics.

Description

Technical Field

[0001] The present application relates to the field of direct writing printing technology, and in particular to a curved surface conformal sensor direct writing printing method based on a five-axis motion platform. Background Art

[0002] As a monitoring device that can convert external motion, light, electricity, sound, chemical and other signals into electrical signals or other forms of easily readable signals, sensors have a wide range of applications and are common and important devices in fields such as health monitoring, wearable electronic devices and intelligent robots.

[0003] Traditional sensor manufacturing methods mainly rely on contact printing and beam lithography. These traditional manufacturing methods can usually only produce sensors on flat substrates. However, the incompatibility between 2D and 3D brings challenges to the production of complex curved surface sensors.

[0004] To meet this challenge and the growing demand for curved sensors, the current mainstream method often uses indirect fabrication via transfer printing. This approach first creates a sensor array on a stretchable flat surface and then attaches it to the curved surface. While this approach can create curved sensors, it suffers from low positioning accuracy and a complex transfer process, making fabrication difficult and the resulting sensor accuracy difficult to guarantee. Summary of the Invention

[0005] In response to the above-mentioned problems and technical needs, this application proposes a surface conformal sensor direct writing printing method based on a five-axis motion platform. The technical solution of this application is as follows:

[0006] A curved surface conformal sensor direct writing printing method based on a five-axis motion platform, the curved surface conformal sensor direct writing printing method comprising:

[0007] Build a straight-writing printing system based on a five-axis motion platform. The straight-writing printing system includes a straight-writing printer mounted on a three-axis motion mechanism and a two-axis rotation mechanism. The printing platform is mounted on the two-axis rotation mechanism, and the print nozzle of the straight-writing printer is located vertically downward above the printing platform.

[0008] Establish a 3D digital model of the 3D structural part, and discretize the printed curved surface in the 3D digital model. Use the discretized grid as a reference to design a target printing trajectory of the sensor array on the printed curved surface.

[0009] According to the initial absolute coordinates of each track point on the target printing track of the printing curved surface in the global coordinate system in the initial state, with the goal of the print nozzle of the straight writing printer extruding ink vertically downward along the normal direction of the contact surface to achieve printing, the rotation control parameters and the translation control parameters during the straight writing printing process along the target printing track are determined;

[0010] The three-dimensional structural part is fixed on the printing platform with the printed curved surface facing upward in the initial state. The two-axis rotation mechanism is controlled according to the rotation control parameters to drive the three-dimensional structural part to rotate for posture adjustment. The three-axis motion mechanism is controlled according to the translation control parameters to drive the straight writing printer and the two-axis rotation mechanism to adjust the position and print. The sensor array is printed on the printed curved surface of the three-dimensional structural part along the target printing trajectory using the straight writing printing system.

[0011] A further technical solution is that determining the rotation control parameters and translation control parameters during the straight writing printing process along the target printing trajectory includes:

[0012] According to the initial absolute coordinates of each track point on the target printing track, the rotation control parameters are obtained by adjusting the target posture so that the tangent plane of the printed surface at each track point is parallel to the horizontal plane;

[0013] The translation control parameters are obtained according to the absolute printing coordinates of each track point on the target printing track in the global coordinate system after the posture adjustment is completed.

[0014] A further technical solution is that obtaining the rotation control parameters includes:

[0015] Determine the normal vector L = (i, j, k) of the printing surface at any trajectory point P with initial absolute coordinates (x, y, z) on the target printing trajectory in the initial state;

[0016] Based on the tangent plane of the printed surface at each trajectory point being parallel to the horizontal plane as the posture adjustment target, the normal vector of the printed surface at the trajectory point P after the posture adjustment is completed is determined to be along the vertical direction

[0017] Determine the rotation angle θ of the two-axis rotation mechanism around the rotation axis U relative to the initial state based on the normal vector of any track point P on the target printing track in the initial state and the normal vector after the posture adjustment is completed U and the rotation angle θ around the rotation axis V relative to the initial state V ;

[0018] According to the rotation angle θ corresponding to each track point along the target printing track U and the rotation angle θ V Get the rotation control parameters.

[0019] Its further technical solution is that, in the initial state, the rotation axis U of the two-axis rotation mechanism is parallel to the horizontal plane and parallel to the y-axis of the global coordinate system, and the rotation axis V of the two-axis rotation mechanism is along the vertical direction and parallel to the z-axis of the global coordinate system; determine the rotation angle θ corresponding to any track point P on the target printing track U and the rotation angle θ V include:

[0020] according to Sure

[0021] Among them, R(θ U ) is the transformation matrix of the two-axis rotating mechanism when it rotates around the rotation axis U, R(θ V ) is the transformation matrix when the two-axis rotation mechanism rotates around the rotation axis V.

[0022] A further technical solution is that obtaining the translation control parameters includes:

[0023] Determine the absolute coordinates of any trajectory point P with initial absolute coordinates (x, y, z) on the target printing trajectory in the global coordinate system after completing the posture adjustment. V )·R(θ U )·P, and obtain the translation control parameters according to the printing absolute coordinates corresponding to each track point along the target printing track.

[0024] A further technical solution is that obtaining the target printing trajectory includes:

[0025] The initial printing trajectory of the sensor array on the printed surface is designed based on the discrete grid as a reference;

[0026] With the goal of achieving printing by extruding ink vertically downward from the print nozzle of a direct writing printer along the normal direction of the contact surface, pre-printing control parameters are determined during the direct writing printing process along the initial printing trajectory.

[0027] During a preliminary experiment of controlling a direct writing printing system according to pre-printing control parameters, the vertical offsets of several calibration points of the initial printing trajectory from the printed curved surface of the three-dimensional structural part are determined;

[0028] The initial printing trajectory is corrected according to the offset to obtain the target printing trajectory.

[0029] A further technical solution is that the target printing trajectory is obtained by correcting the initial printing trajectory according to the offset, including:

[0030] According to any correction point T k The offset L from the printed surface k and the calibration point Tk+1 The offset L from the printed surface k+1 , determine the initial printing trajectory at the correction point T k and correction point T k+1 The correction amount of each track point in the track segment between k+1 is the calibration point T k The next calibration point along the initial print trajectory;

[0031] The initial printing trajectory is offset-corrected according to the correction amount of each trajectory point to obtain the target printing trajectory.

[0032] A further technical solution is to determine the initial printing trajectory at the correction point T k and correction point T k+1 The correction values ​​for each trajectory point in the trajectory segment between include:

[0033] Determine the calibration point T k and correction point T k+1 The correction value of any nth trajectory point in the trajectory segment between Where n∈[0, N k ],N k is the calibration point T k and correction point T k+1 The total number of trajectory points in the trajectory segment between , and the trajectory point when n = 0 is the correction point T k 、n=N k The trajectory point at which the correction point is T k+1 .

[0034] A further technical solution is that obtaining the target printing trajectory further includes:

[0035] Determine any correction point T k and its adjacent correction point T k+1 The midpoint of the trajectory segment between the two points is offset by the vertical direction ΔL from the printed surface of the three-dimensional structure after the offset correction. k ;

[0036] According to the secondary offset ΔL k Determine the calibration point T k and correction point T k+1 The quadratic correction value of any n-th trajectory point in the trajectory segment between

[0037] The initial printing trajectory that has been offset-corrected according to the correction amount of each trajectory point is offset-corrected again according to the secondary correction amount of each trajectory point to obtain a target printing trajectory.

[0038] A further technical solution is to perform mesh discretization processing on the printed curved surface in the three-dimensional digital model, including:

[0039] Select several split points at intervals on the outer edge curve of the printed surface;

[0040] Scaling the outer edge curves of the printed surface according to different scaling ratios to obtain a plurality of groups of first curves, wherein each segmentation point on the outer edge curve has a corresponding mapping point on each of the obtained first curves;

[0041] Connecting each segmentation point on the outer edge curve and its mapping point on each first curve in sequence to form a second curve;

[0042] A plurality of first curves and a plurality of second curves are used to perform grid discretization processing on the printed surface.

[0043] The beneficial technical effects of this application are:

[0044] The present application discloses a method for direct-writing printing of surface conformal sensors based on a five-axis motion platform. This method directly performs trajectory planning on a non-expanded printed surface based on a surface mesh discretization strategy, which simplifies the process of complex surface trajectory design and avoids the trajectory distortion caused by existing two-dimensional to three-dimensional projection methods. Then, a direct-writing printing system based on a five-axis motion platform is used to achieve direct manufacturing on three-dimensional structural parts through posture adjustment combined with position adjustment, thereby improving the production efficiency of surface conformal sensors, avoiding pattern distortion caused by transfer, and improving the accuracy and conformality of the produced surface conformal sensors. The direct-writing printing system based on a five-axis motion platform used in this method can be improved based on the existing three-axis direct-writing printing platform and is easy to build. This solution has the advantages of low cost, fast construction speed, and high printing accuracy, and is suitable for promotion and application in the preparation of curved electronics.

[0045] This method also incorporates a pre-printing and trajectory correction process for the designed initial print trajectory. Through offset correction, the target print trajectory can accurately fit the morphology of the printed curved surface, bridging the gap between the coordinates of the component surface contour and the imported virtual 3D digital model, further improving the accuracy and conformality of the resulting curved conformal sensor. For initial print trajectories with significant curvature variations, a secondary correction method is also introduced to further enhance the trajectory optimization effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a method flow chart of a curved surface conformal sensor direct writing printing method according to an embodiment of the present application.

[0047] Figure 2This is a structural diagram of a straight writing printing system based on a five-axis motion platform built in one embodiment of the present application.

[0048] Figure 3 yes Figure 2 Structural diagram of the two-axis rotation mechanism 2 in .

[0049] Figure 4 This is a schematic diagram of an example of performing mesh discretization processing on a printed curved surface in a three-dimensional digital model and designing a target printing trajectory of a sensor array using the discretized mesh as a reference.

[0050] Figure 5 yes Figure 2 Schematic diagram of the two-axis rotation mechanism driving the printed surface to rotate for posture adjustment.

[0051] Figure 6 This is a flow chart of a method for obtaining a target printing trajectory of a sensor array in another embodiment of the present application.

[0052] Figure 7 This is a schematic diagram of performing offset correction on the initial printing trajectory in one embodiment of the present application.

[0053] Figure 8 The figure is an example of a curved surface conformal sensor obtained by printing on three different curved surfaces of three-dimensional structural parts according to the curved surface conformal sensor direct writing printing method of the present application. DETAILED DESCRIPTION

[0054] The specific implementation of this application will be further described below with reference to the accompanying drawings.

[0055] This application discloses a surface conformal sensor direct writing printing method based on a five-axis motion platform, please refer to Figure 1 As shown in the flowchart, the surface conformal sensor direct writing printing method includes the following steps:

[0056] Step 1: Build a direct writing printing system based on a five-axis motion platform.

[0057] The surface conformal sensor direct writing printing method of this application cannot be directly printed using the existing three-axis direct writing printing platform, but requires the construction of a new direct writing printing system with five degrees of freedom. Figure 2 The structure of the straight-writing printing system shown in FIG. 1 includes a straight-writing printer 1 and a two-axis rotation mechanism 2 mounted on a three-axis motion mechanism, a printing platform 3 mounted on the two-axis rotation mechanism 2, and a printing nozzle 4 of the straight-writing printer 1 vertically downwardly located above the printing platform 3.

[0058] The three-axis motion mechanism includes a first horizontal motion mechanism 5, a longitudinal motion mechanism 6 and a second horizontal motion mechanism 7. A global coordinate system Oxyz is established based on the three-axis motion mechanism. The coordinate origin O of the global coordinate system can be customized. The first horizontal motion mechanism 5 provides translational freedom along the x direction of the global coordinate system, the second horizontal motion mechanism 7 provides translational freedom along the y direction of the global coordinate system, and the longitudinal motion mechanism 6 provides translational freedom along the z direction of the global coordinate system.

[0059] Please refer to Figure 3 The structure of the two-axis rotation mechanism 2 shown in the figure includes a first rotation base 8 and a second rotation base 9. The second rotation base 9 is fixed to the first rotation base 8 via a rotation shaft 10 of the first rotation mechanism, and the printing platform 3 is fixed to the second rotation base 9 via a rotation shaft 11 of the second rotation mechanism. The motor of the second rotation mechanism drives the printing platform 3 to rotate about the rotation shaft 11, thereby providing a rotational degree of freedom about the rotation axis U. The drive motor of the first rotation mechanism 10 drives the second rotation base 9 to rotate about the rotation shaft 10, thereby providing a rotational degree of freedom about the rotation axis V.

[0060] Combined with the three-axis motion mechanism and the two-axis rotation mechanism 2, the straight-writing printing system can provide three translational degrees of freedom and two rotational degrees of freedom. When actually building the straight-writing printing system, one approach is to fix the first rotating base 8 in the two-axis rotation mechanism 2 and mount the straight-writing printer 1 on the three-axis motion mechanism. However, in order to reduce the difficulty of building the straight-writing printing system of the present application, it is directly based on the existing three-axis straight-writing printing platform for transformation and upgrading, and the two-axis rotation mechanism 2 is combined with the base structure of the existing three-axis straight-writing printing platform. In the existing three-axis straight-writing printing platform, the base structure is often mounted on the second horizontal moving mechanism 7, so that the base structure can be translated along the y direction. Therefore, the base structure in the traditional three-axis straight-writing printing platform is directly replaced with the two-axis rotation mechanism 2, thereby directly upgrading to obtain the straight-writing printing system of the present application. Therefore, as shown in FIG. Figure 2 As shown, the first rotating base 8 of the two-axis rotating mechanism 2 is fixed to the second horizontal movable mechanism 7, the straight-writing printer 1 is fixed to the first horizontal movable mechanism 5, and the first horizontal movable mechanism 5 is fixed to the longitudinal movable mechanism 6. This enables the straight-writing printer 1 to have translational degrees of freedom along the x- and z-directions, and the two-axis rotating mechanism 2 to have translational degrees of freedom along the y-direction. However, those skilled in the art will appreciate that regardless of the specific mounting method, as long as it can ensure the five degrees of freedom required by this application, it will not affect the implementation of this application.

[0061] Establish the base coordinate system OUV of the two-axis rotation mechanism 2. To simplify the operation, the coordinate origin O of the base coordinate system OUV is taken to coincide with the coordinate origin O of the global coordinate system. In the initial state, the rotation axis U of the two-axis rotation mechanism 2 is parallel to the horizontal plane and parallel to the y-axis of the global coordinate system, and the rotation axis V of the two-axis rotation mechanism 2 is along the vertical direction and parallel to the z-axis of the global coordinate system, as shown in FIG. Figure 2 shown.

[0062] Step 2: Establish a 3D digital model of the 3D structural part, and discretize the printed surface in the 3D digital model. Use the discretized grid as a reference to design the target printing trajectory of the sensor array on the printed surface.

[0063] The present application's curved surface conformal sensor direct-write printing method is used to directly print the desired sensor array onto the curved printed surface of a three-dimensional structural component. Traditionally, the sensor array's trajectory is designed on a two-dimensional unfolded plane of the printed curved surface, and then the trajectory designed on the two-dimensional unfolded plane is projected onto the printed curved surface of the three-dimensional structural component. This indirect two-dimensional to three-dimensional projection strategy inevitably distorts the trajectory, thereby reducing the accuracy and conformality of the resulting sensor array. Therefore, the present application does not adopt this approach, but instead designs the target printing trajectory of the sensor array directly on the non-unfolded printed curved surface of the three-dimensional structural component.

[0064] In order to accurately design a conformal trajectory on a non-unfolded printed surface, the present application first performs a mesh discretization process on the printed surface. Since the printed surface is a curved surface structure and may not be regular in reality, the traditional specification discretization method cannot be used for mesh discretization. In one embodiment, the mesh discretization process on the printed surface includes the following steps, please combine Figure 4 Example graph:

[0065] (1) Select several segmentation points 13 along the circumferential interval on the outer edge curve of the printed curved surface 12, such as Figure 4 The selection density of the segmentation points 13 is determined according to the density of the grid discretization.

[0066] (2) The outer edge curves of the printed surface are scaled according to different scaling ratios to obtain a plurality of first curves 14, such as Figure 4 (b) in the figure uses scaling to obtain eight sets of first curves 14 as an example. Because scaling is performed directly, each segmentation point on the outer edge curve has a corresponding mapping point 15 on each of the obtained first curves. The resulting first curves 14 are related to the density of the grid discretization. The scaling ratio and number of obtained first curves are determined based on actual conditions.

[0067] (3) Each segmentation point on the outer edge curve and its mapping point on each first curve are sequentially connected to form a second curve 16, such as Figure 4 As shown in (c) in .

[0068] (4) The printed surface can be discretized using a plurality of first curves 15 and a plurality of second curves 16, such as Figure 4 As shown in (d) in .

[0069] Then, using the discrete grid as a reference, according to the location of the desired print sensor array, the corresponding grid points are selected and connected in sequence and then smoothed to obtain the target printing trajectory of the non-expanded printing surface, such as Figure 4 As shown in (e) in the figure, the accuracy of the designed target printing trajectory can be improved by making the mesh density as large as possible after discretization.

[0070] In practical applications, the above-mentioned grid discrete division process can be realized by numerical processing. After selecting r segmentation points 13 on the outer edge curve and determining the corresponding segmentation point coordinates, the set consisting of the mapping points on each first curve can be obtained based on the scaling relationship and expressed as follows: Among them, a rs It represents the mapping point of the rth segmentation point on the outer edge curve on the sth first curve obtained by scaling. The other parameters are the same. Then take the transpose of the set A second curve can be obtained by connecting the positions of the elements in the same column of the set in sequence.

[0071] It's important to note that the target print trajectory depends not only on the position of the sensor array on the printed surface but also on its structure. For example, a sensor array for direct-write printing employs a layered printing structure, consisting of two electrode layers, an isolation layer between them, and a sensor layer. Each layer must be printed individually using the appropriate materials, so a specific target print trajectory must be designed for each layer's structure. Step 2 and Step 1 are not necessarily ordered in the same order.

[0072] Step 3, based on the initial absolute coordinates of each trajectory point on the target printing trajectory of the printed surface in the global coordinate system in the initial state, with the goal of the print nozzle of the straight writing printer extruding ink vertically downward along the normal direction of the contact surface to achieve printing, determine the rotation control parameters and translation control parameters during the straight writing printing process along the target printing trajectory.

[0073] When the built straight writing printing system is in the default state, the three-dimensional structure is fixed on the printing platform with the printed curved surface facing upwards as the initial state. Since the size of the three-dimensional structure is known and the position of the target printing trajectory on the three-dimensional structure is known, the initial absolute coordinates of each trajectory point on the target printing trajectory in the global coordinate system in the initial state can be pre-calibrated.

[0074] When printing with a direct-writing printer, the printer's print nozzle 4 must be aligned with the normal direction of the contact surface and the direction of gravity. This minimizes ink accumulation and flow during extrusion. Based on this printing requirement, conventional 3D direct-writing printing platforms, when printing on a 2D surface, meet this requirement because the printer's print nozzle is always perpendicular to the 2D surface. Therefore, simply controlling the three-axis motion mechanism to move the printer's print nozzle to each point on the target print trajectory is sufficient.

[0075] However, in the printing scenario of the present application, due to the variable morphology of the printed curved surface of the three-dimensional structural parts, when the printing nozzle 4 is consistent with the direction of gravity, it cannot always be guaranteed to be along the normal direction of the contact surface. Therefore, it cannot be printed directly according to this two-dimensional printing method. This is also the reason why printing on the surface of three-dimensional structural parts is currently difficult, and it is also the reason why this application needs to build a straight writing printing system based on a five-axis motion platform to introduce two rotational degrees of freedom.

[0076] Based on the five degrees of freedom provided by the direct writing printing system, this application performs trajectory slicing with the goal of the direct writing printer's print nozzle extruding ink vertically downward along the normal direction of the contact surface to achieve printing, in order to obtain the rotational control parameters and translational control parameters that meet this printing goal. These parameters include:

[0077] 1. Based on the initial absolute coordinates of each track point on the target printing track, the rotation control parameters are obtained by adjusting the target so that the tangent plane of the printed surface at each track point is parallel to the horizontal plane. This includes:

[0078] (a) Determine the normal vector L = (i, j, k) at any point P on the target printing trajectory with the initial absolute coordinates (x, y, z) on the printed surface in the initial state. Please refer to Figure 5 Schematic diagram, taking the printed surface as a hemisphere as an example, it can be seen that in the initial state, the normal vector at the trajectory point P is not along the vertical direction, so it does not meet the printing target.

[0079] (b) The direction of the normal vector at the trajectory point P can be changed by rotating the printed surface around the rotation axis U and the rotation axis V through the two-axis rotating platform. Therefore, based on the attitude adjustment target that the tangent plane of the printed surface at each trajectory point is parallel to the horizontal plane, the normal vector of the printed surface at the trajectory point P after the attitude adjustment is completed is determined to be along the vertical direction. like Figure 5 As shown in the schematic diagram.

[0080] (c) Determine the rotation angle θ of the two-axis rotation mechanism around the rotation axis U relative to the initial state based on the normal vector of any track point P on the target printing track in the initial state and the normal vector after the posture adjustment is completed. U and the rotation angle θ around the rotation axis V relative to the initial state V .

[0081] By calibrating the base coordinate system and the global coordinate system, two rotation angles can be obtained through the rotation relationship. Figure 1 This coordinate system relationship can establish the following relationship:

[0082]

[0083] Among them, R(θ U ) is the transformation matrix of the two-axis rotating mechanism when it rotates around the rotation axis U, R(θ V ) is the transformation matrix of the two-axis rotating mechanism when it rotates around the rotation axis V. When the printed surface rotates around the rotation axis U, the base coordinate system will change, causing the rotation axis V to no longer be consistent with the z-axis. Therefore, after the two-axis rotating mechanism rotates around the rotation axis U, the transformation matrix around the rotation axis V becomes R′(θ V ). The above formula can be used to obtain the rotation angle θ corresponding to any track point P on the target printing track. U and the rotation angle θ V for:

[0084]

[0085] (d) The rotation control parameters obtained according to the above method include the rotation angle θ corresponding to each track point along the target printing track. U and the rotation angle θ V Then the rotation control parameters can be obtained so that the two-axis rotation mechanism can be controlled according to the rotation control parameters according to the required rotation angle θ at each trajectory point. U and the rotation angle θ V Those skilled in the art can obtain corresponding rotation control parameters according to the required rotation angle by combining the structure and control logic of the two-axis rotation mechanism. This is a conventional operation in the art and will not be described in detail in this embodiment.

[0086] 2. Based on the above analysis Figure 5 When the two-axis rotation mechanism drives the printing surface to adjust its posture, the position of the track point P on the target printing trajectory also changes accordingly. The absolute coordinates of any track point P on the target printing trajectory with the initial absolute coordinates (x, y, z) in the global coordinate system after the posture adjustment is completed are P′=R′(θ V )·R(θ U )·P, such as Figure 5 shown.

[0087] Based on this, the printing absolute coordinates corresponding to each track point along the target printing track can be obtained, and then the translation control parameters can be obtained, so that when the three-axis motion mechanism is controlled according to the translation control parameters, the straight writing printer and the two-axis rotation mechanism can be driven in turn to translate to the printing absolute coordinates of each track point for printing. Those skilled in the art can obtain the corresponding translation control parameters according to the required printing absolute coordinates based on the structure and control logic of the three-axis motion mechanism. This is the routine operation of the existing three-axis motion mechanism, and this embodiment will not be described in detail.

[0088] Step 4: Fix the three-dimensional structure on the printing platform with the printed surface facing upward in the initial state. According to the obtained rotation control parameters, control the two-axis rotation mechanism to drive the three-dimensional structure to rotate and adjust the posture, including controlling the two-axis rotation mechanism to rotate the three-dimensional structure according to the corresponding rotation angle θ of each trajectory point of the target printing trajectory. U and the rotation angle θ V Rotate relative to the initial state. And control the three-axis motion mechanism to drive the direct writing printer and the two-axis rotation mechanism to adjust the position and print according to the translation control parameters, including controlling the three-axis motion mechanism to move to the absolute printing coordinates of each track point of the target printing track in sequence for printing, so that the sensor array can be printed on the printed curved surface of the three-dimensional structure along the target printing track using the direct writing printing system.

[0089] Based on the above method, a surface conformal sensor can be made on the printed curved surface of a 3D structural part. However, considering the errors caused by the measurement method, the dimensional error between the 3D structural part and the 3D digital model is difficult to avoid, and the deviation of the coordinate origin positioning during the motion control process is also difficult to eliminate. These errors will lead to an unacceptable gap between the trajectory designed based on the 3D digital model and the surface contour, affecting the printing accuracy and conformality. Therefore, in another embodiment, the trajectory designed based on the discrete grid in the 3D digital model is not directly used as the target printing trajectory for actual printing. Instead, a correction algorithm is introduced to correct it before it is used as the target printing trajectory. Please refer to Figure 6 The flowchart shown includes the following steps:

[0090] 1. Using the discretized grid as a reference, the initial printing trajectory of the sensor array on the printed surface is designed.

[0091] 2. With the goal of achieving printing by having the print nozzle of the straight-writing printer extrude ink vertically downward along the normal direction of the contact surface, determine the pre-printing control parameters during the straight-writing printing process along the initial printing trajectory. The specific method is the same as step 3 above, and the pre-printing control parameters for rotation control and translation control are also obtained.

[0092] 3. During the pre-experiment of controlling the direct writing printing system according to the pre-printing control parameters, the vertical offset between several correction points of the initial printing trajectory and the printed curved surface of the three-dimensional structural part is determined.

[0093] If the error is not considered, the initial printing trajectory should be on the surface of the printing surface. During the pre-experiment of the direct writing printing system controlled by the pre-printing control parameters, the points on the initial printing trajectory should be on the surface of the printing surface. However, due to the existence of errors, the points on the initial printing trajectory may deviate from the surface of the printing surface, such as Figure 7 As shown, the initial printing tracks 200 on the local printed curved surface 100 of the three-dimensional structure do not overlap.

[0094] Several correction points are selected at intervals on the initial printing trajectory. The selection method of the correction points can be customized. In order to optimize the correction effect, the distance between the correction points cannot be too large. Then the offset at each correction point is determined: Since the printing mechanism of this application always keeps the printing nozzle perpendicular to the contact surface, at each correction point, the three-axis motion mechanism is controlled to drive the straight writing printer to move in the vertical direction until it contacts the printed curved surface of the three-dimensional structural part. The distance of the longitudinal movement is the offset between the initial printing trajectory at the correction point and the printed curved surface.

[0095] Any correction point T on the initial printing trajectory k The offset from the printed surface is recorded as L k ,like Figure 7 Schematic diagram showing four correction points on the initial printing trajectory and their respective offsets.

[0096] 4. According to any correction point T k The offset L from the printed surface k and the calibration point T k+1 The offset L from the printed surface k+1 , determine the initial printing trajectory at the correction point T k and correction point T k+1 Correction value of each track point in the track segment between.k+1 is the calibration point T k The next correction point along the initial printing trajectory, k is an integer parameter.

[0097] In one embodiment, the correction point T is determined k and correction point T k+1 The correction value of any nth trajectory point in the trajectory segment between Where n∈[0, N k ],N k is the calibration point T k and correction point T k+1 The total number of trajectory points in the trajectory segment between , and the trajectory point when n = 0 is the correction point T k 、n=N k The trajectory point at which the correction point is T k+1 .

[0098] 5. Correct the initial printing trajectory according to the offset of each trajectory point on the initial printing trajectory to obtain the target printing trajectory.

[0099] According to the above method, the correction amount of each track point in each track segment can be determined, thereby obtaining the correction amount of all track points on the initial printing track. Then, the offset correction is performed according to the correction amount of each track point. In one embodiment, after the initial printing track is offset corrected according to the correction amount of each track point, the target printing track is obtained.

[0100] However, in other embodiments, when the curvature of the initial printing trajectory changes significantly, the initial printing trajectory after the offset correction still cannot fit the printing curved surface well, especially the initial printing trajectory still cannot fit the printing curved surface well at the maximum point. Therefore, in another embodiment, after the initial printing trajectory is offset-corrected according to the correction amount of each trajectory point, a secondary correction is performed to obtain the target printing trajectory. The secondary correction method includes:

[0101] (1) Determine any correction point T k and its adjacent correction point T k+1 The midpoint of the trajectory segment between the two points is offset by the vertical direction ΔL from the printed surface of the three-dimensional structure after the offset correction. k , similar to the above method of determining the offset at the correction point.

[0102] (2) According to the secondary offset ΔL k Determine the calibration point T k and correction point T k+1 The quadratic correction value of any n-th trajectory point in the trajectory segment between

[0103] (3) The initial printing trajectory after the offset correction according to the correction amount of each trajectory point is further offset corrected according to the secondary correction amount of each trajectory point to obtain the target printing trajectory.

[0104] This method of the present application can effectively and flexibly print high-precision conformal sensor arrays on regular or irregular surfaces of three-dimensional structures of various shapes, such as Figure 8 Schematic diagram showing conformal sensor arrays printed on three different curved surfaces of three-dimensional structures. Figure 8 (a) is the reverse side of the vase shape, which contains a continuous transition from positive to negative curvature. Figure 8 (b) in the figure is a saddle-shaped surface with a hyperbolic paraboloid curvature. Figure 8 Figure (c) shows a heart model, representing any 3D surface in real-world engineering. Experiments have shown that this method achieves excellent printing results in all of the aforementioned printing scenarios. The printed samples are highly consistent with the designed 3D drawings, and the printed sensor arrays exhibit high accuracy and conformality.

[0105] The above description is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the scope of protection of the present application.

Claims

1. A surface conformal sensor direct writing printing method based on a five-axis motion platform, characterized in that: The curved surface conformal sensor direct writing printing method comprises: Build a straight-writing printing system based on a five-axis motion platform, the straight-writing printing system comprising a straight-writing printer mounted on a three-axis motion mechanism and a two-axis rotation mechanism, the printing platform being mounted on the two-axis rotation mechanism, and the print nozzle of the straight-writing printer being positioned vertically downward above the printing platform; Establishing a three-dimensional digital model of the three-dimensional structural part, and performing a mesh discretization process on the printed curved surface in the three-dimensional digital model, and designing a target printing trajectory of the sensor array on the printed curved surface using the discretized mesh as a reference; Determining, based on the initial absolute coordinates of each track point on the target printing track of the printing curved surface in the global coordinate system in the initial state, a rotation control parameter and a translation control parameter during straight writing printing along the target printing track with the goal of the print nozzle of the straight writing printer extruding ink vertically downward along the normal direction of the contact surface to achieve printing; The three-dimensional structure is fixed on the printing platform with the printing curved surface facing upward in an initial state, the two-axis rotation mechanism is controlled according to the rotation control parameters to drive the three-dimensional structure to rotate and adjust its posture, the three-axis motion mechanism is controlled according to the translation control parameters to drive the straight-writing printer and the two-axis rotation mechanism to adjust their positions and print, and the sensor array is printed on the printing curved surface of the three-dimensional structure along the target printing trajectory using the straight-writing printing system; Wherein, obtaining the target printing trajectory includes: designing an initial printing trajectory of the sensor array on the printing curved surface using the discretely obtained grid as a reference; determining pre-printing control parameters during the straight writing printing process along the initial printing trajectory with the goal of having the printing nozzle of the straight writing printer vertically downwardly extrude ink along the normal direction of the contact surface to achieve printing; determining the vertical offsets of a plurality of correction points of the initial printing trajectory from the printing curved surface of the three-dimensional structural component during a preliminary experiment controlling the straight writing printing system according to the pre-printing control parameters; and correcting the initial printing trajectory according to the offsets to obtain the target printing trajectory. Wherein, the target printing track is obtained by correcting the initial printing track according to the offset, which includes: Offset from the printed surface and calibration points Offset from the printed surface , determine that the initial printing trajectory is at the correction point and calibration points The correction amount of each track point in the track segment between Is the calibration point The next correction point along the initial printing trajectory; performing offset correction on the initial printing trajectory according to the correction amount of each trajectory point to obtain the target printing trajectory; Wherein, it is determined that the initial printing trajectory is at the correction point and calibration points The correction amount of each track point in the track segment between includes: determining the correction point and calibration points Any of the trajectory segments between Correction value of trajectory point ,in, , Is the calibration point and calibration points The total number of trajectory points in the trajectory segment between , and The trajectory point at which 、 The trajectory point at which ; Wherein, obtaining the target printing trajectory further includes: determining any correction point and its adjacent correction points The secondary offset of the midpoint of the trajectory segment between the two points and the printed curved surface of the three-dimensional structural part in the vertical direction after the offset correction is performed ; According to the secondary offset Determine the calibration point and calibration points Any of the trajectory segments between The secondary correction of the trajectory point The initial printing trajectory after the offset correction is performed according to the correction amount of each trajectory point is again offset corrected according to the secondary correction amount of each trajectory point to obtain the target printing trajectory.

2. The curved surface conformal sensor direct writing printing method according to claim 1, characterized in that: Determining the rotation control parameters and the translation control parameters during the straight writing printing process along the target printing trajectory includes: According to the initial absolute coordinates of each track point on the target printing track, a rotation control parameter is obtained by taking the tangent plane of the printed curved surface at each track point as a posture adjustment target to be parallel to the horizontal plane; The translation control parameters are obtained according to the printing absolute coordinates of each track point on the target printing track in the global coordinate system after the posture adjustment is completed.

3. The curved surface conformal sensor direct writing printing method according to claim 2, characterized in that: The rotation control parameters include: Determine any initial absolute coordinate of the printing surface on the target printing trajectory in the initial state as The trajectory point The normal vector at is ; Based on the tangent plane of the printed curved surface at each track point being parallel to the horizontal plane as the posture adjustment target, it is determined that the printed curved surface is parallel to the horizontal plane at each track point after the posture adjustment is completed. The normal vector at is along the vertical direction. ; Print any track point on the track according to the target The normal vector in the initial state and the normal vector after the posture adjustment are determined by the two-axis rotation mechanism around the rotation axis. Rotation angle relative to the initial state and around the axis of rotation Rotation angle relative to the initial state ; According to the rotation angle corresponding to each track point along the target printing track and rotation angle The rotation control parameter is obtained.

4. The curved surface conformal sensor direct writing printing method according to claim 3, characterized in that: In the initial state, the rotation axes of the two-axis rotation mechanism Parallel to the horizontal plane and parallel to the global coordinate system Axis, the rotation axis of the two-axis rotation mechanism Along the vertical direction and parallel to the global coordinate system Axis; determine any track point on the target printing track Corresponding rotation angle and rotation angle include: according to Sure ; in, The two-axis rotating mechanism rotates around the rotation axis The transformation matrix during rotation, The two-axis rotating mechanism rotates around the rotation axis The transformation matrix for rotation.

5. The curved surface conformal sensor direct writing printing method according to claim 4, characterized in that: The translation control parameters include: Determine any initial absolute coordinate on the target printing trajectory as The trajectory point Print absolute coordinates in the global coordinate system after completing the posture adjustment , and obtain translation control parameters according to the printing absolute coordinates corresponding to each track point along the target printing track.

6. The curved surface conformal sensor direct writing printing method according to claim 1, characterized in that: Performing mesh discretization processing on the printed curved surface in the three-dimensional digital model includes: Selecting a plurality of segmentation points at intervals on the outer edge curve of the printing surface; Scaling the outer edge curves of the printed curved surface according to different scaling ratios to obtain a plurality of groups of first curves, wherein each segmentation point on the outer edge curve has a corresponding mapping point on each of the obtained first curves; Connecting each segmentation point on the outer edge curve and its mapping point on each first curve in sequence to form a second curve; A plurality of first curves and a plurality of second curves are used to perform grid discretization processing on the printed surface.

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