Five-axis multi-nozzle direct writing printing system

Abstract

The invention discloses a five-axis multi-nozzle direct-writing printing system, and relates to the technical field of direct-writing printing, and the system comprises a five-axis motion platform which is used for bearing a printing substrate model and providing translation freedom degrees in the X-axis direction, the Y-axis direction and the Z-axis direction and rotation freedom degrees around the Y-axis direction and the Z-axis direction; the multi-nozzle module comprises at least two independent control nozzles which are used for storing different types of functional materials respectively; the control module is used for controlling Z-axis movement and X-axis synchronous displacement compensation of each spray head to realize multi-material collaborative curved surface printing; and the processor is also used for generating a pose correction parameter of the printing substrate model based on the theoretical coordinates and the actual coordinates of the at least two non-collinear feature points on the printing substrate model so as to readjust the printing path. According to the method, the coupling problem of nozzle interference and base model pose errors in five-axis multi-material printing is solved, and the forming precision and material compatibility of complex curved surface direct writing printing are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of direct writing printing technology, and in particular to a five-axis multi-nozzle direct writing printing system. Background Technology

[0002] In modern manufacturing technology, Direct Ink Writing (DIW) printing, as an additive manufacturing method, has attracted widespread attention due to its advantages in printing multi-material and complex structural parts. However, existing direct ink writing printing systems often face the following technical challenges during the printing process:

[0003] The Challenges of Simultaneous Multi-Material Printing: Mainstream single-nozzle or sequentially switching nozzle systems cannot achieve real-time, synchronous conformal deposition of multiple functional materials (such as conductive, mechanical, and biomaterials). Building multi-material devices requires frequent downtime for material switching, involving nozzle cleaning, barrel replacement, and critical nozzle repositioning and calibration. This discontinuous operation significantly reduces printing efficiency, and the minute precision offsets introduced by repositioning accumulate and amplify in subsequent printed layers, leading to interlayer misalignment, poor interface bonding, and overall structural geometric distortion. This severely damages the precision, integrity, and function of parts, representing a fundamental obstacle to manufacturing multi-material integrated devices.

[0004] Interference issues in multi-nozzle printing on curved surfaces: When introducing multiple nozzles onto non-planar or complex curved substrates, the risk of physical collisions and material interference between nozzles increases dramatically. The complex and variable geometry of curved surfaces requires multiple nozzles to move collaboratively within a confined dynamic space. Existing systems struggle to accurately predict and avoid collisions between nozzles, between the nozzle and the printing structure, and between the nozzle and the curved substrate in real time. Maintaining safe distances limits path optimization, while physical collisions can lead to nozzle damage and structural destruction, severely threatening the stability, reliability, and success rate of multi-nozzle printing (DIW) on curved surfaces.

[0005] Model pose error: The actual position and orientation of the physical model (substrate / preform) often deviate from the CAD theoretical model. This error stems from inaccurate placement of the substrate model, fixture problems, platform positioning errors, or unpredictable micro-deformations (thermal / stress) of the substrate during printing. This initial pose inaccuracy constitutes a systematic error source, causing the printing path generated based on the theoretical pose to act on the offset substrate model, resulting in a systematic positional deviation in material deposition. The consequences manifest as an overall offset, rotation, or distortion of the printed structure relative to the design model, severely impairing part dimensional and shape accuracy and assembly compatibility. It is a key factor in the failure of precision components, multi-layer structures, and multi-nozzle systems. Summary of the Invention

[0006] Addressing the three core problems in direct writing printing technology—lack of material synchronization, interference between multiple printheads on curved surfaces, and initial pose deviation—the inventors propose a five-axis multi-printhead direct writing printing system. This system avoids interference between printheads by controlling the vertical displacement of each printhead and combines a pose correction method based on feature point coordinate matching, significantly improving the printing accuracy and material compatibility of curved surfaces. The technical solution of this invention includes the following key points:

[0007] A five-axis multi-nozzle direct writing printing system includes:

[0008] Precision Motion Fundamentals: A five-degree-of-freedom (DOF) motion platform is constructed, comprising translational degrees of freedom along the X, Y, and Z axes, and rotational degrees of freedom around the Y and Z axes. The translational axes utilize high-precision KK linear modules (600mm stroke, repeatability ±0.01mm); the U / V rotary axes employ a harmonic reducer combined with a hollow rotary platform and stepper motor drive, achieving high-precision rotary positioning of ±0.005°. The platform is equipped with high-precision photoelectric limit switches to ensure repeatability and features automatic origin calibration to ensure motion reliability.

[0009] Multifunctional independent nozzle array: Integrates at least two (expandable) independently controllable nozzle modules. Each nozzle is adapted to extrude thermoplastic conductive / functional pastes (such as carbon paste, silver paste, copper paste), photosensitive resin pastes, and materials encapsulated in cryogenic substrates (such as metal wires, optical fibers). Each nozzle is equipped with an independent air pressure control unit to adjust the nozzle air pressure output to adapt to the rheological properties of different functional materials.

[0010] Dynamic cooperative obstacle avoidance mechanism:

[0011] Z-axis obstacle avoidance: Each printhead is equipped with an independent lifting actuator (such as a cylinder module, Z-axis stroke ±75mm). During printing, only the currently working printhead descends to the set curved surface printing height; all non-working printheads are simultaneously raised to a safe height and remain in place, achieving physical isolation of the printhead group through dynamic height difference to prevent collisions with the printed structure or substrate model.

[0012] X-axis synchronous displacement compensation: When switching printheads, the system first controls all printheads to move synchronously along the X-axis for position compensation, ensuring that the nozzle center of the next printhead is precisely aligned with the target printing position; after compensation is completed, the cylinder of that printhead is triggered to descend for printing. This coordinated action completely avoids multi-printhead interference.

[0013] Synchronous material delivery: The cylinder module and the printing bracket of metal wire / fiber move synchronously to ensure that flexible materials such as metal wire or fiber do not become entangled, stacked or broken during the nozzle lifting and platform movement.

[0014] Fast pose correction algorithm based on contact measurement:

[0015] Contact-based coordinate acquisition: Utilizing the high-precision machine tool coordinate system of the five-axis system, the printhead is temporarily used as a contact probe. The printhead is controlled to lightly touch a preset feature point on the printing substrate model (feature points can be selected from: optical markers, the geometric center of the model contour, preset calibration points of embedded sensors, etc.). The machine tool's high-resolution AOI camera captures and records the machine tool coordinates in real time at the moment the printhead tip touches the feature point, which is used as the actual coordinates (x, y) of that feature point. a ,y a ).

[0016] Initial pose parameter calculation: Select two non-collinear feature points on the printed base model, based on the theoretical coordinates (x, y) of each point. t ,y t ) and measured actual coordinates (x a ,y a Construct the theoretical and actual vectors of the feature points;

[0017] The initial rotation angle θ is obtained by performing dot product and cross product operations on the theoretical vector and the actual vector;

[0018] Using θ and the theoretical and actual coordinates of a set of non-collinear feature points, solve for the initial translation Δx and Δy, and take the average of Δx and Δy corresponding to the two points;

[0019] Collinearity detection and alarm: The system automatically determines whether two selected feature points are collinear. If the cross product of the theoretical vector and the actual vector is not zero, the two selected feature points are considered non-collinear. If they are collinear, the effective pose parameters cannot be calculated, and an alarm is triggered, prompting the selection of suitable feature points.

[0020] Multi-point optimization improves accuracy: To significantly reduce the impact of single-point measurement errors, two or more more feature points are introduced. An optimization objective function is constructed (minimizing the sum of squared distances between the theoretical coordinates of all feature points after transformation by R(θ) and their corresponding actual coordinates). The least squares optimization algorithm is used to iteratively solve for the optimal rotation angle θ and translation amounts Δx and Δy.

[0021] Real-time dynamic path correction: The optimized pose correction parameters (θ, Δx, Δy) are fed back to the motion controller of the five-axis motion platform in real time. Based on these parameters (which can be converted into a rotation matrix R and a translation vector T), the controller performs real-time rigid body transformations on the coordinates of all path points planned in the original G-code, thereby generating a corrected printing path that precisely matches the actual pose of the base model.

[0022] The control module enables integrated closed-loop control and process monitoring.

[0023] The Duet3 6HC control board is used as the core controller of the system to perform the following control functions in a distributed manner:

[0024] 1) The photoelectric limit switch is reset to zero;

[0025] 2) Cylinder solenoid valve control commands: The lifting and lowering actions of each nozzle cylinder are independently controlled by multiple solenoid valves.

[0026] 3) Dispensing controller control commands: By independently adjusting the air pressure output of each nozzle, the extrusion volume and start / stop of different slurries can be precisely controlled;

[0027] 4) Multi-nozzle switching collaborative control command and X-axis displacement compensation command: to realize accurate X-axis position compensation calculation during multi-nozzle switching and avoid multi-nozzle interference.

[0028] 5) Dynamic closed-loop compensation control: The system integrates a high-resolution AOI (Automatic Optical Inspection) vision inspection module, which can monitor the Z-axis height change of the substrate model surface in real time during the printing process. Combined with the platform's high-precision motion feedback (grating ruler / encoder) and automatic calibration function, dynamic closed-loop compensation control of the printing height is achieved to ensure continuous high precision in printing complex curved surfaces.

[0029] The beneficial technical effects of this invention are:

[0030] High-precision printing: By using a pose correction method based on multi-feature point matching and least squares optimization, the pose matching accuracy between the actual placement position and the theoretical position of the printing base model is corrected before printing, so that the printing positioning error is less than ±0.05mm, ensuring high-quality manufacturing of complex structural parts.

[0031] Multi-material compatibility: Supports collaborative printing of various pastes such as carbon paste, silver paste, and copper paste, as well as metal wire and fiber optic sensors, broadening the range of material selection and making it suitable for manufacturing functional and complex structural components, such as smart sensors, conductive structures, and optoelectronic devices.

[0032] Zero-interference dynamic obstacle avoidance: Utilizing a Z-axis lifting actuator (similar to a cylinder) combined with X-axis dynamic compensation, a safe isolation zone is created between the currently working printhead and non-working printheads, preventing interference between multiple printheads and reducing printhead switching time to within 0.5 seconds. The synchronously moving cylinder module and filament / fiber printing bracket design prevent tangling or stacking of filaments or fibers during printing, improving printing stability and success rate.

[0033] Wide applicability: This system can be applied to the manufacture of a variety of complex structural components, including electronic packaging, optical devices, sensors and functionally graded materials, and has broad application prospects.

[0034] Through the above technical effects, this invention not only significantly improves the performance and reliability of the five-axis multi-nozzle direct writing printing system, but also promotes the development of manufacturing technology for complex multi-material structural parts, providing efficient and precise new technology solutions for industrial applications. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall structure of the five-axis multi-nozzle direct writing printing system provided in this application;

[0036] Figure 2 This is a structural diagram of the UV two-axis rotation mechanism provided in this application;

[0037] Figure 3 This is a schematic diagram of the coordinated movement of the multi-nozzle module and the printing bracket provided in this application;

[0038] Figure 4 This is a schematic diagram of the tensioning structure provided in this application;

[0039] Figure 5 This is a flowchart of the method for correcting the pose error of the printed substrate model provided in this application;

[0040] Figure 6 This is a schematic diagram illustrating the calculation of non-collinear feature point calibration and pose correction parameters provided in this application;

[0041] Figure 7 These are comparison diagrams of the pose error correction effect provided in this application, where (a) shows the theoretical base model and its feature points, (b) shows the actual base model and its measurement points, (c) shows the offset direction from theoretical to actual model, and (d) shows the overlap of feature points after correction.

[0042] Figure 8 This is the anti-interference action timing diagram of the multi-nozzle cylinder provided in this application;

[0043] Figure 9 (1), (2), and (3) in this application are schematic diagrams of the surface printing of the conformal sensor provided in this application on the surfaces of three different curved structural parts after pose correction. Detailed Implementation

[0044] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0045] One embodiment of this application provides a five-axis multi-nozzle direct writing printing system, which is described in detail from the following aspects.

[0046] I. System Overall Architecture

[0047] Combination Figures 1-3As shown, the system mainly includes: a five-axis motion platform, a multi-nozzle module, and a control module. The composition and functions of each part are as follows:

[0048] The five-axis motion platform includes a Z-axis height locking mechanism 1c, translation mechanisms 1a and 1b along the X and Y axes, and a fixed rotation axis (U-axis) around the Y-axis and a fixed rotation axis (V-axis) around the Z-axis, used to support the printing base model and adjust the model's pose.

[0049] The multi-nozzle module 3 contains at least two independently controlled nozzles, each storing different types of functional materials. Through distributed signal control, it enables the extrusion and precise start-stop of different functional materials, solving the technical challenge of frequently switching materials when constructing multi-material devices. It supports direct writing printing of various thermoplastic pastes such as carbon paste, silver paste, and copper paste, photosensitive resin pastes, as well as materials such as metal wires and fiber optic sensors.

[0050] Control module 4 is used to control the Z-axis movement and X-axis synchronous displacement compensation of each nozzle during the printing process, realizing multi-material collaborative surface printing. In addition, control module 4 is also used to generate pose correction parameters for the printing substrate model before printing starts, based on the theoretical and actual coordinates of at least two non-collinear feature points on the printing substrate model, in order to readjust the printing path.

[0051] II. Detailed Hardware Design

[0052] 1. Five-axis motion platform

[0053] In this embodiment, the five-axis motion platform uses a high-precision KK linear module (X / Y / Z three-axis travel up to 600mm) paired with a Leadshine 57 stepper motor to ensure the translational accuracy of the platform in the X, Y, and Z axes. Figure 1 As shown. Additionally, each KK module is equipped with an Omron photoelectric limit switch for zeroing the origin.

[0054] The rotating platform cradle structure 2 is equipped with a U-axis and a V-axis, combined with Figure 2 As shown, the hollow rotary platform 21 is designed to be higher than the cradle arm 22, so that the size of the printed substrate model is no longer limited by the cradle arm 22, expanding the effective working space to a diameter of 400mm. In this embodiment, the V-axis uses a hollow rotary platform 21 (DTN130-18, reduction ratio 1:18) paired with a stepper motor, while the U-axis uses a harmonic reducer (CF17-50, reduction ratio 1:50) paired with a stepper motor, which greatly improves the accuracy of the rotary axes, ensures the stable rotation of the substrate model during printing, and adapts to the printing requirements of complex curved surfaces.

[0055] 2. Multi-nozzle module design

[0056] like Figure 3As shown, each printhead in the multi-head module 3 is equipped with an independent lifting actuator 31 and an independent air pressure control unit. The lifting actuator 31 is used to move the printhead up and down to avoid interference between the printheads. For printing different inks, the air pressure control unit selects its appropriate air pressure to drive the ink extrusion pressure. The specific design is as follows:

[0057] In this embodiment, the air pressure control unit and the lifting actuator 31 are implemented using a dedicated dispensing air pressure controller and a vertical motion cylinder, respectively. During the printing process, the control module controls the corresponding lifting actuator 31 through distributed signals, causing the current working printhead to descend to the curved surface printing height, while the remaining non-working printheads are simultaneously raised to a safe height and kept in place. This precise control of the printhead's lifting and lowering displacement via cylinders, along with the dynamic height difference, achieves physical isolation of the printhead group, effectively avoiding motion interference during multi-printhead collaborative operation. When switching working printheads, the control module controls the corresponding lifting actuator 31 and the X-axis translation mechanism 1a through distributed signals, causing all printheads to rise to a safe height and move synchronously along the X-axis a certain compensation distance, aligning the nozzle center of the next working printhead with the target printing position before executing the printing process again. Simultaneously, based on the rheological characteristics of different functional materials, the control module controls each air pressure control unit to independently adjust the nozzle air pressure output through distributed signals, ensuring optimal printing performance for various materials.

[0058] Optionally, the multi-head module of this embodiment includes three independently controllable printheads. Printhead A supports printing with thermoplastic pastes such as carbon paste, silver paste, and copper paste; printhead B supports printing with photosensitive resin paste; and printhead C supports printing with metal wires or optical fibers, meeting the manufacturing needs of complex functional structural parts. Printhead C is also equipped with a printing bracket 32 ​​and a tensioning structure 33. The printing bracket 32, tensioning structure 33, and printhead C are all sequentially installed from top to bottom along the Z-axis on the moving part 311 of the lifting actuator. One end of the metal wire or optical fiber is wound around the printing bracket 32, and the other end is fed into the printhead C through the tensioning structure 33. During printing, the control module drives the printhead C to move along the Z-axis by controlling the lifting actuator 31. At this time, the printing bracket 32 ​​moves synchronously with the moving part 311 of the lifting actuator to prevent the metal wire or optical fiber from tangling or stacking during printing. The tensioning structure 33 is used to adjust the tension of the metal wire or optical fiber during printing to prevent it from loosening or breaking.

[0059] like Figure 4As shown, the tensioning structure includes a housing 41, a screw 42, two opposing pressing portions 43a and 43b located inside the housing, an elastic portion 44, and at least two springs 45. The two springs 45 are symmetrically distributed between the two pressing portions 43a and 43b, with both ends of the springs 45 contacting the surfaces of different pressing portions. In this embodiment, the first pressing portion 43a is designed as a recessed structure, and the second pressing portion 43b is a protruding structure, with the uneven surfaces of the two structures facing each other. The elastic portion 44 is embedded in the working space formed between the pressing portions 43a and 43b, and the metal wire or optical fiber m is placed in the gap between the elastic portion 44 and the first pressing portion 43a. In this embodiment, the elastic portion 44 is made of TPU material. The top of the screw 42 passes through the pre-drilled hole in the housing 41 to reach the surface of the second pressing portion 43b, and the tension of the metal wire or optical fiber is controlled by adjusting the tightness of the screw 42.

[0060] 3. High-resolution AOI (Automated Optical Inspection) visual inspection module

[0061] This module serves two purposes: firstly, it captures and records the machine tool coordinates of feature points on the printing substrate model where the printhead tip lightly touches the surface, serving as the actual coordinates of these feature points; secondly, it monitors the Z-axis height change of the printing substrate model surface in real time during printing. Combined with the platform's high-precision motion feedback (grating ruler / encoder) and automatic calibration function, it achieves dynamic closed-loop compensation control of the printing height, ensuring consistently high precision in printing complex curved surfaces.

[0062] III. Design of Software and Model Pose Error Correction Methods

[0063] 1. Control Module

[0064] The control module in this embodiment is implemented using the Duet3 6HC control board, integrating a multi-nozzle switching program, a motor drive module, a solenoid valve control module, and a dispensing controller module to ensure coordinated operation of all components. The multi-nozzle switching program plans the switching sequence and actions of multiple nozzles through a preset program and uses animation simulation to visualize the nozzle trajectories in advance, ensuring no interference risk during multi-nozzle collaborative operation. The motor drive module integrated into the control board can precisely control the movement of the five-axis motor, including speed, direction, and torque adjustment, ensuring the stability and responsiveness of multi-axis collaborative operation. The solenoid valve control module integrated into the control board controls multiple solenoid valves, which individually control the actions of each nozzle cylinder, achieving nozzle vertical displacement and position locking. The dispensing controller module integrated into the control board outputs different dispensing controller signals to control the nozzle air pressure output, driving the printing of various pastes and ensuring the consistency and stability of material extrusion.

[0065] 2. Pose Error Correction Algorithm

[0066] Problem Description and Assumptions: Under ideal conditions, the system equipment has completed the zeroing operation, the platform is in a horizontal state (Z-axis height is constant), and the rotation angle around the Y-axis remains unchanged; therefore, the main sources of error include: 1) Model pose error: The actual position and orientation of the printed base model placed on the platform (both together constitute the pose) often deviate from the CAD theoretical model, that is, the rotation angle θ and translation amounts Δx and Δy have the following relationship:

[0067]

[0068] Where (x) t ,y t (x) is the theoretical coordinate, (x) a ,y a () are the actual coordinates.

[0069] 2) Observation error: Noise interference in feature point detection. To address the above problem, this embodiment provides a pose error correction algorithm. This method generates pose correction parameters for the printed base model based on the theoretical and actual coordinates of at least two non-collinear feature points on the printed base model, ensuring high-precision alignment between the printed base model and the theoretical model. For example... Figure 5 As shown, it specifically includes the following:

[0070] S1. Obtain the theoretical and actual coordinates of two non-collinear feature points on the printed base model, and construct the theoretical and actual vectors of the feature points.

[0071] Specifically, the theoretical base model is first calibrated in CAD, that is, the first feature point P1 and the second feature point P2 (such as the edges / hole edges of the model) are preset on the theoretical base model, and their theoretical coordinates P1(x) in the high-precision machine tool coordinate system of the five-axis system are recorded. t1 y t1 P2(x) t2 y t2 ),like Figure 6 and Figure 7 As shown in (a) above. Then, the nozzle is instructed to lightly touch the pre-set first feature point Q1 and second feature point Q2 on the surface of the printing substrate model in sequence. The actual coordinates Q1(x) of the feature points in the machine tool coordinate system are acquired in real time using an AOI camera or a contact probe located on the nozzle. a1 y a1 ), Q2(x a2 y a2 ),like Figure 6 and Figure 7 As shown in (b) of the diagram.

[0072] like Figure 6 As shown, the theoretical vector V is constructed based on P1P2. tConstruct the actual vector V based on Q1Q2 a :

[0073]

[0074] When two vectors have different or opposite directions, i.e., vector V t and V a If the cross product is not zero, the two selected feature points are considered non-collinear and subsequent steps can proceed; otherwise, non-collinear feature points that meet the conditions need to be selected again. In this embodiment, vector V is set. t and V a The rotation angle between them is θ, and the coordinates of the center position of the theoretical model are O. t (Also the zero point coordinates in the machine tool coordinate system) and the center position coordinates O of the actual model a (Due to inaccurate model placement and non-alignment with the machine tool's zero-point coordinates) the lateral and longitudinal deviations are Δx and Δy, respectively. Figure 6 and Figure 7 As shown in (c) in the figure.

[0075] S2. The initial rotation angle θ is obtained by performing the dot product and cross product operations on the theoretical and actual vectors, expressed as:

[0076]

[0077] S3. Import the initial rotation angle θ, the machine coordinates (actual coordinates) of a set of non-collinear feature points, and the CAD theoretical coordinates into the rigid body kinematics model (1), solve for the initial translation Δx and Δy, and take the average of Δx and Δy corresponding to the two points. Using the theoretical coordinates P1(x... t1 y t1 ) and actual coordinates Q1(x a1 y a1 For example, it can be represented as:

[0078]

[0079] Where R(θ) is the two-dimensional rigid body transformation matrix.

[0080] S4. Based on (θ,Δx,Δy), the pose of the theoretical model can be corrected to make the theoretical coordinates coincide with the actual coordinates. Figure 7 As shown in (d) in the figure.

[0081] In one possible implementation, to suppress the influence of feature point measurement noise, two or more feature points are introduced to construct an optimization objective function. The optimal rotation angle θ and translation amounts Δx and Δy are then obtained through iterative solving using the least squares method. Finally, the optimal (θ, Δx, Δy) is fed back to the motor drive module to generate correction commands for the five-axis motion platform. The optimization objective function aims to minimize the sum of squared distances between the theoretical and actual coordinates of all non-collinear feature points (i.e., minimize the sum of squared residuals of all feature points). Mathematically, this can be expressed as the following optimization problem:

[0082]

[0083] Among them, (x ai ,y ai (x) is the actual coordinate of the i-th feature point, (x) ti ,y ti ) is the theoretical coordinate of the i-th feature point, and N is the total number of feature points introduced.

[0084] In one possible implementation, in industrial vision environments where feature point detection is unstable, local noise exists, or partial occlusion occurs, to suppress the impact of abnormal feature points (such as noise points or mismatched points) on the optimization results, the weights of each set of feature points are adaptively adjusted in the optimization objective function based on the residual size. Specifically, for abnormal points with residuals greater than a set value, their weights are reduced to weaken their interference with the overall optimization results; for valid points with residuals no greater than the set value, their weights are increased. In this embodiment, an M-estimation method based on weighted robust estimation is introduced. This algorithm can automatically reduce the weights of abnormal points in the optimization, thereby making the pose estimation results more stable and reliable. For example, when the actual and theoretical residuals of a certain feature point are too large, M-estimation will significantly reduce its weight to prevent that point from "skewing" the overall fitting results, thus effectively suppressing abnormal observations. Table 1 shows the relevant parameters of three feature points:

[0085] Table 1. Relevant parameters of the three feature points

[0086] Feature point numbering Theoretical position Pi Actual location Qi Deviation (residual) 1 (10,5) (10.2,5.1) 0.22 2 (20,10) (23.5,12.7) 3.2 3 (30,15) (30.1,14.8) 0.36

[0087] Because the least squares method "considers" all points on an average basis, the second feature point with an error of 3.2 mm has a significant impact on the optimization result. However, M-estimation automatically reduces the weight of this point, thus preventing it from "slanting" the overall fitting result.

[0088] IV. System Collaboration Workflow

[0089] 1. Initialization Phase

[0090] System initialization includes defining the initial coordinate system, calibrating the multi-nozzle module, and configuring control module parameters. During calibration, the initial position and orientation of the printing substrate model are first defined, and then the initial position and range of motion of each nozzle are calibrated.

[0091] 2. Collect feature points

[0092] The actual coordinates of multiple feature points in the printed substrate model are acquired using an AOI camera or the device's built-in nozzle probe. The feature points are selected to ensure non-collinearity and thus the accuracy of the initial calculations.

[0093] 3. Calculation of pose correction parameters

[0094] First, the initial rotation angle θ and translation amounts Δx and Δy are calculated using two non-collinear feature points. Then, more feature points are introduced, and multi-point least squares optimization is used to obtain the optimal pose parameters.

[0095] 4. Real-time path compensation

[0096] Generate a compensation path on the Grasshopper platform: reshape the original theoretical path around the coordinate origin O. t Rotate by an angle θ and translate along the XY axes by Δx and Δy, then re-output the G code to the motion controller.

[0097] 5. Multi-material collaborative printing

[0098] like Figure 8 The diagram illustrates the coordinated movement of cylinder lifting and X-axis compensation during nozzle switching (time axis + displacement change). In multi-material 3D printing, the three printing nozzles are numbered A, B, and C, and precise coordination is achieved through a multi-nozzle switching program controlling the solenoid valves: when the current working nozzle is C, the X-axis displacement compensation is -80mm; when the current working nozzle is A, the compensation is 0mm; and when the current working nozzle is B, the compensation is +80mm. The compensation distance is determined based on the distance between the centers of two adjacent nozzles. Simultaneously, the G-code command "M42 P0 / P1 / P2 S1" precisely controls the lifting and lowering movements of each cylinder, ensuring no mechanical interference during multi-material printing. Special control is required for different printing materials. When printing slurry, the nozzle air pressure parameters need to be adjusted in real time to adapt to its rheological characteristics. When printing metal filaments, the synchronous movement of the printing support and cylinders must be maintained, along with a constant filament tension, to prevent problems such as tangling, loosening, or breakage.

[0099] V. Practical Application Cases

[0100] This invention has been widely used in the manufacturing of smart sensors, conductive structures, and aerospace skins. For example, in the manufacturing process of smart sensors, this system can accurately integrate and print various conductive paste sensors, such as... Figure 9As shown in (1), (2), and (3), schematic diagrams of surface conformal sensors printed on the surfaces of three different curved structural parts after pose correction are presented, confirming that the system can be applied to practical scenarios and significantly improves the performance and reliability of the sensor. In the manufacturing of complex curved functionally graded materials, the system achieves precise control of material composition and structure through dynamic correction and multi-material collaborative printing.

[0101] Through the above specific implementation methods, the present invention not only solves the problems of material limitations, multi-nozzle interference, and pose error in multi-material printing in the prior art, but also significantly improves the flexibility, reliability, and printing accuracy of the printing system, providing an efficient and reliable solution for the manufacturing of complex functional structural parts.

[0102] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A five-axis multi-nozzle direct writing printing system, characterized in that, include: The five-axis motion platform is used to support the printed base model and provides translational degrees of freedom in the X, Y, and Z axes, as well as rotational degrees of freedom around the Y and Z axes. A multi-nozzle module, comprising at least two independently controlled nozzles, each storing different types of functional materials; The control module is used to control the Z-axis movement and X-axis synchronous displacement compensation of each nozzle to achieve multi-material collaborative surface printing; It is also used to generate pose correction parameters for the printing base model based on the theoretical and actual coordinates of at least two non-collinear feature points on the printing base model, so as to readjust the printing path.

2. The five-axis multi-nozzle direct writing printing system according to claim 1, characterized in that, The generation of pose correction parameters for the printed base model based on the theoretical and actual coordinates of at least two non-collinear feature points on the printed base model includes: The theoretical coordinates and actual coordinates of two non-collinear feature points on the printed base model are obtained respectively, and the theoretical vector and actual vector of the feature points are constructed. If the cross product of the theoretical vector and the actual vector is not zero, the two selected feature points are considered to be the non-collinear feature points. The initial rotation angle θ is obtained by performing the dot product and cross product operations on the theoretical vector and the actual vector. Using the initial rotation angle and the theoretical and actual coordinates of a set of non-collinear feature points, the initial translation amounts Δx and Δy are calculated, and the average of Δx and Δy corresponding to the two points is taken, expressed as: Among them, (x a1 y a1 (x) is the actual coordinate of the first feature point. t1 y t1 ) are the theoretical coordinates of the first feature point, and R(θ) is the two-dimensional rigid body transformation matrix.

3. The five-axis multi-nozzle direct writing printing system according to claim 2, characterized in that, When the number of introduced feature points is greater than 2, an optimization objective function is constructed, and the optimal rotation angle θ and translation Δx and Δy are obtained by iterative solution using the least squares method. The optimization objective function aims to minimize the sum of squared distances between the theoretical and actual coordinates of all non-collinear feature points, and is expressed as: Among them, (x ai y ai (x) is the actual coordinate of the i-th feature point, (x) ti y ti ) is the theoretical coordinate of the i-th feature point, and N is the total number of feature points introduced.

4. The five-axis multi-nozzle direct writing printing system according to claim 3, characterized in that, In the optimization objective function, the weights are adaptively adjusted based on the residual magnitude of each set of feature points: For outliers with residuals greater than a set value, their weights are adjusted to be lower. For valid points whose residuals are no greater than the set value, their weights are adjusted to increase.

5. The five-axis multi-nozzle direct writing printing system according to claim 1, characterized in that, The control of the Z-axis movement and X-axis synchronous displacement compensation of each nozzle to achieve multi-material collaborative surface printing includes: Each nozzle is equipped with an independent lifting mechanism; During the printing process, the control module controls the corresponding lifting actuators through distributed signals, so that the current working printhead is lowered to the curved printing height, while the other non-working printheads are simultaneously raised to a safe height and kept in place. The physical isolation of the printhead group is achieved through dynamic height difference. When switching printheads, the control module controls the corresponding lifting actuator and X-axis translation mechanism through distributed signals, so that all printheads are raised to a safe height and move synchronously along the X-axis by a certain compensation distance, so that the nozzle center of the next printhead is aligned with the target printing position, and then the printing process is executed.

6. The five-axis multi-nozzle direct writing printing system according to claim 1, characterized in that, For a printhead whose functional material is metal wire or optical fiber, a lifting actuator, a printing bracket, and a tensioning structure are provided. The printing bracket, the tensioning structure, and the printhead are all mounted on the moving part of the lifting actuator. One end of the metal wire or optical fiber is wound around the printing bracket, and the other end is fed into the printhead through the tensioning structure. During the printing process, the control module drives the printhead to move along the Z-axis by controlling the lifting actuator. The printing bracket moves synchronously with the lifting actuator to prevent the metal wires or optical fibers from getting tangled or stacked during printing. The tensioning structure is used to adjust the tension of the metal wires or optical fibers during printing.

7. The five-axis multi-nozzle direct writing printing system according to claim 6, characterized in that, The tensioning structure includes a housing, a screw, two opposing pressing parts, an elastic part, and at least two springs located inside the housing. The two springs are symmetrically distributed between the two pressing parts, with both ends of the springs contacting the surfaces of different pressing parts. The elastic part is embedded in the working space formed between the pressing parts. The metal wire or optical fiber is placed in the gap between the elastic part and the first pressing part. The top of the screw passes through a pre-drilled hole in the housing to reach the surface of the second pressing part. The tension of the metal wire or optical fiber is controlled by adjusting the tightness of the screw.

8. The five-axis multi-nozzle direct writing printing system according to any one of claims 1-6, characterized in that, Each printhead is equipped with an independent air pressure control unit. Based on the rheological properties of different functional materials, the control module controls each air pressure control unit to independently adjust the nozzle air pressure output through distributed signals, ensuring that various materials are in the best printing performance.

9. The five-axis multi-head direct writing printing system according to any one of claims 1-3, characterized in that, The system also includes an AOI vision inspection module, which is used to capture and record the machine tool coordinates of feature points on the printing substrate model where the nozzle tip lightly touches the model in real time, as the actual coordinates of the feature points. It is also used to monitor the Z-axis height change of the printing substrate model surface in real time during the printing process, so as to realize dynamic closed-loop compensation control of the printing height.

10. The five-axis multi-nozzle direct writing printing system according to claim 8, characterized in that, Supported printing materials include: Thermoplastic slurries, photosensitive resin slurries; Optical fibers or metal wires encapsulated in a low-temperature substrate.

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