Laser powder bed sheet pattern distortion real-time correction system and method based on phase type light valve

Abstract

The invention discloses a laser powder bed sheet pattern distortion real-time correction system and method based on a phase type light valve, and relates to the technical field of metal additive manufacturing. The system comprises a polarization laser, a beam expanding and collimating unit, a reflecting mirror, a phase-type spatial light modulator, a reflecting mirror, a relay optical system, a galvanometer / field lens system, a movable spectroscope, a reference plane mirror and a forming cylinder. A double-loop correction system with a position sensitive detector as an absolute reference and a wavefront sensor as direct feedback is constructed, information of the position sensitive detector and the wavefront sensor is unified in a phase domain through a frequency domain fusion algorithm, and a comprehensive compensation phase diagram capable of completing pattern generation and distortion correction at the same time is generated. And loading to a phase type light valve to carry out high-power laser patterning modulation, and melting metal powder of a powder bed.

Description

Technical Field

[0001] This invention relates to the technical field of metal additive manufacturing, and more particularly to a real-time correction system and method for pattern distortion of laser powder sheet based on a phase-type optical valve. Background Technology

[0002] Laser bed fusion (LPBF) technology, as an important metal additive manufacturing technology, is evolving from traditional single-point scanning to efficient patterned projection printing. In traditional single-point scanning systems, parts are formed by controlling a focused laser point to scan and melt a predetermined trajectory on a powder bed line by line. However, this point-by-point scanning method is inefficient and cannot meet the needs of large-scale industrial applications.

[0003] In recent years, patterned projection printing technology has emerged. This technology uses spatial light modulators (such as DMD and LCoS) to modulate laser light into a two-dimensional surface pattern, which is then rapidly projected onto the surface to be processed by a galvanometer, melting the powder and significantly improving manufacturing efficiency. However, this technology still faces the problem of geometric distortion. Specific sources include: inherent optical distortions (such as pincushion distortion and field curvature) in the combination of the galvanometer scanning system and the F-Theta lens; thermal drift during long-term operation; and dynamic tracking errors in the galvanometer during high-speed scanning. These factors collectively lead to nonlinear geometric distortion in the projected pattern, severely affecting the dimensional accuracy and surface quality of the formed part.

[0004] Existing single-point scanning error correction methods are mainly based on static error mapping tables. These tables establish a position error lookup table through "dot calibration" and pre-compensate for galvanometer commands during scanning. However, this method cannot be directly applied to patterned printing scenarios because: patterned printing involves a massive number of pixels, and full-field point-by-point calibration would lead to an explosion in data volume, making it impractical in engineering; static error mapping tables cannot effectively compensate for time-varying errors (such as thermal drift) during the printing process; and single-point correction methods cannot handle continuous nonlinear geometric deformations across the entire projection field of view.

[0005] Phase-based spatial light modulators offer a novel solution for pattern distortion correction by directly modulating the laser wavefront phase. However, current phase modulation-based correction schemes rely on limited information sources: position sensor-based schemes can obtain high-precision macroscopic distortion information through geometric coordinate inversion, but are insensitive to high-frequency aberrations; wavefront sensor-based schemes can directly measure wavefront aberrations across the entire frequency band, but their absolute measurement reference is prone to drift, affecting long-term stability. Therefore, there is an urgent need in this field for a comprehensive solution that can synergistically utilize the advantages of multiple sensors to achieve full-frequency, high-reliability distortion correction. Summary of the Invention

[0006] The purpose of this invention is to overcome the limitations of existing single-sensor schemes and provide a laser powder bed pattern distortion correction system and method that can integrate absolute position reference and direct wavefront measurement to achieve synergistic compensation for aberrations at different spatial frequencies, thereby improving the comprehensiveness and robustness of the correction.

[0007] To achieve the above objectives, this invention constructs a dual-loop correction system using a position-sensitive detector as the absolute reference and a wavefront sensor as direct feedback. A frequency-domain fusion algorithm unifies the information from both into the phase domain, generating a comprehensive compensated phase map capable of simultaneously performing pattern generation and distortion correction. This map is then applied to a phase-type optical valve for high-power laser patterning modulation to melt the metal powder in the powder bed. The technical solution adopted by this invention is as follows: On one hand, a patterned laser powder bed distortion correction system based on a phase-type optical valve is provided, comprising: Polarized laser, beam expander and collimator unit, first mirror, phase-type spatial light modulator, second mirror, relay optical system, galvanometer-field mirror system, movable beam splitter, reference plane mirror and forming cylinder; The movable beam splitter is positioned after the galvanometer-field mirror system and before the powder bed. It is mounted on a precision linear guide or rotating arm and driven by a motor. The driving modes include a measurement mode and a printing mode. In the measurement mode, the beam splitter enters the main optical path, reflecting a portion of the laser light to the wavefront sensing unit. In the printing mode, the beam splitter completely moves out of the main optical path, ensuring unobstructed projection of the laser light onto the powder bed. The reference plane mirror is mounted on a three-dimensional displacement platform. The platform is used to control the movement of the reference plane mirror in the storage position and the measurement position, respectively, to move it out of the processing area to avoid interfering with printing and to move it precisely to the focal plane of the field lens. The system also includes a position reference sensing unit, a wavefront sensing unit, and a system controller.

[0008] Preferably, the position reference sensing unit is fixedly installed inside the processing chamber and is used to indirectly acquire aberration information through geometric coordinate measurement; the wavefront sensing unit is coupled to the main optical path between the galvanometer-field mirror system and the forming cylinder through a beam splitter and is used to directly measure the phase distribution of the laser wavefront in calibration mode; the system controller is signal-connected to the polarization laser, the phase-type spatial light modulator, the galvanometer-field mirror system, the position reference sensing unit, and the wavefront sensing unit; the system controller adopts a collaborative architecture of industrial computer and FPGA, wherein the FPGA is responsible for high-speed data acquisition and real-time logic control, and the industrial computer is responsible for complex model calculation and system management.

[0009] Preferably, the polarized laser is used to provide a high-power light source with horizontal or vertical polarization, and the degree of polarization is ≥99%; the beam expander and collimator is used to expand the laser beam and collimate it into parallel light; the phase-type spatial light modulator is used to load and fuse the phase map, and simultaneously realize pattern generation and wavefront correction; the relay optical system is used to optimize beam transmission and match the galvanometer incident aperture; the galvanometer-field mirror system is used to control the laser scanning direction, focus the laser, and locate the sub-field of view.

[0010] Preferably, the system controller periodically performs a self-calibration process, as follows: Periodically perform location benchmark calibration to obtain a new low-frequency compensated phase map. Compare the low-frequency compensated phase map with the low-frequency aberrations measured by the current wavefront sensor. If there is a systematic deviation, generate a calibration value to update the subsequent measurement values ​​of the wavefront sensor.

[0011] In another aspect of the present invention, a patterned laser powder bed distortion correction method based on a phase-type optical valve is also provided, comprising the following steps: Offline calibration measurement and database establishment include the calibration and measurement of the position reference path and the wavefront sensing path. The calibration and measurement steps of the position reference path include: controlling the phase-type spatial light modulator to project the feature point array to the position reference sensing unit in a time-division manner; for each feature point, recording its theoretical coordinates and the actual coordinates measured by PSD; fitting the coordinate data using the least squares method to obtain a geometric distortion model describing the distortion of the current sub-field of view; and calculating the corresponding low-frequency compensated phase map based on the angular spectrum diffraction theory and the physical optics inversion algorithm. Real-time pattern generation and correction: Based on the two-dimensional digital pattern to be printed, the pattern generation phase map is calculated by the holographic algorithm. According to the sub-field of view where the current printing target is located, the corresponding wavefront aberration and high-frequency aberration are called from the fusion correction database. Real-time digital superposition is performed in the FPGA to generate the final total driving phase map. The total driving phase map is loaded into the phase-type spatial light modulator to control the laser to emit light. After the modulated laser wavefront passes through the optical system, the target pattern is formed on the powder bed. Adaptive calibration involves periodically performing position reference path calibration to obtain a new low-frequency compensated phase map. This low-frequency compensated phase map is then compared with the low-frequency aberrations measured by the current wavefront sensor. If a systematic deviation exists, a calibration value is generated to update subsequent measurements of the wavefront sensor.

[0012] Preferably, the calibration and measurement steps of the wavefront sensing path include: moving a standard plane mirror to a position conjugate with the focal plane of the powder bed under the same sub-field of view, controlling the phase-type spatial light modulator to load a reference phase, and directly measuring the full-band wavefront aberration of the system through the wavefront sensing unit.

[0013] Preferably, the database establishment process includes: Path 1: Perform Zernike polynomial decomposition on the wavefront aberrations across the entire frequency band, separating them into low-frequency components of low-frequency aberrations and high-frequency components of high-frequency aberrations. Path 2: Achieve this through spatial frequency domain filtering: Perform a two-dimensional Fourier transform on the wavefront aberration to obtain its spatial spectrum; apply a low-pass filter to extract the low-frequency spectral components, and reconstruct the low-frequency aberrations through inverse Fourier transform; subtract the low-frequency aberrations from the original wavefront aberrations to obtain the high-frequency aberrations; Wavefront aberrations are associated with and stored with high-frequency aberrations to form a fusion correction database for that sub-field of view. All sub-fields of view are traversed to complete global calibration.

[0014] Preferably, the process for generating the total driving phase map Φ_total is as follows: ; in, Indicates the phase of pattern generation. Indicates wavefront aberration. This indicates high-frequency aberrations. This superposition operation is performed in the phase domain to ensure that the correction components work together.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. Full-band aberration suppression: By using a fusion strategy that prioritizes low frequencies with PSD and supplements high frequencies with wavefront sensors, collaborative compensation is achieved for low-frequency aberrations that affect macroscopic morphology and high-frequency aberrations that affect edge sharpness, resulting in a more comprehensive correction effect.

[0016] 2. Accuracy Self-Evolution and High Reliability: The wavefront sensor is periodically calibrated using the absolute reference of the PSD, forming a closed-loop self-calibration system that effectively suppresses sensor drift and ensures long-term accuracy stability. The dual sensors provide redundancy, enhancing system robustness.

[0017] 3. High efficiency of functional integration: Through phase superposition, pattern generation and static distortion correction are completed in one go, the control process is highly efficient, and the wavefront control capability of the phase-type spatial light modulator is fully utilized.

[0018] 4. High engineering practicality: By adopting a time-sharing measurement and lookup table mechanism, the engineering challenges of massive data calibration and real-time processing are solved while ensuring accuracy, and the solution is easy to implement. Attached Figure Description

[0019] Figure 1 This is a framework diagram of a patterned laser powder bed distortion correction system based on a phase-type optical valve in a specific embodiment of the present invention; Figure 2 This is a flowchart of a single sub-field-of-view phase difference test in a specific embodiment of the present invention.

[0020] Figure 3 This is a flowchart illustrating the construction of the integrated compensation phase under a single sub-view in a specific embodiment of the present invention.

[0021] Figure 4 This is a flowchart illustrating the pattern generation and correction process in a specific embodiment of the present invention.

[0022] Figure 5 This is a flowchart of the adaptive calibration process in a specific embodiment of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention aims to achieve high-precision correction of full-frequency geometric distortion of laser powder bed projection patterns by fusing absolute coordinate measurement of a position-sensitive detector (PSD) with direct wavefront measurement of a Shaker-Hartmann wavefront sensor.

[0025] Please refer to Figure 1 As shown, this application proposes a patterned laser powder bed distortion correction system based on a phase-type optical valve, comprising: 1. Polarization laser, 2. Beam expander and collimator, 3. First reflector, 4. Phase-type spatial light modulator, 5. Second reflector, 6. Relay optical system, 7. Galvanometer-field mirror system, 8. Movable beam splitter, 9. Reference plane mirror, and 10. Shaping cylinder; The movable beam splitter 8 is positioned after the galvanometer-field mirror system 7 and before the powder bed. It is mounted on a precision linear guide or rotating arm and driven by a motor. The driving modes include a measurement mode and a printing mode. In the measurement mode, the beam splitter enters the main optical path, reflecting a portion of the laser light to the wavefront sensing unit. In the printing mode, the beam splitter completely moves out of the main optical path, ensuring unobstructed projection of the laser light onto the powder bed. The reference plane mirror 9 is mounted on a three-dimensional displacement platform. The platform is used to control the movement of the reference plane mirror 9 in the storage position and the measurement position, respectively, to move it out of the processing area, avoid interfering with printing, and to move it precisely to the focal plane of the field lens. The system also includes a position reference sensing unit 11, a wavefront sensing unit 12, and a system controller 13.

[0026] Polarized laser 1: Used to provide a high-power laser source for processing, such as a fiber laser or semiconductor laser, requiring a polarization degree ≥99%.

[0027] Beam expanding and collimating unit 2: expands and collimates the Gaussian beam emitted from the laser to form a uniform collimated spot that meets the aperture requirements of the phase-type spatial light modulator.

[0028] Phase-type spatial light modulator 4 (SLM): A key component of this invention, preferably a pure phase modulator based on liquid crystal (LCoS), used to modulate the laser wavefront according to the driving signal. Its resolution is typically 1920×1080 pixels or higher, and the phase modulation range is not less than 2π.

[0029] Relay optical system 6: used to image the modulation surface of the SLM onto the entrance pupil of the galvanometer, while performing spatial filtering to eliminate unnecessary diffraction orders.

[0030] Galvanometer-Field Lens System 7: Composed of two high-speed galvanometer motors, this system deflects the laser beam to position the projected pattern on the powder bed. It ensures that the laser beam is focused on the same plane of the powder bed at different deflection angles, maintaining a linear scanning relationship.

[0031] A movable beam splitter 8 is located after the field lens and in front of the powder bed. This beam splitter is mounted on a precision linear guide or rotating arm and is driven by a motor, allowing switching between two modes: Measurement mode: The beam splitter enters the main optical path, reflecting a portion of the laser light to the wavefront sensing unit. Printing mode: The beam splitter is completely removed from the main optical path, ensuring unobstructed laser projection onto the powder bed. The reference plane mirror 9, an optical plane mirror with extremely high surface flatness (typically requiring λ / 10 or higher), is mounted on a high-precision three-dimensional displacement platform. This platform controls the movement of the reference plane mirror in two key positions: Storage position: moved out of the processing area to avoid interfering with printing; Measurement position: precisely moved to the focal plane of the field lens, i.e., the normal forming plane of the powder bed. Molding cylinder 10: Supports the metal powder substrate and the shaped parts.

[0032] Position reference sensing unit 11: preferably a position sensitive detector (PSD) with a resolution of not less than 1 micrometer and a response time of not more than 10 microseconds. It is securely mounted in the machining chamber at a precisely calibrated known global coordinate position.

[0033] Wavefront sensing unit 12: Preferably a Shaker-Hartmann wavefront sensor, coupled to the main optical path after the galvanometer and field lens via a beam splitter. The beam splitter enters the optical path in calibration mode and exits in printing mode.

[0034] Reference Plane Mirror 9: An optical plane mirror with extremely high surface flatness, typically requiring λ / 10 or higher, mounted on a high-precision three-dimensional displacement platform. This platform controls the movement of the reference plane mirror in three key positions: Storage position: moved out of the processing area to avoid interfering with printing. Measurement position: precisely moved to the focal plane of the field lens, i.e., the normal forming plane of the powder bed.

[0035] System Controller 13: Employs a collaborative architecture of an industrial computer and a Field Programmable Gate Array (FPGA). The industrial computer is responsible for upper-level logic, model calculation, and data management; the FPGA is responsible for high-speed data acquisition (PSD signals, encoder signals), real-time phase fusion, and SLM driving.

[0036] Please refer to Figure 2 As shown, in another aspect of the present invention, a patterned laser powder bed distortion correction method based on a phase-type optical valve is provided, comprising: Offline calibration measurement and database establishment include the calibration and measurement of the position reference path and the wavefront sensing path. The calibration and measurement steps of the position reference path include: controlling the phase-type spatial light modulator to project the feature point array to the position reference sensing unit in a time-division manner; for each feature point, recording its theoretical coordinates and the actual coordinates measured by PSD; fitting the coordinate data using the least squares method to obtain a geometric distortion model describing the distortion of the current sub-field of view; and calculating the corresponding low-frequency compensated phase map based on the angular spectrum diffraction theory and the physical optics inversion algorithm. Offline calibration and fusion database establishment: This stage is performed during equipment debugging or regular maintenance, and aims to establish a fusion database containing high-precision low-frequency and high-frequency compensation information for each sub-view.

[0037] a. PSD path calibration and low-frequency compensation phase Φ_PSD calculation: Please see Figure 2 and Figure 3 The flowcharts are for single sub-field-of-view phase difference testing and integrated compensation phase construction under a single sub-field-of-view, respectively. The goal of this step is to establish a mapping from ideal coordinates to actual coordinates and to inversely derive the compensation phase. The position reference sensing unit is a position sensitive detector (PSD), whose absolute coordinates of the center of its photosensitive surface in the global coordinate system of the processing chamber have been precisely calibrated and stored. During position calibration, the system controls the phase-type spatial light modulator to generate patterns containing only single feature points sequentially according to a preset time sequence; simultaneously, the system controls the galvanometer system to deflect the beam corresponding to each feature point to the photosensitive surface of the PSD; the PSD measures the energy center coordinates of each spot at high speed, and the system controller records its corresponding theoretical and actual coordinates for subsequent geometric distortion model fitting.

[0038] Feature point measurement: The system controller divides the machining plane of the forming cylinder into multiple sub-view areas.

[0039] For the i-th sub-field of view, control the galvanometer to deflect to its corresponding command angle.

[0040] A phase-controlled spatial light modulator projects an array of N feature points (e.g., a 10×10 grid, N=100) in a time-division manner. Only one point is projected at any given time to ensure that the PSD can accurately measure the location of its energy center.

[0041] For the i-th feature point, record its theoretical coordinates. and the actual coordinates measured by PSD .

[0042] Geometric distortion model fitting: A polynomial model is used to fit the geometric distortion of the system. This model describes the nonlinear transformation from theoretical coordinates to actual coordinates: ; Where P and Q are the orders of the polynomial (usually P=Q=3 or 4). and Let be the fitting coefficients to be determined. The sum of squared residuals at all feature points is minimized using the least squares method. To find the optimal set of coefficients This set of coefficients constitutes the geometric distortion model M_geo.

[0043] Phase inversion calculation: After obtaining the geometric distortion model M_geo, its compensated phase ΦPSD needs to be calculated. This invention uses an iterative algorithm based on angular spectrum diffraction theory for this calculation.

[0044] 1. Initialization: Assume the target light field is an ideal lattice at ideal coordinates. .

[0045] 2. Forward propagation: propagating the target light field Multiply by an initial guessed phase Φguess (e.g., all zero), and then propagate to the optical valve plane using the angular spectral diffraction formula. The angular spectral propagation formula is: ; Where F and F-1 represent the Fourier transform and inverse Fourier transform, respectively. It is the transfer function, k=2π / λ is the wave number, and z is the propagation distance.

[0046] 3. Apply constraints: Maintain the calculated light field on the light valve plane. phase The amplitude remains unchanged, but is replaced with a uniform amplitude A0 to form a new light field. .

[0047] 4. Backpropagation: Backpropagation back to the target plane: ; 5. Update the target: On the target plane, maintain The amplitude, but using the amplitude of the target light field | | Replace it while preserving its phase. This forms the input light field for the next iteration.

[0048] 6. Iteration: Repeat steps 2-5 until the convergence condition is met (e.g., the phase change is less than the threshold or the maximum number of iterations is reached). The phase ∠USLM obtained after final convergence is the desired low-frequency compensated phase diagram ΦPSD.

[0049] b. Wavefront sensing for path calibration and high-frequency component extraction The wavefront sensing unit is coupled to the optical path between the galvanometer system and the forming cylinder via a beam splitter that can cut into / out of the main optical path. During wavefront measurement, a beam splitter cuts into the optical path, while a high-precision reference plane mirror is driven by a displacement platform to move to a position conjugate to the focal plane of the powder bed, forming a wavefront measurement optical path. After being modulated by the phase-type spatial light modulator, the laser light passes through the scanning system, is reflected by the beam splitter to the reference plane mirror, and returns along the original path. Finally, a portion of the light is transmitted by the beam splitter to the wavefront sensing unit, thereby achieving direct measurement of the emitted wavefront.

[0050] Wavefront Measurement: Under the same sub-field of view, a standard plane mirror is moved to the focal plane of the powder bed. A reference phase is applied by a phase-type spatial light modulator, and the full-band wavefront aberration ΦWFS of the system is directly measured by a wavefront sensor. The wavefront slope measurement principle of the Shaker-Hartmann sensor is as follows: ; in, It is the wavefront slope of the (m,n)th sub-aperture. ΦWFS is the offset of the sub-aperture focal point relative to the reference position, where f is the focal length of the microlens. The wavefront phase ΦWFS can be reconstructed by integrating these slope data.

[0051] Aberration decomposition: Zernike polynomial decomposition is performed on ΦWFS to separate high- and low-frequency components. ; in, It is the k-th Zernike polynomial. These are the corresponding coefficients. The low-frequency aberration ΦWFS_low is reconstructed from the first L terms (e.g., the first 15 terms, corresponding to low-order aberrations such as astigmatism, coma, and spherical aberration): ; The high-frequency aberration ΦWFS_high is the residual part: ; c. Integrated database construction: The calculated (Φ_PSD_i, Φ_WFS_high_i) are stored as a set of data, associated with the region coordinates of the i-th sub-view. All sub-views are traversed to complete global calibration, forming a fusion correction database.

[0052] Real-time pattern generation and correction: Based on the two-dimensional digital pattern to be printed, the pattern generation phase map is calculated by the holographic algorithm. According to the sub-field of view where the current printing target is located, the corresponding wavefront aberration and high-frequency aberration are called from the fusion correction database. Real-time digital superposition is performed in the FPGA to generate the final total driving phase map. The total driving phase map is loaded into the phase-type spatial light modulator to control the laser to emit light. After the modulated laser wavefront passes through the optical system, the target pattern is formed on the powder bed. Please see Figure 4 The flowchart below illustrates the pattern generation and correction process of this invention. In this flowchart, pattern phase calculation involves the system controller's slicing module slicing the 3D CAD model into two-dimensional patterns corresponding to sub-viewpoints. Based on the two-dimensional digital pattern to be printed The Gerchberg-Saxton (GS) algorithm is used to calculate the pattern generation phase Φpattern. Its iterative process is similar to the phase inversion algorithm described above, the difference being that the constraint on the target plane is the light intensity distribution of the pattern. .

[0053] Phase correction call: Based on the sub-field of view m where the current printing target is located, call the corresponding Φ_PSD_m and Φ_WFS_high_m from the fusion correction database.

[0054] Phase fusion: In an FPGA, the total drive phase map Φtotal, which is ultimately loaded onto the phase-type spatial light modulator, is given by the following formula: ; The physical meaning of this formula is as follows: Φpattern is responsible for "generating the pattern", ΦPSD is responsible for "correcting macroscopic geometric distortions", and ΦWFS_high is responsible for "repairing microscopic wavefront defects". After linear superposition, the three components achieve all functions at once through a phase-type optical valve.

[0055] Wavefront Modulation and Projection: Φtotal is loaded onto a phase-type spatial light modulator. The laser beam is controlled, and the modulated laser wavefront passes through an optical system to form a target pattern on a powder bed that is both geometrically distortion-free and retains sharp details.

[0056] Adaptive calibration involves periodically performing position reference path calibration to obtain a new low-frequency compensated phase map. This low-frequency compensated phase map is then compared with the low-frequency aberrations measured by the current wavefront sensor. If a systematic deviation exists, a calibration value is generated to update subsequent measurements of the wavefront sensor.

[0057] To ensure long-term accuracy, the system periodically performs a self-calibration process, the flowchart of which is shown below. Figure 5 As shown.

[0058] Trigger: The system controller triggers adaptive calibration at a preset cycle (e.g., every 100 layers printed).

[0059] PSD recalibration: For the current working sub-view, re-perform PSD recalibration to obtain a new baseline Φ_PSD_new.

[0060] Deviation calculation: Read the low-frequency data Φ_WFS_low measured by the current wavefront sensor and calculate the systematic deviation △Φ=Ф_PSD_new-Ф_WFS_low.

[0061] Judgment and calibration: If △Φ is greater than the preset threshold (e.g.) If the calibration value is generated (or calculated proportionally), the calibration parameters for subsequent measurements of the wavefront sensor will be updated.

[0062] Completed: After calibration, the system continues printing normally. This process effectively suppresses wavefront sensor drift, forming a closed-loop accuracy maintenance system.

[0063] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A patterned laser powder bed distortion correction system based on a phase-type optical valve, characterized in that, Including those connected sequentially: Polarized laser (1), beam expander and collimator (2), first reflector (3), phase-type spatial light modulator (4), second reflector (5), relay optical system (6), galvanometer-field mirror system (7), movable beam splitter (8), reference plane mirror (9), and forming cylinder (10); The movable beam splitter (8) is positioned after the galvanometer-field mirror system (7) and before the powder bed. The movable beam splitter (8) is mounted on a precision linear guide or rotating arm and driven by a motor. The driving modes include measurement mode and printing mode. In measurement mode, the beam splitter enters the main optical path and reflects a portion of the laser to the wavefront sensing unit. In printing mode, the beam splitter is completely moved out of the main optical path to ensure that the laser is projected onto the powder bed without obstruction. The reference plane mirror (9) is mounted on a three-dimensional displacement platform. The platform is used to control the movement of the reference plane mirror (9) in the storage position and the measurement position, respectively, to move it out of the processing area, avoid interfering with printing, and accurately move it to the focal plane of the field lens. The system also includes a position reference sensing unit (11), a wavefront sensing unit (12), and a system controller (13).

2. The patterned laser powder bed distortion correction system based on a phase-type optical valve according to claim 1, characterized in that, The position reference sensing unit (11) is fixedly installed in the processing chamber and is used to indirectly obtain aberration information through geometric coordinate measurement; the wavefront sensing unit (12) is coupled to the main optical path between the galvanometer-field mirror system (7) and the forming cylinder (10) through a beam splitter and is used to directly measure the phase distribution of the laser wavefront in calibration mode; the system controller (13) is signal connected to the polarization laser (1), the phase-type spatial light modulator (4), the galvanometer-field mirror system (7), the position reference sensing unit (11) and the wavefront sensing unit (12); the system controller adopts a collaborative architecture of industrial computer and FPGA, in which the FPGA is responsible for high-speed data acquisition and real-time logic control, and the industrial computer is responsible for complex model calculation and system management.

3. The patterned laser powder bed distortion correction system based on a phase-type optical valve according to claim 1, characterized in that, The polarized laser (1) is used to provide a high-power light source with horizontal or vertical polarization, and the degree of polarization is ≥99%; the beam expanding and collimating unit (2) is used to expand the laser beam and collimate it into parallel light; the phase-type spatial light modulator (4) is used to load and fuse the phase map, and simultaneously realize pattern generation and wavefront correction; the relay optical system (6) is used to optimize beam transmission and match the galvanometer incident aperture; the galvanometer-field mirror system (7) is used to control the laser scanning direction, focus the laser and locate the sub-field of view.

4. The patterned laser powder bed distortion correction system based on a phase-type optical valve according to claim 1, characterized in that, The system controller (13) periodically performs a self-calibration process, as follows: Periodically perform location benchmark calibration to obtain a new low-frequency compensated phase map. Compare the low-frequency compensated phase map with the low-frequency aberrations measured by the current wavefront sensor. If there is a systematic deviation, generate a calibration value to update the subsequent measurement values ​​of the wavefront sensor.

5. A patterned laser powder bed distortion correction method based on a phase-type optical valve, characterized in that, Includes the following steps: Offline calibration measurement and database establishment include the calibration and measurement of the position reference path and the wavefront sensing path. The calibration and measurement steps of the position reference path include: controlling the phase-type spatial light modulator to project the feature point array to the position reference sensing unit in a time-division manner; for each feature point, recording its theoretical coordinates and the actual coordinates measured by PSD; fitting the coordinate data using the least squares method to obtain a geometric distortion model describing the distortion of the current sub-field of view; and calculating the corresponding low-frequency compensated phase map based on the angular spectrum diffraction theory and the physical optics inversion algorithm. Real-time pattern generation and correction: Based on the two-dimensional digital pattern to be printed, the pattern generation phase map is calculated by the holographic algorithm. According to the sub-field of view where the current printing target is located, the corresponding wavefront aberration and high-frequency aberration are called from the fusion correction database. Real-time digital superposition is performed in the FPGA to generate the final total driving phase map. The total driving phase map is loaded into the phase-type spatial light modulator to control the laser to emit light. After the modulated laser wavefront passes through the optical system, the target pattern is formed on the powder bed. Adaptive calibration involves periodically performing position reference path calibration to obtain a new low-frequency compensated phase map. This low-frequency compensated phase map is then compared with the low-frequency aberrations measured by the current wavefront sensor. If a systematic deviation exists, a calibration value is generated to update subsequent measurements of the wavefront sensor.

6. The patterned laser powder bed distortion correction method based on a phase-type optical valve according to claim 5, characterized in that, The calibration and measurement steps of the wavefront sensing path include: under the same sub-field of view, moving a standard plane mirror to a position conjugate with the focal plane of the powder bed, controlling the phase-type spatial light modulator to load a reference phase, and directly measuring the full-band wavefront aberration of the system through the wavefront sensing unit (12).

7. The patterned laser powder bed distortion correction method based on a phase-type optical valve according to claim 5, characterized in that, The database creation process includes: Path 1: Perform Zernike polynomial decomposition on the wavefront aberrations across the entire frequency band, separating them into low-frequency components of low-frequency aberrations and high-frequency components of high-frequency aberrations. Path 2: Achieve this through spatial frequency domain filtering: Perform a two-dimensional Fourier transform on the wavefront aberration to obtain its spatial spectrum; apply a low-pass filter to extract the low-frequency spectral components, and reconstruct the low-frequency aberrations through inverse Fourier transform; subtract the low-frequency aberrations from the original wavefront aberrations to obtain the high-frequency aberrations; Wavefront aberrations are associated with and stored with high-frequency aberrations to form a fusion correction database for that sub-field of view. All sub-fields of view are traversed to complete global calibration.

8. The patterned laser powder bed distortion correction method based on a phase-type optical valve according to claim 5, characterized in that, The process of generating the total driving phase map Φ_total is as follows: ； in, Indicates the phase of pattern generation. Indicates wavefront aberration. This indicates high-frequency aberrations. This superposition operation is performed in the phase domain to ensure that the correction components work together.

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