CN-121988758-A - Laser powder sheet pattern distortion real-time correction system and method based on amplitude type light valve

CN121988758ACN 121988758 ACN121988758 ACN 121988758ACN-121988758-A

Abstract

The invention belongs to the technical field of metal additive manufacturing, and particularly relates to a laser powder sheet pattern distortion real-time correction system and method based on an amplitude type light valve, wherein the distortion real-time correction is realized through three-level closed loop control; and finally, executing self-adaptive calibration logic to update the parameters of the lookup table on line based on visual feedback. And further, the integrated compensation of static distortion, dynamic error and system drift is realized, the problem of geometric distortion in patterned projection is effectively solved, and the forming precision and long-term stability of the laser powder bed are obviously improved.

Inventors

BIAN DONGLIANG
ZHOU XIN
YUAN LUHAO

Assignees

中国人民解放军空军工程大学

Dates

Publication Date: 20260508
Application Date: 20260226

Claims (10)

1. Laser powder sheet pattern distortion real-time correction system based on amplitude type light valve, which is characterized in that the system comprises: The optical path projection unit sequentially comprises a laser, an amplitude type light valve and a galvanometer system along a laser optical path and is used for projecting modulated pattern laser to a powder bed processing plane; the reference position sensing unit is used for acquiring an absolute position reference of the laser beam in real time; the error sensing unit is used for collecting deflection angle data of the vibrating mirror lens in real time; A vision sensing unit configured to acquire image data of a formed area on the powder bed; The system control unit is respectively in communication connection with the light path projection unit, the reference position sensing unit, the error sensing unit and the vision sensing unit, and is configured to: Performing off-line calibration logic, controlling the amplitude type light valve to project a characteristic point pattern in a time-sharing manner, and respectively establishing a static distortion inverse transformation lookup table for a plurality of sub-fields divided by a processing plane of a powder bed based on the absolute position reference data according to laser beams; Executing real-time error fusion logic, calculating a dynamic error vector according to the deflection angle data in the printing process, and carrying out vector superposition on the dynamic error and a static pre-compensation amount obtained by inquiring from a lookup table to generate a comprehensive pre-distortion instruction so as to drive the amplitude type light valve; performing adaptive calibration logic, analyzing geometric residual errors based on the image data, and performing parameter updates on the inverse static distortion look-up table.
2. The system for correcting the pattern distortion of the laser powder bed sheet based on the amplitude-type light valve in real time according to claim 1, wherein the reference position sensing unit is fixedly arranged at a known global coordinate position which is positioned outside the range of a processing plane of the powder bed in the processing cabin and is used for measuring the actual absolute coordinate of the laser beam in the global coordinate system; the error sensing unit is a photoelectric encoder integrated in the vibrating mirror motor; The visual sensing unit is an industrial camera coaxially integrated with the spectroscope and the laser main light path.
3. The system for correcting the pattern distortion of the laser powder bed sheet based on the amplitude-type light valve in real time according to claim 1, wherein the system control unit adopts a cooperative architecture of a field programmable gate array and an industrial computer; The field programmable gate array is responsible for realizing high-speed data acquisition of the error sensing unit, real-time calculation of the dynamic error vector and generation of the comprehensive predistortion instruction; The industrial computer is responsible for executing the calculation process of the off-line calibration logic, the construction and storage of the static distortion inverse transformation lookup table, and the image processing and parameter updating in the adaptive calibration logic.
4. The system for correcting pattern distortion of laser powder bed sheet based on amplitude type light valve as set forth in claim 1, wherein said reference position sensing unit is a position sensitive detector with resolution not less than 1 μm, and when the laser beam is irradiated onto the photosensitive surface of PSD, analog electric signals proportional to the position of the light spot are outputted, and converted into digital coordinates after being processed by a circuit, and the digital coordinates are transmitted to the system control unit.
5. The laser powder sheet pattern distortion real-time correction method based on the amplitude type light valve is applied to the laser powder sheet pattern distortion real-time correction system based on the amplitude type light valve as claimed in claims 1-4, and is characterized by comprising the following steps: S1, dividing a powder bed processing plane into a plurality of sub-fields, controlling an amplitude type light valve to project characteristic point patterns in a time-sharing manner, and establishing a static distortion inverse transformation lookup table for each sub-field based on absolute position data fed back by a fixed position reference sensing unit; S2, inquiring a corresponding static pre-compensation amount from the lookup table aiming at a sub-pattern to be printed currently in the printing process, calculating a dynamic error vector based on data acquired by a dynamic error sensing unit of a galvanometer system in real time, fusing the static pre-compensation amount with the dynamic error vector to generate a comprehensive pre-distortion instruction, and driving the amplitude type light valve to project a pre-distorted pattern; and S3, acquiring a formed pattern image on the powder bed through a visual sensing unit, analyzing geometric residual errors, and updating parameters of a static distortion inverse transformation lookup table based on an analysis result to compensate system drift.
6. The method for correcting the pattern distortion of the laser powder bed sheet based on the amplitude-type light valve in real time according to claim 1, wherein S1 comprises the following substeps: s11, taking a certain fixed angular point (such as the lower left corner) of a processing plane of a powder bed forming cylinder as an origin, establishing a global coordinate system, and dividing the processing plane into sub-view grids; S12, for each sub-view, uniformly constructing a measurement pattern comprising a grid characteristic point array, and controlling an amplitude type light valve to project single characteristic points to a processing plane according to a preset time sequence; S13, projecting the array points to the surface of the powder bed at one time, acquiring an actually formed distorted grid pattern, and identifying the actual coordinates of each characteristic point in the image according to the grid pattern; S14, forming a coordinate pair set by ideal coordinates and measured coordinates of all feature points, and performing polynomial fitting on the set by a least square method to establish a geometric transformation positive model from the ideal coordinates to the measured coordinates in the description sub-view; And S15, after the distortion model is obtained, solving an inverse transformation model of the distortion model, binding the inverse transformation model with a corresponding sub-view field, and constructing a static distortion inverse transformation lookup table.
7. The method for real-time correction of pattern distortions of a sheet of laser powder based on an amplitude-type light valve as set forth in claim 6, wherein in S11, said sub-field of view grids comprise a uniform grid and a non-uniform grid, and each sub-field of view corresponds to a unique galvanometer deflection command.
8. The method for real-time correction of laser powder sheet pattern distortion based on amplitude-type light valve as set forth in claim 6, wherein in S15, the method for searching the static distortion inverse transformation lookup table comprises: the first method is a mathematical inversion method, wherein, for the physical coordinates of a target, a source image coordinate is searched by a Newton iteration method, so that the physical coordinates of the target are as close to the source image coordinate as possible; And secondly, directly calculating an inverse mapping function provided by OpenCV, providing target physical coordinates and positive model parameters obtained through calibration to the inverse mapping function, and directly outputting corresponding source point coordinates according to input by the function.
9. The method for real-time correction of laser powder sheet pattern distortion based on amplitude-type light valve as set forth in claim 5, wherein in S2, the printing process comprises: And slicing the three-dimensional CAD model by using Magics software, wherein the thickness of the slice layer is set to be 50-100 mu m, and a two-dimensional section layer is obtained.
10. The method for real-time correction of pattern distortions of a laser powder sheet based on an amplitude-type light valve as set forth in claim 5, wherein in S2, a dynamic error vector is calculated based on data acquired in real time by a dynamic error sensing unit of a galvanometer system, comprising the sub-steps of: the system control unit reads detection data of the photoelectric encoder in real time, compares the lens angle fed back by the encoder with the instruction angle based on the kinematic model of the vibrating mirror, and calculates a dynamic error vector caused by dynamic tracking error and mechanical inertia of the vibrating mirror in real time.

Description

Laser powder sheet pattern distortion real-time correction system and method based on amplitude type light valve Technical Field The invention belongs to the technical field of metal additive manufacturing, and particularly relates to a laser powder sheet pattern distortion real-time correction system and method based on an amplitude type light valve. Background The Laser Powder Bed Fusion (LPBF) technique is one of the mainstream techniques for metal additive manufacturing, and the precision is of great importance. In the conventional single-point scanning LPBF system, laser focus position errors caused by field lens optical distortion, galvanometer nonlinearity, etc. can be effectively compensated by a pre-generated static error mapping lookup table. The method establishes an error model of the whole scanning field through dotting calibration, and pre-corrects the galvanometer instruction in the scanning process, thereby ensuring the precision of single-point scanning. However, as the demand for molding efficiency increases, patterned laser powder bed additive manufacturing techniques have emerged. The technology modulates laser into a two-dimensional surface pattern through an amplitude type light valve (such as a DMD (digital micromirror device) and a liquid crystal light valve), and projects the whole pattern to a powder bed for melting at one time by using a vibrating mirror, so that the crossing from point-by-point scanning to area array projection is realized, and the manufacturing efficiency is remarkably improved. However, the distortion form is changed from 'point position deviation' to 'geometric deformation of a plane', global and nonlinear distortion (such as pincushion distortion and barrel distortion) can occur in the whole projection pattern, the traditional single-point calibration method cannot be applied, because the whole pattern formed by millions of pixels is subjected to pixel-by-pixel measurement and compensation, the calibration time is extremely long, and the time-varying drift of the system caused by thermal effects and the like in the long-term processing process cannot be captured by a static lookup table, so that the consistency of part precision in mass production is difficult to guarantee. Based on this, a technical solution capable of efficiently and accurately solving the problems of global geometric distortion and systematic time-varying drift peculiar to the patterned projection is urgently needed. Currently, there is a lack of efficient, accurate real-time correction schemes for the unique problems described above faced by patterning laser powder beds. Has become a bottleneck restricting the technology to high-precision industrial application. Disclosure of Invention In order to solve the problems in the prior art, the invention provides a laser powder sheet pattern distortion real-time correction system and method based on an amplitude type light valve. The method solves the problem of how to realize the rapid on-line measurement and real-time compensation of the whole pattern form and carry out real-time correction. The invention aims at realizing the technical scheme that the laser powder sheet pattern distortion real-time correction system based on the amplitude type light valve comprises: The optical path projection unit sequentially comprises a laser, an amplitude type light valve and a galvanometer system along a laser optical path and is used for projecting modulated pattern laser to a powder bed processing plane; the reference position sensing unit is used for acquiring an absolute position reference of the laser beam in real time; the error sensing unit is used for collecting deflection angle data of the vibrating mirror lens in real time; A vision sensing unit configured to acquire image data of a formed area on the powder bed; The system control unit is respectively in communication connection with the light path projection unit, the reference position sensing unit, the error sensing unit and the vision sensing unit, and is configured to: Performing off-line calibration logic, controlling the amplitude type light valve to project a characteristic point pattern in a time-sharing manner, and respectively establishing a static distortion inverse transformation lookup table for a plurality of sub-fields divided by a processing plane of a powder bed based on the absolute position reference data according to laser beams; Executing real-time error fusion logic, calculating a dynamic error vector according to the deflection angle data in the printing process, and carrying out vector superposition on the dynamic error and a static pre-compensation amount obtained by inquiring from a lookup table to generate a comprehensive pre-distortion instruction so as to drive the amplitude type light valve; performing adaptive calibration logic, analyzing geometric residual errors based on the image data, and performing parameter updates on the inverse static distortion look-up