Real-time focusing compensation method and system for femtosecond laser curved surface machining

Abstract

The invention discloses a real-time focusing compensation method and system for femtosecond laser curved surface machining, and particularly relates to the technical field of light beam focusing control in femtosecond laser precision machining. The method is used for solving the technical problem of focus space-time deviation during high-speed curved surface machining caused by mismatching of dynamic response characteristics of an existing galvanometer and a dynamic focusing system. Pre-judging a response asynchronous risk by acquiring system response parameters and combining geometric and dynamic characteristics of a processing track, and identifying a dominant lag type; determining an error contribution distribution relation between the two systems according to the lag type; resolving to obtain a space trajectory error component which should be borne by the dynamic focusing system; and finally, controlling the laser to delay light emission according to the component until the dynamic focusing system is adjusted in place. Accurate diagnosis and quantitative compensation of a focus lag root are realized, and the focus position precision and the process reliability of femtosecond laser processing of a complex curved surface are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of beam focusing control technology in femtosecond laser precision machining, and more specifically, to a real-time focusing compensation method and system for femtosecond laser curved surface machining. Background Technology

[0002] Femtosecond laser processing technology, with its ultrashort pulses and extremely high peak power, exhibits unique advantages in fields such as curved surface micro / nano structure manufacturing and precision drilling, achieving high-precision processing with low thermal damage. To achieve efficient processing of complex three-dimensional curved surfaces, existing technologies generally employ a scheme where a galvanometer scanning system and a dynamic focusing system work together. The galvanometer system controls the laser beam to perform high-speed two-dimensional deflection scanning on the workpiece surface, while the dynamic focusing system, such as an adjustable focal field lens or an axially movable lens, adjusts the axial position of the focal point in real time according to the surface morphology to ensure the laser focus always falls on the surface to be processed. During this process, the CNC system generates deflection commands for the galvanometer and focusing commands for the dynamic focusing system based on a preset three-dimensional processing trajectory.

[0003] However, due to the inherent differences in mechanical inertia and response bandwidth between the rotational inertia of the galvanometer and the moving parts of the dynamic focusing system, it is difficult for the two systems to achieve a completely synchronized dynamic response when executing high-speed machining trajectories on complex curved surfaces, especially in regions where the curvature of the trajectory changes drastically. This asynchronous response leads to a spatiotemporal deviation between the instantaneous actual position of the laser focus in space and its theoretically designed trigger position on the machining trajectory. The rate of geometric change of the trajectory required for high-speed scanning cannot be matched with the limits of the physical response capability of the multi-axis system. This results in the laser possibly emitting light prematurely before the focus reaches the theoretical curved surface position, or emitting light delayedly after the focus has passed that position. In essence, this is a lag or advance of the focus relative to the theoretical machining point, ultimately causing the actual energy density at the machining point to deviate from the process window, resulting in unexpected over-machining, under-machining, or shape errors on the workpiece surface. This severely restricts the reliability of high-precision femtosecond laser machining of complex curved surfaces under high-efficiency requirements. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a real-time focusing compensation method and system for femtosecond laser surface processing to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A real-time focusing compensation method for femtosecond laser surface processing includes the following steps: S1. Obtain the response characteristic parameters of the galvanometer and dynamic focusing system; S2. Based on the spatial geometric features and dynamic motion features of the current processing trajectory segment to be executed, determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system; S3. When it is determined that there is a risk of asynchronous response, analyze the dynamic motion characteristics of the current processing trajectory segment to be executed, and identify the dominant lag type that causes asynchronous response by combining the response characteristic parameters of the galvanometer and the dynamic focusing system. S4. Based on the dominant hysteresis type, determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system to the three-dimensional spatial trajectory error; S5. Based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed, the spatial trajectory error components contributed by the dynamic focusing system are calculated. S6. Based on the spatial trajectory error component contributed by the dynamic focusing system, control the laser to delay emission after the preset trigger time of the galvanometer deflection command until the dynamic focusing system is adjusted to the correct position.

[0006] Furthermore, S1 includes: Test deflection commands containing different frequency components are applied to the galvanometer, and the actual deflection response data of the galvanometer is collected. Based on the comparison and analysis of the test deflection commands and the actual deflection response data, the response characteristic parameters related to the moment of inertia of the galvanometer are obtained. Test focusing commands containing different frequency components are applied to the dynamic focusing system, and the actual axial displacement response data of the dynamic focusing system is collected. Based on the comparison and analysis of the test focusing commands and the actual axial displacement response data, the response characteristic parameters related to the moving parts of the dynamic focusing system are obtained.

[0007] Furthermore, S2 includes: Extract curvature variation information from the spatial geometric features of the current processing trajectory segment to be executed; Extract motion acceleration information from the dynamic motion features of the current processing trajectory segment to be executed; By fusing curvature change information with motion acceleration information, a comprehensive index representing the dynamic complexity of the trajectory is generated; The comprehensive index of trajectory dynamic complexity is compared with the preset risk threshold, and the comparison results are used to determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system.

[0008] Furthermore, S3 includes: Spectral analysis is performed on the dynamic motion characteristics of the current processing trajectory segment to be executed to extract the dominant frequency of the trajectory motion; The dominant frequency of the trajectory motion is compared with the frequency response bandwidth in the response characteristic parameters related to the moment of inertia of the galvanometer to determine whether the dominant frequency exceeds the frequency response bandwidth of the galvanometer. The dominant frequency of the trajectory motion is compared with the frequency response bandwidth in the response characteristic parameters related to the moving parts of the dynamic focusing system to determine whether the dominant frequency exceeds the frequency response bandwidth of the dynamic focusing system. If the dominant frequency exceeds the frequency response bandwidth of the galvanometer only, the dominant hysteresis type is galvanometer dominant hysteresis; if the dominant frequency exceeds the frequency response bandwidth of the dynamic focusing system only, the dominant hysteresis type is dynamic focusing system dominant hysteresis; if the dominant frequency exceeds both the frequency response bandwidth of the galvanometer and the frequency response bandwidth of the dynamic focusing system, the dominant hysteresis type is coupled hysteresis.

[0009] Furthermore, a spectral analysis is performed on the dynamic motion characteristics of the current processing trajectory segment to be executed, and the dominant frequencies of the trajectory motion are extracted, including: Perform a Fourier transform on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed to obtain the motion acceleration spectrum; The frequency component with the largest amplitude is selected from the motion acceleration spectrum as the dominant frequency of the trajectory motion.

[0010] Furthermore, S4 includes: If the dominant hysteresis type is galvanometer-dominated hysteresis, then establish an error contribution allocation relationship with the response characteristic parameters related to the moment of inertia of the galvanometer as the main weighting factors. If the dominant lag type is dynamic focusing system dominant lag, then establish an error contribution allocation relationship with the response characteristic parameters related to the moving parts of the dynamic focusing system as the main weighting factors. If the dominant hysteresis type is coupled hysteresis, then the response characteristic parameters related to the rotational inertia of the galvanometer and the response characteristic parameters related to the moving parts of the dynamic focusing system are combined to establish a cooperative error contribution allocation relationship based on the ratio of the two parameters.

[0011] Furthermore, S5 includes: Based on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed, the theoretical trajectory error of the theoretical processing trajectory in three-dimensional space is calculated. Substitute the theoretical trajectory error into the error contribution allocation relationship; Based on the weights or proportions defined by the error contribution allocation relationship, the spatial trajectory error component corresponding to the responsibility part of the dynamic focusing system is separated from the theoretical trajectory error and used as the spatial trajectory error component contributed by the dynamic focusing system.

[0012] Furthermore, based on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed, the theoretical trajectory error of the theoretical processing trajectory in three-dimensional space is calculated, including: Based on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed, the positional deviation of the theoretical processing trajectory in three-dimensional space caused by the acceleration change is calculated through the kinematic model, which is used as the theoretical trajectory error.

[0013] Furthermore, S6 includes: The spatial trajectory error component contributed by the dynamic focusing system is taken as the axial displacement that the dynamic focusing system needs to compensate for. Based on the response characteristic parameters of the moving parts of the dynamic focusing system, the adjustment time required to complete the axial displacement is calculated. The adjustment time is used as the delay time for laser emission, controlling the laser to emit light after a preset trigger time following the execution of the galvanometer deflection command.

[0014] On the other hand, the present invention provides a real-time focusing compensation system for femtosecond laser surface processing, comprising the following modules: The parameter acquisition module is used to acquire the response characteristic parameters of the galvanometer and the dynamic focusing system; The risk assessment module is used to determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system based on the spatial geometric and dynamic motion characteristics of the current processing trajectory segment to be executed. The type identification module is used to analyze the dynamic motion characteristics of the current processing trajectory segment to be executed when it is determined that there is a risk of response asynchrony, and to identify the dominant lag type that causes response asynchrony by combining the response characteristic parameters of the galvanometer and the dynamic focusing system. The relationship determination module is used to determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system to the three-dimensional spatial trajectory error based on the dominant hysteresis type. The component calculation module is used to calculate the spatial trajectory error components contributed by the dynamic focusing system based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed. The light emission control module is used to control the laser to delay light emission after the preset trigger time of the galvanometer deflection command, based on the spatial trajectory error component contributed by the dynamic focusing system, until the dynamic focusing system is adjusted to the correct position.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. By introducing a predictive mechanism for the risk of asynchronous response between the galvanometer and the dynamic focusing system, and by accurately diagnosing the causes of dominant lag, a fundamental shift in compensation strategy from a one-size-fits-all approach to a targeted approach has been achieved. First, a risk assessment is conducted by comprehensively considering the geometric shape of the trajectory and the dynamic load. Complex calculations are only initiated in high-risk areas where compensation is truly necessary, significantly improving the overall computational efficiency of the system. It creatively decomposes and attributes the complex lag problem of multi-axis coordinated motion to specific types such as galvanometer dominance, focusing system dominance, or coupling of the two. Based on this, a differentiated quantitative error responsibility allocation model is established, transforming the fuzzy dynamic synchronization problem into a clear quantitative relationship based on the system's own response characteristics. This makes the assessment of focus lag no longer a simple geometric deduction, but a precise tracing based on the multi-axis dynamic coupling mechanism, laying a crucial theoretical and data foundation for implementing effective compensation.

[0016] 2. Based on the aforementioned precise error responsibility division, the spatial trajectory error component belonging specifically to the dynamic focusing system's responsibility can be calculated in real time, and a precise laser emission delay command can be generated accordingly. This ensures that the delay control quantity accurately corresponds to the focusing system's own response capability and current motion state, avoiding miscompensation of lag caused by galvanometers or other factors, or insufficient compensation for lag that should be borne by the focusing system. By intelligently synchronizing the laser emission time with the dynamic focusing system's adjustment time, the focus deviation problem caused by the system's response lag is eliminated at its root. Thus, under high-speed and complex curved surface processing conditions, the spatial position accuracy and energy deposition stability of the laser focus are reliably guaranteed, significantly improving the process consistency and finished product quality of femtosecond laser curved surface processing. Attached Figure Description

[0017] Figure 1 This is a flowchart of a real-time focusing compensation method for femtosecond laser surface processing according to the present invention; Figure 2 This is a schematic diagram of the structure of a real-time focusing compensation system for femtosecond laser surface processing according to the present invention. Detailed Implementation

[0018] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: Figure 1 This invention provides a real-time focusing compensation method for femtosecond laser surface processing, comprising the following steps: S1. Obtain the response characteristic parameters of the galvanometer and dynamic focusing system; S2. Based on the spatial geometric features and dynamic motion features of the current processing trajectory segment to be executed, determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system; S3. When it is determined that there is a risk of asynchronous response, analyze the dynamic motion characteristics of the current processing trajectory segment to be executed, and identify the dominant lag type that causes asynchronous response by combining the response characteristic parameters of the galvanometer and the dynamic focusing system. S4. Based on the dominant hysteresis type, determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system to the three-dimensional spatial trajectory error; S5. Based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed, the spatial trajectory error components contributed by the dynamic focusing system are calculated. S6. Based on the spatial trajectory error component contributed by the dynamic focusing system, control the laser to delay emission after the preset trigger time of the galvanometer deflection command until the dynamic focusing system is adjusted to the correct position.

[0020] S1. Obtain the response characteristic parameters of the galvanometer and the dynamic focusing system. The specific implementation is as follows: Test deflection commands containing different frequency components are applied to the galvanometer. These commands are generated by the motion controller in the CNC system, and their waveform is a swept-frequency sine wave covering the galvanometer's expected operating frequency band, for example, from 10 Hz to 2000 Hz. The motion controller sends the test deflection commands to the galvanometer's driver. During the execution of the test deflection commands, a high-precision angle encoder mounted on the galvanometer's shaft acquires the actual deflection response data. The angle encoder records the sequence of the actual angular position of the galvanometer's shaft changing over time at a fixed sampling frequency, for example, 100 kHz. The recorded data is the actual deflection response data.

[0021] Based on the comparative analysis of test deflection commands and actual deflection response data, the response characteristic parameters related to the rotational inertia of the galvanometer are obtained. The specific process of the comparative analysis is as follows: First, the time-series data of the test deflection commands and the time-series data of the actual deflection response are time-aligned. Then, the frequency response function of the galvanometer is calculated using the aligned data. When calculating the frequency response function, Fourier transforms are performed on the test deflection command data and the actual deflection response data respectively to obtain their respective spectra. Then, the ratio of the actual deflection response spectrum to the test deflection command spectrum is calculated to obtain the gain and phase of the system at different frequencies, i.e., the frequency response function. By analyzing the frequency response function, the frequency response bandwidth of the galvanometer can be extracted. This bandwidth refers to the frequency value corresponding to the gain dropping to -3 dB of zero frequency gain. At the same time, the response curve of the galvanometer to the step command needs to be analyzed from the actual deflection response data. By fitting a first-order or second-order system model to the step response curve, the step response time and equivalent rotational inertia parameters of the galvanometer can be obtained. Ultimately, the response characteristic parameters related to the rotational inertia of the galvanometer include frequency response bandwidth, step response time, and damping coefficient.

[0022] Test focusing commands containing different frequency components are applied to the dynamic focusing system. These test focusing commands are generated by the motion controller, and their waveform is also a swept-frequency sine wave. The frequency range is set according to the type of dynamic focusing system; for example, for a focusing lens driven by a voice coil motor, the frequency range can be set from 5 Hz to 500 Hz. The motion controller sends the test focusing commands to the driver of the dynamic focusing system, instructing the focusing lens to move back and forth along the optical axis.

[0023] During the execution of test focusing commands by the dynamic focusing system, it is necessary to collect its actual axial displacement response data. This data acquisition is achieved through a linear displacement sensor mounted on the moving parts of the dynamic focusing system, such as a laser displacement sensor or a grating ruler. The linear displacement sensor records the sequence of changes in the actual axial position of the focusing lens over time at a fixed sampling frequency, for example, 50 kHz. The recorded data is the actual axial displacement response data.

[0024] Based on the comparative analysis of test focusing commands and actual axial displacement response data, the response characteristic parameters related to the moving parts of the dynamic focusing system are obtained. The specific process of the comparative analysis is as follows: First, the timing of the test focusing commands and actual axial displacement response data is aligned. Then, the frequency response function of the dynamic focusing system is calculated using the aligned data. During the calculation, Fourier transforms are performed on both sets of data to obtain the spectra. The ratio of the actual axial displacement response spectrum to the test focusing command spectrum is then calculated to obtain the system's gain and phase at different frequencies, i.e., the frequency response function. By analyzing this function, the frequency response bandwidth of the dynamic focusing system can be extracted. This bandwidth refers to the frequency value corresponding to the gain dropping to -3 dB of zero frequency gain. Furthermore, the response curve of the dynamic focusing system to a step focusing command needs to be analyzed to obtain parameters such as rise time, settling time, and overshoot. For a voice coil motor driven system, the equivalent mass, damping, and stiffness coefficient of the moving parts can be obtained through model fitting. Finally, the response characteristic parameters related to the moving parts of the dynamic focusing system include frequency response bandwidth, step response time, equivalent mass, damping coefficient, and stiffness coefficient.

[0025] Through the above testing and data analysis process, the response characteristic parameters related to the rotational inertia of the galvanometer and the response characteristic parameters related to the moving parts of the dynamic focusing system can be obtained. The galvanometer parameters include at least the frequency response bandwidth and step response time, and the dynamic focusing system parameters include at least the frequency response bandwidth and step response time. These parameters are stored in the CNC system as data files, and the entire testing process is performed during equipment initialization or periodic calibration.

[0026] S2. Based on the spatial geometric and dynamic motion characteristics of the current processing trajectory segment to be executed, determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system. The specific implementation is as follows: First, the curvature variation information is extracted from the spatial geometric features of the machining trajectory segment to be executed. The current machining trajectory segment is provided by the trajectory planning module in the CNC system and consists of a series of discrete three-dimensional coordinate points. The spatial geometric features are calculated from this sequence of three-dimensional coordinate points. The curvature variation information describes the rate of change of the trajectory's curvature. Its calculation method is as follows: first, curve fitting is performed on the three-dimensional coordinate point sequence to obtain a parameterized trajectory curve equation; then, the second derivative of the trajectory curve equation is obtained to get the trajectory curvature; finally, the difference in curvature between adjacent sampling points is calculated along the trajectory curve parameter direction, and the absolute value of this difference is defined as the curvature variation. The maximum value of the curvature variation among all sampling points within the current machining trajectory segment to be executed is taken as the final curvature variation information, with dimensions of curvature variation per millimeter, and a numerical range, for example, between 0 and 2 per millimeter.

[0027] Next, the motion acceleration information is extracted from the dynamic motion features of the current machining trajectory segment to be executed. The dynamic motion features are obtained from the trajectory interpolation and look-ahead control module of the CNC system. The motion acceleration information describes the magnitude of the acceleration as the laser focus moves along the trajectory. Based on the trajectory curve equation and the set machining feed rate, the trajectory interpolation module generates displacement, velocity, and acceleration commands that vary with time. The motion acceleration information is the maximum absolute value of the acceleration commands across all interpolation cycles within the current machining trajectory segment to be executed, measured in meters per second squared (m / s²), with values ​​potentially reaching 100 m / s².

[0028] Then, the curvature change information and motion acceleration information are fused to generate a comprehensive index characterizing the dynamic complexity of the trajectory. The fusion is performed using a weighted summation method, assigning a weight coefficient A to the curvature change information and a weight coefficient B to the motion acceleration information. The weight coefficients A and B are set based on the response characteristic parameters related to the galvanometer's moment of inertia and the response characteristic parameters related to the moving parts of the dynamic focusing system. By analyzing these response characteristic parameters, the weight of the high-frequency motion component's influence on the galvanometer's following error and the weight of the large acceleration command's influence on the dynamic focusing system's tracking lag can be determined. For example, if tests show that the dynamic focusing system is more sensitive to changes in acceleration commands, a higher weight coefficient B (e.g., 0.6) is assigned to the motion acceleration information, and a lower weight coefficient A (e.g., 0.4) is assigned to the curvature change information, with the sum of weight coefficients A and B being 1. Before performing the fusion calculation, the curvature change information and motion acceleration information need to be normalized using a predetermined reference maximum value. The reference maximum value for curvature change information is derived from the statistical value of the maximum curvature change of a typical machined workpiece surface, and can be set to, for example, 5 per millimeter. The reference maximum value for motion acceleration information is set based on the maximum acceleration capability of the machine tool's motion axes, and can be set to, for example, 200 meters per second squared. The normalized curvature change information equals the original curvature change information divided by the reference maximum value for curvature change information, and the normalized motion acceleration information equals the original motion acceleration information divided by the reference maximum value for motion acceleration information. The formula for calculating the trajectory dynamic complexity comprehensive index is: Trajectory Dynamic Complexity Comprehensive Index = Weighting Coefficient A × Normalized Curvature Change Information + Weighting Coefficient B × Normalized Motion Acceleration Information. The generated trajectory dynamic complexity comprehensive index is a dimensionless value, ranging from 0 to 1.

[0029] Finally, the comprehensive dynamic complexity index of the trajectory is compared with the preset risk threshold. Based on the comparison results, it is determined whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system. The preset risk threshold is a constant between 0 and 1, obtained based on historical processing data and system performance calibration. The calibration method is as follows: processing experiments are conducted on test trajectories with various known complexity levels, and the actual response errors of the galvanometer and the dynamic focusing system are recorded. When the response error exceeds the allowable tolerance of processing accuracy, the value of the comprehensive dynamic complexity index of the trajectory corresponding to that test trajectory is recorded. The comprehensive dynamic complexity index values ​​of multiple trajectories that cause deviations are collected, and the minimum value among these values ​​is taken as the initial risk threshold. Then, the initial risk threshold is multiplied by a safety factor, such as 0.8, to obtain the preset risk threshold. For example, if the initial risk threshold obtained through calibration experiments is 0.7, multiplying it by the safety factor 0.8, the preset risk threshold is set to 0.56. During real-time judgment, the comprehensive dynamic complexity index of the current processing trajectory segment to be executed is calculated and compared with the preset risk threshold. If the comprehensive index of trajectory dynamic complexity is greater than or equal to the preset risk threshold, it is determined that there is a risk of asynchronous response between the galvanometer and the dynamic focusing system; if it is less than the preset risk threshold, it is determined that there is no risk of asynchronous response. The judgment result is output in the form of a logic signal.

[0030] S3. When a risk of response asynchrony is determined, analyze the dynamic motion characteristics of the current processing trajectory segment to be executed, and in conjunction with the response characteristic parameters of the galvanometer and dynamic focusing system, identify the dominant hysteresis type causing the response asynchrony. Specifically, the implementation is as follows: First, a spectral analysis is performed on the dynamic motion characteristics of the current machining trajectory segment to be executed to extract the dominant frequencies of the trajectory motion. The motion acceleration information from the dynamic motion characteristics is used as input data for the spectral analysis. This motion acceleration information is a discrete sequence that varies over time and is output by the trajectory interpolation module of the CNC system at fixed periods, with each period corresponding to an acceleration command value. During the spectral analysis, the time series of motion acceleration information is preprocessed, including detrending to eliminate any linear trend components that may exist in the data. After detrending, a window function, such as a Hanning window, is applied to the motion acceleration information time series to reduce spectral leakage. The length of the window function is equal to the length of the motion acceleration information time series. Then, a Fourier transform is performed on the windowed motion acceleration information time series to convert the time-domain motion acceleration information to the frequency domain, obtaining the motion acceleration spectrum. This spectrum is a complex sequence containing amplitude and phase information, and its amplitude spectrum, i.e., the absolute value of the amplitude of each frequency component, needs to be extracted.

[0031] The frequency component with the largest amplitude in the motion acceleration spectrum is selected as the dominant frequency of the trajectory motion. Specifically, the amplitude spectrum of the motion acceleration spectrum is traversed to find the point with the largest amplitude value; the frequency corresponding to this point is the dominant frequency of the trajectory motion. For example, if the amplitude spectrum has a maximum value at 150 Hz, then the dominant frequency of the trajectory motion is 150 Hz. If multiple maximum values ​​with equal amplitude exist, the lowest of these frequencies is taken as the dominant frequency. The frequency resolution and spectral range are determined by the parameters of the Fourier transform. The sampling frequency is equal to the reciprocal of the period of the motion acceleration information output by the trajectory interpolation module; for example, if the interpolation period is 0.1 milliseconds, the sampling frequency is 10 kHz. The number of points in the Fourier transform can be equal to the length of the motion acceleration information time series, or it can be increased to a power of 2 (e.g., 1024 points) by padding with zeros to improve computational efficiency. The frequency range of the calculated motion acceleration spectrum is from 0 Hz to the Nyquist frequency, which is equal to half the sampling frequency.

[0032] Next, the dominant frequency of the trajectory motion is compared with the frequency response bandwidth in the response characteristic parameters related to the moment of inertia of the galvanometer to determine whether the dominant frequency exceeds the frequency response bandwidth of the galvanometer. The frequency response bandwidth of the galvanometer has been obtained through testing in previous steps and stored in numerical form as a scalar value in Hertz, for example, 500 Hertz. The comparison operation is a numerical comparison, and the judgment logic is: if the dominant frequency of the trajectory motion is greater than the frequency response bandwidth of the galvanometer, it is determined that it exceeds the frequency response bandwidth of the galvanometer; if it is less than or equal to it, it is determined that it does not exceed the frequency response bandwidth.

[0033] Simultaneously, the dominant frequency of the trajectory motion is compared with the frequency response bandwidth in the response characteristic parameters related to the moving parts of the dynamic focusing system to determine whether the dominant frequency exceeds the frequency response bandwidth of the dynamic focusing system. The frequency response bandwidth of the dynamic focusing system, also obtained and stored in the previous steps, is a scalar value in Hertz, for example, 200 Hertz. The comparison logic is the same as above: if the dominant frequency is greater than the frequency response bandwidth of the dynamic focusing system, it is determined to exceed the bandwidth; if it is less than or equal to the bandwidth, it is determined not to exceed the bandwidth.

[0034] Based on the above comparison results, identify the dominant lag type: If the dominant frequency only exceeds the frequency response bandwidth of the galvanometer, the dominant hysteresis type is galvanometer dominant hysteresis. This condition assumes that the judgment result for the dominant frequency exceeding the galvanometer's frequency response bandwidth is true, and the judgment result for exceeding the dynamic focusing system's frequency response bandwidth is false. This indicates that the required motion frequency for the trajectory exceeds the galvanometer's tracking capability while the dynamic focusing system's tracking capability meets the requirements; therefore, the galvanometer is identified as the primary responsible party for the asynchronous response.

[0035] If the dominant frequency only exceeds the frequency response bandwidth of the dynamic focusing system, then the dominant hysteresis type is dynamic focusing system dominant hysteresis. This condition assumes that the judgment result for the dominant frequency exceeding the galvanometer's frequency response bandwidth is false, and the judgment result for exceeding the dynamic focusing system's frequency response bandwidth is true. This indicates that the required motion frequency for the trajectory exceeds the tracking capability of the dynamic focusing system, while the galvanometer's tracking capability meets the requirements. Therefore, the primary responsibility for the asynchronous response lies with the dynamic focusing system.

[0036] If the dominant frequency exceeds both the frequency response bandwidth of the galvanometer and the frequency response bandwidth of the dynamic focusing system, the dominant hysteresis type is coupled hysteresis. This condition assumes that both exceedances are true. This indicates that the motion frequency required for the trajectory simultaneously exceeds the tracking capabilities of both the galvanometer and the dynamic focusing system, causing their response hysteresis to couple with each other; therefore, the dominant hysteresis type is identified as coupled hysteresis.

[0037] S4. Based on the dominant hysteresis type, determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system to the three-dimensional spatial trajectory error. The specific implementation is as follows: If the dominant hysteresis type is galvanometer-dominant hysteresis, an error contribution allocation relationship is established with the response characteristic parameters related to the galvanometer's moment of inertia as the main weighting factors. Galvanometer-dominant hysteresis indicates that the dominant frequency of the trajectory motion only exceeds the frequency response bandwidth of the galvanometer. The error contribution allocation relationship is constructed as a linear weighted relationship, distributing the total theoretical trajectory error to the galvanometer and the dynamic focusing system. The main weighting factors are set according to the response characteristic parameters related to the galvanometer's moment of inertia and are proportional to the galvanometer's step response time; that is, the longer the step response time, the larger the value of the main weighting factor. A calibration experiment is used to establish the mapping relationship between the galvanometer's step response time and the main weighting factors: multiple processing tests are conducted under the galvanometer-dominant hysteresis condition, recording the step response time values ​​of different galvanometers and the corresponding optimal error allocation weights. This optimal weight is derived by minimizing the processing error through an optimization algorithm. Then, a linear function of the galvanometer's step response time and the main weighting factors is fitted based on the experimental data. A reference step response time, for example, 1 millisecond, is set. When the step response time of the galvanometer equals this reference value, the primary weighting factor of the galvanometer is set to 0.7, and the secondary weighting factor of the dynamic focusing system is set to 0.3. If the step response time of the galvanometer is greater than the reference value, the primary weighting factor is increased proportionally, with the proportionality coefficient determined by the slope of the linear function from the calibration experiment. Simultaneously, the secondary weighting factor is decreased by an equal amount, keeping the sum of the two at 1. The established error contribution allocation relationship is expressed as follows: the error responsibility component of the galvanometer equals the primary weighting factor multiplied by the theoretical trajectory error, and the error responsibility component of the dynamic focusing system equals the secondary weighting factor multiplied by the theoretical trajectory error.

[0038] If the dominant hysteresis type is dynamic focusing system dominant hysteresis, then an error contribution allocation relationship is established with the response characteristic parameters related to the moving parts of the dynamic focusing system as the main weighting factors. A dominant hysteresis type indicates that the dominant frequency of the trajectory motion only exceeds the frequency response bandwidth of the dynamic focusing system. The error contribution allocation relationship is also constructed as a linear weighted relationship. The main weighting factor is set according to the response characteristic parameters related to the moving parts of the dynamic focusing system and is proportional to the step response time of the dynamic focusing system. A calibration experiment is conducted to establish the mapping relationship between the step response time of the dynamic focusing system and the main weighting factor, under the condition of dynamic focusing system dominant hysteresis. A reference step response time, for example, 2 milliseconds, is set, and when the step response time of the dynamic focusing system equals this reference value, the main weighting factor of the dynamic focusing system is set to 0.8, and the secondary weighting factor of the galvanometer is set to 0.2. If the step response time of the dynamic focusing system is greater than the reference value, the main weighting factor is increased proportionally, while the secondary weighting factor is decreased by an equal amount, keeping the sum of the two at 1. The established error contribution allocation relationship is expressed as follows: the error responsibility component of the dynamic focusing system is equal to the primary weighting factor multiplied by the theoretical trajectory error, and the error responsibility component of the galvanometer is equal to the secondary weighting factor multiplied by the theoretical trajectory error.

[0039] If the dominant hysteresis type is coupled hysteresis, a cooperative error contribution allocation relationship based on the ratio of the parameters of the rotating inertia of the galvanometer and the moving parts of the dynamic focusing system is established. Coupled hysteresis indicates that the dominant frequency of the trajectory motion exceeds the frequency response bandwidth of both the galvanometer and the dynamic focusing system. The cooperative error contribution allocation relationship is established based on the ratio of the frequency response bandwidth of the galvanometer to that of the dynamic focusing system. This ratio is calculated by dividing the frequency response bandwidth of the galvanometer by the frequency response bandwidth of the dynamic focusing system. In the cooperative error contribution allocation relationship, the subsystem with the lower response bandwidth bears a larger share of the error responsibility, and the cooperative weighting factor of the dynamic focusing system is inversely proportional to the ratio. The cooperative weighting factor of the dynamic focusing system is set to be equal to a reference constant divided by the ratio. The reference constant is usually set to 1. Therefore, the cooperative weighting factor of the dynamic focusing system is equal to 1 divided by the ratio, and the cooperative weighting factor of the galvanometer is equal to 1 minus the cooperative weighting factor of the dynamic focusing system. For example, if the frequency response bandwidth of the galvanometer is 500 Hz and the frequency response bandwidth of the dynamic focusing system is 200 Hz, then the ratio is 2.5. The cooperative weighting factor of the dynamic focusing system is 0.4, and the cooperative weighting factor of the galvanometer is 0.6. The established cooperative error contribution allocation relationship is expressed as follows: the error responsibility component of the dynamic focusing system equals its cooperative weighting factor multiplied by the theoretical trajectory error, and the error responsibility component of the galvanometer equals its cooperative weighting factor multiplied by the theoretical trajectory error. The weighting factors of this cooperative error contribution allocation relationship are calculated and updated in real time based on each identified coupling hysteresis. Through the above three rules, the system establishes an error contribution allocation relationship that matches the dominant hysteresis type.

[0040] S5. Based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed, the spatial trajectory error components contributed by the dynamic focusing system are calculated. The specific implementation is as follows: First, based on the motion acceleration information in the dynamic motion characteristics of the current machining trajectory segment to be executed, the theoretical trajectory error in three-dimensional space is calculated. Motion acceleration information is a physical quantity describing the change in acceleration of the laser focus as it moves along the theoretical machining trajectory, and is acquired in real-time from the trajectory interpolation and look-ahead control module of the CNC system in the form of a time series. The theoretical trajectory error characterizes the spatial deviation between the instantaneous position of the focus and the theoretical trajectory point, which is inevitably caused by trajectory kinematic constraints under ideal control conditions. During calculation, the current machining trajectory segment to be executed is discretized into several small interpolation time intervals. For each interpolation time interval, the motion acceleration information within that interval is extracted. This information is a three-dimensional vector, whose components represent the acceleration values ​​along the trajectory tangent direction, normal direction, and binormal direction, respectively. Numerical integration is used to estimate the positional offset caused by acceleration changes. Here, the Euler integral method is employed: For each interpolation time interval, the velocity change caused by acceleration within that interval is calculated, which is equal to the motion acceleration information multiplied by the interpolation time interval. The calculated velocity change for the current interval is added to the cumulative velocity of the previous interval to obtain the cumulative velocity for the current interval. The positional deviation caused by motion within the current interval is equal to the cumulative velocity of the current interval multiplied by the interpolation time interval. Since the theoretical trajectory is curved and the direction of velocity is constantly changing, the scalar value of the positional deviation needs to be multiplied by the unit vector of the motion direction of the current trajectory point to convert it into a three-dimensional vector. This unit vector of motion direction is calculated from the trajectory curve equation. Recursive calculation begins from the start of the trajectory segment, assuming the velocity is zero at the start. The three-dimensional positional deviation vectors calculated for each interpolation time interval are accumulated, ultimately yielding the total theoretical trajectory error vector for the entire currently executed processing trajectory segment. This vector is a three-dimensional spatial vector, with units in meters. For example, for a trajectory segment with a duration of 10 milliseconds, the calculated theoretical trajectory error may reach several micrometers.

[0041] Then, the theoretical trajectory error is substituted into the error contribution allocation relationship. The substitution process involves inputting the calculated numerical value of the theoretical trajectory error as a variable into the rules defined by the error contribution allocation relationship. The numerical value of the theoretical trajectory error is represented by its vector magnitude, which is obtained by calculating the square root of the sum of the squares of its three-dimensional vector components. Assuming the theoretical trajectory error vector components are ΔX, ΔY, and ΔZ, then the magnitude L equals the square of ΔX plus the square of ΔY plus the square of ΔZ, and then the square root of the sum is taken. The magnitude L is then substituted into the error contribution allocation relationship as a scalar representative value of the theoretical trajectory error.

[0042] Next, based on the weights or proportions defined by the error contribution allocation relationship, the spatial trajectory error component corresponding to the responsibility of the dynamic focusing system is separated from the theoretical trajectory error, and this component is taken as the spatial trajectory error component contributed by the dynamic focusing system. The error contribution allocation relationship defines the responsibility division weights between the galvanometer and the dynamic focusing system for the theoretical trajectory error, which are expressed as weighting factors. If the dominant hysteresis type is galvanometer-dominant hysteresis, the spatial trajectory error component contributed by the dynamic focusing system is equal to the secondary weighting factor of the dynamic focusing system multiplied by the magnitude L of the theoretical trajectory error; if the dominant hysteresis type is dynamic focusing system-dominant hysteresis, it is equal to the primary weighting factor of the dynamic focusing system multiplied by L; if the dominant hysteresis type is coupled hysteresis, it is equal to the cooperative weighting factor of the dynamic focusing system multiplied by L. The multiplication operation is performed on a scalar basis. For example, if the magnitude L of the theoretical trajectory error is 20 micrometers and the weighting factor of the dynamic focusing system is 0.4, then the spatial trajectory error component contributed by the dynamic focusing system is 8 micrometers. The resulting spatial trajectory error component contributed by the dynamic focusing system is a scalar value. To be used for subsequent axial compensation control, this scalar value needs to be converted into a spatial vector, based on the direction of the theoretical trajectory error vector. In surface machining, focus hysteresis mainly occurs in the normal direction of the theoretical trajectory, while the optical axis direction is usually aligned with the normal direction of the machined surface. Therefore, the theoretical trajectory normal vector at the current machining point is obtained. This normal vector is calculated based on the trajectory curve equation. Multiplying the calculated scalar error component value by the unit vector in the direction of this normal vector yields the spatial trajectory error component vector contributed by the dynamic focusing system. This vector is a three-dimensional vector. Finally, the axial component of this vector, i.e., the component along the optical axis of the focusing system, is extracted. This axial component is extracted as the axial displacement that the dynamic focusing system needs to compensate for. Through the above steps, the solution from theoretical kinematic error to the specific subsystem responsibility error component is completed, obtaining the spatial trajectory error component contributed by the dynamic focusing system.

[0043] S6. Based on the spatial trajectory error component contributed by the dynamic focusing system, control the laser to delay emission after the preset trigger time of the galvanometer deflection command execution until the dynamic focusing system is adjusted to the correct position. Specifically, this is implemented as follows: First, the spatial trajectory error component contributed by the dynamic focusing system is used as the axial displacement that the dynamic focusing system needs to compensate for. This component is a scalar value calculated in the previous step, representing the focal deviation amplitude caused by the response lag of the dynamic focusing system. This scalar value is directly defined as the compensation distance that the dynamic focusing system needs to move along its optical axis, i.e., the axial displacement, in meters. For example, if the spatial trajectory error component contributed by the dynamic focusing system is 8 micrometers, then the axial displacement is 8 micrometers. This axial displacement is sent as a command value to the driver of the dynamic focusing system.

[0044] Then, based on the response characteristic parameters of the moving parts of the dynamic focusing system, the settling time required to complete the axial displacement is calculated. The response characteristic parameters of the dynamic focusing system have been obtained and stored through testing in previous steps. The key parameters for calculating the settling time are the step response time and maximum acceleration of the dynamic focusing system. The maximum acceleration of the dynamic focusing system is obtained by applying the maximum drive current to the system and measuring its acceleration. When calculating the settling time, the magnitude of the axial displacement and the dynamic response capability of the dynamic focusing system need to be considered. One calculation method is to use a first-order system model for estimation: for small axial displacements, the settling time is approximately equal to the step response time of the dynamic focusing system; for larger axial displacements, the minimum possible time needs to be calculated according to kinematic formulas. Specifically, a critical displacement value is first calculated, which is equal to the maximum acceleration of the dynamic focusing system multiplied by the square of the step response time of the dynamic focusing system, and then divided by 2. If the axial displacement is less than the critical displacement value, the adjustment time is equal to twice the axial displacement divided by the maximum acceleration of the dynamic focusing system, and then the square root of the result is taken. If the axial displacement is greater than or equal to the critical displacement value, the adjustment time is equal to the axial displacement divided by the maximum acceleration of the dynamic focusing system plus the step response time of the dynamic focusing system. Units must be consistent before calculation. For example, if the maximum acceleration of the dynamic focusing system is 50 m / s² and the step response time is 2 ms, the critical displacement value is approximately 0.1 μm. If the axial displacement is 8 μm, greater than the critical displacement value, the adjustment time is approximately 2.00016 ms, approximately equal to the step response time. Another calculation method is the lookup table method: The actual time required for the dynamic focusing system to complete different axial displacements is pre-calibrated experimentally, and a displacement-time correspondence table is established. The corresponding adjustment time is directly obtained by looking up the table based on the current axial displacement. For example, calibration shows that the adjustment time for an axial displacement of 8 μm is 2.1 ms.

[0045] Finally, the calculated adjustment time is used as the laser emission delay time, controlling the laser to emit light after a preset trigger time following the execution of the galvanometer deflection command. The CNC system has a unified timing controller that manages the timing of the galvanometer deflection command, the dynamic focusing system focusing command, and the laser emission command. The preset trigger time refers to the theoretically expected moment when the laser focus should reach a certain surface machining point, as set in the trajectory planning. Without compensation, the laser will emit a pulse at this preset trigger time. The control logic is as follows: when the timing controller reaches the preset trigger time, a timer is started, with its duration set to the calculated delay time. During the timer's operation, the dynamic focusing system begins movement based on the received axial displacement command. When the timer reaches the set delay time, the timing controller sends an emission trigger signal to the laser. For example, if the adjustment time is 2 milliseconds, the delay time is set to 2 milliseconds, and the laser emits light 2 milliseconds after the preset trigger time. In practice, delay control is achieved through a hardware timer in the CNC system: the calculated delay time value is written into the period register of the hardware timer, and the laser emission trigger signal is associated with the output signal of the hardware timer. When the hardware timer completes its countdown, the rising edge of its output signal triggers the laser to emit light. The entire control process ensures that the laser emission time is synchronized with the adjustment time of the dynamic focusing system.

[0046] Example 2: Figure 2 A schematic diagram of a real-time focusing compensation system for femtosecond laser surface processing is provided. This system includes the following modules: The parameter acquisition module is used to acquire the response characteristic parameters of the galvanometer and the dynamic focusing system; The risk assessment module is used to determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system based on the spatial geometric and dynamic motion characteristics of the current processing trajectory segment to be executed. The type identification module is used to analyze the dynamic motion characteristics of the current processing trajectory segment to be executed when it is determined that there is a risk of response asynchrony, and to identify the dominant lag type that causes response asynchrony by combining the response characteristic parameters of the galvanometer and the dynamic focusing system. The relationship determination module is used to determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system to the three-dimensional spatial trajectory error based on the dominant hysteresis type. The component calculation module is used to calculate the spatial trajectory error components contributed by the dynamic focusing system based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed. The light emission control module is used to control the laser to delay light emission after the preset trigger time of the galvanometer deflection command, based on the spatial trajectory error component contributed by the dynamic focusing system, until the dynamic focusing system is adjusted to the correct position.

[0047] All calculations involved in the embodiments are dimensionless numerical calculations, and the preset parameters and thresholds in the calculations are set by those skilled in the art according to the actual situation.

[0048] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0049] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0050] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0051] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or modules may be electrical, mechanical, or other forms.

[0052] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0053] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A real-time focusing compensation method for femtosecond laser surface processing, characterized in that, Includes the following steps: S1. Obtain the response characteristic parameters of the galvanometer and dynamic focusing system; S2. Based on the spatial geometric features and dynamic motion features of the current processing trajectory segment to be executed, determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system; S3. When it is determined that there is a risk of asynchronous response, analyze the dynamic motion characteristics of the current processing trajectory segment to be executed, and identify the dominant lag type that causes asynchronous response by combining the response characteristic parameters of the galvanometer and the dynamic focusing system. S4. Based on the dominant hysteresis type, determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system to the three-dimensional spatial trajectory error; S5. Based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed, the spatial trajectory error components contributed by the dynamic focusing system are calculated. S6. Based on the spatial trajectory error component contributed by the dynamic focusing system, control the laser to delay emission after the preset trigger time of the galvanometer deflection command until the dynamic focusing system is adjusted to the correct position.

2. The real-time focusing compensation method for femtosecond laser surface processing according to claim 1, characterized in that, S1 includes: Test deflection commands containing different frequency components are applied to the galvanometer, and the actual deflection response data of the galvanometer is collected. Based on the comparison and analysis of the test deflection commands and the actual deflection response data, the response characteristic parameters related to the moment of inertia of the galvanometer are obtained. Test focusing commands containing different frequency components are applied to the dynamic focusing system, and the actual axial displacement response data of the dynamic focusing system is collected. Based on the comparison and analysis of the test focusing commands and the actual axial displacement response data, the response characteristic parameters related to the moving parts of the dynamic focusing system are obtained.

3. The real-time focusing compensation method for femtosecond laser surface processing according to claim 1, characterized in that, S2 include: Extract curvature variation information from the spatial geometric features of the current processing trajectory segment to be executed; Extract motion acceleration information from the dynamic motion features of the current processing trajectory segment to be executed; By fusing curvature change information with motion acceleration information, a comprehensive index representing the dynamic complexity of the trajectory is generated; The comprehensive index of trajectory dynamic complexity is compared with the preset risk threshold, and the comparison results are used to determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system.

4. The real-time focusing compensation method for femtosecond laser surface processing according to claim 1, characterized in that, S3 includes: Spectral analysis is performed on the dynamic motion characteristics of the current processing trajectory segment to be executed to extract the dominant frequency of the trajectory motion; The dominant frequency of the trajectory motion is compared with the frequency response bandwidth in the response characteristic parameters related to the moment of inertia of the galvanometer to determine whether the dominant frequency exceeds the frequency response bandwidth of the galvanometer. The dominant frequency of the trajectory motion is compared with the frequency response bandwidth in the response characteristic parameters related to the moving parts of the dynamic focusing system to determine whether the dominant frequency exceeds the frequency response bandwidth of the dynamic focusing system. If the dominant frequency exceeds the frequency response bandwidth of the galvanometer only, the dominant hysteresis type is galvanometer dominant hysteresis; if the dominant frequency exceeds the frequency response bandwidth of the dynamic focusing system only, the dominant hysteresis type is dynamic focusing system dominant hysteresis; if the dominant frequency exceeds both the frequency response bandwidth of the galvanometer and the frequency response bandwidth of the dynamic focusing system, the dominant hysteresis type is coupled hysteresis.

5. The real-time focusing compensation method for femtosecond laser surface processing according to claim 4, characterized in that, Spectral analysis is performed on the dynamic motion characteristics of the current processing trajectory segment to be executed to extract the dominant frequencies of the trajectory motion, including: Perform a Fourier transform on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed to obtain the motion acceleration spectrum; The frequency component with the largest amplitude is selected from the motion acceleration spectrum as the dominant frequency of the trajectory motion.

6. The real-time focusing compensation method for femtosecond laser surface processing according to claim 1, characterized in that, S4 include: If the dominant hysteresis type is galvanometer-dominated hysteresis, then establish an error contribution allocation relationship with the response characteristic parameters related to the moment of inertia of the galvanometer as the main weighting factors. If the dominant lag type is dynamic focusing system dominant lag, then establish an error contribution allocation relationship with the response characteristic parameters related to the moving parts of the dynamic focusing system as the main weighting factors. If the dominant hysteresis type is coupled hysteresis, then the response characteristic parameters related to the rotational inertia of the galvanometer and the response characteristic parameters related to the moving parts of the dynamic focusing system are combined to establish a cooperative error contribution allocation relationship based on the ratio of the two parameters.

7. The real-time focusing compensation method for femtosecond laser surface processing according to claim 1, characterized in that, S5 include: Based on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed, the theoretical trajectory error of the theoretical processing trajectory in three-dimensional space is calculated. Substitute the theoretical trajectory error into the error contribution allocation relationship; Based on the weights or proportions defined by the error contribution allocation relationship, the spatial trajectory error component corresponding to the responsibility part of the dynamic focusing system is separated from the theoretical trajectory error and used as the spatial trajectory error component contributed by the dynamic focusing system.

8. The real-time focusing compensation method for femtosecond laser surface processing according to claim 7, characterized in that, Based on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed, the theoretical trajectory error in three-dimensional space is calculated, including: Based on the motion acceleration information in the dynamic motion characteristics of the current processing trajectory segment to be executed, the positional deviation of the theoretical processing trajectory in three-dimensional space caused by the acceleration change is calculated through the kinematic model, which is used as the theoretical trajectory error.

9. The real-time focusing compensation method for femtosecond laser surface processing according to claim 1, characterized in that, S6 include: The spatial trajectory error component contributed by the dynamic focusing system is taken as the axial displacement that the dynamic focusing system needs to compensate for. Based on the response characteristic parameters of the moving parts of the dynamic focusing system, the adjustment time required to complete the axial displacement is calculated. The adjustment time is used as the delay time for laser emission, controlling the laser to emit light after a preset trigger time following the execution of the galvanometer deflection command.

10. A real-time focusing compensation system for femtosecond laser surface machining, used to implement the real-time focusing compensation method for femtosecond laser surface machining as described in any one of claims 1-9, characterized in that, Includes the following modules: The parameter acquisition module is used to acquire the response characteristic parameters of the galvanometer and the dynamic focusing system; The risk assessment module is used to determine whether there is a risk of asynchronous response between the galvanometer and the dynamic focusing system based on the spatial geometric and dynamic motion characteristics of the current processing trajectory segment to be executed. The type identification module is used to analyze the dynamic motion characteristics of the current processing trajectory segment to be executed when it is determined that there is a risk of response asynchrony, and to identify the dominant lag type that causes response asynchrony by combining the response characteristic parameters of the galvanometer and the dynamic focusing system. The relationship determination module is used to determine the error contribution distribution relationship between the galvanometer and the dynamic focusing system on the three-dimensional spatial trajectory error based on the dominant hysteresis type. The component calculation module is used to calculate the spatial trajectory error components contributed by the dynamic focusing system based on the error contribution allocation relationship and the dynamic motion characteristics of the current processing trajectory segment to be executed. The light emission control module is used to control the laser to delay light emission after the preset trigger time of the galvanometer deflection command, based on the spatial trajectory error component contributed by the dynamic focusing system, until the dynamic focusing system is adjusted to the correct position.

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