A laser focus-pursuing method based on acoustic wave signals, a laser manufacturing method, and a laser manufacturing system

Abstract

The application provides a laser focus-pursuing method based on an acoustic wave signal, a laser manufacturing method and a laser manufacturing system. A workpiece is provided with a loaded track. In the process of ablation of the workpiece surface by laser, an acoustic wave signal in the plasma plume eruption process is collected, the acoustic wave signal is filtered and processed, an RMS value is calculated, and a difference between the RMS value and a preset target value is obtained. A calibration value is output through PID control, which is converted into an axial offset amount of a laser spot. A threshold value of the compensation offset amount is set according to the scale of the ablation effect of the spot axis, the loaded track is automatically corrected and compensated for multiple times, the response speed is fast, the signal is easy to collect and capture, real-time focus-pursuing can be realized, and the application value is great in the processing and manufacturing of complex curved surfaces. In addition, the manufacturing speed can be improved by adopting defocusing processing, and different manufacturing effects can be formed.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, specifically to a laser tracking focusing method, a laser manufacturing method, and a laser manufacturing system based on acoustic signals. Technical Background

[0002] With the development of industries such as aerospace, medical instruments, and chip manufacturing, there is an urgent need for high-precision manufacturing. Compared with traditional processing methods, laser processing technology has advantages such as non-contact processing, high precision, and high flexibility. However, traditional laser processing methods, based on the thermal effect of lasers, rely on the absorption of the light source by the material itself, making it difficult to effectively process transparent materials. Furthermore, due to the large heat-affected zone, it cannot achieve high-quality processing of polymer materials or biological tissues. Ultrafast lasers, with their short pulse time, high peak power, and ability to generate nonlinear absorption, can effectively process transparent materials. Simultaneously, their low thermal effect avoids additional thermal damage when cutting polymer materials or biological tissues, thus showing broad application prospects. However, due to the high precision of ultrafast laser processing systems, even slight deviations in the focal area result in vastly different manufacturing effects. Maintaining the focal point on the surface and precisely controlling the manufacturing process, especially for curved structures, presents new challenges. Currently, image or optical focusing methods are commonly used to determine the laser's position. However, image focusing methods have poor focusing accuracy, and optical focusing systems are highly complex and difficult to promote, posing significant difficulties in applicability to transparent materials and various manufacturing systems.

[0003] Chinese patent CN112255191A mentions an online monitoring system and method combining laser-induced breakdown spectroscopy and acoustic reflection. This system detects changes in material physical processes and composition information during laser processing by using spectral and acoustic signals excited during the process. However, while this technology proposes an acoustic-based detection method, it focuses on the combined effect of image, acoustic, and spectral signals on luminescence properties, rather than using acoustic signals alone for real-time focusing during processing. It also fails to address how to use the detected acoustic signals to provide feedback on the processing trajectory. Furthermore, the addition of image and spectral signals reduces the feedback speed, making real-time focusing impossible.

[0004] Chinese patent CN114083115A discloses a method for laser processing using light sensing or sound control, which describes controlling the movement of the laser beam focus through optical or sound sensors. This method can be used for efficient processing of transparent materials. However, it relies solely on sound signals to determine whether the laser is in direct contact with the material and cannot provide high-precision control over the processing. Summary of the Invention

[0005] This invention relates to a laser tracking focusing method, a laser manufacturing method, and a laser manufacturing system based on acoustic signals. Utilizing acoustic signals as one-dimensional signals, it features fast response speed and easy capture, enabling real-time monitoring and correction compensation of the laser processing process. To solve the aforementioned technical problems, this invention adopts the following technical solution:

[0006] This invention provides a laser tracking method based on acoustic signals. A loading trajectory is set on the workpiece. During the laser ablation of the workpiece surface, acoustic signals from the plasma plume ejection process are collected. The acoustic signals are filtered, the RMS value is calculated, and the difference between the RMS value and a preset target value is obtained. A calibration value is output through PID control and converted into the laser spot axial offset. A threshold for compensating the offset is set according to the scale at which the laser spot axis can produce an ablation effect. The loading trajectory is automatically corrected and compensated multiple times.

[0007]

[0008] In the formula: ΔT represents the length of the time window, and I(t) represents the intensity of the sound wave signal at a certain moment.

[0009] Furthermore, the loading trajectory is located in the xy plane, the correction and compensation direction is the z-axis direction, the axial direction of the laser spot is parallel to the z-axis direction, and the x, y, and z axes are perpendicular to each other.

[0010] Furthermore, a preset target value for RMS is set so that the focal spot is located on the outer side of the workpiece surface.

[0011] Furthermore, a preset target value of 20% or 50% is set.

[0012] The present invention also provides a laser manufacturing method based on acoustic signals, wherein the workpiece is placed on a moving platform, the laser ablates the surface of the workpiece, and the loading trajectory is automatically corrected and compensated multiple times using the above-mentioned laser tracking method based on acoustic signals.

[0013] The present invention also provides a laser manufacturing system based on acoustic signals, comprising:

[0014] A laser generator is used to produce pulsed laser light.

[0015] A reflector that reflects the pulsed laser light generated by a laser generator;

[0016] The objective lens is used to focus the reflected pulsed laser light.

[0017] The xy displacement stage carries the workpiece and controls its movement according to the loading trajectory;

[0018] z-displacement stage, supporting the objective lens;

[0019] Camera, used to capture image information during the laser ablation process;

[0020] Acoustic wave acquisition device to collect acoustic wave signals during the plasma plume ejection process in laser ablation processing;

[0021] The control system is electrically connected to the camera and acoustic wave acquisition unit. It receives the acoustic wave signal acquired by the acquisition unit, filters the signal, calculates the RMS value, and obtains the difference between the RMS value and the preset target value. This difference is then converted into a calibration value by the PID controller, which is used to convert the offset of the z-displacement stage. A threshold for compensating the offset is set according to the scale at which the light spot axis can produce an ablation effect. The system then controls the movement of the z-displacement stage, performing multiple automatic corrections and compensations on the loading trajectory. Specifically:

[0022]

[0023] In the formula: ΔT represents the length of the time window, and I(t) represents the intensity of the sound wave signal at a certain moment.

[0024] Furthermore, the sound wave collector is a microphone.

[0025] Furthermore, a switch and energy regulation device are also provided in the optical path between the laser generator and the reflector.

[0026] Furthermore, a preset target value for RMS is set so that the focal spot is located outside the workpiece surface for defocusing processing.

[0027] Furthermore, a preset target value of 20% or 50% is set.

[0028] This invention offers the following advantages: It acquires acoustic signals during plasma plume eruption in laser processing, filters and calculates the RMS value, and converts the difference between the RMS value and a preset target value into the axial offset of the laser spot. This allows for multiple automatic corrections and compensations of the loading trajectory. Utilizing the one-dimensional properties of acoustic signals, it offers fast response and easy signal acquisition for real-time focusing, making it highly valuable for complex curved surface manufacturing. Furthermore, the defocused spot has a larger effective area and forms regular micro-nano structures on the processing surface. Defocused processing improves manufacturing speed and creates diverse manufacturing effects. Attached Figure Description

[0029] Figure 1a This is an architectural diagram of the laser manufacturing system based on acoustic signals of the present invention;

[0030] Figure 1b This is a schematic diagram of the calibration system for the PID controller of the present invention;

[0031] Figure 2aThis is the test result of the 316 stainless steel surface tracking test in Embodiment 1 of the present invention without correction;

[0032] Figure 2b This is the test result of applying correction in the coking test of 316 stainless steel according to Embodiment 1 of the present invention;

[0033] Figure 2c This is the measurement result of the focus tracking test on the surface of 316 stainless steel in Embodiment 1 of the present invention;

[0034] Figure 3 This is Embodiment 2 of the present invention, which uses a calibration system to perform morphology control testing on the material surface: (a) is the RMS preset target value adjuster; (b)(c)(d) are schematic diagrams of different focusing; (e)(f)(g) are corresponding spot position diagrams; (h)(i)(j) are corresponding images under a microscope and an atomic force microscope.

[0035] In the diagram: 1-Laser generator, 2-Switch, 3-Energy adjustment device, 4-Mirror, 5-Objective lens, 6-Z-displacement stage, 7-Camera, 8-XY-displacement stage, 9-Acoustic wave collector. Detailed Implementation

[0036] Research has found that when a laser acts on a workpiece surface, the induced acoustic signal is closely related to the location of the laser spot. Based on the mapping relationship between the acoustic signal and the location of the laser spot, a system architecture is established as follows: Figure 1a As shown:

[0037] Laser generator 1 outputs laser pulses, switch 2 controls the laser's on / off state, and energy adjustment device 3 controls the laser power. The laser beam passes through mirror 4 and enters objective lens 5. The objective lens module is placed on z-displacement stage 6 to adjust the focal length. The laser is focused on the workpiece surface, which is placed above xy-displacement stage 8. A camera is placed on the side of xy-displacement stage 8 to detect the real-time movement position of the laser spot. An acoustic wave acquisition device 9 is placed on the other side of xy-displacement stage 8 and connected to the control system via USB.

[0038] The sound wave acquisition device 9 uses a commercially available microphone, and the energy adjustment device 3 uses a neutral density filter.

[0039] Design a correction system, such as Figure 1bAs shown, the system is divided into a signal acquisition module and a PID controller. In the initial state, the xy-stage displacement stage 8 moves along the loading trajectory. At this time, the target RMS value of the acoustic signal is set, i.e., the preset target value. The control system receives the acoustic signal from the microphone, then filters the signal and calculates the RMS value. The sampling period is 100ms to ensure good filtering effect. The difference between the RMS value and the preset target value, errorRMS, is input to the controller. If there is a change in the height of the workpiece surface, errorRMS will increase accordingly. The PID controller outputs a calibration value, which is converted into the z-direction displacement of the z-stage displacement stage 6, thereby achieving real-time axial correction. The PID controller is selected to control within a defocus range of 0-700μm to ensure that the output and displacement maintain directional consistency.

[0040] Example 1

[0041] See Figures 2a-2c Focusing tests were conducted on polished 316 stainless steel surfaces, categorized into those without correction. Figure 2a With applying correction Figure 2b Two sets. Tilt the stainless steel sheet at about 30° and move the light spot from the top of the sample. Set the trajectory to move 5 mm along the x-axis and then 100 μm along the y-axis, and repeat this movement.

[0042] Without correction, the motion process is only horizontal, such as... Figure 2a As shown, under a microscope, the lines can be observed to gradually thicken and the boundaries to gradually blur. The evolution of the laser edge is marked by a solid white line in the microscope image. It can be seen that the distance between the two trajectory boundaries gradually decreases and eventually overlaps, becoming indistinguishable. The red circles mark the overlapping lines, which are no longer distinguishable.

[0043] Figure 2b The results of the real-time calibration are shown, including the motion trajectory and motion time. Figure 2a The same applies. The z-axis motion is calibrated in real time using a PID controller based on the feedback RMS signal. A microscopic image of its trajectory is shown below. Figure 2b As shown on the right, the edges of the trajectory are still marked by two white lines in the graph. It can be observed that as the x-axis moves, the two white lines are almost parallel in the y-direction, and the gap between them does not decrease significantly with the movement. At the same time, the distance between the lines remains clearly visible within the red circle.

[0044] The distance between lines within a 1mm range in the x-direction was measured, with a value taken every 100μm. The measurement results were... Figure 2c The triangles represent the uncalibrated results, and the circles represent the calibrated results. As can be seen, after calibration, even positions that were originally far from the surface can achieve good focus tracking.

[0045] Example 2

[0046] In laser manufacturing, the focal point is where the highest precision is achieved. However, for high-throughput processing, relying solely on the focal point is insufficient to meet manufacturing efficiency requirements. By utilizing the larger area of ​​the defocused spot, the overall manufacturing speed can be increased. Furthermore, micro- and nano-structures can be formed on the processed surface, and different manufacturing effects can be achieved by setting different acoustic wave intensity signal thresholds.

[0047] After setting the initial target RMS value, adjust the percentage of the preset target value, and then the z-axis will generate a new compensation value, enabling the system to quickly track the target position. When the percentage of the preset target value is less than 100%, the spot focus is located on the outer side of the workpiece surface. Figure 3 It shows three working states when the initial target value is set to 100%, 50%, and 20%. Figure 3 'a' represents the threshold range that can be manually adjusted within the software during actual work. This section shows the manufacturing effect under three states of real-time adjustment: 100%, 50%, and 20%.

[0048] Figure 3 The diagram of BCD illustrates that the area of ​​interaction between the laser and the workpiece surface varies at different focusing positions. Figure 3 efg shows the position where the light spot is locked after the preset target value is set. Figure 3 hij is a microscopic image of the groove after laser ablation. Figure 3 The view below hij shows magnified AFM images of the channel from different perspectives.

[0049] Figure 3 b represents the position where the laser spot is locked when the threshold is 100%. The area within the red circle is the bright spot formed by the femtosecond laser breaking down the air. Under these conditions, laser ablation will produce... Figure 3 The effect shown in h. During the manufacturing process, the threshold is adjusted to 50%. As the set threshold decreases, the laser spot automatically moves upward, shifting to the position shown in h. Figure 3 The position of f corresponds to a thicker trajectory due to the rising focal position, forming a shape like... Figure 3 The microstructure of i changes with decreasing energy density, and the interaction between the laser and matter changes from ablation to laser-induced periodic surface structures, such as... Figure 3 The view below. Further reducing the threshold to 20% of the target threshold will automatically raise the corresponding spot position to... Figure 3 The position of g, and its microscopic morphology, are as follows: Figure 3j. In principle, with the increase of defocusing, the overall size should increase accordingly, but the fringes in 4j are smaller and narrower than those in 4g. Combined with AFM observation of its surface morphology, it was found that at 100% threshold, a relatively flat and irregular surface was formed, while at 50% threshold, uniform LIPSS fringes were formed. At 25% threshold, although LIPSS formed in some areas, its depth was significantly reduced compared to 50%. Therefore, using acoustic emission technology for feedback control can effectively control the formation of different micromorphologies.

Claims

1. A laser tracking focusing method based on acoustic signals, characterized in that: The workpiece has a set loading trajectory. During the laser ablation of the workpiece surface, acoustic signals from the plasma plume ejection process are collected. The acoustic signals are filtered, the RMS value is calculated, and the difference between the RMS value and the preset target value is obtained. The calibration value is output through PID control and converted into the laser spot axial offset. A compensation offset threshold is set according to the scale at which the laser spot axis can produce an ablation effect. The loading trajectory is automatically corrected and compensated multiple times. In the formula: ΔT represents the length of the time window, and I(t) represents the intensity of the sound wave signal at a certain moment.

2. A laser tracking focusing method based on acoustic signals according to claim 1, characterized in that: The loading trajectory is located in the xy plane, the correction and compensation direction is the z-axis direction, the laser spot axial direction is parallel to the z-axis direction, and the x, y, and z axes are perpendicular to each other.

3. A laser tracking focusing method based on acoustic signals according to claim 1, characterized in that: Set the preset target value of RMS so that the spot focus is located on the outer side of the workpiece surface.

4. A laser tracking focusing method based on acoustic signals according to claim 3, characterized in that: Set the preset target value to 20% or 50%.

5. A laser manufacturing method based on acoustic signals, wherein a workpiece is placed on a moving platform and a laser ablates the surface of the workpiece, characterized in that: The laser tracking method based on acoustic signals, as described in any one of claims 1-4, is used to perform multiple automatic corrections and compensations on the loading trajectory.

6. A laser manufacturing system based on acoustic wave signals, characterized in that: include: A laser generator is used to produce pulsed laser light. A reflector that reflects the pulsed laser light generated by a laser generator; The objective lens is used to focus the reflected pulsed laser light. The xy displacement stage carries the workpiece and controls its movement according to the loading trajectory; z-displacement stage, supporting the objective lens; Camera, used to capture image information during the laser ablation process; Acoustic wave acquisition device, which collects acoustic wave signals during the plasma plume ejection process in laser ablation processing; The control system is electrically connected to the camera and acoustic wave acquisition unit. It receives the acoustic wave signal acquired by the acquisition unit, filters the signal, calculates the RMS value, and obtains the difference between the RMS value and the preset target value. This difference is then converted into a calibration value by the PID controller, which is used to convert the offset of the z-displacement stage. A threshold for compensating the offset is set according to the scale at which the light spot axis can produce an ablation effect. The system then controls the movement of the z-displacement stage, performing multiple automatic corrections and compensations on the loading trajectory. Specifically: In the formula: ΔT represents the length of the time window, and I(t) represents the intensity of the sound wave signal at a certain moment.

7. A laser manufacturing system based on acoustic signals according to claim 6, characterized in that: The sound wave acquisition device is a microphone.

8. A laser manufacturing system based on acoustic signals according to claim 7, characterized in that: A switch and energy regulation device are also installed in the optical path between the laser generator and the reflector.

9. A laser manufacturing system based on acoustic signals according to any one of claims 6-8, characterized in that: Set the preset target value of RMS so that the spot focus is located outside the workpiece surface for defocusing processing.

10. A laser manufacturing system based on acoustic signals according to claim 9, characterized in that: Set the preset target value to 20% or 50%.

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