A laser cutting machine light path coaxial calibration device and method

Abstract

The application relates to the field of laser cutting, and particularly provides a laser cutting machine light path coaxial calibration device and method.The device comprises: a calibration module body provided with a mechanical interface consistent with a cutting head nozzle mounting interface; a radial polarized light modulation module fixed in the body and used for modulating laser into radial polarized light; an annular polarization sensor array fixed in the body and located downstream of the modulation module, comprising a plurality of polarization sensors uniformly distributed along a circumference, each sensor detection surface is located on an array inner wall surface, used for detecting a polarization angle in a respective direction and outputting a signal, and a geometric center of the array represents a nozzle theoretical axis position during calibration module installation; and a data processing and display module in communication connection with each sensor, used for calculating an offset amount of a laser beam center relative to the geometric center based on the polarization angle signal and visually outputting. The application improves the precision and efficiency of laser cutting machine light path coaxial calibration.

Description

Technical Field

[0001] This invention relates to the field of laser cutting, and specifically to a coaxial calibration device and method for the optical path of a laser cutting machine. Background Technology

[0002] Adjusting the laser beam path to the center of the nozzle (i.e., "optical path coaxiality calibration") is a critical operation throughout the entire lifecycle of laser cutting equipment, including installation, use, and maintenance. Its core purpose is to prevent cutting failures, equipment damage, and safety risks caused by optical path misalignment, ensuring precise energy transfer and processing stability during laser cutting. Optical path coaxiality can change due to factors such as equipment transportation, component wear, and mechanical vibration. Optical path coaxiality calibration is necessary after initial equipment installation or relocation, after replacement of critical optical consumables, when cutting quality is abnormal, and after equipment collisions or abnormal vibrations.

[0003] Traditional optical path coaxiality calibration involves attaching transparent tape to the nozzle and using a low-power laser to spot the light. The tape will then capture the nozzle's outline and the laser beam's trajectory. The operator can then determine the direction of deviation by checking if the beam is centered on the outline and adjusting the nuts accordingly in the X and Y directions. This process is repeated until the optical path is perfectly centered on the nozzle, meeting cutting requirements. This process is often repeated multiple times, is very time-consuming, and lacks guaranteed accuracy.

[0004] The relevant technical solution employs a vision-based approach, using special filters and a camera to capture the position of the light path at the nozzle, presenting the real-time position information to the operator in the form of a visual image. This vision-based approach inherently has flaws. First, overexposure causes the light spot to diffuse. When strong light shines on the camera sensor, it causes local brightness saturation, blurring the edges of the light spot and expanding its area (potentially increasing to hundreds of micrometers or even millimeters), far exceeding the actual laser diameter. Second, the centroid calculation is offset; the center of the overexposed area may darken (sensor saturation), causing the center of the light spot (the core basis for determining the beam center in vision methods) to deviate from the actual laser center. Finally, due to hardware limitations, camera-based measuring instruments rely on sensor pixel size. If the actual laser diameter is close to or smaller than the pixel size, or if the light spot diffuses and covers a small number of pixels, the measurement accuracy will drastically decrease. In short, the accuracy limit of the vision method is limited by the image quality of the light spot—even if the actual laser diameter is very small, if the imaged light spot is distorted, the beam center position cannot be accurately determined. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a coaxial calibration device and method for the optical path of a laser cutting machine. By employing radial polarization modulation, nonlinear iterative optimization, and reference coaxial transfer, the accuracy and efficiency of coaxial calibration of the optical path of a laser cutting machine are improved.

[0006] In a first aspect, the technical solution of the present invention provides a coaxial calibration device for the optical path of a laser cutting machine, comprising:

[0007] The calibration module body is equipped with a mechanical interface for mounting to the laser cutting machine head;

[0008] Radial polarization modulation module: Fixedly installed inside the calibration module, used to receive the laser emitted by the cutting head and modulate it into radial polarization light;

[0009] Circular polarization sensor array: Fixedly installed within the calibration module body and located downstream of the radial polarization light modulation module, it contains multiple polarization sensors evenly distributed along the circumference. The detection surface of each polarization sensor is located on the inner wall of the array, used to receive radial polarized light to detect the polarization angle of the laser at its respective orientation, and output the corresponding polarization angle signal; when the calibration module body is installed on the cutting head, the geometric center of the circular polarization sensor array represents the theoretical axis position of the nozzle to be calibrated.

[0010] Data processing and display module: It communicates with each polarization sensor to calculate the offset of the laser beam center relative to the geometric center of the ring polarization sensor array based on each polarization angle signal, and then visualizes the offset.

[0011] Secondly, the technical solution of the present invention provides a method for coaxial calibration of the optical path of a laser cutting machine. This method is based on the above-mentioned device and includes the following steps:

[0012] S1: Install the calibration module body of the calibration device onto the laser cutting machine head through its mechanical interface;

[0013] S2: Turn on the low-power light output mode of the laser cutting machine, so that the laser passes through the radial polarization light modulation module and the ring polarization sensor array in sequence;

[0014] S3: Through each polarization sensor in the ring polarization sensor array, the actual polarization angle of the radially polarized light at its respective location is detected synchronously, and the polarization angle signal is output.

[0015] S4: The data processing and display module calculates the offset of the laser beam center relative to the geometric center of the annular polarization sensor array based on each polarization angle signal;

[0016] S5: Visualize the offset to guide the user in adjusting the optical path and completing the optical path coaxial calibration.

[0017] As can be seen from the above technical solutions, this application has the following advantages:

[0018] Employing a polarization state symmetry detection mechanism, the laser light is modulated into radially polarized light through a radial polarization modulation module, establishing a linear relationship between its vibration direction and spatial position. A ring-shaped polarization sensor array directly detects the polarization angles in all directions, rather than capturing images of the light spot. Since polarization angle detection is intensity-independent, it completely avoids overexposure problems such as sensor saturation, light spot diffusion, and edge blurring caused by strong laser irradiation, and there are no physical limitations on measurement accuracy imposed by pixel resolution. If the polarization angle detection error is ≤0.1°, the corresponding radial distance deviation is only 0.002mm, and the centering accuracy can be stably controlled within one millimeter (0.01mm), significantly improving the accuracy of the vision solution.

[0019] The polarization angle information at multiple azimuths is acquired by a ring polarization sensor array. A nonlinear error function with offset coordinates as the optimization variable is constructed by the data processing and display module. An iterative optimization algorithm is used to accurately solve for the offset (Δx, Δy) of the laser beam center relative to the geometric center of the ring polarization sensor array. The interpretation is transformed into two-dimensional offset coordinates that can be directly displayed and accurately quantified, realizing the standardization and digitization of the calibration process and further improving the calibration accuracy.

[0020] The system can simultaneously acquire polarization angles in all directions with a single low-power light output, and calculate and visualize the offset in a short time. Users only need to adjust the optical path once or several times according to the offset coordinates displayed on the screen to complete the alignment. The calibration time for a single operation is reduced from several minutes, which greatly improves the efficiency of equipment installation, maintenance, and troubleshooting.

[0021] The geometric center of the annular polarization sensor array is defined as the measurement reference characterizing the theoretical axis position of the nozzle to be calibrated. A standard mechanical interface on the calibration module ensures that this geometric center line is collinear with the light output axis of the cutting head in the installed state. A complete traceability chain is established, unifying the three axes: measurement reference, installation reference, and working reference. Adjusting the calibration module to the centering state is equivalent to completing the centering on the actual nozzle. After removing the calibration module and replacing it with the actual nozzle, the coaxiality of the optical path remains unchanged, ensuring the effective transfer and reproduction of the calibration results. Attached Figure Description

[0022] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the central cross-sectional structure of a coaxial calibration device for a laser cutting machine provided in an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the calibration module body installed on the laser cutting machine head.

[0025] Figure 3 This is a top view of a ring polarization sensor array.

[0026] Figure 4 This is a schematic diagram of a laser cutting machine optical path coaxial calibration method provided in an embodiment of the present invention.

[0027] In the figure, 100 is the calibration module body, 110 is the upper body, 120 is the lower body, 130 is the mechanical interface, 140 is the external electrical interface, 200 is the radial polarization light modulation module, 210 is the 1 / 4 wave plate, 220 is the radial polarization converter, 2201 is the S wave plate, 300 is the annular polarization sensor array, and 310 is the polarization sensor. Detailed Implementation

[0028] To make the purpose, features, and advantages of this application more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solution protected by this application. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this application and in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0030] The key terms used in this invention will be explained below.

[0031] Polarization state refers to the direction of light vibration, and laser light is linearly polarized light.

[0032] Radial polarized light: The vibration direction of the light is always pointing towards the center of the beam, and the vibrations diverge outward from the center.

[0033] Quarter-wave plate: Converts laser light into circularly polarized light. A quarter-wave plate is a special quartz mirror. When linearly polarized light passes perpendicularly through a quarter-wave plate, the vibration is split into two parts. The propagation speeds of the two parts are slightly different. When they are finally combined, the direction of light vibration is no longer fixed up and down or left and right, but becomes "circling around the center of the beam" (this is called circularly polarized light).

[0034] Radial polarization converter: The radial polarization converter has a special micro-nano structure that only allows vibrations "pointing towards the center of the beam" to pass through. The final output laser has all vibrations in the "radial" direction (from the edge of the beam to the center) and is uniformly distributed around the center of the beam, which is radially polarized light.

[0035] Polarization sensor: The working principle is to filter light vibrations in a specific direction through a polarization filter, convert the light signal into an electrical signal, calculate the polarization angle of the light, and output the polarization angle as an analog voltage signal.

[0036] Figure 1 This is a schematic diagram of the central cross-sectional structure of a coaxial calibration device for the optical path of a laser cutting machine provided in an embodiment of the present invention, as shown below. Figure 1 As shown, the device includes a calibration module body 100, a radial polarization light modulation module 200, a ring polarization sensor array 300, and a data processing and display module.

[0037] The calibration module body 100 is provided with a mechanical interface 130 for mounting to the laser cutting machine head. The mechanical interface 130 is a threaded interface that is consistent with the nozzle mounting interface of the laser cutting machine head.

[0038] In this embodiment, the calibration module body 100 is made of aluminum alloy or stainless steel through machining. It is used to integrate and install the radial polarization light modulation module 200 and the annular polarization sensor array 300, and provides a mechanical interface 130 for connecting to the laser cutting head.

[0039] The calibration module body 100 comprises two mutually cooperating parts: an upper body 110 and a lower body 120. The upper body 110 has a first mounting cavity inside, used to accommodate and fix the radial polarization modulation module 200. The lower body 120 has a second mounting cavity inside, used to accommodate and fix the annular polarization sensor array 300. The annular polarization sensor array 300 is located at the bottom of the second mounting cavity, and an annular mounting groove can be provided, within which the annular polarization sensor array 300 is embedded. After the upper body 110 and the lower body 120 are connected, the first and second mounting cavities are coaxially connected, forming a complete optical path channel for the laser beam to pass through. The axis of the optical path channel coincides with the geometric center line of the annular polarization sensor array 300, which is the theoretical nozzle axis position characterized by the device in the calibration state.

[0040] Figure 2This diagram illustrates the installation of the calibration module body 100 onto the laser cutting machine head. The calibration module body 100 is detachably installed onto the laser cutting machine head via a mechanical interface 130 located on the top of the upper body 110. The mechanical interface 130 is specifically a threaded interface. The outer circumference of the mechanical interface 130 has external threads, the specifications, pitch, direction of rotation, and tolerance grade of which are consistent with the mounting threads of the original nozzle of the laser cutting machine head. This calibration device can directly replace the actual nozzle and be installed on the existing nozzle mounting seat of the cutting head. During installation, the operator only needs to unscrew the actual nozzle from the cutting head, then screw the calibration device directly into the nozzle mounting seat of the cutting head via the external thread at the top of its upper body 110, and tighten it moderately by hand or with a standard wrench. Because it uses a threaded interface consistent with the actual nozzle, after installation, the axis of the optical path channel of this calibration device automatically maintains a collinear relationship with the output axis of the cutting head, requiring no additional coaxiality adjustment.

[0041] The side wall of the lower body 120 also integrates an external electrical interface 140, used to extract and transmit the polarization angle signal collected by the annular polarization sensor array 300 to the data processing and display module. The external electrical interface 140 includes multiple terminals, each of which is electrically connected to each polarization sensor 310 of the annular polarization sensor array 300 via an internal flexible circuit board or wires. The terminals can be made of gold-plated copper, which has good conductivity and oxidation resistance, and is suitable for frequent plugging and unplugging operations.

[0042] In other alternative embodiments, the external electrical interface may also take the form of aviation plugs, waterproof quick-connect connectors, or integrated cables to adapt to different field conditions and user needs.

[0043] After the calibration module body 100 is installed on the cutting head, the laser cutting machine operates in low-power output mode. The laser beam is emitted from the light outlet of the cutting head, enters the optical path channel vertically, and passes sequentially through the radial polarization modulation module 200 in the upper body 110 and the detection area enclosed by the annular polarization sensor array 300 in the lower body 120, finally exiting from the bottom of the lower body 120. During this process, the annular polarization sensor array 300 simultaneously detects the polarization angle of the radial polarization light in all directions and transmits the signal in real time to the data processing and display module through the external electrical interface 140 for subsequent calculation and display.

[0044] Radial polarization light modulation module 200: Fixedly installed inside the calibration module body 100, used to receive the laser emitted by the cutting head and modulate it into radial polarization light.

[0045] In this embodiment, the radial polarization light modulation module 200 is fixedly installed in the upper body 110 of the calibration module body 100, located in the upstream section of the optical path channel. It is used to receive the original laser emitted from the laser cutting head and modulate it into radial polarization light with a specific polarization state distribution for detection by the downstream annular polarization sensor array 300.

[0046] The radial polarization modulation module 200 includes, in sequence along the optical path: a quarter-wave plate 210 for converting linearly polarized laser light into circularly polarized light; and a radial polarization converter 220 for receiving circularly polarized light and converting it into radially polarized light. The two optical elements are coaxially arranged, and their optical axes coincide with the optical path channel axis of the calibration module body 100.

[0047] The quarter-wave plate 210 is a birefringent crystal waveplate, with its optical axis set at a 45° angle to the polarization direction of the incident laser. The laser emitted by the laser cutting machine is typically linearly polarized light with a fixed vibration direction. When this linearly polarized light is incident perpendicularly onto the quarter-wave plate 210, it is decomposed into two orthogonal components propagating along the fast and slow axes of the waveplate. Due to the different refractive indices of the fast and slow axes, the two components produce a phase difference of π / 2 after passing through the waveplate. This phase difference causes the combined vibrations of the two orthogonal components to trace a circle in a plane perpendicular to the propagation direction, thus forming circularly polarized light. The characteristic of this circularly polarized light is that its vibration direction is no longer fixed to a specific straight line, but rather rotates around the beam propagation direction at a constant angular velocity.

[0048] In this embodiment, the quarter-wave plate 210 is made of quartz crystal material through grinding, and its working wavelength is adapted to the commonly used wavelength band of laser cutting machines (such as 1064nm). The surface of the wave plate is coated with an anti-reflection film to reduce reflection loss and ensure transmittance ≥99%.

[0049] The radial polarization converter 220 is a polarization optical element with a special micro-nano structure. Its function is to allow only polarization components whose vibration direction points to or away from the center of the beam to pass through, thereby converting incident circularly polarized light into radially polarized light.

[0050] In this embodiment, the radial polarization converter 220 includes an S-waveplate 2201, whose fast axis direction rotates continuously along the circumference and is radially distributed. Specifically, each tiny region of this element has a different fast axis orientation, and this orientation has a fixed functional relationship with the azimuth angle of the region. When circularly polarized light is incident, this element introduces different phase delays at different angular positions of the beam, thereby redistributing the uniform circularly polarized state into a radially polarized state. The vibration direction of the emitted laser beam points towards the beam center (or away from the center) within the cross-section and is axially symmetrically distributed around the center.

[0051] This embodiment achieves a two-stage polarization conversion of the linearly polarized light, circularly polarized light, and radially polarized light emitted from the laser cutting machine by sequentially arranging the quarter-wave plate 210 and the radial polarization converter 220 along the optical path. The final output radially polarized light has the following key characteristics:

[0052] The polarization angle is linearly related to the radial distance: the polarization angle θ of any point in the beam cross section and the distance r from that point to the beam center satisfy θ=k·r, where k is the modulation coefficient of the radial polarization converter 220, which is fixed at 50° / mm in this embodiment;

[0053] Vibration direction axisymmetric distribution: The vibration direction in each direction points towards (or away from) the beam center, and is perfectly rotationally symmetrically distributed around the center;

[0054] Stable polarization state distribution: not significantly affected by factors such as laser power fluctuations and changes in ambient temperature.

[0055] The annular polarization sensor array 300 is fixedly installed inside the calibration module body 100 and located downstream of the radial polarization light modulation module 200. It includes multiple polarization sensors 310 evenly distributed along the circumference. The detection surface of each polarization sensor 310 is located on the inner wall of the array. It is used to receive radial polarized light to detect the polarization angle of the laser at its respective orientation and output the corresponding polarization angle signal. When the calibration module body 100 is installed on the cutting head, the geometric center of the annular polarization sensor array 300 represents the theoretical axis position of the nozzle to be calibrated.

[0056] Figure 3 This is a top view of the annular polarization sensor array 300. In this embodiment, the annular polarization sensor array 300 includes eight polarization sensors 310, which are distributed at 45° intervals along the circumference. A terminal block is provided on the calibration module body 100, and each polarization sensor 310 of the annular polarization sensor array 300 is electrically connected to the data processing and display module via an external electrical interface 140.

[0057] In this embodiment, the mechanical interface 130 of the calibration module body 100 coincides with the geometric center line of the annular polarization sensor array 300.

[0058] Specifically, the annular polarization sensor array 300 is fixedly installed within the lower body 120 of the calibration module body 100, located downstream of the optical path of the radial polarization modulation module 200. The annular polarization sensor array 300 has an overall annular structure, and its geometric center is defined as the measurement reference point of this device. The axis passing through this reference point and perpendicular to the array plane is defined as the geometric center line. This geometric center line is used to characterize the theoretical axis position of the actual nozzle to be calibrated when the calibration module body 100 is installed on the laser cutting head.

[0059] The polarization sensor 310 is a miniature integrated polarization light detection element, which integrates a polarization filter, a photodetector unit, and a signal conditioning circuit. Its working principle is as follows: incident light is filtered by the polarization filter to select light components with specific vibration directions. The photodetector unit converts the intensity of this light component into a weak current signal, which is amplified by a transimpedance amplifier and converted from analog to digital. The polarization angle θ of the incident light is then calculated in real time using an on-chip algorithm. The polarization angle θ is defined as the angle between the light vibration direction and a preset reference direction (usually the 0° horizontal direction), with an output range of 0° to 180°.

[0060] The annular polarization sensor array 300 comprises eight polarization sensors 310, uniformly distributed at 45° intervals along the inner circumference of the annular substrate 320. The mounting azimuth angle of each polarization sensor 310 is... Defined as follows: with the geometric center O of the annular substrate 320 as the pole, and the horizontal direction to the right as the 0° reference axis, the following values ​​are sequentially defined in the counterclockwise direction: .

[0061] The geometric center of the annular polarization sensor array 300 is uniquely determined by the spatial symmetry of the photosensitive surfaces of the eight polarization sensors 310. Specifically, this geometric center is the circumcenter of the regular octagon formed by the center points of the eight sensor photosensitive surfaces. This geometric center should be located on the axis of the optical path.

[0062] Data processing and display module: It communicates with each polarization sensor 310 and is used to calculate the offset of the laser beam center relative to the geometric center of the annular polarization sensor array 300 based on each polarization angle signal, and to visualize the offset.

[0063] In this embodiment, the data processing and display module includes:

[0064] Offset calculation unit: It is configured to construct a nonlinear error function with offset coordinates as variables based on each polarization angle signal and the theoretical polarization angle when the center of the laser beam coincides with the geometric center of the ring polarization sensor array 300, and use an iterative optimization algorithm to solve the function to obtain the offset;

[0065] Visualization output unit: Configured to convert the solved offsets into a graphical interface for display.

[0066] Specifically, the data processing and display module and the annular polarization sensor array 300 achieve bidirectional communication connection through an external electrical interface 140 and a signal transmission cable. Its functions include: real-time acquisition of polarization angle signals output by the eight polarization sensors 310; calculation of the two-dimensional offset (Δx, Δy) of the laser beam center relative to the geometric center of the annular polarization sensor array 300 based on a preset physical model and mathematical optimization algorithm; and presentation of this offset in an intuitive graphical form on the display terminal, providing operators with clear and real-time guidance for optical path adjustment.

[0067] In this embodiment, the data processing and display module uses a Raspberry Pi single-board computer as its core hardware platform, running a customized Linux operating system and the polarization signal processing software specific to this invention. This platform has advantages such as small size, low power consumption, sufficient computing power, rich peripheral interfaces, and easy integration with a display screen, making it particularly suitable as a handheld or airborne calibration terminal for laser cutting equipment.

[0068] The offset calculation unit calculates the specific position coordinates of the current laser beam center relative to the geometric center of the annular polarization sensor array 300 based on the polarization angle measurements fed back in real time by the eight polarization sensors 310. This includes the following steps.

[0069] Step 1, based on the first The polarization angle signal output by each polarization sensor Calculate the actual detected polarization angle deviation value. ,in This is the theoretical polarization angle when the center of the laser beam coincides with the geometric center of the ring polarization sensor array.

[0070] The offset calculation unit first preprocesses the raw polarization angle signal output by each polarization sensor 310.

[0071] No. Each polarization sensor 310 outputs in real time the measured value of the absolute polarization angle of radially polarized light at its location, denoted as . This angle value is a relative angle based on the sensor's internal reference zero position, and its range is [range missing]. .

[0072] The theoretical polarization angle reference value is pre-stored in the non-volatile memory inside the offset calculation unit. The physical meaning of this reference value is: the polarization angle value that the eight polarization sensors 310 should theoretically read when the geometric center of an ideal radially polarized light beam completely coincides with the geometric center O of the ring polarization sensor array 300. According to the fundamental constitutive relation of radially polarized light, this theoretical reference value satisfies:

[0073]

[0074] in, The polarization modulation coefficient of the radial polarization converter 220 is determined by the physical characteristics of the component, and in this embodiment, it is the factory calibration value. ; The fixed radial distance from the center of the photosensitive surface of each polarization sensor 310 to its geometric center is, in this embodiment, .

[0075] The offset calculation unit subtracts the original polarization angle measurement value of each sensor from the theoretical reference value to obtain the actual detected polarization angle deviation value of the sensor:

[0076]

[0077] The detection deviation value The physical meaning is: when the center of the beam deviates from the geometric center, in the first... The deviation of the actual polarization angle of each sensor from its ideal centering position. This value can be positive or negative, and its sign is determined by both the direction of beam deviation and the sensor's azimuth angle. The detection deviation values ​​of the eight sensors form an 8×1 dimensional column vector.

[0078] Step 2: Establish the nonlinear functional relationship between the theoretical polarization angle and the offset coordinates, expressed as:

[0079]

[0080] in, Indicates the first The theoretical polarization angle deviation of each polarization sensor The polarization modulation coefficient, This is a fixed radial distance from each polarization sensor to the geometric center of the ring polarization sensor array. For the first The installation azimuth angle of each polarization sensor. The coordinates are the offsets of the laser beam center relative to the geometric center of the annular polarization sensor array.

[0081] Specifically, the offset calculation unit contains a pre-built nonlinear theoretical model describing the physical relationship between beam offset and polarization angle deviation. This model is derived based on rigorous geometric optics and polarization optics principles, establishing the offset coordinates (Δx, Δy) to be solved and the first... The theoretical polarization angle deviation that should occur at each sensor location The deterministic functional relationship between the above terms.

[0082] The derivation of this theoretical functional relationship is based on the following two fundamental physical facts:

[0083] First, the polarization angle of radially polarized light is proportional to the radial distance from its location to the center of the beam, i.e. This relationship is determined by the physical characteristics of the radial polarization converter 220 and is verified and calibrated by precision calibration instruments before leaving the factory.

[0084] Second, when the beam center shifts to (Δx, Δy), it was originally located at a fixed coordinate. The first For each polarization sensor, its actual radial distance to the center of the beam will become:

[0085]

[0086] This distance is the fixed radial distance from the sensor to the geometric center. difference Multiplying this by the polarization modulation coefficient k gives the theoretical deviation value that is linearly mapped to the polarization angle. .

[0087] The theoretical functional relationship is a continuous and differentiable function with respect to (Δx,Δy) and has good local linearity in the neighborhood of (Δx,Δy)=(0,0), which enables the subsequent iterative optimization algorithm to converge quickly and stably.

[0088] Step 3: Based on the nonlinear functional relationship, construct a nonlinear error function with the offset coordinate as the optimization variable. This function is for all... The sum of squares of the deviations of the polarization sensors is expressed as:

[0089]

[0090] Specifically, the offset calculation unit will use the measured detection deviation value obtained in step 1. The theoretical functional relationship established in step 2 By combining these methods, the aforementioned nonlinear error function can be constructed.

[0091] Where N is the total number of polarization sensors, and in this embodiment N=8.

[0092] The mathematical structure of this function is the sum of squares of the differences between the eight sensor detection deviation values ​​and the theoretical deviation values. Its physical meaning is as follows: For any set of guessed offset coordinates (Δx, Δy), we can substitute them into the theoretical function relationship from step 2 to calculate the theoretical polarization angle deviation values ​​that "should" appear at the positions of the eight sensors under the current guessed values. These theoretical values ​​are compared with the eight detection deviation values ​​obtained from the actual measurements in step 1. By subtracting each residual, eight residuals are obtained; each residual is squared (to eliminate the influence of the sign and amplify the weight of larger deviations), and then summed to obtain a non-negative scalar. .

[0093] scalar The size quantitatively characterizes the current guess value The degree of agreement with the actual physical state: if If the theoretical deviation is exactly equal to the actual beam offset, then the theoretical deviation value and the measured deviation value should be highly consistent. Approaching zero; if The greater the deviation from the true value, the greater the difference between the theoretical and measured deviation values. The value of also increases significantly.

[0094] Thus, the offset calculation unit transforms the physical measurement problem of "finding the true position of the beam" into a mathematically rigorous unconstrained nonlinear least squares optimization problem, namely, finding a set of optimal offset coordinates. This makes the aforementioned nonlinear error function Obtain the global minimum value.

[0095] The optimal solution to this mathematical problem This is the optimal estimate of the true offset of the laser beam center relative to the geometric center of the annular polarization sensor array 300, and it is also the calculation result that this device finally outputs to the visualization output unit.

[0096] Step 4: Solve the function using an iterative optimization algorithm. The minimum value, and the corresponding offset coordinate. The output is the offset of the laser beam center relative to the geometric center of the annular polarization sensor array.

[0097] In this embodiment, the iterative optimization algorithm is the Gauss-Newton iteration method: at the current iteration point, the nonlinear function is locally linearized to approximate it, a linear least squares subproblem is solved to obtain the descent direction, and the true optimal solution is approximated through iteration.

[0098] The iterative steps include: calculating the residual vector and Jacobian matrix based on the current offset coordinate guess; solving a system of linear equations to update the offset coordinates; and determining whether the updated offset coordinate changes satisfy the convergence condition. Each element of the residual vector corresponds to the difference between the detection deviation value of a polarization sensor and the theoretical deviation value calculated based on the current offset coordinate guess; the Jacobian matrix is ​​based on a nonlinear function relationship. The partial derivatives with respect to the offset coordinates are constructed; the system of linear equations is obtained by minimizing the residual vector under a locally linear model defined by the Jacobian matrix. Specifically, this includes the following steps.

[0099] Step 4.1, Initialization.

[0100] Set the initial offset guess value This initial value corresponds to the ideal state of "assuming the beam is already centered," and is the most reasonable choice when there is no prior information.

[0101] The convergence accuracy threshold ε is set to 0.001 mm. The physical meaning of this threshold is: when the Euclidean distance between the solution results of two consecutive iterations on the two-dimensional plane is less than 1 micrometer, the algorithm is considered to have converged to the vicinity of the true solution, and the accuracy improvement brought by further iterations has no engineering significance.

[0102] The maximum number of iterations is set to 20. This limit is used to prevent the algorithm from getting stuck in an infinite loop due to abnormal measurement data, model mismatch, or ill-conditioned numerical values, thus ensuring the real-time performance and robustness of the system.

[0103] Step 4.2, Calculation of residual vector and Jacobian matrix.

[0104] In the In the next iteration, the value is guessed based on the current offset coordinate. Calculate the residual vector and Jacobian matrix.

[0105] residual vector : The first of the vectors The element is the first The difference between the detection deviation value of each sensor and the theoretical deviation value under the current guess value, i.e.:

[0106]

[0107] Each component of the residual vector This directly reflects the current iteration step, the... The degree of deviation between the measured values ​​of a sensor and the predicted values ​​of the theoretical model. It is the object that the entire optimization process attempts to gradually compress down to zero.

[0108] Jacobian matrix The first digit of this matrix The row element is the residual vector. The first-order partial derivatives of each component with respect to the optimization variables (Δx, Δy). Based on the theoretical functional relationship established in step 2. These partial derivatives have the following analytical expression:

[0109]

[0110] The Jacobian matrix The physical meaning is: it describes the current iteration point. Nearby, how will the theoretical deviation values ​​of the eight sensors change when the offset coordinates change slightly? It is an 8×2 matrix, with each row corresponding to one sensor and the two columns corresponding to the sensitivity of Δx and Δy, respectively.

[0111] Step 4.3: Solve the system of linear equations to obtain the update direction.

[0112] The core of the Gauss-Newton method is to solve the following normal equation to obtain the offset correction direction for the current iteration step:

[0113]

[0114] in, It is a column vector representing the amount of correction to be applied to the current offset coordinate guess in this iteration.

[0115] The derivation of this system of linear equations is as follows: At the current iteration point Nearby, the nonlinear residual function Perform a first-order Taylor expansion Substitute into the error function Setting its derivative with respect to (Δx, Δy) to zero, we obtain the above expression. It is a solution to the linear least squares problem, guaranteeing... It is the direction in which the error function decreases the fastest after local linearization approximation.

[0116] because It is a 2×2 symmetric positive definite matrix (under full rank condition), and the system of equations is small in size. The offset calculation unit uses analytical inversion or Cholesky decomposition, which can be solved in microseconds.

[0117] Step 4.4, update the offset coordinate guess values.

[0118] The correction amount obtained in step 4.3 Add this to the current estimated offset coordinate to obtain the updated offset coordinate:

[0119]

[0120] This update operation combines the information from the current iteration point with the calculated optimal descent direction, resulting in a new guess value. Compared to the old value A closer approximation of the actual offset.

[0121] Step 4.5, convergence judgment.

[0122] Calculate the change in Euclidean distance of the offset coordinates before and after this iteration update:

[0123]

[0124] Compare the change with the preset convergence accuracy threshold Compare them.

[0125] like The algorithm is considered to have converged to a stable solution, and the iterative process has successfully terminated. Output: This serves as the final result of the beam offset calculation.

[0126] like If the current iteration count is less than the maximum iteration count: the algorithm is considered not to have converged yet, the iteration counter is incremented by 1, and the process returns to step 4.2 to guess the value based on the new offset coordinates. Continue iterating.

[0127] like If the current iteration count equals the maximum iteration count, the algorithm is considered to have failed to converge within the preset maximum iteration count. At this point, the current offset coordinate value is output. The system log will record a warning message "Algorithm not converged" to prompt operators to check the sensor connection status or whether the laser output is normal.

[0128] Once the algorithm converges, the offset calculation unit will provide the optimal solution. As the real-time offset of the laser beam center relative to the geometric center of the annular polarization sensor array 300, it is transmitted to the visualization output unit via the internal data bus.

[0129] This offset is a two-dimensional coordinate vector, which:

[0130] The value indicates that the center of the beam is in the horizontal direction (corresponding to the sensor azimuth angle). (Direction) Distance from the geometric center; positive values ​​indicate deviation to the right, and negative values ​​indicate deviation to the left.

[0131] The value indicates that the center of the beam is in the vertical direction (corresponding to the sensor azimuth angle). (Direction) Distance from the geometric center; positive values ​​indicate upward deviation, and negative values ​​indicate downward deviation.

[0132] offset modulus This indicates the total distance from the center of the beam to the geometric center, in millimeters, accurate to 0.001 mm.

[0133] The foregoing has described in detail an embodiment of a coaxial calibration device for a laser cutting machine optical path. Based on the coaxial calibration device for a laser cutting machine optical path described in the above embodiment, this invention also provides a coaxial calibration method for a laser cutting machine optical path corresponding to the device.

[0134] Figure 4 This is a schematic diagram of a laser cutting machine optical path coaxial calibration method provided by an embodiment of the present invention, as shown below. Figure 4 As shown, the method includes the following steps.

[0135] S1: Install the calibration module body of the calibration device onto the laser cutting head through its mechanical interface.

[0136] The operator first unscrews the original working nozzle on the laser cutting machine head, then takes the calibration device of this invention, aligns the external thread of its mechanical interface 130 with the threaded hole of the nozzle mounting seat on the cutting head, manually screws it in and tightens it appropriately until the top of the calibration module body 100 is tightly fitted with the positioning end face of the nozzle mounting seat. After installation, the optical path channel of the calibration module body 100 automatically remains collinear with the light output axis of the cutting head, and the geometric center line of the annular polarization sensor array 300 represents the theoretical axis position of the nozzle to be calibrated.

[0137] S2: Activate the low-power output mode of the laser cutting machine, allowing the laser to pass sequentially through the radial polarization modulation module and the annular polarization sensor array.

[0138] Turn on the low-power light output mode of the laser cutting machine, so that the laser passes through the radial polarization light modulation module 200 and the annular polarization sensor array 300 in sequence.

[0139] The operator switches the laser output mode to "spot firing" or "calibration" mode via the control panel or handheld control box of the laser cutting machine, and sets the output power to a low power state of 1% to 5% of the rated power. After confirming that the settings are correct, the laser output is triggered. The laser beam is emitted from the output port of the cutting head and enters the optical path channel of the calibration module body 100 vertically. It first passes through the radial polarization light modulation module 200 and is modulated into radial polarized light; then it continues to propagate downwards, passing through the detection area enclosed by the annular polarization sensor array 300.

[0140] S3: Through each polarization sensor in the ring polarization sensor array, the actual polarization angle of the radially polarized light at its respective location is detected synchronously, and the polarization angle signal is output.

[0141] The actual polarization angle of radially polarized light at its respective location is synchronously detected by each polarization sensor 310 in the annular polarization sensor array 300, and the polarization angle signal is output.

[0142] When the modulated radially polarized light passes through the annular polarization sensor array 300, eight polarization sensors 310 evenly distributed along the circumference simultaneously detect it. Each polarization sensor 310, based on its internally integrated polarization filter and photoelectric detection unit, measures the vibration direction angle of the incident light at its location in real time and outputs the polarization angle signal in the form of an analog voltage signal or a digital signal. The output signals of all sensors are transmitted in real time to the data processing and display module through an external electrical interface and transmission cables.

[0143] S4: The data processing and display module calculates the offset of the laser beam center relative to the geometric center of the annular polarization sensor array based on each polarization angle signal.

[0144] The data processing and display module calculates the offset of the laser beam center relative to the geometric center of the annular polarization sensor array based on each polarization angle signal.

[0145] The data processing and display module receives polarization angle signals from eight polarization sensors in real time and calls the internally preset offset calculation unit to execute relevant algorithms. For details of the calculation process, please refer to the embodiment of the coaxial calibration device for the optical path of the laser cutting machine, which will not be repeated here.

[0146] S5: Visualize the offset to guide the user in adjusting the optical path and completing the optical path coaxial calibration.

[0147] The offset is visualized to guide the user in adjusting the optical path and completing the optical path coaxial calibration.

[0148] The visualization output unit of the data processing and display module converts the offset (Δx, Δy) calculated in step S4 into a graphical interface for display. This interface is presented in a two-dimensional coordinate system, with the origin corresponding to the geometric center of the ring polarization sensor array. The position of the current laser beam center is drawn in real time using a bright spot marker. The interface also displays the specific values ​​of Δx and Δy in numerical form and indicates the direction requiring adjustment with arrows.

[0149] The operator observes the position markers and adjustment direction indicators on the screen, and uses a special tool to slightly rotate the reflector adjustment knob on the cutting head, following the sequence of "X-direction adjustment nut—Y-direction adjustment nut." During the adjustment process, the light spot markers on the screen move synchronously, providing real-time feedback. The operator continues to adjust based on the feedback until the light spot markers enter the target area.

[0150] After calibration, the operator turns off the laser beam, removes the calibration device from the cutting head, and reinstalls the actual working nozzle to continue normal laser cutting operations.

[0151] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A coaxial calibration device for the optical path of a laser cutting machine, characterized in that, include: The calibration module body is equipped with a mechanical interface for mounting to the laser cutting machine head; Radial polarization modulation module: Fixedly installed inside the calibration module, used to receive the laser emitted by the cutting head and modulate it into radial polarization light; Circular polarization sensor array: Fixedly installed within the calibration module body and located downstream of the radial polarization light modulation module, it contains multiple polarization sensors evenly distributed along the circumference. The detection surface of each polarization sensor is located on the inner wall of the array, used to receive radial polarized light to detect the polarization angle of the laser at its respective orientation, and output the corresponding polarization angle signal; when the calibration module body is installed on the cutting head, the geometric center of the circular polarization sensor array represents the theoretical axis position of the nozzle to be calibrated. Data processing and display module: It communicates with each polarization sensor to calculate the offset of the laser beam center relative to the geometric center of the ring polarization sensor array based on each polarization angle signal, and visualizes the offset. The data processing and display module includes: Offset calculation unit: It is configured to construct a nonlinear error function with offset coordinates as variables based on each polarization angle signal and the theoretical polarization angle when the center of the laser beam coincides with the geometric center of the ring polarization sensor array, and use an iterative optimization algorithm to solve the function to obtain the offset; Visualization output unit: Configured to convert the solved offsets into a graphical interface for display; Specifically, a nonlinear error function with offset coordinates as variables is constructed, and an iterative optimization algorithm is used to solve this function to obtain the offset. This includes: Based on the The polarization angle signal output by each polarization sensor Calculate the actual detected polarization angle deviation value. ,in This is the theoretical polarization angle when the center of the laser beam coincides with the geometric center of the ring polarization sensor array; The nonlinear functional relationship between the theoretical polarization angle and the offset coordinates is established as follows: in, Indicates the first The theoretical polarization angle deviation of each polarization sensor, The polarization modulation coefficient, This is a fixed radial distance from each polarization sensor to the geometric center of the ring polarization sensor array. For the first The installation azimuth angle of each polarization sensor. The coordinates of the laser beam center to be solved relative to the geometric center of the annular polarization sensor array are the offset coordinates. Based on nonlinear functional relationships, a nonlinear error function is constructed with the offset coordinates as the optimization variable. This function is applicable to all... The sum of squares of the deviations of the polarization sensors is expressed as: The function is solved using an iterative optimization algorithm. The minimum value, and the corresponding offset coordinate. The output is the offset of the laser beam center relative to the geometric center of the annular polarization sensor array.

2. The coaxial calibration device for the optical path of a laser cutting machine according to claim 1, characterized in that, The radial polarization modulation module includes, in sequence along the optical path: 1 / 4 wave plate: used to convert linearly polarized laser light into circularly polarized light; Radial polarization converter: used to receive circularly polarized light and convert it into radially polarized light.

3. The coaxial calibration device for the optical path of a laser cutting machine according to claim 1, characterized in that, The iterative optimization algorithm is the Gauss-Newton iteration method. Its iterative steps include: calculating the residual vector and Jacobian matrix based on the current offset coordinate guess value, solving the linear equation system to update the offset coordinate, and determining whether the updated offset coordinate change satisfies the convergence condition; Each element of the residual vector corresponds to the difference between the detection deviation value of a polarization sensor and the theoretical deviation value calculated based on the guessed value of the current offset coordinates; Jacobian matrices are based on nonlinear functional relationships Constructing the partial derivatives with respect to the offset coordinates; The linear equations are obtained by minimizing the residual vector under a locally linear model defined by the Jacobian matrix.

4. The coaxial calibration device for the optical path of a laser cutting machine according to claim 1 or 2, characterized in that, The mechanical interface of the calibration module body coincides with the geometric center line of the ring polarization sensor array.

5. The coaxial calibration device for the optical path of a laser cutting machine according to claim 1 or 2, characterized in that, The ring polarization sensor array consists of eight polarization sensors, which are distributed at 45° intervals along the circumference.

6. The coaxial calibration device for the optical path of a laser cutting machine according to claim 1 or 2, characterized in that, The calibration module body is equipped with an external electrical interface, and each polarization sensor of the ring polarization sensor array is electrically connected to the data processing and display module through the external electrical interface.

7. The coaxial calibration device for the optical path of a laser cutting machine according to claim 1 or 2, characterized in that, The mechanical interface is a threaded interface that is consistent with the nozzle mounting interface of the laser cutting machine cutting head.

8. A method for coaxial calibration of the optical path of a laser cutting machine, characterized in that, This method is implemented based on the apparatus described in any one of claims 1 to 7. Includes the following steps: S1: Install the calibration module body of the calibration device onto the laser cutting machine head through its mechanical interface; S2: Turn on the low-power light output mode of the laser cutting machine, so that the laser passes through the radial polarization light modulation module and the ring polarization sensor array in sequence; S3: Through each polarization sensor in the ring polarization sensor array, the actual polarization angle of the radially polarized light at its respective location is detected synchronously, and the polarization angle signal is output. S4: The data processing and display module calculates the offset of the laser beam center relative to the geometric center of the annular polarization sensor array based on each polarization angle signal; S5: Visualize the offset to guide the user in adjusting the optical path and completing the optical path coaxial calibration.

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