A machine tool thermal error laser real-time monitoring method

Abstract

This invention discloses a real-time laser monitoring method for machine tool thermal errors, belonging to the field of precision measurement technology. The method involves real-time acquisition of orthogonal signals from a laser interferometer, the spot position of a four-quadrant detector, the reflected light intensity of a multi-wavelength photodetector, and the laser temperature. The original displacement is calculated using the orthogonal signals. Based on the spot offset and laser temperature, a dynamic correction model is used to obtain the beam drift correction amount. Based on the multi-wavelength reflected light intensity ratio, an additional optical path error correction model is used to obtain the oil film thickness correction amount. Furthermore, a coupling-decoupling algorithm is used to separate and obtain the two independent true correction amounts. Finally, the original displacement is subtracted from these two true correction amounts to obtain the compensated true thermal error displacement. This invention achieves real-time, high-precision comprehensive compensation for two main thermal error factors: laser beam pointing drift and guide rail oil film changes, significantly improving the monitoring accuracy of machine tool thermal errors.

Description

Technical Field

[0001] This invention belongs to the field of precision measurement technology, and in particular relates to a method for real-time laser monitoring of machine tool thermal errors. Background Technology

[0002] In the field of precision and ultra-precision machining, thermal deformation of machine tools is one of the main factors affecting machining accuracy. Laser interferometers are widely used for measuring the thermal error of machine tools due to their advantages such as high precision and non-contact operation.

[0003] Currently, the common method for monitoring thermal errors using laser interferometers typically relies on displacement data obtained through laser interferometry, combined with temperature sensor data placed at key points on the machine tool. Empirical models (such as multiple linear regression or neural networks) are then established to predict and compensate for thermal errors. However, these methods primarily focus on the thermal expansion effects of machine tool structural components, and their accuracy is highly dependent on the accuracy of the model and the placement of the sensors.

[0004] Existing technologies have significant shortcomings in handling the measurement errors inherent in laser interferometers. The measurement accuracy of laser interferometers is significantly affected by laser beam pointing drift and fluctuations in the thickness of the oil film on the machine tool guideways. Existing methods either ignore these factors or only perform separate, static corrections, failing to consider the mutual coupling interference between these two factors during actual monitoring. As a result, even in applications requiring high precision, the accuracy of thermal error monitoring remains difficult to guarantee. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a real-time laser monitoring method for machine tool thermal errors, which solves the aforementioned problems.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for real-time laser monitoring of machine tool thermal errors, comprising: S1. Real-time acquisition of the orthogonal signal output by the laser interferometer, the spot position offset output by the four-quadrant detector, the reflected light intensity of at least two wavelengths output by the multi-wavelength oil film monitoring photodetector, and the laser cavity temperature output by the laser temperature sensor. S2. Calculate the interference phase based on the orthogonal signal, and obtain the original displacement by accumulating the phase increments; S3. Based on the spot position offset and the laser cavity temperature, obtain the beam drift correction amount introduced by the laser beam pointing drift through the dynamic correction model. S4. Based on the ratio of the reflected light intensity of multiple wavelengths, the oil film thickness correction amount introduced by the guide rail oil film thickness fluctuation is obtained through the additional optical path error correction model. S5. By using a coupling-decoupling algorithm, the mutual interference between the beam drift correction and the oil film thickness correction is separated, and the true correction values ​​of the two after decoupling are obtained. S6. Subtract the decoupled beam drift correction and oil film thickness correction from the original displacement to obtain the compensated true thermal error displacement.

[0007] Based on the above technical solutions, the present invention also provides the following optional technical solutions: Further technical solution: Step S2 specifically includes: according to Obtain the in-phase and quadrature components of the quadrature signal at time t, and acquire them. Interference phase at time ; Obtain the phase difference between adjacent sampling times ,in The sampling time interval; The original displacement is obtained by accumulating the phase differences. ,in is the laser wavelength.

[0008] Further technical solution: In step S3, the dynamic correction model is represented as:

[0009] in, for Time-based beam drift correction amount , They are respectively The light spot at all times direction and Position offset in direction and They are respectively time direction and Dynamic adaptive correction coefficient for direction.

[0010] Further technical solutions: based on The laser cavity temperature at all times and Accumulated working time of the laser at all times, obtain time Dynamic adaptive correction coefficients for direction and The dynamic adaptive correction coefficient for direction is expressed as:

[0011]

[0012] in, express time Dynamic adaptive correction coefficient for direction. express The basic correction factor for direction. express The laser cavity temperature is constantly monitored. Indicates reference temperature. express The cumulative working time of the laser at all times. Indicates reference time. express The basic correction factor for direction. express Temperature influence coefficient of direction, express Temperature influence coefficient of direction, express The time aging factor of the direction, express The time aging factor of the direction.

[0013] Further technical solution: In step S4, the method for obtaining the oil film thickness correction amount is as follows: based on The intensity of reflected light at the first and second wavelengths at time points is obtained. The ratio of the reflected light intensity of the two wavelengths at a given moment; Based on the first wavelength and the second wavelength of the laser, and The ratio of the reflected light intensity of the two wavelengths at time t is obtained. Oil film thickness at all times; based on The oil film thickness at any given time is determined by obtaining the oil film thickness correction amount introduced by the guide rail oil film thickness fluctuation through an additional optical path error correction model. This additional optical path error correction model is expressed as follows:

[0014] in, express Oil film thickness correction amount at all times. Indicates the refractive index of lubricating oil. express Oil film thickness at all times This indicates the initial oil film thickness.

[0015] Further technical solutions: The ratio of the reflected light intensity at two wavelengths at time t is expressed as:

[0016] in, express The ratio of the reflected light intensity of the two wavelengths at time 1. express The first wavelength at time, express The second wavelength at that moment.

[0017] Further technical solutions: The thickness of the oil film at any given time is expressed as:

[0018] in, express Oil film thickness at all times , These are the laser wavelengths of the first and second wavelengths, respectively. express The ratio of the reflected light intensity of the two wavelengths at time 1. , These are the pre-calibrated maximum and minimum light intensity ratio values, respectively.

[0019] Further technical solution: The coupling and decoupling algorithm in step S5 specifically includes: Establish the coupling coefficient matrix , This represents the cross-interference coefficient of beam drift on oil film measurement. This represents the cross-interference coefficient between oil film changes and beam drift measurements; The correction amount after decoupling is obtained by inverting the matrix:

[0020] in, , They are respectively The actual correction amounts for beam drift and oil film thickness after time-decoupling. for Time-based beam drift correction amount express Oil film thickness correction amount at all times. This represents the cross-interference coefficient of beam drift on oil film measurement. This represents the cross-interference coefficient between oil film changes and beam drift measurements.

[0021] A further technical solution: The actual thermal error displacement in step S6 is expressed as:

[0022] in, express The actual thermal error displacement after time-compensation. Indicates the original displacement. express The actual correction amount of beam drift after decoupling at any moment. express The actual correction amount of oil film thickness after decoupling at any time.

[0023] This invention provides a method for real-time laser monitoring of machine tool thermal errors, which has the following advantages compared with the prior art: 1. This invention incorporates two key but often overlooked sources of thermal error—laser beam pointing drift and guide rail oil film thickness fluctuation—into a real-time monitoring and correction system. By collecting multiple physical quantities, it achieves a more comprehensive and fundamental perception and compensation for machine tool thermal errors, breaking through the limitations of traditional methods that only compensate for structural thermal expansion.

[0024] 2. By introducing a dynamic correction model, this invention adjusts the correction coefficient in real time according to the laser temperature and cumulative working time, which can effectively track the nonlinear characteristics of beam drift caused by laser aging and temperature rise. At the same time, based on the ratio of multi-wavelength reflected light intensity, the oil film thickness is accurately inverted, and the additional optical path error introduced by the thermal fluctuation of the oil film is accurately quantified.

[0025] 3. This invention can effectively separate the mutual interference between beam drift and oil film thickness change in measurement through the coupling and decoupling algorithm, eliminating the influence of the coupling between the two on the correction accuracy, so that the final true correction amount of beam drift and oil film thickness are more accurate, significantly improving the compensation effect of the final thermal error displacement and the reliability of the monitoring data. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0029] Please see Figure 1 The present invention provides a method for real-time laser monitoring of machine tool thermal errors, comprising: S1. Real-time acquisition of the orthogonal signal output by the laser interferometer, the spot position offset output by the four-quadrant detector, the reflected light intensity of at least two wavelengths output by the multi-wavelength oil film monitoring photodetector, and the laser cavity temperature output by the laser temperature sensor. S2. Calculate the interference phase based on the orthogonal signal, and obtain the original displacement by accumulating the phase increments; S3. Based on the spot position offset and the laser cavity temperature, obtain the beam drift correction amount introduced by the laser beam pointing drift through the dynamic correction model. S4. Based on the ratio of the reflected light intensity of multiple wavelengths, the oil film thickness correction amount introduced by the guide rail oil film thickness fluctuation is obtained through the additional optical path error correction model. S5. By using a coupling-decoupling algorithm, the mutual interference between the beam drift correction and the oil film thickness correction is separated, and the true correction values ​​of the two after decoupling are obtained. S6. Subtract the decoupled beam drift correction and oil film thickness correction from the original displacement to obtain the compensated true thermal error displacement:

[0030] in, express The actual thermal error displacement after time-compensation. Indicates the original displacement. express The actual correction amount of beam drift after decoupling at any moment. express The actual correction amount of oil film thickness after decoupling at any time.

[0031] The method in this embodiment enables real-time, high-precision monitoring of machine tool thermal errors. Various technical features work closely together to collect data from multiple dimensions, dynamically correct errors, and innovatively solve the coupling interference problem between error sources. Ultimately, it outputs more reliable thermal error displacement data, providing crucial support for the precision machining of machine tools.

[0032] In existing technologies, only the thermal expansion effect of machine tool structural components is typically considered, and prediction and compensation are performed using empirical models. However, the measurement errors inherent in laser interferometers, particularly laser beam pointing drift and guide rail oil film thickness fluctuations, have a significant impact on high-precision measurements. Existing methods either ignore these factors or only perform individual, static corrections.

[0033] The method in this embodiment, through real-time acquisition of multi-source data in step S1, provides a comprehensive data foundation for subsequent refined error correction. Unlike existing technologies that may only acquire temperature or single displacement data, this embodiment simultaneously acquires the spot position offset, multi-wavelength reflected light intensity, and laser cavity temperature, making it possible to identify and quantify multiple error sources.

[0034] Furthermore, steps S3 and S4 dynamically correct the errors introduced by laser beam pointing drift and guide rail oil film thickness fluctuation, respectively. For example, in the prior art, beam drift correction may use fixed empirical values, which cannot adapt to the performance changes of the laser under different operating conditions. However, the dynamic correction model of this embodiment can dynamically adjust the correction coefficient according to real-time parameters such as laser cavity temperature and cumulative operating time, so that the beam drift correction amount is closer to the actual situation. Similarly, for oil film thickness, the prior art may only estimate based on a single wavelength or static assumptions, while this embodiment achieves more accurate quantification of oil film thickness fluctuation through multi-wavelength reflected light intensity ratio and additional optical path error correction model, thereby obtaining a more accurate oil film thickness correction amount.

[0035] Crucially, this embodiment introduces a coupling-decoupling algorithm in step S5. The mutual interference between beam drift and oil film thickness fluctuation is a problem that is generally overlooked or not effectively addressed in existing technologies. Existing methods often treat these error sources as independent when making corrections, resulting in residual errors in the corrected results. This embodiment effectively separates these mutual interferences by establishing a coupling coefficient matrix and performing matrix inversion, thereby obtaining their respective independent true correction values. This innovative approach significantly improves the accuracy and reliability of error correction, avoiding repeated corrections or insufficient corrections caused by the mutual influence of error sources.

[0036] Finally, in step S6, the original displacement is subtracted from the decoupled beam drift correction and oil film thickness correction to obtain the compensated true thermal error displacement. Compared with existing technologies that only compensate for structural thermal expansion or correct a single error source, this embodiment provides a more comprehensive and accurate thermal error monitoring result. This method not only considers the thermal deformation of the machine tool structure but also deeply addresses the problem of correcting the measurement error of the laser interferometer itself. In particular, through coupling and decoupling processing, it ensures the accuracy of thermal error monitoring in high-precision machining environments, thus providing solid technical support for improving machine tool machining accuracy.

[0037] Preferably, step S2 specifically includes: according to Obtain the in-phase and quadrature components of the quadrature signal at time t, and acquire them. Interference phase at time ; Obtain the phase difference between adjacent sampling times ,in The sampling time interval; The original displacement is obtained by accumulating the phase differences. ,in is the laser wavelength.

[0038] Among them, according to In-phase components of quadrature signals at time 1 and orthogonal components , obtain Interference phase at time This step clarifies the method for calculating the interference phase. Laser interferometers typically output two orthogonal signals, i.e., in-phase components. and orthogonal components There is a 90-degree phase difference between these two signals. The current interference phase can be accurately calculated from these two signals using the arctangent function. This phase value directly reflects the change in optical path and is the basis for displacement measurement. This process can be performed in real-time by a digital signal processor (DSP) or microcontroller (MCU), or by pre-calculating and storing a table of arctangent function values, and then quickly obtaining the phase value during runtime through a table lookup, thus improving computational efficiency.

[0039] Obtain the phase difference between adjacent sampling times ,in The sampling time interval represents the change in the interference phase between two consecutive sampling moments. Since the interference phase is periodic, directly accumulating the phase values ​​can lead to a "jump" problem. Calculating the phase difference can avoid this jump, ensuring the continuity and accuracy of the displacement accumulation. This phase difference can be achieved by subtracting the current phase value from the previously stored phase value in the data processing unit, or in some high-speed systems, by using hardware logic circuits to compare the phase values ​​of adjacent moments and output their difference.

[0040] The original displacement is obtained by accumulating the phase differences. ,in The formula, where λ is the laser wavelength, is the core of laser interferometry for converting phase changes into actual displacement. The principle of a laser interferometer is based on the interference phenomenon of light waves. When the optical path length of the measuring arm changes, the interference fringes shift, causing a change in the interference phase. The total displacement is obtained by multiplying the accumulated phase difference by a scaling factor related to the laser wavelength. This accumulation process can be achieved by setting an accumulator in a digital signal processor or microcontroller, continuously adding the displacement increment calculated at each sampling interval to the original displacement value from the previous moment. Since floating-point numbers are involved, a floating-point arithmetic unit is typically used for precise calculations.

[0041] The solution in this application utilizes the real-time orthogonal signals output by the laser interferometer, i.e., the in-phase components. and orthogonal components As input, the interference phase at the current moment is first accurately calculated using the arctangent function. This calculation method fully utilizes the phase information of orthogonal signals, providing continuous and high-resolution phase values, effectively avoiding the quantization errors and direction discrimination uncertainties that may exist in traditional counting methods. Subsequently, the phase difference between adjacent sampling times is obtained. This step ensures the continuity of phase changes, avoiding jumps caused by phase periodicity, thus providing a stable increment for subsequent displacement accumulation. Finally, these continuous phase differences are multiplied by a factor equal to the laser wavelength. Relevant proportional coefficients The displacements are then accumulated to obtain the machine tool's original displacement in real time and accurately. This series of steps forms a complete displacement calculation chain with a well-defined mathematical model, providing an accurate and reliable displacement reference for subsequent thermal error correction, and effectively solving the technical challenge of accurately and continuously obtaining displacement information from the original interference signal.

[0042] As a specific implementation method, in the real-time laser monitoring of machine tool thermal errors, a He-Ne laser with a wavelength of 632.8 nm can be used as the light source for the laser interferometer. The system uses a sampling time interval of 1 millisecond. Data acquisition is performed. At each sampling time... The data processing unit receives the in-phase component output by the laser interferometer. and orthogonal components The voltage signal. For example, if at a certain moment... Collected It is 0.5V. If the voltage is 0.866V, then the interference phase at the current moment is approximately... Radius. If at the immediately preceding sampling time... The calculated interference phase If the phase difference is 0 radians, then the phase difference between adjacent sampling times is... for In radians. At this point, according to the formula, the increment of the original displacement is calculated to be 52.73 nanometers. This increment will be added to the original displacement of the previous moment. This allows for real-time updates and the acquisition of the original displacement at the current moment. .

[0043] Through the above technical solution, this application provides a clear and high-precision method for interferometric phase calculation and displacement accumulation. This method directly extracts the phase from orthogonal signals using the arctangent function, effectively avoiding counting errors and direction discrimination problems that may occur in traditional methods, ensuring the continuity and accuracy of phase information. By calculating and accumulating the phase difference between adjacent sampling times, the phase change can be stably converted into the actual original displacement, thus providing a more accurate and reliable displacement reference for subsequent thermal error correction. This significantly improves the accuracy and robustness of real-time laser monitoring of machine tool thermal errors, providing a solid data foundation for machine tool machining accuracy.

[0044] Preferably, in step S3, the dynamic correction model is represented as:

[0045] in, for Time-based beam drift correction amount , They are respectively The light spot at all times direction and Position offset in direction and They are respectively time direction and Dynamic adaptive correction coefficient for direction; time The dynamic adaptive correction coefficient for direction is obtained as follows: based on The laser cavity temperature at all times and Accumulated working time of the laser at all times, obtain time Dynamic adaptive correction coefficients for direction and The dynamic adaptive correction coefficient for direction is expressed as:

[0046]

[0047] in, express time Dynamic adaptive correction coefficient for direction. express The basic correction factor for direction. express The laser cavity temperature is constantly monitored. Indicates reference temperature. express The cumulative working time of the laser at all times. Indicates reference time. express The basic correction factor for direction. express Temperature influence coefficient of direction, express Temperature influence coefficient of direction, express The time aging factor of the direction, express The time aging factor of the direction.

[0048] This dynamic correction model is used to calculate the beam drift correction amount introduced by laser beam pointing drift. It combines the positional offsets of the light spot in the x and y directions. , and dynamic adaptive correction coefficient , To quantify the impact of beam drift on measurement results, this model can dynamically adjust the correction amount based on the real-time monitored spot position shift, thereby more accurately compensating for the error caused by laser beam pointing drift. This can be achieved by using a pre-established mathematical function relationship or by training historical data through machine learning algorithms to predict and correct beam drift. , These two coefficients are key parameters in the dynamic correction model. They reflect the proportional relationship between the spot position offset and the actual beam drift correction, and can adaptively adjust according to the external environment and the laser's own state. The dynamic nature of these coefficients allows the correction model to better adapt to the constantly changing conditions during machine tool operation. These coefficients can be obtained by real-time monitoring of the laser cavity temperature. Cumulative working time of laser And combined with the preset temperature influence coefficient , and time aging coefficient , Calculations can be performed; alternatively, iterative optimization can be achieved through online calibration or self-learning algorithms, based on actual measurement data and known errors, or by assigning values ​​based on expert experience. Laser cavity temperature. It is an important environmental parameter affecting the stability of the laser output beam. Changes in the internal temperature of the laser can cause slight changes in the optical properties of the laser resonator, such as its size and refractive index, which in turn can cause laser beam drift. Real-time monitoring of the laser cavity temperature is crucial. It can provide crucial temperature-related information for calculating dynamic correction coefficients, thereby enabling adaptive correction based on temperature changes. This temperature can be measured in real time using a temperature sensor built into the laser cavity, or through non-contact temperature monitoring of the laser casing using an infrared thermal imager. (Laser cumulative operating time) It is an important indicator for measuring the aging degree of a laser. After a long period of operation, the internal optical components and electronic devices of a laser may age, which will cause the pointing stability of the laser beam to gradually decrease. Incorporating this into the calculation of the dynamic correction coefficient can make the correction model take into account the performance degradation caused by the long-term operation of the laser, thereby realizing adaptive correction based on time aging. This duration can be accumulated and recorded by the timing module inside the laser, or the operating time of the laser can be statistically analyzed by the system software. , These two coefficients represent the conditions under ideal or reference conditions (e.g., at a reference temperature). and reference time (Below) The basic proportional relationship between the spot position offset and the beam drift correction amount is the reference value for calculating the dynamic correction coefficient, which is usually obtained through initial calibration in a controlled environment. , These coefficients quantify the laser cavity temperature. Deviation from reference temperature The influence of the dynamic adaptive correction coefficients in the x and y directions is measured, which reflects the sensitivity of the laser beam pointing drift to temperature changes. These coefficients can be determined by experimental measurements and data fitting at different temperatures or by expert assignment. , These coefficients quantify the cumulative operating time of the laser. The influence of the dynamic adaptive correction coefficients in the x and y directions reflects the effect of long-term laser aging on the laser beam pointing drift. These coefficients can be determined by conducting long-term laser operation tests and recording its performance changes, or by gradually assigning values ​​based on experience.

[0049] The solution in this application introduces a dynamic correction model in step S3 to obtain the beam drift correction amount introduced by laser beam pointing drift. The core of this dynamic correction model is that it does not rely solely on the real-time acquired spot position offset. and More importantly, a dynamic adaptive correction coefficient was introduced. and These two coefficients are not fixed values, but rather depend on the laser cavity temperature. Cumulative working time of laser Real-time adjustments are made. Specifically, when the laser cavity temperature... Deviation from reference temperature At that time, temperature influence coefficient , This will make the correction factor , Adjustments are made accordingly to reflect the impact of temperature changes on beam pointing stability. Simultaneously, adjustments are made as the laser's cumulative operating time increases. The increase in time aging coefficient , This will also prompt the correction factor , Adjustments are made to compensate for the performance degradation caused by long-term laser operation. In this way, the dynamic correction model can adaptively adjust the beam drift correction amount in real time. This allows the laser beam to more accurately reflect its actual pointing drift under current operating conditions. This dynamic adaptive correction mechanism enables a more precise correction of the beam drift during subsequent error separation and compensation processes, thereby significantly improving the accuracy and robustness of the entire machine tool thermal error monitoring system.

[0050] The following is a specific example. As a concrete implementation method, in the real-time laser monitoring of machine tool thermal errors, a high-precision four-quadrant detector can be used to acquire the real-time positional offset of the laser spot in the x and y directions. and Meanwhile, a highly sensitive thermistor or thermocouple can be installed inside or immediately outside the laser cavity as a laser temperature sensor to monitor the laser cavity temperature in real time. Cumulative operating time of the laser Accumulation and recording can be performed using the system's built-in timer module. During the system initialization phase, a series of calibration experiments can be conducted on the laser in a constant temperature and humidity laboratory environment to determine its performance at the reference temperature. and reference time The basic correction factor , Subsequently, by conducting tests at different temperatures and for different cumulative working durations, and combining this with data fitting methods, the temperature influence coefficient can be accurately determined. , and time aging coefficient , In actual operation, these parameters are loaded into the control system, and the system collects data in real time. , , and At that time, the control system will operate according to a preset mathematical model, i.e. and The current dynamic adaptive correction coefficient is calculated in real time. and Then, these dynamic coefficients are substituted into the dynamic correction model. Thus, the beam drift correction amount at the current moment is obtained. .

[0051] Through the above technical solution, this application can achieve more accurate and real-time dynamic correction of errors introduced by laser beam pointing drift. By considering the influence of laser cavity temperature and cumulative operating time on beam pointing stability, the calculated beam drift correction amount can better adapt to the actual working conditions of the machine tool under different environmental conditions and operating cycles. This avoids the problems of insufficient or over-correction that may occur with traditional fixed correction coefficients, thereby improving the accuracy of beam drift correction. Ultimately, this helps to obtain more realistic and reliable machine tool thermal error displacement in subsequent error separation and compensation stages, significantly improving the machining accuracy of the machine tool and the overall performance of the measurement system.

[0052] Preferably, in step S4, the oil film thickness correction amount is obtained as follows: based on The intensity of reflected light at the first and second wavelengths at time points is obtained. The ratio of the reflected light intensity at two wavelengths at a given time is as follows:

[0053] in, express The ratio of the reflected light intensity of the two wavelengths at time 1. express The first wavelength at time, express The second wavelength at time; Based on the first wavelength and the second wavelength of the laser, and The ratio of the reflected light intensity of the two wavelengths at time t is obtained. The oil film thickness at any given time is as follows:

[0054] in, express Oil film thickness at all times , These are the laser wavelengths of the first and second wavelengths, respectively. express The ratio of the reflected light intensity of the two wavelengths at time 1. , These are the pre-calibrated maximum and minimum light intensity ratio values, respectively; based on The oil film thickness at any given time is determined by obtaining the oil film thickness correction amount introduced by the guide rail oil film thickness fluctuation through an additional optical path error correction model. This additional optical path error correction model is expressed as follows:

[0055] in, express Oil film thickness correction amount at all times. Indicates the refractive index of lubricating oil. express Oil film thickness at all times This indicates the initial oil film thickness.

[0056] Among them, the ratio of the reflected light intensity of the two wavelengths is obtained. The aim is to provide fundamental data for calculating oil film thickness by measuring the reflection characteristics of laser light at different wavelengths on the oil film surface. Specifically, a multi-wavelength oil film monitoring photodetector can be used. This detector can simultaneously receive and distinguish at least two different wavelengths of reflected light. For example, two independent narrowband filters and photodiodes can be combined, corresponding to the first and second wavelengths respectively, to accurately measure the intensity of their respective reflected light. Alternatively, a broadband detector combined with a spectral analysis module can be used to separate and measure the intensity of different wavelengths in real time. By calculating the ratio of the reflected light intensities of these two wavelengths, common-mode interference such as light source intensity fluctuations and detector response inhomogeneities can be effectively eliminated, thus more accurately reflecting the physical characteristics of the oil film. Oil film thickness at all times Based on the principle of multi-wavelength interference, the ratio of reflected light intensity is converted into the actual oil film thickness. As a thin film, the thickness of the oil film affects the interference effect of different wavelengths of light, causing the reflected light intensity to exhibit periodic variations. The maximum value of the reflected light intensity ratio under different oil film thicknesses is pre-calibrated. and minimum value By combining the laser wavelength and the refractive index of the lubricating oil, the real-time measured light intensity ratio is... The current oil film thickness $d_{oil}(t)$ is calculated in reverse. The oil film thickness correction amount is obtained by adding an optical path error correction model. The aim is to convert the calculated oil film thickness into a correction factor for the laser optical path. When the laser passes through the oil film, the difference in refractive index between the oil film and air introduces an additional optical path. Fluctuations in the oil film thickness directly lead to changes in the additional optical path, thus affecting the displacement measurement results of the laser interferometer. The additional optical path error correction model uses the real-time oil film thickness... With a preset initial oil film thickness Compare and take into account the refractive index of the lubricating oil. The additional optical path error caused by the change in oil film thickness is calculated. This error is the oil film thickness correction amount that needs to be subtracted from the original displacement to eliminate its impact on measurement accuracy.

[0057] The proposed solution achieves its intended function in the following manner: First, the system acquires the reflected light intensity of the first and second wavelengths in real time. This light intensity data directly reflects the physical state of the oil film. Subsequently, the ratio of the reflected light intensity of these two wavelengths is calculated. This effectively suppresses the effects of common-mode noise such as ambient light variations, light source power fluctuations, and detector drift, allowing the obtained ratio to more accurately characterize the inherent optical properties of the oil film. Next, based on this reflected light intensity ratio... and the preset first wavelength Second wavelength Lubricating oil refractive index The maximum / minimum light intensity ratio obtained from calibration , The system uses a mathematical model based on the principle of thin-film interference to accurately calculate the oil film thickness at the current moment. This process, which converts optical signals into specific physical dimensions, is crucial for quantifying oil film errors. Finally, the real-time calculated oil film thickness is... Substituting the values ​​into the additional optical path error correction model, which takes into account the refractive index of the lubricating oil... And a reference initial oil film thickness By comparing the current oil film thickness with the initial oil film thickness and multiplying by a coefficient related to the refractive index, the additional optical path error caused by fluctuations in oil film thickness can be accurately calculated. This correction directly reflects the degree of interference of the oil film on the laser optical path. Through the above steps, the scheme of this application can convert multi-wavelength reflected light intensity signals into accurate oil film thickness correction amounts. This, together with the beam drift correction in the above method, allows the original displacement measurement results to simultaneously eliminate errors caused by beam pointing drift and oil film thickness fluctuations, thereby significantly improving the accuracy and reliability of machine tool thermal error monitoring. This refined oil film error quantification mechanism compensates for the shortcomings of traditional methods in insufficiently considering the influence of the oil film, providing a more accurate input for subsequent decoupling and the final acquisition of the true thermal error displacement.

[0058] The following is a concrete example. To obtain the ratio of reflected light intensity between two wavelengths, two independent laser diodes can be used as light sources, emitting light at wavelengths of [wavelength value missing]. (e.g., 632.8nm) and Laser beams (e.g., 780nm) are used. After passing through a beam splitter, part of the laser beam serves as a reference beam, while the other part illuminates the surface of the guide rail oil film and is reflected. The reflected light is received by two photodetectors, each with a narrowband filter corresponding to the wavelength in front to ensure that only the reflected light intensity of a specific wavelength is received. and The analog signal output by the detector is converted into a digital signal by an analog-to-digital converter (ADC), and then calculated by a microcontroller or digital signal processor (DSP). In obtaining Oil film thickness at all times At that time, the microcontroller or DSP uses pre-stored calibration data, including , and the refractive index of lubricating oil (For example, for commonly used lubricating oils,) (Potentially between 1.45 and 1.55), will be calculated in real time. Substitute into the formula Perform the calculations. Among them, and This can be obtained through experimental measurements at different known oil film thicknesses. The oil film thickness correction amount is then obtained using an additional optical path error correction model. At that time, the microcontroller or DSP will calculate the... With the preset initial oil film thickness (For example, the average oil film thickness obtained through multiple measurements under normal machine tool operating conditions) is compared and combined with the refractive index of the lubricating oil. Through formula Calculate The calculation result is then fed into the coupling / decoupling algorithm module for further processing along with the beam drift correction.

[0059] Through the above technical solution, this application can accurately quantify the additional optical path error introduced by guide rail oil film thickness fluctuations to laser displacement measurement. Compared with correction methods that only consider beam drift, this solution dynamically calculates the oil film thickness by introducing the ratio of multi-wavelength reflected light intensity and converts it into a specific correction amount, effectively solving the problem of the impact of oil film thickness changes on measurement accuracy. This enables the machine tool thermal error monitoring system to more comprehensively and accurately identify and compensate for displacement errors caused by various heat sources, significantly improving the machining accuracy and stability of the machine tool under long-term operation and complex working conditions. Especially in scenarios requiring high-precision positioning and machining, real-time accurate correction of oil film thickness fluctuations can avoid measurement drift caused by oil film changes, thereby ensuring the reliability of the final compensated true thermal error displacement.

[0060] Preferably, the coupling / decoupling algorithm in step S5 specifically includes: Establish the coupling coefficient matrix , This represents the cross-interference coefficient of beam drift on oil film measurement. This represents the cross-interference coefficient between oil film changes and beam drift measurements; The correction amount after decoupling is obtained by inverting the matrix:

[0061] in, , They are respectively The actual correction amounts for beam drift and oil film thickness after time-decoupling. for Time-based beam drift correction amount express Oil film thickness correction amount at all times. This represents the cross-interference coefficient of beam drift on oil film measurement. This represents the cross-interference coefficient between oil film changes and beam drift measurements.

[0062] Coupling-decoupling algorithms are techniques used to handle the mutual influence between multiple interrelated physical quantities or signals. Their core lies in identifying and quantifying these interactions, then separating them mathematically to obtain the true, independent contributions of each physical quantity or signal. These algorithms can use linear or nonlinear mathematical models to describe the coupling relationships and achieve decoupling by solving these models. For example, besides the matrix inversion method used in this application, complex coupling-decoupling can also be achieved using methods based on Kalman filtering, neural networks, or adaptive control. (Coupling coefficient matrix) It is a mathematical tool used to quantify the degree of interaction between different physical quantities. In this application, it specifically describes the influence of beam drift on oil film measurement and the influence of oil film change on beam drift measurement. The off-diagonal elements in the matrix are the cross-interference coefficients. and These coefficients represent the intensity and direction of the mutual interference, respectively. They can be obtained through experimental calibration, system identification, theoretical calculations based on physical models, or expert assignment. For example, they can be determined by individually changing the beam drift or oil film thickness under controlled conditions and monitoring the impact on another measurement. Matrix inversion is a mathematical operation used to find the inverse of a matrix. In coupling-decoupling algorithms, by inverting the coupling coefficient matrix, mutually coupled measurements can be converted into decoupled real physical quantities. This method is suitable for linearly coupled systems. Besides direct matrix inversion, iterative algorithms or numerical optimization methods can also be used to solve linear equation systems, achieving a similar decoupling effect. The decoupled beam drift is the actual correction amount. And the true correction amount for oil film thickness This indicates the actual impact of beam drift and oil film thickness variation on the measured displacement after eliminating mutual interference. These are more accurate correction values ​​obtained after processing by the coupling and decoupling algorithm, which are used for subsequent thermal error displacement compensation.

[0063] This application's solution introduces a coupling-decoupling algorithm to accurately separate the mutual interference between the beam drift correction and the oil film thickness correction, thereby obtaining a more accurate true correction value. Specifically, after obtaining the initial beam drift correction value... And oil film thickness correction amount Subsequently, considering the potential mutual influence between the two, this application first establishes a coupling coefficient matrix. This matrix is ​​obtained through cross-interference coefficients. and This is used to quantify the impact of beam drift on oil film measurement and the impact of oil film changes on beam drift measurement. Once this coupling relationship is accurately described by the mathematical model, the original, potentially interfering, correction values ​​can be obtained by inverting the coupling coefficient matrix. and Converted into the true correction amount of decoupled beam drift And the true correction amount for oil film thickness This process ensures that each correction independently reflects its corresponding physical effect, avoiding the superposition or cancellation of errors caused by interactions, thus providing a more accurate input for subsequent original displacement compensation. In this way, this application effectively solves the problem of cross-interference that may exist between beam drift and oil film thickness variation during measurement and correction, significantly improving the accuracy of thermal error monitoring.

[0064] The following is a concrete example to illustrate this. In practical applications, in order to determine the coupling coefficient matrix... Cross-interference coefficient in and Pre-calibration experiments can be performed. For example, during machine tool operation, a known amount of beam drift can be artificially introduced while monitoring changes in oil film thickness measurements. This allows for quantification of the impact of beam drift on oil film measurement, and thus determination. Similarly, the effect of oil film variation on beam drift measurement can be determined by controlling the change in guide rail oil film thickness and observing the change in spot position offset, thereby obtaining... Once these coefficients are determined, they can be stored in the processor of the monitoring system. During real-time monitoring, the system acquires the spot position offset and multi-wavelength reflected light intensity, and calculates the preliminary beam drift correction. And oil film thickness correction amount Then, a dedicated digital signal processor (DSP) or embedded controller can perform matrix inversion operations, which will be based on a preset coupling coefficient matrix. Using the matrix inversion formula, in real time... and Converted to the true beam drift correction after decoupling And the true correction amount for oil film thickness The entire calculation process can be completed within milliseconds to meet the requirements of real-time monitoring.

[0065] Through the above technical solution, this application can effectively solve the problem of mutual interference between beam drift and oil film thickness variation in the process of thermal error monitoring. By establishing a coupling coefficient matrix and performing matrix inversion, the actual influence of beam drift and oil film thickness on displacement measurement can be accurately separated, thereby obtaining a more accurate correction amount. This avoids the inaccuracy of correction caused by the interaction of error sources, significantly improves the accuracy and reliability of real-time laser monitoring of machine tool thermal errors, and makes the final compensated true thermal error displacement closer to the actual situation, providing a solid data foundation for the precision machining of machine tools.

[0066] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for real-time laser monitoring of machine tool thermal errors, characterized in that, include: S1. Real-time acquisition of the orthogonal signal output by the laser interferometer, the spot position offset output by the four-quadrant detector, the reflected light intensity of at least two wavelengths output by the multi-wavelength oil film monitoring photodetector, and the laser cavity temperature output by the laser temperature sensor. S2. Calculate the interference phase based on the orthogonal signal, and obtain the original displacement by accumulating the phase increments; S3. Based on the spot position offset and the laser cavity temperature, obtain the beam drift correction amount introduced by the laser beam pointing drift through the dynamic correction model. S4. Based on the ratio of the reflected light intensity of multiple wavelengths, the oil film thickness correction amount introduced by the guide rail oil film thickness fluctuation is obtained through the additional optical path error correction model. S5. By using a coupling-decoupling algorithm, the mutual interference between the beam drift correction and the oil film thickness correction is separated, and the true correction values ​​of the two after decoupling are obtained. S6. Subtract the decoupled beam drift correction and oil film thickness correction from the original displacement to obtain the compensated true thermal error displacement.

2. The machine tool thermal error real-time laser monitoring method according to claim 1, characterized in that, Step S2 specifically includes: according to Obtain the in-phase and quadrature components of the quadrature signal at time t, and acquire them. Interference phase at time ; Obtain the phase difference between adjacent sampling times ,in The sampling time interval; The original displacement is obtained by accumulating the phase differences. ,in is the laser wavelength.

3. The machine tool thermal error real-time laser monitoring method according to claim 1, characterized in that, In step S3, the dynamic correction model is represented as follows: in, for Time-based beam drift correction amount , They are respectively The light spot at all times direction and Position offset in direction and They are respectively time direction and Dynamic adaptive correction coefficient for direction.

4. The machine tool thermal error real-time laser monitoring method according to claim 3, characterized in that, time Dynamic adaptive correction coefficients for direction and The dynamic adaptive correction coefficient of the direction is based on laser cavity temperature at all times and The cumulative operating time of the laser at any given moment is obtained and represented as follows: in, express time Dynamic adaptive correction coefficient for direction. express The basic correction factor for direction. express The temperature of the laser cavity is constantly monitored. Indicates reference temperature. express The cumulative working time of the laser at all times. Indicates reference time. express The basic correction factor for direction. express Temperature influence coefficient of direction, express Temperature influence coefficient of direction, express The time aging factor of the direction, express The time aging factor of the direction.

5. The method for real-time laser monitoring of machine tool thermal error according to claim 1, characterized in that, In step S4, the oil film thickness correction amount is obtained as follows: based on The intensity of reflected light at the first and second wavelengths at time points is obtained. The ratio of the reflected light intensity of the two wavelengths at a given moment; Based on the first wavelength and the second wavelength of the laser, and The ratio of the reflected light intensity of the two wavelengths at time t is obtained. Oil film thickness at all times; based on The oil film thickness at any given time is determined by obtaining the oil film thickness correction amount introduced by the guide rail oil film thickness fluctuation through an additional optical path error correction model. This additional optical path error correction model is expressed as follows: in, express Oil film thickness correction amount at all times. Indicates the refractive index of lubricating oil. express Oil film thickness at all times This indicates the initial oil film thickness.

6. The machine tool thermal error real-time laser monitoring method according to claim 5, characterized in that, The ratio of the reflected light intensity at two wavelengths at time t is expressed as: in, express The ratio of the reflected light intensity of the two wavelengths at time . express The first wavelength at time, express The second wavelength at that moment.

7. The machine tool thermal error real-time laser monitoring method according to claim 5, characterized in that, The thickness of the oil film at any given time is expressed as: in, express Oil film thickness at all times , These are the laser wavelengths of the first and second wavelengths, respectively. express The ratio of the reflected light intensity of the two wavelengths at time . , These are the pre-calibrated maximum and minimum light intensity ratio values, respectively.

8. The method for real-time laser monitoring of machine tool thermal error according to claim 1, characterized in that, The coupling decoupling algorithm in step S5 specifically includes: Establish the coupling coefficient matrix , This represents the cross-interference coefficient of beam drift on oil film measurement. This represents the cross-interference coefficient between oil film changes and beam drift measurements. The correction amount after decoupling is obtained by inverting the matrix: in, , They are respectively The actual correction amounts for beam drift and oil film thickness after time-decoupling. for Time-based beam drift correction amount express Oil film thickness correction amount at all times. This represents the cross-interference coefficient of beam drift on oil film measurement. This represents the cross-interference coefficient between oil film changes and beam drift measurements.

9. The method for real-time laser monitoring of machine tool thermal error according to claim 1, characterized in that, The actual thermal error displacement in step S6 is expressed as follows: in, express The actual thermal error displacement after time-mapping compensation Indicates the original displacement. express The actual correction amount of beam drift after decoupling at any moment. express The actual correction amount of oil film thickness after decoupling at any time.

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