A guide rail straightness error inertial measurement method based on time-space synchronization

Abstract

The present invention discloses an inertial measurement method for guide rail straightness error based on spatiotemporal synchronization. The method primarily comprises: first, using an acquisition card to acquire low-frequency accelerometer signals fastened to the guide rail motion platform being measured; second, using an eddy current displacement sensor pulse marker signal to trigger the synchronous acquisition of multiple acceleration signals from the acquisition card; then, integrating the acquired acceleration signals to eliminate the error caused by the guide rail inclination angle using a multi-speed measurement scheme; using a multi-point control method, using an eddy current displacement sensor to eliminate the integral trend term; and finally, using a multi-speed measurement scheme, performing frequency-band processing and fusion to obtain the guide rail straightness error. Compared to existing measurement methods, this method offers advantages such as low cost, flexibility, efficiency, and simplicity, enabling online measurement of full-band guide rail straightness error.

Description

Technical Field

[0001] The present invention belongs to the field of motion measurement, and more specifically, relates to a method for measuring the straightness error of a guide rail. Background Art

[0002] Precision is the most important performance metric for CNC machine tools, and exploring high-precision machining and manufacturing technologies has always been a constant goal for manufacturing companies. However, compared to high-end foreign machine tools, approximately 50% of domestically produced machine tools still lag behind in terms of precision retention. This degradation in precision can severely limit the accuracy and quality of processed products and reduce the service reliability of critical components. To achieve real-time accuracy for CNC machine tools, long-term monitoring of machine tool errors and timely compensation are necessary to extend the tool's service life. Therefore, developing a convenient and fast online method for measuring multi-degree-of-freedom errors in high-precision CNC machine tools is crucial.

[0003] Currently, commonly used methods for measuring machine tool straightness errors include direct optical measurement and indirect sample measurement. The most widely used direct optical measurement method is laser interferometry, which utilizes the principle of laser interferometry and a corresponding prism to measure machine tool straightness errors. Direct optical measurement offers advantages such as high measurement accuracy and strong noise immunity. However, due to complex optical path adjustment, low sampling rate, and poor flexibility, it is difficult to apply to error measurement on large-travel machines. Furthermore, the low sampling rate makes it difficult to leverage detailed error characteristics for early identification of wear patterns. Indirect sample measurement requires only a standard test piece to measure machine tool straightness errors. This method offers the advantages of low measurement cost, simplicity, and flexibility. However, due to the coupling effects of errors in individual motion axes and other various error sources, this method is primarily used for machine tool accuracy verification. Currently, both methods are primarily used in offline measurement scenarios, making online real-time monitoring difficult. Inertial sensor measurement offers advantages such as high efficiency, flexibility, and low cost. With the increasing application of inertial sensors, their measurement scope has expanded to micron-level precision error measurement, making it suitable for measuring machine tool straightness errors. However, using only inertial sensors will increase the uncertainty of the straightness error calculation due to the phase delay of multiple actual measurements and the error of the integral trend term, and it is impossible to trace the error. Therefore, the method of eddy current displacement sensor is used to realize the synchronous acquisition of inertial sensor signals through marker pulse signals, which improves the inertial measurement accuracy while reducing the complexity and cost of the measurement system and increasing flexibility.

[0004] To address the shortcomings of current machine tool guide rail straightness error measurement methods, which suffer from complex measurement systems, significant limitations, high costs, low sampling rates, and difficulty achieving online real-time measurement, this paper proposes a highly efficient, accurate, flexible, and low-cost eddy current displacement sensor measurement method. This method, triggered by a marker pulse signal, enables temporally and spatially consistent straightness error measurement of inertial sensors, facilitating error tracing in machine tools and providing the foundation for multi-degree-of-freedom error measurement. Summary of the Invention

[0005] In view of the shortcomings of current machine tool straightness error measurement methods, such as complex measurement systems, large limitations, high costs, low sampling rates, and difficulty in achieving online real-time measurement, the present invention proposes an efficient, accurate, flexible, and low-cost straightness error measurement method, including:

[0006] Acquisition of the linearity error acceleration signal of the machine tool guide rail: The data acquisition card of the ultra-low frequency accelerometer collects the linearity error acceleration signal of the linear guide rail with a sampling rate of 1000-2000Hz to ensure that the straightness error can be accurately measured;

[0007] Triggering and acquisition of the marker pulse signal: Utilizing the principle that the eddy current displacement sensor can open or close the circuit in an area where physical contact is permitted through its internal circuit, it is set as a synchronous pulse trigger for the accelerometer and data acquisition card. By triggering the eddy current displacement sensor to generate a marker pulse signal, the acquisition card is set to trigger the pulse, achieving time domain correspondence between the pulse signal and the accelerometer acquisition signal, ultimately achieving temporal and spatial consistency between the straightness error signal and the accelerometer acquisition signal.

[0008] Eliminating the influence of inclination error at the guide rail position: Based on the sine superposition method, the guide rail straightness error model and the guide rail inclination error model are established. A multi-speed measurement scheme is sampled and the velocity value with inclination error is calculated by integrating the acceleration signal. The measurement error introduced by the inclination related to the guide rail position is eliminated, and the acceleration caused only by the straightness error is obtained.

[0009] Elimination of acceleration integral trend term error: Utilizing the control point constraint control method, eddy current displacement sensors are used to obtain the initial values ​​of the straightness errors at the front, rear, and middle points of the guide rail. The integral trend term data is then rotated and corrected using the coordinate transformation method to eliminate the integral trend term error.

[0010] Guide rail straightness error calculation: In order to make full use of the optimal frequency response area of ​​the accelerometer, based on the multi-speed measurement scheme, the low-frequency item of the high-speed measurement error, the medium-frequency item of the medium-speed measurement error, and the high-frequency item of the low-speed measurement error are calculated. The spatial frequency data of the machine tool error corresponding to adjacent speed measurements are continuous in the spatial band. The machine tool straightness error is obtained by fusing the frequency division solution signals.

[0011] A guide rail straightness error inertial measurement method based on time-space synchronization, the measurement method comprises the following steps:

[0012] S1: The ultra-low frequency accelerometer is fastened to the guide rail moving platform, and the data acquisition card of the ultra-low frequency accelerometer collects the linear guide rail straightness error acceleration signal with a sampling rate of 1000-2000Hz;

[0013] S2: Based on the successful installation of the ultra-low frequency accelerometer in step S1, an eddy current displacement sensor is set as a synchronous pulse trigger for the ultra-low frequency accelerometer and its data acquisition card. The eddy current displacement sensor is triggered by the trigger to generate a marker pulse signal. The data acquisition card is set to trigger the pulse to achieve time domain correspondence between the pulse signal and the signal collected by the ultra-low frequency accelerometer, and finally the straightness error signal of the guide rail is consistent with the signal collected by the ultra-low frequency accelerometer in time and space.

[0014] S3: Based on step S2, synchronous acquisition is achieved, and the guide rail straightness error model and guide rail inclination error model are established using the sine superposition method. A multi-speed measurement scheme is sampled, and the velocity value with inclination error is obtained by integrating the acceleration signal. The measurement error introduced by the inclination related to the guide rail position is eliminated, and the acceleration caused only by the straightness error is obtained.

[0015] S4: Based on the straightness error acceleration value obtained in step S3, a secondary integration is performed, and the initial values ​​of the straightness errors of multiple points at the head, tail, and middle of the machine tool are obtained using an eddy current displacement sensor. The integral trend item data is rotated and corrected using a coordinate transformation method using a control point constraint control method to eliminate the integral trend item error;

[0016] S5: Based on steps S3 and S4, the solution algorithm of the ultra-low frequency accelerometer is determined, and the guide rail moving platform is set to move at high speed. The ultra-low frequency accelerometer measures its low-frequency error, the medium-frequency error of the medium-speed measurement error, and the high-frequency error of the low-speed measurement error. The spatial frequency data of the machine tool error corresponding to adjacent speed measurements are continuous in the spatial band. The frequency division solution signal is fused to obtain the machine tool straightness error.

[0017] Eliminating the inclination error at the relevant position of the guide rail specifically includes:

[0018] (1) Establishing straightness error model and guide rail inclination error model

[0019]

[0020] Where: E(x) represents the straightness error of the guide rail at position x; A i Indicates the guide rail error amplitude; f i Indicates the spatial frequency of the guide rail straightness error; represents the initial phase angle of the guide rail. Θ(x) represents the inclination error of the guide rail at position x; Bj Indicates the guide rail inclination error amplitude; f j Indicates the spatial frequency of the guide rail inclination; represents the initial phase angle of the guide rail; i represents the number of sinusoidal signals of the guide rail straightness; j represents the number of sinusoidal signals of the guide rail inclination error.

[0021] (2) Elimination of the influence of guide rail inclination error

[0022] The actual measurement of the accelerometer with the influence of tilt angle actually collects the signal as follows:

[0023]

[0024] Where: A(t) represents the accelerometer signal collected in the actual measurement; v represents the velocity of the guide rail platform; t represents the time it takes for the guide rail platform to move once; Θ(x) represents the inclination error of the guide rail at position x. Integrating the measured acceleration data into velocity, using the relationship between the guide rail position and velocity x = vt, the velocity signal related to position x is obtained as:

[0025]

[0026]

[0027] Where: V E (x) is the straightness error velocity signal related to position x; V Θ (x) is the integral error signal introduced by the guide rail inclination related to position x; C is the integral trend term error caused by the unknown initial value.

[0028] From equations (3) and (4), we can see that the integrated straightness error measurement speed signal is V(x)=V E (x)+V Θ (x), when adopting the multi-speed measurement scheme, the measurement error introduced by the inclination angle related to the guide rail position can be eliminated by formula (5).

[0029]

[0030] Where: v k A is the measurement speed; k (x) is the acceleration signal of the straightness error measurement after eliminating the influence of the inclination angle.

[0031] 3. The method for measuring planar motion displacement and trajectory based on time-space synchronization according to claim 1, characterized in that:

[0032] The filtering algorithm in the multi-speed measurement scheme is frequency domain filtering, and the cutoff frequency f corresponding to the corresponding measurement speed is cd and f cu :

[0033]

[0034] Where: v k Represents three measurement speeds: high, medium and low; f cu 、f cd are the upper and lower cutoff frequencies of the filter respectively; f i Represents the error spatial frequency, where i = 0, 1, 2.

[0035] A planar motion displacement and trajectory measurement device based on time-space synchronization comprises: a long-stroke linear guide rail (1), a work surface (2), an accelerometer (3), an acquisition card (4), a data processing and display unit (5), an eddy current displacement sensor (6), a marker pulse signal (7), an error acceleration signal (8), and a signal transmission device (9).

[0036] The working table (2) of the long-stroke linear guide (1) provides multi-speed linear motion; the ultra-low frequency accelerometer (3) is fastened to the working table, and the two have consistent motion displacement; the eddy current displacement sensor (6) is used as a marker pulse signal source to realize multi-point control of acceleration integration; the marker pulse signal (7) is set as a trigger source of the acquisition card (4), triggering the acquisition card (4) to synchronously acquire an error acceleration signal (8); the signal transmission device (7) transmits the straightness error acceleration signal acquired in a time-space consistent manner; the processing and display unit (5) processes the acquired error acceleration signal, and saves and displays the guide rail straightness error measurement result.

[0037] The planar motion displacement and trajectory measurement method of the present invention has the following advantages:

[0038] (1) The method of the present invention is stable, reliable and practical. Compared with optical measurement, it can be simultaneously applicable to the measurement of machine tool straightness errors with different error space wavelengths.

[0039] (2) The method of the present invention has a simple, flexible, efficient and low system cost in the measurement process. Compared with the optical measurement method with complex optical path and time-consuming light alignment, only one accelerometer is needed to measure the straightness error of different error spatial frequencies.

[0040] ⑶ The method of the present invention realizes high-precision machine tool straightness error measurement perpendicular to the moving main axis through a multi-speed measurement fusion scheme.

[0041] (4) The method of the present invention belongs to a planar motion measurement method, which uses an ultra-low frequency accelerometer to achieve high-precision machine tool straightness error measurement within a certain frequency range.

[0042] ⑸ The method of the present invention fuses the data of the eddy current displacement sensor and the accelerometer to achieve temporal and spatial consistency and multi-point control, which is beneficial to the tracing of the linear error of the machine tool and provides an effective way for online real-time monitoring of the multi-degree-of-freedom errors of the machine tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Attachment Figure 1 A schematic diagram of a device for implementing the method of the present invention;

[0044] Attachment Figure 2 This is a flow chart of inertial measurement of guide rail straightness error based on time-space synchronization;

[0045] Attachment Figure 3 、 4 This is a diagram showing the guide rail straightness error measurement results of a specific implementation example of the method of the present invention. DETAILED DESCRIPTION

[0046] Current methods for measuring machine tool straightness errors suffer from complex measurement systems, significant limitations, high costs, low sampling rates, and difficulty achieving online, real-time measurement. This present invention proposes an efficient, accurate, flexible, and low-cost method for measuring straightness errors. This method utilizes eddy current displacement sensors and accelerometers to achieve spatiotemporally consistent inertial measurement of machine tool straightness errors across the entire frequency range. The present invention is described in detail below with reference to the accompanying drawings and specific implementation examples.

[0047] refer to Figure 1 The present invention is a schematic diagram of a real-time example device of the method of the present invention, which mainly includes: a long-stroke linear guide rail (1), a work surface (2), an accelerometer (3), an acquisition card (4), a data processing and display unit (5), an eddy current displacement sensor (6), a marker pulse signal (7), an error acceleration signal (8), and a signal transmission device (9). The device is characterized in that: the work surface (2) of the long-stroke linear guide rail (1) provides multi-speed linear motion; the ultra-low frequency accelerometer (3) is fastened to the work surface, and the two have consistent motion displacement; the eddy current displacement sensor (6) serves as a marker pulse signal source to achieve multi-point control of acceleration integration; the marker pulse signal (7) is set as a trigger source of the acquisition card (4), triggering the acquisition card (4) to synchronously acquire the error acceleration signal (8); the signal transmission device (7) transmits the straightness error acceleration signal acquired in a time-space consistent manner; the processing and display unit (5) processes the acquired error acceleration signal, and saves and displays the guide rail straightness error measurement result.

[0048] refer to Figure 2 This is a flow chart of inertial measurement of machine tool straightness error based on time-space synchronization. The measurement method of the present invention mainly includes the following steps:

[0049] Step S1: The data acquisition card of the ultra-low frequency accelerometer collects the linear guide rail straightness error acceleration signal with a sampling rate of 1000-2000 Hz;

[0050] Step S2: triggering and collecting the marker pulse signal, which includes: setting a limit sensor as a synchronous pulse trigger for the accelerometer and the data acquisition card, generating a marker pulse signal by triggering the limit sensor, setting the acquisition card pulse trigger, achieving time domain correspondence between the pulse signal and the accelerometer acquisition signal, and ultimately achieving temporal and spatial consistency between the straightness error signal and the accelerometer acquisition signal;

[0051] Step S3: Eliminating the influence of the inclination error at the guide rail position, which includes: establishing a guide rail straightness error model and a guide rail inclination error model based on the sine superposition method, sampling a multi-speed measurement scheme, obtaining a velocity value with inclination error by integrating the acceleration signal, eliminating the measurement error introduced by the inclination related to the guide rail position, and then obtaining the acceleration caused only by the straightness error;

[0052] Step S4: eliminating the acceleration integral trend term error, which includes: using an eddy current displacement sensor to obtain the initial values ​​of the straightness errors of multiple points at the front, rear, and middle of the machine tool, using a control point constraint control method, and rotating and correcting the integral trend term data using a coordinate transformation method to eliminate the integral trend term error;

[0053] Step S5: Machine tool guide rail straightness error solution: Based on the multi-speed measurement scheme, the high-speed measurement error low-frequency item, the medium-speed measurement error medium-frequency item, and the low-speed measurement error high-frequency item, the adjacent speed measurement corresponding machine tool error spatial frequency data are continuous in the spatial band, and the frequency division solution signal is fused to obtain the machine tool straightness error.

[0054] The specific parameters of the device of this embodiment are as follows: a single-track linear motor vibration table (5m) provides three sections of motion speed, namely low, medium and high, for the accelerometer fastened to the work surface, and provides a uniform speed stroke of at least 1m; an ultra-low frequency accelerometer is used; an eddy current displacement sensor (PRWL18-DN-V) is fastened to one side of the linear guide rail of the vibration table to achieve time-space consistent measurement and multi-point control of integral trend items; a sensor signal acquisition card (INV3062) with a sampling rate of 4kHz and 32-bit accuracy is selected.

[0055] In order to verify the accuracy of the inertial measurement method of machine tool straightness error based on time-space synchronization of the present invention, the inertial measurement of the straightness error of the guide rail within the length range of 0 to 550 mm was realized using the method of the present invention. Figure 3-4 is the inertial measurement result of the guide rail straightness error. Figure 3 The measurement results shown are the multi-point control integral trend results of the eddy current displacement sensor; refer to Figure 4 The measurement results shown are time-space consistent inertial measurement results with the laser tracker, and the RMS error with the laser interferometer measurement is 2.64μm.

[0056] The above description is a detailed description of an embodiment of the present invention and is not intended to limit the present invention in any form. Those skilled in the art may make a series of optimizations, improvements, and modifications based on the present invention. Therefore, the scope of protection of the present invention shall be defined by the appended claims.

[0057] The planar motion displacement and trajectory measurement method of the present invention has the following advantages:

[0058] (1) The method of the present invention is stable, reliable and practical. Compared with optical measurement, it can be simultaneously applicable to the measurement of machine tool straightness errors with different error space wavelengths.

[0059] (2) The method of the present invention has a simple, flexible, efficient and low system cost in the measurement process. Compared with the optical measurement method with complex optical path and time-consuming light alignment, only one accelerometer is needed to measure the straightness error of different error spatial frequencies.

[0060] ⑶ The method of the present invention realizes high-precision machine tool straightness error measurement perpendicular to the moving main axis through a multi-speed measurement fusion scheme.

[0061] (4) The method of the present invention belongs to a planar motion measurement method, which uses an ultra-low frequency accelerometer to achieve high-precision machine tool straightness error measurement within a certain frequency range.

[0062] ⑸ The method of the present invention fuses the data of the eddy current displacement sensor and the accelerometer to achieve temporal and spatial consistency and multi-point control, which is beneficial to the tracing of the linear error of the machine tool and provides an effective way for online real-time monitoring of the multi-degree-of-freedom errors of the machine tool.

[0063] The above description is a detailed description of an embodiment of the present invention and is not intended to limit the present invention in any form. Those skilled in the art may make a series of optimizations, improvements, and modifications based on the present invention. Therefore, the scope of protection of the present invention shall be defined by the appended claims.

Claims

1. A guide rail straightness error inertial measurement method based on time-space synchronization, characterized by: The measuring method comprises the following steps, S1: The ultra-low frequency accelerometer is fastened to the guide rail moving platform, and the data acquisition card of the ultra-low frequency accelerometer collects the linear guide rail straightness error acceleration signal with a sampling rate of 1000-2000Hz; S2: Based on the successful installation of the ultra-low frequency accelerometer in step S1, an eddy current displacement sensor is set as a synchronous pulse trigger for the ultra-low frequency accelerometer and its data acquisition card. The eddy current displacement sensor is used to trigger the generation of a marker pulse signal, which triggers the data acquisition card to acquire the acceleration signal of the ultra-low frequency accelerometer, thereby achieving time domain correspondence between the marker pulse signal and the signal acquired by the ultra-low frequency accelerometer, and ultimately achieving temporal and spatial consistency between the straightness error signal of the guide rail and the signal acquired by the ultra-low frequency accelerometer; S3: Based on step S2, synchronous acquisition is achieved, and the guide rail straightness error model and the guide rail inclination error model are established using the sine superposition method. A multi-speed measurement scheme is adopted, and the velocity value with inclination error is obtained by integrating the acceleration signal to eliminate the measurement error introduced by the inclination related to the guide rail position, thereby obtaining the acceleration affected only by the straightness error; S4: Based on the straightness error acceleration value obtained in step S3, a secondary integration is performed, and the initial values ​​of the straightness errors of multiple points at the beginning, end, and middle of the guide rail are obtained using an eddy current displacement sensor. The integral trend item data is rotated and corrected using a coordinate transformation method using a control point constraint control method to eliminate the integral trend item error; S5: Based on steps S3 and S4, a solution algorithm of the ultra-low frequency accelerometer is determined, the guide rail moving platform is set to move at high speed, and the ultra-low frequency accelerometer measures its low-frequency error; The guide rail platform is set to move at a medium speed, and the ultra-low frequency accelerometer measures its error medium-frequency term; the guide rail platform is set to move at a low speed, and the ultra-low frequency accelerometer measures its error high-frequency term; the spatial frequency data of the guide rail error corresponding to adjacent speed measurements are continuous in the spatial band, and the frequency division solution signals are fused to obtain the guide rail straightness error; The elimination of the measurement error introduced by the inclination angle related to the position of the guide rail specifically includes: (1) Establish straightness error model and guide rail inclination error model; Where: E(x) Indicates that the guide rail is in position x Straightness error at ; A i Indicates the guide rail error amplitude; f i Indicates the spatial frequency of the guide rail straightness error; φ i Indicates the initial phase angle of the guide rail; Θ(x) Indicates that the guide rail is in position x The inclination error at B j Indicates the guide rail inclination error amplitude; f j Indicates the spatial frequency of the guide rail inclination; φ j Indicates the initial phase angle of the guide rail; i Indicates the number of sinusoidal signals of guide rail straightness; j Indicates the number of sinusoidal signals of guide rail inclination error; (2) Elimination of the influence of guide rail inclination error; The actual measurement of the accelerometer with the influence of tilt angle actually collects the signal as follows: Where: A(t) Indicates the accelerometer acquisition signal in actual measurement; v Indicates the movement speed of the guide rail moving platform; t Indicates the time it takes for the guide rail moving platform to move once; Θ(x) Indicates that the guide rail is in position x The inclination error at Integrate the measured acceleration data into velocity and use the relationship between the guide rail position and velocity x=vt , get the position x The relevant speed signal is: Where: V E (x) For and location x Related straightness error velocity signal; V Θ (x) For and location x The integrated error signal introduced by the relevant guide rail inclination; C is the integral trend term error caused by unknown initial value; From equations (3) and (4), we can know that the integrated straightness error measurement speed signal is: V(x)=V E (x)+V Θ (x) , when adopting the multi-speed measurement scheme, the measurement error introduced by the inclination angle related to the guide rail position is eliminated by formula (5); Where: v k To measure speed; A k (x) In order to eliminate the straightness error caused by the inclination angle, the acceleration signal is measured; k represents the serial number of the measurement speed, corresponding to the three measurement speeds of high, medium and low.

2. The guide rail straightness error inertial measurement method based on time-space synchronization according to claim 1 is characterized in that: The filtering algorithm in the multi-speed measurement scheme is frequency domain filtering, and the cutoff frequency corresponding to the corresponding measurement speed f cd and f cu : Where: v k Represent three measurement speeds: high, medium and low; f cu 、 f cd are the upper and lower cutoff frequencies of the filter respectively; f i represents the error spatial frequency, where i =0,1,2.

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