Large range displacement measurement device and method based on absolute compound fringe scale

Abstract

The application provides a large-range displacement measurement device and method based on an absolute compound scale, which comprises an absolute compound scale, a displacement measurement sliding platform, an imaging module and an image processing system; the absolute compound scale is provided with an absolute compound scale on a base surface in advance; the displacement measurement sliding platform is installed in parallel with the absolute compound scale; the imaging module is fixed on the sliding platform and can perform linear reciprocating motion along a sliding rail; the image processing system processes the compound scale gray scale image in the storage module through the measurement method provided by the application to solve the linear displacement information mapped by the image. The application is an absolute visual displacement measurement method, which can ensure the accuracy of large-range linear displacement measurement and has the characteristics of high efficiency, non-contact and less disturbance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of machine vision measurement, in particular to a large-range displacement measurement device and method based on an absolute compound scale. BACKGROUND

[0002] The manufacturing precision of a product depends on the machining precision of a machining device, and the position measurement precision and real-time performance directly affect the control precision of the machining device. Modern manufacturing needs to have high-speed, high-precision, and high-reliability measurement technology to provide information support, so as to better promote the leap-forward improvement of the production and manufacturing level of major demand equipment.

[0003] At present, high-precision numerical control machine tools and precision high-end devices mainly use magnetic grating displacement sensors and grating sensors as displacement measurement sensors. The magnetic grating displacement sensor has the advantages of low cost, simple structure, convenient installation, wide measurement range, etc., and is widely used in linear displacement measurement. However, the magnetic grating is easy to demagnetize and is susceptible to coil magnetic field interference. The grating sensor gradually replaces the magnetic grating sensor and is applied to mobile device position measurement, and the technology is mature. However, high-precision gratings are expensive, and the measurement system has high installation standards. Therefore, it is necessary to study a new linear displacement device position measurement method. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a large-range displacement measurement device and method based on an absolute compound scale, which allows an imaging module to image the absolute compound scale, transmits the collected compound scale image to a storage module for processing and calculation by an image processing system; by processing and segmenting the collected compound scale image, algorithm calculation and vibration correction, a linear mapping relationship between the absolute compound scale and the actual displacement information is established to realize precise measurement of the displacement to be measured. The device can non-contactly obtain the displacement information of the target object, avoid interference or damage caused by contact, and adapt to various environments, so as to reduce the use cost of the measurement device while ensuring the linear displacement measurement precision.

[0005] To achieve the above purpose, the present application adopts the following technical scheme: a large-range displacement measurement device based on an absolute compound scale, comprising an absolute compound scale, a displacement measurement sliding platform, an imaging module, and an image processing system; the imaging module comprises a camera module, a storage module, an image transmission module, and a light source.

[0006] In a preferred embodiment, the absolute compound scale is composed of an absolute compound scale and a base scale, the surface of the base scale is flat, and the absolute compound scale is pre-prepared on the surface of the base scale to establish a mapping relationship between the linear displacement to be measured and the absolute compound scale.

[0007] In a preferred embodiment, the absolute composite stripes include three groups of stripes, wherein the grayscale changes of two groups are both sinusoidal changes in two-dimensional space, with the same period density, but the initial phase difference is The two-dimensional sinusoidal stripes with the same frequency are sine stripes and cosine stripes respectively; a group of m-sequences containing the code element information of each state of the pseudo-random sequence wrap the positioning stripes, and the code element information stripes change in the form of a biased one-period sine, that is, when the code element information is 1, the stripe amplitude is in [0,1], and when it is 0, the stripe amplitude is in [-1,0].

[0008] In a preferred embodiment, the imaging plane of the camera module in the imaging module is parallel to the plane of the absolute composite stripe ruler, and the imaging optical axis is perpendicular to the plane of the absolute composite stripe ruler; the camera module collects the composite stripe grayscale image at a preset frame rate and transmits it to the storage module through the transmission module; the light source provides appropriate illumination so that the grayscale amplitude change of the collected composite stripe image meets the measurement requirements.

[0009] In a preferred embodiment, the guide rail in the displacement measurement sliding platform is parallel to the absolute composite fringe ruler to ensure that the displacement mapped by the sampled composite fringe grayscale image is the same as the displacement information to be measured.

[0010] In a preferred embodiment, the displacement measuring sliding platform is connected to the object to be measured, and its position changes with the movement of the object to be measured; the displacement principal axis of the displacement measuring sliding platform is parallel to the displacement principal axis of the object to be measured.

[0011] In a preferred embodiment, the image processing system processes the composite stripe grayscale image in the storage module of the imaging module by the measurement method proposed by the present invention, and calculates the linear displacement information of the image mapping.

[0012] The present invention also provides a method for measuring large-scale displacement based on an absolute composite stripe ruler, which uses the large-scale displacement measuring device based on an absolute composite stripe ruler, and includes the following steps:

[0013] Step S1: pre-fabricate the absolute composite stripes on the surface of the base ruler, and install the absolute composite stripe ruler parallel to the sliding guide rail of the displacement measurement sliding platform; adjust the position of the camera module so that its field of view is filled with the absolute composite stripes as required; set the camera module to continuously image the absolute composite stripe ruler at a fixed frame rate, and transmit the captured absolute composite stripes to the image processing system;

[0014] Step S2: Remove noise from the collected composite fringe grayscale image using the eigenvalue decomposition method; intercept the composite fringe grayscale image to ensure that the initial phase difference between the grayscale sequences of the sine fringe area and the cosine fringe area is And the integrity of each code element information of the m-sequence package positioning stripe;

[0015] Step S3: If the image to be processed is a calibration image, add a Hanning window to each column of the normalized sine and cosine stripes, perform Fourier transform to obtain the corresponding spectrum of the grayscale change sequence; use the energy center of gravity method to correct the spectrum peak to obtain the accurate frequency of the grayscale change sequence; based on the calculated average frequency of each column, generate the initial phase of 0 and Two sets of preset ideal reference fringes with the same number of sampling points and interception interval rows;

[0016] Step S4: Perform Pearson cross-correlation calculation on the grayscale change sequence of each column of the normalized sinusoidal stripes and two sets of preset ideal reference stripes; the result of the cross-correlation calculation with the preset ideal reference stripes with an initial phase of 0 is called the correlation phase sine, and the result of the cross-correlation calculation with the other set of reference stripes is called the correlation phase cosine. The arc tangent of the result of dividing the correlation phase sine by the correlation phase cosine is the sinusoidal stripe correlation phase; the cosine stripe correlation phase can be obtained in the same way; since the initial phase of the cosine stripes is more than the initial phase of the sine stripes, Therefore, the phase associated with the cosine fringe needs to be subtracted

[0017] Step S5: Convolve the normalized m-sequence fringe grayscale change sequence and its absolute value sequence with a preset convolution kernel, binarize the two convolution results using a predetermined threshold, and obtain the intervals where the peak values ​​of the current symbol sequences of the m-sequence fringe are located. Perform a modulo-2 operation on the two intervals to obtain the symbol values ​​of the m-sequence at the measured position. Calculate the corresponding associated phase wrapping period using each symbol value, and combine it with the associated phase obtained in step S4 to obtain the unwrapped associated phase.

[0018] Step S6: Using a polynomial fitting method, fit the peak intervals of each symbol sequence of the absolute value sequence of grayscale changes of the m-sequence wrapped positioning fringe, and find the position where its derivative is 0, that is, the peak position corresponding to this interval; subtract each peak position from the peak position of the calibration image, and the result is the vibration of the device under test in the imaging coordinate system when measuring the sampled fringe image;

[0019] Step S7: The unwrapped sine fringe correlation phase and the cosine fringe correlation phase are mapped to obtain two sets of displacement information, and the average value of the two sets of displacement information is corrected using the measured vibration result to obtain accurate displacement information;

[0020] Compared with existing technologies, the present invention offers the following advantages: It provides a method and device for measuring displacement over a wide range and with high precision based on an absolute composite stripe ruler. Absolute encoding of displacement information is achieved through the absolute composite stripe ruler, and an imaging module is used to image the composite stripes on the surface of the absolute composite stripe ruler. The proposed displacement measurement method enables high-precision measurement of absolute linear displacement. Compared to existing visual measurement devices and methods, this method achieves absolute displacement measurement, avoiding cumulative errors; corrects for vibrations during the movement of the positioning device, ensuring high-precision measurement of linear displacement over a wide range; and offers the advantages of high efficiency, low cost, non-contact operation, and minimal interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the device structure of an embodiment of the present invention.

[0022] Figure 2 FIG. 4 is a flowchart of absolute composite fringe processing according to an embodiment of the present invention.

[0023] In the figure, 1 is an absolute composite fringe ruler; 2 is an imaging module; 3 is a displacement measurement sliding platform; 4 is a base; and 5 is an image processing system. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form, and it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0027] like Figure 1As shown, this embodiment provides a large-range, high-precision displacement measurement method and device based on an absolute composite stripe ruler, which is characterized by including an absolute composite stripe ruler, an imaging module, a displacement measurement sliding platform, a base, and an image processing system. The absolute composite stripe ruler comprises a base ruler and absolute composite stripes, and is used to establish a mapping relationship between composite stripe encoding information and a linear displacement to be measured. The displacement measurement sliding platform is connected to the measured object, and its position changes with the movement of the measured object. The displacement principal axis of the displacement measurement sliding platform is parallel to the displacement principal axis of the measured object, and the guide rail is mounted on the base in parallel with the absolute composite stripe ruler to ensure that the displacement information is consistent with the displacement mapped by the sampled composite stripe grayscale image. The imaging plane of the camera module in the imaging module is parallel to the plane of the absolute composite stripe ruler, and the imaging optical axis is perpendicular to the plane of the absolute composite stripe ruler. The camera module captures the composite stripe grayscale image at a preset frame rate and transmits it to the storage module via the transmission module. The light source provides appropriate illumination so that the grayscale amplitude of the captured composite stripe image changes to meet the measurement requirements. The image processing system processes the composite stripe grayscale image in the storage module of the imaging module using the measurement method proposed by the present invention to calculate the linear displacement information mapped by the image.

[0028] The measurement method includes the following steps:

[0029] Step S1: pre-fabricate the absolute composite stripes on the surface of the base ruler, and install the absolute composite stripe ruler parallel to the sliding guide rail of the displacement measurement sliding platform; adjust the position of the camera module so that its field of view is filled with the absolute composite stripes as required; set the camera module to continuously image the absolute composite stripe ruler at a fixed frame rate, and transmit the captured absolute composite stripes to the image processing system.

[0030] Step S2: Remove noise from the collected composite fringe grayscale image using the eigenvalue decomposition method; intercept the composite fringe grayscale image to ensure that the initial phase difference between the grayscale sequences of the sine fringe area and the cosine fringe area is And the completeness of each code element information of the m-sequence stripe;

[0031] Step S3: If the image to be processed is a calibration image, add a Hanning window to each column of the normalized sine and cosine stripes, perform Fourier transform to obtain the corresponding spectrum of the grayscale change sequence; use the energy center of gravity method to correct the spectrum peak to obtain the accurate frequency of the grayscale change sequence; based on the calculated average frequency of each column, generate the initial phase of 0 and Two sets of preset ideal reference fringes with the same number of sampling points and interception interval rows;

[0032] Step S4: Perform Pearson cross-correlation calculation on the grayscale change sequence of each column of the normalized sinusoidal stripes and two sets of preset ideal reference stripes; the result of the cross-correlation calculation with the preset ideal reference stripes with an initial phase of 0 is called the correlation phase sine, and the result of the cross-correlation calculation with the other set of reference stripes is called the correlation phase cosine. The arc tangent of the result of dividing the correlation phase sine by the correlation phase cosine is the sinusoidal stripe correlation phase; the cosine stripe correlation phase can be obtained in the same way; since the initial phase of the cosine stripes is more than the initial phase of the sine stripes, Therefore, the phase associated with the cosine fringe needs to be subtracted

[0033] Step S5: Convolve the normalized m-sequence fringe grayscale change sequence and its absolute value sequence with a preset convolution kernel, binarize the two convolution results using a predetermined threshold, and obtain the intervals where the peak values ​​of the current symbol sequences of the m-sequence fringe are located. Perform a modulo-2 operation on the two intervals to obtain the symbol values ​​of the m-sequence at the measured position. Calculate the corresponding associated phase wrapping period using each symbol value, and combine it with the associated phase obtained in step S4 to obtain the unwrapped associated phase.

[0034] Step S6: Using a polynomial fitting method, fit the peak intervals of each symbol sequence of the absolute value sequence of grayscale changes of the m-sequence wrapped positioning fringe, and find the position where its derivative is 0, that is, the peak position corresponding to this interval; subtract each peak position from the peak position of the calibration image, and the result is the vibration of the device under test in the imaging coordinate system when measuring the sampled fringe image;

[0035] Step S7: The unwrapped sine fringe correlation phase and the cosine fringe correlation phase are mapped to obtain two sets of displacement information, and the average value of the two sets of displacement information is corrected using the measured vibration result to obtain accurate displacement information;

[0036] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A large-range displacement measuring device based on an absolute composite stripe ruler, characterized in that: It includes an absolute composite stripe ruler, a displacement measurement sliding platform, an imaging module and an image processing system; the imaging module includes a camera module, a storage module, an image transmission module and a light source; The absolute composite stripe ruler is composed of absolute composite stripes and a base ruler. The base ruler has a flat surface, and the absolute composite stripes are pre-formed on the base ruler surface to establish a mapping relationship between the linear displacement to be measured and the absolute composite stripes. The absolute composite stripes include three groups of stripes, two of which have grayscale changes in two-dimensional space in the form of sinusoidal changes, with the same period density, but with an initial phase difference of Two-dimensional sinusoidal stripes with the same frequency are sine stripes and cosine stripes respectively; a set of m-sequences containing the code element information of each state of the pseudo-random sequence wraps the positioning stripes, and the code element information stripes change in a biased one-cycle sine form, that is, when the code element information is 1, the stripe amplitude is in [0,1], and when it is 0, the stripe amplitude is in [-1,0]; A large-scale displacement measurement method based on an absolute composite stripe ruler employs the above-mentioned large-scale displacement measurement device based on an absolute composite stripe ruler, and includes the following steps: Step S1: pre-fabricate the absolute composite stripes on the surface of the base ruler, and install the absolute composite stripe ruler parallel to the sliding guide rail of the displacement measurement sliding platform; adjust the position of the camera module so that its field of view is filled with the absolute composite stripes as required; set the camera module to continuously image the absolute composite stripe ruler at a fixed frame rate, and transmit the captured absolute composite stripes to the image processing system; Step S2: removing noise from the collected composite fringe grayscale image using the eigenvalue decomposition method; The composite fringe grayscale image is intercepted to ensure that the initial phase difference of the grayscale sequence of the sine fringe area and the cosine fringe area is , and the integrity of each code element information of the m-sequence package positioning stripe; Step S3: If the image to be processed is a calibration image, add a Hanning window to each column of the normalized sine and cosine stripes, perform Fourier transform to obtain the corresponding spectrum of the grayscale change sequence; use the energy center of gravity method to correct the spectrum peak to obtain the accurate frequency of the grayscale change sequence; based on the calculated average frequency of each column, generate the initial phase of 0 and , two sets of preset ideal reference fringes with the same number of sampling points and the same number of interception interval rows; Step S4: Perform Pearson cross-correlation calculation on the grayscale change sequence of each column of the normalized sinusoidal stripes and two sets of preset ideal reference stripes; the result of the cross-correlation calculation with the preset ideal reference stripes with an initial phase of 0 is called the correlation phase sine, and the result of the cross-correlation calculation with the other set of reference stripes is called the correlation phase cosine. The arc tangent of the result of dividing the correlation phase sine by the correlation phase cosine is the sinusoidal stripe correlation phase; the cosine stripe correlation phase can be obtained in the same way; since the initial phase of the cosine stripes is more than the initial phase of the sine stripes, , so the phase of the cosine fringe should be subtracted ; Step S5: Convolve the normalized m-sequence fringe grayscale change sequence and its absolute value sequence with a preset convolution kernel, binarize the two convolution results using a predetermined threshold, and obtain the intervals where the peak values ​​of the current symbol sequences of the m-sequence fringe are located. Perform a modulo-2 operation on the two intervals to obtain the symbol values ​​of the m-sequence at the measured position. Calculate the corresponding associated phase wrapping period using each symbol value, and combine it with the associated phase obtained in step S4 to obtain the unwrapped associated phase. Step S6: Using a polynomial fitting method, fit the peak intervals of each symbol sequence of the m-sequence wrapped positioning fringe grayscale change absolute value sequence, and find the position where its derivative is 0, i.e., the peak position corresponding to this interval; subtract each peak position from the peak position of the calibration image, and the result is the vibration of the device under test in the imaging coordinate system when measuring the composite fringe grayscale image; Step S7: The unwrapped sine fringe associated phase and the cosine fringe associated phase are mapped to obtain two sets of displacement information, and the average value of the two sets of displacement information is corrected using the measured vibration result to obtain accurate displacement information.

2. The large-range displacement measuring device based on an absolute composite stripe ruler according to claim 1, characterized in that: In the imaging module, the imaging plane of the camera module is parallel to the plane of the absolute composite stripe ruler, and the imaging optical axis is perpendicular to the plane of the absolute composite stripe ruler; the camera module collects the composite stripe grayscale image at a preset frame rate and transmits it to the storage module through the transmission module; the light source provides appropriate illumination so that the grayscale amplitude change of the collected composite stripe image meets the measurement requirements.

3. The large-range displacement measuring device based on an absolute composite stripe ruler according to claim 1, characterized in that: The guide rail in the displacement measurement sliding platform is parallel to the absolute composite stripe ruler to ensure that the displacement mapped by the sampled composite stripe grayscale image is the same as the displacement information to be measured.

4. The large-range displacement measuring device based on an absolute composite stripe ruler according to claim 1, characterized in that: The displacement measurement sliding platform is connected to the object to be measured, and its position changes with the movement of the object to be measured; the displacement principal axis of the displacement measurement sliding platform is parallel to the displacement principal axis of the object to be measured.

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