Instantaneous rotational speed measuring device and method based on circumferential single-frequency fringe of a rotating body

Abstract

The application relates to a kind of instantaneous rotational speed measuring device and method based on circumferential single-frequency stripe of rotary body, the measuring device includes single-frequency sinusoidal stripe sticker, linear array camera, light source and image processing system;The single-frequency sinusoidal stripe sticker is attached to the circumferential surface of the rotary body to be measured, to perceive the rotational speed information of the rotary body to be measured;The light source carries out light supplement to the stripe on the surface of the rotary body to be measured in the imaging range of linear array camera, to strengthen stripe feature;The linear array camera collects the stripe on the surface of the rotary body to be measured, and transmits the collected stripe image to image processing system;The image processing system analyzes and processes stripe image, obtains the instantaneous rotational speed information of the rotary body to be measured.The measuring device is simple in structure, the measurement method is easy to realize, the data processing amount is small, and the measurement efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of machine vision measurement of rotational speed, specifically to an instantaneous rotational speed measurement device and method based on circumferential single-frequency stripes of a rotating body. Background Technology

[0002] Rotational speed is a crucial kinematic parameter for measuring rotating machinery, and real-time monitoring of it helps to accurately and promptly understand the machinery's operating status. Currently, common methods for measuring rotational speed include mechanical measurement, electrical measurement, and visual measurement. Mechanical tachometers have complex internal structures, making them difficult to inspect and maintain, and their measurement accuracy needs improvement. Electrical measurement methods are currently the primary method for measuring rotational speed, offering considerable accuracy; however, photoelectric encoders require sophisticated manufacturing processes for their internal mechanical structures, have strict requirements for the measurement environment, and need to improve their ability to overcome factors such as motor vibration and noise. Summary of the Invention

[0003] The purpose of this invention is to provide an instantaneous rotational speed measuring device and method based on circumferential single-frequency fringes of a rotating body. The measuring device has a simple structure, the measuring method is easy to implement, the data processing volume is small, and the measurement efficiency is high.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: an instantaneous rotational speed measurement device based on circumferential single-frequency fringes of a rotating body, comprising a single-frequency sinusoidal stripe sticker, a line scan camera, a light source, and an image processing system; the single-frequency sinusoidal stripe sticker is attached to the circumferential surface of the rotating body to be measured, for sensing the rotational speed information of the rotating body; the light source provides supplementary illumination to the fringes on the surface of the rotating body to be measured within the imaging range of the line scan camera, to enhance the fringe features; the line scan camera acquires the fringes on the surface of the rotating body to be measured and transmits the acquired fringe images to the image processing system; the image processing system analyzes and processes the fringe images to obtain the instantaneous rotational speed information of the rotating body to be measured.

[0005] The present invention also provides a method for measuring instantaneous rotational speed based on circumferential single-frequency fringes of a rotating body using the above-mentioned device, comprising the following steps:

[0006] Step S1: Attach a single-frequency sinusoidal stripe sticker to the circumferential surface of the rotating body to be tested; fix the line scan camera in a suitable position, adjust the focus and aperture of the lens, and set the corresponding parameters in the acquisition software so that the circumferential stripes of the rotating body to be tested are symmetrical about the plane formed by the central axis of the rotating body and the optical axis of the camera and are clearly imaged in the sensor of the line scan camera.

[0007] Step S2: As the rotating body under test rotates, the sinusoidal fringes on its circumferential surface rotate accordingly, and the fringe signal imaged in the sensor of the line scan camera also changes accordingly. During the rotation of the rotating body under test, the line scan camera continuously images the fringes on the circumferential surface of the rotating body under test.

[0008] Step S3: The acquired stripe signal is transmitted to the image processing system. The image processing system preprocesses the stripe signal and extracts the instantaneous rotational speed information of the rotating body under test.

[0009] Furthermore, step S3 specifically includes the following steps:

[0010] Step S31: Perform stripe preprocessing on the obtained stripe signals, in rows as units;

[0011] Step S32: Except for the first row, perform correlation calculations between the normalized fringes of the preprocessed rows of fringes and the normalized fringes of the previous row of fringes to obtain the corresponding correlation coefficients;

[0012] Step S33: Substitute the obtained correlation coefficients into the rotational speed-correlation coefficient mapping relationship to obtain the instantaneous rotational speed information of the rotating body under test.

[0013] Furthermore, the fringe preprocessing includes performing a Fourier transform on the original fringe signal, retaining the two signals with the highest amplitude except for the DC signal, performing an inverse Fourier transform on these two signals while retaining their phase information, and performing normalization processing on the fringe after the inverse Fourier transform to obtain normalized fringe.

[0014] Furthermore, the rotational speed-correlation coefficient mapping relationship is as follows:

[0015]

[0016] Where n(i) is the instantaneous rotational speed calculated from the (i+1)th row of stripes and the i-th row of stripes, ρ(i) is the correlation coefficient between the (i+1)th row of preprocessed stripes and the i-th row of preprocessed stripes, fs is the sampling frame rate of the linear array camera, and P is the number of stripe cycles that the rotating body under test passes through per revolution.

[0017] Compared with the prior art, the present invention has the following beneficial effects: It provides an instantaneous rotational speed measurement device and method based on circumferential single-frequency fringes of a rotating body. By attaching a single-frequency sinusoidal stripe sticker to the circumferential surface of the rotating body, and then acquiring the circumferential surface fringe image of the rotating body during rotation using a line scan camera, the fringe image is finally analyzed and processed by an image processing system to obtain the instantaneous rotational speed information of the rotating body under test. The entire measurement device has a simple structure, the measurement method is easy to implement, no additional calibration steps are required, the data processing volume is small, the measurement efficiency is high, and it has strong practicality and broad application prospects. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the measuring device structure according to an embodiment of the present invention. The direction of the motor axis is the Z-axis, the direction of the camera optical axis is the X-axis, the direction perpendicular to the X-axis and Z-axis is the Y-axis, and the dotted line indicates the imaging position of the camera on the circumferential surface of the rotating body.

[0019] Figure 2 This is a schematic diagram illustrating the implementation process of fringe preprocessing in an embodiment of the present invention. (a) is a fringe image of the rotating body surface captured by a line scan camera; (b) is the intensity curve of the dashed fringe in (a); (c) is the amplitude-frequency diagram obtained after Fourier transform at the dashed line in (a); and (d) is the normalized fringe curve obtained by retaining the two signals with the highest amplitude (excluding the DC signal) in (c), preserving the phase information, performing an inverse Fourier transform, and then normalizing.

[0020] Figure 3 This embodiment of the invention describes the mapping relationship between the normalized fringe correlation coefficient of adjacent frames and the rotation speed in a 3ds Max simulation environment with a sampling frame rate of 1000fps and a fringe period of 20. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] like Figure 1As shown, this embodiment provides an instantaneous rotational speed measurement device based on circumferential single-frequency fringes of a rotating body, including a single-frequency sinusoidal stripe sticker, a line scan camera, a light source, and an image processing system. The rotating body under test is mounted on a servo motor and rotates synchronously with the output shaft of the servo motor. The single-frequency sinusoidal stripe sticker is attached to the circumferential surface of the rotating body under test to sense its rotational speed information. The light source provides supplementary illumination to the fringes on the surface of the rotating body under test within the imaging range of the line scan camera to enhance the fringe features. The line scan camera acquires the fringes on the surface of the rotating body under test and transmits the acquired fringe images to the image processing system via a communication network cable. The image processing system analyzes and processes the fringe images to obtain the instantaneous rotational speed information of the rotating body under test.

[0025] In this embodiment, the image processing system is computer-based and equipped with a preprocessing module and a rotational speed information extraction module. It can obtain normalized fringes from the original fringes through preprocessing, and calculate the instantaneous rotational speed of the rotating body under test based on the correlation coefficient obtained from the normalized fringes of adjacent frames.

[0026] This embodiment also provides a method for measuring instantaneous rotational speed based on the above-mentioned device and circumferential single-frequency fringes of a rotating body, including the following steps:

[0027] Step S1: Attach a single-frequency sinusoidal stripe sticker to the circumferential surface of the rotating body to be tested; fix the line scan camera in a suitable position, adjust the focus and aperture of the lens, and set the corresponding parameters in the acquisition software so that the circumferential stripes of the rotating body to be tested are symmetrically and clearly imaged in the sensor of the line scan camera with the plane formed by the central axis of the rotating body (i.e., the camera axis) and the optical axis of the camera, i.e., the XZ plane.

[0028] Step S2: As the rotating body under test rotates, the sinusoidal fringes on its circumferential surface rotate accordingly, and the fringe signal imaged in the sensor of the line scan camera also changes accordingly. During the rotation of the rotating body under test, the line scan camera continuously images the fringes on the circumferential surface of the rotating body under test.

[0029] Step S3: The collected stripe signal is transmitted to the image processing system via a communication network cable. The image processing system preprocesses the stripe signal and extracts the instantaneous rotational speed information of the rotating body under test.

[0030] In this embodiment, step S3 specifically includes the following steps:

[0031] Step S31: Perform stripe preprocessing on the obtained stripe signal in rows.

[0032] The fringe preprocessing includes performing a Fourier transform on the original fringe signal, retaining the two signals with the highest amplitude except for the DC signal, performing an inverse Fourier transform on these two signals while retaining their phase information, and normalizing the fringe after the inverse Fourier transform to obtain normalized fringes.

[0033] Figure 2 This is a schematic diagram of the preprocessing process of the original stripes in this embodiment. Among them, (a) is the stripe image of the surface of the rotating body obtained by the line scan camera; (b) is the grayscale curve of the dashed stripe in Figure (a); (c) is the amplitude-frequency diagram obtained after Fourier transform of the dashed area in Figure (a), and the low-frequency part is locally magnified; (d) is the normalized stripe curve obtained by retaining the two signals with the highest amplitude except the DC signal in Figure (c), retaining the phase information, performing inverse Fourier transform, and normalizing.

[0034] Step S32: Except for the first row, perform correlation calculations on the normalized fringes of the preprocessed rows of fringes and the normalized fringes of the previous row of fringes to obtain the corresponding correlation coefficients.

[0035] Step S33: Substitute the obtained correlation coefficients into the rotational speed-correlation coefficient mapping relationship to obtain the instantaneous rotational speed information of the rotating body under test.

[0036] Figure 3 This embodiment illustrates the mapping relationship between the normalized fringe correlation coefficient and rotational speed between adjacent frames in a 3ds Max simulation environment with a sampling frame rate of 1000fps and a fringe period of 20. For example... Figure 3 As shown, when the rotational speed increases linearly, the correlation coefficient of the normalized fringe of adjacent frames with the rotational speed follows a cosine function, with the preset function as follows:

[0037] ρ = cos(ω·n)

[0038] Where ω is an undetermined coefficient, and the function passes through (0,1), (n max Two points, n and -1, where n max Given a fixed sampling frame rate fs and a fixed number of fringe periods P per revolution of the rotating body, the maximum rotational speed that the system can measure is given by the Nyquist theorem:

[0039]

[0040] From the above known conditions, the mapping relationship between rotational speed and correlation coefficient can be obtained as follows:

[0041]

[0042] Where n(i) is the instantaneous rotational speed calculated from the (i+1)th row of stripes and the i-th row of stripes, ρ(i) is the correlation coefficient between the (i+1)th row of preprocessed stripes and the i-th row of preprocessed stripes, fs is the sampling frame rate of the linear array camera, and P is the number of stripe cycles that the rotating body under test passes through per revolution.

[0043] In actual measurement, the normalized fringes obtained after preprocessing adjacent frame fringes are correlated, and the correlation coefficients are substituted into the above formula to obtain the corresponding instantaneous rotational speed.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for measuring instantaneous rotational speed based on circumferential single-frequency fringes of a rotating body, characterized in that, A device for measuring instantaneous rotational speed is provided, comprising a single-frequency sinusoidal stripe sticker, a line scan camera, a light source, and an image processing system. The single-frequency sinusoidal stripe sticker is attached to the circumferential surface of the rotating body under test to sense the rotational speed information of the rotating body. The light source provides supplementary illumination to the stripes on the surface of the rotating body under test within the imaging range of the line scan camera to enhance the stripe features. The line scan camera acquires the stripes on the surface of the rotating body under test and transmits the acquired stripe images to the image processing system. The image processing system analyzes and processes the stripe image to obtain the instantaneous rotational speed information of the rotating body under test; The instantaneous rotational speed measurement method based on the aforementioned device includes the following steps: Step S1: Attach a single-frequency sinusoidal stripe sticker to the circumferential surface of the rotating body to be tested; fix the line scan camera in a suitable position, adjust the focus and aperture of the lens, and set the corresponding parameters in the acquisition software so that the circumferential stripes of the rotating body to be tested are symmetrical about the plane formed by the central axis of the rotating body and the optical axis of the camera and are clearly imaged in the sensor of the line scan camera. Step S2: As the rotating body under test rotates, the sinusoidal fringes on its circumferential surface rotate accordingly, and the fringe signal imaged in the sensor of the line scan camera also changes accordingly. During the rotation of the rotating body under test, the line scan camera continuously images the fringes on the circumferential surface of the rotating body under test. Step S3: The acquired stripe signal is transmitted to the image processing system. The image processing system preprocesses the stripe signal and extracts the instantaneous rotational speed information of the rotating body under test. Step S3 specifically includes the following steps: Step S31: Perform stripe preprocessing on the obtained stripe signal, in rows; Step S32: Except for the first row, perform correlation calculations on the normalized fringes of the preprocessed fringes of other rows and the normalized fringes of the previous row of fringes to obtain the corresponding correlation coefficients; Step S33: Substitute the obtained correlation coefficients into the rotational speed-correlation coefficient mapping relationship to obtain the instantaneous rotational speed information of the rotating body under test; The speed-correlation coefficient mapping relationship is as follows: in, For the first Row stripes and the first The instantaneous rotational speed calculated from the stripes. The correlation coefficient between the (i+1)th row of preprocessed fringes and the ith row of preprocessed fringes. The sampling frame rate of the line scan camera. The number of stripe cycles per revolution of the rotating body under test.

2. The instantaneous rotational speed measurement method based on circumferential single-frequency fringes of a rotating body according to claim 1, characterized in that, The fringe preprocessing includes performing a Fourier transform on the original fringe signal, retaining the two signals with the highest amplitude except for the DC signal, performing an inverse Fourier transform on these two signals while retaining their phase information, and normalizing the fringe after the inverse Fourier transform to obtain normalized fringe.

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