A flexible bearing detection method

Abstract

The present invention discloses a method for detecting a flexible bearing, belonging to the technical field of blood analysis. By applying a resonant load to the probe end, the single-degree-of-freedom system is forced to vibrate under the action of the resonant load, the original signal is collected, the original signal is preprocessed to obtain the vibration signal, the frequency spectrum curve is drawn by analyzing the vibration signal, the natural frequency of the detection is obtained according to the frequency spectrum curve, and then the actual stiffness k is calculated. The theoretical value of the stiffness is compared with the detected value, and whether the quality of the flexible bearing is qualified is judged according to the comparison between the change amount and the preset tolerance value.

Description

Technical Field

[0001] The present invention relates to the technical field of blood analysis, and particularly to a method for detecting a flexible bearing. Background Art

[0002] During blood coagulation, fibrin, platelets, and blood cells form a three-dimensional cross-linked network structure. Under the action of plasmin, fibrin dissolves. During this process, the viscoelasticity of blood changes. By detecting the change in blood viscoelasticity during blood coagulation for qualitative or quantitative analysis of the coagulation process, it can help doctors understand the coagulation function information of patients and make accurate diagnoses and treatments.

[0003] Existing thromboelastography devices use flexible bearings to replace torsion springs and bearing support measurement elements to solve the measurement errors caused by parasitic movement of suspension wires. However, existing flexible bearings require external devices for detection and cannot achieve on-line stiffness detection and automatic correction of flexible bearings. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, one of the purposes of the present invention is to provide a method for detecting a flexible bearing, which can detect on-line and comprehensively evaluate the state change of the flexible bearing without the need for external devices.

[0005] One of the purposes of the present invention is achieved by adopting the following technical solutions:

[0006] A method for detecting a flexible bearing includes the following steps:

[0007] Obtain the theoretical value of the stiffness of the flexible bearing;

[0008] Install a probe at the bottom of the flexible bearing to form a single-degree-of-freedom system;

[0009] Apply a harmonic load to the probe end. The single-degree-of-freedom system is forced to vibrate under the action of the harmonic load, and collect the original signal of the angular displacement θ at the moment t(n). Where: t(n)=nΔt, Δt is the sampling interval time, and n = 0, 1,... N - 1;

[0010] For the original signal Perform preprocessing to obtain the vibration signal θ(n), correct the waveform distortion caused by baseline deviation, and eliminate the interference and influence of high-frequency noise mixed in the signal. Perform Fourier transform on the vibration signal θ(n) to obtain the complex signal Θ(k);

[0011] Take the frequency ω of the complex signal Θ(k) as the abscissa and the angular displacement θ as the ordinate to draw a frequency spectrum curve;

[0012] In the frequency spectrum curve, when θ = θ max ω = ω n ωn is the natural frequency, and the detected natural frequency ω is obtained according to the frequency spectrum curve n ;

[0013] According to solve the actual stiffness k of the flexible bearing, where J is the moment of inertia;

[0014] Compare the theoretical value of the stiffness with the detected value, and judge whether the quality of the flexible bearing is qualified according to the comparison between the change amount and the preset tolerance value.

[0015] Further, the resonant load is m(t) = m m sinωt, where t is time and m m is the load amplitude.

[0016] Further, performing a Fourier transform on the vibration signal θ(n) to obtain the complex signal Θ(k) specifically: Performing a Fourier transform on the vibration signal θ(n) to obtain Θ(k) specifically: k = 0, 1, … N - 1; f s is the sampling frequency, f s = 1 / Δt, where Δt is the sampling interval time.

[0017] Further, preprocessing the original signal specifically: Subtracting the least squares best fit line from the original signal to obtain the vibration signal θ(n) by removing the linear trend from the original signal data, which can focus the analysis on the fluctuations of the vibration signal θ(n).

[0018] Further, the flexible bearing detection method further includes a correction step, and the correction step specifically: Establish a flexible bearing stiffness model and correct the flexible bearing stiffness model.

[0019] Further, the establishment of the flexible bearing stiffness model specifically: Perform a finite element analysis on the flexible bearing and establish a stiffness model according to the finite element analysis results.

[0020] Further, the establishment of the flexible bearing stiffness model specifically: For a double leaf flexible bearing, the leaf endpoints are collinear with the inner and outer ring centers, each leaf contains 3 blades, and the flexible bearing uses the Euler beam model for qualitative analysis, and its torque - angle equation can be expressed as d o is the outer ring diameter of the flexible bearing, r c is the diameter of the curved surface blade, EI is the material elastic modulus, I is the polar moment of inertia of the blade cross - section, m is the torque, η is the correction coefficient, and the exponents a and b are structure constants respectively.

[0021] Further, select do and r c Perform multi - level orthogonal design simulation on o and r, linearize the stiffness model, and solve for the undetermined coefficients η, a, and b according to the least - squares method.

[0022] Further, the modified flexible bearing stiffness model is specifically: Calculate its stiffness according to the natural frequency and correct the torque - angle equation using the measured stiffness correction coefficient η.

[0023] Further, according to the torque - angle equation, it can be known that: the stiffness of the flexible bearing According to the definition of natural frequency Solve to get Substitute into the flexible bearing stiffness formula and solve to get:

[0024] Compared with the prior art, a flexible bearing detection method of the present invention does not require external equipment. By applying a resonant load to the probe end, the single - degree - of - freedom system undergoes forced vibration under the action of the resonant load, collect the original signal, pre - process the original signal to obtain the vibration signal, analyze the vibration signal to draw the frequency spectrum curve, obtain the detected natural frequency according to the frequency spectrum curve, and then calculate the actual stiffness k. Compare the theoretical value of the stiffness with the detected value, and judge whether the quality of the flexible bearing is qualified according to the comparison between the change amount and the preset tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the mechanical model of the flexible bearing detection method of the present invention;

[0026] Figure 2 is the frequency spectrum curve diagram of the angular displacement complex signal of the flexible bearing detection method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] It should be noted that when a component is referred to as "fixed to" another component, it can be directly on the other component or there may be another intermediate component through which it is fixed. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be another intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be another intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0030] Please refer to Figure 1 , a flexible bearing is used to detect the viscoelasticity change of blood during blood coagulation. A probe is installed at the bottom of the flexible bearing, and the probe is in the measuring cup. The measuring cup is used to hold blood. The flexible bearing, the probe and the blood in the measuring cup form a single-degree-of-freedom system.

[0031] The present invention relates to a detection method for a flexible bearing. The detection principle is as follows: by applying a harmonic load to the probe end, the single-degree-of-freedom system is forced to vibrate under the action of the harmonic load, the original signal is collected, the original signal is preprocessed to obtain the vibration signal, the frequency spectrum curve is drawn by analyzing the vibration signal, the natural frequency of the detection is obtained according to the frequency spectrum curve, and then the actual stiffness k is calculated. The theoretical value of the stiffness is compared with the detected value, and whether the quality of the flexible bearing is qualified is judged according to the comparison between the change amount and the preset tolerance value. When the flexible bearing has fatigue damage, its actual stiffness will deviate from the allowable value.

[0032] Specifically, a detection method for a flexible bearing according to the present invention includes the following steps:

[0033] Obtain the theoretical value of the stiffness of the flexible bearing;

[0034] Install a probe at the bottom of the flexible bearing to form a single-degree-of-freedom system;

[0035] Apply a harmonic load to the probe end, and the single-degree-of-freedom system is forced to vibrate under the action of the harmonic load, and the original signal of the angular displacement θ at the moment t(n) is collected where: t(n) = nΔt, Δt is the sampling interval time, and n = 0, 1,... N - 1;

[0036] For the original signal Preprocess to obtain the vibration signal θ(n), correct the waveform distortion caused by baseline deviation, and eliminate the interference and influence of high-frequency noise mixed in the signal. Perform Fourier transform on the vibration signal θ(n) to obtain the complex signal Θ(k);

[0037] Use the frequency ω of the complex signal Θ(k) as the abscissa and the angular displacement θ as the ordinate to plot the frequency spectrum curve;

[0038] In the frequency spectrum curve, when θ = θ max ω = ω n , ω n is the natural frequency. Obtain the detected natural frequency ω n ;

[0039] According to Solve for the actual stiffness k of the flexible bearing, where J is the moment of inertia;

[0040] Compare the theoretical value of the stiffness with the detected value, and judge whether the quality of the flexible bearing is qualified according to the comparison between the variation amount and the preset tolerance value.

[0041] The specific process is as follows:

[0042] Obtain the theoretical value of the stiffness of the flexible bearing. At this time, the stiffness of the flexible bearing is the original data, that is, there are no problems such as bending of the elastic element and relaxation of the assembly stress. At this time, the result of the stiffness of the flexible bearing is accurate.

[0043] The theoretical derivation of the stiffness calculation of the flexible bearing is as follows:

[0044] When the flexible bearing of the thromboelastography measuring device makes a forced vibration under the impact response, the displacement θ of its measuring element satisfies the motion differential equation

[0045]

[0046] In the formula, J is the moment of inertia, c is the damping coefficient, and k is the elastic coefficient (stiffness).

[0047] Assume that all initial conditions are zero, and perform Laplace transform on equation (1) to obtain the equation:

[0048] [Js 2 +cs + k]Θ(s) - M(s) = 0 (2)

[0049] Its transfer function is

[0050] Let Solve for the angular displacement θ of Θ(jω) as

[0051] Θ(jω) = θexp(-jα) (4)

[0052]

[0053] According to Solve for the stiffness k of the flexible bearing, where J is the moment of inertia.

[0054] The actual detection of the flexible bearing stiffness calculation is as follows:

[0055] Apply a harmonic load to the probe tip, the thromboelastograph makes a forced vibration, and collect the original signal of the angular displacement θ at the moment t(n). Where: t(n) = nΔt, Δt is the sampling interval time, n = 0, 1, … N - 1;

[0056] For the original signal Perform preprocessing, correct the waveform distortion caused by the baseline deviation, and eliminate the interference and influence of high-frequency noise mixed in the signal through a band-pass filter. Specifically, for the original signal The preprocessing is as follows: eliminate the trend term. The linear trend represents the systematic increase or decrease of the data, usually the systematic error introduced by the measurement link. Subtract the least squares best fit line from the original signal By removing the linear trend from the original signal The analysis can be focused on the fluctuations of the vibration signal θ(n). The equation of the least squares best fit line is

[0057]

[0058] Where

[0059]

[0060] Perform a Fourier transform on the vibration signal θ(n) to obtain the complex signal Θ(k).

[0061]

[0062]

[0063] Where k = 0, 1, … N - 1; f s is the sampling frequency, f s = 1 / Δt, Δt is the sampling interval time.

[0064] Taking the frequency ω of the complex signal Θ(k) as the abscissa and the angular displacement θ as the ordinate, plot the frequency spectrum curve.

[0065] In the frequency spectrum curve, when θ = θ max , ω = ω n , ω n is the natural frequency, and obtain the detected natural frequency ω according to the frequency spectrum curve.n ;

[0066] According to Solve for the actual stiffness k of the flexible bearing, where J is the moment of inertia;

[0067] Compare the theoretical value of the stiffness with the measured value, and judge whether the quality of the flexible bearing is qualified according to the comparison between the change amount and the preset tolerance value.

[0068] The flexible bearing detection method also includes a correction step, and the correction step is specifically:

[0069] Establish a stiffness model based on the finite element analysis results to facilitate parametric design.

[0070] This method is for double leaf spring flexible bearings, where the endpoints of the leaves are collinear with the centers of the inner and outer rings, and each leaf spring contains 3 leaves. The flexible bearing can be qualitatively analyzed by referring to the Euler beam model, and its torque-angle equation can be expressed as

[0071]

[0072] where d o is the outer ring diameter of the flexible bearing, r c is the diameter of the curved leaf, EI is the material elastic modulus, I is the polar moment of inertia of the leaf cross-section, m is the torque, η is the correction coefficient, and the exponents a and b are structural constants respectively.

[0073] Select d o and r c Conduct multi-level orthogonal design simulation, linearize the stiffness model, and solve for the undetermined coefficients η, a, and b according to the least squares method.

[0074]

[0075] The specific method for correcting the flexible bearing stiffness model is: calculate its stiffness according to the natural frequency, and correct the torque-angle equation using the measured stiffness correction coefficient η.

[0076] According to the torque-angle equation, it can be known that: the stiffness of the flexible bearing According to the definition of the natural frequency Solve to get Substitute into the flexible bearing stiffness formula, and solve to get:

[0077] Compared with the prior art, a flexible bearing detection method of the present invention does not require external equipment. By applying a resonant load to the probe end, the single-degree-of-freedom system is forced to vibrate under the action of the resonant load, the original signal is collected, the original signal is preprocessed to obtain the vibration signal, the frequency spectrum curve is drawn by analyzing the vibration signal, the natural frequency of the detection is obtained according to the frequency spectrum curve, and then the actual stiffness k is calculated. The theoretical value of the stiffness is compared with the detected value, and whether the quality of the flexible bearing is qualified is judged according to the comparison between the change amount and the preset tolerance value. When the flexible bearing has fatigue damage, its actual stiffness will deviate from the allowable value. When the stiffness of the flexible bearing needs to be corrected, the measurement error caused by the stiffness change is corrected online through the correction coefficient.

[0078] The above embodiments only express several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made. These are all equivalent modifications and evolutions made to the above embodiments based on the substantial technology of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A flexible bearing detection method, characterized in that, It includes the following steps: Obtain the theoretical value of the stiffness of the flexible bearing; Install a probe at the bottom of the flexible bearing to form a single-degree-of-freedom system; Apply a resonant load to the probe tip. The single-degree-of-freedom system undergoes forced vibration under the action of the resonant load, and collect the original signal of the angular displacement θ at the moment t(n). Where: t(n) = nΔt, Δt is the sampling interval time, and n = 0, 1, … N - 1; For the original signal Preprocessing is performed to obtain the vibration signal θ(n), correct the waveform distortion caused by baseline deviation, and eliminate the interference and influence of high-frequency noise mixed in the signal. The vibration signal θ(n) is subjected to Fourier transform to obtain the complex signal f s is the sampling frequency, and f s = 1 / Δt, where Δt is the sampling interval time; Set the frequency ω in the complex signal Θ(k) as the abscissa and the angular displacement θ as the ordinate, and plot the frequency spectrum curve; In the frequency spectrum curve, when θ = θ max , ω = ω n , ω n is the natural frequency, and the detected natural frequency ω n is obtained according to the frequency spectrum curve; According to Solve for the actual stiffness k of the flexible bearing, where J is the moment of inertia; Compare the theoretical value of the stiffness with the measured value, and judge whether the quality of the flexible bearing is qualified according to the comparison between the change amount and the preset tolerance value.

2. The flexible bearing detection method according to claim 1, characterized in that: The resonant load is f(t) = m m sinωt, where t is time and m m is the load amplitude.

3. The flexible bearing detection method according to claim 1, wherein: For the original signal The preprocessing is specifically as follows: Subtract the least squares best fit line from the original signal to obtain the vibration signal θ(n) by removing the linear trend from the original signal data, which can focus the analysis on the fluctuations of the vibration signal θ(n).

4. The flexible bearing detection method according to claim 1, wherein: The flexible bearing detection method further includes a correction step, and the correction step is specifically: establish a flexible bearing stiffness model and correct the flexible bearing stiffness model.

5. The flexible bearing detection method according to claim 4, wherein: The establishment of the flexible bearing stiffness model is specifically: perform finite element analysis on the flexible bearing, and establish a stiffness model according to the finite element analysis results.

6. The flexible bearing detection method according to claim 4, characterized in that: The specific establishment of the flexible bearing stiffness model is as follows: For the double cantilever flexible bearing, the endpoints of the blades are collinear with the centers of the inner and outer rings. Each cantilever contains 3 blades. The Euler beam model is used for qualitative analysis of the flexible bearing, and its torque-angle equation can be expressed as d o is the outer ring diameter of the flexible bearing, r c is the diameter of the curved blade, EI is the material elastic modulus, m is the torque, η is the correction coefficient, and the exponents a and b are structure constants respectively.

7. The flexible bearing detection method according to claim 6, wherein: Select d o and r c Perform multi-level orthogonal design simulation, linearize the stiffness model, and solve for the undetermined coefficients η, a, and b according to the least squares method.

8. The flexible bearing detection method according to claim 6, characterized in that: The correction of the flexible bearing stiffness model is specifically: calculate its stiffness according to the natural frequency, and correct the torque-angle equation by using the measured stiffness correction coefficient η.

9. The flexible bearing detection method according to claim 8, characterized in that: According to the torque-angle equation, the flexible bearing stiffness According to the definition of natural frequency Solve to get Substitute into the flexible bearing stiffness formula and solve to get:

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