Screw rotational speed and material speed measuring method based on electrostatic primary and secondary frequency signals

Abstract

The present application relates to a kind of helical rotation speed and material speed measurement method based on electrostatic primary and secondary frequency signal, the material transported is granular material, with two electrodes as electrostatic sensor, two electrodes are fixed on the inner wall of material conveying pipeline of screw conveyor, the angle of elevation of two electrodes is consistent with the helical angle of screw conveyor, and helical rotation speed and material speed detection includes the following steps: collecting the electrostatic signal of two electrodes of electrostatic sensor;Two electrode electrostatic signals are Fourier transformed, and according to frequency spectrum analysis, the primary frequency and secondary frequency of two electrode electrostatic signals are determined;Primary frequency mainly reflects the motion of helical blade, selects the primary frequency of any electrode of two electrodes, calculates the helical rotation speed, and secondary frequency mainly reflects the motion of granular material, uses harmonic wavelet to extract the narrow-band signal of two electrode secondary frequency respectively, and the speed of granular material is calculated by cross correlation.

Description

Technical Field

[0001] This invention belongs to the field of screw conveyor detection and relates to a method for measuring screw rotation speed and material velocity based on electrostatic primary and secondary frequency signals. Background Technology

[0002] A screw conveyor is a machine that uses rotating helical blades to propel materials within a pipe. It is a commonly used conveying equipment for the continuous, short-distance transport of bulk materials such as coal and wood chips. Due to its simple structure, large conveying capacity, compact design, and enclosed conveying, it can load materials at any one or more points on the conveying channel. Therefore, it is widely used in industries such as ports, agriculture, chemicals, and mining.

[0003] During operation, the screw conveyor causes collisions and friction between materials, between materials and the screw blades and sleeves, resulting in material breakage and mechanical wear. Moreover, when overloaded or transporting materials with high viscosity, it is very easy to cause blockage, which can damage the device or even cause shaft breakage [1]. Therefore, it is necessary to obtain the conveying status of the screw conveyor in real time, and the screw speed and material speed are the key to knowing the conveying status.

[0004] The material is conveyed by a screw conveyor in a closed pipe. The interaction between the metal components and the material is complex, and the speed is difficult to measure. Therefore, many studies are limited to simulation[2]. Some teams have proposed a method of adding radioactive tracer particles to the material for measurement[3]. However, this method involves radiation and is only applicable to laboratory conditions, making it difficult to apply to online detection in actual industrial processes.

[0005] During screw conveying, static electricity is generated in the material due to collisions, friction, and crushing. This invention designs a novel electrode structure to detect the static electricity carried by the material. By extracting the primary and secondary frequency signals of the static electricity, simultaneous measurement of screw rotation speed and material velocity is achieved.

[0006] Related literature

[0007] [1] Zhang Meng. Analysis and discussion on the causes of shaft breakage failure in shield tunnel screw conveyor [J]. Construction Mechanization, 2020, 41(10):46-49.

[0008] [2]Zhao R, Guo L, Gao W, et al. Structure Optimization Design ofScrew Conveyor based on EDEM[C] / / Journal of Physics: Conference Series. IOPPublishing, 2022, 2200(1): 012002.

[0009] [3]Uchida K, Okamoto K. Measurement technique on the diffusioncoefficient of powder flow in a screw feeder by X-ray visualization[J]. Powder Technology, 2008, 187(2): 138-145. Summary of the Invention

[0010] The purpose of this invention is to propose a method for measuring the electrostatic conveying system based on electrostatic primary and secondary frequency signals. This method obtains the electrostatic information carried by the conveyed material through an electrostatic detection system, performs spectral analysis on the signal using Fourier transform, and determines the primary and secondary frequencies of the signal. A frequency band range that can fully express the secondary frequency information is selected, representing the bandwidth of the harmonic wavelet. The information in this frequency band is extracted using the harmonic wavelet, and the velocities of the screw and coal powder particles are calculated through cross-correlation. This method has the advantages of simplicity and good real-time performance. The technical solution of this invention is as follows:

[0011] A method for measuring screw rotation speed and material velocity based on electrostatic primary and secondary frequency signals, wherein the conveyed material is granular, a dual-electrode electrostatic sensor is used, the two electrodes are fixed on the inner wall of the material conveying pipe of the screw conveyor, and the rise angle of the two electrodes is consistent with the screw rise angle of the screw conveyor. The screw rotation speed and material velocity detection includes the following steps:

[0012] 1) Collect the electrostatic signals from the two electrodes of the electrostatic sensor;

[0013] 2) Perform Fourier transform on the electrostatic signals of the two electrodes, and determine the dominant frequency of the two electrode electrostatic signals based on spectrum analysis. f first and sub-frequency f second These are used to determine the screw speed. V spiral and material speed V gum ;

[0014] The dominant frequency primarily reflects the motion of the propeller blades. The dominant frequency of either of the two electrodes is selected. f first Calculate the screw speed:

[0015]

[0016] in, num The number of times the helical blade passes one electrode in one revolution is determined by the structure of the screw conveyor;

[0017] 3) The secondary frequency mainly reflects the movement of granular materials. The narrow-band signals of the secondary frequencies of the two electrodes are extracted using harmonic wavelets, and the velocity of the granular materials is calculated by cross-correlation.

[0018] Furthermore, the following method is used to extract narrow-band signals of the sub-frequencys of the two electrodes using harmonic wavelets, and to calculate the velocity of the particulate material through cross-correlation:

[0019] Select the electrostatic signals of a certain frequency band from the two extracted electrodes, perform harmonic wavelet transform, and extract the narrow-band signals of the second frequency of the two electrodes, denoted as follows: x(A) and y(B) ;

[0020] calculate x(A) and y(B) Cross-correlation function of cross-correlation operation R xy :

[0021] ,

[0022] in, N It is the number of points calculated by cross-correlation. j It is the delay in points. L It is the distance between the two electrodes of the electrostatic sensor;

[0023] according to R xy Peak corresponding j Value, obtain x(A) and y(B) transit time between two signals τ 0 Thus, the material velocity is obtained. V gum :

[0024] . Attached Figure Description

[0025] Figure 1 Schematic diagram of an electrostatic sensor.

[0026] Figure 2 : Front view of the structure and dimensions of the spiral blade and electrostatic sensor.

[0027] Figure 3 Side view of the structure and dimensions of the helical blades and electrostatic sensor.

[0028] Figure 4 Schematic diagram of an electrostatic detection system.

[0029] Figure 5 Electrostatic signal diagram.

[0030] Figure 6 : Spectrum diagram.

[0031] Figure 7 Flowchart for measuring screw conveyors.

[0032] Explanation of icon numbers:

[0033] 1. Electrode A; 2. Electrode B; 4. Electrostatic sensor; 5. Flange; 6. Screw conveyor; 7. Signal conditioning circuit; 8. Data acquisition unit; 9. Computer Detailed Implementation

[0034] The present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0035] The present invention relates to a method for measuring screw rotation speed and material velocity based on electrostatic primary and secondary frequency signals. It uses electrodes as sensors and simultaneously utilizes the electrostatic signals of charged particles for spectrum analysis. The method employs cross-correlation to detect the screw rotation speed and the velocity of granular material, i.e., coal powder particles. It includes two aspects: the design of electrostatic sensors and the detection of screw and coal powder particle velocities.

[0036] The structure of the electrostatic sensor is shown in the attached figure. Figure 1 As shown, it consists of electrode A1 and electrode B2. The two electrodes are smoothly embedded in the inner wall of the material conveying pipe. Let the helix angle of the screw conveyor be the angle of ascent of the two electrodes. It should satisfy equation (1).

[0037] (1)

[0038] This allows the spiral blades to pass by and leave the electrode simultaneously.

[0039] The detection of screw speed and coal powder particle velocity includes the following steps:

[0040] 4) Collect electrostatic signals from the two electrodes on the electrostatic sensor.

[0041] 5) Perform Fourier transform on the electrostatic signals of the two electrodes, and determine the dominant frequency of the electrostatic signals of the two electrodes based on spectrum analysis. f first and sub-frequency f second These are used to determine the speed of the spiral. V spiral (rpm) and the velocity of pulverized coal particles V gum (m / s).

[0042] 6) The main frequency reflects the motion of the propeller blades. The main frequency of either electrode A or electrode B is selected. ffirst According to the conversion formula between speed and frequency, the rotational speed of the screw is given by equation (2).

[0043] (2)

[0044] in num The number of times the helical blades pass over the electrode for one revolution of the helical conveyor is determined by the structure of the helical conveyor; for example, a double-helical structure... num =2.

[0045] 7) The sub-frequency mainly reflects the movement of coal powder particles. Narrow-band signals of the sub-frequency of electrodes A and B are extracted using harmonic wavelets, denoted as follows: x(A) and y(B) The velocity of pulverized coal particles is calculated using cross-correlation, as follows:

[0046] Harmonic wavelet transform can decompose signals by selecting any frequency band. The general form of harmonic wavelet is Equation (3).

[0047] (3)

[0048] in m The lower bound frequency of the narrow-band signal is the frequency of the electrode sub-frequency. n The upper bound frequency, k The number of steps.

[0049] x(A) and y(B) Cross-correlation function of cross-correlation operation R xy For equation (4), and according to R xy Peak corresponding j The value indicates the transit time between two signals. τ 0 The traveling speed of the coal powder particles is given by equation (5).

[0050] (4)

[0051] (5)

[0052] in, N It is the number of points calculated by cross-correlation. j It is the delay in points. L It is the distance between the two electrodes of the electrostatic sensor.

[0053] The embodiments of the present invention are as follows.

[0054] The main view of the structure and dimensions of the spiral blade and electrostatic sensor is attached. Figure 2As shown: 4 is an electrostatic sensor. The electrode spacing is 10mm, the electrode length is 15mm, and the width is 5mm. The distance between electrode A and electrode B is 10mm, and the longitudinal spacing is 3mm.

[0055] The side view of the structure and dimensions of the helical blade and electrostatic sensor is attached. Figure 3 As shown, the electrode is 2mm thick. The electrostatic sensor is embedded in the inner wall of the material conveying pipe of the screw conveyor, so that the planes of the two electrodes on the electrostatic sensor are flush with the inner wall of the pipe. The electrostatic sensor is fixed to the screw conveyor using a flange.

[0056] Electrostatic detection system as attached Figure 4 As shown: It consists of a screw conveyor 6, a signal conditioning circuit 7, a data acquisition unit 8, and a computer 9. The signal conditioning circuit uses a current amplification circuit with a signal sampling rate of 10kHz. The electrostatic signal measured by the electrostatic sensor is converted into a current signal after passing through the signal conditioning circuit.

[0057] 1) Connect each electrode on the electrostatic sensor to the signal conditioning circuit through a signal shielding wire.

[0058] 2) The feed inlet of the screw conveyor is filled with pulverized coal to completely fill the material conveying pipeline. The screw speed is detected using a contact-type digital tachometer with a sampling time of 10 seconds. The screw speed is 251 rpm. The electrostatic signal at this speed is shown in [link to electrostatic signal data]. Figure 5 .

[0059] 3) Perform Fourier transform on the electrostatic signal at a screw speed of 251 rpm, and obtain the main frequency through spectrum analysis. f first The frequency is 8.4 Hz, and the secondary frequency is f second The frequency is 4.2 Hz; see the spectrum diagram below. Figure 6 .

[0060] 4) The main frequency primarily reflects the motion of the spiral blades. Both electrode A and electrode B can obtain the main frequency of the electrostatic signal to determine the spiral speed. Therefore, taking electrode A as an example, since the screw conveyor has a double-spiral structure, the spiral blades pass the electrode twice per revolution. num Given a value of 2, calculate the speed of the spiral. V spiral = f first / num 60 = 252 rpm.

[0061] 5) The sub-peak information is expressed in the frequency band of 4.1~4.3Hz. Harmonic wavelet transform is used to extract the electrostatic signals of electrodes A and B in the range of 4.1~4.3Hz.

[0062] 6) The transit time of the extracted signal is calculated using a cross-correlation algorithm. τ 0 The time is 0.2286 seconds, and the distance between the two electrodes is 10 mm, so the travel speed of the coal powder particles is... V gum = L / τ 0 =0.0482m / s, see the flow chart for screw conveyor measurement. Figure 7 .

[0063] 7) Adjust the motor frequency so that the screw speed is within the range of 180rpm-290rpm, and repeat 2) to 6) to obtain the corresponding screw speed and coal powder speed.

Claims

1. A method for measuring screw rotation speed and material velocity based on electrostatic primary and secondary frequency signals, wherein the conveyed material is granular, a dual-electrode electrostatic sensor is used, the two electrodes are fixed on the inner wall of the material conveying pipe of the screw conveyor, and the rise angle of the two electrodes is consistent with the screw rise angle of the screw conveyor. The screw rotation speed and material velocity detection includes the following steps: 1) Collect the electrostatic signals from the two electrodes of the electrostatic sensor; 2) Fourier transform of the two electrodes electrostatic signals, according to the frequency spectrum analysis, determine the main frequency f first and the secondary frequency f second of the two electrodes electrostatic signals, respectively used to calculate the screw rotation speed V spiral and the material speed V gum ; The main frequency mainly reflects the motion of the helical blade, and the main frequency f of any one of the two electrodes is selected first , and the helical rotation speed is calculated: Where num represents the number of times the helical blade passes one electrode in one revolution, which is determined by the structure of the screw conveyor; 3) The secondary frequency mainly reflects the movement of granular materials. The narrow-band signals of the secondary frequencies of the two electrodes are extracted using harmonic wavelets, and the velocity of the granular materials is calculated by cross-correlation.

2. The method for measuring screw speed and material velocity according to claim 1, characterized in that, The method of extracting narrow-band signals of the sub-frequencys of the two electrodes using harmonic wavelets and calculating the velocity of the particulate material through cross-correlation is as follows: Select the electrostatic signals of a certain frequency band of the two extracted electrodes, perform harmonic wavelet transform, and extract the narrow frequency band signals of the two electrodes, which are denoted as x(A) and y(B) respectively. Calculate the cross-correlation function R of x(A) and y(B) for cross-correlation operation. xy : Where N is the number of points for cross-correlation calculation, j is the number of points for delay, and L is the distance between the two electrodes of the electrostatic sensor. According to R xy The j value corresponding to the peak value is used to obtain the transit time τ0 between the two signals x(A) and y(B), and then the material velocity V is obtained. gum :

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