CN107246901B - Coal bunker material level detection system and method based on string vibration - Google Patents

Abstract

The invention relates to material height detection, in particular to a coal bunker material level detection system and method based on string vibration. It solves the technical problems of slow measurement speed and inaccurate measurement results in the current detection of the material level height inside the coal bunker. A coal bunker material level detection system based on string vibration, including a string vertically connected between the top and bottom of the silo used to hold materials, a mechanical string striker for striking the string, and a string for collecting the string The sound wave spectrum analyzer of the linear vibration frequency and the computer system; the signal output end of the computer system is connected with the signal input end of the mechanical hammering device; the signal input end of the sound wave spectrum analyzer is connected with the signal input end of the computer system. The detection system of the present invention overcomes the problem that the measurement accuracy and measurement speed of the current commonly used measurement methods cannot be balanced, and is easily interfered by dust and hanging objects, and realizes the continuous and accurate detection of the height of the coal bunker material level, and is not affected by the dust and dust in the silo. Suspension effects.

Description

Coal bunker material level detection system and method based on string vibration

technical field

The invention relates to material height detection, in particular to a coal bunker material level detection system and method based on string vibration.

Background technique

For coal mines, coal washing plants, power plants, etc., the material level detection of coal bunkers is an important indicator of coal stock and coal quality detection, and the automatic and continuous monitoring of material level is an important manifestation of the improvement of automation. Due to the characteristics of complex working conditions, large dust, and easy sticking and hanging, the accurate and continuous measurement of material level has become a major difficulty in level measurement technology. At present, the most commonly used methods for automatic measurement of coal bunker material level mainly include weight hammer method, ultrasonic distance measurement method and laser distance measurement method. Among them, the heavy hammer method converts the height of the material level according to the falling distance of the heavy hammer. The principle is simple and reliable, and it can avoid the interference of dust and hanging objects. Conducive to continuous monitoring; the ultrasonic method measures the time taken for an ultrasonic pulse from sending out to returning to the whole process. However, due to the serious dust in the coal bunker and the effect of various suspended objects, false echoes will be generated, which will affect the measurement results. At the same time, the ultrasonic divergence angle Large and limited power, it is difficult to achieve long-distance measurement, and the range is limited; the laser method measures the time from sending out to returning of the laser pulse, and it will also be affected by dust in the coal bunker and various hanging objects to generate false echoes. At the same time, due to Laser propagation speed is extremely fast, so the propagation time is small, and the relative error of time measurement is relatively large. In addition, for coal bunkers, coal is black, which has a strong absorption effect on light waves, and the reflected light intensity is very low, which is not conducive to measurement.

Contents of the invention

In order to solve the technical problems of slow measurement speed and inaccurate measurement results in the current detection of the internal material level height of the coal bunker, the invention provides a coal bunker material level detection system and method based on string vibration.

The coal bunker material level detection system based on string vibration according to the present invention is realized by adopting the following technical scheme: a coal bunker material level detection system based on string vibration, which includes a and the string between the bottom end, the mechanical hammering device for striking the string, the sound wave spectrometer and the computer system for collecting the vibration frequency of the string; the signal output terminal of the computer system and the signal input of the mechanical hammering device The signal output terminal of the acoustic spectrum analyzer is connected with the signal input terminal of the computer system.

Based on the string vibration theory, the system measures the sound frequency emitted by the string vibration, uses polynomial fitting to obtain the calibration model of the string length and vibration frequency, and accurately calculates the string length to determine the height of the material level. The whole measurement process includes striking strings, sound spectrum measurement, and data analysis and processing.

The coal bunker material level detection method based on string vibration of the present invention is realized by adopting the following technical scheme: a coal bunker material level detection method based on string vibration, comprising the following steps:

(a) Suppose the height of the silo is H , the height of the material level is h , the length of the chord, that is, the length of the free vibration of the string is l , when the material level in the silo changes, the length l of the free vibration of the chord changes; then the length of the chord The relationship with material level height is h = H - l ;

(b), material level calibration

When the material level of the silo changes, the length l of the free vibration of the string also changes. At the same time, the change of the material level will also cause a slight change in the tension of the string, and the vibration frequency f of the string will also change accordingly; A mathematical model of chord length l and frequency f is established, and regression analysis is used to obtain a calibration model; the relationship between chord length l and frequency f is expressed by a high-order polynomial as follows:

l = a ₀ + a ₁ f + a ₂ f ² +…+ a _n f ⁿ

In the formula, a ₀ , a ₁ ,..., a _n are the regression coefficients of each order, and the specific order n is determined by the amount of data used for calibration; at different material level heights, the computer system controls the motor to drive the linkage lever to hit string, and the vibration frequency of the string is collected by the acoustic spectrum analyzer, and then the vibration frequency f ₁ , f ₂ , ..., f _m of the corresponding string is measured when the material level height is l ₁ , l ₂ , ..., l _m , Among them, m > n , the regression equation can be obtained:

After the mathematical model is established, the computer system, with the support of the corresponding software, combines the relevant data for fitting, and obtains the values of the regression equation coefficients a ₀ , a ₁ ,..., a _n , and establishes the quantitative relationship between the chord length l and the frequency f ;

(c) The computer system controls the motor to drive the linkage lever to strike the string, and after measuring the vibration frequency of the string through the acoustic spectrum analyzer, the formula l = a ₀ + a ₁ f + a ₂ f ² +…+ a _n f ⁿ Calculate the chord length l of free vibration and put it into h = H - l formula to get the actual material level height in the silo.

For a specific material, calibration is required before measurement, that is, materials of different heights are filled in the silo, and then the vibration frequency of the string at each height under the same frequency of external force is measured, and the corresponding polynomial, and then fit the regression coefficients of each order according to the above-mentioned multiple polynomials, and complete the calibration; after that, the actual measurement can be carried out.

The detection system of the present invention overcomes the problem that the measurement accuracy and measurement speed of the current commonly used measurement methods cannot be balanced, and is easily interfered by dust and hanging objects, and realizes the continuous and accurate detection of the height of the coal bunker material level, and is not affected by the dust and dust in the bin. Suspension effects. The method has accurate measurement and fast processing speed, and can meet the needs of current coal mines, power plants, and coal washing plants; it can be used not only for coal measurement, but also for material level measurement of other ores and chemical raw materials. The whole system has simple structure and low cost.

Description of drawings

Fig. 1 is a schematic structural diagram of the coal bunker material level detection system of the present invention.

1-silo, 2-string, 3-acoustic spectrum analyzer, 4-computer system, 5-motor, 6-linkage lever.

Detailed ways

The mechanical striking device includes a motor 5 and a linkage lever 6; the signal input end of the motor 5 is connected with the signal output end of the computer system 4, and the power output end of the motor 5 is connected with a linkage lever 6 for firing the string 2 .

The sound wave spectrometer 3, the motor 5 and the linkage lever 6 are all located at the position where the string 2 is close to the top of the silo 1. String line 2 adopts steel wire rope.

Example

1. Device structure

The system structure is shown in FIG. 1 . The system includes: a string 2, a mechanical hammering device, a sound wave spectrum analyzer 3, and a computer system 4. The string 2 is a vertically installed steel wire rope with a diameter of about 3 to 5 cm and a length equivalent to the height of the silo 1. The upper and lower ends of the string are respectively fixed to the top and bottom of the silo 1; 5 and linkage lever 6, its rotational speed and torque are controlled by the computer system 4, that is, the striking frequency and the striking force can be adjusted within a certain range; the computer system 4 receives the measurement data of the acoustic spectrum instrument 3, processes and analyzes it, and obtains the material level At the same time, the computer system 4 also performs sequential control of hammering, sound spectrum measurement, and data analysis and processing.

2. Measuring principle

According to the theory of string vibration, when a continuous uniform string with fixed ends vibrates, its motion can be expressed as the superposition of multiple standing waves. For the nth standing wave, the amplitude and frequency of harmonic vibration at each point of the string are:

（1）amplitude

(1)

（2）frequency

(2)

In the formula, l is the string length, T is the string tension, and ρ is the string density. Wherein, when n =1, the corresponding vibration frequency is the fundamental frequency, and when n is other values, it is each harmonic frequency. It can be seen from the above formula that the vibration of the string includes multiple frequencies, but the strength of the fundamental frequency is much stronger than other harmonic frequencies, so it determines the frequency of the string, so the present invention calculates the length of the string by measuring the fundamental frequency of the string vibration. According to formula (2), the fundamental frequency of string vibration is related to string length, string tension and string density. For a certain string, its density is a constant.

When the material level in the silo changes, the length l of the free vibration of the string 2 changes, as shown in Figure 1, assuming that the silo height is H and the material level height is h , then the relationship between the chord length and the material level height is:

h = H − l (3)

3. Material level calibration

When the material level of silo 1 changes, the length l of free vibration of the string also changes, and at the same time, the change of material level will also cause a slight change in the tension of the steel wire string. If the measured vibration frequency is directly calculated according to the formula (2), the string length will be cause calculation errors. However, the change law of tension to material level height is not easy to be quantitatively described by mathematical formulas. Based on this, the present invention uses polynomial fitting to establish a mathematical model of chord length l and frequency f , and utilizes regression analysis to obtain the calibration model. The relationship between the chord length l and the frequency f is expressed by a high-order polynomial as follows:

l = a ₀ + a ₁ f + a ₂ f ² +…+ a _n f ⁿ (4)

In the formula, a ₀ , a ₁ ,..., a _n are the regression coefficients of each order respectively, and the specific order n is determined by the amount of data used for calibration. By using the hammer method to measure the corresponding vibration frequencies f ₁ , f ₂ , ..., f _m when the material level height is l ₁ , l ₂ , ..., l _m (among them, m > n ), multiple groups of structures can be obtained Form (regression equation):

After the mathematical model is established, the relevant parameters can be fitted by software such as MATLAB, SPSS, etc., and the values of the coefficients a ₀ , a ₁ ,..., a _n of the regression equation can be obtained, and the quantitative relationship between the chord length l and the frequency f can be established.

After measuring the vibration frequency of the string, calculate the length l of the free vibration string from formula (4), and bring it into formula (3) to get the material level height.

The speed of the motor is controlled by the computer, and the string is continuously struck at a frequency of 5-20 Hz to realize continuous measurement of the material level.

Claims (4)

1. The coal bunker material level detection method based on string vibration is realized by adopting a coal bunker material level detection system based on string vibration, and comprises a string (2) vertically connected between the top end and the bottom end inside a silo (1) for containing materials, a mechanical string striking device for striking strings, an acoustic wave spectrometer (3) for collecting the vibration frequency of the string (2) and a computer system (4); the signal output end of the computer system (4) is connected with the signal input end of the mechanical string striking device; the signal output end of the acoustic wave spectrometer (3) is connected with the signal input end of the computer system (4);

the mechanical string striking device comprises a motor (5) and a linkage lever (6) connected to the power output end of the motor (5) and used for firing the string (2); the signal input end of the motor (5) is connected with the signal output end of the computer system (4);

the acoustic wave spectrometer (3), the motor (5) and the linkage lever (6) are all positioned at the position of the chord line (2) close to the top end of the silo (1);

the string (2) adopts a steel wire rope; frequency of vibration of string (2)fLength of free vibration with string (2)lThe relation is:

，Tfor the tension of the string (2),ρfor the density of the strings (2), the frequencies of the strings are determined taking into account the fundamental frequency, taken heren =1；

The method is characterized by comprising the following steps of:

(a) The height of the silo (1) is set asHThe material level is as followshThe chord length, i.e. the length of the free vibration of the string (2), islWhen (when)When the material level in the silo (1) changes, the string (2) freely vibrates in lengthlChanges occur; the relationship between chord length and level height ish=H-l；

(b) Fill level calibration

When the material level of the silo (1) changes, the string (2) freely vibrates in lengthlAlso changes, and at the same time, the change of the material level can also cause the tension of the string (2) to change slightly, and the vibration frequency of the string (2)fCorresponding changes may occur; for this, a polynomial fit is used to build the chord lengthlSum frequencyfObtaining a calibration model by regression analysis; will chord lengthlSum frequencyfThe relation of (2) is expressed as follows by a higher order polynomial:

l=a ₀ +a ₁ f+a ₂ f ² +…+a _n f ⁿ

in the middle ofa ₀ 、a ₁ 、…，a _n Regression coefficients of each order, the specific ordernDetermined by the amount of data used for scaling; under different material level heights, a motor (5) is controlled by a computer system (4) to drive a linkage lever (6) to strike strings, and the vibration frequency of the strings (2) is collected by a sound wave spectrometer (3), so that the material level heights are measured respectivelyl ₁ 、l ₂ 、…、l _m Vibration frequency of corresponding string (2)f ₁ 、f ₂ 、…、f _m Wherein, the method comprises the steps of, wherein,m>nthe regression equation can be obtained:

the method comprises the steps of carrying out a first treatment on the surface of the After the mathematical model is established, the computer system (4) combines the related data to perform fitting under the support of the corresponding software to obtain the regression equation coefficienta ₀ 、a ₁ 、…，a _n Is to establish the chord lengthlSum frequencyfQuantitative relationship between the two;

(c) The motor (5) is controlled by the computer system (4) to drive the linkage lever (6) to strike the string, and the string is passed throughAfter the vibration frequency of the string (2) is measured by the ultrasonic spectrometer (3), the ultrasonic spectrometer usesl=a ₀ +a ₁ f+a ₂ f ² +…+a _n f ⁿ Calculating free vibration chord lengthlIs brought intoh=H-lThe actual material level height in the silo (1) can be obtained by the formula.

2. The method for detecting the level of a coal bunker based on string vibration according to claim 1, further comprising the step of (d): the computer system (4) is used for controlling the rotating speed of the motor (5) and continuously striking strings at the frequency of 5-20 Hz, so that the real-time continuous measurement of the material level height can be realized.

3. The method for detecting the material level of the coal bunker based on the string vibration according to claim 1, wherein in the step (b), different material level heights are detected by adopting a weight method.

4. A coal bunker level detection method based on string vibration as claimed in any one of claims 1 to 3, wherein the computer system (4) uses MATLAB or SPSS software to fit a regression equation to obtain regression coefficientsa ₀ 、a ₁ 、…，a _n Is a value of (2).

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