SU1670464A1 - Method of determining dynamic characteristics of a linear mechanical system - Google Patents

Abstract

The invention relates to a vibration measuring technique and can be used to determine the dynamic characteristics of a linear mechanical system. The purpose of the invention is to improve accuracy. This is achieved by exciting oscillations of the system in a single form under study. The system is affected by a harmonic oscillator with a monotonously varying frequency, the frequency and amplitude of the effect are recorded at the time of passage of the resonant frequency of the system, the values of eight oscillation samples are measured in less than half the period of action, and dynamic characteristics are determined from the relationships given in the text of the invention . 1 il.

Description

The invention relates to a vibration measuring technique and can be used to determine the dynamic characteristics of a linear mechanical system.

The purpose of the invention is to improve accuracy.

The drawing shows a block diagram of the device that implements the method.

The essence of the method is as follows.

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The mechanical system is affected by a harmonic exciter with monotonously varying frequency. After passing through the resonant frequency of the system, the frequency of exposure and amplitude are fixed. Then, during the half period of the harmonic action, eight current values of the system oscillations at the resonant frequency are measured. Dynamic characteristics: attenuation parameter a, resonance frequency fp, frequency of forced oscillations f are determined from the relations:

, 1 iАз - AI Chl

fp r Aarccos T (

where L is the time interval between measurements of oscillation values:

I / k Az and A4 - the coefficients are determined by solving a system of fourth-order linear equations

AI X p - 1 -DHH p - 2 + Az X p - c

- L4 X p - 4 Lp

п к, (к + 1), (к + 2), (к + 3), 3

Xk-n, ... Xk + 3 - current values of oscillations at time points (K - 4) L., (K + 3) L

A device that implements the method contains connected in series

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a non-generator 1 and a conversion unit 2, which effects a vibration load on a linear mechanical system 3, a frequency control unit 4 connected by an output to a generator input, a vibration converter 5 mounted on system 3 and connected to the inputs of an amplitude detector 6 and an analog-digital converter (ADC ) 7 through a switch 8. The output of the detector b is connected via a delay unit 9 to the input of the comparison unit 10, the other input of which is connected to the output of the detector 6 directly. The outputs of the comparator unit 10 are connected to the inputs of the control unit 4 and the switch 8. The device comprises delays connected in series 11-17, the input and output of each of them are connected to the inputs of the calculating unit 18, the output of which produces signals corresponding to the attenuation parameter a, the resonant frequency fp of the system and the frequency of forced oscillations f. The input element 11 of the delay is also connected to the output of the ADC 7.

The device works as follows.

Generator 1 generates a harmonic signal of a given frequency. This signal is fed to the input of the electric signal-to-mechanical oscillation unit 2, which acts on the mechanical system 3, exciting oscillations in it. The frequency change of the harmonic signal is carried out by the frequency control unit 4. From the output of the vibrating converter 5, the signal enters depending on the mode of operation (formation of a signal in the form of beats or determination of dynamic characteristics) to the input of detector 6 or ADC 7. One of them is selected by switch 8. When the harmonic frequency changes, switch 8 connects the output of the vibrating converter 5 with detector input 6; at a fixed harmonic frequency, the switch 8 connects the output of the vibrator 5 to the input of the ADC 7. Before the harmonic frequency passes through the resonance of the mechanical system 3, the output of the vibrator 5 is connected to the input of the detector 6. The detector 6 selects the envelope of the incoming signal. From the output of the detector 6, the signal simultaneously arrives at the inputs of the delay unit 9 and the comparison unit 10. Block 9 delays the signal arriving at its input for a specified time. In block 10, the signals arriving at its inputs from the outputs of detector 6 and block 9 are compared. If the level is

If the signal is higher than the second signal level, then a signal with a constant voltage Ui is generated at the output of the comparator unit 10, otherwise with a constant voltage 1) 2. The signal from the output of the comparator unit 10 is fed to the inputs of the generator frequency control unit 4 1 and the switch 8. If their inputs receive a signal with a voltage Ui, then the control unit 4 is monotonic

changes the frequency of the harmonic oscillations generated by the generator 1, and the switch 8 connects the output of the vibrator 5 to the input of the detector 6. If the inputs of block 4 and the switch

8 receives a signal with voltage U2, the control unit 4 fixes the frequency of generator 1, and switch 8 connects the output of the vibrator 5 to the input of ADC 7. Prior to the passage, the variable frequency of the harmonic effect passes through the envelope resonance of the mechanical system monotonously matures. This corresponds to a signal with a voltage Ui at the output of the comparison unit 10, After the passage

the monotonically changing frequency of the harmonic effect through the resonance of the oscillation envelope begins to decrease. This corresponds to a signal with a voltage U2 at the output of the comparison unit 10 and the start of the ADC

7. From the output of the ADC 7, the signal enters the input of element 11 and further to the inputs of elements 12 - 17 of the delay, each of which delays the signal by time D. At the outputs of the ADC 7 and the delay elements 11-17, the samples Xk-4, Xk-3 are formed, respectively. Xk-2, Xk-i, Xk, Xk + 1, Xk + 2, Xk + 3, which are fed to the inputs of the computation unit 18, which solves the system of linear equations and determination.

A 1 A 2 Az A A, o .. f pf.

Claims (1)

Claims The method of determining the dynamic characteristics of a linear mechanical system, which consists in effecting a harmonic oscillator on a system with a monotonously varying frequency, measures the current oscillation values, determines the dynamic characteristics, characterized in that, in order to improve accuracy, the frequency is fixed and the amplitude of the effect at the time of passage through the resonant frequency of the system, eight values of oscillations are measured in a time less than half the period of action, dynamic x Characteristics are determined from the ratios but one fp tg-rAarccos AZ - Ai 2 vflj (1 -AO , 1Ai -Az f - 0 A arccos 0 / / D2 (1- / 4) where or is the attenuation parameter; fp is the resonant frequency; f is the frequency of forced vibrations; 5D is the time interval between measurements; A 1, A2, AZ and XA - coefficients.