RU2008628C1 - Random vibration test facility - Google Patents

Abstract

FIELD: test technology. SUBSTANCE: each shaper channel has three controlled channels and channel adder. Nonlinearity is checked by measuring coherence function of channels at input and output of vibration exciter-part path first at low-level signals and then at desired-level signal and comparing coherent functions obtained under two conditions in each subband. If they differ in subband of any subchannel of shaper, desired level is reduced in this subband at the same time increasing levels in other subbands of this shaper channel so that mean spectrum level in particular band corresponds to desired level. EFFECT: improved accuracy of random vibration desired spectrum shaping, extended class of tested parts due to reducing nonlinearity effect of vibration exciter-part path.

Description

 The invention relates to vibration tests, namely, devices for testing for random vibration.

 A device for forming a spectrum of broadband random vibrations, containing parallel channels of formation, each of which includes a noise generator, a bandpass filter with adjustable Q factor, an adjustable attenuator, the output of which is connected to the control input of the bandpass filter, and the input to the output of the filter, and an adjustable amplifier, the second output of which is connected via a functional converter to the control input of the attenuator. The outputs of all amplifiers are connected to an adder, the output of which through a power amplifier is connected to the input of the oscillator. The device also contains a vibration sensor, the output of which is connected to the input of the feedback circuits, each of which includes a band-pass analyzing filter, a dispersion meter and a comparison unit, the output of which is connected to the control input of an adjustable amplifier [1].

 However, this device allows you to generate a given spectrum of vibrations only with a linear amplitude characteristic of the vibrator in the operating frequency range. If there is a nonlinearity of the vibration path at the control point of the test product, uncontrolled spectral components arise that distort the specified vibration spectrum. This leads to additional imitation errors, in some cases to a complete violation of the controllability of the forming channels and the impossibility of testing.

 The prototype of the present invention is a device [2], containing parallel channels for the formation of oscillations, each of which includes a noise generator, a band-pass filter with adjustable quality factor, an adjustable attenuator, the output of which is connected to the control input of the band-pass filter, and the input to the output of the filter, and an adjustable amplifier , the second output of which is connected through a functional converter to the control input of the attenuator. The outputs of all amplifiers are connected to an adder, the output of which through a power amplifier is connected to the input of the exciter of mechanical vibrations. The device also contains a vibration sensor, feedback channels, each of which includes a band-pass analyzing filter, a dispersion meter, a comparison circuit, the output of which is connected to the control input of the corresponding adjustable amplifier, a key whose input is connected to the output of the vibration sensor, and the output to the inputs of the feedback channels connected in series with a switch, correlometer, ADC, fast Fourier transform block, the first memory block, a computer, the first output of which is connected to the input of the second memory block, the second the move is to the input of the third memory block, the comparison circuit, the first input of which is connected to the output of the second memory block, the second input to the output of the third memory block, the outputs of the comparison circuit are connected to the inputs of the mode switch, the outputs of which are connected to the second inputs of the feedback channel comparison circuits as well as a control unit, the first output of which is connected to the control input of the key, the second output - to the control input of the switch, the third output - to the control inputs of the second and third memory blocks, the fourth output - to the control input of the first memory block, the fifth output is to the second control inputs of the adjustable amplifiers, the sixth output is to the control input of the mode switch.

 Such a device allows random vibration testing in the presence of nonlinearity of the vibration path. However, in those frequency bands where the non-linearity of the vibration path is manifested, it is not possible to achieve the required level of vibration. This leads to an under-testing of the object in this frequency band, which affects the quality of the tests.

 The aim of the invention is to improve the accuracy of vibration testing and the expansion of the class of tested products by reducing the influence of the nonlinearity of the path exciter-product.

 This goal is achieved in that in a device containing a series-connected driver, each channel of which contains a noise generator, a bandpass filter and an adjustable amplifier, a common adder, a power amplifier, a vibration exciter of mechanical vibrations, a vibration sensor, a switch, the first input of which is connected to the vibration sensor, the second input - with the output of a power amplifier, a correlator, an analog-to-digital converter and a fast Fourier transform unit, one output of which is connected to the first input of the first memory block, the output of which is connected to the first computer, the first and second outputs of which are connected respectively to the first inputs of the second and third memory blocks, the outputs of which are connected to the inputs of the first comparison circuit, the outputs of which are connected to the mode switch, the output of which is connected to the first input of the second comparison circuit, the outputs of which are connected to the corresponding control inputs of the adjustable amplifiers of the shaper, the second outputs of the control unit are connected to the third control inputs of the shapers, the third output is the second input of the first memory block, the fourth output with the second inputs of the second and third memory blocks, the fifth output with the control input of the mode switch, the sixth output with the control input of the switch, a second computer is introduced, the input of which is connected to the other output of the fast Fourier transform unit, the outputs of the second computer are connected to the second inputs of the second comparison circuit, the control input of the second computer is connected to the first outputs of the control unit, in addition, each channel of the shaper contains three channel, channel adder.

 Nonlinearity is controlled by measuring the coherence function of the signals at the input and output of the path of the vibration exciter - product. The device has two operating modes. In the first mode, coherence functions are measured and stored when a small level signal is exposed to the path. In the second mode, an excitation signal is generated at a given level of random vibration while measuring the coherence function and comparing it with the value obtained in the first mode. If they differ in the same frequency subbands, they reduce the set level in these subbands; otherwise, tuning is carried out in the usual way. This eliminates the influence of the nonlinearity of the exciter-product path and eliminates the possibility of destruction of the test product due to the appearance of uncontrolled signals in the formation channels caused by non-linear distortions.

 The proposed technical solution meets the criterion of significant differences.

 In FIG. 1 is a block diagram of a device for testing for random vibration; in FIG. 2 and 3 - graphs of vibration spectra; in FIG. 4 is a control block diagram; in FIG. 5 and 6 are diagrams of the operation of the control unit and a table of codes generated by the control unit and their functions.

 The device for testing for random vibration contains serially connected parallel channels of the driver 1, each subchannel 2 of which includes a noise generator 3, a bandpass filter 4, an adjustable amplifier 5, the second input of which is connected to the second comparison circuit 22, the third input is connected to the second output of the control unit 23 The outputs of the amplifiers 5 subchannels are connected to the adder 6 of the subchannel, the output of which is connected to a common adder 7. The device also contains a series-connected power amplifier 8, a vibration exciter 9 mechanical vibrations and a vibration sensor 10, a switch 11, the first input of which is connected to the output of the vibration sensor 10, and the second to the output of the power amplifier 8, the correlator 12, the analog-to-digital converter (ADC) 13 and the fast FFT transform unit 14 the first output of which is connected to the input of the second computer 15, and the second output is connected to the first input of the memory unit 16, the output of which is connected to the input of the first computer 17, the first and second outputs of which are connected to the first inputs of the memory units 18 and 19, the outputs of which are connected to the inputs of the first comparison circuit 20, the outputs of which are connected to the inputs of the mode switch 21, the outputs of which are connected to the inputs of the second comparison circuit 22, the other inputs of which are connected to the outputs of the second calculator 15. The outputs of the second comparison circuit 22 are connected to the second control inputs of adjustable amplifiers 5 subchannels of 2 formation. The first, third and sixth outputs of the control unit 23 are respectively connected to the control input of the second calculator 15, the second input of the first memory block 16, the second inputs of the second and third memory blocks 18 and 19, the control input of the mode master 21 and the control input of the switch 11. Second outputs of the block control 23 are connected respectively to the third control inputs of adjustable amplifiers 5 subchannels of formation.

 The device operates as follows.

;

Δω_ij-i-я подполоса в j-полосе формирования;
G_x(Δω_ij) - спектр сигнала на входе тракта вибровозбудитель-изделие в подполосе Δω_ij;
G_y( Δω_ij) - спектр сигнала на выходе тракта вибровозбудитель-изделие в подполосе Δω_ij;
G_xy( Δω_ij) - взаимный спектр сигналов на входе и выходе тракта вибровозбудитель-изделие в подполосе Δω_ij.From the second output of the control unit 23, a control signal is supplied to the third control inputs of the adjustable amplifiers of the formation subchannels, and the latter have a gain corresponding to a low level of the output signal. A random signal with a continuous spectrum in the operating frequency range from the noise generator 3 is supplied through a bandpass filter 4 and an adjustable amplifier 5 to the channel adder 6. From the output of the adder 6, the total signal of the three subchannels of the former is supplied to one of the inputs of the common adder 7. From the output of the last random signal , which is the sum of the signals of the channels of the shaper 1, is fed to the input of a power amplifier 8, which controls the vibration exciter 9 of mechanical vibrations. Mechanical vibrations are converted by the vibration sensor 10 into an electrical signal, which then goes to the first input of the switch 11, the second input of which receives a signal from the output of the power amplifier 8. According to the control signals from the sixth output of the control unit 23, the switch 11 is sequentially connected to the inputs of the correlator 12 the output of the power amplifier 8 and the vibration sensor 10. The signal from the output of the correlator 12 describes, respectively, the correlation function of the signal at the input and output of the vibration exciter-product path and the cross correl ionic function signals at the input and output path exciter-product. This signal, converted into digital form in the ADC 13, is input to the fast Fourier transform unit 14, in which the spectra at the input and output of the vibration exciter-product path and the mutual spectrum of the signals at the input and output of the path are calculated. The value of the spectra and the mutual spectrum at the input and output of the path of the vibration exciter-product are recorded in the first memory block 16 at the address set at its control input by the control unit 23. The signal connection time to the inputs of the correlator 12 is determined by the total conversion time of the correlator 12, ADC 13, block 14 and is set by the control unit 23. After recording the measured spectra in the first memory block 16 in the first calculator 17, the coherence function in each subband (Δω _ij ) of the formation is calculated by the formula
γ ² (Δω _ij ) =

;

Δω _{ij is the} i-th subband in the j-band of formation;
G _x (Δω _ij ) is the signal spectrum at the input of the vibration exciter-product path in the subband Δω _ij ;
G _y (Δω _ij ) is the spectrum of the signal at the output of the vibration exciter-product path in the subband Δω _ij ;
G _xy (Δω _ij) is the mutual spectrum of signals at the input and output of the vibration exciter-product path in the subband Δω _ij .

G

(ω)dω, G_y(ω)=

G_nrect (Δω_n), где rect (Δω_n)=

G_n - отсчеты функции G_y( ω).Spectrum data is received in the first calculator 17 from the first memory block 16, and the results are recorded from the output of the first calculator 17 in the second memory block 18 at the address supplied from the fourth output of the control unit 23, in the form of γ ² (ω) samples in the entire operating range frequencies. From the first output of the FFT unit 14, the signal in the form of samples corresponding to the spectral density of the signal at the output of the vibration sensor 10 is fed to the input of the second calculator 15, the control input of which receives a control signal for calculating the dispersion in the subbands Δω _ij according to the formula q (Δω _ij ) =

G

(ω) dω, G _y (ω) =

G _n rect (Δω _n ), where rect (Δω _n ) =

G _n - samples of the function G _y (ω).

Then, the obtained dispersion values q (Δω _ij ) are compared in the comparison circuit 22 with the given variances q _ass (Δω _ij ) coming from the mode switch 21. The signals generated at the output of the comparison circuit 22 corresponding to the difference between the measured variances q (Δω _ij ) and given dispersions q _ass (Δω _ij ) are supplied to the second inputs of the adjustable amplifiers 5 and change the gain so that the difference between q (Δω _ij ) and q _ass (Δω _ij ) is reduced to the minimum achievable value Δ q _min . The minimum difference between q (Δω _ij ) and q _ass (Δω _ij ), which is achieved in the control loop when adjusting the gain and amplifier 5, is determined by the total gain of the feedback circuit formed by the circuit: vibration sensor 10, correlator 12, ADC 13 and FFT 14. If the measured variance is equal to the given variance q (Δω _ij ), q _ass (Δω _ij ) in some frequency subband Δω _ij, the tuning process in the given frequency subband Δω _ij stops. A similar tuning process continues until the process of establishing the given dispersion of vibrations is carried out in all frequency subbands. At the end of the setup, the system is ready to exit at a given vibration level.

To bring the system to the desired level of vibration, the gain of the adjustable amplifiers 5 in each subband Δω _{ij is} increased by ΔK _ij . According to the control signal from the fifth output of the control unit 23, the command for sequential (step-by-step) discrete approach to the required level of vibration is sent to the control input of the moderator 21. The changed value of the level of a given dispersion in each subband Δω _{ij is} supplied to a comparison circuit 22, where the dispersion q (Δω _ij ) from the second computer 15 is compared with a given (changed) dispersion q _ass (Δω _ij ). The difference in the values obtained between q (Δω _ij ) and q _ass (Δω _ij ) at the output of the second comparison circuit 22 is supplied to the second control inputs of the adjustable amplifiers 5 and changes the gain so that the difference between q (Δω _ij ) and q _ass (Δω _ij ), sought to Δ q _min . Then, in the mode dial 21, a new increase occurs and the whole process is repeated until the system reaches the desired vibration level.

In the process of bringing the system to a given vibration level (at each step, see Fig. 2 of the discrete approximation), a new coherence function γ _ij (f) is estimated for each band, i.e., a new value of the coherence function γ _ij (f) is calculated for each increase in gain by Δ K _ij . The process of calculating γ _ij (f) is performed in the above order. The calculation results at the output of the first calculator 17 are recorded in the third memory block 19 at the address supplied from the fourth output of the control unit 23. The values of the coherence functions γ _ij (f) stored in the second 18 and third 19 memory blocks go to the first comparison circuit 20, where comparing the obtained value of the coherence function γ _ij (f) with an increased value of the gain of adjustable amplifiers by Δ K _ij recorded in the third memory block 19 with the value of the coherence function γ _ass (f) calculated in the small level of the excitation signal recorded in the second memory block 18. The coherence function γ _ij (f) is calculated in each subband and a comparison is also made.

When comparing in the first comparison scheme 20 of two two coherence functions γ _zadij (f), calculated with a small excitation signal, when the non-linearity of the vibration exciter-product path is not connected, and γ _ij (f), calculated in the process of reaching a given vibration level at each increment step gain ΔK _ij , there are two possible comparison results:
a) At the next step of the gain increment, the nonlinearity of the exciter-product path does not appear, and the value of the coherence function in each subband γ _ij (f) does not change compared to the coherence function γ of the _target (f) calculated at a low level of the excitation signal, i.e. . the condition is met
γ _referenceij (f) -Δγ ≅γ _ij (f) ≅γ _referenceij (f) + Δγ, where ± Δγ is the measurement error that determines the tolerance field. The tolerance field is determined from the specific test conditions of the facility.

 In case of non-manifestation of the path non-linearity of the vibration exciter-product, the mode of reaching the specified vibration level is carried out according to the given order.

b) At the next step of the gain increment Δ К _ij , the vibration exciter-product path is nonlinear and the value of the coherence function in a certain subband γ _ij (f) is excellent compared to the coherence function γ _ass (f) calculated at a low level of the excitation signal, t. . ie the condition γ _ij (f) ≅ γ _zadij (f) - Δ γ.

 In this subband, where non-linearity is manifested, the gain increase of the corresponding adjustable amplifier 5 is stopped (see Fig. 3).

, где j= 1 и 3.In FIG. Figure 3 shows the case of the manifestation of the nonlinearity of the exciter-product path in the subband Δω _{i, 2} bands Δω _i . In this case, the gain of the adjustable amplifier 5 of the subband Δω _{i, 2} does not reach the specified value of the gain. The missing value of the gain δ _{i, 2} = (K _{i, 2} -K _{i.2 is} set) is compensated by the corresponding increment of δ _{i, j of} the gain of the adjustable amplifiers 5 of the subband Δω _{i, 1} and Δω _{i, 3} , which is determined from the condition
δ _ij =

where j = 1 and 3.

q_ij(Δω_ij)= q

(Δω_i).In this case, in the band Δω _i the requirement of equality of the variances of a given vibration and the variance of the excited vibration is satisfied, i.e., the condition

q _ij (Δω _ij ) = q

(Δω _i ).

In this case, the non-uniformity of δ _{i of the} spectrum of the excited vibration in the band Δω _i must not exceed the permissible value of δ _iq , i.e., the condition δ _i ≅ δ _iq must be satisfied, where δ _iq is determined from the specific test conditions (see Fig. 2, c) .

 The proposed device was implemented in the process of performing research. A significant part of the device is implemented from standard units and blocks widely used in equipment for testing for random vibration. So, for example, the implementation of noise generator 3 is based on the recommendations of the book by V. N. Zhovinsky (V. N. Zhovinsky. Noise generation for the study of automatic systems. M.: Energy, 1968) using standard circuitry. Band-pass filter 4, channel and common adders 6 and 7 are implemented according to standard schemes based on operational amplifiers of the K 140UD6 or K 140UD7 series (Gutnikov V. S. Application of operational amplifiers in measuring equipment). The adjustable amplifier 5 is made on a DAC chip K 572 PA2 or KR 572 PA2, an analog-to-digital converter 13 is made on a K 572 PV1 chip (B. Fedorkov and V. Telets. A. PAC and ADC chips: Operation, parameters, application. M .: Energoatomizdat, 1990). Block 14 of the fast Fourier transform - on the microprocessor K 1815 VFZ (Basmanov S.S. and Shirokov Yu.F. Microprocessors and single-chip microcomputers: Nomenclature and functionality. - Edited by Dr. V.G. Domrachev. M.: Energoatomizdat, 1988, p. 122). Switch 11 can be implemented on K172KT1 or K561KTZ world circuits (Shilo V. L. Popular digital circuits. M.: Radio and communications, 1987). Correlator 12 - based on the functional diagrams given in the book. Mirsky (Mirsky G. Ya. Characteristics of stochastic possibility and their measurement. M.: Energoizdat, 1982).

 The memory blocks 16,18 and 19 are made on the basis of a series K 565 RU5 microcircuit (O. N. Lebedev. Memory microcircuits and their use M.: Radio and communications, 1990); comparison schemes 20 and 22 are based on digital comparators - K 555 SP1 microcircuits (Shilo V. L. Popular digital microcircuits. M.: Radio and communications, 1987). Computers 15 and 17 - based on personal computers of the DVK-3 type. The mode dial 21 is made on the basis of digital memory elements K 155 RU2. As a power amplifier 8, a vibration exciter 9 and a vibration sensor 10, a VEDS-100 type vibration stand with a preamplifier and an IS-318 vibration sensor is used.

 The control unit is made on a 155 series chip, in FIG. 4 shows a block diagram of a control unit. The control unit generates control signals in the form of codes shown in the table of FIG. 6, and in FIG. 5 shows diagrams of the operation of the control unit in the first mode (small signal mode).

 (56) 1. USSR author's certificate N 913095, cl. G 01 M 7/00, 1981.

 2. USSR copyright certificate N 1427194, cl. G 01 M 7/00, 1988.

Claims (1)

 A device for TESTING FOR RANDOM VIBRATION, containing an N-channel driver, a series-connected adder, a power amplifier, a vibration exciter of mechanical vibrations, a vibration sensor, a switch, a correlator, an analog-to-digital converter, a fast Fourier transform unit, the first memory unit and the first calculator, the second and third a memory unit, the first inputs of which are connected respectively to the first and second outputs of the first calculator, connected in series to the first comparison circuit, the mode dial and the second circuit comparison, the control unit, the first output of which is connected to the control input of the mode switch, the second output - with the second input of the first memory block, the third output - with the second inputs of the second and third power supplies, respectively, the fourth output - with the control input of the switch, the third input of which is connected with the output of the power amplifier, the second output with the second input of the correlator, the inputs of the first comparison circuit are connected respectively to the outputs of the second and third memory blocks, characterized in that, in order to increase the accuracy of the vibration testing and expanding operational capabilities by reducing the influence of path non-linearity, the vibration exciter - product is equipped with a second computer, the first input of which is connected to the output of the fast Fourier transform unit, the second input - with the fifth output of the control unit, and the output - with the second input of the second comparison circuit, each of the N channels of the shaper is made in the form of three controlled subchannels and an additional adder, the inputs of which are connected to the output of each of the subchannels, and the output to the corresponding Nth input ohm adder, each of the subchannels is made in the form of a series-connected noise generator, a bandpass filter and an adjustable amplifier, the output of which is the output of each of the subchannels, the second inputs of the adjustable amplifiers of each of the subchannels are combined and connected to the output of the second comparison circuit, the third inputs of the adjustable amplifiers are combined and connected to the sixth output of the control unit.

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