RU1773164C - Method of vibration test of objects - Google Patents

Abstract

FIELD: testing equipment. SUBSTANCE: method involves operations of determination of natural frequency f_o and durability Q of tested object, subjection of object to effect of harmonic vibration with amplitude chosen in compliance with values of f_o and Q from condition of equality of maximum responses of object under harmonic and simulated random vibrations. Novelty of method consists in determination of dependences of f_o and Q on amplitude of harmonic vibration and use of these dependences for computation of shock spectrum of simulated random process, in finding maximum response A_m from this spectrum and in determination of amplitude A_h of harmonic vibration as ratio

. Value A_h is found by method of successive approximations. EFFECT: increased accuracy of determination of amplitude of harmonic vibration. 2 dwg

Description

 The invention relates to a test technique, and in particular to methods of vibration testing, involving the impact on the test object of harmonic vibration that simulates a real random process.

 The need to simulate a real random vibrational process (SP) using harmonic vibration (GV) arises in a number of practically important cases: in the absence of equipment for testing for a SP; with a high dispersion of the joint venture, when the equipment (vibration stand) does not have enough power to reproduce it, with unsteady (for example, fast-damping) joint ventures, when it is difficult to reproduce it on existing equipment; in determining the resistance to the action of high-frequency SPs of small-sized devices and elements with high natural frequencies (modern systems for setting the SPs are limited to a frequency of 2 kHz, and the natural frequencies of devices and the upper frequencies of real SPs reach 10 kg or more).

 Known methods of vibration testing, according to which, when determining the parameters of the GW, the equality of the energy characteristics of the GW and SP is taken as the equivalence criterion. With this approach, either dispersion variances are equated for HS and SP, or the SP implementation is represented as a limited number of harmonic components, and they try to ensure approximation of the laws of amplitude distribution for HS and SP due to the equality of a finite number of spectral moments or due to the equality of the dispersion of oscillations.

 The disadvantage of methods in which the equality of energy characteristics is taken as the equivalence criterion is their low reliability during vibration tests of objects critical to the maximum displacement of elements (physical parameters sensors with contact output, electronic circuits with possible short-term contact closure, etc.). The low accuracy of these methods is determined mainly by the fact that they ensure the correspondence of the hot water and the joint venture only by averaged energy characteristics. Compliance with the maximum reactions of the facility during hot water and joint venture is not ensured.

, (1) где f₀, Q соответственно собственная частота и добротность испытуемого объекта, определенные предварительно;
S_o спектральная плотность СП в резонансном диапазоне частот.Known methods of vibration testing, based on a comparison of the maximum reactions of the test object in HS and SP. Such methods are most often used in vibration testing of objects critical to the maximum displacement of elements. According to these methods, it is assumed that the implementation of the SP can be replaced by the GW subject to the equality of the maximum reactions at the resonant frequency. In particular, it is proposed that the reaction maximum A _{m be} limited to 3 σ (σ is the rms value of the SP reaction) and to determine the equivalent amplitude of the GW (A _g ) from the relation
A _g = 3

, (1) where f ₀ , Q, respectively, the natural frequency and quality factor of the test object, previously determined;
S _{o the} spectral density of the SP in the resonant frequency range.

The latter method is the closest to the proposed invention in technical essence and the achieved result. However, it does not provide the required test accuracy for the following reasons: the criterion A _m 3 σ does not always obey practical results, the calculation of A _g by formula (1) is difficult for a variable value of S ₀ (for example, if the frequency f ₀ lies at the junction of two 1/3 octave bands); formula (1) does not take into account the dependence of Q on the level of input exposure A _g or on the level of the maximum reaction A _m (meanwhile, these dependencies can be very significant); formula (1) allows one to determine the equivalent amplitude A _g only for linear systems, while many real objects have a non-linear characteristic (such objects are characterized by an asymmetric shape of the resonance curve and a significant dependence of f ₀ and Q on the input exposure level A _g or maximum reactions A _m .

 The purpose of the invention is to increase the accuracy of determining the amplitude of harmonic vibration.

сравнивают уточненное значение амплитуды гармонической вибрации A_г1 с средним ее значением

, и при их расхождении на величину Δ больше заданной величины ε указанный процесс повторяют до выполнения условия Δ ≅ ε
Способ осуществляют следующим образом.The goal is achieved in that according to the method of vibration testing of objects, which consists in preliminarily determining the natural frequency f ₀ and the quality factor Q of the test object, then the object is subjected to harmonic vibration with an amplitude selected in accordance with the condition of equality of the maximum reactions of the object under harmonic vibration and random vibration process is determined depending on the natural frequency f ₀ and Q-Q on the amplitude A _{g 0} f harmonic vibration (A _r), Q (A _g) of Preparation dependencies are the value of the natural frequency f ₀₁ and Q-Q ₁ when the amplitude value of the average A _r of the setpoint range, is then calculated at Q Q ₁ corresponding shock spectrum random vibration process at a specific range are maximal response A _m1 object at the natural frequency f ₀₁ is determined the specified value of the amplitude A _g1 harmonic vibration according to the formula
A _g1 =

compare the specified value of the amplitude of the harmonic vibration A _g1 with its average value

, and when they differ by a value of Δ more than a given value of ε, the specified process is repeated until the condition Δ ≅ ε
The method is as follows.

ΔA_г например, по литературным данным. Повторяя измерения на нескольких уровнях базового ускорения в диапазоне

ΔA_г, формируют зависимости f₀(A_г) и Q(A_г).The dependences f ₀ (A _g ) and Q (A _g ) are determined, for example, experimentally. To do this, install the object on the table of the vibration bench and fix the base vibration sensor (at the place of attachment of the object) and the control (at the object). Under the action of GW with a constant level of basic acceleration A _g ; determine the natural frequency f ₀ ; an object by the method of fixed frequencies or by scanning, for example, with a frequency meter at the maximum reaction A _m1 (maximum acceleration amplitude at the object), and its Q factor Q _i , as the ratio at the frequency f _{01 of the} reaction A _mi to the base acceleration A _gi. The initial level of basic acceleration A _g is determined, for example, by the formula (1) at approximate values and (for example, calculated) and the range of its change

ΔA _g for example, according to published data. Repeating measurements at several levels of basic acceleration in the range

ΔA _g , form the dependence of f ₀ (A _g ) and Q (A _g ).

.From the obtained dependencies find the values of f _o and Q ₁ with an average value

.

When the Q factor is Q _{1, the} shock spectrum corresponding to the simulated SP is calculated (methods for calculating shock spectra are well known), and the maximum response A _{m1 is} found from the shock spectrum at the natural frequency f ₀₁ .

Проводят сравнение величины A_г1 и

, для чего определяют, например, относительное отклонение
Δ

Сравнивают Δ с заданной величиной ε (например, ε 0,1). ЕслиΔ ≅ ε вычисление прекращают. Если Δ > ε проводят дальнейшее уточнение величины A_г по вышеприведенной методике.The specified value of the amplitude of the hot water is determined
A _g1 =

A comparison of the values of A _g1 and

why determine, for example, the relative deviation
Δ

Compare Δ with a given value of ε (for example, ε 0.1). If Δ ≅ ε, the calculation is stopped. If Δ> ε, further refinement of the value of A _{g is} carried out according to the above procedure.

As an example of the implementation of the method in FIG. 1, 2 are block diagrams of automated determination of amplitude A _g .

 The block diagram of FIG. 1 contains an oscillating frequency generator 1, a power amplifier 2, a vibrating stand 3, a test object 4, a basic acceleration sensor 5, a control acceleration sensor 6, preamplifiers 7, 8, a frequency counter 9, analog-to-digital converters 10, 12, a resolving device 11, a divider 13, a memory device 14, plotters 15, 16.

 The test object 4 is installed on the table of the vibrating stand 3, the sensor 5 is fixed at the installation site of the test object 4, the control sensor 6 on the test object 4.

ΔA_г). Сигнал с базового датчика 5 через предусилитель 8 подают на вход отрицательной обратной связи генератора 1, тем самым обеспечивают постоянную величину амплитуды ускорения A_гi. Выходной сигнал с датчика 6, определяемый реакцией объекта 4 на ГВ, поступает через предусилитель 7 на аналого-цифровой преобразователь 10, в качестве которого используется, например, цифровой вольтметр, и в виде цифрового сигнала на первый вход решающего устройства 11, на второй вход которого поступает значение частоты f_0i, измеренное частотомером 9, а на вход три значение сигнала A_гi с аналого-цифрового преобразователя 12, в качестве которого используется, например, цифровой вольтметр. Решающее устройство 11 производит сравнение значений выходного сигнала A_вых и большее из этих значений хранится в памяти устройства 11, причем хранится и значение частоты f_0i, соответствующее этому большему результату и значение A_гi на частоте f_0i.Using the oscillating frequency generator 1 and power amplifier 2 provides a change in the frequency of harmonic vibration over time in the range from f _n to f ₀ when the acceleration amplitude of the table of the _{vibrating stand} 3 is equal to A _gi (from the range of set values

ΔA _g ). The signal from the base sensor 5 through the preamplifier 8 is fed to the input of the negative feedback of the generator 1, thereby providing a constant value of the acceleration amplitude A _gi . The output signal from the sensor 6, determined by the response of the object 4 to the GV, is fed through the preamplifier 7 to the analog-to-digital converter 10, which is used, for example, as a digital voltmeter, and in the form of a digital signal to the first input of the solver 11, to the second input of which the value of the frequency f _0i measured by the frequency meter 9 is supplied, and the input value three is the signal A _gi from the analog-to-digital converter 12, which is used, for example, as a digital voltmeter. The solver 11 compares the values of the output signal A _o and the larger of these values is stored in the memory of the device 11, and the frequency value f _0i corresponding to this larger result and the value A _gi at the frequency f _{0i are also stored} .

When the oscillation frequency of the generator 1 reaches its upper limit f _o , the results of the calculation appear at the output of the solver 11;
the first maximum value of the reaction amplitude of the test object 4 A _mi ;
the second frequency value f _0i (resonant frequency of the test object), corresponding to the maximum value of the reaction A _mi ;
the third value is A _gi .

Значение f_0i, Q_i и A_гi записываются в запоминающее устройство 14 и занимают три ячейки памяти. При изменении амплитуды входного сигнала цикл измерения повторяется, в результате появляются новые три результата, и т.д. до окончания процесса измерения. Массив значений f_oi, Q_i и A_гi, полученный в процессе измерения, позволяет построить зависимости f₀(A_г) и Q(A_г) (графопостроители 15, 16).The values of A _mi and A _gi go to the divider 13, the output of which appears the result
Q _i =

The value of f _0i , Q _i and A _{gi are} recorded in the storage device 14 and occupy three memory cells. When the amplitude of the input signal changes, the measurement cycle repeats, as a result, three new results appear, etc. until the end of the measurement process. The array of values of f _oi , Q _i and A _gi obtained in the measurement process allows us to build the dependencies f ₀ (A _g ) and Q (A _g ) (plotters 15, 16).

 The block diagram of FIG. 2 contains an analog-to-digital converter 1, for example, a digital oscilloscope, a memory device 2 (see device 14 in FIG. 1), a resolver 3, a divider 4, a calculator 5, switches 6, 8, a comparison device 7, a recorder 9.

), на выходе появляются значения Q_i и f₀i, соответствующие этому входному сигналу. Эти сигналы Q_i и f_0i поступают на первый и второй входы решающего устройства 3, сюда же через аналого-цифровой преобразователь 1 поступает запись случайного процесса (например, с магнитофона). Решающее устройство 3 производит вычисление максимальной амплитуды A_mi реакции испытуемого объекта на СП. Вычисленное значение A_mi поступает на первый вход делителя 4, на второй вход которого подается значение Q_i на выходе делителя 4 появляется уточненное значение A_гi, которое поступает на первый вход вычислителя 5, на второй вход которого поступает значение A_гi-1 (в первом случае

) и производится вычисление относительного отклонения
Δ

(Δ

первое вычисление). Вычислительное значение Δ поступает на устройство сравнения 7 по условию Δ ≅ ε Если Δ > ε то значение A_гi через коммутатор 8 подается на запоминающее устройство 2 и начинается новый цикл уточнения величины A_г. Если Δ ≅ ε то коммутатор 8 разомкнут, а коммутатор 6 замкнут, процесс вычисления величины A_г закончен. Регистратор 9 показывает значение амплитуды гармонической вибрации A_г, эквивалентной заданному случайному процессу.At the input of the storage device 2, which contains a record of the dependencies f ₀ (A _g ) and Q (A _g ) obtained in the block diagram of FIG. 1, the value A _gi-1 is supplied (in the first case, A _g

), the output shows the values of Q _i and f ₀ i corresponding to this input signal. These signals Q _i and f _0i are fed to the first and second inputs of the deciding device 3, here, through an analog-to-digital converter 1, a random process is recorded (for example, from a tape recorder). The solving device 3 calculates the maximum amplitude A _{mi of the} reaction of the test object in the SP. The calculated value A _mi arrives at the first input of the divider 4, the second input of which supplies the value Q _i; at the output of the divider 4, the updated value A _{gi appears} , which goes to the first input of the calculator 5, the second input of which receives the value A _gi-1 (in the first case

) and the calculation of the relative deviation
Δ

(Δ

first calculation). The computational value Δ is supplied to the comparison device 7 by the condition Δ ≅ ε. If Δ> ε, then the value of A _gi through the switch 8 is supplied to the storage device 2 and a new cycle of refinement of the value of A _g begins. If Δ ≅ ε then switch 8 is open and switch 6 is closed, the process of calculating the quantity A _{g is} completed. The registrar 9 shows the value of the amplitude of harmonic vibration A _g equivalent to a given random process.

 A fundamentally new construction of the algorithm for determining the amplitude of harmonic vibration that simulates a real random process, provides the proposed method with high accuracy tests.

Claims (1)

METHOD OF VIBRATION TESTS OF OBJECTS, which consists in first determining the natural frequency f ₀ and the Q factor of the test object, then the object is subjected to harmonic vibration with an amplitude selected in accordance with the condition of equality of the maximum reactions of the object during harmonic vibration and random vibration process, characterized in that, in order to improve the accuracy of determining the amplitude of harmonic vibration, determine the dependence of the natural frequency f ₀ and quality factor Q from the amplitude A _g ha harmonic vibration f ₀ (A _g ), (Q (A _g ), from the obtained dependences find the values of the natural frequency f _{0 1} and Q factor Q ₁ with the average value of the amplitude A _g from the range of set values, then the corresponding impact spectrum is calculated at Q factor Q ₁ random vibration process, for a specific spectrum find the maximum reaction A _{m 1 of the} object at its own frequency F _{0 1} determine the specified value of the amplitude A _{g 1} harmonic vibration by the formula

compare the specified value of the amplitude of the harmonic vibration A _{g 1} with its average value

and when they differ by a value of Δ more than a given value of e, this process is repeated until the condition D ≅ ε is fulfilled.