RU1832183C - Resonance frequency measurement device for structural members - Google Patents

Abstract

The invention relates to the field of studying the dynamic properties of structural elements and is intended to study frequency characteristics. The purpose of the invention is to increase accuracy and expand functionality by assessing the symmetry of characteristics. The device implements a method by which the shifted resonant frequencies ω and У ultrasound are recorded as the frequency increases and decreases with a speed vi and ftfc, UM at a speed V2, the resonant frequency coi is determined by the formula (Ш С04 - Шг Gu) / (+ ОМ) - (W2 + Uz). and symmetry - by the difference m (w - od) and (vdz - hell). To implement the method, the device includes a vibration stand and blocks realizing the necessary ratios. 2 ill.

Description

The invention relates to a testing technique and can be used to determine the parameters of the dynamic characteristics of objects during vibration testing.

The purpose of the invention is to expand the scope of the method for determining the resonant frequency of structural elements by making it possible to determine the asymmetry of the linear resonance characteristic and there is no need to introduce two amplifiers with amplification factors determined depending on two frequencies of frequency sweeps.

The goal is achieved by the fact that by the method of determining the resonant frequency of structural elements, namely, that they twice affect the structure with exciting oscillations of a changing frequency, at each excitation, the phase shift between the exciting vibrations and vibrations of the structural elements is measured and the frequency is fixed at where the vibrations of structural elements lag behind the exciting vibrations by l / 2, they change the frequency of the exciting vibrations with a constant speed VL after the phase shift between the exciting By fucking and vibrating the structural elements, the quantities / 2 repeat the frequency sweep with another constant speed V2, in accordance with the invention, they twice act on the structure with exciting vibrations of varying frequency at sweep speeds vi, va, and the direction of the frequency change is opposite to the direction changes in the first and second exposure, and fix the third and fourth

00

with

N5

SB GJ

the frequency at which the vibrations of the structural elements are ahead of the driving ones by / 2 at the scan speeds vi and V2, respectively, and the value of the resonant frequency (Do is determined from the ratio of ohms - o% o)

(OH + OM) - (flJ2 + uu)

whereol, hell, из from and цц are the first, second, third and fourth frequencies, at which the phase difference of the vibration of structural elements and exciting oscillations is equal to / 2.

In addition, first and second quantities are determined equal to the differences of the first and second, fourth and third fixed frequencies, respectively, and when the conditions AI Ae are satisfied; Ai A2; Ai Ag fix the asymmetry at which the pre-resonant branch of the resonant characteristic has a greater, smaller, and equal slope with the resonant branch of the resonant characteristic, respectively.

The introduced new algorithm for determining the resonant frequency of structural elements allows the resonant frequency to be determined irrespective of the frequency sweep speeds from the frequency range, which eliminates the need to introduce amplifiers whose transmission coefficients depend on the frequency sweep speeds. At the same time, the asymmetry of the resonance characteristic is determined by determining the relative steepness of the pre-resonance and resonance branches of the resonance characteristic.

It is known that the maximum shift of the resonance dynamic characteristic at a frequency sweep speed v is

X Z, u, (1)

where. (2)

ft, for generalized detuning

.

ABOUT)

where Q is the quality factor of the symmetric resonance characteristic.

On the basis of expressions (1), (2), (3) at a frequency sweep speed vi (v2) in the direction of increasing (decreasing) it and Q-factor Qi (Qa) of the pre-resonance (resonance) branch of the resonance characteristic, we write the relations

es a

R P

(4a) (46) (4c) (4g)

0

5

0

5

0

5

0

5

0

5

(5a)

(56)

(6)

From relations (4a) and (4c), al a

From relations (46) and (4d) a-Yuo a

ftlo-um d

From relations (5a) and (56) we obtain

 al UM o) s 0) 0 (wi + UAJ) - (hell + sis) From relations (4a) and (46) we obtain

l

ol-th 7T- (vi-v2) Qi; Sho

0) 4-0) 3 - (V1-V2) Q2. Sho

Since K 4 / flJb (vi-v2) for fixed vi, V2, oh is a constant coefficient, then

Ai (wi - ufc) KQu Ae ("u - use) K 02. (7)

From relations (7) Ai Qi AI Q2 If

Ai (- 0) 2) A2 (OM - SHZ),

then QI 02, i.e. the steepness of the pre-resonant branch is greater than the steepness of the resonant branch.

If

Ai (al - zr) Dg (UM - b "s), then Qi 02, i.e. the steepness of the pre-resonant branch is less than the steepness of the non-resonant branch.

If

Ai (al - 0) 2) - Ae (am - hell) then 01 Q2, i.e. the steepnesses of the pre-resonant and resonant branches of the resonant characteristic are the same.

Figure 1 is a block diagram of a device for measuring the resonant frequency of structural elements; Fig. 2 is a diagram of a frequency sweep control unit.

The device includes a frequency sweep control unit 1, a master oscillator 2, an amplitude regulator 3, a power amplifier 4, a vibration stand 5 with a test object 6 installed on it, vibration transducers 7 and 8, matching amplifiers 9 and 10, a phase detector 11, a feedback block 12 zi, the first zero-organ 13, frequency-voltage converters 14, switches 15 and 16.17 and 18, three memory blocks 19.20 and 21, switch 22, decoder 23, four triggers 24, 25, 26 and 27, four delay elements 28, 29, 30 and 31, two blocks 32 and 33, multiplication, six adders 34, 35, 36, 37, 38 and 39, division block 40, reg trattoria 41, the comparison unit 42, a second zero-body 43, the entrance 44 Start.

The frequency sweep control unit 1 comprises pulse generators 45 and 46, triggers 47, 48 and 49, keys 50, 51 and 52,

a charging resistor 53, a storage capacitor 54, three OR elements 55, 56 and 57, a step voltage generator 58 made on the switches 59 and 60, a capacitor 61, a matching amplifier 62, a current-stabilizing two-terminal 63 and a single-oscillator 64, inputs 65, 66, 67, 68 and control unit output 69, common bus 70, two delay elements 71 and 72, input 73 Reset.

The device blocks are connected as follows.

 The output of the frequency sweep unit 1 is connected to the control input of the master oscillator 2, the output of which through series-connected amplitude regulator 3 and power amplifier 4 is connected to the excitation coil (not shown in the figures) of the vibration stand 5 with the test object 6 mounted on it. On the vibration stand 5 and object 6 under test, vibration transducers 7 and 8 are installed, connected by outputs to the inputs of matching amplifiers 9 and 10, respectively, the outputs of which are connected to the inputs of phase detector 11. Matching output th amplifier 9 via the unit 12 feedback connected to the control input of regulator 3 amplitude. In the output of the matching amplifier 10 is connected to the input of the frequency-voltage converter 14, the output of which is connected to the combined inputs of the keys 15, 16, 17, 18. The outputs of the keys 15, 16. 17 are connected to the inputs of the memory blocks 19, 20, 21, respectively. The output of the memory unit 19 is connected to the combined summing inputs of the adders 36, 38 and the input of the multiplication unit 33. The output of the memory unit 20 is connected to the combined summing input of the adder 35, subtracting the input of the adder 39 and the input of the multiplying unit 33. The output of the memory unit 21 is connected to the combined summing input of the adder 35, subtracting the input of the adder 38 and the input of the multiplying unit 33. The output of the key 18 is connected to the combined summing inputs of the adders 36, 39 and the input of the multiplication unit 32. The outputs of the multiplication blocks 32 and 33 are connected to the summing and subtracting inputs of the adder 34, the output of which is connected to the dividend input of the division block 40. The outputs of adders 35 and 36 are connected to the subtracting and summing inputs of the adder 37, the output of which is connected to the input of the Divider of the division unit 40, the output of which is connected to the input of the recorder 41. The outputs of the adders 38 and 39 are connected to the inputs of the comparison unit 42, the output of which is connected to the second input registrar 41. The outputs of the adders 38. 39 are connected to the inputs

the second null-organ 43, the output of which is connected to the third input of the recorder 42. The output of the null-organ 13 is connected to the input of the switch 22, the first output of which

5 is connected to the control input of the key 15 and the recording input of the memory unit 19 directly, and through the delay element 28 to the single input of the trigger 25. The second output of the switch 22 is connected to the control

10 to the input of the key 16 and the input Record of the memory unit 20 directly, and through the delay element 29 to the single input of the trigger 25. The second output of the switch 22 is connected to the control input of the key 16 and the input

15 Writing the memory block 20 directly, and through the delay element 29 to the single input of the trigger 26. The third output of the switch 22 is connected to the control input of the key 17 and the recording input of the memory block 21

0 directly, and through the delay element ЗО to the single input of the trigger 27, the fourth output of the switch 22 is connected to the control input of the key 18 and the inputs Read memory blocks 19,20,21 directly, and through the delay element 31 to the zero combined inputs of the triggers 24,

25,26, 27. The direct outputs of the triggers 24. 25,

26.27 connected to the inputs of the decoder 23, the outputs of which are from first to fourth

0 are connected to the combined control inputs of the frequency scanning unit 1 and the switch 22 from the first to the fourth, respectively. The fifth input of the frequency sweep unit 1 and the single input of the trigger 24 are connected to the external input 44 Start.

The elements of the control unit are connected as follows.

The inputs of the generators 45, 46 are combined and connected through a delay element 71 with

0 input 65 start. The outputs of the generators 45 and 46 are connected to the R- and S-inputs of the trigger 47, respectively, the inverse and direct outputs of which through the keys 50 and 51 are respectively connected through in series

5 connected the charging resistor 53 and the storage capacitor 54 to a common bus 70. A key 52 is connected in parallel to the capacitor 54. A common connection point of the resistor 53 and the key 52 is connected to the output 69

0 of the frequency sweep control unit 1. The control inputs of the keys 50 and 51 are connected to the inverse and direct outputs of the trigger 48, respectively, whose R-input through the OR element 55 is connected to the input 65

5 Start, and the S-input through the OR element 56 - with the control ramp 66 of the control unit 1. The second input of the OR element 55 is connected to the control input 67, and the second input of the OR element 56 through the element 72

delay connected to control input

68. The control input of the key 52 is connected to the output of the OR element 57. The first input of which is connected to the output of the one-shot 64 and the second to the direct output of the trigger 49. The first input 65 of the control unit is connected to the external Start input, combined with the R-input of the trigger 49, whose S-input is connected to input 73 Reset. The direct output of flip-flop 49 is connected to the control input of switch 59. The potential input of power supply E is connected through a series-connected current-stabilizing two-terminal 63, switch 60 and matching amplifier 62 to the control input of pulse generator 46. The control input of the key 60 is connected to the output of the one-shot 64, the control input of which is connected to the input 67. The output of the key 60 is connected through a parallel capacitor 61 and the key 59 to the common bus 70. The control inputs of the generators 45 and 46 are connected to the inverse output of the trigger 49 . At the outputs of the generators 45, 46, pulse sequences are formed only if there is a unit at the control inputs, i.e. if there is a unit potential at the control input 65 Start.

The device operates as follows.

In the initial state, the triggers 24, 25, 26,27 are set to zero, the frequency of the master oscillator 2 is set equal to the lower frequency of the frequency sweep range. The switch 22 is set to the neutral position, while its input is disconnected from the outputs, and the frequency sweep unit 12 is set to the initial state in which the frequency of the generator 2 is fixed.

Upon receipt of a signal at input 44 Start, trigger 24 is set to one. At the same time, a signal arriving at the first control input of the switch 22 and the first control input of the frequency scanning unit 1 appears at the first output of the decoder 23. The decoder 23 operate as follows.

If there is a code combination 0000 at the inputs of the decoder 23, there are no signals at its outputs, if there is a code combination 0001, a signal appears at the first output of the decoder 23, and if there are code combinations 0011, 0111, 1111, the signals at the outputs of the second decoder 3 appear , third and fourth outputs of the decoder, respectively.

If there are signals at the first input of the frequency sweep unit 1, the frequency of the generator 2 increases from the initial value determined, for example, by the lower frequency of the frequency sweep range, with a speed vi. If there is a signal at the second input of the frequency sweep unit 1, the frequency of the generator 2 decreases with a speed of V2 VL. If there are signals at the third (fourth) input of the frequency sweep block 1, the frequency of the generator 2 increases (decreases) with the speed of V2. The signal from the output of the generator 2

through the amplitude regulator 3 and the power amplifier 4, it enters the coil of the moving part (excitation winding) of the vibrostand 5 with the test object 6 installed on it. The signal from the output of the vibration transducer 7 through the matching amplifier 9 and the feedback unit 12 is fed to the control input of the controller 3 amplitudes to stabilize the level of excitation of the vibration stand 5. Signals from the outputs of matching

amplifiers 9 and 10 are fed to the inputs of the phase detector 11.

Initially, the frequency sweep mode of the generator 2 is entered at a speed vi. If the current frequency a) (i) of the excitation of the vibration stand 5 coincides with the resonant frequency of the structural element 6 (object 6), the phase difference of the signals at the inputs of the phase detector 11 is equal to / 2, and the signal at the output of the detector 11 is zero. In this case, a pulse signal appears at the output of the null organ 13, which is fed through the switch 22 to the control input of the key 15, and a voltage equal to the value of the frequency of the resonance peak shifted relative to the resonance frequency uh in the static mode. In addition, the pulse signal from the output of the switch 22 through the delay element 28 is supplied to a single input of the trigger 25,

setting it to one. In this case, a signal appears at the second output of the decoder 23, and the frequency of the generator 2 begins to change with the speed vi in the direction of its decrease.

If the current frequency o (t) of the excitation of the vibration stand 5 coincides with the resonant frequency of the structural element 6, the phase difference of the signals at the inputs of the phase detector 11 is again equal to l / 2, and the signal at the output

detector 11 is zero. At the same time, a pulse signal again appears at the output of the null-organ 13, which is fed through the switch 22 to the control input of the key 16 and to the Write input of the memory unit 20, as a result of which a voltage equal to the value of the frequency resonant peak. The same pulse signal from the output of the switch 22 through the element 29 delay arrives at a single

trigger input 26, setting it to one. In this case, a signal appears at the third output of the decoder 23, and the frequency of the generator 2 begins to change in the direction of it in the increase with the speed V2 VL

If the current excitation frequency y (t) of the vibrating stand 5 coincides with the resonant frequency Sho of the structural element 6 on which the vibration transducer 8 is mounted, the phase difference of the signals at the inputs of the phase detector 11 is again equal to / 2, the output of the detector 11 shows a zero signal, and at the output of the null-organ 13, a pulse signal is generated, which is supplied through the switch 22 to the control input of the key 17 and to the Write input of the memory unit 21, as a result of which a voltage equal to the frequency value 0) 2 is introduced into the memory unit 20. resonant peak. The same pulse signal from the output of the switch 22 through the delay element 29 is supplied to the single input of the trigger 27, setting it to unity. In this case, a signal appears at the fourth output of the decoder 23, and the frequency of the generator 2 begins to change in the direction of its decrease with the speed va.

If the current frequency w (t) of the excitation of the vibration stand 5 coincides with the resonant frequency of the element 6 of the structure, the phase difference of the signals at the inputs of the phase detector 11 is equal to / 2, and the signal at the output of the detector 11 is zero. At the output of the null organ 13, a pulse signal appears, which is fed through the switch 22 to the control input of the key 18 and the inputs Read memory blocks 19, 20, 21 directly, and through the delay element 31 to the zero inputs of the triggers 24, 25, 26 , 27, setting them to zero, and the device to its original state. The signals from the outputs of the memory block 19 and the key 18 are fed to the inputs of the multiplication block 32 and the inputs of the adder 36. The signals from the outputs of the memory blocks 20 and 21 are fed to the inputs of the multiplication block 33 and the inputs of the adder 35. The signals from the outputs of the memory blocks 19 and 21 arrive at the summing and subtracting inputs of the adder 38, respectively. The signals from the outputs of the key 18 and the memory unit 20 are fed to the summing and subtracting inputs of the adder 39, respectively. The signals from the outputs of the blocks 32 and 33 of the multiplication are fed to the summing and subtracting inputs of the adder 34, the output signal of which is fed to the input of the Divisor of the division unit 40. At the input of the Divider block 40 receives a signal from the output of the adder 37. to the summing and subtracting inputs of which the signals from the outputs of the adders 35 and 36, respectively. The output signals of the adders 38 and 39 are input to the comparator 42 and the inputs of the second null-organ 43. The signals from the outputs of the division unit 40, comparator 42 5 and the null-organ 43 are fed to the first, second, and third inputs of the recorder 41, respectively.

The presence and magnitude of the signal at the first input correspond to the resonance

0 frequency of the structural element, the presence of a signal at the second input corresponds to the fulfillment of the condition Ai Yes (the steepness of the pre-resonant branch is greater than the steepness of the resonant branch), the presence of the signal at

5, the third input corresponds to the condition AI Dz (the steepness of the pre-resonant and the non-resonant branches are equal).

The advantage of the proposed method for determining the resonant frequency depending on the scanning speeds in the frequency range due to the exclusion of amplifiers with transmission coefficients depending on the scanning speeds while determining the asymmetry

5 of the resonant branch, greater than, less than or equal to the steepness of the resonant branch of the resonant characteristic.

The frequency sweep control unit 1 operates as follows.

The oscillation frequencies of the pulse generators 45 and 46 are chosen close so that the beat frequency, which determines the period of repetition of the generated linearly varying

5, the voltage was several orders of magnitude lower, and the ramp time was such that the frequency range of the reproduced vibrations was overlapped. To get the day off

0, the signal with increasing frequency is tuned so that the frequency of generator 46 is higher than the frequency of generator 45. In the initial state, trigger 49 is set to one.

5 When a signal is received at input 65 on

pulses are generated by the outputs of the generators 45, 46. The output pulses of the generators 45 and 46 control the state of the trigger 47, at which one output

0 is a sequence of rectangular pulses of linearly increasing duration, and on the other is a sequence of pulses of linearly decreasing duration. In this case, the trigger 48 is set to

5 is zero, key 50 is closed, key 51 is open. Through a closed key 50, pulses of linearly increasing duration through a resistor 53 are supplied to a capacitor 54, as a result of which, with the switch 52 open (since the trigger 49 is set to zero), an increasing section of the output voltage is formed at the output 69.

When a signal arrives at the second control input 66, the trigger 48 is set to a single state, with the key 51 closing and the key 50 opening. The charge resistor 53 and the storage capacitor 54 are connected to the direct input of the trigger 47, on which a train of pulses of linearly decreasing duration is formed, and a linearly falling section of the output voltage is formed at the output 69.

When a signal appears at the third control input 67, the trigger 48 is set to zero, with a high potential present at the control input of the OR element 55 and at the output 69, an increasing portion of the output voltage is formed again. At the same time, the signal supplied to input 67 starts a single-shot 64, at the output of which a pulse is generated, which passes through the OR element 57 to the control input of the switch 52. Thus, the voltage on the capacitor 54 is set to zero. The pulse signal from the output of the one-shot 64, which enters the control input of the key 60, closes the key 60. In this case, the capacitor 61 is charged through the current-stabilizing two-terminal 63 and the key 60 from the power supply E by the voltage D U (the key 59 is open, so as trigger 49 is set to zero). The voltage A U is supplied through the matching amplifier 62 to the control input of the generator 46 and its frequency increases, which leads to an increase in the beat frequency and the steepness of the linearly varying output voltage.

When a signal appears at control input 68, trigger 48 is again set to a single state, key 51 closes, and key 50 opens. Thus, a stepwise increasing voltage is generated at the output of step voltage generator 58, and a triangular voltage is generated at output 69 different steepness.

When a signal appears at input 73, the reset trigger 49 is set to one state, the keys 52 and 59 are closed, the capacitors 54 and 62 are discharged through the keys 52 and 59, respectively, and the generators 45 and 46 are turned off. The device is reset.

Compared with the prototype, the proposed method for determining resonance

the frequency of structural elements has the advantage of a wider range of applications due to the simplification of the implementation of the method due to the absence of need

the use of amplifiers with adjustable gain factors determined by the values of the frequency sweep rates, and by determining the nature of the asymmetry of the linear resonance characteristic.

Claims (1)

0 Formula and acquisition A device for measuring the resonant frequency of structural elements, containing a serially connected frequency sweep control unit defining 5 a generator, an amplitude controller, a power amplifier and a vibration stand designed to install the test object, a first vibration transducer mounted on the moving part of the vibration stand, a second vibration transducer designed to be installed on the test object, the first and second matching amplifiers, the inputs of which are connected to the corresponding vibration transducer mi phase detector 5 inputs of which are connected to the outputs of the matching amplifiers, a feedback unit, the input of which is connected to the output of the first matching amplifier, and the output is connected to the control input of the amplitude controller, a frequency-voltage converter, the input of which is connected to the output of the second matching amplifier, serially connected null-organ, the input of which is connected to the output of the phase detector, and 5 a switch, a decoder, the outputs of which are connected to the corresponding control inputs of the frequency sweep control unit and the switch, the first and second triggers, the unit outputs of which are connected to the corresponding inputs of the decoder, the key whose input is connected to the output of the frequency-voltage converter, and the control input - with the first output of the switch, the first element 5 delays, connecting the first output of the switch with the single input of the second trigger), the second delay element and the recorder, which is different. that, with the aim of increasing the accuracy of expansion 0 functionality by assessing the symmetry of the characteristics, it is equipped with third and fourth triggers, the unit outputs of which are connected to the corresponding inputs of the decoder, 5 single inputs through the second and third delay elements - with the second and third inputs of the decoder, and zero inputs - with zero inputs of the first and second triggers and through the fourth delay element - with the fourth output of the decoder, second, third and fourth keys, the inputs of which are connected to the output of the frequency-voltage converter, and the control inputs with the corresponding outputs of the switch, three memory blocks, the inputs of which are connected to the outputs of the corresponding keys, and the Record inputs are with the corresponding outputs of the switch , the first block of multiplication, the inputs of which are connected to the outputs of the first block of memory and the fourth key, with the second block of multiplication, the inputs of which are connected to the outputs of the second and fourth blocks of memory, the first adder, the inputs of which are connected to the outputs of the first and second blocks of multiplication, the second the adder, the inputs of which are connected to the outputs of the second and third memory units, the third adder, the inputs of which are connected to the inputs of the first multiplication unit, the fourth adder, the inputs of which are connected to the outputs of the second and third adders, the fifth adder, the inputs of which are connected to the outputs of the first and third memory units, the sixth adder, the inputs of which are connected to the outputs of the second memory unit and the fourth key, a divider, the dividend input of which is connected to the output of the first memory block, and the input of the Divider is connected to the output of the fourth memory block, and the output - to the first input of the recorder, a comparison unit whose inputs are connected to the outputs of the fifth and sixth adders, and the output to the second input of the recorder, and the second zero-organ, the inputs of which are connected to the inputs of the comparison unit, and the output to the third input of the registrar. L 5b G7Ј 65 66 67 6873 Fig 1