PL231337B1 - Device for identification of free vibration frequencies, preferably for the continuous vibroacoustic systems - Google Patents

Description

Description of the invention

The subject of the invention is a device for identifying natural frequencies, in particular for continuous vibroacoustic systems.

The subject of the invention relates to modal analysis issues. It is performed in order to identify the natural frequencies, the damping factor and the amplitude of normal modes of continuous vibroacoustic systems.

The existing methods of modal analysis are based on the Fourier transform, which are characterized by low resolution due to the uncertainty principle. This causes a large error in determining the eigenfrequencies when the modal distribution of the examined structure is characterized by a high mode density.

There is known from the publication WO0133182 (A1) a method of analyzing vibrations of vibroacoustic systems, which consists in analyzing the signals from one or more vibration sensors by calculating the spectral power density matrix and its decomposition by means of singular value distribution by means of a Fourier transform. The method enables the determination of the values of natural frequencies, damping coefficients and vibration modes.

He is known from the publication of EGE, Kerem; BOUTILLON, Xavier; DAVID, Bertrand. High-resolution modal analysis. Journal of Sound and Vibration, 2009, 325.4: 852-869, a modal analysis method using the signal parameter estimation method known as ESPRIT and the perturbation method known as ESTER.

The aim of the invention is to be able to identify the natural frequencies of a continuous vibroacoustic system without the need to use signal processing techniques with high computational complexity, especially the fast Fourier transform.

The device for identifying natural frequencies, in particular of continuous vibroacoustic systems, has at least one measurement sensor, preferably a microphone and / or an accelerometer and / or a piezoelectric film, a preamplifier circuit, an anti-aliasing filter, an analog-to-digital converter and a digital signal processing circuit, which includes the following blocks:

- digital low-pass filter with a cut-off frequency of 1/8 of the sampling frequency,

- digital filter with infinite impulse response, whose polynomial of the complex variable Z of the transmittance numerator has four real roots equal to zero, and the denominator polynomial is of fourth degree, and only the coefficients of even and zero degrees are different from zero,

- normalizing system,

- effective value converter,

- amplitude discriminator,

- hysteresis loop system,

- differential circuit,

- zero cross detector,

- copying system,

- display,

- and a system that transforms the value of the coefficient at the second power of the polynomial into frequency.

The measuring sensor recording the response of the tested system is connected via a preamplifier and an anti-aliasing filter with an analog-to-digital converter. The output of the converter is connected through the input of the signal processing system with a low-pass filter with a cut-off frequency equal to at most 1/8 of the sampling frequency. The output of the low-pass filter is connected to the digital filter input of an infinite impulse response filter with two coefficients: the factor that determines the goodness of the filter and the coefficient that determines the center frequency of the filter. The output of the bandpass filter is connected to the input of an RMS converter directly or preferably through a normalizing circuit. The RMS converter output is connected to the input of the hysteresis loop system through the amplitude discriminator system, the output of which is connected to the input of the hysteresis loop system. The output of the hysteresis loop is connected to the input of the differentiator. The output of the derivative is connected through the zero cross detector to the trigger input of the copier, which copies the current value of the coefficient determining the center frequency of the bandpass filter to the circuit

Converting the value of the center frequency setting factor of the bandpass filter to frequency. The circuit for converting the value of the coefficient determining the center frequency of the bandpass filter to frequency can be implemented in the form of a lookup table or a mathematical function.

The set of filters that make up the high Q bandpass filter allows to achieve high frequency resolution. The tuning system of this filter uses the fact that the vibroacoustic system, stimulated by a signal with a frequency equal to its natural frequency, emits signals of high energy to the environment. A characteristic feature of the tuning system is the method of transforming the response of the tested system into the value of the excitation frequency. The purpose of the nonlinear transformation is to obtain a smooth waveform, the derivative of which is applied to the zero crossing detector as a trigger for the trigger circuit.

The subject of the invention is shown in the drawing, in which Fig. 1 shows a block diagram of the device.

P r z k ł a d

The device for identifying natural frequencies, especially continuous vibroacoustic systems, is equipped with a measuring sensor 1 (microphone), a preamplifier circuit 2, an anti-aliasing filter 3, an analog-to-digital converter 4 and a digital signal processing system 5, which includes the following blocks:

digital low-pass filter 6 and cut-off frequency equal to 1/8 of the sampling frequency, digital filter with infinite impulse response 7 containing two coefficients 7a and 7b: filter factor factor 7a and filter center frequency factor 7b, polynomial of the complex variable Z transmittance count of the digital filter o of the infinite impulse response 7 has four real roots equal to zero and the polynomial of the denominator of this transmittance is of the fourth degree and only the coefficients of the even and zero polynomial are different from zero, normalizing system 8, RMS converter 9, amplitude discriminator 10, hysteresis loop system 11, system a derivative 12, a zero crossing detector 13, a copier 14, and a circuit for converting the coefficient value at the second power of the polynomial to a frequency value 15. The frequency value is displayed on the display 16.

The measuring sensor 1, recording the response of the tested system 17, is connected via the preamplifier 2 and the anti-aliasing filter 3 to the analog-to-digital converter 4. The converter output 4 is connected through the input of the signal processing system 5, with a low-pass filter with a cut-off frequency equal to 1/8 of the sampling frequency. The output of the filter 6 is connected to the input of the digital filter with infinite impulse response 7 having two coefficients: a coefficient that determines the goodness of the filter 7a and a coefficient that determines the center frequency of the filter 7b. The output of the digital filter with infinite impulse response 7 is connected to the input of the RMS converter 9 directly through the normalizing circuit 8. The output of the circuit 9 is connected to the input of the hysteresis loop circuit 11 through the amplitude discriminator circuit 10. The output of the circuit 11 is connected to the differential circuit 12. The output of circuit 12 is connected via a zero-crossing detector 13 to a trigger input 14a of copier 14, which copies the current value of the coefficient 7b to the coefficient-to-frequency converter. Arrangement 15 can be implemented in the form of a lookup table or a mathematical function. The frequency value is shown on display 16.

The device according to the invention requires fewer arithmetic and logic operations than the number of such operations required to calculate the fast Fourier transform used in WO0133182 (A1) and requires fewer arithmetic and logic operations than the number of such operations necessary for the implementation of ESPRIT and ESTER methods known from the publication EGE, Kerem; BOUTILLON, Xavier; DAVID, Bertrand. High-resolution modal analysis. Journal of Sound and Vibration, 2009, 325.4: 852-869.

Claims (4)

Patent claims 1. A device for identifying natural frequencies, in particular continuous vibroacoustic systems having at least one measuring sensor, a preamplifier circuit, an anti-aliasing filter, an analog-to-digital converter, a digital signal processing system and a display, characterized in that the digital signal processing system (5) consists of from the following blocks: - digital low-pass filter (6) with a cut-off frequency of 1/8 of the sampling frequency, - digital filter with infinite impulse response (7), whose polynomial of the complex variable Z of the transmittance numerator has four real roots equal to zero, and the denominator polynomial is of fourth degree, and only the coefficients of even and zero degrees are different from zero, - normalizing system (8), - RMS converter (9), - amplitude discriminator (10), - hysteresis loop system (11), - the differential circuit (12), - zero crossing detector (13), - copying system (14), - and a system converting the value of the coefficient at the second power of the polynomial into frequency (15), where the measuring sensor (1) is connected through the preamplifier (2) and the anti-aliasing filter (3) with the analog-to-digital converter (4) and the converter output (4) is connected is through the input of the digital signal processing system (5) with a low-pass filter (6) with a cut-off frequency equal to at most 1/8 of the sampling frequency, the output of the low-pass filter (6) is connected to the input of the digital filter with infinite impulse response (7) with two coefficients : a factor that determines the quality of the filter (7a) and the factor that determines the center frequency of the filter (7b), in addition, the output of the digital filter with infinite impulse response (7) is connected to the input of the RMS converter (9) and the output of the RMS converter (9) is connected to the input of the amplitude discriminator circuit (10), the output of which is connected with the input of the hysteresis loop system (11), moreover, the output of the hysteresis loop system (11) is connected to the input of the differentiator (12), the output of which is connected through the zero crossing detector (13) with the triggering input (14a) of the copying circuit (14) . 2. The device according to claim A device according to claim 1, characterized in that a microphone or an accelerometer or a piezoelectric film is used as the measuring sensor (1). 3. The device according to claim A device according to claim 1, characterized in that the transforming circuit (15) is implemented in the form of a look-up table or a mathematical function. 4. The device according to claim The method of claim 1, characterized in that the output of the digital filter with infinite impulse response (7) is connected to the input of the RMS converter (9) through a normalizing circuit (8).