JPS6147521A - Apparatus for measuring attenuation ratio - Google Patents

Abstract

PURPOSE:To simply calculate an attenuation ratio with good accuracy in a vibration system inferior to a coherence characteristic, by measuring the attenuation ratio by using frequency regardless of its mobility. CONSTITUTION:A band pass filter 6, of which the center frequency fi can be set variably, is connected to the real number part data output terminal of a Fourier transforming device 14. When the center frequency of the band pass filter 6 is set to aimed frequency, a signal with a predetermined band having the aimed frequency as central frequency is outputted from the band pass filter 6 as shown by the drawing C. A central processing unit (CPU) 18 is connected to the output terminal of the band pass filter 6 and CPU18 differentiates the data frequency of a frequency axis inputted from the band pass filter 6 and operates an attenuation ratio xsi on the basis of formula. The attenuation ratio xsi is displayed on a display device 12 or printer 10.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a damping ratio measuring device, and is particularly applicable to measuring the damping ratio of a vibration system with poor coherence characteristics, such as periodic data such as a round bar, with high accuracy. The present invention relates to a damping ratio measuring device that can measure damping ratios.

[Conventional technology]

Conventionally, a vibration system is vibrated to detect periodic data related to time changes such as acceleration, and the transfer characteristic A / F expressed as the ratio of the input F to the output, that is, the change in mobility (level) with respect to the frequency freq is calculated. As shown in Fig. 2, the frequency of mobility f u is 3 dB lower than the mobility of the focused frequency (e.g., resonance point) fi.
s f L k was determined, and the damping ratio ζ was determined based on the following formula.

[Problem that the invention seeks to solve]

However, in such conventional attenuation ratio measurement methods, if the coherence characteristic is poor at the focused frequency, it is difficult to accurately determine the mobility at the focused frequency fi, so the value of the frequency afu, f+, which is 3 dB lower, is also inaccurate, and as a result, The problem that the accuracy of the damping ratio deteriorates is b.
Tsuda. That is, in FIG. 2, the coherence function represented by the broken line at the resonance point has a value close to 0, indicating a state in which the coherence characteristics are poor, but the coherence characteristics are very poor at the frequency f1, so The accuracy of the mobility is poor, and therefore the accuracy of the damping ratio is also poor.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention has been made by focusing on frequencies unrelated to mobility, and includes a detection means for detecting periodic data of a vibration system related to time changes, and a 7-lier transform of the periodic data. converting means for performing all custom transmission calculations; band-passing means for passing only data in a predetermined frequency band centered on the nine frequencies of the real part data of the transfer characteristic; and data passed through the band-passing means. Find the frequency that shows the maximum value and the frequency that shows the minimum value, and then calculate the maximum ! and calculation means for calculating the damping ratio based on the frequency representing the minimum value and the frequency representing the minimum value.

[Function] Next, the present invention will be explained in detail. As shown in the three causes of freshness, 1
The equation of motion of the spring-mass-dashpot system with degrees of freedom is expressed as follows.

M″x”+cx+Kx=f ・・・・・・・・・
...(2) where M is the mass, C is the damping coefficient, K is the spring constant, f is the external force, X is the displacement, and i is the time t of each X.
These are the first-order differential and the second-order differential with respect to.

Here, x=×ejw1 (however, j=v”T,
When formula (2) is transformed by assuming that w is the frequency, the following formula (3) is obtained.

(Mv7+K) X ejWt+jcwX e jw
't=F=(3) Next, when A=vine, A/Fi is calculated as follows.

Equation (4) above is expressed as a function with frequency W as a variable, and since input corresponds to output and F corresponds to input, Equation (4) above is the Fourier transform form of output. Input 7-
This represents a transfer function G expressed as a ratio to the Rie transform form.

Let p be the bundle number part of the above equation (4), and differentiate this real number part p with respect to the frequency W, as follows.

Here, wt such that dp/dw=0 is determined. Since the vibration system is vibrating, W ”-, O, dp
/dw=o, it is necessary to satisfy the following equation.

M(KM-C")v'-2MK" is 10KB=0...
・・・・・・(6) When we calculate the roots rt and rzt of the two-arrow equation when w”=r, From the above equations (7) and (8), By the way, the critical damping coefficient Cc is cc=2Vi [・・・・・・・・・・・・・・・(lO
), the above equation (9) can be written as:
It represents the damping ratio.

In the above equation (11), rl"W1!, r2=W2"
Therefore, the damping ratio ζ is expressed as follows.

wl”-W2 friend ζ=□ ... song... song (12) ws ” +
w22 In the above, we considered a vibrating system with l degrees of freedom, but the vibration characteristics of a general vibrating system with many degrees of freedom can be considered to be a superposition of the vibration characteristics of vibrating systems with l degrees of freedom, and vice versa. If we focus on the @-reaching characteristic in a specific frequency band, it can be considered as a vibration system with one degree of freedom, so if we apply the above principle to a vibration system with multiple degrees of freedom, we can find the damping ratio.

The present invention measures the damping ratio based on the above principle, in which the detection means detects the periodic data of the vibration system regarding time changes, and the conversion means converts the periodic data f7-
The transfer characteristic shown in equation (4) above is calculated by converting the IJ The frequency indicating the maximum value and the frequency indicating the minimum value of the data passed through the band pass means are determined, and the attenuation ratio is calculated using the above equation (12). Here, in order to calculate the transfer characteristics, it is necessary to use acceleration data as input,
When the detection means detects periodic data of displacement, it is converted to acceleration data by second-order differentiation, and when the detection means detects periodic data of velocity, it is converted to acceleration data by first-order differentiation. can do.

[51! Embodiment] An embodiment of the present invention will be described in detail below with reference to FIG. This embodiment is suitable for measuring the damping ratio of an automobile body, etc.

The accelerometer 2 is attached to the vibrating base and detects acceleration as periodic data regarding time changes.

The signal output from this accelerometer 2 is shown in (A) in Figure 1.
The data is on a time axis as shown in . This accelerometer 2 is connected to a Fourier transformer 4 comprised of a microprocessor. This Fourier transformer 4 has the same configuration as the conventional one, and performs high-speed 7-lier transform on the input time axis data and calculates the transfer characteristic as frequency axis data. The data is as shown in FIG. 1(B). A bandpass filter 6 whose center frequency fit can be set variably is connected to the real part data output terminal of the Fourier transformer 4. When the center frequency t of the band-pass filter is set to the focused frequency, the band-pass filter 6 outputs a signal of a predetermined band having the focused frequency as the center frequency, as shown in FIG. 1(C). A central processing unit (CPU) 8 is connected to the output end of the bandpass filter 6. The CPU 8 differentiates the frequency axis data input from the bandpass filter 6 with respect to frequency, and the differential coefficient is 0. The frequency wl,
Wl f is determined, and the damping ratio ζ is calculated based on the above equation (12).

Then, the attenuation ratio ζ calculated by the CPU 8 is displayed on the display device 12 or the 7' link 10.

That is, by setting the frequency for determining the damping ratio (the frequency of interest)'t-band pass filter and inputting time axis data, the damping ratio will be displayed.

Although the following explanation has been given above using an accelerometer, a displacement needle or a speedometer may also be used, and in this case, the data is converted into acceleration data using a Fourier transformer and processed. Also, a 7-lier transformer, a bandpass filter and a C
It may be configured with one computer.

〔Effect of the invention〕

As explained above, since the present invention measures the damping ratio at a frequency that is not related to mobility, it is possible to obtain the damping ratio accurately and easily in a vibration system with poor coherence characteristics. .

[Brief Description of the Drawings] Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram for explaining a conventional method of determining a damping ratio, m
Figure 3 is a diagram showing the spring quality meter dashpot system. 2... Accelerometer, 4... Fourier transformer, 6...
Bandpass filter, 8...CPU.

Claims (1)

[Claims] (1) A detecting means for detecting periodic data of a vibration system related to time changes, a converting means for calculating a transfer characteristic by Fourier transforming the periodic data, and a center frequency of a focused frequency of the real part data of the transfer characteristic. a band pass means for passing only data in a predetermined frequency band, and a frequency indicating a maximum value and a frequency indicating a minimum value of the data passed through the band pass means, and a frequency indicating the maximum value and a frequency indicating the minimum value. A damping ratio measuring device comprising: calculation means for calculating a damping ratio based on the above.