JPS60227136A - Measuring method of frequency response function - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a truncation error and take an accurate measurement by turning on and off the driving coil of a dynamic exciter and generating a transient irregular wave, and short-circuiting the driving coil once the driving coil is turned off. CONSTITUTION:A structure 1 to be tested is excited by the exciter 2 fitted through a load meter 4 and the vibration response of the structure 1 is measured by a vibration meter 5. A signal processor 6 calculates a frequency response function from the ratio of the vibration response and exciting force. A movable part 12 is mounted on the field system 10 of the exciter 2 across a spring 11 and the driving coil 13 is provided to the movable part 12. A switch S7 such as a switching element is interposed between a signal generator 3 and the exciter 2 and a stationary irregular wave is outputted from the generator 3 to turn on and off S7, sending the transient irregular wave to the exciter 2. Namely, the contact is placed at a position P1 and returned to a position P2 after the transient irregular wave is generated for a specific time to break the contact while short- circuiting the coil 13. Thus, the occurrence of a truncation error is prevented and an accurate measurement is taken.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an open side method of a frequency response function of a structure.
The purpose is to measure frequency response functions with high accuracy.

<Prior art> The frequency response function of the structure is the same as that of the test structure K[! + and measure the response with a vibration meter.

Figure 1 shows the configuration of this vibration experiment, in which a load cell (41f:
) is vibrated by a signal generated from a signal generator (3), and the structure (1) is entirely vibrated. Then, the excitation force acting on the structure (1) is measured with a load meter (4), and the vibration response of the structure (1) is measured with a vibration meter (5). These measured values are input to a signal processing device (6), where the ratio of vibration response to excitation force is determined as a function of frequency. This yields a frequency response function.

Here, irregular waves are often used as the excitation signal from the signal generator (3). This is because the frequency components of irregular waves are distributed over a wide range, so it is possible to simultaneously excite the structure (1) at all frequencies within the required range. However, this irregular wave As shown in Fig. 2, when an interval of finite length T is digitized for frequency E answer function calculation, the first value of this data S! and the last value Sn will generally be different values, so this data can be reduced to a finite 7-
The disadvantage of the RIE conversion is that it produces an error called a truncation error or a leakage error.

In order to prevent this, there is a known method of using a transient irregular wave in which the irregular wave is generated for a time T shorter than T, as shown in Figure 3, and digitizing it to include this time T'. 2.

However, when such an excitation signal is used, new problems arise, such as poetry in which a structure is actually vibrated. That is, the fourth
As shown in the figure, when the vibration exciter is vibrated using the excitation signal a, the actual excitation force has a waveform different from that of the signal a due to the characteristics of the structure. After reaching 0, the excitation force becomes almost 0. However, even after the excitation force becomes 0, some vibration remains in the structure, and damped free vibration is observed in the vibration response C.

Therefore, when this waveform is digitized, the beginning of the data is 0.
However, if the end of the data is a value other than 0, a truncation error will occur.

Even when transient irregular waves are used in this way, the truncation error cannot be completely eliminated, and this has been an obstacle to measuring the entire frequency response function with high accuracy.

<Summary of the Invention> The present invention has been made to improve the drawbacks of the prior art described above, and uses an electrodynamic vibrator as the vibrator, and generates transient irregular waves by intermittent driving coils. The basic feature is that when the drive coil is cut off, the drive coil is simultaneously short-circuited.

Figure 5 shows the basic configuration of the electrodynamic shaker that is most often used in general vibration experiments. QO is a magnetic field, and a movable part (c) is attached thereto via a spring OJJ. When a current is passed through the drive coil α1 provided in the movable part (2), a force from the field αq acts, and the movable part (12) moves.

In the present invention, this drive coil α3 is turned on and off to generate a transient irregular wave. That is, as shown in Fig. 6, a switch (7) such as a switching element is interposed between the signal generator (3) and the vibrator (2), and a steady disturbance is transmitted from the signal generator (3). A regular wave is outputted, and the switch (7) is turned on and off to cause the exciter (2) to generate a transient irregular wave. That is, after the contact is set at the pl position and a T transient irregular wave is generated for a certain period of time, the contact is returned to the P2 position to be disconnected, and at the same time, the drive coil (2) is short-circuited.

In this way, during the time T, the excitation signal a, the excitation force b
, vibration response C are the same as in the conventional case, but after one hour, they behave differently.

That is, after a period of time has elapsed, the drive coil 01 is short-circuited and becomes an independent coil. On the other hand, the structure no longer receives the excitation force and begins force-free vibration, and the drive coil (4) also vibrates accordingly.
At this time, the free vibration of the structure is rapidly attenuated because it receives a force that prevents vibration from the magnetic field created by the field (lfj).As a result, even when data for only the length of time T is digitized. The beginning and end of the data are 0, and no truncation error occurs.This is shown in FIG.

<Effects of the Invention> As explained above, according to the method of the present invention, the drawbacks of conventional transient irregular wave excitation can be improved and the occurrence of truncation error 70 can be prevented, so accurate frequency response functions can be measured. effective.

[Brief explanation of drawings]

Figure 1 is a storage diagram of the vibration experiment method, and Figures 2 to 7 are graphs for explaining the method of the present invention. (1)...Structure, (2)...Vibrator, (4)...
- Load needle, (5)... Vibration meter, (6)... Signal processing device, (7)... Switch, 01... Drive coil. Patent applicant: Nippon Kokan Co., Ltd. Inventor: Ryudo Ikeuchi Masaaki Shirai Patent attorney: Shozo Yoshihara 1M 1 Figure tgZ Figure 1113 Figure 1!4c Figure 5 Figure 6 Figure 7 Figure 7 01Ω

Claims (1)

[Claims] In a method of exciting a measured object with an electrodynamic vibrator and measuring the response vibration of the measured object to measure a frequency response function, the drive coil of the electrodynamic vibrator is intermittent. A method for measuring a frequency response function characterized by generating a transient irregular wave and simultaneously short-circuiting the driving coil when the driving coil is disconnected.