Method for deriving vibration characteristics and measurement system

Abstract

To provide a technique to derive the vibration characteristics of a mechanical structure.SOLUTION: A shooting device 3 causes a shooting body 4 to collide with a mechanical structure 2. A vibration measurement device 5 measures the vibration of the excited mechanical structure 2. A processor 10 derives vibration characteristics from the measured vibration.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to techniques for deriving vibration characteristics of a mechanical structure. [Background technology]

[0002] Impact (impulse) hammers equipped with built-in force sensors are widely used to derive the vibration characteristics of mechanical structures such as machine tools. In vibration tests, a person strikes the object to be measured (mechanical structure) with the impact hammer, and the excitation force at the time of striking is measured by a force sensor, while the vibration of the object to be measured is measured by a three-axis accelerometer attached to the object to be measured, and the compliance transfer function is derived.

[0003] Figure 1(a) shows the frequency components of the vibration displacement derived by converting the measured vibration acceleration into displacement through a fast Fourier transform (FFT). Here, the vibration acceleration is converted into displacement through a fast Fourier transform (-ω 2 ) to obtain the frequency components of the displacement.

[0004] Figure 1(b) shows the frequency components of the excitation force derived by performing a fast Fourier transform on the measured excitation force. Figure 1(b) only shows the measurement results of the excitation force from 0.0023 to 0.0043 seconds, but in reality, the excitation force is measured from 0 to 0.08 seconds, just like the vibration acceleration shown in Figure 1(a).

[0005] Ideally, the excitation force when the impact hammer strikes the object to be measured should show an impulse-like waveform with a time width of zero and an infinite peak value, and show a constant value over a wide frequency range. However, as shown in Fig. 1(b), in reality, the excitation force has a time width and a finite peak value, so the excitation force in the high frequency range is lower and the phase lags compared to the low frequency range. Therefore, when calculating the compliance transfer function, a correction process must be performed in which the actual excitation force is divided in the complex domain to raise the amount of the decrease in the excitation force in the high frequency range and advance the phase.

[0006] Figure 1(c) shows the compliance transfer function corrected using the measured excitation force. Conventionally, since it is not possible to apply an ideal impulse-like excitation force, the compliance transfer function is calculated by dividing the frequency component of the vibration by the measured excitation force. Summary of the Invention [Problem to be solved by the invention]

[0007] In order to shorten the time that the impact hammer strikes the object being measured (strike time or collision time) and bring the excitation force closer to an ideal impulse waveform, it is recommended to use a tip made of a high elastic modulus material such as aluminum alloy or steel. By using a tip made of a high elastic modulus material, the impact time can be shortened compared to tips made of rubber or resin. However, it is still difficult to say that the impact time can be sufficiently shortened, and it is still necessary to measure the excitation force and correct the vibration measurement results.

[0008] Furthermore, since high modulus materials generally have high hardness, if the hardness of the vibrating part of the hammer is not sufficiently low compared to the object being measured, there is a problem of leaving a mark on the object being measured. For this reason, it is necessary to attach a tip with low hardness to the vibrating part, but if the tip hardness is low, the impact time will be long, which creates a problem of reducing the high frequency components of the vibration force. In this way, it is necessary to adjust the tip hardness (more precisely, the modulus of elasticity) in vibration tests using impact hammers, and this adjustment requires experience.

[0009] In conventional vibration testing, the impact speed is determined by the speed at which a person swings the hammer, so it does not vary significantly from person to person (the impact speed does not vary by an order of magnitude from person to person). Therefore, in order to generate an excitation force that makes the vibration measurement level large enough against disturbances and noise, it is necessary to increase the hammer mass. On the other hand, if the hammer mass becomes close to the equivalent mass of the object to be measured, the double-hit problem is likely to occur, so it is not acceptable to make the hammer mass too large. In this way, in vibration testing using an impact hammer, the hammer mass needs to be appropriately adjusted for each object to be measured, and this adjustment requires experience.

[0010] In addition, when deriving the vibration characteristics of a mechanical structure with a rotating body, it is dangerous for a person to strike the rotating body with an impact hammer. Even if it is possible to strike the rotating body with a hammer, if the striking time is not short enough, the measured vibration will be affected by the peripheral speed of the rotation, making it difficult to measure the vibration characteristics accurately.

[0011] The present disclosure has been made in light of these circumstances, and an object of the present disclosure is to provide a new technique for deriving vibration characteristics of a mechanical structure. [Means for solving the problem]

[0012] One aspect of the present disclosure is a method for deriving vibration characteristics of a mechanical structure, the method comprising the steps of: impacting a projectile against the mechanical structure to vibrate the mechanical structure; measuring the vibration of the excited mechanical structure; and deriving the vibration characteristics from the measured vibration.

[0013] Another aspect of the present invention is a measurement system for deriving vibration characteristics of a mechanical structure, comprising a launching device for impacting a projectile against the mechanical structure, a vibration measuring device for measuring vibrations of the excited mechanical structure, and a processing device for deriving vibration characteristics from the measured vibrations.

[0014] Any combination of the above components and conversion of the expressions of the present disclosure between methods, devices, systems, etc. are also valid aspects of the present disclosure. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1(a) shows the frequency components of the vibration displacement derived by performing a fast Fourier transform on the vibration acceleration and converting it into displacement, FIG. 1(b) shows the frequency components of the excitation force derived by performing a fast Fourier transform on the excitation force, and FIG. 1(c) shows the compliance transfer function corrected using the excitation force. [Diagram 2] FIG. 4 is a diagram showing longitudinal vibration in a vibration unit. [Diagram 3] FIG. 4 is a diagram showing an example of an excitation force waveform. [Figure 4] FIG. 13 is a diagram showing the results of frequency analysis of an excitation force waveform. [Diagram 5] FIG. 1 is a diagram illustrating an example of the configuration of a measurement system according to an embodiment. [Figure 6] FIG. 1 is a diagram showing the relationship between the size of a BB bullet and the upper limit frequency of a frequency band. [Figure 7] FIG. 13 is a diagram showing a waveform of an excitation force approximated by a half-sine wave. [Figure 8] FIG. 13 is a diagram showing the results of frequency analysis of an excitation force waveform. [Figure 9] FIG. 1 illustrates a configuration for measuring a force waveform when a projectile impacts an object. [Figure 10] FIG. 13 is a diagram showing the measurement results of the excitation force. [Figure 11] FIG. 13 is a diagram showing the results of frequency analysis of an excitation force waveform. [Figure 12] FIG. [Figure 13] FIG. 13 is a diagram showing the results of frequency analysis of the tool speed. [Figure 14] FIG. 1 illustrates a quantitative compliance transfer function. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present inventors have investigated new vibration means from the viewpoint of sufficiently shortening the impact time (collision time or contact time) while applying a sufficient vibration force. In the course of this investigation, they have found that the parameter that has a large effect on the impact time is the size of the vibration part (mainly the mass part of the hammer in the case of an impact hammer) that is equal to or greater than the longitudinal elastic modulus (Young's modulus) of the tip, and that the smaller the size of the vibration part, the shorter the impact time can be. This finding will be explained below.

[0017] In order to apply an excitation force with a short impact time close to an ideal impulse, the dimensions of the excitation part must be relatively small compared to the dimensions of the object to be measured. Also, in order not to leave a mark, the hardness of the excitation part must be relatively low compared to the hardness of the object to be measured. Generally, the Young's modulus of a material with low hardness is low. Therefore, the following conditions are prerequisites. (1) The dimensions of the vibration part are sufficiently smaller than the dimensions of the object to be measured. (2) The hardness and modulus of elasticity of the vibration part are relatively small compared to the hardness and modulus of elasticity of the object to be measured.

[0018] When these conditions are satisfied, the present inventors have come up with the idea that the impact time can be roughly calculated as the time during which the vibration part collides (contacts) with the rigid wall. The collision time with the rigid wall can be roughly calculated as half the basic (first order) natural vibration period during which the vibration part repeats contraction and expansion in the impact direction. To explain the behavior of the vibration part colliding with the rigid wall, the collision starts at the neutral position of vibration, and after applying the maximum vibration force at the dead point where the vibration part is most contracted, the vibration part expands, and at the moment when it returns to the neutral position again, it leaves the rigid wall. Therefore, the time during which the vibration part collides with the rigid wall is half the natural vibration period.

[0019] Figure 2 shows the longitudinal vibration (compression wave) that repeats contraction and expansion in the excitation part. The fundamental natural vibration period T [sec] is the time obtained by dividing twice the dimension L [m] of the excitation part by the speed of sound v [m / sec].

number

[0020] The impact time Δt can be considered as approximately half of the fundamental natural vibration period T, so

number

[0021] The impact time will be calculated for a representative material used as the vibrating part. For aluminum alloys, ρ ≒ 2700 kg / m 3 , E ≈ 73 GPa, so Δt ≈ 1.9 × 10 -4 L [sec], For ABS resin, ρ ≒ 1025 kg / m 3 , E ≈ 2500 MPa, so Δt ≈ 6.4 × 10 -4 L [sec], For steel, ρ ≒ 7850 kg / m 3 , E ≈ 206 GPa, so Δt ≈ 2.0 × 10 -4 L [sec]. As a concrete example, when L = 0.1 m, the impact time Δt is ≒ 19 μsec for aluminum alloy, Δt is ≒ 64 μsec for ABS resin, and Δt is ≒ 20 μsec for steel. Since the impact time Δt is proportional to the dimension L, the impact time Δt can be reduced by making the dimension L smaller.

[0022] Next, we consider how short the impact time should be in order to approach the ideal impulse waveform. It is known that the excitation force waveform can be approximated by a half sine wave. Figure 3 shows an example of an excitation force waveform, where the fundamental natural vibration period is set to 1 msec. Figure 4 shows the results of frequency analysis of the excitation force waveform shown in Figure 3. Figure 4(a) shows that the excitation force starts to decrease in the region of several hundred Hz, and Figure 4(b) shows that the phase lags linearly as the frequency increases.

[0023] If the allowable values ​​of excitation force drop and phase lag are set and an excitation force that can be considered substantially constant in a frequency range (frequency domain) that does not cause practical problems can be obtained, the division calculation in the complex domain can be omitted when deriving the vibration characteristics, and the calculation cost can be reduced. In the example shown in Fig. 4, the upper limit frequency of the frequency band that can be considered constant is about 370 Hz if the allowable value of excitation force drop is 3%, and about 145 Hz if the allowable value of phase lag is 10 degrees (0.175 rad). In general, the vibration characteristics of machine structures such as machine tools, tools, and workpieces are often known up to a few kHz, so when the excitation force shown in Fig. 3 is applied, correction processing (division calculation in the complex domain) based on the excitation force is required when deriving the vibration characteristics (compliance transfer function).

[0024] Conversely, if it is possible to obtain an excitation force that can be regarded as substantially constant up to a few kHz, it will be possible to omit the correction process based on the actual excitation force when deriving the waveform of the vibration characteristics of the mechanical structure. In this case, the value of the waveform of the vibration characteristics (the actual value on the vertical axis) is determined by the "impulse" at the time of impact, but if a vibration device that always keeps the impulse constant is prepared, it is sufficient to measure and record the impulse before the vibration test, and there is no need to measure the impulse during the vibration test. This means that there is no need to provide an expensive force sensor in the vibration unit that vibrates the measured object.

[0025] In the conventional method, the vibration unit cannot be made small because it is necessary to mount a force sensor, and if the vibration unit is made small, sufficient vibration force cannot be obtained, but these problems are caused by a person striking with a hammer equipped with a force sensor. Therefore, this disclosure proposes a method in which a small projectile is fired from a firing device at a predetermined high speed to strike and vibrate the object to be measured.

[0026] 5 shows an example of the configuration of a measurement system 1 according to an embodiment. The measurement system 1 includes a machine structure 2 of a machine tool, which is an object to be measured, a launcher 3 that launches a projectile 4 toward the machine structure 2, a vibration measuring device 5 that measures the vibration of the machine structure 2 excited by the projectile 4, and a processing device 10 that derives vibration characteristics from the measured vibration. The processing device 10 includes a vibration data acquisition unit 11, an impulse value holding unit 12, and a vibration characteristic derivation unit 13. In this example, the launcher 3 launches one projectile 4, which collides with a tool attached to a spindle in the machine structure 2, thereby exciting the machine structure 2. The distance from the launcher 3 to the tool (the flight distance of the projectile 4) is set to a predetermined value D.

[0027] The vibration measuring device 5 in the embodiment is a laser Doppler velocimeter that detects the velocity of the vibrated mechanical structure 2 in a non-contact manner, but may be a laser displacement meter that detects the displacement of the vibrated mechanical structure 2 in a non-contact manner. The vibration measuring device 5 may also be a three-axis accelerometer that is directly attached to the mechanical structure 2 and detects the acceleration of the vibrated mechanical structure 2. The vibration data acquisition unit 11 acquires vibration data that indicates the time change in vibration of the mechanical structure 2 measured by the vibration measuring device 5. The vibration data may be any data that indicates the time change in vibration of the mechanical structure 2, such as velocity data, displacement data, or acceleration data.

[0028] The dimensions of the projectile 4 are set to extremely small dimensions that, when launched from the launching device 3 and colliding with the mechanical structure 2, will extremely shorten the impact time and generate a substantially constant excitation force in a range below a predetermined frequency (hereinafter also referred to as the "target frequency"). The target frequency is the upper limit of the frequency range of the vibration characteristic to be derived, and may be, for example, 10 kHz, or may be a few kHz lower than 10 kHz. Furthermore, the substantially constant excitation force means an excitation force in which the decrease in the excitation force in the frequency range below the target frequency is within a tolerable value and the phase delay is within a tolerable value. Therefore, the projectile 4 of the embodiment has dimensions in which the decrease in the excitation force in the frequency range below the target frequency is within a predetermined tolerable value.

[0029] The projectile 4 is preferably formed of a material having a sufficiently low hardness compared to the iron-based material that is the material of many of the mechanical structures 2. For example, the projectile 4 may be formed of a resin or an aluminum alloy. If the part of the mechanical structure 2 that is vibrated by the projectile 4 is called the "vibrated part," the projectile 4 is formed of a material having a lower hardness than the vibrated part of the mechanical structure 2.

[0030] Since the projectile 4 is launched from the launching device 3, it is preferable that the projectile 4 has an axisymmetric shape with respect to the direction of launch, i.e., the vibration direction, so that the projectile 4 flies on a stable trajectory relative to the mechanical structure 2. For example, the projectile 4 may have a spherical shape, but may also have a bullet-like shape. In the embodiment, the launching device 3 is an air gun (toy gun), and the projectile 4 may be a BB bullet. The air gun can fire BB bullets at a constant speed.

[0031] In the measurement system 1 of the embodiment, before a vibration test, the launching device 3 launches the projectile 4, and the impulse when the projectile 4 collides with an object at a distance D is measured in advance and recorded in the impulse value storage unit 12. If the launch speed of the projectile 4 is the same, the impact force (impulse or momentum change) that the projectile 4 imparts to the object at the position of the distance D does not substantially change depending on the material and structure of the object and its vibration characteristics.

[0032] The momentum change (impulse) is determined, within the elastic limit, roughly by the mass and velocity of the colliding (strike) projectile 4. The restitution coefficient also has an effect, but for a very small projectile 4, if the surface of the object is sufficiently hard and the collision occurs within the elastic range, the restitution coefficient will be constant at close to 1. In order to prevent plastic deformation of the projectile 4 upon collision, it is preferable for the launching device 3 to determine the launching velocity of the projectile 4 so that the impact force is equal to or less than the elastic limit of the projectile 4.

[0033] Since the launching device 3 of the embodiment can always collide the projectile 4 with the mechanical structure 2 at the same speed, the impulse (momentum change) is the same when the projectiles 4 launched at different timings collide with an object at a distance D. Therefore, by having the impulse value holding unit 12 hold the impulse measured in advance, it is not necessary to measure the impulse in real time when the projectile 4 collides with the mechanical structure 2 in the vibration test, and therefore the projectile 4 does not need to be equipped with a force sensor.

[0034] As a result of the collision of the projectile 4 with the mechanical structure 2, a substantially constant excitation force is applied to the mechanical structure 2 in a frequency domain equal to or lower than the target frequency, so that the vibration characteristic deriving unit 13 does not need to consider a change depending on the frequency of the excitation force (does not need to divide by the actual excitation force in the complex domain), and can identify the shape of the vibration characteristic of the mechanical structure 2 in the target frequency domain based on the vibration data acquired by the vibration data acquiring unit 11. As described above, according to the embodiment, since it is not necessary to correct the vibration characteristic based on the actual excitation force, it is not necessary to measure the excitation force in real time, and the calculation cost spent on the correction process can be reduced. In addition, the impulse value holding unit 12 holds the impulse measured in advance, so that the vibration characteristic deriving unit 13 can assign a value to the waveform of the vibration characteristic using the impulse recorded in the impulse value holding unit 12.

[0035] By using the launching device 3 of the embodiment, it is possible to collide the projectile 4 with the mechanical structure 2 at a much higher speed than when a person strikes the mechanical structure with an impact hammer. By shortening the impact time while increasing the impact force (collision force), a large constant excitation force can be generated over a wide frequency range, and a large vibration signal strength can be obtained relative to noise during measurement. It is desirable that the peak of the impact force does not exceed the elastic limit of the projectile 4, and within the elastic range, the restitution coefficient is constant at approximately 1, and the impulse applied depends approximately only on the speed (it also depends on the mass of the projectile, but the mass is assumed to be constant here).

[0036] According to the present disclosure, the launching device 3 launches the projectile 4 to strike the mechanical structure 2, so that it is possible to give a substantially constant (same value) impulse to the mechanical structure 2 each time within the elastic limit of the projectile 4. The impulse value holding unit 12 may hold the impulse when the projectile 4 is struck from a plurality of different distances. By having the impulse value holding unit 12 hold the impulses from a plurality of distances, it becomes possible to select the distance between the mechanical structure 2 and the launching device 3 from among a plurality of distances in the vibration test. The impulse value holding unit 12 may hold the amplitude of the excitation force that shows a substantially constant value in a target frequency range below the target frequency.

[0037] Figure 6 shows the relationship between the dimensions of the BB bullet and the upper limit frequency of the frequency band where the excitation force can be considered to be substantially constant. In other words, the upper limit frequency is the upper limit of the frequency band where the excitation force can be considered to be substantially impulse excitation, and substantially impulse excitation means excitation that does not require complex division when deriving the vibration characteristics. As shown in the figure, the upper limit frequency can be increased by reducing the dimensions of the BB bullet.

[0038] As shown in Fig. 6, when the dimensions of the BB bullet are reduced by one order of magnitude, the upper limit frequency increases by one order of magnitude. In the figure, 0.1%, 0.5%, and 2.5% indicate the allowable values ​​of the reduction rate of the excitation force amplitude, and 0.5% means that the amplitude is reduced by only 0.5% (reduced to 99.5% amplitude) compared to the amplitude of the extremely low frequency (specifically, the static component of frequency 0). In other words, below this upper limit frequency, the excitation force amplitude can be considered to be substantially constant (the difference is 0.5% or less). The ellipse in the figure indicates the range of the upper limit frequency that can be excited when various tips are combined with three types of conventionally used impact hammers (ultra-small hammer, medium hammer, and large hammer). It should be noted that at these frequencies, the excitation force amplitude is reduced by -20 dB, or 1 / 10, compared to the extremely low frequency component. This means that in an excitation test using an impact hammer, it is necessary to measure the excitation force using a force sensor to correct the large reduction in the excitation force amplitude.

[0039] As shown in Figure 6, in a vibration test using an impact hammer, in a frequency range where correction processing (complex division) is assumed, the method of the embodiment can perform excitation without the need for correction processing. The reason why there is a large difference even when comparing similar dimensions is that the fundamental natural frequency in the excitation direction is significantly reduced because the conventional hammer has a low-rigidity spring element called a force sensor or tip added to the head, which is the mass. In the method of the embodiment, the projectile 4 does not include a force sensor or tip, so the fundamental natural frequency in the excitation direction is maintained high, making it possible to perform substantial impulse excitation.

[0040] In the following, we consider the use of a toy gun that fires commercially available BB bullets (e.g., made of ABS resin, 0.25 g, 6 mm diameter) as a specific example of the projectile 4 and launcher 3. From (Equation 2), the impact time within the elastic limit is 0.006√(1025 / 2500) = 3.8 μsec, and it can be seen that the impact time can be shortened by making the dimension L small.

[0041] Figure 7 shows the waveform of the excitation force with a collision time of 3.8 μsec approximated by a half sine wave. Figure 8 shows the results of frequency analysis of the excitation force waveform shown in Figure 7. As shown in Figure 8(a), the magnitude of the excitation force at 10 kHz only drops by about 0.13%, and as shown in Figure 8(b), the phase lag at 10 kHz is only about 5.4 degrees. This shows that in the frequency domain up to a few kHz (i.e., the target frequency), which is often required for mechanical structures, it is possible to correctly identify the shape and phase of the vibration characteristics without correction processing (complex domain division).

[0042] The impulse of this excitation force waveform is calculated by integrating a half-wave of a sine wave. F_max×2×Δt / π=500*2*3.8e -6 / pi=0.0012 [Ns]. In an actual vibration test, the impulse is measured in advance and recorded in the impulse value storage unit 12, and the vibration characteristic derivation unit 13 converts this impulse value into the vibration force (all constant values) at each frequency in accordance with the vibration measurement conditions, and quantifies the vibration characteristics by dividing each frequency component of the vibration measurement results by the constant value. An example of the procedure is shown below.

[0043] Figure 9 shows a configuration for measuring the force waveform when a projectile collides with an object. In this example, a launcher 3 launches a projectile 4, which collides with a force measuring device 20. In this example, an impact hammer with a built-in force sensor is used as the force measuring device 20. Note that the initial velocity of an air gun is approximately several tens of m / sec, and the impact time of a tiny bullet is extremely short, so the responsiveness of the impact hammer is not sufficient to accurately measure the force waveform, but the impulse can, in principle, be accurately identified.

[0044] Figure 10 shows the measurement results of the excitation force. As shown in Figure 10, the excitation force measured by the force measuring device 20 does not have an impulse-like waveform, but rather resembles the waveform of a response vibration. This is due to the vibration of the impulse hammer caused by the collision of the projectile 4.

[0045] Fig. 11 shows the results of frequency analysis of the excitation force waveform shown in Fig. 10. Fig. 11 shows the vibration characteristics of the impact hammer, showing that no decrease in the excitation force is observed up to about 30 kHz, and multiple resonance modes of the impact hammer are observed at frequencies slightly higher than 30 kHz. From this result, it can be seen that the excitation by this BB bullet can provide a constant excitation force amplitude up to at least about 30 kHz, and the excitation force amplitude is about 0.21 N under these measurement conditions. The impulse value storage unit 12 may store this excitation force amplitude.

[0046] If the measurement conditions are different, the following conversion is necessary. First, calculate the impulse: 0.21 N force amplitude, 1 μs sampling interval for this measurement, and half the number of measurement points, 2 15 (i.e., half the measurement time 2 15 The impulse is calculated as 0.0069 Ns by multiplying the impulse by 1.0 μs. This impulse value is roughly constant if the same launching device 3 (air gun) is used. The impulse value storage unit 12 stores the calculated impulse. For reference, the impulse when a mechanical structure is vibrated using a commercially available impact hammer was investigated, and the impulse (0.0069 Ns) from the air gun used was more than four times that of a super-compact hammer and about half that of a medium-sized hammer. Therefore, the method of the embodiment can be used as a vibration device in place of these two types of hammers, without adjusting the mass or tip.

[0047] Next, a BB bullet was collided with a tool fixed to a rotating spindle and the generated vibration was measured. Figure 12 shows the tool speed measured by a laser velocimeter. In this figure, time 0 on the horizontal axis indicates the moment when the measured speed starts to change significantly, that is, the moment when vibration starts. Figure 13 shows the results of frequency analysis of the tool speed shown in Figure 12. In Figure 13, the frequency analysis results are converted into displacement.

[0048] As shown in Fig. 11, the excitation force from the projectile 4 is constant in the frequency range up to 30 kHz, so the response displacement shown in Fig. 13 can be considered as an impulse response displacement. In other words, the shape of the response displacement shown in Fig. 13 is similar to the compliance transfer function, only the scale of the vertical axis is different, and the phase can be considered to be exactly the same. In fact, since there is a phase delay before and after each resonance peak, it is considered that the phase delay of the impulse excitation force can be ignored.

[0049] FIG. 14 shows a quantitative compliance transfer function. The vibration characteristic deriving unit 13 derives a quantitative compliance transfer function by using the value of the excitation force or impulse stored in the impulse value storage unit 12. The measurement this time has the same sampling interval and number of data as the measurement in FIG. 11 (i.e., the measurement time is the same), so the compliance transfer function can be calculated as shown in FIG. 14 by dividing the response displacement shown in FIG. 13 by the force amplitude value 0.21 N shown in FIG. 11. If the sampling conditions are different, the force amplitude F_amp can be calculated by using the impulse value M=0.0069 Ns that does not depend on the sampling conditions and dividing it by N / 2, which is half the sampling interval dt and number of data during vibration measurement. That is, it can be calculated by F_amp=M / (dt×(N / 2)).

[0050] The present invention has been described above based on the embodiments. These embodiments are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present disclosure.

[0051] An overview of an aspect of the present disclosure is as follows: An aspect of the present disclosure is a method for deriving vibration characteristics of a mechanical structure, the method including a step of vibrating the mechanical structure by impacting a projectile against the mechanical structure, a step of measuring vibration of the excited mechanical structure, and a step of deriving vibration characteristics from the measured vibration.

[0052] According to this embodiment, it is possible to apply a sufficient excitation force while sufficiently shortening the impact time, which eliminates the need to measure the excitation force in the vibration test and correct the vibration measurement results.

[0053] The step of vibrating the mechanical structure may include a step of firing a projectile from a firing device toward the mechanical structure. By using the firing device, it is possible to shoot the projectile at high speed. The step of vibrating the mechanical structure may include a step of colliding a projectile having a lower hardness than a vibrated part of the mechanical structure with the mechanical structure, and the projectile may have a dimension such that a decrease in the excitation force is within a predetermined tolerance in a frequency range equal to or lower than a target frequency.

[0054] The step of deriving the vibration characteristics does not perform a correction process based on the excitation force when the projectile collides in a frequency range equal to or lower than the target frequency. By causing the projectile to collide and performing substantial impulse excitation, a constant excitation force can be obtained in the target frequency range, and therefore the correction process is not required.

[0055] The step of vibrating the mechanical structure may include a step of impacting a rotating part of the mechanical structure. The rotating part may include a rotating tool or workpiece, a holder or chuck for fixing the rotating tool or workpiece, and a rotating spindle. Since the vibration is applied using a launching device rather than manually by a person, it is possible to derive the vibration characteristics of the rotating part.

[0056] The projectile preferably has an axisymmetric shape with respect to the direction of launch, i.e., the direction of vibration, as an axis. The projectile is preferably made of resin.

[0057] This method may further include a step of retaining the impulse or excitation force when the projectile collides, and the step of deriving the vibration characteristic may include a step of deriving the vibration characteristic using the retained impulse or excitation force. By retaining the impulse or excitation force in advance, it is possible to quantitatively obtain the vibration characteristic.

[0058] Another aspect of the present disclosure is a measurement system for deriving vibration characteristics of a mechanical structure, comprising a launching device for impacting a projectile against the mechanical structure, a vibration measuring device for measuring vibrations of the excited mechanical structure, and a processing device for deriving vibration characteristics from the measured vibrations.

[0059] According to this embodiment, it is possible to apply a sufficient excitation force while sufficiently shortening the impact time, which eliminates the need to measure the excitation force in the vibration test and correct the vibration measurement results. [Explanation of symbols]

[0060] 1 Measurement system, 2 Mechanical structure, 3 Launching device, 4 Projectile, 5 Vibration measurement device, 10 Processing device, 11 Vibration data acquisition unit, 12 Impulse value storage unit, 13 Vibration characteristic derivation unit, 20 Force measuring device.

Claims

1. 1. A method for deriving vibration characteristics of a mechanical structure, comprising the steps of: A step of vibrating the mechanical structure by impacting a projectile against the mechanical structure; Measuring vibrations of the excited mechanical structure; Deriving vibration characteristics from the measured vibration; A method for deriving vibration characteristics, comprising:

2. The step of vibrating the machine structure includes a step of firing a projectile from a firing device toward the machine structure. The vibration characteristic deriving method according to claim 1 .

3. The step of vibrating the mechanical structure includes a step of impacting the mechanical structure with a projectile having a hardness lower than that of a vibrated portion of the mechanical structure; The projectile has a size such that the decrease in the excitation force is within a predetermined tolerance in a frequency range below the target frequency. The vibration characteristic deriving method according to claim 2 .

4. The step of deriving the vibration characteristics does not perform a correction process based on the excitation force when the projectile collides in a frequency region equal to or lower than the target frequency. The vibration characteristic deriving method according to claim 3 .

5. The step of vibrating the mechanical structure includes a step of impacting a rotating part of the mechanical structure with a projectile. The method for deriving vibration characteristics according to claim 1 .

6. The projectile has an axisymmetric shape, The vibration characteristic deriving method according to claim 1 .

7. The projectile is made of resin. The method for deriving vibration characteristics according to claim 1 .

8. and further comprising the step of holding the impulse or excitation force when the projectile impacts; The step of deriving the vibration characteristic includes a step of deriving the vibration characteristic using the held impulse or excitation force. The method for deriving vibration characteristics according to claim 1 .

9. 1. A measurement system for deriving vibration characteristics of a mechanical structure, comprising: a launcher for impacting a projectile against the machine structure; A vibration measuring device that measures vibrations of an excited mechanical structure; A processing device that derives vibration characteristics from the measured vibration; A measurement system comprising:

Images