JPH065190B2 - Vibration control device - Google Patents

Description

The present invention relates to a vibration control device used for simulating a vibration environment.

[Prior Art] It is generally well known that vibrations that occur during transportation and operation can be a cause of equipment failure. Therefore, at each stage of trial manufacture and mass production, a simulator is used to check the vibration resistance, which is called a vibration test. In this vibration test, the vibration control device controls the vibration generator.

The vibration applied to the equipment placed in the actual operating environment or transportation environment generally has an irregular waveform, and no clear regularity such as that seen in a sine wave is found. It is difficult to add such an irregular waveform itself to the device. Therefore, the power spectrum density of the irregularly added waveform is calculated, and a waveform having the target power spectrum density (referred to as the target spectrum) is added to the device.

What should be considered here is that the vibration generator itself also has a frequency response characteristic. Therefore, simply
The vibration having the target spectrum cannot be applied to the device only by applying the target spectrum to the vibration generator. Therefore, the frequency response characteristic of the vibration generator is taken into consideration, the target spectrum is corrected, and this is given to the vibration generator as the drive spectrum.

FIG. 4 shows the configuration of a conventional vibration control device. The vibration generator 2 generates vibration based on the input electric signal. The device to be subjected to the vibration test is fixed to the vibration generator 2 as the sample 4. Specimen 4
An acceleration pickup 6 is attached, and its output is given to an A / D converter 8. Therefore, specimen 4
The analog signal representing the vibration state of is converted into a digital signal by the A / D converter 8. This digital signal is input to the Fourier transforming means 10 and the power spectrum density as the absolute value of the phase angle is calculated. This power spectral density is called a response spectrum. In order to execute such an operation on a computer, it is necessary to discretize the transform, and in practice, the discrete Fourier transform is performed. At this time, it is general to use a fast Fourier transform FFT algorithm which has a high calculation speed.

The response spectrum calculated in this way is compared with the target spectrum in the control calculation means 12. As a result of the comparison, the spectrum to be given next is calculated. This is called a drive spectrum. Inverse Fourier transform means 14
Gives a random phase to this drive spectrum and performs an inverse Fourier transform. That is, it is reconverted into digital data of a time function. This digital data is converted into an analog signal by the D / A converter 18 and given to the vibration generator 2.

The above operation is repeated, and the vibration having the target spectrum is applied to the sample 4.

By the way, the series of operations described above requires time. Therefore, if the data for one frame is similarly created from the data for T seconds (referred to as one frame) input to the Fourier transform means 10 and given to the D / A converter 18, the processing cannot be completed in time. Become. Therefore, it is necessary to create data for several frames based on the input data for one frame.

Randomizing means 16 does this.

First, one frame of data is stored in the circulating memory, and the read head position is randomly changed to create a plurality of frames of data. Next, the plurality of frames thus obtained are given to the vibration generator 2 via the D / A converter 18. At this time, the data between the frames must have continuity. Otherwise, unnecessary spectrum will be generated due to discontinuity between frames.

Conventionally, window operation has been performed in order to provide continuity between frames. This window operation will be described with reference to FIGS. FIG. 5 shows two frames 101 and 102 created based on one frame. Although these data are actually digital signals, they are displayed in the form of analog signals for easy understanding.
Each of these signals 101 and 102 is multiplied by a half sine wave (sine function for half wavelength) to obtain waveforms 201 and 202 shown in FIG. An output signal 300 is obtained by superimposing the waveforms 201 and 202 while shifting them on the time axis.

As described above, the continuity between the frames is obtained.

[Problems to be Solved by the Invention] However, in the conventional vibration control device as described above,
There were the following problems.

First, the use of a half-sine wave as a window function as in the related art causes an extra amplitude component when superimposing each frame. Such a problem is obvious because a ripple is generated in the output when a DC component is applied to the conventional randomizing means. For example, when a half-sine wave is used as a window function, ripples as shown in FIG. 7A will occur. Further, when an AC component having a constant amplitude is given, its envelope curve becomes wavy as shown in FIG. 8A.

Secondly, when a plurality of frames are created from one frame, it is also clear that the obtained frames are not random simply by randomly changing the read start position. That is, some regularity is introduced into a plurality of obtained frames, and regularity is also introduced into a signal obtained by combining these frames. When such regularity occurs, it becomes impossible to give a Gaussian irregular signal having a target spectrum.

The reason that such regularity is brought about in the prior art is as follows. That is, when the window operation is performed, the frames are overlapped with each other by shifting the time at regular intervals. Conventionally, the extraction start position was randomly selected without taking into account the time of the fixed interval, so that regularity occurred.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a vibration test apparatus capable of simulating Gaussian random vibration with high accuracy without causing unnecessary components in amplitude. .

[Means for Solving the Problems] The vibration test apparatus according to claim 1 uses a window function as a window function. Here, where T is the time length of one frame and t is time, 0 ≦ t ≦ T ω ₁ = 2π / T ω _K = ω ₁ · K, K = 1,2,3, ... When K = nI, where n is a natural number and I is the number of overlaps, a _K and b _K are characterized to be substantially zero.

The vibration test apparatus according to the second aspect is characterized in that the leading position taken out by the randomizing means is randomized according to Add _i = τ _i + (N / I) · (i-1). Here, N represents the number of words included in one frame, I represents the number of superposed frames, and i represents the number of 1 to I corresponding to the order of superposed frames. Add _i is Ad corresponding to i
d ₁ , Add ₂ , Add ₃ ... Add _I , and τ _i indicates τ ₁ , τ ₂ , τ ₃ ... τ _I corresponding to i.

The vibration test apparatus according to claim 3 is a window function. Here, where T is the time length of one frame, 0 ≦ t ≦ T ω ₁ = 2π / T ω _K = ω ₁ · K, K = 1,2,3, ... R, and n is a natural number, When K = nI as the number of I overlaps, the one that satisfies that a _K and b _K are substantially 0 is used, and the randomizing means also takes out the leading position Add _i = τ _i + (N / I) -Characterized by randomization according to (i-1). Here, N represents the number of words included in one frame, and i represents the number of 1 to I corresponding to the order of frames to be superimposed. Add _i
Indicates Add ₁ , Add ₂ , Add ₃ ... Add _I corresponding to i, and τ _i indicates τ ₁ , τ ₂ , τ ₃ ... τ _I corresponding to i.

[Operation] As a window function, Where T is the time length of one frame and 0 ≦ t ≦ T ω ₁ = 2π / T ω _K = ω ₁ · K, K = 1,2,3, ... R, and n is a natural number When K = nI, by using one satisfying that a _K and b _K are substantially 0, it is possible to prevent an extra amplitude component from being generated when overlapping in the window operation. The reason is as follows.

Here, the fact that no extra amplitude component is introduced means that when the window functions are overlapped and superposed, the sums thereof cancel each other out except for the DC component (a ₀ ), and become zero. That's what it means. Below, we will examine the conditions for reaching zero in order.

The phase rotation amount of the Kth component of the qth window of the window function W (t) is Here, K = 1,2,3, ... Rq = 0,1,2, ... (I-1).

Hereinafter, for simplicity, consider the cosine component of W (t).

From the above, the sum for each K-order component of each window is Is represented. For convenience of calculation, if the above expression is expressed in complex, Therefore, The condition that satisfies

here, Focusing on the fact that is the I-th root of 1, it suffices to avoid only when this satisfies the following condition.

(2π / I) K = 2πn Therefore, excluding the case of K = nI, y _k (t) becomes 0. Since the above is similarly applied to the sine component of w (t), the sum of the Fourier components other than a _{o of} w (t) is 0 except for the case of K = nI.

That is, if a window function that does not include an order that is an integral multiple of the number of overlaps I is used, no extra amplitude component appears.

Further, by randomizing the extraction start position of the randomizing means according to Add _i = τ _i + (N / I) · (i-1), an extra frequency component is brought about when superposed in the window operation. Will disappear.

[Embodiment] A basic block diagram of a vibration control device according to the present invention is as follows.
It is similar to the conventional device (see FIG. 4). A theoretical circuit can be used to realize the functions of these blocks, but a microcomputer may be used as shown in FIG. Also, in FIG. 2, the randomizing means
Although 16 are provided independently, the same function can be provided by the calculation by the CPU 150. In this case, the bus
An output will be output from the D / A converter 18 from 50.

An embodiment of the randomizing means 16 which is a characteristic part of the present invention is shown in FIGS. 1A and 1B. 1A shows a data processing unit, and FIG. 1B shows an address generating unit. Here, the number of frames I to be created based on one frame I
There are four. That is, in the window operation, the number of overlaps of each frame is four times. In the past, the number of overlaps was two, but by setting it to four as in this embodiment, the continuity between frames is further improved. The number of overlaps can be an arbitrary integer of 2 or more.

First, the operation of creating four random frames from one frame will be described. In FIG. 1A,
Data resulting from the inverse Fourier exchange is sent from the system bus 50 from the CPU 150 (see FIG. 2).
This data flow corresponds to the flow from the inverse Fourier exchange means 14 to the randomization means 16 in FIG. Now, returning to FIG. 1A, the data for one frame sent via the bus 50 is stored in the input buffer 54. Here, it is assumed that one frame is composed of N words. The input buffer 54 is a so-called double buffer and is composed of a buffer 54a and a buffer 54b. This is to save the data by writing to the other buffer while reading from the one buffer.

The data stored in the buffer 54 is read according to the Xran read address signal. The Xran read address signal is generated by the circuit of FIG. 1B. N for processing
The counter 70 receives the processing clock and receives 0, 1, 2, ... N-2, N
-1,0,1,2 ... and its output 70a are changed. Here, this processing clock has to be I (overlap count) times or more as fast as the output D / A clock. The processing N counter 70 outputs 70b when it changes from N-1 to 0.
Carry more. Upon receiving this carry, a random number generator
76 generates a random number, and the τ register 78 holds the random number. The output of the τ register 78 is input to the second adder 82.

On the other hand, the output of the processing N counter 70 is inputted to the first adder 80, and the output thereof is given to the other input of the second adder 82. It should be noted that both the adders 80 and 82 return to 0 and perform addition when the addition result exceeds N-1. Therefore, from the output of the second adder 82, the address of N words is output in synchronization with the processing clock, with the random number of the random number generator 76 as the leading address. Since four frames of data are now obtained based on one frame of data, the above operation is repeated four times. Then, based on the above address, the window operation is performed while shifting each frame read from the input buffer by 1/4 frame.

By the way, the reading as described above is the same as that of the conventional technique, and as pointed out as a problem, a certain regularity is brought about. That is, the read start address is Ad
If d _i , in the above case, Add _i = τ _i , and the start address is randomly selected. However, in the window operation, the frames are overlapped by shifting each frame by N / 4 (when the number of overlaps I is 4).
Therefore, taking this deviation into account, the effective start address Add _i ′ becomes Add _i ′ ＝ τ _i- (N / 4) (iI), which gives some restriction to the selection of the start address. Will end up.

Therefore, in this embodiment, the overlap counter 7
2. A shifter 74 is provided. Overlap counter 7
2 operates by receiving a carry from the processing N counter 70. If the number of overlaps is I, then 0,1,2, ... I-2, I
The count is repeated -1,0,1,2 ... to indicate how many times the overlap is currently performed. In this embodiment, since the overlap is four times, the count is repeated 0,1,2,3,0,1,2 ... The output of the overlap counter 72 is given to the shifter 74. The shifter 74 multiplies a given number by I / 4.

Specifically, when I = 2 ⁿ and I = 2 ^m , the shifter 74 operates as n-
It shifts left by m bits. Since the operation result is given to the other input of the first adder 80, Xr
The read start address is finally expressed by the following equation.

Add _i = τ _i + (N / 4) (iI) Therefore, when the frames obtained in this way are overlapped, the effective start address Add _i ′ becomes Add _i ′ = τ _i, and Randomization can be achieved.

Next, an operation of multiplying the data read from the input buffer 54 as described above by a window function and superimposing them while shifting them by N / 4 will be described. For the concept of superposition, see FIG. In order to perform such superposition, the circuits of FIGS. 1A and 1B are used.

First, the data read from the buffer 54 is stored in the multiplier 5
8. It is multiplied with the data of W table 56. The W table 56 stores discrete window function values corresponding to O to N words. Therefore, from the multiplier 58,
The windowed data will be output.

Next, this data is added by shifting by N / 4 for each frame. In this embodiment, this is realized by using the intermediate buffer 60 in order to simplify the circuit. FIG. 3 illustrates the operation. In this figure, for convenience of explanation, the window function is shown as a triangle function. Also, it is assumed that time elapses in the order of A, B, C ... H, and each state A, B, C ... H indicates N words.

As can be seen from this figure, the output buffer write enable signal (see FIGS. 1A and 1B) is used to sequentially write the calculated data to the output buffer 66. Then, for the data that has been output in the previous state, an addition prohibition signal is issued (see FIGS. 1A and 1B, especially pay attention to AND62), and only new data is added to prepare the next addition data. is doing. The output buffer 66 is a double buffer and is composed of a buffer 66a and a buffer 66b.
That is, when data is being written in one buffer, the written data in the other buffer is sequentially read out and given to the D / A converter 18 (see FIG. 4).

In the above window operation, the following window function W (t) was used in this embodiment.

In the form of, the one called Hanning Window, that is, a ₀ = 0.5, a ₁ = 0.5, (R = 1).

What is called a Blackman Window, _{i.e., a 0 = 0.42, a 1} = 0.5, a 2 = 0.08, (R =
2) What is.

What is called Blackman-Harris Window, that is, a ₀ = 0.35875, a ₁ = 0.48829, a ₂ = 0.14128, a ₃ = 0.0
1168, (R = 3)

What is called Nuttall Window, ie a
₀ = 0.3653819, a ₁ = 0.4891775, a ₂ = 0.1365995, a ₃ = 0.
0106411, (R = 3).

7B and 8B show the outputs when a DC and an AC having a constant amplitude are input to the randomizing means by using the Hanning Window with the number of overlaps being 4. 7th
In FIG. B, it is apparent that direct current is output as it is with respect to direct current input and no ripple is generated. Further, in FIG. 8B, it is clear that an alternating current having a constant amplitude is output as it is and is not subjected to an extra amplitude change. These are the conventional examples shown in FIGS. 7A and 8A.
It is especially clear when compared to the bluff.

It should be noted that FIG. 7 and FIG.
The plot output uses the pseudo-random spectrum output (that is, the state of the line spectrum).

None of the window functions described above includes a component having an order that is an integral multiple of the number of overlaps I (4 times in this embodiment). Therefore, no extra amplitude component is introduced into the waveforms superimposed by the window operation.

It should be noted that in the above-described embodiment, a component which does not include a component of an order which is an integral multiple of the overlap count I is used. But,
Even if a window function in which such a component is smaller than the components of other orders and can be regarded as substantially zero is used, the same effect can be obtained.

Also, the number of overlaps has been described as 4, but this number can be arbitrarily selected.

[Effect of the Invention] The vibration test apparatus according to claim 1 can be used as a window function. In this form, a component that does not include a component of an order that is an integral multiple of the number of overlaps I is used. Therefore, components other than a ₀ do not cancel each other out during the superimposition of window operations, resulting in no extra amplitude.

The vibration control device according to a second aspect is characterized in that the extraction start position of the randomizing means is randomized according to Add _i = τ _i + (N / I) (i-1). Therefore, each frame is completely randomized without offsetting the (N / I) · (i-1) regular shifts introduced by the windowing operation, and without generating extra spectrum.

The vibration test apparatus according to claim 3 combines the means of claims 1 and 2. Therefore, windowing does not result in extra amplitude as well as extra spectrum.

That is, according to the present invention, it is possible to provide an apparatus capable of suppressing the occurrence of unnecessary vibration due to window operation and simulating Gaussian random vibration with high accuracy.

[Brief description of drawings]

1A and 1B are block diagrams of the randomizing means according to an embodiment of the present invention, and FIG. 2 shows a case where a part of the functions of the vibration control device according to the embodiment is configured by using a CPU. Block diagram, FIG. 3 is a diagram for explaining the operation of FIGS. 1A and 1B, FIG. 4 is a block diagram generally showing a vibration control device, and FIGS. 5 and 6 are window operations. 7A is a diagram showing ripples that occur when a sine half wave is used as a window function for a DC input, and FIG. 7B is a Hanning Window for a DC input. FIG. 8A is a diagram showing an output when used as a function, FIG. 8A is a diagram showing an output when a half-sine wave is used as a window function for an AC input, and FIG. 8B is a Hanning Window for an AC input. It is a figure which shows the output at the time of using as a window function. 2 ... Vibration generator 4 ... Specimen 6 ... Accelerometer 8 ... A / D converter 10 ... Fourier transform means 12 ... Control calculation means 14 ... Inverse Fourier exchange means 16 ... Randomization means 18 ...... D / A converter

Claims (3)

[Claims] 1. A / A for converting a detection signal from an acceleration pickup for measuring the acceleration of a specimen into a digital signal.
D converter, Fourier transform means for analyzing the digital signal into a frequency spectrum and outputting it as a response spectrum, control operation means for comparing the response spectrum with a target spectrum and obtaining a drive spectrum, and giving a random phase to the drive spectrum After that, an inverse Fourier transform means for converting into a digital signal of the time function, a predetermined number N of words of the time function digital signal are set as one frame, and the digital signal of the one frame is placed in a storage means having a cyclic action. , Randomizing means for generating multiple frames by changing the extraction start position, multiplying each frame by the window function data, and superimposing each frame while shifting them, the output from the randomizing means to an analog signal A D / A converter for converting and giving to the vibration generator, In the vibration control device, as the window function, the vibration control device which is characterized by using the one that satisfies the following equation. Here, where T is the time length of one frame, 0 ≦ t ≦ T ω ₁ = 2π / T ω _K = ω ₁ · K, K = 1,2,3, ... R, and n is a natural number, As for the number of frames in which I is superposed, when K = nI, a _K and b _K are substantially 0. 2. A / A for converting a detection signal from an acceleration pickup for measuring the acceleration of a specimen into a digital signal.
D converter, Fourier transform means for analyzing the digital signal into a frequency spectrum and outputting it as a response spectrum, control operation means for comparing the response spectrum with a target spectrum and obtaining a drive spectrum, and giving a random phase to the drive spectrum After that, an inverse Fourier transform means for converting into a digital signal of the time function, a predetermined number N of words of the time function digital signal are set as one frame, and the digital signal of the one frame is placed in a storage means having a cyclic action. , Multiple frames are generated by changing the extraction start position, and each frame is multiplied by the window function data, and then each frame is shifted and superposed while shifting the output from the randomizing means to an analog signal. A D / A converter for converting and giving to the vibration generator, In the vibration control device, the vibration control apparatus of the take-out head position Add _i of said randomizing means and randomizing according to the following equation. Add _i = τ _i + (N / I) · (i−1) where N is the number of words included in one frame, I is the number of frames to be superimposed, and i is 1 corresponding to the order of frames to be superimposed. ~ Indicates the number of I. Add _i indicates Add ₁ , Add ₂ , Add _3, ... Add _I corresponding to i, and τ _i is i
Τ ₁ , τ ₂ , τ ₃ ... τ _I are shown corresponding to, and are random numbers. 3. A / A for converting a detection signal from an acceleration pickup for measuring the acceleration of a specimen into a digital signal.
D converter, Fourier transform means for analyzing the digital signal into a frequency spectrum and outputting it as a response spectrum, control operation means for comparing the response spectrum with a target spectrum and obtaining a drive spectrum, and giving a random phase to the drive spectrum After that, an inverse Fourier transform means for converting into a digital signal of the time function, a predetermined number N of words of the time function digital signal are set as one frame, and the digital signal of the one frame is placed in a storage means having a cyclic action. , Multiple frames are generated by changing the extraction start position, and each frame is multiplied by the window function data, and then each frame is shifted and superposed while shifting the output from the randomizing means to an analog signal. A D / A converter for converting and giving to the vibration generator, In the vibration control device, as the window function, using those that satisfy the following equation, Here, where T is the time length of one frame, 0 ≦ t ≦ T ω ₁ = 2π / T ω _K = ω ₁ · K, K = 1,2,3, ... R, and n is a natural number, When K = nI as the number of frames to be overlapped with I, a _K and b _K are substantially 0, and the extraction start position of the randomizing means is randomized according to the following formula. Vibration control device. Add _i = τ _i + (N / I) · (i-1) where N is the number of words contained in one frame, and i is the number of 1 to I corresponding to the order of frames to be superimposed. . Add _i indicates Add ₁ , Add ₂ , Add ₃ ... Add _I corresponding to i, and τ _i indicates τ ₁ , τ ₂ , τ ₃ ... τ _I corresponding to i.
Is a random number.