JPH0758240B2 - Electrodynamic low noise shaker - Google Patents

Description

The present invention relates to an electrodynamic low noise exciter.

An electrodynamic exciter for vibration resistance test generally produces noise vibration of about 0.03 to 0.3 m / S ² as noise. This value is equivalent to 30 to 100 times that of microtremor. However, if this noise can be suppressed, the noise will be reduced to a level lower than that of an exciter with a small excitation force.
There is an advantage that the upper limit of the mass of the sample to be excited can be increased. In addition to the above vibration resistance test, it becomes possible to carry out an experiment of the influence of external vibration exerted on precision measuring equipment and a calibration of a vibrometer with a minute vibration close to the usage state of those measuring equipment. In order to achieve these objects, the present inventors have already reported that the improvement of the DC power supply is effective as one of the measures for improving the SN ratio of the vibration exciter (Shiraishi, Ishigami: Micro vibration). Exciting shaker, Proceedings of the Seiki Society Spring Meeting, 1979, 639-640).

However, in order to achieve the above object, it is not enough to improve the power supply and negative feedback control is required.However, since the vibration exciter is a system with many phase rotations within the frequency band used, the conventional primary system It is difficult to construct a servo system using the phase compensation circuit of In addition, the vibration resistance test is usually a constant acceleration test in the band of about 10 Hz or higher. this is,
The same applies when performing comparative calibration of an ordinary piezoelectric vibrometer or vibration level meter. Therefore, it is more convenient for the transfer function of the vibration exciter to handle the acceleration characteristic rather than the displacement characteristic.

An object of the present invention is to realize a stable servo system in the above-mentioned conventional electrodynamic vibrator for vibration resistance test, which enables phase compensation by a secondary system based on the acceleration signal of the electrodynamic vibrator. To keep the noise low.

It should be noted that the above-mentioned phase rotation means, in the vibration exciter system in FIG. 1 described later, that the phase difference between the signals at the input end A and the output end B increases as the frequency of the applied signal increases. I mean. In addition, the phase compensation is
Similarly, referring to FIG. 1, in the same figure, the signal path from the phase compensation circuit to the equalization circuit, the low-pass filter, the DC blocking circuit, and the input end A to the feedback end C of the vibration exciter system. , The phase rotation (phase lag) angle increases, and at low and high frequencies, there are frequencies that satisfy positive feedback rather than negative feedback. Therefore, in order to prevent positive feedback, the phase is delayed at these low frequencies and the phase is advanced at these high frequencies. Rotating the phase for the purpose of preventing positive feedback is called phase compensation.

The electrodynamic low noise exciter of the present invention for achieving the above object is a phase compensating circuit of a secondary system for compensating the phase advance in the low range and the phase delay in the high range of the electrodynamic exciter. A secondary system equalization circuit for equalizing the acceleration characteristic of the output of the electrodynamic vibrator in a specific band, a low-pass filter to which the signal after the equalization is added, A DC blocking circuit to which the output signal of the low-pass filter is applied, and an electrodynamic exciter to which the output of the DC blocking circuit is applied are further provided, and the mechanical output of the exciter is detected as an acceleration signal. And a negative feedback circuit for negatively feeding back the servo accelerometer to the input side of the phase compensation circuit.

Embodiments of the present invention will be described below in detail with reference to the drawings.

The electrodynamic low-noise exciter according to the present invention is constructed as shown in FIG. 1, that is, a phase compensation circuit in which the band of the input is set by a bandpass filter circuit and the output of each is formed by a secondary system. In addition to the equalization circuit, in order to realize a flat servo system in the band of acceleration characteristics of 1 to 100 Hz after compensating for the phase lead in the low range and the phase delay in the high range in the phase compensation circuit, etc. The frequency equalization is performed by the equalization circuit in the band of 1 to 100 Hz including the frequency band of the vibration level meter, the signal after the equalization is added to the low pass filter, and the servo accelerometer described later is set to the upper limit frequency or less. The signal output from the low-pass filter is added to the exciter system through the DC blocking circuit, the signal is amplified by the power amplifier in the exciter system, and then the Electrodynamic type for vibration resistance test In addition to the exciter, the mechanical output of the electrodynamic exciter driven by it is detected as an acceleration signal by a servo accelerometer as an acceleration sensor,
After the acceleration signal is amplified by the amplifier, it is negatively fed back to the preceding stage of the phase compensation circuit by the negative feedback circuit, so that the noise of the electrodynamic exciter is removed and suppressed. The phase compensation circuit may be arranged such that its transfer function is included in the open loop transfer function of the negative feedback control circuit.
For example, it can be provided in the negative feedback circuit.

In the vibration exciter having the above configuration, the signal is output as an output from the phase compensation circuit, the equalization circuit, the low-pass filter, the DC blocking circuit, and the path from the input end A to the output end B of the vibration exciter system. Become. During this period, the noise mainly generated from the electrodynamic exciter will appear in the output, but the output including this noise is detected by the servo accelerometer, amplified by the amplifier, and then phase-compensated via the negative feedback circuit. Negative feedback is applied to the input side of the circuit. That is, FIG. 1 shows a negative feedback control circuit. Then, the transfer function from the phase compensation circuit to the output end B of the vibration exciter system is expressed by α,
N is the noise generated at the output end B of the vibration exciter system, β is the transfer function from the servo accelerometer to the amplifier and the negative feedback circuit, and F is the transfer function of the band-pass filter circuit. The transfer function G of the circuit is Becomes However, the bandpass filter circuit and its transfer function F are
It is provided for setting the input band and has no relation to the present invention.

Therefore, for example, when the open loop transfer function αβ = 1, the noise N is suppressed to 1/2.

Next, the characteristics of the vibration exciter system used in the experiment and the frequency equalization method by the equalization circuit (see FIG. 3) configured according to the characteristics will be described in detail.

In the above equalization circuit, the frequency characteristic of the gain between the input and the output of the electrodynamic vibrator of FIG. 1 (FIG. 2) is not flat, so that the frequency characteristic is flattened only within a certain frequency band. The frequency equalization method is a circuit added for the purpose of flattening the frequency characteristic by using the equalization circuit.

The exciter system used was a corvo accelerometer as an acceleration sensor with excellent low-frequency characteristics, and an electrodynamic exciter for vibration resistance tests had an excitation force of 6.6 KN and a rated excitation current of 4
It is excited by 19A at 0A and driven by a DC amplifier with an output of 500VA. This electrodynamic exciter, when the exciting current is 19A, can obtain a sufficient approximation in the second-order system without using the commonly used equalization circuit in the band below 500Hz. . The frequency characteristic of the vibration exciter system is obtained by actual measurement as shown in FIG.

Now, ignoring the reactance of the drive coil of the above-mentioned electrodynamic exciter and assuming that the movable part has one degree of freedom, the transfer function G (s) in the form of the generated acceleration with respect to the input voltage is expressed by the equation (1). become.

In the above equation, ζ is the damping ratio, fo is the natural frequency, B _l is the product of the magnetic flux density of the magnetic field in which the drive coil is placed and the effective winding length of the drive coil, and M is the effective mass of the movable part. , K is the spring constant of the movable part support spring, C _d is the damping coefficient of the movable part support part, and R _d is the resistance of the drive coil. Product
B _l is obtained by mounting a weight of known mass on an electrodynamic exciter, and then applying a current to the drive coil until the deflection of the movable part support spring is restored, and the natural frequency fo is the drive coil current. It can be obtained from the frequency transfer function in the form of the generated velocity with respect to the peak at the frequency fo. In this embodiment, the product B _l and the frequency fo are B _l = 26N /
It is obtained with A, fo ≈ 15Hz. However, the spring constant K tends to decrease as the amplitude increases. Therefore, the method of obtaining the mass M from the natural frequency fo and the spring constant K cannot be used. Although it is not possible to obtain each constant, (1)
When the curve of the relative gain is drawn assuming the damping ratio ζ = 2 in the equation, it can be overlapped with the measured value of FIG. 2 with a maximum deviation of about 3 dB. From this, in the electrodynamic vibrator of FIG. 1, the control system can be designed on the assumption that the transfer function is the second-order Sumi-system of the formula (1).

Next, in order to flatten the gain characteristic of FIG. 2, equalization is performed with an element having a transfer function G _i (s) that is the reciprocal of the transfer function G (s). The transfer function G _i (s) is expressed by equation (4) when α, β, and γ are constants.

In the circuit that realizes the transfer function G _i (s), the integration time constant is set to a small value in order to minimize the effects of drift, semiconductor noise, power supply voltage fluctuations, etc.
The constant α of _i (s) is set to about 1/100, and a DC blocking path is inserted in the output stage of the component system. And the transfer function G
The circuit of FIG. 3 is used to approximate _i (s).

Next, the phase compensation circuit based on the secondary system will be described in detail.

Even if the characteristic of the above-mentioned electrodynamic exciter is equalized by the circuit of FIG. 3, the phase advances in the low range due to noise suppression measures at 1 Hz or less. Further, in order to use the servo accelerometer below its upper limit frequency, a low-pass filter with a cut-off frequency of 480 Hz is added to the forward facing element. Therefore, the phase delay at about 100 Hz or more of the open-loop frequency transfer function when the servo system is configured is further larger than that in FIG. Therefore, phase compensation is required for both low and high frequencies.

A conventional phase compensation circuit as a phase compensation circuit and a phase pass circuit are respectively shown in FIGS. 4 (a) and 5 (a).
Shown in. Frequency transfer function G of the phase delay circuit
(Jω) is given by equation (5), and its vector locus becomes a semicircle as shown in FIG. 4 (b). In this characteristic, when the frequency decreases from infinity to zero, the maximum phase delay φmax represented by the relational expression (6) occurs. But,
The gain increases monotonically.

Since the gain of the frequency transfer function G ₁ (jω) increases only when the phase is delayed, it is very difficult to obtain the gain margin and the phase margin appropriately by applying it to such an exciter system. Is. This also applies to the phase-passing circuit shown in FIG. 5 (a). Therefore, for the phase delay circuit, it is necessary to consider a circuit having a frequency band in which the phase is delayed and the gain is decreased.

Now, in the vector locus of FIG. 4 (b), if the semicircular portion is squared, the cardioid is halved. This is to make the second term on the right side of the equation (5) a quadratic lag system, and the vector locus has a frequency band in which the gain decreases as the phase delays. If the frequency transfer function G ₂ (jω) is expressed by the equation (7), the circuit can be easily realized.

In the above equation, the damping ratio ζ has a relation of A = 3−2ζ with the amplification factor A of the operational amplifier used, and ψ and ξ are also constants.

In the above equation (7), the damping ratio ζ = 1, that is, the amplification factor A =
If it is 1, the phase lag circuit by the secondary system and the vector locus of its frequency transfer function are respectively shown in FIG. 6 (a).
It becomes like (b), and the constant in (7) is Becomes Here, ω is the angular frequency. The phase delay circuit includes a circuit for transmitting the signal applied to this circuit to the adder as it is, and a low-pass filter circuit for transmitting the signal to the adder after passing through the secondary low-pass filter circuit. Operational amplifier IC configured to configure the above low-pass filter circuit ₁
Although the amplification factor A of 1 is 1, it can take a value in the range of 1 ≦ A <3. If the amplification factor A> 1, the phase delay is further increased. However, even if the amplification factor A = 1 as shown in FIG. 6 (a), a considerable effect can be expected. The resistance can be reduced by two than the case. Also, FIG. 6 (a)
When the capacitor C and the resistor R ₁ are exchanged with each other, the phase pass circuit shown in FIG. 7 (a) is obtained, and the vector locus of the frequency transfer function thereof is as shown in FIG. 7 (b).

The servo system shown in FIG. 1 described above is configured by using the above-mentioned vibrator system, phase compensation circuit and equalization circuit by the secondary system, and the experimental results by the servo system will be described below.

The open loop frequency transfer circuit targeted OdB or more at 1 Hz and 100 Hz, and obtained the results shown in FIG. 8 and Table 1.

It seems that the gain surplus is somewhat small in the high range, but since the gain surplus in the high range increases as the mounting mass increases, it can be used at this level. The acceleration waveform and its spectrum at 1Hz have been improved from those shown in Figures 9 (a) and (b) to those shown in Figures 10 (a) and (b), and the noise when there is no signal is 0.1m / s ² (Rms) was improved to 3 mm / s ² (rms). The effect of operating the final stage of the power amplifier with a battery is often shown in the noise reduction. The magnitude of the open-loop frequency transfer function is small, but the effect of the negative feedback control is great in terms of waveform improvement in the low range around 1 Hz. The overall frequency characteristic is 1
Gain deviation was within 1.5 dB in the 100 Hz band. From the above, it can be understood that a low level acceleration vibrometer can be calibrated. For example, when calibrating a vibration level meter at a vibration acceleration level of 80 dB and 1 Hz, the acceleration waveform distortion rate
4.0% is obtained.

As described above, according to the electrodynamic low-noise exciter of the present invention, the noise of the electrodynamic exciter can be suppressed to a low level.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a Bode diagram showing frequency characteristics of an exciter system, FIG. 3 is a block diagram of an equalizing circuit, and FIGS. ) And FIG. 5 (a) (b)
Is a diagram showing respective configuration diagrams of a conventional phase delay circuit and a phase shift circuit, and a diagram showing a vector locus of a frequency transfer function, and FIGS. 6 (a) and (b) and FIGS. 7 (a) and (b) are secondary systems. FIG. 8 is a configuration diagram of each of the phase delay circuit and the phase shift circuit and a diagram showing a vector locus of the frequency transfer function. FIG. 8 is a Bode diagram of the open loop frequency transfer function of the negative feedback control system shown in FIG. FIGS. 10 (a) and 10 (b) and FIGS. 10 (a) and 10 (b) are diagrams showing acceleration waveforms and spectra before and after the waveform improvement measure according to the present invention is implemented.

Claims (1)

[Claims] 1. A secondary phase compensating circuit for compensating a phase lead in a low range and a phase lag in a high range of an electrodynamic exciter, and an acceleration characteristic of an output of the electrodynamic exciter is specified. Equalization circuit for equalization in order to flatten in the band, low-pass filter to which the signal after the equalization is added, and DC blocking circuit to which the output signal of the low-pass filter is added And a dynamic exciter to which the output of the DC blocking circuit is added, and further, a negative feedback from the servo accelerometer that detects the mechanical output of the exciter as an acceleration signal to the input side of the phase compensation circuit. An electrodynamic low-noise exciter characterized by being constructed by providing a negative feedback circuit for