JP2002035693A - Method and device for generating monopulse-like displacement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To directly generate monopulse-like displacement to a body to be excited. SOLUTION: An exciting body is driven with such a waveform that the area surrounded by a displacement curve on the plus side from the equilibrium position and the time axis is approximately equal to the area surrounded by a displacement curve on the minus side from the equilibrium position and the time axis, and the beginning and the end of displacement have moderate curves, thus, the monopulse-like displacement is generated to the body to be excited. This device for generating monopulse-like displacement is provided with a wave form storing means 20 which stores the wave form information, a CPU 22 which reads out the wave form information from the wave form storing means and sets and outputs an amplitude and the time axis, a D/A converter 24 which converts a digital signal from the CPU to an analog signal, an amplifier 26 which amplifies the analog signal and a driving mechanism, such as an exciting source 34, which drives the exciting body according to the amplified analog signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for generating a monopulse displacement on a vibrating body. More specifically, the present invention contemplates a method of vibrating by a vibrating body and a vibration waveform. Accordingly, the present invention relates to a method and an apparatus for imparting a waveform displacement having a small number of peaks and valleys to a vibrating body. This technique is particularly useful for geological surveys such as seismic exploration and velocity logging, or for various types of flaw detection.

[0002]

2. Description of the Related Art Vibration sources in geological surveys include explosives of explosives, falling weights, hits, air guns, etc. due to impact energy, and hydraulic vibrators, electromagnetic vibrators, and magnetostrictive vibrators driven by vibration signals. And an electrostrictive vibrator. Magnetostrictive vibrators and electrostrictive vibrators are also driven by shock pulse signals.

In the case of a vibration source caused by an impact, a burst-like wave having many natural frequency components of the vibration source and a natural frequency component in the vicinity of the vibration source when the vibration source is only energy is generated. appear. This vibration means that the wave sequence will continue for many peaks, and the resolution of the wave sequence will be reduced when dealing with waveforms (stratum propagation wave, refraction wave, reflected wave), except when dealing only with the P wave that arrives first. There are problems such as badness, noise in the after-phase, and difficulty in numerical analysis. For this purpose, attempts have been made to reduce the number of wave trains of the generated vibration (that is, to shorten the reverberation time), that is, to make a so-called monopulse.

The conventional monopulse conversion methods include: (1) a method of using a plurality of vibration sources, arranging them in an array, and obtaining a monopulse by synthetic polymerization of the vibrations (often used for large vibration sources); A method of mounting a vibration source with a damping function to increase the attenuation and reduce the number of wave trains (Mount a lead-containing damper on the back of the ultrasonic transducer) (3) On the front of the vibration source Method of placing several matching layers (ultrasonic transducer for flaw detection, ultrasonic transducer for medical use, etc.) (4) Mechanically or electrically input vibration of opposite phase to after phase of target signal (5) A method (sweep vibrator, etc.) in which the transmission frequency is gradually changed, cross-correlation between received vibrations is reduced, and the number of peaks and valleys is reduced so that they can be treated as apparently monopulses. Ri has done to.

[0005]

The conventional monopulsing method as described above takes measures against generated vibration. Therefore, good monopulses are often not obtained. Also, for large sources such as those used for seismic surveys, there is no other way than to arrange multiple sources in an array.
There are problems such as an increase in the size of the apparatus and the cost and time required for implementation.

An object of the present invention is to provide a method capable of directly generating a monopulse-like displacement on a vibrating body by devising a drive waveform and a displacement generating mechanism itself, and an apparatus effective therefor. That is.

[0007]

According to the present invention, the area enclosed by a displacement curve on the plus side from the equilibrium position and the time axis is substantially equal to the area enclosed by the displacement curve on the minus side and the time axis from the equilibrium position. In addition, this is a monopulse displacement generating method in which the exciter is driven by a waveform exhibiting a gentle curve at the beginning and end of the displacement to generate a monopulse displacement on the vibrator. A monopulse displacement is generated by driving a vibrator having a wide frequency band with a monopulse signal without having a resonance frequency within a use frequency range.

Here, it is preferable that the displacement curve for driving the vibrating body is a waveform in which the number of peaks and the number of valleys are 2 to 5 in total, and the peak frequency of the frequency spectrum is variable. More preferably, the displacement curve is a waveform having substantially three or five peaks and valleys in total and substantially symmetrical on the time axis. As a specific displacement curve for driving the vibrating body, for example, a waveform represented by any one of a first derivative, a second derivative, a third derivative, and a fourth derivative of a Gaussian curve, or a waveform equivalent thereto ( (Including those having opposite polarities).

Further, according to the present invention, the area enclosed by the displacement curve on the plus side from the equilibrium position and the time axis is substantially equal to the area enclosed by the displacement curve on the minus side and the time axis from the equilibrium position, and the beginning and end of the displacement Is a waveform storage means for storing waveform information exhibiting a gentle curve, a CP for reading out waveform information from the waveform storage means, setting an amplitude and a time axis, and outputting the same.
U, a D / A converter for converting a digital signal from the CPU into an analog signal, an amplifier for amplifying the analog signal,
This is a monopulse displacement generator including a drive mechanism for driving a vibrator in accordance with the amplified analog signal.

In the relationship between the vibrating body and the vibrating body, for example, when the contact state is bad and the displacement of the vibrating body cannot be directly transmitted to the vibrating body, the vibration of the vibrating body is reduced. It is preferable to provide a vibration sensor for detection and feed back the detection signal to adjust the amplitude and the time axis.

[0011]

BACKGROUND OF THE INVENTION Vibration of an object means that the object makes angular velocity motion. Therefore, consider a case where an object having a certain weight is moved until a certain speed is reached, and then stopped. An object cannot instantaneously enter a constant movement speed and always has a transition portion, and an object moving at a constant speed cannot instantaneously stop and always has a transition portion. Then, a large force in the opposite direction is required to stop the exercise rapidly. The same can be said when the object is vibrated. When an object is vibrated, the vibration vibrates with a phase slightly delayed from the vibrating force. The vibration cannot be stopped suddenly, and a large force is required to stop it. The frequency characteristic of the object to be vibrated and the vibration waveform generated by the temporal change of the applied force change.

An example will be considered in which the electrostrictive ultrasonic transducer is driven by a simple pulse waveform (narrow pulse, half-period sine pulse, one-period sine pulse). The vibrator has a cylindrical shape, and a rubber containing tungsten powder is attached to its inner surface to perform damping. The reception was performed by installing a standard hydrophone near the vibrator. There is a time lag in the recording that propagates through the water. The levels of the drive pulse and the received signal are arbitrary.

(1) When driven by a narrow pulse (see A in FIG. 1) There is a displacement having a delay of rising from the drive pulse.
Subsequently, the vibration is damped by the natural vibration. (2) When driven by a half-period sine pulse (refer to B in FIG. 1) The waveform rises at a phase slightly delayed from the drive pulse at the rise of the pulse, and starts to vibrate. Oscillation does not stop at the zero line, but it oscillates for one cycle and stops after damping oscillation. Its frequency is getting smaller. The vibration that starts damping vibration from the end of the half-period sine pulse (to balance the energy obtained by half-period driving) and the vibration generated by the reaction force due to stopping the driving are added to reduce the frequency. It is thought that there is. (3) When driven by a one-cycle sine pulse (see C in FIG. 1) The waveform rises and starts oscillating with a phase slightly delayed from the drive pulse at the rise of the pulse. Vibration does not stop at the zero line at the end of one cycle, but stops with damped vibration. This is considered to be because the vibration generated by stopping the driving is attenuated. The waveform has almost the same shape when driven by a half-period sine pulse and when driven by a one-period sine pass.

From the above description, it can be seen from the above description that sudden movement causes vibration to be unable to follow the vibration and starts vibration with a delay in phase, and sudden stopping causes new vibration. Therefore, when vibrating, drive slowly. It turns out that it is necessary to stop slowly.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to consider an ideal driving method for generating a monopulse-like vibration waveform, as shown in FIG. 2A, a suspended weight 10 (for example, a sandbag suspended from a ceiling) is used. The method of driving the vibration source will be described by taking as an example the case of moving the vibration source. The vertically suspended state is a zero position, the left side of the drawing is a minus side, and the right side is a plus side position.

(1) When the weight is moved only in the plus direction (see FIG. 2B) The weight starts moving slowly from the equilibrium position to the plus side, gradually increases the speed, and maintains a constant speed (here, vibration is a problem). And that means angular velocity). Move in the opposite direction at the right end and gradually reduce the speed when it approaches zero, then stop at the equilibrium position. As shown in FIG. 2B, driving is performed with a waveform having a curve (shown by a broken line) close to an exponential curve curve on both sides of a half-wave sine waveform (shown by a solid line). This satisfies that it moves slowly and stops slowly, but it gives only positive energy to the object, so a wave on the opposite side occurs to keep the energy balance, which damps and oscillates, and the energy balance Will be maintained. Therefore, vibration having the same waveform as the drive waveform cannot be obtained with this drive waveform.

(2) When the weight is moved in the plus direction and the minus direction (see C in FIG. 2) The weight starts moving slowly from the equilibrium position to the plus side, gradually increases the speed, and reaches a constant speed (angular speed). Take. Move in the opposite direction at the right end, pass through the zero position,
Move in the opposite direction at the left end. When the speed approaches zero, gradually reduce the speed and stop at the equilibrium position. As shown in FIG. 2C, driving is performed with a waveform having a curve (shown by a broken line) close to an exponential curve curve at the beginning and end of a sine waveform of one wavelength (shown by a solid line). This satisfies the slow moving and the slow stopping, and the energy balance in the plus direction and the minus direction is almost maintained. With this drive waveform, a vibration having the same waveform as the drive waveform is obtained. (3) When moving the weight with recoil (Refer to D in Fig. 2) Move the weight slowly and slightly to the minus side, and then gradually increase the speed to the plus side to maintain a constant speed (angular speed). To go. Move in the opposite direction at the right end. After passing through the equilibrium position, slightly invert it and move it to the plus side. Then slowly approach zero. When the weight is moved with the reaction as described above, the weight can be smoothly moved. That is, vibration having the same waveform as the drive waveform can be generated smoothly. Further, the energy in the positive direction and the energy in the negative direction can be balanced. In addition, the waveform has a temporally symmetric axis. In this way, a method of once driving a little in the opposite direction and then driving in a target direction can be said to be a driving method most suited to the physical phenomenon.

With a curve obtained by combining a sine curve and an exponential function as a curve representing the manner of movement as described above, it is difficult to explain a natural phenomenon. Therefore, a Gaussian curve (normal distribution curve) is adopted as a curve for explaining these. The Gaussian curve is a curve as shown in FIG.
This curve can be expressed as Y = b × exp (−a ² × x ² ). Here, it is assumed that a = 1 and b = −1, and a curve of Y = −1 × exp (−x ² ) is shown. When the first to fifth derivatives of this curve are obtained, those curves are as shown in BF of FIG. The third derivative curve of the Gaussian curve is a waveform in which the polarity of the first derivative curve is reversed and small vibration waveforms are attached to both sides.
The fourth derivative curve of the Gaussian curve reverses the polarity of the second derivative curve, and has a waveform with small vibration waveforms on both sides. The fifth derivative curve of the Gaussian curve reverses the polarity of the third derivative curve and becomes a waveform having small vibration waveforms on both sides. It is difficult to say that the fifth-order differential curve is a vibration waveform having a small wave number. The differential curves from the third to fifth order of the Gaussian curve also have almost the same energy balance in the positive and negative directions. From the above, the first derivative, second derivative, third derivative of the Gaussian curve,
It can be seen that it is better to drive the vibration source with a waveform represented by a fourth derivative curve and a waveform similar thereto. B to E in FIG. 3 satisfy the conditions of the above consideration.

FIG. 3C showing the second derivative has the same shape as a Ricker wavelet derived from a large amount of waveform data in seismic exploration or a Mexican hat wavelet well known in weblet analysis. The equations are as follows: Second derivative of Gaussian curve: Y ″ = 2 (1-2t ² ) × ex
p (−t ² ) Ricker Wavelet: R = (1-2π ² × fp ² ×
t ² × exp (−π ² × fp ² × t ² ) Mexican hat wavelet: M = (1-t ² ) ×
from exp (-t ^2/2) These equations, in the second derivative of the Gaussian curve is the basic form, Ricker wavelet and Mexican Hat wavelet is practical, has a formula as a modification of the bit factor.

FIG. 4A shows a second derivative curve of a Gaussian curve and its spectrum curve. FIG. 4B shows a Ricker wavelet curve and its spectrum curve, and FIG. 4C shows a Mexican hat wavelet curve and its spectrum curve. Of course, they have similar curvilinear shapes. The width of the frequency distribution is wide, ranging from a very low frequency to a frequency approximately three times as high as the peak frequency.

The electrostrictive vibrator used in the driving experiment of FIG. 1 is driven by the second derivative curve of the Gaussian curve shown in FIG. 3C, and the waveform received by the standard hydrophone is shown in FIG.

The characteristics of these waveforms are as follows: (a) The area enclosed by the zero axis (time axis) is equal to the area of the positive waveform and the area enclosed by the zero axis (b) on the time axis It is a symmetrical waveform. (C) Vibration slowly starts at the beginning of vibration, and ends at the end of vibration. (D) It can be said that it has a wide frequency component. From the above, to obtain a monopulse vibration, it is best to drive with a monopulse vibration waveform satisfying the above conditions.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although a continuous sine wave has one frequency component, the frequency component gradually increases as the number of peaks (or valleys) of the wave decreases. Similarly, a monopulse-shaped vibration has a small number of peaks (or valleys) of waves, and thus has a wide frequency component as already seen in the spectrum. Therefore, it is necessary to provide a device that can respond to this. That is, it is necessary that the frequency band is wide, the frequency characteristics are as flat as possible (the natural resonance frequency is at a sufficiently high place), and electrical and mechanical braking is applied. As the vibration source itself, various known vibration sources can be used. For example, a plate-like or cylindrical ultrasonic vibrator, an electrokinetic vibrator,
An arbitrary vibration source, such as a hydraulic vibrator, may be used according to the intended use or use condition.

FIG. 6 is a block diagram showing an embodiment of the monopulse displacement generator according to the present invention. Waveform information that the area enclosed by the displacement curve on the plus side and the time axis from the equilibrium position and the area enclosed by the displacement curve on the minus side and the time axis from the equilibrium position are almost equal, and the beginning and end of the displacement are gentle curves. , A CPU 22 for reading out waveform information from the waveform storage means 20 and setting and outputting an amplitude and a time axis, and a D / A converter 24 for converting a digital signal from the CPU 22 into an analog signal. ,
An amplifier 26 for amplifying the analog signal and a drive mechanism for driving the vibrator with the amplified analog signal are provided. The CPU 22 is controlled by a clock signal (CLK) from a clock signal generator 28. The signal of the amplifier 26 is amplified by the power amplifier 30, and the amplified power is supplied to the drive mechanism of the vibration source 34 via the interface unit (I / F) 32.

Here, the vibration source 34 is a vibrator or a vibration device having a natural resonance frequency higher than the operating frequency.
At low frequencies it is better to be as flat as possible and extend down. If necessary, a damper 36 is mechanically attached and damped to suppress resonance at the natural resonance frequency (to reduce the mechanical Q value). Furthermore,
When transmitting vibrations in water, use a vibrator with low mechanical impedance or cover the surface with a mechanical matching material to reduce the mechanical impedance. The equipment on the ground has an uneven structure to improve the contact with the stratum, so that a load can be applied. In the interface section for driving the vibration source, impedance matching is performed in order to use electric signals effectively. Also, braking can be applied electrically by a braking resistor.

As described above, the monopulse driving waveform is stored in the waveform storage means 20. The waveform information is CP
Read and used by U22. By changing the clock to be read, the frequency position of the main frequency component (FIG. 7)
Wavelet width a and zero point transit time b) as shown in
Can be changed. By changing the frequency, the frequency dependence of the formation can be measured.
The numerical value read from the waveform storage means 20 is converted into an analog signal by the D / A converter 24, and is used as a monopulse for driving the vibration source 34 via the amplifier 26.
Therefore, the amplifier 34 must be capable of faithfully amplifying the driving waveform monopulse signal.

In the seismic survey, the measurement is performed by moving the vibration source. Therefore, the location where the vibration source is installed may be a hard stratum or a soft stratum. Therefore, even if the vibration source is faithfully driven in this way and a faithful vibration waveform is produced, the waveform of the vibration source does not directly become the ground vibration, the waveform is distorted, and the amplitude of the waveform may change significantly. is expected. In such a use state, it is desirable to provide a feedback loop as shown in FIG. Since the basic configuration is the same as that shown in FIG. 6, corresponding portions are denoted by the same reference numerals for simplification of description, and description thereof will be omitted. The ground vibration is detected by the vibration sensor 40 for monitoring, the signal is amplified by the amplifier 42, and the signal is amplified by the CPU 22 through the A / D converter 44.
And a feedback function for feeding back to the target waveform and amplitude. In the case of performing feedback control, the drive waveform is corrected several times until the ground produces a desired monopulse-like displacement. After the desired displacement is obtained, the necessary measurements are made.

In speed logging and flaw detection, installation conditions do not change so much because water, oil, grease and the like are used, and a monitoring sensor may not be necessary. Of course, even in such a case, if a more accurate waveform is to be emitted, it is preferable to install a monitoring sensor and perform feedback control in this manner.

FIG. 9 shows an example of a hydraulic vibrator type vibration source suitable for applying the method of the present invention at the time of ground survey. A hydraulic vibrator body (hydraulic actuator) 52 is installed on the vibration base 50, and hydraulic pressure is supplied from a hydraulic pressure generating mechanism (not shown) via a servo unit 54.
The servo unit 54 controls the direction and intensity of the force applied to the vibration base 50 to generate vibration. The vibration base 50 is in a state of being pressed against the ground (the vibrating body) by the pressure piston cylinder 56. Of course, the vibration source is not limited to such a structure.

Since the monopulse vibration source according to the present invention drives the vibration source in a frequency region other than the resonance point, it has lower energy efficiency than the vibration source that vibrates at the resonance point. However, the vibrations emitted from the monopulse source have various frequency components even in the formations with different hardness as described above, so the formations can be vibrated smoothly, and the disadvantage of poor energy efficiency can be compensated. . Further, since the original waveform is known, it is easy to detect from the received vibration buried in noise.

[0031]

As described above, the present invention is a method in which the driving waveform to the vibrating body is devised so as to generate a monopulse displacement on the vibrating body. A vibration monopulse with a component can smoothly vibrate the stratum and can measure vibrations that directly reflect the physical properties of the stratum, such as when passing through the stratum and reflecting off the stratum boundary. Until now, the process of extracting the target data from the measured data by a complicated calculation process is halved, and the accuracy of the obtained data is improved.

As a result, specifically, the accuracy of P-wave and S-wave velocity measurement in velocity logging and seismic exploration is improved.・ Measurement accuracy of reflected waves in seismic survey is improved.・ Permeability and true S-wave velocity can be measured in velocity logging.・ Since the transmitted vibration waveform is known, numerical analysis becomes easy. Further, the reverse analysis is facilitated.・ Easy analysis of wave dispersion.・ As a result, it becomes easier to obtain physical property information.・ In addition, new information may be obtained. And the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a simple pulse drive waveform and a received waveform.

FIG. 2 is an explanatory view of a suspended weight and a driving method thereof.

FIG. 3 is a graph showing a Gaussian curve and its first to fifth derivatives.

FIG. 4 is a graph showing a second derivative of a Gaussian curve, a Ricker wavelet, a Mexican hat wavelet, and spectra thereof.

FIG. 5 is an explanatory diagram showing a relationship between a driving waveform corresponding to a second derivative of a Gaussian curve and a reception waveform.

FIG. 6 is a block diagram showing an example of a monopulse displacement generator according to the present invention.

FIG. 7 is an explanatory diagram showing an example of a driving waveform according to the present invention.

FIG. 8 is a block diagram showing another example of the monopulse displacement generator according to the present invention.

FIG. 9 is an explanatory diagram showing an example of a vibration source used in the present invention.

[Explanation of symbols]

 Reference Signs List 20 waveform storage means 22 CPU 24 D / A converter 26 amplifier 30 power amplifier 32 interface unit 34 source

Claims (6)

[Claims] 1. The area enclosed by a displacement curve on the plus side from the equilibrium position and the time axis is substantially equal to the area enclosed by the displacement curve on the minus side and the time axis from the equilibrium position, and the beginning and end of the displacement are gradual. A monopulse displacement generating method characterized in that a vibrator is driven by a waveform exhibiting a simple curve to generate a monopulse displacement on the vibrator. 2. The displacement curve has a total number of peaks and valleys of 2 to 2.
5. The monopulse-like displacement generating method according to claim 1, wherein the peak frequency of the frequency spectrum is variable. 3. The monopulse-like displacement generating method according to claim 2, wherein the displacement curve has a total number of peaks and valleys of 3 or 5, and has a substantially symmetric waveform on a time axis. 4. The displacement curve is a first derivative of a Gaussian curve, 2
2. The monopulse-like displacement generating method according to claim 1, wherein the waveform is a waveform represented by any one of a second derivative, a third derivative, and a fourth derivative, or a waveform equivalent thereto (including a waveform having the opposite polarity). 5. The area enclosed by a displacement curve on the plus side from the equilibrium position and the time axis is substantially equal to the area enclosed by the displacement curve on the minus side and the time axis from the equilibrium position, and the beginning and end of the displacement are gradual. Storage means for storing waveform information exhibiting various curves, a CPU for reading out waveform information from the waveform storage means, setting and outputting an amplitude and a time axis, and the CP
D / A to convert digital signal from U to analog signal
A monopulse displacement generating device, comprising: a converter, an amplifier for amplifying the analog signal, and a driving mechanism for driving a vibrator according to the amplified analog signal. 6. The monopulse displacement generator according to claim 5, further comprising a vibration sensor for detecting a vibration of the body to be vibrated, wherein the detection signal is fed back to adjust the amplitude and the time axis.