JPH058071B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a method for finding a fundamental resonant frequency among many sub-resonant frequencies of an ultrasonic transducer, and then
This invention relates to an ultrasonic transducer drive control method that can track and control the drive frequency.

Conventional technology Normally, it is most desirable from the viewpoint of electromechanical conversion efficiency to drive an ultrasonic transducer at a fundamental resonance frequency specific to its vibration form, but in general, the sharpness Q of the resonance is quite high, and the driving Even if the frequency slightly deviates from the resonant frequency, the conversion efficiency will drop significantly. Therefore, drive oscillators equipped with automatic tracking devices that automatically detect the resonance point of the ultrasonic transducer and perform tracking oscillation are often used.

However, if the resonance length of the mechanical vibration system including the ultrasonic transducer, horn, tools, etc. is up to about one wavelength and the amplitude expansion rate is not large, it will not cause a major problem, but if the resonance length is longer than that, When the magnification rate is increased, there will be many sub-resonant frequencies near the fundamental resonant frequency, and oscillation may shift to sub-resonant points at the start of oscillation or when the load suddenly changes. This significantly impairs the reliability of the device. In addition, in a mechanical amplitude system that has many sub-resonance points, if the horn or tool is replaced with a different one, and the fundamental resonance frequency of each is different, it will be difficult to select the necessary fundamental resonance frequency and to oscillate the tracking oscillation. It becomes very difficult to operate.

Many methods have been put into practical use as resonant frequency automatic tracking devices, but the vibration speed of the ultrasonic transducer is detected and the drive voltage range is adjusted to the frequency of the drive signal so that the phase relationship with the drive current is constant. There are many things that control. Here, the method of detecting the vibration velocity signal includes, for example, a method in which a detection element such as an electrostrictive element is attached to a part of a mechanical vibrator and the generated voltage is extracted, and a method in which a detection element such as an electrostrictive element is attached to a part of the mechanical vibrator and the generated voltage is extracted. There are some that use a differential configuration to detect different motional signals depending on the vibration stress generated.

Now, FIG. 1a shows an example of the frequency characteristics of the phase relationship of the detection signal, and FIG. 1b shows the frequency characteristics of the drive current amplitude flowing through the converter.
Normally, the tracking control range of the oscillator is limited to an area where the phase advances in the low range and the phase lags in the high range with the resonance frequency f ₀ as the center, for example, within the range of f ₁ to f ₂ . It is driven by tracking changes in the resonance frequency. However, changes in the resonant frequency beyond that,
For example, if the vibration reaches the resonant frequency f ₀ shown in FIG. 2, even if the tracking range of the oscillator is expanded, an abnormal vibration state will occur in which oscillation occurs at a sub-resonant point such as point B in FIG. 2.

In this way, when replacing horns and tools that are connected to an ultrasonic transducer with a variety of horns and tools, that is, horns and tools with different resonance frequencies, conventional tracking methods are Detection of the resonant frequency would become impossible.

Furthermore, as a solution to the above drawbacks, JP-A-Sho
The one shown in Japanese Patent No. 60-34776 is known.

In other words, after searching the frequency characteristics of the drive current of the converter together with the phase characteristics of the vibration speed detection signal and finding a resonance point on the current characteristics, if there is a zerox point on the phase characteristics corresponding to it, it is found. This is determined to be the fundamental resonance point.

Problems to be Solved by the Invention However, in the above-mentioned conventional techniques, it takes time to find the dip or peak value of the converter drive current, especially when the required fundamental resonance point is located at the end of the sweep range. In some cases, several resonance points on the current characteristics are searched for, and each one is determined to be unsuitable by referring to the phase characteristics, so it takes a considerable amount of time to complete the search. .

Measures to solve the problem: Refer to the drive current characteristics from the required zero-crossing point on the phase characteristics of the vibration speed detection signal, confirm that there is a dip or peak nearby, and confirm that it is the resonance point, and then set the zero-crossing point. The point is determined to be the basic resonance point and PLL tracking oscillation begins.

Embodiment An embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the system control is performed by a microcomputer, and the input/output of control data to and from the microcomputer is indicated by thick arrows in the figure, and the direction of data flow is indicated by the direction of the arrow.

First, in FIG. 4, a voltage controlled oscillator 21 that determines the driving frequency of the ultrasonic transducer 20 has a sweep input terminal 22 and a PLL input terminal 23, and the frequency is controlled by the voltage applied to these input terminals. The output voltage is output from the output terminal 24 to the amplifier 2.
5, and the power is amplified. The amplified output is transformed by an output transformer 26, co-matched by a series inductor 27, and then applied to electrostrictive elements 30 and 31 of the ultrasonic transducer 20.

Here, since the insulating plate 34 is inserted between the ground side electrode 32 of the electrostrictive element 31 and the ground terminal 33 of the converter 20, which is the ground side electrode of the electrostrictive element 30, the electrostrictive element 31 The current flowing through terminal 3
2, flows through one current detection transformer 35, and flows to the secondary coil of the output transformer 26. Further, the current flowing through the electrostrictive element 30 passes through the terminal 33, flows through the other current detection transformer 36, and returns to the secondary coil of the output transformer 26 as well.

Therefore, the secondary voltages es ₁ and es ₂ of the current detection transformers 35 and 36 have values proportional to the currents flowing through the electrostrictive elements 31 and 30, respectively. The detection signal es ₁ is input to the digital control amplifier 37 and amplified based on the data given by the microcomputer, and then the detection signal
es ₂ is created by a differential amplifier 38,
It becomes one input of the phase comparator 40.

Here, the amplification degree of the digital control amplifier 37 can be changed by data control from a microcomputer, and when the amplification degree is set to 1, the differential amplifier 3
8 is the output of each electrostrictive element 3 of the ultrasonic transducer 20.
The output is proportional to the difference between the currents flowing at 0 and 31, that is, a vibration velocity signal, and the frequency characteristic of the phase difference of this signal with respect to the converter current is as shown in FIG. 1a, for example.

In one method, the detection signals es ₁ and es ₂ are added by a summing amplifier 39, and the output voltage, that is, a signal proportional to the converter drive current is input to the other input of the phase comparator 40 so that the phase with the differential signal is compared, integrator 4
1. A signal representing the phase relationship between the vibration velocity signal and the converter current passes through a DC amplifier 42 and is connected to a zero cross detector 43, a window comparator 44, and a make contact of a switch 45. The break contact of the switch 45 is grounded, and the common terminal is connected to the PLL input terminal 23 of the voltage controlled oscillator 21. Further, the output of the digital/analog converter 49 is connected to the sweep input terminal 22.

The converter current signal from the summing amplifier 39 is rectified by a rectifier 46 and then smoothed by an integrator 47, and the frequency characteristic of its envelope is obtained, for example, as shown in FIG. 48, the signal is taken into the microcomputer as a digital signal.

The apparatus configured as described above operates as follows. First, the amplification degree of the digital control amplifier 37 is set to 1 by digital control from the microcomputer, and then the digital/analog converter 4
While increasing the output voltage of 9 from zero over time and sweeping the oscillation frequency of the voltage controlled oscillator 21 from low to high, the detected phase difference output is increased or decreased at each frequency step, that is, leading or trailing. The magnitude of the converter current is determined by the zero cross detector 43, and the magnitude of the converter current is input as a digital signal into the memory of each microcomputer as data. When the frequency sweep and data storage are completed, first, the data of the phase difference of the detection signal is searched, and if the search is from a low frequency to a high frequency, a frequency that is reversed from positive to negative is determined.

Next, referring to the converter current data at that frequency, it is checked whether there is a minimum point within a certain frequency range that is below a predetermined level.

As a means of checking the minimum point, first, shift the frequency higher or lower than the frequency at which the detected phase difference is inverted, find the direction in which the current data decreases, and find the minimum point and value in that direction. A certain range above the frequency at which the phase difference data is inverted, e.g. 100Hz
If there is a minimum point of current within the range, that frequency is considered to be the resonance point, and using that frequency as a reference, search within a certain frequency range, for example ±500Hz, and find that it is at least not lower than the reference value, and If at least a certain value, for example greater than 5, exists between the extreme values of the frequency width, that reference point is regarded as the minimum value, and the zero crossing point at that time is determined as the fundamental resonance point.

If the level is above the predetermined level,
Even if it is below that level, the minimum value is, for example, 100Hz.
If it is not within the range, it is determined that the zero-crossing point is not the fundamental resonance frequency, and the search for the next zero-crossing point is continued.

Now, in Fig. 1, points B, A, and C are obtained as the required zero-crossing points from the phase characteristics, but points D and F on the current characteristics are excluded because they are too far from the zero-crossing points, and point A is It is determined to be the fundamental resonance point.

These criteria are based on the fact that the phase characteristic rapidly reverses at the fundamental resonance point, and that the current minimum point exists very close to the fundamental resonance point.

Figure 5 shows the detection phase characteristics a and converter current characteristics b when the horn and tools are replaced with ones different from those in Figure 1, and the fundamental resonance frequency f ₀ is considerably lower than that in Figure 1. For example, if the frequency increases by 2KHz,
It is impossible to determine the fundamental resonant frequency only from the zero-crossing point of the phase characteristics, and points B and E can only be narrowed down by referring to the current characteristics. That is, A,
Points C and D are all selected because there is no current dip nearby. Point B in FIG. 5 can be removed by setting the maximum value of the current level.

Therefore, as a selection procedure, we refer to the current characteristics at the falling zero cross point on the phase characteristics and check from low frequencies to see if there is a dip that is below level K and nearby, but this is just a judgment operation. The fundamental resonance point f ₀ is found in an extremely short time.

When the fundamental resonance point is determined as the zero crossing point in this way, the digital/analog converter 49 sets the voltage controlled oscillator 21 to that frequency, and then the switch 45 is switched to drive the ultrasonic transducer 20 as PLL control. . Electrostrictive element 3
The currents flowing through 0 and 31 are taken out as detection voltages es ₁ and es ₁ , and the difference between them is used as a vibration speed detection signal.
Further, the sum is used as a converter drive current for phase comparison, and a voltage proportional to the phase difference controls the voltage controlled oscillator 21 as the output of the DC amplifier 42.

As a result, a feedback loop is formed and the frequency of the voltage controlled oscillator is controlled by tracking the zero crossing point.

In the tracking drive state, the maskro computer monitors the output of the window comparator 44 to determine whether the phase difference is within a set value. When the mechanical vibration system becomes abnormal or the phase difference deviates significantly and tracking becomes impossible, the wind comparator 44
The output of will change and the computer will stop the operation of the device.

Next, a further improved method will be explained. As shown in Fig. 1a, it is desirable that the detection phase characteristics have approximately the same frequency width from the fundamental resonant frequency f ₀ to the zero cross point in the low and high ranges. Depending on the configuration of the vibration system including the tool, an asymmetrical phase inversion part may appear, for example, as shown in Figure 3a, the low range becomes significantly narrower than the high range for f ₀ , inhibiting stable frequency tracking. There are cases where These greatly vary depending on the difference in damping capacity of each electrostrictive element of the converter, the differential detection accuracy, the level of the detection signal, the configuration of the mechanical vibration system, etc.

Therefore, at the time when the basic resonance point is determined by checking the detected phase signal, the differential balance is set as follows and the phase characteristics are corrected.

In other words, once the fundamental resonance point is determined by searching for the zero cross point, a certain frequency range, for example 1KHz, is searched for the low frequency range around the resonance point, and a check is made to see if there is a phase reversal. Digitally controlled amplifier 3 in the extending direction
Adjust the differential balance by changing the amplification degree of 7.
Simultaneously check and adjust the high frequency side in pairs.

By adjusting the differential balance in this manner, the detected phase characteristics shown in FIG. 3a become almost symmetrical as shown in FIG. 3b.

In this correction operation, under adverse conditions where 1KHz cannot be corrected for both high and low frequencies, for example,
The width is gradually narrowed to 800Hz and then 600Hz to establish symmetry.

Due to this setting operation, the detection phase characteristics during PLL tracking operation are always kept in the best condition, making it possible to further improve the compatibility of the mechanical vibration system and locking the resonance frequency when changing tools, etc. The frequency range becomes wider or the effect thereof is exhibited.

Note that when searching for the resonance point based on the converter drive current characteristics, if the converter drive method is parallel resonance operation as shown in Figure 4, the minimum current value point is found as described above, but if the converter drive method is series resonance operation, the minimum current value point is found. Find the maximum current value point.

Effects of the Invention As described above, the present invention provides that a mechanical vibration system including an ultrasonic transducer has a large number of sub-resonance points near its fundamental resonance frequency, and that the fundamental resonance frequency fluctuates due to changes in tools, etc. When driving an object, the vibration velocity signal and drive voltage range are determined not only based on the phase difference characteristics with the current as in the conventional method, but also based on the correlation with the resonance point on the drive current characteristics to determine the fundamental resonance frequency. Furthermore, since the current characteristics are referred to using the zero crossing of the phase characteristics as a reference, the search time is fast, and the oscillation operation is then performed by tracking the phase difference signal. It enables compatibility in mechanical vibration systems, which was considered impossible with symmetry, and there is no unstable operation such as the resonant frequency jumping to the sub-resonant point when oscillation starts or sudden load changes, and stability is achieved. This has many effects such as enabling high oscillation drive operation.

[Brief explanation of drawings]

Figures 1a and b are the phase of the detection signal and frequency characteristics of each drive current, Figures 2a and b are the phases of the detection signal and frequency characteristics of each drive current, and Figure 3a,
b, c are the phase of the detection signal, the phase after its correction, and the frequency characteristic diagram of each drive current, Figure 4 is the drive circuit diagram, and Figure 5 a, b are the phase of the detection signal, the frequency characteristic diagram of each drive current. It is.

Claims (1)

[Claims] 1. After determining the required zero cross from the phase characteristics of the vibration speed detection signal, confirming that it is a resonance point from the converter current characteristics, determining the zero cross point as the basic resonance point, and performing PLL tracking. An ultrasonic transducer drive control method characterized by entering oscillation. 2 After finding the required zero cross from the phase characteristics of the vibration speed detection signal, confirm that it is the resonance point from the converter current characteristics, judge that zero cross point as the basic resonance point, and calculate the phase characteristics of the vibration speed detection signal. An ultrasonic transducer drive control method characterized by controlling the differential balance so that high and low frequencies are symmetrical about the resonance point, and then entering PLL tracking oscillation.