JPH081091A - Ultrasonic transducer drive - Google Patents

Abstract

(57) [Summary] [Purpose] Even with a simple configuration, the vibration speed is always kept constant even when the load increases or decreases. The driving device 10 includes an oscillator 102 for generating a frequency signal Vs, a power amplifier 106 for power-amplifying the frequency signal Vs generated by the oscillator 102 to generate a driving voltage Vd ₂ for the ultrasonic transducer 11, The vibration speed detecting means 12 that outputs the detection voltage Vp corresponding to the vibration speed v of the acoustic wave vibrator 11, and the amplification degree for the frequency signal Vs are changed so that the detection voltage Vp output from the vibration speed detecting means 12 is negatively fed back. Voltage control variable gain amplifier 14 for

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an ultrasonic vibrator used in ultrasonic processing technology, ultrasonic welding technology, and the like, and more specifically, to make the vibration speed (amplitude) of the ultrasonic vibrator constant. Drive device capable of

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a conventional ultrasonic vibrator driving device. Hereinafter, description will be given based on this figure.

The driving apparatus 100 comprises an oscillator 102 for generating a frequency signal Vs, and a power amplifier 106 for power-amplifying the frequency signal Vs generated by the oscillator 102 to generate a driving voltage Vd for the ultrasonic transducer 104. It is a thing.

The frequency of the frequency signal Vs is, for example, 40 [kH
z]. The power amplifier 106 includes a power amplification IC 108 having an amplification degree (gain) G and a step-up transformer 1 having a winding ratio of 1: n.
It is composed of 10 and. The ultrasonic oscillator 104 is a bolted Langevin type oscillator in which a piezoelectric ceramic is sandwiched between metal blocks and bolted. A horn 112 and a cutter blade 114 are attached to the ultrasonic transducer 104.

Here, it is assumed that the ultrasonic vibrator 104 is in a resonance state, and a joint surface A'between the ultrasonic vibrator 104 and the horn 112 is taken as a mechanical terminal. The vibration speed v at the mechanical terminal is Vd = GnVs in consideration of

V = F / (r _m + r _l ) = A · Vd / (r _m + r _l ) = {A / (r _m + r _l )} · G · n · Vs (1)

Can be expressed as: Here, F is the driving force generated at the mechanical terminal by the driving voltage Vd of the ultrasonic transducer 104, A is the force coefficient, r _m is the equivalent mechanical resistance at the mechanical terminal, and r _l is the load mechanical resistance r _{l at} the tip surface of the horn 112. It is a value obtained by converting'to the joint surface A '. The force coefficient is defined as "a complex ratio between a driving force generated when a voltage is applied to an electric terminal with a vibrating end face fixed and an applied voltage."

By the way, when the vibration system is placed in the air, it must be used the values r _a in terms of 'bonding surface A a' radiation resistance r _a to air at the tip of the horn 112 as r _l. If the vibration velocity at this time is v _o , from equation (1),

V _o = {A / (r _m + r _a )} · G · n · Vs (2)

[0010] Therefore, the rate of change δ ₁ of the vibration velocity v at no load (in air) and at load is calculated by the equations (1) and (2).
From

Δ ₁ = (v−v _o ) / v _o = (Vp −Vpo) / Vpo = (r _a −r _l ) / (r _m + r _l ) ≈−1 / (1 + r _m / r _l ). ... (3)

Is calculated as Where r _a << r _l
I put it. Further, since it is not easy to directly measure the vibration velocity v, the detection voltage Vp obtained by dividing the voltage Vp ′ generated from the ultrasonic transducer 104 is used. The detection voltage Vp is the vibration speed v
It is considered to be proportional to. Note that Vpo is the value of Vp under no load (in air).

FIG. 4 shows the result of measuring the rate of change δ ₁ by applying straw paper half-width to the cutter blade 114 at a right angle. 4, the solid line curve (a) is a measure of the rate of change [delta] ₁ of the detected voltage Vp for the number N of the paper, the curve of one-dot chain line (a ') is the change in the detected voltage Vp for r _l / r _m Rate δ
₁ is drawn according to the equation (3). Note that Vp 'and Vp were measured by the method shown in FIG.

As described above, in the conventional ultrasonic vibrator driving device, the vibration speed v decreases as the load increases.

[0015]

However, when the vibration velocity v is reduced, the ultrasonic energy emitted is reduced, so that, for example, in the case of an ultrasonic processing machine, the processing speed is reduced. To solve this problem, there is a technology that always obtains the maximum amplitude by detecting the change in the resonance frequency, processing the numerical data with a microcomputer, and following the change in the resonance frequency based on the processing result. It is known (for example, JP-A-62-140685). However, since such a technique requires a very complicated configuration of detecting a change in the resonance frequency and using a microcomputer, the size is increased,
This caused problems such as high prices.

[0016]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a driving device for an ultrasonic vibrator, which has a simple structure and whose vibration speed is always constant even if the load increases or decreases.

[0017]

The present invention has been made in order to achieve the above-mentioned object, and an oscillator for generating a frequency signal and an ultrasonic transducer for amplifying the frequency signal generated by the oscillator are provided. It is an improvement of a driving device for an ultrasonic vibrator including a power amplifier that generates a driving voltage.

That is, a vibration speed detecting means for outputting a detection voltage corresponding to the vibration speed of the ultrasonic vibrator, and an amplification degree for the frequency signal so that the detection voltage output from the vibration speed detecting means is negatively fed back. And a voltage-controlled variable gain amplifier for changing

The ultrasonic vibrator is made of piezoelectric ceramic, the power amplifier has electrodes for applying the drive voltage to the piezoelectric ceramic, and the vibration velocity detecting means is proportional to the vibration velocity from the piezoelectric ceramic. It may have an electrode for obtaining the above-mentioned detected voltage.

In addition to the above, the voltage control variable gain amplifier has a voltage variable resistance portion whose resistance value increases or decreases according to the detection voltage proportional to the vibration speed, and an amplification degree increases or decreases depending on the resistance value of the voltage variable resistance portion. It may have an amplifier.

[0021]

The frequency signal generated by the oscillator is amplified by the power amplifier and becomes the driving voltage for the ultrasonic transducer. This drive voltage causes the ultrasonic transducer to vibrate. The vibration speed at this time is output as a detection voltage by the vibration speed detecting means. The detected voltage is negatively fed back by the voltage controlled variable gain amplifier.

That is, the operation of the voltage controlled variable gain amplifier is as follows. It is assumed that the vibration speed and the detected voltage have a proportional relationship. When the detected voltage decreases below a certain value (vibration speed decreases), the detection voltage is increased (vibration speed is increased) by increasing the amplification degree of the frequency signal and increasing the drive voltage. On the contrary, when the detection voltage increases above a certain value (vibration speed increases), the detection voltage is decreased (vibration speed is decreased) by lowering the amplification degree of the frequency signal and lowering the drive voltage.

[0023]

1 to 3 show an embodiment of a driving device according to the present invention, FIG. 1 is a block diagram showing the entire structure, FIG. 2 is an enlarged sectional view of an essential part showing an ultrasonic transducer, and FIG. FIG. 4 is a circuit diagram showing a voltage controlled variable gain amplifier. Hereinafter, description will be made based on these drawings. However, the same parts as those in FIG.

The driving device 10 according to the present invention includes an oscillator 102 for generating a frequency signal Vs, and a power amplifier for power-amplifying the frequency signal Vs generated by the oscillator 102 to generate a driving voltage Vd ₂ for the ultrasonic transducer 11. 106, the vibration velocity detecting means 12 for outputting the detection voltage Vp corresponding to the vibration velocity v of the ultrasonic transducer 11, and the detection voltage Vp outputted from the vibration velocity detecting means 12 for the frequency signal Vs so as to be negatively fed back. And a voltage controlled variable gain amplifier 14 for changing the amplification degree.

The ultrasonic transducer 11 includes a pair of piezoelectric ceramics 11a and 11b and a pair of piezoelectric ceramics 11c and 1c.
1d is piled up and these are metal block 1 from both sides.
The structure is such that it is sandwiched between 1e and 11f and then fastened and fixed with a bolt 11g. Piezoelectric ceramics 11a, 11b,
11c and 11d have + and-polarized structures, and
And +, − and − are superimposed. An electrode 11h is provided between the metal block 11e and the piezoelectric ceramic 11a, and an electrode 1 is provided between the piezoelectric ceramics 11a and 11b.
1i has an electrode 11 between the piezoelectric ceramics 11b and 11c.
j is an electrode 11k between the piezoelectric ceramics 11c and 11d.
Are inserted respectively. Driving voltage V is applied to the electrode 11k.
d ₂ is applied, electrodes 11h and 11j are grounded, and electrode 1
A voltage Vp 'proportional to the vibration speed v is obtained from 1i.

The vibration velocity detecting means 12 has resistors 30 and 32 for dividing the voltage Vp 'extracted from the electrode 11i to obtain the detection voltage Vp.

The voltage-controlled variable gain amplifier 14 has a rectified voltage Vp proportional to the detected voltage Vp proportional to the vibration speed v.
The rectifying unit 34 for obtaining r and the resistance value r by the rectified voltage Vr
Voltage variable resistance unit 35 in which _d increases and decreases, and voltage variable resistance unit 3
The amplification unit 36 increases or decreases the gain Gv according to the resistance value r _{d of} 5. The rectification unit 34 detects the detection voltage V
Operational amplifier A ₂ for inputting and amplifying p, and operational amplifier A
Resistor for determining the _second amplification degree of R _1, R _2, and a rectifying the amplified detected voltage Vp and smoothing diodes Dr, a resistor Rr and capacitor Cr. The voltage variable resistance unit 35 includes an N-channel junction type FET 38 having a resistance value r _d between the source and the drain, and a resistor R that determines the gate voltage V _G of the FET 38 based on the rectified voltage Vr.
It is composed of _G1 and R _G2 . Amplifier 36, an operational amplifier A ₁ for amplifying the frequency signal Vs and outputs a driving voltage Vd ₁ to the power amplifier 106, amplification degree G of the operational amplifier A ₁
It consists of a resistor Rf which determines v.

Next, the operation of the drive unit 10 will be described.

Frequency signal Vs generated from oscillator 102
Is amplified by the voltage controlled variable gain amplifier 14 to become the driving voltage Vd ₁ and is applied to the power amplifier 106. In this case, the voltage controlled variable gain amplifier 14 detects the detection voltage Vp.
Therefore, the detected voltage Vp is used as a function instead of the vibration speed v.

That is, K is a constant of proportionality,

Vp = K · v (4)

From equation (1), we can write

[0033] Vp = A · K / (r m + r l) · Gv · n · Vs ····· (5)

It becomes On the other hand, the gain G of the operational amplifier A ₁
v, when the resistance value of the resistor Rf and r _f,

Gv = 1 + r _f / r _d (6)

It becomes r _d is the drain resistance of the FET 38 and is represented by the following equation.

[0037] _{r d = r dO / (1} -V G / 2V PO) ····· (7)

[0038] r _dO the value of r _d at the time of the gate voltage V _G = 0 of FET38, the V _PO is a pinch-off voltage. For the derivation of equation (7), CDTodd: ^ FETs as v
oltage-variable resisters ", Electronic Design, pp.
66-69, Sep. 13.1965.

Further, the gate voltage V _G is the operational amplifier A ₂
Is the rectified DC voltage (rectification efficiency η) obtained via
That is, V _G = η · Vp and equation (7) are substituted into equation (6), and this is further substituted into equation (5) to rearrange,

[0040] Vp = a · Ko / (r m + r l + Ko + Qo) ····· (8)

It becomes Where Ko = A · K · Gv · n
· Vs, a = 1 + r f / r dO, Qo = η · r f / (2r
_dO · V _PO ).

When the vibration system is placed in the air, Vp → V
As po, r _l → r _a , from equation (8),

[0043] Vpo = a · Ko / (r m + r a + Ko + Qo) ····· (9)

Is obtained. Therefore, the change rate of Vp in this case, that is, the change rate δ ₂ of the vibration speed v is

Δ ₂ = (Vp −Vpo) / Vpo = (v−v _o ) / v _o = (r _a −r _l ) / (r _m + r _l + K _o · Q _o ) ≈−1 / {1+ (r _m ＋ Ko ・ Qo) / r _l } ・ ・ ・ ・ ・ (10)

It is However, r _a << r _l was set.

Next, as in the case of the prior art, a half-paper was applied to the cutter blade 114 at a right angle and the rate of change δ ₂ was measured. The result is shown by the solid curve (b) in FIG. By using the voltage-controlled variable gain amplifier 14, the load characteristics are remarkably improved, and the change rate δ ₂ of the vibration speed v for 30 sheets of paper is 10
%.

From FIG. 4, r _l when the rate of change δ ₁ is 50%
/ R _m is 1, the number N of the paper at this time is N ≒ 15.
Since δ ₂ corresponding to this is δ ₂ ≈5% from FIG. 4,
From equation (10), Ko and Qo are

Ko * Qo = 18r _m

Is obtained. Using this value, the formula (1
0) is calculated and the result is shown by the chain line curve (b ′) in FIG.
Shown in As is clear from FIG. 4, the theoretical curve (b ′) and the experimental curve (b) agree fairly well.

The main parts used in this embodiment will be described. The power amplifier IC 108 is "OPA541AM" manufactured by BURR-BROWN, the piezoelectric ceramics 11a, ... are "DA41540PC" manufactured by NTK, and the operational amplifiers A ₁ and A ₂ are "OPA" manufactured by PMI.
15 ", FET38" VCR7N "manufactured by Siliconix, step-up transformer 110 primary 25 [μH], secondary 32 [μH], winding ratio n = 11, respectively. Also, each constant is G = 3.3,
r _f / r _dO = 10, Vpo = 5 [V], η≈2.8, Vs = 0.5 [V]
Is.

The vibration velocity detecting means 12 may have any structure as long as it outputs the detection voltage Vp corresponding to the vibration velocity v. For example, the detection voltage Vp and the vibration velocity v
The configuration may be such that and are in an inversely proportional relationship.

[0053]

According to the present invention, the vibration speed detecting means converts the vibration speed of the ultrasonic vibrator into a detection voltage, and the voltage control variable gain amplifier changes the amplification degree so that the detection voltage is negatively fed back. Since the drive voltage of the ultrasonic vibrator is controlled by the above, the vibration speed can be stabilized against an increase / decrease in load with an extremely simple structure.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of a drive device according to the present invention.

FIG. 2 is an enlarged sectional view of an essential part showing an ultrasonic transducer according to the embodiment of FIG.

3 is a circuit diagram showing a voltage-controlled variable gain amplifier in the embodiment of FIG.

FIG. 4 is a graph showing load characteristics in the example of FIG. 1 and the conventional example of FIG.

FIG. 5 is a block diagram showing an overall configuration of a conventional drive device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Drive device 12 Vibration velocity detection means 14 Voltage control variable gain amplifier 35 Voltage variable resistance part 36 Amplification part 102 Oscillator 11 Ultrasonic vibrator 11a, 11b, 11c, 11d Piezoelectric ceramics 11h, 11i, 11j, 11k Electrode Vs Frequency signal Vd ₂ Drive voltage v Vibration speed Vp Detection voltage

Claims (3)

[Claims] 1. An ultrasonic transducer driving device comprising: an oscillator that generates a frequency signal; and a power amplifier that amplifies the frequency signal generated from the oscillator to generate a driving voltage for the ultrasonic transducer, wherein: Vibration speed detection means for outputting a detection voltage corresponding to the vibration speed of the ultrasonic vibrator, and voltage control variable for changing the amplification degree for the frequency signal so that the detection voltage output from the vibration speed detection means is negatively fed back. A drive device for an ultrasonic transducer, which is provided with a gain amplifier. 2. The ultrasonic transducer is made of piezoelectric ceramic, the power amplifier has electrodes for applying the drive voltage to the piezoelectric ceramic, and the vibration velocity detecting means is proportional to the vibration velocity from the piezoelectric ceramic. The drive device for the ultrasonic transducer according to claim 1, further comprising an electrode that obtains the detected voltage. 3. The ultrasonic vibrator driving device according to claim 2, wherein the voltage-controlled variable gain amplifier has a voltage variable resistance unit whose resistance value increases or decreases according to the detection voltage proportional to the vibration speed, and the voltage variable resistance unit. A driving device for an ultrasonic transducer, comprising: an amplification unit whose amplification degree increases and decreases depending on a resistance value of a variable resistance unit.