DE4230491A1 - Control device for ultrasonic generator - in which switch circuit adjusts induction in resonance oscillating circuit in response to generator output sensor - Google Patents

Abstract

Control switch circuit for an ultrasonic generator consists of a sensor (4) which measures the output signal from the generator (1) and a switch circuit (5) which can variably set the frequency of the generator by variably adjusting the oscillating frequency of the resonance oscillating circuit (2) in response to the output signal from sensor (4). USE/ADVANTAGE - Used in ultransonic machines, esp. ultrasonic welding equipment. A frequency control over a wide range is achieved as is a power or voltage control.

Description

The present invention relates to a control device for an ultrasonic generator. In particular, it affects one Control circuit for an ultrasonic generator, which in a Ultrasound machine, such as B. an ultrasonic welding apparatus and the like can be used.

Conventional control devices for ultrasonic generators have a frequency control from which in a state another state is switched, for example is switched from one frequency to another frequency.

However, these known devices have disadvantages that the area of application in which the output or Frequency can be changed, is limited, and the changes can only be carried out in stages. A performance control is therefore only possible in a narrow area and the Setting the frequencies inaccurately, d. that is, the frequency in becomes stable if the output power over a wide range Area is regulated.

The present invention has for its object a Trainee control device for an ultrasonic generator that frequency control over a wide range is possible is.

Another object of the present invention is Trainee control device for an ultrasonic generator that a power or output voltage control over a wide range is possible.  

Another object of the present invention is the control device so that the frequency and Power or output voltage control with great accuracy can be carried out.

The objects are solved by the features of claim 1.

The present invention includes a resonant circuit for operating an ultrasonic generator, one Power control circuit for regulating an output power or an output voltage of the resonant circuit and a frequency detector that detects the output frequency of the Ultra perceives sound generator, or a sensor for measuring the Oscillation voltage of the ultrasonic generator and one Circuit for variably setting the frequency that the Reso resonance circuit according to the sensor or detector controls.

One possibility for setting the vibration amplitude and the frequency of an ultrasound generator 1 is described below. An output power control circuit 3 or a driver circuit is actuated at the beginning in order to feed rectangle waves into a resonant circuit 2 . Each compo nent of the output control circuit 3 is then controlled such that the resonant circuit 2, provided it delivers result. A switch 10 is then actuated to be selectively connected to a CR oscillator 11 which is used for test purposes. The oscillation frequency f ₀ is then set to 40 kHz, for example. At the same time, each component of the output power control circuit 3 is controlled so that the resonant circuit 2 provides the predetermined effect.

Then the oscillation frequency f _{0 of} the CR oscillator is increased or decreased a little, and the voltage output V _{G of} a voltage control circuit 5 A is controlled in such a way that the resonant circuit 2 is constantly tuned to the oscillation frequency f ₀ . After the above-described control process is completed, the changeover switch 10 is switched back to its initial position, so that it is connected to the frequency detector 4 , with the entire device going into the operating state. In addition, the amplitude of the ultrasonic generator 1 can be controlled by a reference voltage, which is emitted by a reference voltage setting circuit 31 A, which is arranged within the power control circuit 3 .

Another way of control is through the switching circle for variable frequency setting by the this circuit the oscillation voltage of the ultrasound genes rators constantly monitored by a sensor becomes. It can also induce a resonant circuit control in such a way that the relationship of Oszil Lation voltage of the ultrasonic generator to an applied Voltage of the resonant circuit in a resonant circuit frequency increases.

Based on the drawings, two embodiments of the Invention described in more detail. Show it:

Fig. 1 is a diagram of the basic circuit of the first and second embodiment,

Ses Fig. 2 is a block diagram of a Leistungssteuerschaltkrei or a driver circuit of FIG. 1,

3 is a block diagram approximately example. Of a circuit for setting the frequency varia ble of FIG. 1 according to a first exporting,

FIGS. 4 and Fig. 5 are diagrams of measurements erge Ben, in which the variable inductance component L ei _ie nes resonant circuit with the control voltage V _G of Fig. 3 changes, and

Fig. 6 is a block diagram of a circuit for variably setting the frequency of Fig. 2 according to a second exemplary embodiment.

The first embodiment is described with reference to FIGS. 1 to 5. It comprises: a resonant circuit 2 for driving an ultrasonic generator or ultrasonic generator 1 and a power control circuit or voltage control circuit 3 for regulating the output power or the output voltage of the resonant circuit 2 . The ultrasound generator 1 is provided with a frequency perception detector 4, sensing an output frequency of the ultrasonic generator. 1 A circuit 5 for variably setting the frequency is connected to the resonant circuit 2 , the circuit 5 for variably setting the frequency being provided with a function for variably setting the frequency, which enables an oscillation frequency of the resonant circuit 2 to be continuously dependent the output of the frequency detector 4 is output.

The output of the frequency detector 4 is entered into the power control circuit 3 via a changeover switch 10 . The switch 10 is connected to a CR (capacitance-resistance) oscillator 11 at one terminal thereof, which generates a sine wave of a predetermined frequency for test purposes.

In particular, according to the present invention, a PZT element (lead (Pb) zirconate titanate semiconductor) with a capacitance C _{0 forms} the basis of the ultrasound generator 1 . The resonance resonant circuit 2 comprises a resistor R ₀ , a fixed inductance L and a variable inductance L _ie , all of which are connected in series with respect to the PZT element, which has a capacitance of C ₀ . Furthermore, an output pulse of the power control circuit 3 , which occurs in predetermined cycles, is output to the resistor R ₀ .

In FIG. 2, the power control circuit 3 is shown, comprising:
a rectifier 31 for rectifying a predetermined frequency signal output from the frequency detector 4 , a comparison amplifier 32 which compares the output of the rectifier 31 with a predetermined value (ie, the value of the output of a circuit for setting a reference value 31 A ), being amplified for output, a Schmidt circuit 33 for converting the input signals into a square wave, a differentiating circuit 34 for differentiating the output of the Schmidt circuit 33, and a sawtooth signal oscillator circuit 35 for outputting a sawtooth-shaped signal according to the output of the Differentiating circuit 34 . The power control circuit 3 is further provided with a comparison circuit 36 which modulates a pulse width of the output of the comparative amplifier 32 according to the output of the sawtooth oscillation circuit 35 . An output signal of the comparison circuit 36 causes an on-off control of a switching transistor Tr, the output of a TC voltage supply V _{S being applied} to the resonant circuit 2 described above in predetermined cycles via a transformer T ₁ .

That is, the cycle of the square wave applied to the resonance resonance circuit 2 is controlled by a voltage derived from the ultrasonic generator 1 through the frequency detector 4 as described above. Furthermore, an amplitude of the square wave is controlled by an output of the above-mentioned circuit 31 A for setting the reference value, which is provided in the comparison amplifier 32 .

In particular, as shown in Fig. 3, the circuit 5 is provided for variable frequency setting, comprising: two isolation amplifiers G ₁ and G ₂ , which are connected in series with a resistance element R ₁ , a field effect transistor 51 for Controller (hereinafter referred to as "FET"), which is connected to an output terminal of the resistance element R ₁ , a control voltage circuit 5 A for generating a predetermined control voltage V _G , which is applied to a gate of the FET 51 , and a secondary coil L ₂ a transformer T, which is connected to a positive input terminal of an isolation amplifier G ₁ . The output of the other isolation amplifier G ₂ is fed to the positive input terminal of an isolation amplifier G ₁ via a coil 52 with an inductance component L ₀ . In addition, the control voltage circuit 5 A is provided with an F / V (frequency-voltage) converter circuit 5 B at an input stage thereof, which converts the output of the above-mentioned frequency detector 4 into a corresponding voltage of a predetermined value.

The symbol L _ie represents an inductance component of the entire coil from the perspective of the primary side of the transformer T. In addition, the symbol V _{G represents} the output of the control voltage circuit 5 A.

It is now described how in the circuit of Fig. 3, the output V _{G of} the control voltage circuit 5 A causes a variable adjustment of the amount of the inductance component L _ie the entire coil from the viewpoint of the primary side of the transformer T.

At the beginning, the total gain G of the two isolation amplifiers G ₁ and G _{2 is} :

G = R₂ / (R₁ + R₂) (1),

where R _{2 represents} the internal resistance r _DS between drain (D) and source (S) of the field effect transistor 51 . The inductance component when charging for the first time or the bootstrap inductance component L _{0 of} the coil 52 uses G to determine the effective inductance L _i from the point of view of the input side of G ₁ as follows:

L _i = L₀ / (1-G) (2)

By inserting (1) into (2) you get:

L _i = L₀ [1 + (R₂ / R₁)] (3)

Below, when the effective inductance L _{i is} connected to the secondary side of the transformer T, the effective inductance L _ie from the primary side point of view:

L _ie = L₁- [M² / (L _i + L₂)]
= L₁ [L _i / (L _i + L₂)] (4),

where L ₁ and L _{2 represent} the primary inductance and the secondary inductance of the transformer T, and M denotes the mutual inductance between the primary and secondary side of the transformer T. Further, the coupling between the primary and secondary sides of the transformer T is made strong, and the coupling coefficient "k = 1" is defined using the following relationship: M ² = L ₁ · L ₂ .

From (3) and (4) one obtains:

L _ie / L₁ = 1 / [1 + (L₂ / L _i )]
= 1 / [1 + (L₂ / L₀) / (1 + R₂ / R₁)] (5)

The internal resistance r _DS between drain (D) and source (S) of the field effect transistor 51 is now used as R₂, the following formula being used:

r _DS = R₀ / [1 - (V _G / V _P )] (6),

where V _{P is} the disconnected voltage or freewheeling voltage and R₀ is the value for r _DS at '' V _G = 0 ''.

Then insert the expression (6) into the expression (5) one gets:

L _ie / L₁ = 1 / [1 + (L₂ / L₀) / (1 + r _DS / R₁)]
= 1 / [1 + L _2/0 / {1 + R _0/1 / (1 - V _G V _P )}] (7),

wherein L _2/0 = L ₂ / L ₀ and R _0/1 = R ₀ / R ₁ applies.

As is obvious from (7), L _{ie can be} changed depending on V _G.

Fig. 4 and Fig. 5 show measurement results of V _G and L _ie , which are associated with the values of electrical elements in Fig. 3, if the values are selected appropriately. Curve K represents calculated values, while curve J shows measured values.

The setting of the oscillation amplitude and the frequency according to the first exemplary embodiment is described below with reference to FIG. 1. The power control circuit or the driver circuit 3 is operated at the beginning to feed a square wave into the resonant circuit 2 . Each component of the power control circuit 3 is then controlled so that the resonant circuit 2 provides the predetermined effects. Subsequently, the switch 10 is switched so that it is selectively connected to the CR oscillator 11, which is used for test purposes. The oscillation frequency f ₀ is then set to 40 kHz, for example. At the same time, each component of the power control circuit 3 is controlled so that the resonant circuit 2 provides the predetermined effects.

Subsequently, the oscillation frequency f _{0 of} the CR oscillator 11 is increased or decreased a little, and the output V _{G of} the control voltage circuit 5 A is regulated so that the resonance circuit 2 is constantly tuned to the oscillation frequency f ₀ . After the control process described above is completed, the changeover switch 10 is switched back to its original position so as to be connected to the frequency perception detector 4 so as to put the entire apparatus into an operating state. As described above, the amplitude of the ultrasonic generator 1 is now controlled by a reference voltage, which is supplied by a circuit 31 A for setting a reference value, which is arranged within the power control circuit 3 .

In summary it can be said that with this first out example of a closed control loop for controlling the Frequency is formed at which the frequency is sampled becomes.

Next, a second embodiment will be described, which according to FIG. 1 and FIG. The first embodiment 2 is formed, and the first embodiment except for the differences described below corresponds.

In this exemplary embodiment, the ultrasound generator 1 is provided with a sensor 4 for sensing the oscillation voltage.

The changeover switch 10 is used in the same manner as in the first embodiment.

Fig. 6 shows the circuit 5 for variable setting of the frequency according to the second embodiment. It also includes a first isolation amplifier G ₁ and a second isolation amplifier G ₂ , but the latter forms a bootstrap circuit. Both isolation amplifiers are connected in series via an opposing R ₁ . There is a field effect transistor 51 for control, which is connected to the resistor R ₁ , and to which the control voltage V _{G of} the voltage control circuit 5 A is present at the gate. The second coil L _{2 of} the transformer T is connected to the positive input of the isolation amplifier G ₁ . The output of the second isolation amplifier G ₂ is fed back to the positive input of the first isolation amplifier G ₁ via a coil 52 with the inductance L ₀ .

Here a technique is used that is commonly known as "Bootstrap" is referred to as having a positive return from an output to an input of an operational amplifier  is carried out in order to increase the apparent input impedance hen.

Furthermore, instead of the DC voltage source V _{S of} the power control circuit according to FIG. 2, an AC voltage source with a downstream rectifier and a smoothing device can also be used.

With reference to expression ( 7 ), L _{ie can} be changed as a function of V _G as in the first exemplary embodiment. In particular, changes in V _G allow the control of the resonance frequency of the resonant circuit 2 , as represented by the following expression:

fr = 1/2 π · (8)

The operation of the control voltage circuit 5 A according to the second embodiment will be described below.

The control voltage circuit 5 A monitors an applied voltage of the ultrasonic generator 1 for each cycle by checking the voltage value supplied by the F / V converter circuit 5 B.

When the voltage V _{0 is applied} to a series circuit comprising a resistor R, a coil L and a capacitor C, the flowing current I is usually determined by the following expression, where the angular frequency is ω:

I = V₀ / R + j (ωL - 1 / ωC)

If R is a small value, the current I changes rapidly with the changes in the angular frequency ω. An angular frequency, which is referred to as resonance angular frequency ω ₀ , is such that the current I reaches its maximum absolute value. When a voltage is applied across the coil L and a different voltage is applied across the capacitor C, V _L and V _C are respectively obtained, the value Q and the quality Q, which describes the properties of a resonant circuit, being defined as follows is:

Q = | V _L / V₀ | ω = ω₀
= | V _C / V₀ | ω = ω₀ (9)

The value Q of the resonant circuit 2 is determined by the expression ( 9 ), where V _{0 is} an output voltage which is output from the power control circuit 3 to the resistor R _{0 of} the resonant circuit 2 . V _C is determined by the voltage applied to the ultrasonic generator 1 , that is, the value of the voltage is determined which is output by the F / V converter circuit 5 B.

Assuming that the voltage is shifted a little from the resonance voltage, the voltage applied to the ultrasonic generator 1 is calculated to be of a larger value so that the value Q of the resonant circuit 2 is increased, and the value V _G , which results from the fact that the impedance control circuit 5 C is fed.

The control voltage circuit 5 A provides continuous operation in such a way that the value Q of the resonance resonant circuit 2 is always larger.

The operation of the power control circuit 3 according to the second embodiment will be described below.

The rectifier 31 rectifies the frequency signal from the sensor 4 and then supplies the resulting signal to the comparison amplifier 32 .

The comparison amplifier 32 compares the output of the rectifier 31 with the output of the circuit 31 A that sets the reference value and amplifies the result thereof to be fed into the comparison circuit 36 .

The Schmidt circuit 33 or Schmidt trigger converts the frequency signal from the sensor 4 into a square wave, which is then fed into the differentiating circuit 34 .

The differentiating circuit 34 differentiates the output of the Schmidt circuit 33 to thereafter feed the resulting output into the circuit 35 generating the sawtooth signal.

The sawtooth signal generating circuit 35 generates a sawtooth-shaped signal according to the output of the differentiating circuit 34 , which is delivered to the comparison circuit 36 .

The comparison circuit 36 modulates a pulse width of the output of the comparison amplifier 32 in accordance with the output of the sawtooth signal generating circuit 35 which is applied to the gate of the switching transistor Tr.

The switching transistor Tr provides an on-off operation depending on the output of the comparison circuit 36 . The output pulse is applied with a predetermined cycle to the resistor R _{0 of} the resonant circuit 2 via the transformer T ₁ .

The resonance frequency f _{0 of} the resonant circuit 2 is synchronized with a switching frequency of the power control circuit 3 so as to be constantly tuned to the switching frequency.

In particular, when the frequency of the ultrasonic generator 1 is shifted due to a change in load or temperature, the power control circuit 3 can be synchronized with such a shifted frequency of the ultrasonic generator 1 . In addition, an oscillation amplitude of the ultrasonic generator 1 can be changed as a function of changes in the output or the output level of the circuit 31 A for setting the reference voltage. Thus, even if the vibration amplitude of the ultrasonic generator 1 is changed by a load or a temperature change, the vibration amplitude can be kept constant because the cycles of the transistor Tr are controlled.

In summary it can be said that the device according to the second embodiment, a closed control loop forms, in which the amplitude of the output signal of the Ultra sound generator is measured and in dependence on this Measured value changes the frequency of the resonant circuit which changes its value Q and the amplitude of the output signal of the ultrasonic generator.

According to the present invention, the above is illustrated Structure of a control device for an ultrasonic generator controlled with each oscillation cycle of the ultrasonic generator ert. This enables such improved control to provide the ultrasonic generator so that an output with stable frequency is achieved over a wide range.

A control device for an ultrasound generator is provided, which has a driver circuit 3 for controlling the output from a resonant circuit 2 . The ultrasound generator 1 is provided with a sensor 4 for sensing the frequency or the amplitude of the output of the ultrasound generator 1 . A circuit 5 for variably setting the frequency of the ultrasound generator 1 is provided in the resonant circuit 2 , the resonant circuit being tuned by changing an inductance. The circuit for variably setting the frequency is designed such that the frequency of the resonant circuit 2 can be changed as a function of the sensor signal.

Claims (4)

1. Control circuit for an ultrasonic generator, comprising a resonant circuit ( 2 ) for operating the ultrasonic generator ( 1 ) and a power control circuit ( 3 ) for regulating the output of the resonant circuit, characterized in that the output signal of the ultrasonic generator ( 1 ) with a detector or Sensor ( 4 ) is provided, which samples the output signal of the ultrasonic generator ( 1 ), and a circuit ( 5 ) for variably setting the frequency of the ultrasonic generator is provided, which is connected to the resonant circuit ( 2 ), the circuit ( 5 ) for variably setting the frequency is provided with a function for variably setting the frequency, which makes it possible to continuously set the oscillation frequency of the resonant circuit ( 2 ) as a function of the output from the detector or sensor ( 4 ). 2. Control circuit according to claim 1, characterized in that the output signal of the ultrasonic generator is sampled by a frequency detector ( 4 ). 3. Control circuit according to claim 1, characterized in that the output signal of the ultrasonic generator is sampled by a sensor ( 4 ) for measuring the voltage, and that the circuit ( 5 ) for variably setting the frequency, the resonant circuit ( 2 ) depending on the output of Sen sors ( 4 ) controls so that a larger ratio of the vibration voltage of the ultrasonic generator to a resonance circuit ( 2 ) applied to the resonance is provided. 4. A circuit according to claim 2, characterized in that the circuit ( 5 ) for variable setting of the frequency is provided with an F / V converter circuit which converts the frequency perceived by the frequency detector ( 4 ) into a corresponding voltage, and a Voltage control circuit ( 5 A) is provided, which adjusts an inductance component in accordance with the output of the frequency detector ( 4 ), which corresponds to the voltage converted by the F / V converter circuit, which is measured as a reference value.