EP0217694A1 - Method and device for electrically powering a transducer generating sonic and ultrasonic vibrations - Google Patents

Abstract

The invention relates to a method for supplying electric power to a transducer for generating sonic or ultrasonic vibrations. It is characterized in that in the automatic control stage, the control device (11) is kept within said command and control loop and, by means of its processor and as a function of the data furnished to this processor and in particular data emitted by the analyisis means (6-8) furnishing the phase displacement (Df) and the direction (Sf) of the phase displacement between the current (I) and the voltage (U) of the power supply of the transducer, adapter control signals (12) are processed, each of which determines an output frequency and by way of which, not taking into account anything but the possible existence of a phase displacement requiring correction, whatever the value and the direction of this phase displacement, the progressive modification of the frequency is commanded, in the direction dictated by the direction of the phase displacement, until arriving at one of two situations, which are either the disappearance of the difference of the phases requiring correction, or the arrival at a previously fixed limit of the modification of the frequencies since the frequency at the beginning of this modification.

Description

The invention relates to a method and a device for supplying power to a transducer which generates both sound and ultrasonic vibrations.

So that the transducer behaves in a certain way and for example as a pure resistive load, inducing no phase difference between voltage and current, and not as a more inductive or capacitive load, we know that the frequency of the supply must be determined with reference to the resonant frequency of the acoustic line constituting the load of the transducer such as a tool and more precisely with reference to one of the two resonant frequencies which are present, a series resonant frequency and a parallel resonant frequency called anti-resonance.

We therefore start by looking for one of the resonance frequencies specific to each acoustic line supplied by the device.

To this end, the characteristic is exploited that, at said resonant frequencies, the phase shift between the voltage and the current of the power supply is zero.

For this, while measuring the phase shift between the voltage and the current of the power supply, the frequency of this power supply is gradually modified to sweep a certain frequency range until it stops on that where there is cancellation of the phase shift.

The corresponding frequency is then retained as the reference frequency of the corresponding acoustic line when it is used in the research conditions.

For this research step, in most of the known devices, an oscillator controlled by a voltage is used which delivers a signal whose frequency is a function of the control voltage applied to it and which comes from a control member, either manual, more generally automatic such as a microcomputer.

This microcomputer then receives either, from a continuous sampling device, signals representative of the current and the voltage, or, from a phase comparator, a signal representative of the phase shift between the aforementioned signals and this information received by the microcomputer are converted from their initial analog form into a digital form acceptable by said microcomputer, just as its output instructions are then from their initial digital form converted into an analog form compatible with the controlled oscillator.

The conversion, in particular from the analog form to the digital form, however requires allowing the result to stabilize before it is used, which in particular slows down the process of finding the tuning frequency if one wishes to avoid errors.

• - en cas d'augmentation de la puissance d'alimentation et/ou de la charge de l'outil mais encore,
• - suite à des influences extérieures telles la dérive en température, l'arrosage ...

The use of an oscillator controlled by a voltage also returns errors related to the drift of said oscillator. When at least one of the resonant frequencies of an acoustic line has been identified, it is of course necessary for the use of this acoustic line to ensure that its supply takes place at a working frequency determined with reference to this frequency of resonance but also take into account that this reference frequency is only valid under the conditions of the search stage and, for example, a new frequency will have to be sought:

• - in the event of an increase in the power supply and / or the load of the tool but also,
• - following external influences such as temperature drift, watering ...

This is why, in addition to the procedure and the means of prior search for at least one of the resonance frequencies, in all the known embodiments (DE-A-3,428,523 and US-A-4,275,363) are provided. a control procedure and means ensuring that the supply of the transducer is then, from the reference frequency, adjusted as a function of the effect on the phase shift of the evolution of the conditions which were those of the step of research.

For this control, in all known devices, use is made of a circuit constituting a phase locked loop or operating as such, namely that instead of the control voltage produced by the control means which, during the 'research stage produced the frequency sweep, the controlled oscillator receives an analog signal representative' of the significant change in plus or minus the phase difference between the voltage and the current of the transducer supply for, via the oscillator controlled, try to achieve a sufficient correction of the frequency, which of course requires that in the meantime, the frequency has hardly had time to change.

This analog signal is therefore produced by the phase comparator.

• - la plage de rattrapage est fixe et étroite et ne permet par exemple pas toujours des variations de puissance et/ou charge sans passer par une nouvelle étape de recherche et,
• - la réaction de la boucle a une vitesse qui varie avec l'importance du rattrapage à réaliser.

However, being able to supply only limited voltages, such a phase-locked loop is only suitable for catching up with developments remaining within fairly strict limits in importance and speed because:

• the take-up range is fixed and narrow and does not, for example, always allow variations in power and / or load without going through a new search stage and,
• - the reaction of the loop at a speed which varies with the importance of the catch-up to be carried out.

• C'est ainsi que :
• - pour limiter l'évolution des conditions influant sur la fréquence d'accord, on réserve l'application du dispositif à des taches ne nécessitant qu'une utilisation intermittente et à faible puissance telle la soudure et le lavage pour entre autre limiter les dérives en température du transducteur et de la boucle, dérives qui détruiraient la stabilité de la fréquence et,
• - pour limiter l'évolution du déphasage résultant de l'évolution des conditions de l'étape de recherche, on ne travaille de préférence qu'à la fréquence de résonance série, vers laquelle les variations de fréquences en fonction de l'évolution des dites conditions sont moins importantes et moins rapides que vers la fréquence de résonance parallèle avec incidemment l'avantage découlant du fait qu'à la fréquence série, le courant est élevé et, de ce fait, le courant comme la tension peuvent être aisément mesurés en vue d'en contrôler le déphasage même si en fait l'adoption de cette fréquence de résonance série présente l'inconvénient de ce que la puissance disponible est plus faible pendant le travail donc lorsqu'elle serait nécessaire que pendant le repos où elle ne peut que provoquer inutilement un échauffement et donc une dérive du transducteur. De tels dispositifs à boucle de verrouillage de phase ne permettent pas non plus de tenir compte d'une tolérance ou d'un écart entre la fréquence de travail et celle de référence, par exemple, pour limiter les actions de rattrapage.

This is why the known embodiments are only used in applications where the changes in the conditions of the research stage and / or their impact on the phase shift will in principle remain within such limits as to their importance and / or their speed.

• Thus :
• - to limit the evolution of the conditions influencing the tuning frequency, the application of the device is reserved for stains requiring only intermittent use and at low power such as welding and washing in order, inter alia, to limit drift in temperature of the transducer and the loop, drifts which would destroy the stability of the frequency and,
• - to limit the evolution of the phase shift resulting from the evolution of the conditions of the research step, we preferably work only at the series resonance frequency, towards which the frequency variations as a function of the evolution of the said conditions are less important and less rapid than towards the parallel resonant frequency with incidentally the advantage arising from the fact that at the series frequency, the current is high and, therefore, both the current and the voltage can be easily measured in view to control the phase shift even if in fact the adoption of this series resonance frequency has the disadvantage that the available power is lower during work so when it would be necessary than during rest where it can only unnecessarily cause heating and therefore drift of the transducer. Such phase-locked loop devices also do not make it possible to take into account a tolerance or a difference between the working frequency and that of reference, for example, to limit the catch-up actions.

Given the narrowness of the catch-up limits allowed by this loop, limits for example controlled by a window comparator, these limits are frequently crossed and the servoing procedure and therefore the operation of the transducer must be just as frequently interrupted to return in the research position, which greatly disrupts production.

in view of the above, it is understood that, in particular because of their control loop, the known supply devices are not at all suitable when their transducer has to work, on the one hand, at high power, hence unequal variations in speed and in importance of the resonant frequency, but also, on the other hand, in a lasting, if not continuous, manner from which results in particular heating and wear of the sonotrode also inducing significant variations in the frequency of resonance.

This inadequacy is also linked to the fact that, given their importance, frequency changes can exceed the frequency difference between the series resonance and parallel resonance frequencies, which is only a few tens of hertz, and reach in a frequency zone where the phase shift has a sign similar to that of a change in the other direction, which can then lead the loop to impose a correction opposite to that necessary.

A result which the invention aims to obtain is a method and a device for supplying power to a transducer with which the agreement on the working frequency follows the very rapid and significant modifications of this frequency. Is also a result which the invention aims to obtain, a method and an intelligent device which, while following the very rapid and significant modifications of the resonant frequency, makes it possible to disregard it within a certain limit fixed beforehand.

Another result which the invention aims to obtain is such a method and such a device with which the agreement is sufficiently precise to be made both with reference to the series resonant frequency and to the parallel resonant frequency where the power under load is stronger than at rest and where, therefore, the maximum power is provided at the time useful for work where optimal performance and although at this frequency, the current is very low and difficult to measure. Is also a result such a method and such a device which allow uses requiring different frequencies and powers and for example both for tasks requiring a large power such as machining and assistance electroerosion, electrochemical polishing, extrusion, than for conventional stains such as welding and washing.

To this end, it relates to a process of the aforementioned type, in particular characterized in that, during the servoing step, instead of disconnecting the control member and closing the command and control loop to make it operate like a phase locked loop, the control member is maintained in said control and command loop and, by means of its processor and, as a function of the information provided to this processor and in particular of information from means of analysis and supply of the phase shift and of the direction of the phase shift between the current and the voltage of the transducer supply, adapter control signals are each produced determining an output frequency and by which, by not taking account that of the possible existence of a phase shift requiring correction, whatever the value and that of the direction of this phase shift, the progressive modification of the frequency is controlled in the direction required by the direction of the phase shift until 'upon the occurrence of one of the two situations which are either the disappearance of the phase difference requesting correction, or the arrival at the limit previously fixed to the modification of the frequencies from the starting frequency of this modification.

It also relates to the supply device implementing this method.

• Figure 1 : le dispositif d'alimentation et le transducteur,
• Figure 2 : des courbes d'impédance en fonction de la fréquence, l'une au repos A, l'autre en charge B avec en abrégé l'indication des positions de fréquencede résonance série fr_s et résonance frp.

The invention will be better understood with the aid of the description below given by way of nonlimiting example with regard to the appended drawing which schematically represents:

• Figure 1: the supply device and the transducer,
• Figure 2: impedance curves as a function of frequency, one at rest A, the other under load B with abbreviated indication of the frequency positions of series resonance fr _s and resonance frp.

Referring to the drawing, it can be seen that, in the device on the main circuit 1 for the electrical supply of a transducer 2, means 3 known as are provided continuous sampling, taking signals U and I representative of the current and voltage of the power supply of the transducer 2.

These means 3 are connected by lines 4, 5 to means 6 to 8 which analyze them and provide information on the voltage and the current of the supply of the transducer 2 and in particular on their phase shift D _f and on the direction Sf of this phase shift.

The main circuit 1 has its end opposite to that connected to the transducer 2 which is connected to the output of an adapter 14 ensuring the electrical supply of said transducer 2.

This adapter has a main input 15 and a control input.

The main input 15 of the adapter 14 is connected to the sector 16 by a suitable member 17 such as a rectifier and possibly an autotransformer.

Between this member 17 and the adapter 14 can be interposed a circuit breaker 22 and, optionally, a suppressor 23 such as an integrator circuit.

For the step of finding the tuning frequency of an acoustic line, the adapter 14 has its control input which, by a line 13, is connected to a control member 11 comprising a processor and which sends signals 12 each determining a different value of the frequency at the output of the adapter 14, which makes it possible to control a frequency sweep until the phase shift is canceled.

In the case of a highly damped load such as for example in the presence of water, the transducer 2 may lose its ability to resonate in the frequency search range, and in this situation, the device may not make it possible to find the frequency of agreement in spite of a sweep during which, for example, the phase shift has varied between minus ninety degrees and minus twenty degrees or seventy degrees but therefore without going through zero degree, that is to say by the frequency of agreement.

In this case, for example by influence of one of the analysis means 6 to 8 or even of the control member 11, a fictitious phase shift C _f , for example of thirty degrees, is created between U and I, and, at low power, a second scan is carried out which, taking the example above and due to the fictitious phase shift, will lead to a phase shift of minus sixty to plus ten degrees which will therefore go through zero degrees, that is to say by the tuning frequency.

In a case taken outside of this example where after a second scan, the agreement would not be found, we can obviously create an even stronger fictional phase shift and start a scan again.

When the agreement is found, for after such a procedure to operate the adapter, the power is increased so that the device maintains the agreement and then the fictitious phase shift is eliminated, which shows a real phase shift, of opposite direction and same value but that, in the manner described below, the device detects which allows it to immediately control a catch-up.

In order to operate the adapter 14 at a working frequency determined with reference to the previously desired tuning frequency and the evolution of working conditions, the device is controlled.

For this control step, the adapter 14 has its control input which receives signals 12 and which, for this purpose, by a circuit 9, 10 is connected to the analysis means 6, 7 and 8 for, in particular, with the adapter, the main circuit 1, the lines 4, 5 and the analysis means 6 to 8 form a command and control loop for the adapter 14.

According to an essential characteristic of the method according to the invention, during the control step, instead of disconnecting the control member 11 and closing the command and control loop 3 to 10 and 12 to 14 to make it operate as a phase locked loop, the control member 11 is maintained in said control and command loop and, by means of its processor and, as a function of the information supplied to this processor and in particular of information from means 6 to 8 for analyzing and supplying the phase shift D _f and the direction S _f of the phase shift between the current I and the voltage U of the power supply of the transducer 2, signals 12 for controlling the adapter are produced each determining an output frequency and by which, taking into account only the possible existence of a phase shift requesting correction, whatever the value and only in the direction of this phase shift, the progressive modification of the frequency is controlled in the direction required by the direction of the phase shift until one of the two situations occurs, either the disappearance of the phase difference requiring correction, or the arrival at limit previously fixed to the modification of the frequencies since the starting frequency of this modification.

Of course, when at the working frequency of the transducer, the phase shift is zero or considered to be such, the corresponding frequency is obviously not changed.

On the other hand, it is noted that when it is not zero, with the aforementioned method instead of using a phase locked loop, the real value and the direction of the phase difference measured between U and I, then a single voltage is generated which is a function of this real value and of this direction and, finally, with this single voltage we adapt the output frequency of an oscillator controlled by a voltage, according to the invention, during the enslavement step taking into account at the phase shift only the existence of such a phase shift requiring correction, whatever the value and that the direction of this phase shift, it is developed using the processor of the control unit 11 the signals 12 determining the progressive modification by the adapter of the power supply frequency. For example, at the level of the control member, in order to avoid excessively hasty modifications, a phase shift tolerance is allowed in which this phase shift is considered to be zero and therefore as not or no longer request correction.

It is also possible to admit a variation in phase shift which is greater but limited in time or to order operation at a working frequency different from the reference frequency and for which the correction is therefore not or no longer required.

Depending on the factors set out in the preamble, the modifications to the position of the working frequency chosen so as to take account of changes in working conditions during the servo-control of the device naturally have limits by detecting the crossing which we detect abnormal operation such as a machining incident, tool break ...

In an alternative embodiment of the method according to the invention, during the servo-control of the device, the frequency modification is interrupted at at least one of these normal operating limits and, possibly, after at least one new attempt, issues a fault signal such as a visual or audible alarm and / or an installation shutdown command. Depending on the application, the position and the extent of the frequency modification, the phase shift tolerance and the limits of normal operation are determined by a low power analysis of the overall behavior of the load and as a function of the frequency at which it is desired. to work.

In order to benefit from optimum efficiency, the device is preferably adjusted so that the working frequency of the transducer corresponds to the parallel resonant frequency as shown in the above, the device can also operate at the frequency of resonance or any other frequency.

• - un fonctionnement plus stable,
• - un rattrapage de phase dont la vitesse est indépendante de l'amplitude du déphasage,
• - une plage de capture qui ne présente pas les contraintes inhérentes à une boucle à verrouillage de phase et qui est réajustée à chaque rattrapage en fréquence,
• - la carte à processeur peut donner un signal plus stable en fréquence qu'un oscillateur contrôlé par une tension,
• - un fonctionnement entièrement automatique du dispositif pour une tâche donnée,
• - un suivi intelligent de la fréquence de travail par la connaissance de modifications de cette fréquence limitée en importance et en rapidité au delà desquelles une modification n'est pas commandé,
• - une adaptabilité du dispositif à l'ensemble des utilisations des ultrasons en puissance et notamment à des applications telles l'usinage.

This process ensures in particular:

• - more stable operation,
• - phase catch-up whose speed is independent of the amplitude of the phase shift,
• - a capture range which does not have the constraints inherent in a phase locked loop and which is readjusted at each frequency catch-up,
• - the processor card can give a more stable signal in frequency than an oscillator controlled by a voltage,
• - fully automatic operation of the device for a given task,
• - intelligent monitoring of the working frequency by knowing changes in this frequency limited in size and speed beyond which a change is not ordered,
• - adaptability of the device to all the uses of power ultrasound and in particular to applications such as machining.

The processor card 11 offers a choice of programs adapted to each task and other advantages such as adjustment and control of the power supplied to the transducer.

• - au dialogue avec une machine outil,
• - aux mesures de vibrations, de profondeur d'usinage, d'usure. Au lieu d'un circuit 3 à 10 et 12 à 14 duquel serait déconnecté l'organe de commande 11 à processeur pour avec l'adaptateur 16 et les moyens d'analyse fonctionner comme une boucle _d verrouillage de phase, les moyens d'asservissement du dispositif d'alimentation comprennent un circuit 3 à 14 incluant le dit organe de commande 11 à processeur dont, pendant l'asservissement la sortie reste reliée à l'entrée de contrôle de l'adaptateur 14 et lui fournit des signaux 12 déterminant chacun une fréquence de sortie.

The system also makes it possible to envisage extensions:

• - dialogue with a machine tool,
• - vibration, machining depth, wear measurements. Instead of a circuit 3 to 10 and from 12 to 14 which is disconnected the controller 11 to processor 16 with the adapter and the analysis means as a function _of phase lock loop, the control means of the power supply device comprise a circuit 3 to 14 including the said processor control member 11, the output of which, during the servo-control, remains connected to the control input of the adapter 14 and provides it with signals 12 each determining a output frequency.

To this end, the analysis means 6 to 8 comprise a filter 6 responsible for finding the fundamental signal before addressing it by a circuit 7 by means 8 consisting of a shaping means 8 which analyzes it to extract it. the two aforementioned pieces of information which are one the phase shift D _f and the other the direction of phase shift S _f between U and I.

For high frequency stability without requiring measurement of this frequency, the control member 11 may include a synthesizer.

Rather than a controlled oscillator, the adapter 14 preferably consists of at least one power inverter 19, the switches of which, by a card 20, are controlled sequentially as a function of the synthesis of the signals 12 received at its input, which signals are preferably digital in nature.

The device also comprises means, which can be integrated into processor control devices ensuring power regulation 21 by acting either on the member 17 by which the device is connected to the sector 16 if it 1 includes a controlled rectifier or a variable autotransformer, either on inverter 19.

The circuit breaker 22 can be controlled from several points and for example from a frame controller (voltmeter, ammeter), a setpoint, the processor card of the member 11 or the fault signal.

In addition to this protection by the circuit breaker, the inverters preferably have a limiter 24 ensuring them faster personal protection.

Thus produced, the entire device is monitored and controlled by the processor card which supplies the main frequency 12, the command 21 for adjusting the power and tripping 25, the display 26 of the tasks performed and of the causes of stoppage.

Claims (10)

1. A method of supplying power to a transducer that generates both sound and ultrasonic vibrations by means of a device which comprises: - a main circuit (1) which, at its end opposite to that of the transducer, is connected to the output of an adapter (14) of the frequency of the power supply of said transducer (2), which adapter has an input main (15) and a control input, - On this main circuit (1) supplying the transducer (2), means (3) called continuous sampling, taking signals (U) and (I) representative of the current and the voltage of the supply of the transducer (2), which means (3) are connected by lines (4, 5) to means (6 to 8) which analyze them and provide information on the voltage and current of the supply to the transducer (2) and in particular on their phase shift (O _f ) and on the direction (S _f ) of this phase shift, according to which method: during the step of finding the tuning frequency of an acoustic line, the adapter (14) has its control input which, by a line (13), is connected to a control member (11) comprising a processor which sends it signals (12) each determining a different frequency value at the output of the adapter (14), which makes it possible to control a frequency sweep until the phase shift is canceled, . in order to operate the adapter (14) at a working frequency determined with reference to the previously desired tuning frequency and to take account of changes in working conditions, this adapter is controlled, this process being CHARACTERIZED in what, during the control step, instead of disconnecting the control member (11) and closing the command and control loop (3 to 10 and 12 to 14) to operate it as a phase-locked loop, the control member (11) is maintained in said control and command loop and, by means of its processor and, as a function of the information provided to this processor and in particular of information from means (6 to 8) for analyzing and supplying the phase shift (O _f ) and the direction (S _f ) of the phase shift between the current (I) and the voltage (U) of supplying the transducer (2), signals (12) for controlling the adapter are each produced determining an output frequency and by which, taking into account only the possible existence of a phase shift requiring correction, whatever 'is either the value and that of the direction of this phase shift, the progressive modification of the frequency is commanded in the direction required by the direction of phase shift until one of the two situations, namely, the disappearance of the difference of phases requiring correction, ie the arrival at the limit previously fixed for the modification of the frequencies from the starting frequency of this modification. 2. Method according to claim 1 characterized in that, to avoid too hasty modifications, at the level of the control member 11, a phase shift tolerance is allowed in which this phase shift is considered to be zero and therefore as not or not no longer ask for correction. 3. Method according to claim 1 or 2 characterized in that, depending on the application, the position and the extent of the frequency modification, the phase shift tolerance and the normal operating limits are determined by a low power analysis of the overall behavior of the load and according to the frequency at which we want to work. 4. Method according to any one of claims 1 to 3 characterized in that, during the servo-control of the device, the frequency modification is interrupted at at least one of these normal operating limits and, possibly, after at minus a new attempt, a fault signal is issued. 5. Method according to any one of claims 1 to 4 characterized in that, when searching for the reference frequency despite scanning over a certain range of frequencies, this reference frequency is not found, by influence of one of the means (6 to 8) of analysis or even of the control member (11), a fictitious phase shift (C _f ) is created between (U) and (I) then, at low power, a another scan. 6. Method according to claim 5 characterized in that, when the agreement is found, the power is increased so that the device maintains the agreement and then we remove the fictitious phase shift which shows a real phase shift, opposite direction and of the same value but that the control means detect which allows them to immediately control a catch-up. 7. Device for supplying power to a transducer generating both sound and ultrasonic vibrations according to the method of any one of claims 1 to 6, which device comprises: - a main circuit (1) which, at its end opposite to that of the transducer, is connected to the output of an adapter (14) of the frequency of the power supply of said transducer (2), which adapter has an input main (15) and a control input, - On this main circuit (1) supplying the transducer (2), means (3) called continuous sampling, taking signals (U) and (I) representative of the current and the voltage of the supply of the transducer (2), which means (3) are connected by lines (4, 5) to means (6 to 8) which analyze them and provide information on the voltage and current of the supply to the transducer (2) and in particular on their phase shift (D _f ) and on the direction (S _f ) of this phase shift, and in which device: during the step of finding the tuning frequency of an acoustic line, the adapter (14) has its control input which, by a line (13), is connected to a control member (11) comprising a processor which sends it signals (12) each determining a different frequency value at the output of the adapter (14), which makes it possible to control a frequency sweep until the phase shift is canceled, . in order to operate the adapter (14) at a working frequency determined with reference to the previously desired tuning frequency and to take account of changes in working conditions, this adapter is controlled, this device being CHARACTERIZED in that instead of a circuit (3 to 10 and 12 to 14) short-circuiting the control member (11) with processor for with the adapter (16) and the analysis means to function as a loop phase lock, a circuit (3 to 14) including said processor control member (11) the output of which remains connected to the control input of the adapter (14) and supplies it with signals (12) each determining an output frequency. 8. Device according to claim 7 characterized in that the analysis means (6 to 8) comprise a filter (6) responsible for finding the fundamental signal before addressing it by a circuit (7) by means (8) consisting a formatting means (8) which analyzes it to extract the two aforementioned information, one of which is the phase shift (D _f ) and the other the direction of phase shift (S _f ) between (U) and (I ). 9. Device according to claim 7 or 8 characterized in that, for high frequency stability without requiring measurement of this frequency, the control member 11 may include a synthesizer. 10. Device according to any one of claims 7 to 9 characterized in that it comprises means such as the processor card ensuring power regulation (21) by acting either on the member (17) by which the device is connected to the sector (16) or to the inverter (19).

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