FR2607651A1 - Supply circuit for ultrasonic tartar removal instrument - Google Patents

Abstract

The supply circuit has a control device (7) supplying voltage pulses to the energising coil (1) of a magnetostrictive transducer at a pulse rate selected to independence on the transducer resonance frequency. At the beginning of the operating cycle the energising pulses are supplied at different rates, with the current monitored to detect the pulse rate corresponding to the resonance of the magnetostrictive transducer, with subsequent operation of the energising coil (1) at this pulse rate. Pref. the variation in the pulse rate is effected in small increments.

Description

DEVICE FOR SUPPLYING AN ULTRASONIC GENERATOR,
IN PARTICULAR FOR A TEETH SCALING APPARATUS
The present invention relates to a device for supplying an ultrasound generator, in particular for a device for scaling teeth, comprising a magnetostriction transducer which has an excitation coil, and a control device which produces the supply of this excitation coil into excitation pulses, the rate of which, ie the frequency, can be adjusted to the resonant frequency of the transducer
magnetostriction tor.

DE-OS 29-29 646 already discloses an ultrasonic generator which comprises a magnetostriction transducer and an oscillator which supplies a signal producing periodic switching on and off of the transducer and the frequency of which can be adjusted to the resonant frequency of the transducer by an adjustment voltage. For the production of this adjustment voltage, an integrator is used which is charged and / or discharged at the rate of switching off and on of the transducer and which produces the adjustment voltage from the sum of a fixed voltage and of the return voltage which appears on the transducer or on its winding when the transducer is switched off and in periodic circuit. These means make it possible, when the resonance frequency of the magnetostriction transducer is known, to operate it
at this frequency. However, when said resonant frequency varies, for example due to aging, the known ultrasound generator no longer functions as desired.

 The object of the present invention is to improve the device indicated above so that, by relatively simple means, the magnetostriction transducer always operates at its resonant frequency.

 The invention achieves this object with a device of the type indicated at the start thanks to the fact that at the start of each start-up are first sent to the excitation coil of the magnetostriction transducer of excitation pulses at different rates, or excitation frequencies; that the current passing each time through the excitation coil is determined; that the rate of the excitation pulses for which the magnetostriction transducer is in resonance is determined; and that thereafter, the emission of the excitation pulses is continued at this determined rate.

 The invention provides the advantage that a relatively small total expenditure of material is sufficient to be able to always operate the magnetostriction transducer at its resonant frequency, that is to say under optimal conditions. For this, according to the invention, at each start-up, first, in a calibration or alignment phase is determined the current resonance frequency of the magnetostriction transducer, and in the following operating phase, the device operates the magnetostriction transducer at this resonant frequency. This means that in the present invention there is no manual or fixed adjustment of the frequency at which the magnetostriction transducer should operate. In addition, the blade packages ordinarily used for a magnetostriction transducer of the indicated type can be changed and replaced with new packages without this being accompanied by a complicated new adjustment of the transducer. The ultrasonic generator, and in particular the teeth scaling device in which the magnetostriction transducer is used, provide in all cases the maximum power.

In addition, a drift due to temperature influences plays absolutely no role.

 It is also advantageous that if the magnetostriction transducer is used in a tooth scaling device, packs of blades from different transducers from different treatment units can be changed and the transducer used nevertheless works in all cases. at maximum power.

 According to an advantageous form of the invention, an indication is given in the case where it is found that the resonance frequency of the magnetostriction transducer is outside a fixed range of pulse rates. It is thus relatively easy to obtain an indication in the case where, for example in the case of a dental scaling appliance using the magnetostriction transducer, the treatment tip of this appliance is not in place or the transducer blade package is defective.

 Advantageously, the excitation coil of the magnetostriction transducer is sent pulses at a fixed number of rates, in successively smaller and smaller rate ranges. This results in the advantage that the resonance frequency of the magnetostriction transducer can be determined with great accuracy in a relatively simple manner.

 Preferably, for the determination of the current flowing each time in the excitation coil, there is provided a resistor in series with this coil and to which is connected a voltage evaluation device which sends to the control device a corresponding digital signal. to the voltage drop across the resistor. This results in the advantage of a relatively simple possibility of determining the current flowing each time in the excitation coil and obtaining a determining control quantity for the control device.

 The voltage operating device advantageously comprises a voltage-frequency converter connected to the resistor which sends pulses at a rate corresponding to the voltage drop in the resistor to a counter which counts the pulses occurring during a fixed period of time and whose the status at the end of this period of time is taken up in the control device. This has the advantage of providing a voltage operating device that can be performed relatively simply.

 Another embodiment of the voltage exploitation device comprises a DC voltage suppression device connected to the resistor which suppresses the DC components of the voltage drop in this resistor and downstream of which is mounted a low-pass filter downstream which is mounted an analog-digital converter which is connected on the output side to the control device. This also results in a relatively low expenditure of material for the production of the voltage operating device.

 In the embodiment of the invention considered last, it is advantageous that the device for removing DC voltage comprises an amplifier. this brings the advantage that the voltage to be exploited, free of the DC components, has a sufficient level for exploitation.

 Preferably, the control device is connected on the output side to another counter which is actuated so as to emit on the output side, pulses at a rate determined by the value of the digital signal for the excitation of the excitation coil of the magnetostriction transducer. This has the advantage of providing a control device which can be implemented relatively simply. This control device only needs to use for the control of said other counter the digital signals which are sent to it from the input side.

 In the embodiment of the invention which has just been considered, the control device is also advantageously connected to a pulse control device which fixes the efficiency of the pulses emitted by said other counter. This has the advantage of making it possible to be satisfied with a particularly simple command of the other counter, the pulses of which it emits are made active by the pulse control device.

 Downstream of the pulse control device is preferably mounted a pulse width control device which makes it possible to adjust the width of the pulses emitted by the pulse control device. By this means, it is particularly simple to control the intensity of the magnetostriction transducer.

 The control device is advantageously connected to an adjustment member which sends an adjustment voltage to this device by which the intensity of the pulses sent to the excitation coil of the magnetostriction transducer can be adjusted. This means preferably serves to adjust the width of the pulses emitted by the pulse control device by means of the pulse width control device.

 Finally, it is advantageous that the excitation coil of the magnetostriction transducer is located in the collector circuit of a transistor in the emitter circuit of which the resistance is located and at the base of which the excitation pulses are sent. This in fact gives a particularly simple possibility of supplying the excitation coil and determining the current flowing therein.

Examples of embodiment of the invention are explained in detail below with the aid of the drawings, in which
FIG. 1 shows in the form of a functional diagram an embodiment of the device of the invention,
FIG. 2 shows in the form of a functional diagram a voltage exploitation device which can be used in place of the voltage exploitation device used in the device of FIG. 1,
FIGS. 3a) to 3d) show diagrams of signals or pulses to which reference is made in connection with the explanation of the device represented in FIG. 1, and
FIGS. 4a) to 4d) show diagrams of signals or pulses to which reference is made in connection with the explanation of the device represented in FIG. 2.

 In FIG. 1, there is shown in the form of a functional diagram a device for supplying an ultrasound generator, a generator which is intended to be used in particular for a device for scaling teeth and which comprises a magnetostriction transducer comprising an excitation coil 1. This coil 1 is located in the collector circuit of a transistor 2 which is in the case shown a PNP transistor. In the emitter circuit of this transistor 2, a resistor 3 is provided, which serves here as a measurement resistor. The end of this resistor 3 opposite the emitter of transistor 2 is earthed or at ground potential. The end of the excitation coil 1 opposite to the collector of transistor 2 is connected to a circuit point where a voltage + U of for example 12 V can be applied.

 At point 4 of the circuit, between the emitter of transistor 2 and the resistor 3, is connected a voltage operating device which, as shown in Figure 1, includes a voltage-frequency converter (U / f converter) 5 and a counter 6 placed downstream of this converter 5. The function of this voltage evaluation device is to determine the voltage drop in the resistor 3 and to send a digital signal corresponding to this voltage drop to a control device 7 . For this, the voltage-frequency converter 5 sends, on the output side, pulses at a rate, that is to say a frequency, representative of the voltage drop in the resistor 3, on the counting input T of the counter 6 , which counts these pulses. The counter 6 is released separately at an input G from the control device 7 and receives at an input CLR reset signals which put it in a determined initial state, in particular at zero. .

The counter 6 can thus count the pulses coming from the voltage-frequency converter 5 which appear during a determined period of time. Its state at the end of this period of time is then taken up in the control device 7. This state, which corresponds to N bits, represents the mentioned digital signal which is sent by the voltage evaluation circuit, that is to say - say by the counter 6, to the control device 7.

 The control device 7 is connected on the output side to another counter 8 which it operates so that it supplies pulses on the output side at a rate determined, from the output of the counter 6, by the value of the digital signal. These pulses are, as shown in Figure 1, sent to the base of transistor 2; they thus serve to excite the excitation coil 1 of the magnetostriction transducer.

 The control device 7 is further connected to a pulse control device 9 which transmits, for a fixed period of time T, pulses of determined duration which, in association with the excitation pulses emitted by the other counter 8, serve to fix the duration during which the excitation pulses emitted in total by the other counter 8 act, that is to say lead to an excitation of the excitation coil 1. Preferably, downstream of the control device d pulses 9 is mounted a pulse width control device 10 which makes it possible to adjust the width of the pulses emitted by the pulse control device, as indicated in broken lines in FIG. 1. The adjustment in the control device pulse width 10 of the width of the pulses emitted by the pulse control device 9 as well as the fixing of the pulses to be transmitted by the pulse control device 9 as well as their succession are produced ts by the control device 7.

 As shown in Figure 1, the control device 7 is connected to an adjustment member 11, which may for example be a potentiometer, which is adjustable by means of a pedal and emits a voltage corresponding to its adjustment and for example between 0 and 10 V.

 Finally, to the control device 7 is also connected an indicator device 13 which can be formed from an incandescent lamp or from a light-emitting diode and can be used to indicate a fault as will be seen below.

 In FIG. 2 is shown another embodiment of the voltage operating device described with reference to FIG. 1. The voltage operating device represented in FIG. 2 comprises on the input side an amplifier 20 downstream, on the side output, of which there is a DC voltage suppression device 21 which is followed on the output side of a low-pass filter 22. Downstream of this low-pass filter 22 is an analog-digital converter 23.

The voltage operating device shown in FIG. 2 can be placed between the circuit point 4 and the control device 7 in place of the voltage operating device shown in FIG. 1. It should be noted here that in the device shown in FIG. 2, the amplifier 20 is not necessary if a voltage to be exploited of relatively large amplitude is sent to this voltage evaluation device.

 The operation of the device of the invention is explained below using the pulse or signal diagrams of FIGS. 3 and 4. First, the operation of the device shown in FIG. 1 will be explained in detail.

 At the start of each start-up of the device of the invention, firstly, in a calibration or alignment phase, the resonance frequency of the magnetostriction transducer for which the coil is to be supplied is determined. excitation 1. For this, excitation pulses are sent at different rates.

For this, the control device 7 sends corresponding counting or adjustment signals to the counter 8 and to the pulse control device 9. The pulse control device 9 emits successive pulses at an interval T for the duration of each of which, at the circuit point 12 of FIG. 1, the pulses emitted by the counter 8 act as excitation pulses of the excitation coil 1. It should be noted that the period of time T and the duration d of the impulses are here kept constant. It is however perfectly possible to vary the time T and the duration d.

 The excitation pulses at different rates sent to the excitation coil 1 at the start of each start-up of the device of the invention mean that, apart from the case of resonance of the magnetostriction transducer comprising said coil, it appears at the terminals of the resistor 3 of FIG. 1 first of the voltages U3 having the shape as a function of time t represented in FIG. 3 jazz The shape as a function of time t of the voltage of the pulses which appear at the circuit point 12 of Figure 1 is shown in Figure 3b) by U12.

When the excitation pulses appear at a rate for which the magnetostriction transducer is in resonance, there appears, at the terminals of the resistor 3 of FIG. 1, a voltage U3r whose shape is indicated in FIG. 3c). The pace of tension
U12r of the corresponding excitation pulses which appear at the circuit point 12 in FIG. 1 is indicated in FIG. 3d).

 A comparison of the voltages at the terminals of the resistor 3 represented in FIGS. 3a) and 3c) shows that in the case of the resonance of the magnetostriction transducer, the total voltage drop in the resistor 3 is greater than in the case of the non-resonance. A precise examination of the conditions shows that the voltage drop in the resistor 3 is maximum when the magnetostriction transducer is in resonance.

 Regarding the different amplitudes of the pulses represented in FIGS. 3b) and 3d), it should be noted that these can also be used for controlling the intensity and thus the amplitude of the magnetostriction transducer.

 The alignment or calibration phase of the device of the invention described with reference to FIG. 3b) leads to the determination of the resonant frequency of the magnetostriction transducer from the maximum voltage drop in the resistor 3 of the Figure 1 in the case of the resonance of the transducer.

In the following operating phase, the operation continues at this resonance frequency, that is to say that to the excitation coil 1 of the magnetostriction transducer are sent excitation pulses at the rate for which the resonance of the transducer was found.

 The above-mentioned resonance situation is determined by determining the maximum state of the counter 6 in different counting cycles.

For this, as already mentioned, a fixed frequency domain is traversed by fixed steps. Thus, in a first calibration, for example, the frequency or pulse rate range from 17 to 19 kHz is traversed in steps of 200 Hz. For duration d, pulses at 10 rates are then counted and stored in the counter 6. For an even more precise determination of the resonant frequency of the magnetostriction transducer, in a second calibration, one works in a smaller frequency domain, the maximum of the previous measurement being in the middle thereof. In this second calibration, for example, the frequency domain or pulse rate of 17.5 to 18 kHz is traversed in steps of 50 Hz.

(10 pulse rates). In a possible additional calibration, for example, the range from 17.7 to 17.9 kHz is traversed in 20 Hz steps (10 pulse rates). The resonance value thus finally determined is then used in the operating phase considered. This operating phase automatically follows the alignment or calibration phase explained above.

 It can be seen from the preceding explanations that during the alignment or calibration phase, the resonance frequency of the magnetostriction transducer is determined first in a coarse measurement and then in one or more fine measurements, and that thereafter to the excitation coil of the magnetostriction transducer are sent excitation pulses at a rate for which the transducer is in resonance. Thus, at the start of each start-up of the apparatus which comprises the magnetostriction transducer, a small number of measurement cycles is sufficient to then be able to operate the transducer at its optimum frequency.

If, however, it is not possible to resonate the transducer within a fixed frequency range, the control device 7 can in this case provide an indication by means of the indicator device 13 which is there. connected.

 If, in the device represented in FIG. 1, instead of the voltage operating device provided therein (which includes the voltage-frequency converter 5 and the counter 6), the voltage operating device shown in Figure 2, we have conditions similar to the conditions explained above using Figure 3, and we see in Figure 4. In Figure 4a) is shown the pace.

U24 of the pulse-shaped voltages which appear at the circuit point 24 of FIG. 2 in the case where the magnetostriction transducer is not in resonance.

These pulse-shaped voltages correspond to the voltages which appear at the terminals of the resistor 3 in FIG. 1, but are of greater amplitude and free of DC components.

 In Figure 4b) is shown the DC output voltage U25 which appears at the circuit point 25 of Figure 2 under the conditions shown in Figure 4a).

 FIG. 4c) shows the shape of the amplitude U24r of the voltage at the circuit point 24 of FIG. 2 in the case of the resonance of the magnetostriction transducer.

 In FIG. 4d) finally, the shape of the voltage U25r is shown at the circuit point 25 in FIG. 2 under the conditions corresponding to FIG. 4c).

 A comparison of FIGS. 4a) and 4c) clearly shows that at the resonance of the magnetostriction transducer, the voltage in the form of pulses which appears at the circuit point 24 of FIG. 2 has a markedly different shape than in the case of the non-resonance. A comparison of the voltage patterns shown in FIGS. 4b) and 4d) shows that at the resonance of the magnetostriction transducer, the DC voltage which appears at the circuit point 25 is clearly greater than in the case of non-resonance.

 It should also be noted, with regard to the conditions represented in FIG. 4, that, during the duration of the voltage changes in the form of pulses represented in FIGS. 4a) and 4c), pulses 2 are sent in FIG. 1 at different rates as has been explained with reference to FIG. 3. The analog-digital converter 23 provided in the device of FIG. 2 can thus, as a result of voltages of different amplitudes which are sent to it on the input side, transmit on the side digital signals output corresponding to the different states of the counter 6 provided in the device of FIG. 1.

 The operation of the invention has been explained in the foregoing assuming that the control device 7 in FIG. 1 uses the digital signals sent to it by the voltage exploitation device for direct control of the counter. 8 and of the pulse control device 9. The adjusting member 11 indicated in FIG. 1 then makes it possible to modify the efficiency of the excitation pulses thus to be sent to the excitation coil 1 of the magnetostriction transducer, as this has been mentioned for example in connection with the pulse width control device 10 of FIG. 1 or in relation to the pulses represented in FIG. 3d). It is however also also possible to jointly use the explained means for controlling the intensity of the excitation pulses to be sent to the excitation coil 1 of the magnetostriction transducer.

Claims (12)

 1. Device for supplying an ultrasonic generator, in particular for a device for scaling teeth, comprising a magnetostriction transducer which comprises an excitation coil (1), and a control device (7) which produces supplying the excitation coil (1) with excitation pulses, the rate or frequency of which can be adjusted to the resonant frequency of the magnetostriction transducer, characterized in that at the start of each start-up are first sent to the excitation coil (1) of the magnetostriction transducer, excitation pulses at different rates; that the current flowing in the excitation coil (1) each time is determined; that the rate of the excitation pulses for which the magnetostriction transducer is in resonance is determined; and that thereafter, the emission of the excitation pulses is continued at this determined rate.  2. Device according to claim 1, characterized in that at the excitation coil (1) of the magnetostriction transducer are sent pulses at a fixed number of rates in successive smaller and smaller rate ranges.  3. Device according to one of claims 1 and 2, characterized in that, for the determination of the current passing each time in the excitation coil (1), a resistance (3) is provided in series with this coil (1 ) and to which is connected a voltage evaluation device (5, 6; 20, 21, 22, 23) which sends to the control device (7) a digital signal corresponding to the voltage drop in the resistor (3) .  4. Device according to claim 3, characterized in that the voltage operating device comprises a voltage-frequency converter (5) connected to the resistor (3) which sends pulses at a rate corresponding to the voltage drop in the resistance (3) to a counter (6) which counts the pulses appearing during a fixed period of time (d) and whose state at the end of this period of time is taken up in the control device (7).  5. Device according to claim 3, characterized in that the voltage operating device comprises a DC voltage suppression device (21) connected to the resistor (3) which suppresses the DC components of the voltage drop in this resistor (3), and that downstream of this DC voltage suppression device (21) is placed a low-pass filter (22) and downstream of this is placed an analog-digital converter (23) which is connected on the outlet side to the control device (7).  6. Device according to claim 5, characterized in that the DC voltage suppression device comprises an amplifier (20).  7. Device according to one of claims 1 to 6, characterized in that the control device (7) is connected on the output side to another counter (8) which is actuated so as to transmit pulses on the output side to a rate determined by the value of the digital signal for the excitation of the excitation coil (1) of the magnetostriction transducer.  8. Device according to claim 7, characterized in that to the control device (7) is further connected a pulse control device (9) which fixes the effectiveness of the pulses emitted by said other counter (8).  9. Device according to claim 8, characterized in that downstream of the pulse control device (9) is placed a pulse width control device (10) which makes it possible to adjust the width of the pulses emitted by the pulse control device (9).  10. Device according to one of claims 1 to 9, characterized in that to the control device (7) is connected an adjustment member (11) which sends to this device (7) an adjustment voltage by which the intensity of the pulses sent to the excitation coil (1) of the magnetostriction transducer can be adjusted.  11. Device according to one of claims 3 to 10, characterized in that the excitation coil (1) of the magnetostriction transducer is located in the collector circuit of a transistor (2) in the emitter circuit of which is the resistor (3) and at the base of which the excitation pulses are sent.  12. Device according to one of claims 1 to 11, characterized in that an indication is given in the case where it is found that the resonance frequency of the magnetostriction transducer is outside a fixed range of rate of impulses.