EP0285469A1 - Method and apparatus to detect and correct the electrode position, in particular for shock wave generators with a hydraulic jack as a feeler in the focal point - Google Patents

Abstract

The invention relates to a method and to apparatus for detecting and correcting the positions of electrodes. The device comprises means for advancing the electrodes to cause them to advance and retract, preferably in an individual and independent manner, together with detector means (10) capable of being disposed at and of being retracted from the focus (F) at which an electric arc or discharge is to be provided between the electrodes (2, 4) and said detector means being suitable for detecting the presence of an electrode at said focus. Position correction then consists in successively bringing each electrode to the focus (F) into contact with said detector means which are advantageously constituted by a rod (12) of an actuator (14), prior to retracting each electrode through a predetermined distance d. The invention makes it possible to detect and correct the positions of electrodes at will, in an entirely simple manner capable of being automated.

Description

The present invention essentially relates to a method and device for detecting and correcting the position of electrodes, in particular used in devices for generating shock waves using a feeler finger brought to the focal point in particular constituted by the rod of a cylinder.

It is known from US Patent RIEBER No. 2,559,227, an apparatus for generating shock waves of high frequency, comprising a truncated ellipsoidal reflector 80 for reflecting shock waves, comprising a cavity 80A constituting a chamber for reflecting said waves shock, of the same truncated ellipsoidal shape, one of the two focal points of the ellipsoid being disposed in said chamber opposite the truncated part, said chamber being filled with a liquid for transmitting shock waves 83, for example a oil. This apparatus also comprises a device for generating shock waves, usually comprising two electrodes 12, 13, which is disposed at least partially inside the chamber 80A, with the two electrodes arranged to generate a discharge or electric arc at hearth located in the chamber opposite the truncated part, means 10, 11 being provided to selectively deliver an electrical voltage instantly to the electrodes 12, 13 thereby causing the discharge or electric arc between the electrodes and thus generating the waves shock in the liquid contained in the chamber (see Figure 3 and column 7, line 51 to column 9, line 30).

The electrodes 12 and 13 are made of highly conductive material such as copper or brass and are mounted on an insulator 26 which is pivotally supported by means of a device 11a, 11b, so as to adjust the spacing between it (see column 4, lines 42 to 53 and column 8, lines 41 to 47).

Document FR-A-2 247 195 also describes a similar device in which the liquid consists of water (page 3, lines 23-24).

When using the Rieber device or similar device, it has been observed that the discharge at the electrodes is accompanied by a metal tearing causing wear of the electrodes which is a function of the intensity of the discharge creator of the plasma between the electrodes and generator of the sudden pressure wave. This wear of the electrodes is relatively rapid, for example for electrodes with a diameter of 2 mm in Z 80 steel, the wear speed is 1 mm for 800 discharges, which constitutes a major drawback radically increasing the cost of using the device.

Document EP-124 686 has already proposed a device for advancing the electrodes 36, 38, FIG. 3, comprising a control member 48, simultaneously controlling a movement of approaching or moving the electrodes by rotation in one direction or in reverse (see page 9, line 11 to page 10, line 11).

The production of the support and advancement structure of the electrodes is relatively complicated and of high cost.

On the other hand, there has also been proposed in patent FR-A-86,01380 and again in patent FR-86 06318, devices for advancing the electrodes of a much simpler embodiment allowing greater accuracy of advancement. electrodes.

However, none of these prior devices makes it possible to detect with great precision the value of the wear of the electrodes.

Furthermore, none of these prior devices can detect and correct the position of the electrodes at any time.

The applicants recently proposed in patent application FR-87 00592, unpublished, a method and a device for detecting and correcting electrode wear, in particular used in devices for generating shock waves by lighting them with a light source.

This method and this device also make it possible to correct the distance between the electrodes (see page 8, lines 24 to 29 in particular).

This process and this device recently proposed by the applicants give complete satisfaction.

However, on an industrial scale, it is necessary to simplify the method for detecting and correcting the position of the electrodes and to provide a device the production of which is simple, inexpensive and highly reliable.

On the other hand, in the case where this prior device is permanently mounted on the ellipsoidal reflector, which is desirable, the vibrations emitted during discharges risk damaging the device. In addition, variations in light intensity between two different bulbs require recalibration of the system. Shock waves repeated thousands of times can damage the protective glass, deposits can be made on the glass and may change the setting at the detector device which is generally of the CCD type.

The present invention therefore aims to solve a new technical problem consisting in the supply of a solution making it possible to detect with great precision or accuracy the position of each of the electrodes in order to allow correction of the position of the electrodes with great precision or accuracy at all times; this solution must be of a particularly simple design, very practical to produce at low cost and of high reliability for use at an industrial level.

Another object of the present invention is to provide a method and a device for detecting and correcting the position of the electrodes which are applicable for all types of apparatus using electrodes, but preferably which are particularly suitable for use. in shock wave generation apparatus, and more preferably in shock wave generation apparatus comprising a shock wave generation device comprising a truncated ellipsoidal reflector.

These technical problems are solved for the first time by the present invention in a satisfactory manner.

Thus, according to a first aspect, the invention provides a method for detecting and correcting the position of electrodes, in particular used in devices for generating shock waves, said electrodes having to be arranged at a predetermined distance and symmetrically at a precise point in the space where the generation of a discharge or electric arc between them is provided, known as the focal point, characterized in that:
a detector means capable of detecting the presence of an electrode at said detection point is available at a predetermined point in space, called the detection point, located either at the focal point or on the path of the movement of the electrodes;
- Advancing an electrode until it comes into contact with said detector means disposed at said detection point;
- The presence of the electrode at said detection point is detected;
- The electrode is withdrawn until a positioning thereof is obtained at said predetermined distance;
- the procedure is the same with the other electrode or the other electrodes; and
- said detector means are removed from said detection point,
which allows to correct at will the position of the electrodes, which are new or worn after a certain number of discharges.

Preferably, the detection point coincides with the focal point.

According to a particular embodiment of this method, the aforementioned detector means comprises a feeler finger which is brought to the detection point so that it constitutes an obstacle to the advancement of each electrode.

According to a particularly preferred embodiment, this feeler finger consists of the rod of a jack whose axis of movement is in a plane passing through the detection point, perpendicular to the axis of advance of the electrodes, and advantageously coincides with the axis of the ellipsoidal reflector.

According to an alternative embodiment of the invention, this detector means can be constituted by a light beam or by a beam of electromagnetic waves.

According to a particularly advantageous characteristic of the invention, the presence of the electrode at the detection point is detected by detecting the variation in resistance between the detector means and the electrode grounded at least momentarily.

According to a second aspect, the present invention also provides a device for detecting and correcting the position of electrodes, in particular used in devices for generating shock waves, said electrodes having to be arranged at a predetermined distance and symmetrically to a precise point in the space where the generation of an electric discharge or arc between them is provided, known as the focal point, means for advancing the electrodes being provided for advancing and withdrawing them, preferably so individualized and independent, characterized in that it comprises a detector means mounted to be displaceable in the device so as to be disposed at a determined point in space, called the detection point, located either at the focal point or on the path of the movement advancement or withdrawal of the electrodes, and capable of detecting the presence of an electrode.

According to a preferred embodiment, this detector means comprises a feeler finger capable of being brought to the detection point so that it constitutes an obstacle to the advancement of the electrode.

According to a particular embodiment, this feeler finger is constituted by a rod of a jack whose axis of displacement is in a plane passing through the detection point, perpendicular to the advancement axis of the electrodes.

According to a particular characteristic, the detector means comprises a device for measuring the electrical resistance between the feeler finger and the electrode, and an element signaling the variation of this resistance.

According to another particular characteristic, this device comprises a means for temporarily grounding the positive electrode.

According to another characteristic of the invention, the aforementioned jack rod is in electrical contact with the jack body, which makes it easier to measure the electrical resistance between the feeler finger and the electrode.

According to another advantageous characteristic, it is possible for this device according to the invention to include a means for detecting mechanical contact between the electrodes.

It is also possible according to another particular characteristic that this device according to the invention possibly includes a position contact of the piston of the jack in the withdrawn position.

According to another particularly advantageous characteristic, provision may be made for the means for temporarily grounding the positive electrode to comprise a switch produced in the form of a double-acting contact.

For safety, it can also be provided that the switch which is connected to the positive electrode comprises a very fine wire or a fuse which is destroyed in the event of the passage of a high voltage current.

It is thus understood that it is possible with the present invention to detect with very high accuracy the position of each of the electrodes and to carry out an extremely precise correction of this position by correcting the distance between the electrode and the focal point where it is intended discharge or electric arc until it is substantially equal to a predetermined reference value.

This correction can advantageously be carried out in an extremely simple manner by giving advancement orders to electrode advancement devices as described in the prior documents of applicants FR-86 01380 and especially FR-86 06318.

Other objects, characteristics and advantages of the present invention will become apparent in the light of the explanatory description which follows, given with reference to the appended drawings representing a currently preferred embodiment of the device for detecting and correcting the position of 'electrodes according to the invention, given simply by way of illustration and which therefore cannot in any way limit the scope of the invention.

• - la figure 1 représente le mode de réalisation actuellement préféré d'un dispositif de détection et de correction de la position des électrodes selon la présente invention, utilisé, dans l'exemple représenté, dans un appareil de génération d'ondes de choc comprenant un reflecteur ellipsoïdal tronqué du type décrit dans le brevet US RIEBER, selon une coupe longitudinale passant par le point focal, dans le plan des électrodes ;
• - les figures 2a et 2b représentent une vue de détail agrandie montrant le moyen détecteur ici de préférence au point focal avec l'électrode en position initiale (figure 2a), en position de contact (2b) et en position de retrait selon une distance prédéterminée, en trait fantôme (figure 2b) ;
• - la figure 3 représente une vue de détail agrandie du corps du vérin constituant un moyen détecteur particulier ; et
• - la figure 4 représente le schéma électrique pour la détection de la position des électrodes par mesure de la résistance électrique entre le moyen détecteur et les électrodes.

In the drawings:

• - Figure 1 shows the currently preferred embodiment of a device for detecting and correcting the position of the electrodes according to the present invention, used, in the example shown, in an apparatus for generating shock waves comprising a truncated ellipsoidal reflector of the type described in US patent RIEBER, in a longitudinal section passing through the focal point, in the plane of the electrodes;
• - Figures 2a and 2b show an enlarged detail view showing the detector means here preferably at the focal point with the electrode in the initial position (Figure 2a), in the contact position (2b) and in the withdrawal position according to a predetermined distance , in phantom line (Figure 2b);
• - Figure 3 shows an enlarged detail view of the cylinder body constituting a particular detector means; and
• - Figure 4 shows the electrical diagram for detecting the position of the electrodes by measuring the electrical resistance between the detector means and the electrodes.

Referring to the figures, in particular Figures 1 to 3, there is shown a currently preferred embodiment of a device for detecting and correcting the position of the electrodes 2, 4 used, in the example shown, in a shock wave generation apparatus comprising a truncated ellipsoidal reflector 6 of the type described in US Patent RIEBER 2,559,227.

For correct operation, the electrodes 2, 4 must be placed at a predetermined distance d and symmetrically at a precise point F in the space where the generation of a discharge or electric arc between the electrodes, usually called focal point, is provided.

According to the present invention, the device for detecting and correcting the position of the electrodes 2,4 is characterized in that it comprises a detector means represented by the general reference number 10, mounted movable in the device to be arranged at a predetermined point in space, called the detection point, located either at the focal point or on the path of the advancing or withdrawing movement of the electrodes, and capable of detecting the presence of an electrode there. Preferably, as shown, the detection point coincides with the focal point (F).

According to a particular embodiment, this detector means 10 comprises a feeler finger 12 capable of being brought to the focal point F so that it constitutes an obstacle to the advancement of the electrode 2 or 4, as clearly visible in the figure. 2.

According to a currently preferred embodiment, this feeler finger 12 is constituted by the rod of a jack 14 whose axis of movement XX lies in a plane passing through the focal point, perpendicular to the axis of advance of the electrodes YY.

According to a particular embodiment, this detector means 10 comprises a device 16 for measuring the electrical resistance between the feeler finger 12 and the electrode (2 or 4) by the presence of suitable electrical conductors 18, 20, 22. This device measuring device 16 can incorporate an element signaling the variation in resistance and can also transmit information to a control means 30, which can include a computer and transmit commands to means for advancing the electrodes 2, 4 which are provided for advancing and withdrawing the electrodes preferably so that individualized and independent, this device for advancing the electrodes preferably being as described in the applicants' prior documents FR-86 01380 or especially FR-86 06318.

It is thus understood that the detector means 10 can also comprise means for detecting the contact between the electrodes. Here, since each electrode 2, 4 is connected to the measuring device 16 by a conductor 20, 22, it suffices to measure the electrical resistance between the electrodes by these conductors 20, 22 to enable the contact between the electrodes to be detected, as will be explained later in the explanations of the operation of said device according to the invention.

Advantageously, there is provided according to the invention a means 32 for momentary grounding of the positive electrode, for example here the electrode 2. For the negative electrode, this means is not usually necessary since the negative electrode is permanently grounded. Preferably, this means 32 for momentary grounding of the positive electrode is constituted by a switch 34, advantageously double effect for an off-circuit position and a closed position of the circuit for grounding. The off position is shown in Figure 4.

By way of security, it can be provided that this means (32) for momentary grounding of the positive electrode is produced by a contact operating as a fuse which is destroyed in the event of the passage of a high voltage current. This can be obtained by placing a very thin wire 36 between the switch 34 and the positive electrode, here the electrode 2. It is naturally also possible to provide a fuse interposed on this conductor 36.

Usually the cylinder rods are isolated from the cylinder body.

Therefore, to ensure electrical contact between the rod 12 and the body 13 of the jack 14, an electrical contact 40 can be provided, for example fixed on the body 13 of the jack 14 and coming to take a sliding contact against the rod 12. It can be with a simple metal strip.

A variant of bringing the rod of the jack 12 into electrical contact with the body 13 of the jack 14, each being naturally electrically conductive, is to provide a conductive silicone gasket 42 around the piston 12a secured to the rod 12.

It is also possible to provide a contact 44 for the position of the piston 12a of the jack 14 in the withdrawn position, therefore at the rear or at the base of the body 13 of the jack 14, as shown in FIG. 3. We can understand from the above, that this device according to the invention allows the implementation of the method for detecting and correcting the position of the electrodes previously described.

Indeed :
At the start, the rod 12 of the actuator 14 is arranged at the focal point F which constitutes an integral part of the detector means 10 by acting on the actuator 14 which may for example be a pneumatic actuator. Usually, the electrodes 2, 4 will be located on either side of the rod 12, as shown in FIG. 2.

Then, an electrode is advanced, for example here the electrode 4, until it comes into contact with the rod 12 forming an integral part of the detector means 10, disposed at the focal point F.

We then detect the presence of the electrode, here 4, at the focal point F, that is to say in fact in contact with the rod 12. To do this, we measure the resistance between the rod 12 and the electrode , here 4, that is to say in fact the resistance from the measuring device 16 in the conductive electrical circuit 18-cylinder body 13-cylinder rod 12-electrode 4-conductor 22.

When the electrode, here 4, comes into contact with the rod 12, the resistance drops suddenly.

Having detected this sudden drop in resistance, we then proceed to withdraw the electrode, here 4, from the predetermined distance d for a correct position of the electrode 4 relative to the focus F.

The same is done with the other electrode or the other electrodes.

Here, the electrode 2 being the positive electrode, to carry out these operations, the positive electrode is firstly grounded by closing the switch 34. The resistance in the conductive circuit 20-electrode is then detected 2-rod 12-body 13 of actuating cylinder 18 and the fall in this resistance is detected in the same way during contact of the electrode 2 with the rod 12 before removing this electrode 2 from the same predetermined distance (d).

The resistance measuring devices 16 are well known to those skilled in the art and need not be explained here. It can be a simple ohmmeter.

Naturally, after the measurement, the switch 34 is again put in the open position, off circuit, shown in FIG. 4.

It is understood that with the method and the device according to the invention it is possible to detect and correct the position of the electrodes, in a perfect manner.

It will be observed that this method and this device lend themselves well to complete automation because when there is no contact between the electrode which is controlled and the rod 12 of the detector means 10, it is possible to give a numerical value 0 and when there is contact and the resistance drops suddenly, the numerical value 1 can be given, which allows computer processing of these data.

Furthermore, if it is assumed that the jack 14 breaks down, and that the rod 12 is not advanced, then during the advancement of an electrode, the latter will end up going to touch the other electrode . This defect could be detected by detecting the contact between the two electrodes, again thanks to the measuring device 16 by detecting the resistance by means of the conductors 20 and 22, connected to the electrodes 2 and 4.

In the case where the jack does not return to its initial withdrawal position, this defect can be detected by the absence of contact between the piston 12a of the rod 12 and the contact 44. It is understood that this security is imperative and must be reliable because it is essential to remove the rod 12 from the focal point F for correct generation of the shock waves at the focal point F.

On the other hand, it is also essential that the means 32 for momentary grounding of the positive electrode, here 2, is in the open position, off, so as not to divert the electric current supplying the positive electrode 2, from the capacitor 50, with the advantageous presence of a discharge means 52 of the "spark gap" type well known to those skilled in the art. For this extreme case, provision is made, as a safety measure, for the conductive wire 36 between the positive electrode 2 and the grounding means 32 to be very fine and to be destroyed in the event of the passage of a voltage current. high, or the presence of a fuse playing the same role.

Finally, in the case where originally, the electrodes are too off center and the rod 12 cannot advance to the focal point F, where there is already an electrode, then a contact is detected and there is instead of rolling back the electrode. We then find ourselves in the classic case shown in Figure 2.

It is thus understood that the invention includes all the means constituting technical equivalents of the means described and shown as well as their various combinations.

Claims (16)

1. Method for detecting and correcting the position of electrodes (2,4), in particular used in devices for generating shock waves, said electrodes (2,4) having to be arranged at a predetermined distance (d) and symmetrically at a precise point (F) in the space where the generation of an electric discharge or arc between the electrodes is provided, called the focal point, characterized in that:
- there is at a predetermined point in space, said detection point, located either at the focal point (F) or on the path of the movement of the electrodes, a detector means capable of detecting the presence of an electrode (2 or 4) at said detection point;
- Advancing an electrode (2 or 4) until it comes into contact with said detector means disposed at said detection point;
- Detecting the presence of the electrode (2 or 4) at said detection point;
- the electrode (2 or 4) is removed until a positioning thereof is obtained at said predetermined distance (d);
- the procedure is the same with the other electrode or the other electrodes;
- removing said detector means (10) from said detection point;
which allows to correct at will the position of the electrodes, whether new or used after a certain number of discharges. 2. Method according to claim 1, characterized in that the detector means (10) comprises a feeler finger (12) which is brought to the detection point, preferably the focal point (F), so that it constitutes a obstacle to the advancement of each electrode (2 or 4). 3. Method according to claim 2, characterized in that the feeler finger (2) consists of the rod of a jack (14), the axis of movement of which lies in a plane passing through the detection point (F), perpendicular to the advancement axis (YY) electrodes (2,4). 4. Method according to claim 1, characterized in that the above-mentioned detector means comprises a light beam or a beam of electromagnetic waves passing through the detection point (F) perpendicular to the axis of advance of the electrodes. 5. Method according to one of claims 1 to 3, characterized in that the presence of the electrode (2 or 4) at the detection point (F) is detected by detecting the variation in resistance between the detector means ( 10) and the electrode (2 or 4) grounded at least momentarily. 6. Device for detecting and correcting the position of electrodes, in particular used in devices for generating shock waves, said electrodes (2 or 4) having to be arranged at a predetermined distance (d), symmetrically at a point (F) precise of the space where the generation of an electric discharge or arc is provided between said electrodes, means (30) for advancing the electrodes being provided for advancing and withdrawing them, preferably individually and independently, characterized in that it comprises a detector means (10) mounted displaceable in said device so as to be disposed at a predetermined point in space, called detection point, located either at the focal point, or on the path of the advancing or withdrawing movement of the electrodes and capable of detecting the presence of an electrode (2 or 4). 7. Device according to claim 6, characterized in that the above-mentioned detector means (10) comprises a feeler finger (12) capable of being brought to the detection point (F) so that it constitutes an obstacle to the advancement of the electrode (2 or 4). 8. Device according to claim 6 or 7, characterized in that the feeler finger (12) consists of a rod of a jack (14) whose axis of movement is in a plane passing through the detection point (F), perpendicular to the advancement axis (YY) of the electrodes. 9. Device according to one of claims 6 to 8, characterized in that the aforementioned detector means (10) comprises a device (16) for measuring the electrical resistance between the feeler finger (12) and the electrode (2 or 4); and an element indicating the variation of this resistance. 10. Device according to one of claims 6 to 9, characterized in that it comprises a means (32) for momentary grounding of the positive electrode (2). 11. Device according to claim 10, characterized in that the means (32) for momentary grounding of the positive electrode is a switch (34), advantageously with double effects. 12. Device according to claim 11, characterized in that the switch (34) is connected to the electrode (2) by a very fine wire or a fuse which is destroyed in the event of the passage of a high voltage current 13. Device according to one of claims 6 to 12, characterized in that it comprises means for detecting the mechanical contact between the electrodes (2, 4). 14. Device according to one of claims 8 to 13, characterized in that it comprises a contact (44) for positioning a piston (12a) of the jack (14) in the withdrawn or retracted position. 15. Device according to one of claims 8 to 14, characterized in that the rod (12) of the jack (14) is in electrical contact with the body (13) of the jack (14). 16. A shock wave generating apparatus characterized in that it is equipped with at least one device as defined in any one of claims 6 to 15.

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