EP1317031B1 - Manipulator for wire conductors, apparatus and inserting method comprising such a manipulator - Google Patents

Description

The present invention relates to a wire handling apparatus, to a method for inserting an end of a portion of a wireline into a socket of a connector, and to an insertion machine incorporating such a handling apparatus.

The technical field of the invention is that of the production of automatic machines for the production of cable strands.

The patent US 5,615,478 describes various types of electrical wire section handling pliers, their integration into wire-bundle preparation machines, and a method and apparatus for inserting wire ends into receptacles of connectors or similar electrical components.

From the publication FR 2 669 156 A1 a device for automatically inserting a cable lug into a socket is known. The wire with the cable lug is gradually introduced in several phases in the socket. First, the wire with the cable lug is bent by a certain angle by means of a guide. Then the cable lug by a forward movement against the edge pressed the socket. Subsequently, the cable lug is moved sideways until one side of the cable lug bears against the lateral edge of the bushing. Then the cable lug is pushed into the socket.

The object of the present invention is to propose such improved tongs, insertion methods and devices.

An object of the invention is to propose a reliable and inexpensive system that systematically controls the quality of insertion of a wire into a socket of a component, regardless of whether the wire has previously been connected by crimping or the like to a cable lug.

In the document EP 902 509 For example, there has been proposed a system for controlling the quality of crimping a lug at the end of a section of electrical wire using a force sensor which contains two discs of a piezoelectric ceramic; the force sensor is mounted on a crimping press between a support for a crimping tool and a carriage which is driven for alternating translational movement by an eccentric rotary motor, so that the sensor is sensitive to the crimping force exerted by the press on the crimping shoe to be crimped is.

The use of this type of force sensor generally requires calibration to compensate for the detected precision and linearity errors, which complicates the practical use of these sensors; this disadvantage is particularly significant in the case where it is desired to measure the force for insertion of a wire end into a socket, since an insertion handling device often operates with very small series of completely equal successive insertion operations; it is even common that an insertion-handling device successively requires the insertion of ends provided with different lugs for which the different insertion forces must be controlled; In comparison, a crimping press generally performs large series with completely identical crimping processes.

The piezoelectric ceramic sensors whose sensitivity is on the order of 100 or several hundred pico-coulombs / newton when provided for measuring a crimp force, which is generally greater than 2000 Newton, are for the measurement of an insertion force - is generally in a range of 1 to 100 Newton, poorly suited.

In addition, a dynamic force sensor of this type is inertial forces because of its low response time sensitive resulting from detected accelerations of movable organs of the crimping press with which it is associated; Now, the search for high duty cycles causes large accelerations and, consequently, large inertial forces that interfere with the measurement to be performed.

In addition, the signals provided by the piezoelectric sensors are often disturbed when the organs - such as connectors and wire leads - are subjected to movement to connect the sensor to an electronic device for processing sensor-supplied signal, such as a charge amplifier; namely, these movements can generate parasitic electrical charges, in particular by the triboelectric effect; therefore, it is difficult to use such sensors which are "embedded" (mounted) in moving parts of the machine; this point becomes particularly important as soon as the results of force measurement are used as a criterion for assessing the quality of the relevant (introductory) operation.

After numerous infertile experiments, it is surprisingly possible, considering certain conditions according to the invention, to use this type of sensor for measuring the insertion force for a wire end in a socket of a connector with a sufficient measuring reliability, so that the results of these measurements for the control of the introduction quality can be used.

According to one aspect of the invention, there is provided a wire handling apparatus comprising a body and a wire-holding member movably mounted on the body, the wire-holding member having a sensor sensitive to a force exerted by that member.

In particular, the invention proposes a pair of pliers for inserting one end of a wireline into a socket of a connector which includes a body and an arm provided with a wire jaw and movably mounted with respect to the body, the arm being a piezoelectric Has sensor for the measurement of an insertion force.

By virtue of the fact that the sensor is integrated into the movable member of the forceps (the handling device) and thus are very close to the jaws for gripping the wire section, the sensitivity of the sensor to the force required to insert the end into a socket is increased while at the same time reducing the sensitivity of the sensor to parasitic forces resulting, in particular, from inertial effects and mechanisms for displacing and opening the forceps (handling device).

Preferably, the sensor includes two rings - or thin pieces in plate or disc form - of a polarized ceramic material which are identical, juxtaposed and pressure biased between two parallel faces of two parts belonging to the arm or manipulator; this allows the realization of a simple and compact sensor in which each disc is sensitive to compressive forces of the ring as well as to axial expansion forces of the disc; thus allowing the measurement of an insertion force (conventionally positive) and a force in the opposite direction (and of opposite sign); this allows the measurement of a tensile force exerted on the wire after its insertion to check that the insertion has been made correctly and completely, in particular in the case of insertion into a bushing of a Cable lug, which is provided with locking tongues.

In order to increase the sensitivity of the sensor to forces exerted along an axis different from the central axis of the two sensitive elements, it is preferable to provide opposite mounting of both of them; in this way the sensitivity of the eccentric force sensor (with respect to this central axis) is increased, in particular for forces exerted in the vicinity of a longitudinal end of the arm or wire holding member and a torque applied to the sensor - or force moment - have as a consequence.

It is advantageous to perform this opposite mounting by oppositely arranging the two sensitive elements and to provide an equipotential surface conductor on each of the surfaces of the parts which clamp the sensitive elements; a first equipotential surface connecting the positive pole of a first sensitive element to the negative pole of a second sensitive element and a second equipotential surface connecting the negative pole of the first sensitive element to the positive pole of the second sensitive element; each equipotential surface is preferably connected - via a coaxial conductor - to a corresponding input of a charge amplifier which converts the changes in charge of the sensor into a voltage or a current; this in particular makes it possible to reduce the number of electrical connections on the input side of the amplifier and thus to limit the disturbance of the measuring signal which might result from a leakage current resulting from these connections.

Alternatively, in some cases, such an opposite Mounting - providing the addition of the sensitivities of the two sensitive elements without reversing the polarities of the two juxtaposed elements; In this case, however, additional electrical connections must be provided.

Incidentally, in the case where the insertion axis coincides with the central axis of the sensitive elements, the opposite mounting is replaced by a simple parallel arrangement, alternatively a single sensitive element could be used.

By virtue of the use of sensitive elements (in the form of a ring) in which a central aperture is provided, it is possible to provide an elongate connecting member, such as a screw, extending through the aperture and serving the parts of the arm or retainer , which extend on either side of the sensor to attach to each other, and also serves to hold the sensitive element; in order to allow expansion of the sensitive element, it is favorable to choose a material and a cross-section for this connecting element, such that the radius of this connection is much smaller than the radius of the sensitive element; this can be realized in particular by a steel screw or a steel pin whose cross section is smaller than the support surface (and / or the transverse cross section) of the ring; this connecting member then forms an axial extension of one of the sensitive elements of the sensor, a return spring, which has the exercise of an eccentric force on the arm (or the wire-holding member) result.

When the forceps or handling device has two arms or wire retainers - which are generally movably mounted with respect to the body - preferably each of them is provided with a force sensor; this allows by summation of the measurement signals to increase the sensitivity of the whole; this can also allow the use of redundancy of the sensors by an OR operation, which replaces the summation and is applied to the two measuring signals, which increases the reliability of the introduction control system; In addition, the use of several sensitive elements, in particular at least three or four sensitive elements, allows to determine several force components by means of differential measurements, and therefore makes it possible to determine the direction thereof.

In order to limit the disturbances of the insertion force measurement signal resulting from the accelerations of the forceps or manipulator, it is important that the mass of the "sensor suspended" portion of the arm or retainer be as small as possible; For this purpose, it is also advantageous to approach the center of gravity of this section to the central axis of the sensitive elements until they match if necessary.

In order to limit the disturbances of the measuring signal, resulting from deformations of the cable connecting the sensor to an amplifier (charge / voltage or charge / current converter), it is convenient to arrange this amplifier in the vicinity of the sensor, in particular on the body the pliers or handling device.

In addition, or otherwise, in an insertion method according to the invention in the course of insertion of a cable lug or a wire end into a socket of a connector, the force which is at least partially removed from is measured and controlled in real time and controlled, when it is determined that the measurement result deviates from a reference value by a distance which is outside a predetermined maximum deviation range, the stop of an organ for the displacement of the Pliers or the handling device is commanded to stop the introduction procedure, which allows avoiding damage to the connector and / or the cable lug.

Preferably, the sensor is used with piezoelectric ceramic having its output connected to a charge amplifier, the input and / or the output of the amplifier being reset to zero prior to each insertion operation to eliminate residual charges resulting from the previous insertion operation and / or one or more gripping movements and / or the approach of the cable lug or the wire end could result.

Preferably, for several consecutive launch operations, multiple force introduction data measured for each operation is entered into or on a volume of a computer such that statistical data representing the launch quality and its evolution over time can be computed and / or made available ,

• eine Zange oder eine Handhabungsvorrichtung gemäß der Erfindung,
• einen Verbinder-Träger,
• wenigstens einen Aktuator für die Verlagerung der Zange (Handhabungsvorrichtung) zu einem am Verbinder-Träger befestigen Verbinder,
• Mittel zum Steuern der Verlagerung der Zange (Handhabungsvorrichtung) durch den Aktuator in Abhängigkeit von einem Kraftmeßsignal, das von dem in die Zange (Handhabungsvorrichtung) integrierten Sensor geliefert wird.

According to another aspect of the invention, a machine for the insertion of wires or cable lugs in sockets of connectors comprises:

• a forceps or a handling device according to the invention,
• a connector carrier,
• at least one actuator for the relocation of the Pliers (handling device) to a connector fastened to the connector carrier,
• Means for controlling the displacement of the forceps (handling device) by the actuator in response to a force measurement signal provided by the sensor integrated into the forceps (handling device).

• Fig. 1 ist eine schematische perspektivische Ansicht einer Einführungsmaschine gemäß der Erfindung.
• Fig. 2 ist eine perspektivische Ansicht einer Zange (Handhabungsvorrichtung) gemäß der Erfindung.
• Fig. 3 ist eine auseinandergezogene perspektivische Ansicht von Fig. 1, die die Hauptkomponenten der Zange veranschaulicht.
• Fig. 4 ist eine Stirnansicht der Zange der Fig. 2 und 3, die zwei Arme zeigt, die an ihrem unteren Ende durch Spannbacken oder Klemmbacken zum Ergreifen eines Drahtteilstücks abgeschlossen sind.
• Fig. 5 ist eine Seitenansicht der Zange der Fig. 2 bis 4; in dieser Figur ist außerdem ein Ladungsverstärker gezeigt, der mit dem Kraftsensor durch einen Leiterdraht verbunden ist.
• Fig. 6 ist ein Graph, der die Änderungen der Einführungskraft (auf der Ordinatenachse aufgetragen) in Abhängigkeit von der längs einer Einführungsachse gemessenen relativen Position (auf der Abszissenachse aufgetragen) des Endes des Drahtteilstücks (oder eines auf ein solches Ende gecrimpten Kabelschuhs) in bezug auf eine Buchse eines Verbinders veranschaulicht.
• Fig. 7 ist eine schematische Teilansicht einer Zange ähnlich jener der Fig. 2 bis 5, die die Anbringung zweier Ringe aus einem piezoelektrischen Keramikwerkstoff zwischen den Teilen eines Arms der Zange zeigt.
• Fig. 8 ist ein Schaltplan, der die Hauptkomponenten der Mittel zum Messen der Kraft durch Verarbeitung von Signalen veranschaulicht, die von zwei Paaren piezoelektrischer Elemente geliefert werden, die in zwei entsprechende bewegliche Arme einer Zange wie etwa jener, die in den Fig. 2 bis 7 gezeigt sind, integriert sind.

Further advantages and features of the invention will become apparent in the course of the following description, which refers to the accompanying drawings, which show, without any limiting characteristic, preferred embodiments of the invention.

• Fig. 1 is a schematic perspective view of an insertion machine according to the invention.
• Fig. 2 is a perspective view of a forceps (handling device) according to the invention.
• Fig. 3 is an exploded perspective view of Fig. 1 , which illustrates the main components of the pliers.
• Fig. 4 is an end view of the forceps Fig. 2 and 3 , which shows two arms, which are closed at their lower end by jaws or jaws for gripping a wire section.
• Fig. 5 is a side view of the forceps Fig. 2 to 4 ; Also shown in this figure is a charge amplifier connected to the force sensor by a conductor wire.
• Fig. 6 is a graph showing the changes of the insertion force (plotted on the ordinate axis) depending on of the relative position (plotted on the abscissa axis) measured along an insertion axis of the end of the wire section (or a crimp terminal crimped on such an end) with respect to a socket of a connector.
• Fig. 7 is a schematic partial view of a pair of pliers similar to that of Fig. 2 to 5 showing the attachment of two rings of a piezoelectric ceramic material between the parts of an arm of the forceps.
• Fig. 8 FIG. 12 is a circuit diagram illustrating the main components of the means for measuring the force by processing signals provided by two pairs of piezoelectric elements arranged in two corresponding movable arms of a pair of pliers, such as those shown in FIGS Fig. 2 to 7 are shown integrated.

As in particular in Fig. 1 1, the insertion machine 1 is specifically designed for insertion of a crimp terminal 2 crimped onto the end 3 of a wire section 4 (partially shown) into one of the sockets 5 of a connector 6.

To this end, the machine 1 comprises a connector support 7 which is movably mounted about a shaft 10 with respect to a vertical translatory movement pedestal 8 (not shown) and a rotary movement 9; the axis 10 is parallel to the longitudinal axes of the bushes; the insertion of the cable lug 2 into a bushing takes place by an insertion movement by translation along the longitudinal axis of this bushing, such as the axis 11.

For this purpose, the cable lug 2 and the end 3 are aligned during this insertion movement substantially held on this axis 11 by the jaws 12, 13 which are provided at the lower ends of the arms 14 and 15 of the insertion pliers 16, which clamps the end 3.

The insertion results from a displacement 17 along the axis 11 of the pliers 16 which holds the wire; For this purpose, the pliers with respect to a forceps support 18 along this direction 17 and along a direction perpendicular to the directions 8 and 11 direction 19 is movably mounted.

To control that the force for inserting the lug into the socket remains within predetermined limits, the approach movement 17 of the pincer and connector 6 is under the action of an actuator (such as a motor M) under the control of an electronic unit UC for processing of signals and data in dependence on the one hand of Kraftmeßsignalen and on the other hand of measuring signals with respect to the position of the pliers along the axis 11, which from a position sensor C ( Fig. 8 ) to the unit UC.

For this purpose, the unit UC may contain a memory (or other data carrier) in which for each type of female / cable shoe pairs several data in the form of tables or graphs such as that of Fig. 6 which correspond to (reference) nominal values for force or ranges of force ratings against which the force readings are compared during an induction cycle; these force ratings can be obtained by measuring the force exerted by the sensor integrated into the clamp by learning during preparatory cycles performed under conditions that represent the actual induction conditions.

The pliers 16 ( Fig. 1 to 5 and 7 ) comprises a body 20, the two sections include: a rear portion 21 forms a hollow body (cylinder) of a Stellzylindes, which serves to close the jaws 12, 13 of the pliers; To this end, the portion 21 comprises a bore 22 in which a piston 23 is mounted so that it can slide along a longitudinal axis 24 of the body 20 and the pliers 16; this axis 24 is parallel to the axis 11, along which the clamping jaws 12, 13 pinch the end 3 of the wire 4; two sections 25 connect this actuating cylinder with a (not shown) compressed air circuit for the supply of compressed air; the longitudinal end 26 of the piston 23 is profiled to form two cams, which are supported on two corresponding parts 28, 29, which are respectively fixedly connected to the two movable arms 14, 15 of the pliers; a return spring 30 with axis 31 keeps the parts 28, 29 spaced apart from each other when the pneumatic actuating cylinder 22, 23 is not actuated; the front portion 32 of the body 20, which is rigidly secured to the portion 21, protects the front portion of the piston 23 and carries a shaft with axis 31 (perpendicular to the axis 24), to which the parts 28 and 29 are slidably mounted to the To allow removal or approximation of the jaws 12, 13 under the action of the adjusting cylinder 22, 23 and the spring 30.

As in particular from the Fig. 2 to 4 As can be seen, the forceps 16 and in particular their organs 14, 15, 28, 29, which are translationally movable along the axis 31, with respect to a longitudinal center plane 33 is substantially symmetrical.

As in particular in the Fig. 3 and 7 5, each of the two movable units for crimping the wire except the arm 14, 15 and the sliding part 28, 29 includes a force sensor 34 interposed and clamped between the arm and the sliding part.

Each sensor 34 comprises two identical annular elements 35 made of zirconate and lead titanate-based ceramic material; On each of the two flat annular surfaces of each element 35 is formed an electrode corresponding to the positive pole and the negative pole of the polarized element, respectively.

Each sensor also includes two rectangular plates 36, 37 which are substantially coincident; each plate is supported on two coplanar electrodes provided on the respective annular surfaces of the two elements 35; the plates are at least partially made of an electrically insulating material, further provided on the inner surface 38, 39 of each plate 36, 37 is an electrically conductive coating to form an equipotential surface connecting the electrodes of the elements supporting these equipotential surfaces ; Each plate - and its equipotential surface - can be realized in particular in the form of a printed circuit.

Each equipotential surface is connected to a terminal 40 or 41 of a terminal support 42 of the sensor 34; a coaxial cable 43 connects these terminals to the inputs of a charge amplifier 44 which is attached to the portion 21 of the body 20 of the forceps 16 ( Fig. 5 ).

Each sensor 34 also includes an intermediate plate 50 (in FIG Fig. 7 not shown) penetrated by two apertures through which the discs extend, this plate forming with the plates 36, 37 a housing enclosing the two sensitive elements; the plates 36 and 37 are each penetrated by two openings 51 whose center distance corresponds to that of the two discs 35, while each part 14, 15 of two openings 52 are separated, which are separated by the same pitch, and each part 28, 29 has two threaded holes 53, which are also separated by the same pitch.

This allows the respective connection of each arm 14, 15 with one of the parts 28, 29 by two screws 54 with axis 55th

The head of each screw rests on an arm 14 or 15; each screw extends through one of the apertures 52, through an aperture 51 of each plate 36, 37, and through the central aperture of an element 35; each screw is engaged in a bore 53; by tightening the screws, each element 35 is sandwiched between the plates 36, 37 and clamped between their faces 38 and 39, the plates also being clamped between the parts 14 and 28 (and 15 and 29 respectively).

Each module 44, Fig. 8 comprising an amplifier 45 and a capacitor 46 connected between the negative input of the amplifier 45 and its output; the negative input is connected to a negative terminal 41 of the sensor, while the positive input is connected to the positive terminal 40 of the sensor and to ground; this circuitry forms an integrator which provides at the output a voltage which is proportional to the accumulated charge changes of the two sensitive elements 35 disposed opposite one another between the plates 36, 37.

This voltage is supplied to the unit UC via a cable 47.

A REED on / off switch 48 or a FET transistor is connected to the terminals of the capacitance 46 so as to be connected in parallel therewith; the closing of the on / off switch 48 (normally open) is controlled by a signal provided by the unit UC prior to each insertion operation to reset the output of the integrator to zero, which corresponds to the point 49 of the graph of FIG Fig. 6 equivalent.

The operation of the device is the following: The approach of the cable lug 2 with respect to a socket 5 is effected by the actuator M; due to the cumulative mass of the lug 2, the end 3 of the wire and the part 14 or 15 of the arm suspended on each sensor, the acceleration results in an inertial force 57 exerted on the center of gravity of the system suspended from the sensor, generally located near the center of gravity 56 (FIG. Fig. 7 ) of the arm 14 (or 15); when this force is on the external environment of the part of the plane of Fig. 7 which is exerted between the two axes 55 of the sensitive elements is applied, they are differentially stressed; the element 35, which is left in Fig. 7 is compressed while the second element 35 (located right in FIG Fig. 7 located) of the same sensor is "relieved", ie the compression stress (along its axis 55) decreases; from this force 57 results due to the elasticity of the screws 54, which connects them together, an infimal rotational displacement of the parts 15 and 36 with respect to the parts 37 and 29; this minimum amplitude rotation is essentially about an axis 58 which is to the plane of Fig. 7 is vertical.

The changes in the compressive forces exerted on the two elements 35 under the action of this force 57 and opposite to each other cause changes in charge in opposite directions, which add by virtue of the opposite mounting of the polarities of the elements 35, which facilitates the detection and measurement of the force by the force measuring means (44, UC); this corresponds to the part of the graph of Fig. 6 which extends between points 49 and 59 and which is described in the direction indicated by the parts 60, the point 59 substantially corresponding to the contact between the cable lug and the walls of the bushing.

In particular, the actual insertion of the lug into the socket requires the application of sufficient force to overcome the friction of the lug on the walls of the socket and, in general, the forces necessary to deform the lug and / or the walls of the socket; this results in a force 61 which is applied to the jaws of each arm of the tong substantially along the wire tensioning axis 11 in the same direction as the inertial force 57; the insertion force 61, in the same way as explained above for the force 57, causes a differential loading of the two elements 35 of each sensor 34, resulting in a force signal, such as that of the part of the graph of FIG Fig. 6 corresponding between points 59 and 62; when the lug is fully inserted, the forward movement of the pliers is stopped, wherein the insertion force is eliminated in the backward movement; optionally, an opposite (pulling) force acts on the wire to test the resistance to loosening of the mechanical connection between the inserted cable lug and the female socket receiving it, which is the part of the graph of FIG Fig. 6 which extends between points 62 and 63 where the force is negative; the jaws 12, 13 of the forceps are then actuated the adjusting cylinder 22, 23 away from each other to release the wire end, after which the pliers 16 is displaced to the rear to assume their original position, which is the part of the graph of Fig. 6 corresponds between the points 63 and 49 extends.

Claims (14)

1. Device for manipulating a wire, with a body (20), with a member (28; 29) that is mounted movably on the body (20), with a wire-holding element (14; 15) which is joined to the member (28; 29), and with a sensor (34) which is sensitive to a force that is exerted by the wire-holding element (14; 15) and which is arranged between the member (28; 29) and the wire-holding element (14; 15).
2. Device according to Claim 1, in which the sensor (34) is embodied as a piezoelectric sensor (34) for measuring the force for inserting a wire-end (2, 3) of the wire (4) into a bush (5) of a connector (6).
3. Device according to Claim 1 or 2, in which the sensor (34) comprises two thin pieces (35) of a polarised ceramic material.
4. Device according to Claim 3, in which the thin pieces (35) are placed head-to-tail so as to form a head-to-tail assembly.
5. Device according to one of claims 1 to 4, in which the sensor (34) is sensitive to a torque or moment resulting from the application of a force (61) that is exerted close to a longitudinal wire-end of the supporting member (14; 15).
6. Device according to one of claims 1 to 5, which contains an amplifier (44) that is connected to the sensor (34) and tightly fastened to the body (20).
7. Device according to one of claims 3 to 6, in which, assigned to each thin piece (35), is at least one elongated linking member (54), such as a screw, traversing an orifice of a thin washer-shaped piece (35), ensuring the compressing of the thin piece (35) and forming a spring that counteracts the expansion of the thin piece (35).
8. Device according to one of claims 1 to 7, with a further wire-holding element (15) and a further sensor (34), and with a means (70) for summing the signals delivered by the two sensors (34).
9. Device according to one of claims 1 to 8, in which the body (20) contains a jack (22, 23), and in which the two wire-holding elements (14, 15) are mounted in such manner that, under the effect of the jack (22, 23) and a return element (30), they can slide relative to the body (20) between an open position and a closed position.
10. Device according to one of claims 1 to 9, in which each of the wire-holding elements (14, 15) has an arm (14, 15) with a clamping jaw (12, 13).
11. Machine with a device for manipulating a wire according to one of patent claims 1 to 10, with a support (7) for supporting a connector (6), with an actuator (M) for moving the manipulator (16) towards the connector (6) that is secured to the support (7), and with a means (44, C, UC) for controlling the movement of the manipulator (16) by the actuator (M) according to a force-measurement signal that is delivered by the sensor (34).
12. Use of the device for manipulating a wire according to one of claims 1 to 10 for measuring and controlling in real-time the force employed when inserting a wire-lug (2) or a wire-end (3) of a wire (4) into a bush (5) of a connector (6).
13. Method for operating the device for manipulating a wire according to one of claims 1 to 10, in which a measurement and control is made in real-time of the force transmitted to the wire (4), and when it is detected that the measurement-result differs from a reference value by an amount that lies outside a predetermined maximum deviation range, an order is given to stop the actuator (M) so as to stop the insertion procedure, thus avoiding damage to the connector (6) and/or the wire-lug (2).
14. Method according to Claim 13, in which a piezoelectric ceramic sensor (34) is used whose output is connected to a charge amplifier (44) and the input and/or output of the charge amplifier (44) is reset to zero before each insertion operation so as to eliminate any residual charges likely to result from the preceding insertion operation and/or likely to result from one or more gripping and/or approach movements of the wire-lug (2) or wire-end (3).

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