FR2791588A1 - Numerically controlled electroerosion machining unit has articulated extension part attached to head and comprising mutually articulated primary and secondary segments - Google Patents

Abstract

Unit comprises plate (3) forming the base of vessel (4) containing electrolyte, machining head (7) facing the plate (3), articulated extension part (8) attached to head (7) and comprising mutually articulated primary (9) and secondary (10) segments, and motor-driven device that modifies the angle between segments (9, 10) and controlled by control signals transmitted to the extension part (8). The machining head (7) and the plate (3) move relative to each other in three orthogonal directions X, Y and Z. The primary and secondary segments (9, 10) are mutually articulated at their ends along an articulation geometrical axis perpendicular to Z. The extension part (8) is attached to the head (7) by the free end of the primary segment (9). Electrode (13) can be attached to the free end of the secondary segment (10).

Description

Numerical control EDM machine

Description

  TECHNICAL FIELD OF THE INVENTION The invention relates to machine tools with numerical control of machining known as "by 1o electroerosion", that is to say allowing to machine metal parts by electrical discharges using an electrode , and more particularly to such machines

  comprising particular means for automatic positioning of the electrode.

  State of the art and problem to be solved Electroerosion machining is well known in the industry for machining metallic materials or more generally electrically conductive materials. Machining is carried out by electrical discharges between a machining electrode and the workpiece in the presence of a dielectric liquid. This machining technique is more particularly used to machine parts made of high-strength metal alloys and / or for

  print the shape of an electrode in a room.

  In what follows, numerically controlled machines allowing machining by EDM will be simply called "machines". These machines usually include a table capable of carrying the workpiece, said table being submersible, that is to say capable of being immersed, in a tank containing the dielectric liquid, said machine also comprising a head capable of facing the table. to receive an electrode to perform the machining. The table is usually horizontal. Usually, the head and the table move relatively with respect to each other by translations in three orthogonal directions X, Y and Z, Z being by convention perpendicular to the table, X and Y being by convention parallel to the table. Usually, the head can pivot along Z. In what follows, the space in which machining operations are likely to be carried out by the machine is called "workspace", this workspace obviously being

  located between the head and the table inside the tank.

  Usually, the machines are said to be "numerically controlled", that is to say that the relative movements of the head relative to the table are controlled by signals emitted by a computer executing a program established as a function of the part to be manufactured. The commands are usually interactive, i.e. there is an exchange of signals between the machine and the computer, the machine transmitting situation information to the computer, for example on the position of the moving parts, and the computer transmitting control signals to the machine, for example to move the moving parts, the exchanges between the machine and the computer being effected by means of appropriate interfaces. The computer is usually external to the machine and usually controls several machine tools which can be of

  different types. Such equipment is well known to those skilled in the art.

  With such a machine, the part being positioned on the table and immersed in the tank, the electrode mounted at the end of the head is usually brought above the machining to be carried out by translations along X and Y, and we approximate the 'electrode of the part by a translation along Z to perform plunge machining. By eccentricating the electrode with respect to Z and rotating the head along Z, it is also possible to generate circular surfaces. Oblique dives can also be performed by mounting the electrode on an oblique support and by performing said dive by a combination of translations along X, Y and Z respectively. It is known to interpose between the head and the electrode of the spacers and various electrode holders allowing this electrode to be given

  specific positions relative to the head as required.

  When the part is complex, for example a turbomachine rotor stage in the shape of a drum, and it is necessary to carry out successively several machining operations at different places of this part, some of these places may not be directly accessible from above the tank, the operator may have to carry out the following operations before each new machining: - change the electrode support in order to give the electrode a new position relative to the head, - give the workpiece a new position which is favorable to the new machining to be carried out, this operation necessitating removing said part from the tank, dismantling it, positioning it otherwise, fixing it on the table, submerging it again in the tank and palpate to recognize exactly its new position. Positioning can be facilitated by using a plate swiveling along two axes, said plate being positioned on the table, the piece being itself positioned on said plate. All these operations are time wasters and frequently require the use of specific tools to position the electrodes and / or the part. The operations of moving the part are even longer and more delicate

  when the parts are heavy and require significant handling resources.

  A first problem to be solved is to carry out machining at various places of the

  part without disassembly and reassembly neither of the part nor of the electrode.

  A second problem to solve is to carry out machining in places of the part

  which are not directly accessible from the top of the tank.

  SUMMARY OF THE INVENTION The invention therefore provides a numerically controlled electroerosion machining machine comprising a table capable of carrying the workpiece, said table being capable of being immersed in an electrolyte contained in a tank, said machine also comprising a machining head, that is to say capable of receiving an electrode for machining by electroerosion a piece placed on the table, said head being facing the table, said head and said table move relatively one by relative to the other by translations in three orthogonal directions X, Y and Z, the head being able to pivot according to Z. Such a machine is remarkable in that it comprises an articulated extender attached to the head, said extender comprising a primary segment and a secondary segment hinged together by one of their ends along a geometric axis of articulation perpendicular to Z, said extension r being attached to the head by the free end of the primary segment, an electrode being capable of being attached to the free end of the secondary segment, said extension also comprising motorized means for automatically changing the angle a between said primary segment and said secondary segment, said motorized means being controlled from

  of control signals transmitted to the extender.

  It is understood that such an extension attached to the head makes it possible to automatically modify the inclination with respect to Z of an object such as an electrode attached to the free end of the secondary segment, the modification being carried out automatically on the basis of signals from commands sent to the extender. It is also understood that such an extension, combined with the other means of controlled movement of the machine, makes it possible to position this electrode with any orientation at any point in the work space above the table, this positioning s 'Obviously performing within the limits of the possibilities of movement of the head and of the extension in relation to the table. It is understood that the extension can be attached to the head directly or by means of spacers. It is also understood that the electrode can be attached to the extension directly or by

  through spacers or electrode holders.

  It is understood that by sending the appropriate control signals to the machine and to the extender, it is possible to automatically bring an electrode into positions suitable for the successive machining operations to be carried out on a complex part, which makes it possible to carry out these machining operations without modifying the position of said part or avoiding changing or adjusting the support of the electrode. It is obvious that this supply can be carried out in a very short time compared to that of the necessary operations of art.

prior.

  It is also understood that such an arrangement is made possible by the fact that the extension undergoes only reduced forces, since the electrode does not come into contact

  of the surface to be machined during machining.

  Finally, it is understood that the extender constitutes an essential means of the invention. In practice, the two segments of the extension will be short, and the operator will be able to extend them by spacers as required, which increases the possibilities.

use of said extension.

  The invention has the advantage of allowing an acceleration of the change of the electrodes. This change can be manual. It suffices to introduce into the program of the computer controlling the machine instructions bringing, at the end of a machining, the secondary segment into an appropriate position, for example oriented along Y towards the front of the machine at above the tank. The electrode is then easily accessible and can be easily changed by the operator. This change can also be completely automatic, the computer program comprising instructions for pointing the secondary segment towards a magazine presenting the tools awaiting use, the program also comprising instructions causing the translation of the secondary segment towards said magazine in order to drop a tool at the end

  or to enter a new tool.

  In practice, the motorized means comprise an angle measurer making it possible to establish the angle ac between the primary segment and the secondary segment, the control signals of the motorized means then being given to correct the difference between this angle a and a setpoint angle which is obviously given by the program of the computer controlling the machine. The accuracy of the angle measurer a will be at least 0.02 in order to

  to guarantee sufficient precision in the positioning of the electrode.

  Advantageously: - the motorized means are sealed, - the primary segment is arranged in the extension of the head along Z,

  - while the secondary segment is likely to be aligned with the primary segment.

  Since the secondary segment is articulated to the primary segment, the term "capable of being aligned with the primary segment" means that the range of angular displacement of the secondary segment relative to the primary segment includes

  position in which the secondary segment is aligned with the primary segment.

  Conventionally, a = O in this position.

  It is understood that with such an arrangement, the head, the primary segment and the secondary segment can be aligned with respect to each other along Z, which has the effect of limiting their size around Z. The space located around the being thus released, one can then successively: - lower the extension into the electrolyte tank along a vertical wall of the part, by a translation along Z and with a = O, -bend the extension to have example a = 90, this operation possibly being possible during the final phase of the descent, - then carry out machining in places of the part which are not directly accessible from the top of the tank,

  - then remove the electrode and the extender from the tank by the reverse process.

  Advantageously, the length L of the extension is less than 1.5E, E being the lateral size of the extension taken along the geometric axis of articulation, L being taken between the free ends of the primary segment and of the secondary segment when said segments are aligned, ie when a = O. A short extension is paradoxically more flexible to use, because the operator can, as the case may be: - directly attach the free end of the primary segment to the machine head and attach directly the electrode at the free end of the secondary segment when a reduced distance is required between the electrode and the head, - or, on the contrary, attach the free end of the primary segment to the head by means of spacers and / or the electrode at the free end of the secondary segment when a longer distance between the electrode and the head is required, or when it is necessary to reach parts of the workpiece which are not not directly accessible from above

tank.

Description of the figures

  The invention will be better understood, and the advantages it provides will appear more

  clearly in view of the detailed description of an embodiment and the figures

  attached. Figure 1 illustrates a numerically controlled EDM machine

according to the invention.

  Figures 2 illustrates an exemplary embodiment of the extension.

  FIG. 3 illustrates an example of drilling carried out at three different locations of a

  part, as well as the corresponding positions of the articulated extension and the electrode.

  Figure 4 illustrates an example of holes made in one part of a part, which

  are not directly accessible from the top of the tank.

detailed description

  Reference will first be made to FIG. 1. The numerically controlled electroerosion machining machine 1 comprises a frame 2 as well as a table 3 which is horizontal and capable of being immersed in a tank 4 containing an electrolyte. The machine 1 also comprises a horizontal carriage 5 supported by the frame 2, as well as an upper body 6 supported by said horizontal carriage 5, said horizontal carriage 5 being capable of moving relative to the frame 2 in two directions X and Y perpendicular and horizontal, X and Y being consequently parallel to the table 3, the upper body 6 being itself capable of moving relative to said horizontal carriage 5 in a vertical direction Z, therefore perpendicular to the table 3. The upper body 6 has at its end opposite the table 3 a head 7 pivoting along a geometric axis 7a parallel to Z. For convenience of language, it is said that the head 7 is pivotable along Z. In this type of machine 1, the head 7 is simply constituted by the opposite end of the table 3 of a pivoting spindle of geometric axis 7a, said spindle being internal to the upper body 6 and not visible in FIG. 1. The head te 7 is capable of receiving an object such as an electrode, an electrode holder, a spacer, etc. It is understood that the head 7, and consequently an object placed under the head 7, can be moved relative to the table 3 by a translation along the three orthogonal directions X, Y and Z combined with a pivoting along Z. According to the invention, an extension 8 is attached under the head 7 opposite the table 3. The extension 8 has a primary segment 9 d geometric axis 9a and a secondary segment 10 of geometric axis 10a, said segments 9,10 being hinged together by one end along a geometric axis of articulation 11. The free end of the primary segment 9 is attached to the head 7 , and the geometric axis 9a of said primary segment 9 then merges with the geometric axis 7a of the head 7. The geometric axis a of the secondary segment 10, the geometric axis 9a of the primary segment 9 and the axis of joint 11 intersect at a point d single intersection referenced 12 in FIG. 2, said geometric axes 9a and 10a forming between them an angle ca and being perpendicular to said geometric axis of articulation 11, said angle a varying over a range of 90. A sealed sheath 12 is connected to the primary segment 9 and brings electrical cables, not shown, which will make it possible to control motorized means described below, said motorized means making it possible to vary over

  controls angle a as required.

  In this example, an electrode 13 is attached to the end of the secondary segment and in the geometrical axis 10a of said secondary segment 10. This electrode 13 has the shape of a rod and makes it possible to drill 14 in a part 15 placed on the table 3. To make a hole 14, the orientation of the electrode 13 is controlled parallel to the hole to be made by pivoting the secondary segment 10 along the geometric axis of articulation 11, so as to give the angle ca an appropriate value, and by pivoting the head 6 along Z. Then, the electrode 13 is brought in front of the hole 14 by translations along X, Y and Z, and the electrode 13 is pushed into the part 14 by a translation along the geometric axis 10a of the secondary segment 10, this translation then being an appropriate combination of translations along X, Y and Z. In this example, other holes 14a of the same diameter, or of slightly different diameters, but d '' directions and of different positions, can very simply be machined on the surface of the part 15 without any disassembly either of the electrode 13 or of the

Exhibit 15.

  o10 We will now refer to FIG. 2. The primary segment 9 of geometric axis 9a successively comprises in this example a primary sole 20 attached by its surface 20a to the head 7 by the usual means for this type of machine, for example by a preemption rod 21 positioned in the geometric axis 7a of said head 7, as well as a casing 22 attached by four screws 23 to said primary sole 20. The surface 20a of

  the primary sole 20 is perpendicular to the geometric axis 9a of the primary segment 9.

  It will be understood that the surface 20a of the primary sole 20 constitutes the free end of the primary segment 9. The casing 22 has a shape essentially of revolution along the geometric axis of articulation 11. The casing 22 is sealed and has a plurality of bores 24 centered on the geometric axis of articulation 11, said bores 24 radially delimiting an internal cavity 25 opening out on either side of the casing 22, said internal cavity 25 being closed by two flanges 26 and 27 on either side 'other of the housing 22, said flanges 26, 27 being in this example simply held on the housing by screws not referenced, said flanges 26,27 also being sealed relative to the housing 22 by O-rings not shown. The end of the sheath 16 is screwed onto one of the flanges 26 and makes it possible to bring electrical cables 28 into the interior cavity 25. The casing 22 also comprises, in its part opposite to the primary sole 20, therefore of the free end 20a of the primary segment 9, and laterally a radial slot 29 whose walls 29a are mutually parallel and perpendicular to the geometric axis of articulation 11, said walls 29a being substantially equidistant

  of the geometric axis 7a of the head 7.

  The secondary segment 10 of geometric axis 10a comprises a ferrule 30 journalling in the interior cavity 25 along the geometric axis of articulation 11 by means of a bearing 31 with crossed rollers, said secondary segment 10 also comprising a mat 32 attached by one end 32a to the ferrule 30 for example by screws not shown, said mat 32 passing through the radial slot 29 of the casing 12, the other end 32b of said mat 32 opening out of the casing 22, said end 32b being extended by a secondary sole 33 comprising a surface 33a opposite the ferrule 30, said surface 33a being plane and perpendicular to the geometric axis 10a of segment 10, said surface 33a constituting the free end of said secondary segment 10, said mat 32 consequently connecting said ferrule 30 to said free end 33a of the secondary segment 10. In this example, a spacer 34 of common type is

  attached by four screws 35 to the free end 33a of the secondary segment 10.

  The surface 30a at the periphery of the ferrule 30 makes limited play with one 24a of the bores 24, and two annular seals 36 centered on the geometric axis of articulation 11 and situated on either side of the radial slot 29 are housed in this bore 24a and come into contact with said surface 30a, said seals 36 thus ensuring sealing between the casing 22 and the periphery of the ferrule 30, therefore with the

secondary segment 10.

  In this example, the geometric axis 9a of the primary segment 9 merges with the geometric axis 7a of the head 7. When the extender 8 is straight, the geometric axis 10a

  of the secondary segment 10 merges with the geometric axis 9a of the primary segment 9.

  When the extension 8 is bent, the geometric axes 10a and 9a, respectively of the secondary segment 9 and of the primary segment 10, form an angle a which can vary between 0 and 90 under the action of the motorized means 40 below. This angle a is not

  visible in Figure 2, but it appears in Figures 3 and 4.

  We will now describe the motorized means 40 for ensuring the angular positioning of the secondary segment 10 relative to the primary segment 9 by pivoting along the geometric axis of articulation 11. In this example, the components of said motorized means are all housed in the internal cavity 25 of the casing 22 between the flanges 26 and 27 closing said internal cavity 25 at its two ends, said components being centered on the geometric axis of articulation 11. The motorized means 40 comprise an electric and rotary motor 45 receiving signals

  electrical control by electric cables 28, said motor 45 comprising itself

  even a stator 46 attached to the housing 22 and a rotor 47 attached to a first end 51 called "driven" of a shaft 50. This shaft 50 has a middle portion 52 and a

  second end called "braked" 53 widened in the form of a shoulder 54.

  The braked end 53 of the shaft 50 is linked in rotation to a brake 55, said brake 55 comprising a movable disc 56 disposed against the shoulder 54, this movable disc 56 being linked in rotation to the shoulder 54 but retaining a freedom in translation along the geometric axis of articulation 11, for example by pins sliding in holes. This brake 55 also includes an electromagnet 57 attached to the casing 22 by means of one of the flanges 27, said electromagnet 57 being opposite the braked end 53 of the shaft 50, said electromagnet 54 being capable of attracting and sticking against it the mobile disc 56 under the effect of electrical control signals arriving

  by the electric cables 28, which produces the desired braking effect.

  A reduction gear 60 of the cartridge type, that is to say with an elliptical bearing and flexible gear, is disposed inside the ferrule 30 and surrounds the middle part 52 of the shaft 50. This type of reduction gear is well known and will be briefly described for a good understanding of the invention. In the present case, a cartridge reducer of the brand "Harmonic Drive" is used, model "Harmonic Drive 1/100" distributed in France by a company whose corporate name is "Gammatic". Such a reducer 60 successively comprises, starting from the center towards the periphery, a ring 61 called "inlet" attached to the middle part 52 of the shaft 50, a ring 62 called "outlet" attached to the ferrule 30, and a fixed ring 63 attached to the housing 22. The inlet ring 61 rotates the outlet ring 62 with a large reduction in speed thanks to an elliptical ball bearing 64 whose periphery is a flexible male gear 65 meshing in a female gear 66 surrounding said flexible gear 65, said female gear 66 being attached to the output ring 62, said flexible gear 65 being linked in rotation to the fixed ring 63 by a radially flexible spacer not shown. The output ring 62 pivots in the fixed ring 63 by means of the crossed roller bearing 31, and the input ring 61 pivots simultaneously in the fixed ring 63 by means of a first ball bearing 66, and in the shell 30 via a

second ball bearing 67.

  It is understood that the ferrule 30 pivots in the casing 22 using means of the reducer 60, namely successively the output ring 62, the crossed roller bearing 31 and the fixed ring 63, which makes it possible to reduce the size of the extender according to the geometric axis of articulation 11. It is also understood that for the same advantage,

  it is the reduction gear 60 which turns the shaft 50 in the casing 22.

  An annular support 70 is attached to the ferrule 30 on the side of the brake 55, said annular support 70 supporting an angle measurer 71 by means of its rotor 72, said angle measurer 71 also comprising a stator 73 attached to the casing 22, said angle measurer 71 transmitting by electrical cables 28 signals information signals making it possible to establish the angle a made by the rotor 72 in its current position relative to the stator 73. In this example, the measurer angle 71 is an incremental encoder with 5000 lines of the "Heidenhain" brand marketed by the reason company

  Social "Araxe", this angle measurer 71 ensuring an angular precision of 0.004.

  The control of the motorized means by the computer is conventionally carried out as follows: - consultation of the information signals emitted by the angle measurer 71 and establishment of the corresponding angle a, i0 establishment of the difference entre between the current value of the angle a and the set value that it should have, - sending to the brake 55 of a signal controlling the release of the shaft 50, in practice in this example by interrupting the electric current supplying the electromagnet 57, - sending of a signal controlling the rotation of the motor 45 in the appropriate direction to reduce the difference 5,

  - return to the first operation, until the difference ô is zero.

  It is understood that from the control signals received, the motor 45 rotates the shaft 50 by its driven end 51, said shaft 50 driving in rotation by its central part 52 the input ring 61 of the cartridge reducer 60, said input ring 61 causing the radial deformation of the flexible gear 65 by means of the elliptical bearing 64, said flexible gear 65 driving the female gear 66 in a greatly multiplied rotational movement, said female gear 66 driving in rotation the ferrule 30 by means of the outlet ring 62 of the cartridge reducer 60, this drive being carried out by bearing on the casing 22 successively by means of the flexible spacer not shown and the fixed ring 63, said ferrule 30 causing the secondary segment 10 to rotate, as well as any object such as a spacer 34 attached to the surface 33a of the secondary sole 33

  by means of the radial mat 30 leaving the casing 22.

  It will be understood that the secondary segment 10 pivots with precision relative to the primary segment 9 by means of the bearing 31 with crossed rollers placed in the vicinity of the geometric axis 10a of the secondary segment 10, such a crossed roller bearing 31 having already a clearance very low, the presence of said crossed roller bearing 31 in the vicinity of said geometric axis 10a reducing the overhang of the secondary segment 10 and by consequence the axial play along said geometric axis 10a. In practice, the crossed roller bearing 31 will be positioned at a distance from the geometric axis 10a of the

  secondary segment 10 less than 50% of the diameter of said crossed roller bearing 31.

  It is also understood that a very compact mechanism is ensured by the following means: - the shaft 50 passes through the center of the ferrule 30 and of the reduction gear 60, - the ferrule 30, the reduction gear 60 and therefore the crossed roller bearing 31 are positioned at the middle part 52 of the shaft 50, and therefore in the vicinity of the radial mast 32, the motor 45 and the angle measurer 71 being arranged on either side of the ferrule 30 and the reduction gear 60 , The shaft 50 supporting them being itself held at its median part 52 by the reduction gear 60, - the brake 55 and the shoulder 54 penetrate at least partially inside the annular support 70 of the angle measurer , said brake 55 and said shoulder 54 being therefore partially at least partially buried in the center of the measurer

corner 71.

  Reference will now be made to FIG. 3. The part 15 is placed on the table 3 and is immersed in the electrolyte 90 contained in the tank 4. In a first position 91, drilling is carried out by plunging an electrode 13 according to Z, the primary segment 9 and the secondary segment 10 then being aligned with ac = 0. In a second position 92, a drilling is made at 45 by plunging the electrode 13 along X and Z combined, with a (x = 45. In a third position 93, a horizontal drilling is carried out in the side of the part by plunging the electrode 13 along X. The extender 8 is here attached to the head 7 by means of a spacer 80, which makes it possible to immerse said extender 8 in the electrolyte 90 to perform horizontal drilling , the head 7 remaining above the tank 4. This spacer 80 does not stand in the way of other drilling to be carried out, it is therefore understood that these three drilling can be carried out one after the other without dismantling the extension 8 and / or part 15, the extension 8 being put in each time

  automatically in the appropriate position.

  Reference will now be made to FIG. 4. In this example, the part 15 is a turbomachine rotor of general shape of revolution, and drilling is carried out inside

  the rim 94 of said rotor 15 by diving the electrode 13 along X with a = 90.

  The interior of the rim 94 not being directly accessible from above the tank 4, the primary segment 9 is attached to the head 7 by means of a first spacer 80, and the electrode 13 is attached to the sole 33 of the secondary segment 10

  via a second spacer 34.

Claims (10)

Claims   1. CNC machining machine, said machine (1) comprising a table (3) capable of carrying a workpiece (15), said table (3) being capable of being immersed in an electrolyte (90 ) contained in a tank (4), said machine (1) also comprising a machining head (7) facing the table (3), said head (7) and said table (3) move relatively one relative to each other by translations in three orthogonal directions X, Y and Z, the head (7) being able to pivot along Z, characterized in that it comprises an articulated extension (8) attached to the head o10 (7) , said extension (8) comprising a primary segment (9) and a secondary segment (10) hinged together by one of their ends (22,30) along a geometric axis of articulation (11) perpendicular to Z, said an extension (8) being attached to the head (7) by the free end (20a) of the primary segment (9), an electrode (13 ) being capable of being attached to the free end (33a) of the secondary segment (10), said extension (8) also comprising motorized means (40) for automatically changing the angle a (between said primary segment (9) and said secondary segment (10), said motorized means (40) being controlled from electrical signals of   command transmitted to the extender (8).   2. Machine according to claim 1, characterized in that the motorized means (40) comprise an angle measurer (71) making it possible to measure the angle a (, and in that the control signals of the motorized means (40) are given to correct the deviation   between this angle a and a set angle.   3. Machine according to claim 2 characterized in that the angle measurer (71) has   an accuracy at least equal to 0.02.   4. Machine according to any one of claims 1 to 3, characterized in that the   motorized means (40) are sealed, in that the primary segment (9) is arranged in the extension of the head (7) along Z, and in that the secondary segment (10) is   capable of being aligned with the primary segment (9).   5. Machine according to any one of claims 1 to 4, the lateral size of the   extension (8) taken along the geometric axis of articulation (11) being noted E, characterized in that the length L of the extension takes the free ends (20a, 33a) of the primary segment (9) and of the secondary segment respectively ( 10) is less than 1.5E.   6. Machine according to any one of claims 1 to 5, characterized in that the   primary segment (9) comprises a sealed casing (22), said casing (22) containing the motorized means (40).   7. Machine according to claim 6, characterized in that the casing (22) has in its part opposite its free end (20a) and laterally a radial slot (29), in that the secondary segment (10) has a ferrule (30) journalling in the internal cavity (25) along the geometric axis of articulation (11), said secondary segment also comprising a radial mast (32) whose upper part (32a) is attached to the ferrule (30), said radial mat (32) passing through the radial slot (29), said radial mat (32)   connecting the free end (33a) of the secondary segment (10) to the ferrule (30).   8. Machine according to claim 7, the peripheral surface of the ferrule (30) being referenced (30a), characterized in that two annular seals (36) seal between the casing (22) and said peripheral surface (30a), said seals (36) being centered on the geometric axis of articulation (11) and being located   on either side of the radial slot (29).   9. Machine according to any one of claims 6 to 8, characterized in that the   motorized means (40) comprise a motor (45), a shaft (50), a cartridge reducer (60), a brake (55) and an angle measurer (71), said shaft (50) successively having a driven end (51), a middle part (52) and a braked end (53), said reduction gear (60) itself comprising an inlet ring (61), an outlet ring (62) and a fixed ring (63) , said shaft (50) passing through the center of the ferrule (30) and of the reduction gear (60), and in that the motor (45) drives the shaft (50) through its driven end (51), said shaft ( 50) being linked in rotation to the brake (55) by its braked end (53), said shaft (50) being attached by its central part (52) to the inlet ring (61) of the reduction gear (60), the ring outlet (62) of said reducer (60) being attached to the ferrule (30), the fixed ring (63) of said reducer being attached to the casing (22), the angle measurer (71) being attached to the braked end (53) of said tree (50), the motor (45) and the brake (55) receiving control signals by cables electric (28).   10. Machine according to claim 9 characterized in that the ferrule (30) journals in the casing (22) via the outlet ring (62) and the roller bearing   crossed (31) of the cartridge reducer (60).