Stabilized machining machine, stabilization kit for machining machine and method for controlling such a machine

Abstract

The present invention relates to a stabilized machining machine, a stabilization kit for a machining machine and a stabilization method, characterized in that they comprise a stabilizer also controlled by said control unit (CU) and comprising: - at least one support (2) mounted integral with the ground and provided with at least three tensioners (20) distributed around said head (10), preferably equidistant from each other, - at least three cables (21) connecting said head (10) to said tensioners (20), - adjustable means (22) for tensioning said cables (21) between said head (10) and said tensioners (20), - means (23) for moving said tensioners (20) on said support (2), said control unit (CU) controlling the individual movement of each of the tensioners and the tension of each of the cables (21) as a function of said positions and inclinations of said head (10) during machining. Figure for abstract: Figure 1

Description

Title of the invention: Stabilized machining machine, stabilization kit for machining machine and method for controlling such a machine

[0001] The present invention relates to the field of machining machines (or robots). The terms "machine" and "robot" (or "machine tool" or even "automaton") are used interchangeably in the present application to designate the robotic devices used for the design of parts, whether by milling, welding, 3D printing, etc. The term machining is therefore used in the present application to designate factory manufacturing by robots or automatons and is not limited to the type of tool equipping the machine.

[0002] In particular, the present invention relates to a stabilized machining machine and a stabilization kit for machining machines.

[0003] In this field of machining machines, there is a problem of stability, particularly at the end of the machine that carries out the machining of the parts. Indeed, machining machines are generally large robotic arms mounted on a base and having a movable end (called "head" in the present application) which carries the machining tools (cutting, milling, printing, welding tool, etc.) and moves in the three directions of space in order to machine the parts with various orientations. In the present application, the term "robotic arm" is used to designate all types of robotic machining machines with several axes, such as for example robotic arms or linear axis machines, etc.In general, since the overhang between the base and the head is significant, it is expected that the base will be heavy and / or fixed to the ground and that the arm will be configured (particularly in terms of dimensions and rigidity) to combat the vibrations and forces exerted by the tools on the parts being machined, which may limit the precision of the machining. However, this problem remains recurrent in the prior art and no known solution makes it possible to improve the stability and / or the precision of the machines, at least without generating significant additional costs.

[0004] An aim of the present invention is therefore to overcome at least certain drawbacks of the prior art by proposing a stabilized machining machine.

[0005] This aim is achieved by a machining machine comprising at least one robotic arm having a first end mounted on a base and a second end provided with a head carrying at least one machining tool, said robotic arm being articulated and motorized to move the head into various positions and inclinations relative to parts to be machined, as a function of parameters determined by at least one control unit controlling the movement of said head during machining, characterized in that it comprises a stabilizer also controlled by said control unit and comprising: - at least one support mounted securely on the ground and fitted with at least three tensioners distributed around said head, preferably equidistant from each other, - at least three cables connecting said head to said tensioners, - adjustable means for tensioning said cables between said head and said tensioners, - means for moving said tensioners on said support, said control unit controlling the individual movement of each of the tensioners and the tension of each of the cables according to said positions and inclinations of said head during machining.

[0006] According to another feature, the tensioners and the cables are configured in pairs, with at least three pairs distributed around said machining head and, within each pair, the tensioners are arranged on either side of the machining head, so that the tension force exerted on said machining head by each of the tensioners has at least one component in the opposite direction to that of the other tensioner of the same pair.

[0007] According to another feature, the control unit controls the movement of each of the tensioners and the tension of each of the cables so that the forces exerted by the different cables on the machining head compensate each other, preferably so that their sum is zero.

[0008] According to another feature, each of said cables is mounted on the head using a fastener free to pivot depending on the inclination of the cables relative to the horizontal.

[0009] According to another feature, each of said fasteners is configured to move freely on a plate secured to the head, along a circular path centered on said head, so that the pivots are positioned according to the orientation and length of each of the cables.

[0010] According to another feature, said support comprises at least one wall having a circular or elliptical cross-section surrounding said robotic arm.

[0011] According to another feature, said support comprises at least one wall having a rectangular or square section surrounding said robotic arm.

[0012] According to another feature, said support comprises at least three posts perpendicular to the ground and distributed around said robotic arm, preferably equidistant from each other.

[0013] According to another feature, each of said means for moving said tensioners on said support comprises a motorized carriage controlled by said control unit to move on a rail in order to adjust the height of said tensioner relative to the ground.

[0014] According to another feature, the stabilizer also comprises means for de- lateral placement of the tensioners, to adjust their respective positions around the head.

[0015] According to another feature, said adjustable means for tensioning said cables comprise at least one cable winder controlled by said control unit and forming said tensioner.

[0016] An aim of the present invention is to overcome at least certain drawbacks of the prior art by proposing a stabilization kit for machining machines, in order to improve the stability and / or the precision of the machining machines of the prior art.

[0017] This aim is achieved by a stabilization kit for a machining machine, characterized in that it comprises a stabilizer according to various embodiments.

[0018] An aim of the present invention is to overcome at least certain drawbacks of the prior art by proposing a method for controlling and / or stabilizing a machining machine, in order to improve the stability and / or precision of the machining machines of the prior art.

[0019] This aim is achieved by a method for controlling a machining machine according to various embodiments, characterized in that it is implemented by a control unit carrying out the following steps at each movement of the machining head: - determination of the position of the head of the robotic arm in space, in particular in relation to the base, - determination of the inclination of the head of the robotic arm relative to the vertical, - determination, from said position and inclination of the head, of the necessary positions of said tensioners so that they are located in the same plane, the inclination of which depends on that of the head, - controlling the movement means and the adjustable cable tensioning means to position said tensioners at said determined necessary positions and provide cable tension to stabilize the head in said plane.

[0020] This aim is also achieved by a method for controlling a machining machine according to the invention, characterized in that it is implemented by a control unit carrying out the following steps at each movement of the machining head: - determination of the position of the head of the robotic arm in space, in particular in relation to the base, - determination of the inclination of the head of the robotic arm relative to the vertical, - determination, from said position and inclination of the head, of the necessary positions of said tensioners for mutual compensation between the different components of the tension forces exerted by all the tensioners on the machining head, - controlling the movement means and the adjustable cable tensioning means to position said tensioners at said determined necessary positions and provide cable tension such that the different forces exerted on the head compensate each other, preferably with a zero resultant.

[0021] Other features and advantages of the present invention will appear more clearly on reading the description of various embodiments below, given with reference to the appended drawings, in which:

[0022] [Fig-1] [Fig.l] represents a perspective view of a machining machine according to certain embodiments;

[0023] [Fig.2] [Fig.2] represents a top view of a machining machine of [Fig.l]

[0024] [Fig.3] [Fig.3] represents a perspective view of a machining machine according to certain embodiments;

[0025] [Fig.4] [Fig.4] represents a perspective view of detail 4 of [Fig.4] showing a tensioner of a machining machine according to certain embodiments;

[0026] [Fig.5] [Fig.5] represents a top view of a machining machine according to certain embodiments;

[0027] [Fig.6] [Fig.6] represents a perspective view of a machining machine according to certain embodiments;

[0028] [Fig.7] [Fig.7] represents a perspective view of a machining machine according to certain embodiments.

[0029] The present application relates to a stabilized machining machine and a stabilization kit for a machining machine. Machining machines, as defined in a non-limiting manner in the preamble of the present application, generally comprise at least one robotic arm (1) having a first end mounted on a base (11) and a second end provided with a head (10) carrying at least one machining tool, said robotic arm (1) being articulated and motorized to move the head (10) into various positions and inclinations relative to parts to be machined, as a function of parameters determined by at least one control unit (CU) controlling the movement of said head (10) during machining, characterized in that it comprises a stabilizer also controlled by said control unit (CU) and comprising: - at least one support (2) mounted securely on the ground and provided with at least three tensioners (20) distributed around said head (10), preferably equidistant from each other, - at least three cables (21) connecting said head (10) to said tensioners (20), - adjustable means (22) for tensioning said cables (21) between said head (10) and said tensioners (20), - means (23) for moving said tensioners (20) on said support (2), said control unit (CU) controlling the individual movement of each of the tensioners and the tension of each of the cables (21) as a function of said positions and inclinations of said head (10) during machining.

[0030] It is understood that a machining machine is thus obtained whose head is stabilized. thanks to the fact that a control unit (the same as that of the machine itself or another dedicated control unit) moves the tensioners of the cables connected to the head in order to exert a tension that limits the risks of movements or vibrations of the head and thus improves the precision of the machine thanks to the help of a solid support anchored to the ground (such as a chassis, a frame or a container).

[0031] In some embodiments, the tensioners (20) and the cables (21) are configured in pairs, with at least three pairs distributed around said machining head (10). In this case, within each pair, the tensioners (20) are arranged on either side of the machining head (10), so that the tension force exerted on said machining head (10) by each of the tensioners (20) has at least one component in the opposite direction to that of the other tensioner of the same pair.

[0032] Furthermore, in certain embodiments, the control unit (CU) controls the movement of each of the tensioners (20) and the tension of each of the cables (21) so that the forces exerted by the different cables on the machining head (10) compensate each other, preferably so that their sum is zero.

[0033] It is understood that, in the case of at least three cables, the control unit (CU) distributes the cables in the same plane, preferably horizontally. In the case of at least three pairs of cables, the distribution is three-dimensional so that the machining head is stabilized vertically and transversely. Preferably, the tensioners and cables are arranged in pairs so that the tensions they exert on the machining head can be compensated within the same pair, at least for one component, for example vertical. Indeed, by providing pairs comprising an upper tensioner and a lower tensioner, it is easier to ensure that the vertical components are compensated (a tension component upwards and a tension downwards, respectively). Thus, within the same pair, the vertical components are compensated while the horizontal components will be compensated from one pair to another.It is also possible to provide that the pairs rather concern two tensioners diametrically opposed with respect to the head, but it is simpler to design the system with pairs of tensioners aligned vertically. Thus, in the example of [Fig.6], the upper tensioner can move vertically on a rail, but it remains aligned with respect to the lower tensioner which moves vertically on its own rail. In the example of [Fig.7], only the lower tensioner moves vertically on its own rail while the upper tensioner remains stationary, but these tensioners of the same pair preferably remain aligned vertically to facilitate the compensation of tension forces and the piloting by the control unit. In another example not shown, the two tensioners (upper and lower) both move vertically on a single common rail.

[0034] It will be noted that the control unit is described here in a functional manner and that it can take various forms within the reach of those skilled in the art (for example electronic cards and / or computer means comprising at least one processor, possibly with microcontrollers to control the motors, etc.) and the use of several control units cooperating together is also possible. Thus, a stabilization kit comprising a dedicated control unit communicating with the control unit of the machine itself is also envisaged. The present application therefore also relates to a stabilization kit for a machining machine, comprising a stabilizer as described in the present application. In addition, it is understood that the present application also relates to a machining stabilization method or a method for controlling a stabilized machining machine as described in the present application and that, depending on the embodiment variants, it is possible to provide stabilization in only one plane or three-dimensional stabilization (i.e., in the three dimensions of space). In the case of a plane, such a method is implemented by a control unit (CU) carrying out the following steps at each movement of the machining head (10): . - determination of the position of the head (10) of the robotic arm (1) in space, in particular in relation to the base (11), - determination of the inclination of the head (10) of the robotic arm (1) relative to the vertical, - determination, from said position and inclination of the head (10), of the necessary positions of said tensioners (20) so that they are located in the same plane, the inclination of which depends on that of the head, - controlling the displacement means (23) and the adjustable means (22) for tensioning the cables (21) to position said tensioners (20) at said determined necessary positions and provide tension to the cables (21) to stabilize the head (10) in said plane.

[0035] This common stabilization plane (by tensioning) may depend on the position and inclination of the head but also on the type of machining carried out and the resulting forces. In addition, this plane may depend on a possible pivoting machining support (14) on which the part to be machined may be placed, as well known to those skilled in the art and illustrated for example in [Fig.7].

[0036] On the other hand, in the case of three-dimensional stabilization, the control method may take into account the vertical and horizontal components of forces. In this case, the method may include: - determination of the position of the head (10) of the robotic arm (1) in space, in particular in relation to the base (11), - determination of the inclination of the head (10) of the robotic arm (1) relative to the vertical, - determination, from said position and inclination of the head (10), of the necessary positions of said tensioners (20) for mutual compensation between the different components of the tension forces exerted by all the tensioners on the machining head, - control of the displacement means (23) and the adjustable means (22) for tensioning the cables (21) to position said tensioners (20) at said determined necessary positions and provide tension in the cables (21) so that the different forces exerted on the head compensate each other, preferably with a zero resultant.

[0037] The tension of the cables (and their control, as well as possibly the resultant of the tension forces) may be adjusted according to the type of machining in progress and in particular the tools used (cutting, milling, printing, welding tool, etc.) since they do not all have the same torques and do not exert the same forces on the head.In particular, a "hybrid" machining machine is envisaged, including a 3D printing head, to complete the type of operations possible with the machine. Preferably, various types of sensors will be used by the control unit to correctly adjust the various parameters that come into play for stabilization. In particular, at least one tension sensor (e.g., tensiometer) will be present, preferably for each of the cables, in order to check that the correct tension is applied and avoid forcing the robotic arm (1). Furthermore, the stabilizer preferably comprises at least one electronic level arranged at least at the head.The stabilizer will therefore comprise at least one level positioned for example at least on the plate (12), but preferably also on the cables (21), for example near the tensioners, to check the correct inclination of the cables, following the positioning of the tensioners according to the inclination detected at the head. It is understood that the control unit can thus control the various devices using various types of sensors and that the examples provided here are not limiting.

[0038] In certain embodiments, each of said cables (21) is mounted on the head (10) using a fastener (210) free to pivot according to the inclination of the cables (21) relative to the horizontal.Such a fastener may be formed by a pivot (e.g. with a spherical head retained in a housing, allowing movement of the cable in a cone whose apex is centered on this spherical head), but since these are cable ties, this freedom of movement may simply be provided by the cable itself. The use of a pivot will nevertheless limit wear on the cables by subjecting them less to the forces which are concentrated at this fastener.

[0039] In certain embodiments, each of said fasteners (210) is configured to move freely on a plate (12) secured to the head (10), along a circular path centered on said head (10), so that the fasteners (210) are positioned according to the orientation and length of each of the cables (21). Casters are for example provided to facilitate movement on the plate (12) forming for example a crown on which the fasteners are retained, the rollers of which ensure the mobility and solidity of the assembly. Indeed, as the head (10) can move relative to the position of the tensioners (20) on the support (2), in order to allow the tensions exerted by the different cables (the respective length of which is adjusted according to the movements of the head) to be correctly distributed around the head, it is preferable that the position of the fasteners (210) of the cables on the head can adapt automatically to the orientation of the cables, which is preferably obtained simply by the fact that the fasteners move on a common crown or on respective arcs of circles in order to allow a movement of the fixing which remains centered relative to the center of the head.Conversely (and not exclusively of these movements of the fasteners), it may be useful for the tensioners to be movable around the head and not only vertically for the inclination of the cables but also for the orientation of the cables (therefore radially relative to the center of the head). Thus, in certain embodiments, the stabilizer also comprises means (24) for lateral movement of the tensioners (20), to adjust their respective positions around the head (10), for example by moving the posts or the rails on which the carriages move. [Fig.3] and [Fig.5] show illustrative and non-limiting examples of such means (24) of movement. In these examples, the posts move, for example using motorized carriages on rails (24) (arranged on the ground in these examples but they can be on the ceiling and preferably on the ground and the ceiling in order to stiffen the assembly).In these examples, the rails follow a curvilinear path but a rectilinear path is of course also possible. The means (23) for moving the tensioners in height are the only ones necessary for good balancing but their association with such means (24) for lateral (transverse) movement makes it possible to adjust the position of the tensioners in two dimensions and to better distribute the tension forces relative to the head, in particular when the positions potentially taken by the head (10) are likely to interfere with the path of the cables (which can then be moved using these lateral movement means).

[0040] In certain embodiments, said support (2) comprises at least three posts perpendicular to the ground and distributed around said robotic arm (1), preferably equidistant from each other. The number of posts may vary depending on the number of cables (and tensioners, etc.). In general, three cables may be sufficient (for example as illustrated in [Fig.5]), provided that they are correctly distributed around the head (preferably equidistant from each other), but four or more cables may be provided, in particular to obtain even more stability and / or to facilitate integration, in particular in cabins usually housing machining machines. Thus, in certain embodiments not exclusive of those comprising posts, said support (2) comprises at least one wall having a rectangular or square section surrounding said robotic arm (1). In these embodiments, the cables and tensioners are preferably four in number, distributed at the corners of the structure. Illustrative examples of such embodiments are shown in [Fig.l] and [Fig.2] showing a cabin, such as for example a container, housing the machining machine within a support formed of four vertical walls distributed to form a rectangular parallelepiped and provided with reinforcement posts. Reinforcements may also be provided at the top (at the summit or on the roof) of the structure forming the support (2), to stabilize the assembly and in particular to avoid any unwanted movement of the tensioners, for example as shown in an illustrative and non-limiting manner in [Fig.2].

[0041] In other embodiments not illustrated, said support (2) comprises at least one wall having a circular or elliptical cross-section surrounding said robotic arm (1). In this case, the cabin is of circular or elliptical section and the radius may vary according to the reach of the head relative to the base. On the other hand, it is possible that it is not the wall which defines a circular path, but rather that it is the means (24) of transverse movement, for example as shown in an illustrative and non-limiting manner in [Fig. 5]. In this example, three posts move on a circular rail (24) centered on the machine tool. [Fig. 3] represents, in an illustrative and non-limiting manner, another variant where the means (24) of transverse movement are formed by arcs of a circle centered on the machine tool.In fact, whether the system has three or four supports (or more), it is generally not necessary to go all the way around the machine to allow good positioning of the cables. On the other hand, the transverse displacement means (24) can be means of displacement on the walls of the container.

[0042] In certain embodiments, each of said means (23) for moving said tensioners (20) on said support (2) comprises a motorized carriage (230) controlled by said control unit (CU) to move on a rail (231) in order to adjust the height of said tensioner (20) relative to the ground.

[0043] In certain embodiments, said adjustable means (22) for tensioning said cables (21) comprise at least one cable reel controlled by said control unit (CU) and forming said tensioner (20). Such a reel may for example be a ball screw. [Fig. 4] represents an illustrative and non-limiting example of the tensioners (20) with their adjustable tension means (22) and the vertical displacement means (23) comprising a carriage (230) moving on a rail (231).

[0044] It is therefore understood that the present application makes it possible to respond to the problem of stabilizing machining in machine tools. Indeed, at the level of the machining head, different forces can be exerted between the tools used and the part to be machining (torsion, recoil, shocks, vibrations, etc.) and risk causing slight movements of the head, which generally requires oversizing the robotic arm (which is expensive) but is often accompanied, despite everything, by a limitation of the machining precision. By proposing to place the machining head in a "concentric" system of tensions (which converge towards the center, for example the geometric center or preferably the center of gravity) of the machining head, these forces exerted during machining are then compensated. As these forces are generally exerted in the three dimensions of space, the preferred embodiments are those where the tensioners and cables are distributed around the head to compensate for the tensions in the three dimensions of space.Thus, it is possible to provide at least 3 pairs of tensioners distributed on the surface of a sphere (virtual or whose parts are physically formed by suitable structures) centered on the machining head. However, for ease of implementation, it is generally preferable to use more pairs of tensioners, as for example illustrated in figures 6 and 7. In these figures, 4 upper tensioners (and cables) are arranged above the horizontal plane in which the center of the head is located and 4 lower tensioners (and cables) are arranged below this plane. Thus, the different tensioners make it possible to compensate for the forces exerted on the head both vertically and horizontally. Their distribution around the head in a horizontal plane and their height (i.e., their vertical position) allow the control unit to adjust the forces exerted according to the position of the machining head and / or the type of machining in progress.This makes it possible to limit the risks of resulting movements and therefore to improve the precision of the machine and / or to limit its size (and therefore its cost).

[0045] The present application describes various technical features and advantages with reference to the figures and / or to various embodiments. Those skilled in the art will understand that the technical features of a given embodiment may in fact be combined with features of another embodiment unless the opposite is explicitly mentioned or it is obvious that these features are incompatible or that the combination does not provide a solution to at least one of the technical problems mentioned in the present application. In addition, the technical features described in a given embodiment may be isolated from the other features of this embodiment unless the opposite is explicitly mentioned.

[0046] Detailed list of references in the figures: 1 robotic arm 10 head 11 base 12 platinum CU control unit 2 supports 20 tensioner 21 cable 210 attachment 22 adjustable tension means 23 ways to move the tensioner on the support 230 trolley 231 rail 24 ways to move the support

Claims

Claims

1. Machining machine comprising at least one robotic arm (1) having a first end mounted on a base (11) and a second end provided with a head (10) carrying at least one machining tool, said robotic arm (1) being articulated and motorized to move the head (10) in various positions and inclinations relative to parts to be machined, according to parameters determined by at least one control unit (CU) controlling the movement of said head (10) during machining, characterized in that it comprises a stabilizer also controlled by said control unit (CU) and comprising: - at least one support (2) mounted integral with the ground and provided with at least three tensioners (20) distributed around said head (10), preferably equidistant from each other, - at least three cables (21) connecting said head (10) to said tensioners (20), - adjustable means (22) for tensioning said cables (21) between said head (10) and said tensioners (20),- means (23) for moving said tensioners (20) on said support (2), said control unit (CU) controlling the individual movement of each of the tensioners and the tension of each of the cables (21) as a function of said positions and inclinations of said head (10) during machining.,

2. Machining machine according to claim 1, characterized in that: - the tensioners (20) and the cables (21) are configured in pairs, with at least three pairs distributed around said machining head (10), - within each pair, the tensioners (20) are arranged on either side of the machining head (10), so that the tension force exerted on said machining head (10) by each of the tensioners (20) has at least one component in the opposite direction to that of the other tensioner of the same pair.

3. Machining machine according to any one of claims 1 and 2, characterized in that the control unit (CU) controls the movement of each of the tensioners (20) and the tension of each of the cables (21) so that the forces exerted by the different cables on the machining head (10) compensate each other, preferably so that their sum is zero.

4. Machining machine according to any one of claims 1 to 3, characterized in that each of said cables (21) is mounted on the head (10) using a clip (210) free to pivot depending on the inclination of the cables (21) relative to the horizontal.

5. Machining machine according to claim 4, characterized in that each of said fasteners (210) is configured to move freely on a plate (12) secured to the head (10), along a circular path centered on said head (10), so that the pivots (210) are positioned according to the orientation and length of each of the cables (21).

6. Machining machine according to any one of claims 1 to 5, characterized in that said support (2) comprises at least one wall having a circular or elliptical cross-section surrounding said robotic arm (1).

7. Machining machine according to any one of claims 1 to 35 characterized in that said support (2) comprises at least one wall having a rectangular or square section surrounding said robotic arm (1).

8. Machining machine according to any one of the preceding claims, characterized in that said support (2) comprises at least three posts perpendicular to the ground and distributed around said robotic arm (1), preferably equidistant from each other.

9. Machining machine according to any one of the preceding claims, characterized in that each of said means (23) for moving said tensioners (20) on said support (2) comprises a motorized carriage (230) controlled by said control unit (CU) to move on a rail (231) in order to adjust the height of said tensioner (20) relative to the ground.

10. Machining machine according to any one of the preceding claims, characterized in that the stabilizer also comprises means (24) for lateral movement of the tensioners (20), to adjust their respective positions around the head (10).

11. Machining machine according to any one of the preceding claims, characterized in that said adjustable means (22) for tensioning said cables (21) comprise at least one cable winder controlled by said control unit (CU) and forming said tensioner (20).

12. Stabilization kit for a machining machine, characterized in that it comprises a stabilizer according to any one of the preceding claims.

13. Method for controlling a machining machine according to any one of the Claims 1 to 11, characterized in that it is implemented by a control unit (CU) carrying out the following steps at each movement of the machining head (10): - determination of the position of the head (10) of the robotic arm (1) in space, in particular in relation to the base (11), - determination of the inclination of the head (10) of the robotic arm (1) relative to the vertical, - determination, from said position and inclination of the head (10), of the necessary positions of said tensioners (20) so that they are located in the same plane, the inclination of which depends on that of the head, - control of the displacement means (23) and of the adjustable means (22) for tensioning the cables (21) to position said tensioners (20) at said determined necessary positions and provide tension of the cables (21) to stabilize the head (10) in said plane.

14. Method for controlling a machining machine according to any one of claims 2 to 11, characterized in that it is implemented by a control unit (CU) carrying out the following steps at each movement of the machining head (10): - determination of the position of the head (10) of the robotic arm (1) in space, in particular in relation to the base (11), - determination of the inclination of the head (10) of the robotic arm (1) relative to the vertical, - determination, from said position and inclination of the head (10), of the necessary positions of said tensioners (20) for mutual compensation between the different components of the tension forces exerted by all the tensioners on the machining head, - control of the displacement means (23) and of the adjustable means (22) for tensioning the cables (21) to position said tensioners (20) at said determined necessary positions and provide tension in the cables (21) so that the different forces exerted on the head compensate each other, preferably with a zero resultant.

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