MECHANISM FOR CONTROLLING THE RECIPROCATING MOVEMENT OF WEFT CARRYING GRIPPERS IN A WEAVING LOOM

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an improved mechanism for controlling the reciprocating movement of the carrying and drawing grippers of a weaving loom, by which weft transport and insertion inside the shed is performed.

[0002] The invention relates in particular to a mechanism of this type in which the conversion of the continuous circular motion of the main motor of the loom, in a reciprocating rectilinear movement of the grippers, comprises a coupling between a slider, provided with a reciprocating rectilinear movement, and a variable-pitch worm screw, driven in a reciprocating rotary movement by said slider.

[0003] In particular, the invention relates to a device of this type which, in comparison to similar devices already on the market, exhibits a lower friction, a reduction of the passive loads and therefore an improved efficiency of conversion of the reciprocating movement of the slider in a reciprocating rotary movement of the worm screw.

BACKGROUND ART

[0004] Weaving looms are normally classified into several major categories according to the system with which the weft is inserted into the shed formed by the warp. The present invention falls into the category of shuttleless looms and, specifically, of gripper looms. As it is well known by those skilled in the art, in this type of looms the weft is carried into the shed and until the middle of the fabric being formed by a carrying gripper, while a corresponding drawing gripper moves from the other end of the shed up to the middle of the fabric. In this position the weft yarn exchange between the two grippers takes place and thereafter the two grippers return back in their starting positions out of the shed, thus achieving the complete insertion of the weft into the shed.

[0005] The weft thus inserted in the shed is then beaten up against the fabric being formed, thanks to the reciprocating movement of a reed which is mounted on the upper end of the so-called sley, an oscillating element that lies across the width of the loom and is hinged on the basement thereof.

[0006] Therefore, in this type of looms there is the need to convert the continuous rotary motion of the main rotation shaft of the loom in a rectilinear reciprocating movement of the grippers, which movement occurs in a direction perpendicular to the warp and therefore usually parallel to the axis of the main shaft of the loom.

[0007] The currently most advanced solution to this problem is the one disclosed by US-4,052,906 patent. In fact, this document discloses a particular application of a dual slider/worm screw assembly to control the reciprocating rotary movement of respective toothed gears of large diameter, each of them driving, in turn, the reciprocating movement of the two grippers of the loom, by means of perforated flexible straps engaging the teeth of said gears. The slider of said assembly, which performs the function of a nut, is drawn into a rectilinear reciprocating movement by a traditional rod/crank device controlled by the rotary motion of the main axis of the loom, thanks to guide means of the same which prevent any rotation thereof. Each worm screw is preferably a variable-pitch screw, free to rotate on bearings which also prevent any axial displacement of the same, said screw having an axis perpendicular to the main rotation shaft of the loom, and being coaxial to a respective one of said toothed gears which is keyed at one of its ends.

[0008] The reciprocating rectilinear movement imparted to the slider-nut is converted into reciprocating rotary movement of the worm screw, thanks to the presence of pairs of wheels or rollers idle-pivoted on the slider and sliding on the flanks of each of the threads of said worm screw.

[0009] This solution has allowed to obtain extraordinary advantages compared with existing solutions, especially in terms of reduction of clearances, compactness of the mechanism and high possibility of adjusting at will the law of motion of the grippers - in particular lower speeds in the steps of gripping/releasing and exchanging the weft and higher speeds during the carrying step of the weft - by varying the variable-pitch thread shape of the worm screw. This solution of course made it possible to significantly increase the working speed of the looms, without encountering the problems associated with previous traditional mechanical solutions based on levers and cams. The reduction of clearances has in fact allowed to keep always constant, even at different speeds of the loom, the arrival point of the grippers at the middle of the shed, i.e. the position where the weft exchange among the grippers takes place. The higher adjustability of the law of motion of the grippers - which can be obtained in this solution thanks to the variable pitch of the control worm screw - has then allowed to keep the travel speed of the same low enough in the two steps which are more critical for weft integrity, namely at the time of the first catching of the weft by the carrying gripper and at the time of the exchange of said weft with the drawing gripper.

[0010] However, the same loom speed increase made possible by the adoption of the gripper control system described above also resulted in some problems in this solution and, in particular, an excessively fast wear of the wheels or rollers through which the reciprocating movement of the slider is transferred to the worm screw. At such high speeds, in fact, reciprocating displacement and rotation of the coupled elements is very rapid and, especially during movement reversal steps, a skidding of thread-following rollers on the thread of the worm screw can occur. This skidding is of course responsible for a premature wear of the rollers, especially taking into account the fact that the contact between the rollers and the thread of the screw is a substantially linear contact and therefore characterized by high specific loads.

[0011] A solution to this new problem has been proposed in the following patent EP-0164627, in which the pairs of wheels or rollers of the original solution were replaced by pairs of sliding blocks, so that the contact of these elements with the screw thread was no longer a linear contact, as in the original version of the device, but a surface contact. Each pair of sliding blocks is accommodated inside a bush, integral with the slider, and each sliding block is individually pivoted within said bush, along an axis of rotation corresponding to the side inclination of the screw thread, so that the sliding block sliding surface remains substantially parallel to the side wall of the thread when the inclination of said thread along the variable-pitch screw changes.

[0012] The adoption of this new sliding block guide device has thus brought to a marked improvement in the duration of the same sliding blocks compared to previous guide rollers, which improvement allowed a further increase of the speed of the loom. However, the reciprocating rotation that the sliding blocks perform around their own support pin, to adapt to the continuous change of the angle of the variable-pitch screw thread, necessarily causes a lateral misalignment of the same with respect to the straight line joining their centres of rotation. When designing this device, the angle of the pair of sliding blocks with respect to the supporting bush is thus determined in such a way that this misalignment is zero in correspondence of an intermediate value of the inclination of the thread of the variable-pitch screw, so as to make as low as possible the value of such misalignment, respectively at one side and at the opposite side, when the thread of the screw has inclinations greater or less than the above said intermediate value. The presence of this variable misalignment between the opposite sliding blocks does of course give rise to a corresponding torque between the reaction forces arising between the sliding blocks and the thread and causes a greater interaction between the sliding blocks and the thread and therefore a greater wear, compared to an ideal condition in which sliding blocks could be always perfectly aligned with each other. Therefore, the need is still felt for an improvement of the duration of the useful life of sliding blocks and a reduction of the extent of mechanical interactions between the screw and sliding blocks, in order to increase the efficiency of the guide mechanism and to reduce the noise thereof.

ABSTRACT DESCRIPTION OF THE INVENTION

[0013] The object of the present invention is therefore to provide a mechanism for controlling the movement of the grippers of a weaving loom which overcomes the above mentioned drawback and makes it possible to further improve the efficiency of the above-described slider/worm screw mechanical coupling.

[0014] This object is achieved through an improved mechanism having the features defined in claim 1. Preferred additional features of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further features and advantages of the improved mechanism for controlling the grippers of a weaving loom will anyhow become more evident from the following detailed description of a preferred embodiment of the same, given by mere way of non-limiting example and illustrated in the accompanying drawings, wherein:

Fig. 1 is a perspective view of the general structure of the two control assemblies of the grippers, which illustrates the essential constituent elements of the improved control mechanism of the grippers according to the present invention;

Fig. 2 is an exemplary perspective view of the coupling between a worm screw and a pair of sliding blocks according to the prior art disclosed by the above cited patent EP-0164627;

Figs. 3A, 3B and 3C are front views of the coupling of Fig. 2 in three different positions of the variable-pitch screw, which illustrate the different possible misalignments between the sliding blocks;

Fig. 4 is an exemplary perspective view of the coupling between a worm screw and a dual single-piece sliding block according to the present invention;

Figs. 5A, 5B and 5C are front views of the coupling of Fig. 4, in the same different positions of the variable-pitch screw of Fig. 2, illustrating the constant perfect alignment of the two opposed portions of the single-piece sliding block; and

Fig. 6 is an enlarged-scale and perspective view of an embodiment of the dual single-piece sliding block according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0016] The control mechanism of the grippers of the present invention incorporates, as said in the introductory part of the present description, the general structure of the known control assemblies. Such assemblies, illustrated schematically in Fig. 1, thus each comprise mechanical elements apt to convert the continuous circular motion of a main shaft A of the loom (of which only the two terminal lengths are shown for easiness) in a rectilinear reciprocating movement of the grippers according to a path parallel to the axis of the main shaft A.

[0017] Such mechanical elements comprise, in particular:

• a crank 1, integral with the shaft A, on which a connecting rod 2 is articulated, apt to determine, through the small end of the connecting rod 2a, the reciprocating rectilinear movement of a slider 3 along a fixed slide 4, in a direction perpendicular to the axis of shaft A:
• a variable-pitch worm screw 5, free to rotate around its own longitudinal axis on suitable bearings that prevent any axial displacement thereof, coupled to the slider 3 by means of pairs of opposing sliding blocks P (best illustrated in Figs. 2 and 3), pivotally attached to the slider 3, to determine the reciprocating rotary movement of a toothed gear D, keyed to and coaxial with the worm screw 5;
• a flexible strap N, provided with holes F on at least part of its length, adapted to engage with said holes the teeth of the toothed gear D to cause the reciprocating rectilinear movement of a weft inserting gripper, fixed to the free end Np of said strap N, in a direction parallel to the axis of shaft A.

[0018] In the more advanced prior art solution, the operation of which is schematically illustrated in Figs. 2 and 3 with reference to a two-threaded worm screw 5, the coupling between said worm screw and the slider comprises two pairs of sliding blocks P, each pair of sliding blocks being housed inside a respective bush integral to said slider. In particular, in said known art, two mutually opposite bushes are provided, in each of which two opposing sliding blocks P are pivoted around concurrent axes X lying in a plane A, having a set fixed inclination, crosswise the thread of the worm screw 5 . The X axes are arranged symmetrically with respect to the line of intersection of plane A with a plane B perpendicular to the axis of the worm screw 5, and form between them an angle equal to the thread section angle, so that the contact surfaces of the four sliding blocks P can operate simultaneously in sliding contact on the two opposite flanks of the two threads of the worm screw 5.

[0019] In this construction of the prior art, and as clearly illustrated in Figs. 3, while the slider moves with reciprocating rectilinear movement along the variable-pitch screw 5, the two sliding blocks P oscillate freely, each around its own pivoting axis X - due to the sliding contact with the thread of the screw 5 which has a variable inclination caused by the continuous variability of the pitch - always remaining with their surface of contact parallel to the wall of said thread.

[0020] As an example of the different positions that the sliding blocks P can take during the movement of the slider, Fig. 3A shows a portion of the screw 5, having a long pitch and thus a smaller angle with respect to the longitudinal axis H of the screw 5, Fig. 3C represents a short-pitch portion and thus with a larger angle with respect to said axis, and Fig. 3B shows an intermediate-pitch portion. These portions are distributed along the screw as a function of the law of motion that the grippers are provided with, and that in general, as already mentioned in the introductory part of the present description, provides a lower speed at the beginning and end of the stroke of the gripper and a higher speed in the intermediate portion of its path.

[0021] When looking at these figures, it is immediately possible to note that in the above said different positions of the slider, and then of the sliding blocks P, the inclination of the plane A - of which Fig. 3 shows the track in the drawing plane - remains constant. Therefore, while in one of said positions (for example, in the drawings, the one represented in Fig. 3B) this inclination is exactly perpendicular to the thread of the variable-pitch screw 5, in the other positions (illustrated in Fig. 3A and 3C) it proportionally deviates from perpendicularity. Despite this variation of the relative position between the plane A and the worm screw 5, as the slider position along the screw 5 changes, the parallelism of contact surfaces of the sliding blocks P with respect to the flanks of the thread is always maintained, thanks to the rotation of the sliding blocks P around their own pins of axis X and thus with respect to the bush on which they are pivoted. However, this rotation involves a continuous misalignment of sliding blocks P - which have already been discussed in the introductory part of the present description - said sliding blocks being therefore perfectly opposed, and therefore balanced in the passive forces that are loaded on the thread of the screw, only in a particular working position corresponding to a certain pitch of the screw 5 (Fig. 3B), while in all other positions (Figs. 3A and 3C) the sliding blocks P have a variable degree of misalignment, and then said passive forces give rise to the formation of resistant torques which increase the energy losses due to friction and, consequently, accelerate the wear of the sliding blocks P.

[0022] Figs. 4 and 5 finally represent the constructive solution proposed by the present invention, according to which the sliding blocks 6 are assembled on the slider 3 according to a fully innovative design, which allows to brilliantly solve the drawback described above. According to this solution, in fact, each pair of sliding blocks 6 is securely fixed inside a bush 7, preferably of cylindrical shape (shown schematically in Fig. 4 in dashed lines and in greater detail in Fig. 6), while the whole bush is axially pivoted on the slider 3 according to an axis Z which is the intersection between a plane A, perpendicular to the screw thread, and a plane B, perpendicular to the axis H of the screw 5. The axis Z about which the bush 7 is free to rotate is thus simultaneously perpendicular to the screw thread 7 and to the axis H of said screw.

[0023] The two sliding blocks 6 preferably have a symmetrical configuration with respect to the plane A and are positioned on opposite sides with respect to the axis Z and mutually spaced apart at a sufficient extent to allow them to closely fit the thread of screw 5 between them. The sliding blocks 6, and in particular their contact surfaces with the flanks of said thread, preferably extend for the entire width of the bush 7 and are inclined and shaped so as to fit exactly the inclination and shape of said flanks, as schematically represented in Figs. 4 and 6. According to this provision, the contact surface of sliding blocks 6 with the thread flanks of the worm screw 5 is maximised, and then correspondingly the specific load between these elements is reduced.

[0024] The assembly of the sliding blocks 6 and the bush 7 thus forms a dual single-piece sliding block T, the double contact surface of which extends substantially in correspondence of a diameter of said cylindrical bush 7, and which is axially pivoted on the slider 3 along the axis Z. Bush pivoting can be achieved by a standard axial pin integral to the bush 7 or, alternatively, it is the same bush 7 which, with its cylindrical side wall, forms a large-diameter pin housed in a mating cylindrical hole formed in the slider 3.

[0025] A similar dual single-piece sliding block T is obviously pivoted on the slider 3, about the same axis (Z), on the opposite side of the worm screw 5, and is adapted to cooperate with the second thread of the screw. A third single-piece sliding block T may of course be provided in case of use of a three-threaded worm screw 5.

[0026] Thanks to this particularly simple and effective construction, when the slider 3 moves along the screw 5, the sliding contact of the sliding blocks 6 on the flanks of the threads causes the rotation of each dual single-piece sliding block T about the axis Z, thus continuously adapting the inclination of the dual single-piece sliding block T with respect to the thread of the screw 5. Since the sliding blocks 6 are mounted on a single support, i.e. the bush 7, their mutual position obviously does not change during the movement of the slider 3 and the consequent rotation of the bush 7; the contact surfaces of the opposed sliding blocks 6 therefore remain constantly parallel and aligned between each other, thus avoiding completely the misalignment problem posed by the sliding blocks P of the known devices and thus fully achieving the object of the invention.

[0027] The different positions that the dual single-piece sliding block T takes on in correspondence of the various portions of the variable-pitch screw 5 are illustrated schematically in Figs. 5A, 5B and 5C. These figures clerly show how in this case the plane A, thanks to the particular construction described above, is maintained always perpendicular to both the thread and the contact surface of the sliding blocks 6, in all the different positions of the screw, and then correspondingly varying its inclination with respect to the longitudinal axis H of the screw 7.

[0028] The solution described above, in addition to having solved the problem of misalignment between opposed sliding blocks P of the known art, also involves various other advantages and, in particular, a substantial stress reduction on the slider 3 and the screw 5 and thus a greater useful life of these components. In fact, the dual single-piece sliding block T according to the present invention provides a large surface area of sliding contact between the sliding blocks 6 and the screw 5, and then a low specific contact load. In addition, the large surface of rotational contact formed between the dual single-piece sliding block T and the slider 3, in particular when the same bush 7 performs the function of pin, determines a quite lower specific load in comparison with the prior art solution illustrated above, which entailed the use of four small-diameter pins, for the separate pivoting of each sliding block P, said pins thus being more easily subject to wear and deformation.

[0029] The particular structure of the dual single-piece sliding block T of the present invention, thanks to the reduced overall dimensions of the support structure, also allows to decrease the value of the vertex angle of the thread cross section of the worm screw 5, which is substantially triangular, to values less than 15°, resulting in an increase of the transmittable torque in the slider/worm screw coupling, thanks to the increase of the active component (parallel to the thread) of the transmitted force, the lever arm bein the same. For the same reason, the passive component (perpendicular to the thread) of the force transmitted in the coupling - in addition to being perfectly opposed between the two sliding blocks 6 housed in a single bush 7, thanks to their constant alignment - also shows a reduced absolute value with respect to the sliders of the prior art and then the slider 3 undergoes a reduced stress. The control mechanism of the present invention is therefore apt to offer a better overall mechanical efficiency with respect to known mechanisms.

[0030] In terms of maintenance, it can be finally observed that the very compact conformation of the dual single-piece sliding block T allows the use of a suitable hydrostatic lubrication system, apt to ensure the formation of a continuous meatus of lubricating substance on the coupling between the sliding blocks 6 and the worm screw 5, even in the positions of movement reversal of the slider 3 and in the toughest working conditions. This allows to further reduce the wear of the sliding blocks 6, with a considerable advantage in terms of lower cost of replacement parts and fewer interruptions of the weaving operations for replacement of such parts.

[0031] It should be understood, however, that the invention is not to be considered as limited by the particular arrangements illustrated above, which represent only exemplary embodiments of the same, but different variants are possible, all within the reach of a person skilled in the art, without departing from the scope of the invention itself, which is exclusively defined by the following claims.

Claims

1. Mechanism for controlling the reciprocating movement of the grippers in a shuttleless weaving loom, comprising a slider (3) provided with an reciprocating rectilinear movement, a variable-pitch worm screw (5) drawn by such slider (3) into an reciprocating rotary movement, a toothed gear (D) coaxial and integral with said variable-pitch worm screw (5), and perforated flexible straps (N) which engage, on one end, with the teeth of said gear and which control, with the opposite end, said grippers and wherein the movement from said slider (3) to the variable-pitch worm screw (5) is transferred through a coupling comprising multiple pairs of opposite sliding blocks (P, 6), pivoted on said slider (3) and slidable on the opposite lateral surfaces of the threads of said variable-pitch worm screw (5), characterised in that said pairs of sliding blocks (6) are integral to each other and with a common support pivoted idle on the slider (3) according to an axis (Z) orthogonal to the axis (H) of the variable-pitch worm screw (5).

2. Control mechanism as in claim 1, wherein said common support of the sliding blocks (6) consists of a cylindrical bush (7), the longitudinal axis of which coincides with the pivoting axis (Z) of said bush (7) on the slider (3).

3. Control mechanism as in claim 2, wherein said bush (7) comprises a coaxial pin for pivoting on the slider (3).

4. Control mechanism as in claim 2, wherein said bush (7) is directly pivoted, through its own lateral cylindrical surface, in a corresponding hole formed in said slider (3).

5. Control mechanism as in claims 3 or 4, wherein said sliding blocks (6) are symmetrical with respect to a plane (A) passing through the pivoting axis (Z) of the bush (7) and perpendicular to the thread of the variable-pitch worm screw (5).

6. Control mechanism as in claim 5, wherein the contact surfaces of the sliding blocks (6) with the flanks of said thread extend across the entire width of said bush (7) and are inclined and shaped according to the inclination and shape of said flanks.

7. Control mechanism as in claim 6, wherein said contact surfaces of the sliding blocks (6) substantially extend in correspondence of a diameter of said bush (7).

8. Control mechanism as in any one of the preceding claims, wherein the thread of the variable-pitch worm screw (5) has a substantially triangular cross section, the vertex angle thereof being lower than 15°.

9. Control mechanism as in any one of the preceding claims, furthermore comprising a hydrostatic lubrication system of the thin gap formed between said sliding blocks (6) and the flanks of the thread of the variable-pitch worm screw (5).

Ansprüche

1. Mechanismus zum Steuern der Hin- und Herbewegung der Greifer in einer schiffchenlosen Webmaschine, umfassend einen Schieber (3), der eine hin- und hergehende geradlinige Bewegung ausführt, eine von einem solchen Schieber (3) in eine hin- und hergehende Drehbewegung gezogene Schneckenschraube (5) mit variabler Steigung, ein Zahnrad (D), das koaxial und integral mit der Schneckenschraube mit variabler Steigung (5) ist, und perforierte flexible Bänder (N), die an einem Ende mit den Zähnen des Zahnrads in Eingriff stehen und die mit dem gegenüberliegenden Ende die Greifer steuern, und wobei die Bewegung von dem Schieber (3) zu der Schneckenschraube (5) mit variabler Steigung durch eine Kupplung übertragen wird, die mehrere Paare von gegenüberliegenden Gleitblöcken (P, 6) umfasst, die an dem Schieber (3) angelenkt sind und auf den gegenüberliegenden Seitenflächen der Gewindegänge der Schneckenschraube (5) mit variabler Steigung verschiebbar sind, dadurch gekennzeichnet, dass die Paare von Gleitblöcken (6) integral miteinander und mit einer gemeinsamen Lagerung sind, die auf dem Schieber (3) entsprechend einer Achse (Z) orthogonal zu der Achse (H) der Schneckenschraube (5) mit variabler Steigung frei verschwenkbar ist.

2. Steuermechanismus nach Anspruch 1, bei dem die gemeinsame Lagerung der Gleitblöcke (6) aus einer zylindrischen Buchse (7) besteht, deren Längsachse mit der Schwenkachse (Z) der Buchse (7) an dem Schieber (3) zusammenfällt.

3. Steuermechanismus nach Anspruch 2, wobei die Buchse (7) einen koaxialen Stift zum Schwenken auf dem Schieber (3) aufweist.

4. Steuermechanismus nach Anspruch 2, bei dem die Buchse (7) direkt durch ihre eigene zylindrische Mantelfläche in ein entsprechendes Loch geschwenkt, das in dem Schieber (3) ausgebildet ist.

5. Steuermechanismus nach Anspruch 3 oder 4, bei dem die Gleitblöcke (6) bezüglich einer durch die Schwenkachse (Z) der Buchse (7) verlaufenden Ebene (A) symmetrisch und senkrecht zu den Gewindegängen der Schneckenschraube (5) mit variabler Steigung sind.

6. Steuermechanismus nach Anspruch 5, dadurch gekennzeichnet, dass sich die Kontaktflächen der Gleitblöcke (6) mit den Flanken der Gewindegänge über die gesamte Breite der Buchse (7) erstrecken und gemäß der Neigung und Form der Flanken geneigt und geformt sind.

7. Steuermechanismus nach Anspruch 6, wobei sich die Kontaktflächen der Gleitblöcke (6) im Wesentlichen in Entsprechung zu einem Durchmesser der Buchse (7) erstrecken.

8. Steuermechanismus nach einem der vorhergehenden Ansprüche, bei dem die Gewindegänge der Schneckenschraube (5) mit variabler Steigung einen im Wesentlichen dreieckigen Querschnitt aufweisen, dessen Scheitelwinkel kleiner als 15° ist.

9. Steuermechanismus nach einem der vorhergehenden Ansprüche, ferner umfassend ein hydrostatisches Schmiersystem des zwischen den Gleitblöcken (6) und den Gewindeflanken der Schneckenschraube (5) mit variabler Steigung gebildeten dünnen Spaltes.

Revendications

1. Mécanisme pour commander le mouvement de va-et-vient de pinces dans un métier à tisser sans navette, comprenant un coulisseau (3) ayant un mouvement de va-et-vient rectiligne, une vis sans fin à pas variable (5) tirée par ledit coulisseau (3) en un mouvement rotatif alternatif, une roue dentée (D) coaxiale à ladite vis sans fin à pas variable (5) et d'un seul tenant avec elle, et des courroies souples perforées (N) qui s'engagent, d'une part, avec les dents de ladite roue dentée et qui commandent, avec l'extrémité opposée, lesdites pinces et dans lequel le mouvement dudit coulisseau (3) à la vis sans fin à pas variable (5) est transféré par le biais d'un accouplement comprenant de multiples paires de blocs coulissants opposés (P, 6), pivotant sur ledit coulisseau (3) et aptes à coulisser sur les surfaces latérales opposées des filets de vis de ladite vis sans fin à pas variable (5), caractérisé en ce que lesdites paires de blocs coulissants (6) sont formées d'un seul tenant et comportent un support commun pivotant fou sur le coulisseau (3) suivant un axe (Z) perpendiculaire à l'axe (H) de la vis sans fin à pas variable (5).

2. Mécanisme de commande selon la revendication 1, dans lequel ledit support commun des blocs coulissants (6) consiste en une douille cylindrique (7), dont l'axe longitudinal coïncide avec l'axe de pivotement (Z) de ladite douille (7) sur le coulisseau (3).

3. Mécanisme de commande selon la revendication 2, dans lequel ladite douille (7) comprend une tige coaxiale pour pivotement sur le coulisseau (3).

4. Mécanisme de commande selon la revendication 2, dans lequel ladite douille (7) pivote directement, par sa propre surface cylindrique latérale, dans un trou correspondant formé dans ledit coulisseau (3).

5. Mécanisme de commande selon la revendication 3 ou 4, dans lequel lesdits blocs coulissants (6) sont symétriques par rapport à un plan (A) passant par l'axe de pivotement (Z) de la douille (7) et perpendiculaire au filet de vis de la vis sans fin à pas variable (5).

6. Mécanisme de commande selon la revendication 5, dans lequel les surfaces de contact des blocs coulissants (6) avec les flancs dudit filet de vis s'étendent sur toute la largeur de ladite douille (7) et sont inclinées et conformées en fonction de l'inclinaison et de la forme desdits flancs.

7. Mécanisme de commande selon la revendication 6, dans lequel lesdites surfaces de contact des blocs coulissant (6) s'étendent sensiblement en correspondance d'un diamètre de ladite douille (7).

8. Mécanisme de commande selon l'une quelconque des revendications précédentes, dans lequel le filet de vis de la vis sans fin à pas variable (5) a une section transversale sensiblement triangulaire, son angle de sommet étant inférieur à 15°.

9. Mécanisme de commande selon l'une quelconque des revendications précédentes, comprenant, en outre, un système de lubrification hydrostatique du mince espace formé entre lesdits blocs coulissants (6) et les flancs du filet de vis de la vis sans fin à pas variable (5).

Drawing