EP1852531B1 - Mechanism for forming a shed, weaving loom equipped with such a mechanism and method of selecting the mobile hooks of such a mechanism - Google Patents

Abstract

The mechanism for forming a shed (7) on a jacquard weaving loom useful in carpet and velvet, comprises movable hooks (13) between a position of upper and lower dead points. The hooks are moved by a knife (14), and are immobilized by a selector device. The hooks comprise a body (20) equipped by a nozzle (202) to give a support on the corresponding knife, and a flexible harness fixed on the body with possibilities of relative clearance and to interact with a retained lever so that a selection lever form a rail for sliding a portion of an elastic harness. The mechanism for forming a shed (7) on a jacquard weaving loom useful in carpet and velvet, comprises movable hooks (13) between a position of upper and lower dead points. The hooks are moved by a knife (14), and are immobilized by a selector device. The hooks comprise a body (20) equipped by a nozzle (202) to give a support on the corresponding knife, and a flexible harness fixed on the body with possibilities of relative clearance and to interact with a retained lever so that a selection lever form a rail for sliding a portion of an elastic harness when the hook reaches a vicinity of upper dead point in which the retained lever belongs to the selector device. A component (FA+ FB + FC) is parallel to a displacement direction of the movable hooks of the resultant efforts (RA, RB, RC) applied on the flexible harness when the harness comes in contact with the rail at the vicinity of upper dead point of its trajectory and at starting point of the its descending displacement. The selection lever is directed downwards. The rail extends according to its average direction which makes an angle of 8-15[deg] with respect to the displacement direction of the hook, and is equipped with undulations. The rail is in a tangential curved form, which makes an angles of 8-12[deg] in relation to the displacement direction of the hook. The average direction of lower and upper rails form a first and a second angle with the displacement direction of the hook respectively. The first angle has a value of 5-12[deg], and the second angle has a value of 7-15[deg]. Independent claims are included for: (1) a weaving loom; and (2) a process of selecting a movable hooks for forming a shed on a jacquard loom.

Description

The invention relates to a shedding mechanism and to a loom equipped with such a mechanism. The invention also relates to a method for selecting the movable hooks of such a mechanism.

In a Jacquard loom, a shedding mechanism selectively raises heddles, each comprising an eyelet through which a warp thread passes, which yarn is located, depending on the position of a hook to which the yarn is attached. upper end of the bar, above or below a weft yarn moved by the loom. Such a known mechanism, for example of EP-A-1,413,657 comprises movable hooks each provided with a lateral nose capable of cooperating with knives animated vertical reciprocating movements in opposition of phase. Each mobile hook is equipped with a flexible metal blade for interacting with a retaining lever belonging to the selection device, which gives overall satisfaction. In addition, an elastic stop is disposed on the path of the movable hooks when they reach the vicinity of the top dead center of their trajectory. In accordance with the technical teaching of EP-A-0 823 501 this movable stop overcomes the frictional forces exerted on the movable hook when it begins its downward movement, which avoids having to oversize the return springs of the movable hooks. Such an elastic stop has the effect of suddenly overloading the shedding mechanism when the movable hooks are moved upwards, near the top dead center of their respective trajectories. Indeed, these movable hooks all meet substantially simultaneously the corresponding stops which are loaded by a prestressed compression spring. In addition, this elastic stop has a cost, which decreases the overall economic performance of a mechanism incorporating such a stop.

It is these drawbacks that the invention intends to remedy more particularly by proposing a new mechanism for forming the shed in which the direction of movement of the movable hooks can easily be reversed in the vicinity of the top dead center of their respective trajectory, without excessive overloading of the drive means of the knives and with a reasonable cost.

For this purpose, the invention relates to a mechanism for forming the shed on a Jacquard weaving loom, this mechanism comprising movable hooks each displaced by a knife, between a top dead center position, in or near which each hook can be immobilized by a selection device, and a bottom dead center position, each movable hook comprising a body, provided with a spout intended to bear against the corresponding knife, and a flexible blade, fixed on this body with possibility of relative movement and intended to interact with a retaining lever belonging to the selection device, while the selection lever forms a sliding ramp of a portion of the elastic blade when the hook is moved in the vicinity of its position of top dead center. This mechanism is characterized in that the sliding ramp of the selection lever is shaped so that the component parallel to the direction of movement of the hook of the resultant of the forces applying to the flexible blade when it is in contact with the ramp, near the top dead center of its trajectory and at the beginning of its descent movement, is directed downwards.

In the sense of the present invention, the bottom of the mechanism corresponds to the side of this mechanism facing the crowd when the mechanism is installed above the loom, in normal configuration of operation. The top of the mechanism is defined as the opposite of the bottom of this mechanism. In addition, an upper portion of the mechanism is disposed above a lower portion of the mechanism, i.e. the opposite of the lower portion with respect to the shed of the loom in a normal configuration. installation of the mechanism.

Thanks to the invention, the sliding ramp of the selection lever makes it possible to exert on the flexible blade a downward force which compensates for the friction forces experienced by the flexible blade, which makes it possible to dispense with an elastic stop of the type of EP-0 823 501 .

• La rampe s'étend selon une direction moyenne qui fait un angle compris entre 5 et 15° par rapport à la direction de déplacement du crochet, alors que la rampe est pourvue d'ondulations.
• L'angle précité est avantageusement compris entre 8 et 15°.
• La rampe est courbe, avec des tangentes qui forment, par rapport à la direction de déplacement du crochet, des angles compris entre 5 et 15°. Ces angles sont avantageusement compris entre 8 et 12°.
• La rampe peut être pourvue d'ondulations.
• La rampe se décompose en une partie inférieure de rampe, dont la direction moyenne forme un premier angle avec la direction de déplacement du crochet, et une partie supérieure de rampe, située au-dessus de la partie inférieure de rampe et dont la direction moyenne forme un deuxième angle avec la direction de déplacement du crochet, le deuxième angle ayant une valeur supérieure à celle du premier angle. En pratique, le premier angle peut avoir une valeur comprise entre 5 et 12°, alors que le deuxième angle a une valeur comprise entre 7 et 15°.

According to advantageous but non-mandatory aspects of the invention, such a mechanism may incorporate one or more of the following features:

• The ramp extends in an average direction that is at an angle between 5 and 15 ° relative to the direction of movement of the hook, while the ramp is provided with corrugations.
• The aforementioned angle is advantageously between 8 and 15 °.
• The ramp is curved, with tangents which form, relative to the direction of movement of the hook, angles between 5 and 15 °. These angles are advantageously between 8 and 12 °.
• The ramp may be provided with corrugations.
• The ramp is broken down into a lower part of the ramp, the mean direction of which forms a first angle with the direction of movement of the hook, and an upper part of the ramp, situated above the lower part of the ramp and whose mean direction forms a second angle with the direction of movement of the hook, the second angle having a value greater than that of the first angle. In practice, the first angle may have a value between 5 and 12 °, while the second angle has a value between 7 and 15 °.

The invention also relates to a loom equipped with a mechanism for forming the crowd as previously described, such a loom is more economical and can operate at higher speeds than the known trades.

Finally, the invention relates to a method of selecting mobile hooks in a shedding mechanism as described above. This method is characterized in that it consists in exerting, by means of the selection lever and on the elastic blade of each hook when it is at the beginning of its downward movement, in the vicinity of the top dead center of its trajectory, a individual effort whose component parallel to the direction of movement of the hook is directed downwards and whose intensity is greater than the intensity of the friction forces then experienced by the blade.

• la figure 1 est une représentation schématique de principe illustrant un métier à tisser de type Jacquard incorporant l'invention ;
• la figure 2 est une coupe longitudinale à plus grande échelle du mécanisme de formation de la foule du métier de la figure 1 ;
• les figures 2A et 2B sont des sections partielles respectivement selon les lignes A-A et B-B à la figure 2 ;
• la figure 3 est une vue à plus grande échelle du détail III à la figure 2,
• la figure 4 est une vue à plus grande échelle d'un crochet mobile et d'une partie d'un levier de retenue du mécanisme de la figure 2 ;
• la figure 5 est une vue dans le sens de la flèche V à la figure 4 ;
• la figure 6 est une vue de face d'un levier de sélection du mécanisme des figures 2 à 5 ;
• la figure 7 est une vue à plus grande échelle du détail VII à la figure 6, et
• la figure 8 est une vue analogue à la figure 6, pour un mécanisme conforme à un second mode de réalisation de l'invention.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of two embodiments of a crowd-forming mechanism according to its principle, given solely for example and with reference to the accompanying drawings, in which:

• the figure 1 is a schematic representation of principle illustrating a loom Jacquard type incorporating the invention;
• the figure 2 is a longitudinal section on a larger scale of the crowd forming mechanism of the craft of the figure 1 ;
• the Figures 2A and 2B are partial sections respectively along the lines AA and BB at the figure 2 ;
• the figure 3 is a larger-scale view of detail III to the figure 2 ,
• the figure 4 is a view on a larger scale of a movable hook and a part of a lever of the mechanism of the figure 2 ;
• the figure 5 is a view in the direction of arrow V to the figure 4 ;
• the figure 6 is a front view of a mechanism selection lever Figures 2 to 5 ;
• the figure 7 is a larger-scale view of detail VII to the figure 6 , and
• the figure 8 is a view similar to the figure 6 for a mechanism according to a second embodiment of the invention.

In these figures, for the sake of clarity, the efforts are not all represented on the same scale.

In the loom M represented at figure 1 a warp of warp 1 comes from a beam 2. Each warp 1 passes through the eyelet 3a of a stringer 3 intended to open the step to allow the passage of a pick to constitute the fabric which wound on a reel 4. Only two smooth 3 and 3 'are represented at the figure 1 , the arm 3 being in the high position, while the arm 3 'is in the low position. The lower end of each rail is connected to the frame of the loom by a tension spring 5, while its upper end is secured to an arch 6.

A shedding mechanism 7 associated with an electronic control unit 8 makes it possible to lift the arches 6 more or less against a return force exerted by the springs 5. As shown only for the arcade associated with the arm 3, each arch has an end 6a integral with a housing 10 of the mechanism 7, this arch passing in a mitt 11 suspended from a cord 12 whose two ends are respectively integral with two movable hooks 13 to be selectively raised by knives 14 animated by a movement of vertical oscillations in phase opposition, as shown by the arrows F ₂ .

Only a part of the constituent elements of the crowd-forming mechanism is represented in the figure 1 for the clarity of the drawing.

As is clear from the Figures 2 to 5 each hook 13 is formed of a plastic body 20 in the lower end 201 of which is overmolded an end 12a of the cord 12.

The body 20 forms a single spout 202 which extends laterally with respect to a principal longitudinal axis XX 'of the body 20. This spout 202 is intended to bear on the upper surface 14a of a knife 14. The hook 13 can thus be regularly lifted by a single knife 14.

When resting on the knife 14 adjacent, each hook 13 is moved along its axis X-X '.

The hook 13 also comprises a flexible metal blade 21 partially overmolded in the body 20. In practice, the blade 21 comprises a portion 211 overmolded in a zone 203 of the body 20, located near its lower end 201, that is, that is, below the portion 204 of the body 20 from which the mouth 202 extends laterally.

The portion 211 is open downwards, which allows the passage of the end 12a of the cord 12 which can be overmolded in the body 20 to a length L ₁₂ .

The blade 21 extends over a length L ₂₁ above its portion 211, this length being relatively large compared to the total length L _'21 of the blade 21

The blade 21 comprises two lateral uprights 212 and 212 'defining between them a window 213 in which is housed most of the body 20.

The amounts 212 and 212 'extend beyond the window 213 to a curved upper end 214 of the blade 21. The amounts 212 and 212' are connected by a cross member 215 which separates the window 213 from a opening 216 arranged between the parts 212, 212 ', 214 and 215 of the blade 21.

Given their respective fastening mode, the elements 20 and 21 are integral at the bottom of the hook 13, while the portion of the blade 21 which extends along the length L ₂₁ above the zone 203 of the body 20 , is capable of lateral deflections, as represented by the double arrow F ₃ at the figure 4 . These lateral deflections F ₃ correspond, in fact, to a relative movement of the blade 21 relative to the body 20.

The mechanism 7 also comprises an electromagnet 15 overmolded in a part of the housing 10. The housing 10 comprises two fixed axes 10a on which are pivotally mounted two retaining levers 16 intended to cooperate respectively with the two movable hooks 13 connected to the two ends of the same cord 12.

Each lever 16 comprises a metal armature 30 provided with a circular section circular bore 301 adapted to the outside diameter of an axis 10a, so that the armature 30 can be mounted about an axis 10a with the possibility of pivoting, as represented by the double arrows F ₄ at the figure 2 . The bore 301 of each armature 30 is formed in an end 302 of this armature.

At its opposite end, the frame 30 is overmolded in a body 31 made of a non-magnetic material, such as a plastic material. The body 31 forms a spout 311 retaining a movable hook 13 near its top dead center position. The body 31 is also provided with a centering heel 312 with respect to a spring 32 exerting on the body 31 a force F ₅ tending to pivot the lever 16 towards the outside of the housing 10. This effort tends to penetrate the beak 311 in the opening 216 of the blade 21 of a neighboring mobile hook, which allows to retain such a movable hook in the upper position.

The metal armature 30 of a lever 16 makes it possible to control its pivoting thanks to the electromagnet 15, a lever 16 that can be moved by the bent end 214 of a blade 21, and possibly held in position at against the force F ₅ , when the electromagnet 15 is excited.

Furthermore, the amounts 212 and 212 'of the blade 21 of a hook 13 slide in grooves 10b formed on the height of the housing 10 and extending parallel to the central axis X ₁₀ -X' ₁₀ of the housing, as shows it figure 2 where the cords 12 have been partially shown so that the grooves 10b are visible. Thus, the guide of a lever 13 relative to the housing 10 is performed accurately and with minimal wear. As envisaged in EP-A-1,413,657 each groove 10b of the housing 10 is delimited by two ribs 10f and 10f 'between which it extends, which allows effective guidance of the upright 212 or 212' which it receives parallel to the axes XX 'and X ₁₀ -X' ₁₀ . Each rib has this shape from the bottom of the housing 10 to approximately the location of the upper curved portion of the nozzle 202 on the right of the figure 2 where the rib 10f 'is removed, while the rib 10f is extended upwards. The removal of the outer edge 10f 'of the groove, that is to say the fact that it is open towards the outside of the housing near the retaining lever 16, allows the outward movement of the blade 21 , in the direction of the arrow F ₇ to 1a Figure 2B , when the blade 21 bears against the lever 16 next to, as shown on the left of the figure 2 to exert a leveling effort F ₆ .

In practice, most of the bending of the blade 21 takes place at the part of the housing 10 where the groove 10b has no external edge, this portion extending over a height H, between the position of the top of the beak 202 on the right of the figure 2 and the zone of interaction between the blade 21 and the lever 16 during leveling.

According to a variant not shown of the invention, the outer rib 10f 'which forms the outer edge of the groove 10b may not be removed on the height H but deviate from the rib 10f to leave the blade 21 a gap of sufficient clearance.

The bent end 214 of the blade 21 is also dimensioned so that it can bear and exert a force F ₆ against a ramp 313 formed by the edge of the body 31 of each lever 16 opposite the X axis ₁₀ -X _'10 . This momentary support of a hook 13 on a lever 16 makes it possible to level the lever 16, that is to say its bearing on the electromagnet 15, with elastic preload due to the bending of the blade 21 which provides the function of the elastic tongue described in EP-A-0 219 437 . The blade 21 thus provides a leveling function.

When the knife 14 starts its descent path parallel to the axes XX 'and X ₁₀ -X' ₁₀ as represented by the arrow F ₁₄ on the left of the figure 2 , the flexible blade 21 is in contact with the housing 10 at the two grooves 10b in which are engaged its amounts 212 and 212 '. It is also in contact with the ramp 313 of the corresponding lever 16 on which slides its end 214.

At the beginning of this downward movement, the lever 16 undergoes a leveling effort on the part of the blade 21. blade is moved parallel to the axis XX 'and undergoes forces which are considered in the following they are exercised at three contact zones. A first contact zone A is located in the lower part of the blade 21, in which part the blade 21 slides in the groove 10b. In this zone, the blade 21 undergoes a reaction force R _A whose component N _normal to the axis XX 'is directed outwards, that is to say away from the axis X ₁₀ -X _'10 . The reaction R _A also has a component F _A parallel to the axis X-X ', which corresponds to the friction experienced by the blade 21 and which is oriented upwards, that is to say in a direction opposite to the movement of the blade 21. If K _A is noted as the coefficient of friction between the blade 21 and the groove 10b, the relationship between the aforementioned forces is of type $${\mathrm{F}}_{\mathrm{AT}}\mathrm{=}{\mathrm{K}}_{\mathrm{AT}}\mathrm{\times }{\mathrm{NOT}}_{\mathrm{AT}}\mathrm{.}$$

In its middle part B, the blade 21 rubs against the upper part of the rib 10f ', which induces a reaction force R _B whose component N _B normal to the axis XX' is oriented towards the X axis ₁₀ - X _'10 , while its component F _B parallel to the axis XX' is oriented upwards. This component F _B corresponds to the friction forces; it is proportional to the normal component of this reaction R _B according to the relationship F _B = K _B x N _B where K _B is the coefficient of friction between the blade 21 and the upper part of the rib 10f '.

If the rib 10f 'is not interrupted, as envisaged in variant above, the blade bears against this rib, which generates a reaction of the same type as the reaction R _B. The point of contact B is then where the rib 10f 'deviates from the rib 10f.

• F₂₁ résulte de l'effet de la déformation élastique de la lame 21, cet effort étant sensiblement proportionnel à la déformation d de la lame 21 par rapport à son axe de coulissement X-X' en partie basse et
• F₃₁₃ résulte de l'effet du frottement de l'extrémité 214 sur la rampe 313.

At the zone C, which corresponds to the curved end 214 of the blade 21, the blade 21 undergoes a reaction R _C normal to the ramp 313 and which decomposes into a component N _C normal to the axis XX 'and an F _C component parallel to this axis. This reaction R _C corresponds to the sum of two efforts F ₂₁ and F ₃₁₃ where:

• F ₂₁ results from the effect of the elastic deformation of the blade 21, this force being substantially proportional to the deformation d of the blade 21 relative to its sliding axis XX 'at the bottom and
• F ₃₁₃ results from the effect of the friction of the end 214 on the ramp 313.

Thus, the reaction force seen by the blade 21 can be defined as a reaction R _C equal to the sum of the effects of the elastic deformation of the blade 21 and the friction of the end 214 on the body 31.

D _{313 is} a straight line defining the mean direction of the ramp 313 in the plane of the figure 3 . We note β the angle between the line D ₃₁₃ and the axis XX '.

In practice, the force F ₃₁₃ is parallel to the straight line D ₃₁₃ ·

It is noted that the effort F _C is directed downwards, that is towards the crowd of the loom equipped with the mechanism 7 and that this component opposes the components F _A and F _B resulting from friction of the blade 21 on the housing 10.

By a judicious choice of the angle β, the sum of the components F _A , F _B and F _C is directed downwards. For this, the intensity of the force F _C is greater than the sum of the intensities of the friction forces F _A and F _B.

In practice, this is achieved with a lever 16 whose ramp 313 is oriented on average along a line D ₃₁₃ which forms with the axis XX 'an angle β between 5 and 15 °.

A value of the angle β between 8 and 15 °, or even between 8 and 12 °, makes it possible to achieve quite satisfactory results insofar as the hook 13 is not braked too suddenly when it reaches the top dead center of its trajectory by being raised by a knife 14, while it is effectively sent down when the knife 14 initiates its downward movement, the blade 21 also initiating its downhill movement.

As represented in figure 6 , the ramp 313 is generally rectilinear and extends in the direction of the line D ₃₁₃ .

According to one aspect of the invention which is shown only in figure 7 , the ramp 313 may be provided with corrugations formed by a succession of bumps 313a and recesses 313b which make it possible to reduce the friction force F ₃₁₃ by decreasing the coefficient of friction between the ramp 313 and the end 214 of the blade 21. Indeed, these corrugations can hold on the ramp 313 a lubricant such as grease or equivalent.

According to an aspect of the invention which is not shown, the portion of the spout 311 against which the end 214 of the blade 21 slides may also be provided with such undulations.

In practice, the corrugations have an amplitude corresponding to the distance between the ridge of the bumps 313a and the bottom of the recessed portions 313b, much smaller than the dimensions of the body 31. This amplitude may be of the order of 0.2 mm.

According to a variant not shown of the invention the ramp 313 could however be curved. In this case, the tangents to the ramp 313 are such that they each form an angle of between 5 and 15 °, preferably between 8 and 12 °, relative to the axis X-X '.

As represented in figure 8 , the ramp 313 can be broken down into two parts, respectively a lower portion 313A and an upper portion 313B, the portion 313A being closer to the hook 311 than the portion 313B.

D _313A and D _{313B denote} the lines defining the average directions of the portions 313A and 313B at the figure 8 . The line D _313A forms an angle β _A with the axis XX ', whereas the line D _313B forms an angle β _B , greater than the angle β _A , with respect to this same axis. In practice, the angle β _A can have a value between 5 and 12 °, while the angle of β _B has a value between 7 and 15 °.

The configuration of the figure 8 has the advantage of generating a force F _C directed down relatively low intensity when the blade approaches the ramp 313 by its portion 313A, when the hook 13 is raised by the knife 14 corresponding. The docking between the blade 21 and the hook 16 is thus progressive and not brutal. The orientation of the portion 313B of the ramp 313 makes it possible effectively to exert a return force sufficient to overcome the friction forces, of the type of the components F _A and F _B , when the hook initiates its downward movement bearing on the knife 14 if it is not retained in the high position by the spout 311 of the lever 16.

Whatever the embodiment considered, the ramp 313 is shaped so that the component F _C of the force it exerts on the blade 21 when the blade initiates its downward movement is sufficient to overcome the frictional forces F _A and F _B. In other words, the resultant components parallel to the axis XX 'of the forces experienced by the blade 21 is then directed downwards, which makes it possible to dispense with an elastic stop of the type of that described in FIG. EP-A-0 823 501 .

Thus, according to the invention, the blade 21 and the selection lever 16 exert an individual force F _C whose component parallel to the axis XX 'is greater than the intensity of the friction forces F _A and F _B.

The invention relates to two-position shedding mechanisms used for weaving so-called "flat" fabrics, unlike the three-position mechanisms used for carpets and velvets. However, the invention can be used in the context of combining two-position mechanisms making it possible to obtain a three or four-position crowd, as described, for example, in EP-B-0 399 930 or FR-B-2,715,666 .

Claims (10)

1. Mechanism for forming a shed (7) on a Jacquard type weaving loom (M), this mechanism comprising mobile hooks (13), each moved by a knife (14) between a top dead centre position, in or near to which each hook may be immobilised by a selection device (15, 16), and a bottom dead centre position, each mobile hook comprising a body (20) provided with a nose (202) intended to be supported on the corresponding knife, and a flexible blade (21) fixed on the body with the possibility of relative deflection (F₃) intended to interact with a retaining lever (16) belonging to the selection device, whereas the selection lever forms a sliding slope (313) of a portion (214) of the flexible blade, when the hook is moved near to its top dead centre position, characterised in that the sliding slope of the selection lever is made so that the component (F_A + F_B + F_C) parallel to the direction of movement (X-X') of the mobile hook (13) as a result of forces (R_A, R_B, R_C) being applied to the flexible blade (21), when it is in contact with the slope (313), near to the top dead centre of its path at the start of its descending movement (F₁₄), is directed downwards.
2. Mechanism according to claim 1, characterised in that the slope (313) extends in a mean direction (D₃₁₃) which makes an angle (β, β_A, β_B) of between 5 and 15° in relation to the direction (X-X') of movement of the hook (13) and in that the slope (313) is provided with undulations (313a, 313b).
3. Mechanism according to claim 2, characterised in that the slope (313) extends in a mean direction (D₃₁₃) which makes an angle (β₃, β_A, β_B) of between 8 and 15° in relation to the direction (X-X') of movement of the hook (13).
4. Mechanism according to one of the previous claims, characterised in that the slope (313) is curved with tangents, which form angles of between 5 and 15° in relation to the direction of travel of the hook (X-X').
5. Mechanism according to claim 4, characterised in that the angles between the tangents to the slope and the direction of movement of the hook are between 8 and 12°.
6. Mechanism according to one of claims 3 to 5, characterised in that the slope (313) is provided with undulations (313a, 313b).
7. Mechanism according to one of claims 1 to 3 or 6, characterised in that the slope (313) is made up of a bottom part of the slope (313A), the mean direction of which (D_313A) forms a first angle (β_A) with the direction (X-X') of movement of the hook (13), and a top part of the slope (313B) situated above the bottom part of the slope, the mean direction of which (D_313B) forms a second angle (β_B) with the direction of movement of the hook, the second angle (β_B) having a greater value than that of the first angle (β_A).
8. Mechanism according to claim 7, characterised in that the first angle (β_A) has a value of between 5 and 12°, whereas the second angle (β_B) has a value of between 7 and 15°.
9. Weaving loom (M) fitted with a mechanism for forming a shed (7) according to one of the previous claims.
10. Method of selecting mobile hooks (13) of a mechanism for forming a shed (7) on a Jacquard type weaving loom (M), this mechanism comprising mobile hooks (13), each moved by a knife (14) between a top dead centre position, in or near to which each hook may be immobilised by a selection device (15, 16), and a bottom dead centre position, each mobile hook comprising a body (20) with a nose (202) intended to be supported on the corresponding knife and a flexible blade (21) fixed on the body with the possibility of relative deflection (F₃) intended to interact with a retaining lever (16) belonging to the selection device, whereas the selection lever forms a sliding slope (313) of a portion (214) of the flexible blade, when the hook is moved near to its top dead centre position, characterised in that it consists of exerting an individual force (R_C) by means of the selection lever (16) on the flexible blade (21) of each hook, when it is at the start of its descending movement near to the top dead centre of its path, the component (F_C) parallel to the direction (X-X') of movement of the hook (13) of which is directed downwards, the intensity of which is greater than the intensity of the friction forces (F_A, F_B) suffered by the blade.

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