Abstract:
Hooks for controlling movement of heddle cords in a Jacquard weaving loom are each displaced by a knife, between a position of top dead center, wherein each hook may be immobilized by a selection device, and a position of bottom dead center. Each hook includes a body provided with a catch that engages a corresponding knife and a metal blade that is relatively movable with respect to portions of the body adjacent the catch and that interacts with the selection device to selectively retain the hook in the top dead position thereof.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a shed forming mechanism and to a weaving loom equipped with such a mechanism. 
   2. Brief Description of the Related Art 
   In a Jacquard type weaving loom, a shed forming mechanism selectively lifts heddles, each comprising an eye in which a warp yarn passes, this yarn being located, as a function of the position of a hook to which the upper end of the heddle is fixed, above or below a weft yarn displaced by the loom. Such a known mechanism, for example disclosed by EP-A-0 219 437, comprises, inter alia, mobile hooks each provided with a lateral catch capable of cooperating with knives animated by vertical reciprocating movements in phase opposition. Each mobile hook is provided with a curved end allowing it to be immobilized by cooperation of shapes with a retaining lever. 
   Each mobile hook is also provided with an elastic tongue in one piece with the hook and intended to control the displacement of the retaining lever. Such a tongue is subjected to repeated, relatively intense efforts likely to induce permanent deformation by creeping, and even rupture thereof. In that case, the shed obtained presents “faults”. 
   It is a particular object of the present invention to overcome these drawbacks by proposing a shed forming mechanism of which the mobile hooks are robust and dimensioned precisely, this ensuring reliable operation of the loom, while they are compact in height, i.e. parallel to their direction of displacement. This makes it possible to create a compact mechanism, hence a saving of space and improved economic performances. 
   SUMMARY OF THE INVENTION 
   To that end, the invention relates to a shed forming mechanism on a weaving loom of a Jacquard type, this mechanism comprising mobile hooks, each displaced by a knife, between a position of top dead center, wherein each hook may be immobilized by a selection device, and a position of bottom dead center, and wherein each hook includes a body provided with a catch abuts with the afore-mentioned knife. This mechanism is characterized in that each hook further comprises a metal blade intended to interact with the selection device and fixed on the body in such a manner that the blade is relatively movable with respect to portions of the body adjacent the area of the catch. 
   Thanks to the invention, the two-part nature of the mobile hooks, of which the body is advantageously made of synthetic material, makes it possible to benefit from the robustness of the body for the mechanical link between the hook and the knife, while the geometry of the metal blade is defined with high precision, this rendering the interactions between the mobile hook and the selection device highly reliable. As the metal blade is fixed on the body in the lower part when the hook is in configuration of operation of the mechanism, the flexibility of the blade, over substantially the whole of its height, may be used for the transverse displacement of its part more particularly intended to come into engagement with a corresponding part of the selection device. The fact that a relative clearance is possible between the blade and the body of the hook may come from the suppleness of the blade and/or from that of the body. 
   According to advantageous, but non-obligatory aspects of the invention, this mechanism incorporates one or more of the characteristics of the dependent Claims. 
   In particular, the electromagnet of the selection device may be molded in one of the sides of a box for receiving and for guiding the mobile hook in translation. Such molding induces a precise positioning of the electromagnet with respect to the other functional parts of the device, such as the pins of the retaining levers, the stops and the bearings of these levers, as well as grooves for guiding the mobile hooks. Due to this high precision, the amplitudes of the movements of the mobile parts may be reduced, particularly concerning the oscillation of the retaining levers and the bending of the blades of the mobile hooks. This also contributes to the compactness of the mechanism. 
   The invention also relates to a weaving loom equipped with a shed forming mechanism as described hereinabove. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood and other advantages thereof will appear more clearly on reading the following description of three forms of embodiment of a shed forming mechanism in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings, in which: 
       FIG. 1  schematically shows a weaving loom of Jacquard type incorporating the invention. 
       FIG. 2  is a longitudinal section on a larger scale of the shed forming mechanism of the loom of  FIG. 1 . 
       FIGS. 2A and 2B  are partial sections respectively along lines A—A and B—B in  FIG. 2 . 
       FIG. 3  is a view on a larger scale of a mobile hook and a part of a retaining lever of the mechanism of  FIG. 2 . 
       FIG. 4  is a view in the direction of arrow IV in  FIG. 3 . 
       FIG. 5  is a view similar to  FIG. 2  for a mechanism in accordance with a second form of embodiment of the invention. 
       FIG. 6  is a partial longitudinal section through a mechanism in accordance with a third form of embodiment, and 
       FIG. 6A  is a partial section along line A—A in  FIG. 6 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to the drawings,  FIG. 1  shows a weaving loom M in which a lap of warp yarns  1  comes from a beam  2 . Each warp yarn  1  passes in the eye  3   a  of a heddle  3  intended to open the shed to allow the passage of a pick with a view to constituting the fabric which is wound on a reel  4 . Only two heddles  3  and  3 ′ are shown in  FIG. 1 , heddle  3  being in upper position, while heddle  3 ′ is in lower position. The lower end of each heddle is connected to the frame of the weaving loom by an extension spring  5 , while its upper end is fast with harness cords  6 . 
   A shed forming mechanism  7  associated with an electronic control unit  8  makes it possible to lift the harness cords  6  more or less against a return effort exerted by the springs  5 . As shown solely for the harness cord associated with the heddle  3 , each harness cord has one end  6   a  fast with a box  10  of the mechanism  7 , this harness cord passing in a pulley block  11  suspended from a cord  12  of which the two ends are respectively fast with two mobile hooks  13  intended to be selectively lifted by knives  14  animated by a vertical oscillatory movement in phase opposition, as represented by arrows F 2 . 
   Only a part of the elements constituting the shed forming mechanism has been shown in  FIG. 1  in order to render the drawing clearer. 
   As is more particularly visible in  FIGS. 2 to 4 , each hook  13  is formed by a body  20  of plastic material, in the lower end  201  of which is molded an end  12   a  of the cord  12 . 
   The body  20  forms a single catch  202  which extends laterally with respect to a principal longitudinal axis X–X′ of the body  20 . This catch  202  is intended to come into abutment on the upper surface  14   a  of a knife  14 . The hook  13  may thus be regularly lifted by a single knife  14 . 
   Taking into account its constituent material, the body  20  presents a certain suppleness, allowing it to adapt itself to a possible defect of position or of parallelism of the respective paths of this body and of the knife  14  associated therewith. This possibility of elastic deformation of the body  20  is represented by the double arrow F 20  in  FIG. 2 . In practice, the suppleness of the body  20  makes it possible to obtain a self-positioning of the catch  202  on the knife  14 . 
   The hook  13  also comprises a metallic blade  21  partially molded in the body  20 . In practice, the blade  21  comprises a part  211  molded in a zone  203  of the body  20 , located near its lower end  201 , i.e. below the part  204  of the body  20  from which the catch  202  extends laterally. 
   The part  211  is open downwardly, this allowing the passage of the end  12   a  of the cord  12  which may therefore be molded in the body  20  over a relatively great length L 12 . 
   The blade  21  extends over a length L 21 , above its part  211 , this length being relatively great with respect to the total length L′ 21  of the blade  21 . 
   The blade  21  comprises two lateral uprights  212  and  212 ′ defining therebetween a window  213  in which is housed the major part of the body  20 . 
   The uprights  212  and  212 ′ extend beyond the window  213  as far as a curved end  214 . The uprights  212  and  212 ′ are connected by a crosspiece  215  which separates the window  213  from an opening  216  made between parts  212 ,  212 ′,  214  and  215  of the blade  21 . 
   Taking into account how they are mounted, the elements  20  and  21  are secured in the lower part of the hook  13 , while that part of the blade  21  which extends over the length L 21  above the zone  203  of the body  20 , is capable of lateral movements, as represented by the double arrow F 3  in  FIG. 3 . These lateral movements F 3  correspond, in fact, to a relative clearance of the blade  21  with respect to the body  20 . 
   The mechanism  7  also comprises an electromagnet  15  molded in a part of the box  10 . This molding ensures a precise positioning of the electromagnet  15  with respect to the box  10  and to the elements that it supports or guides. 
   The box  10  comprises two fixed pins  10   a  on which are pivotally mounted two retaining levers  16  intended to cooperate respectively with the two mobile hooks  13  connected to the two ends of the same cord  12 . 
   Each lever  16  comprises a metallic armature  30  provided with a cylindrical bore  301  of circular cross-section adapted to the outer diameter of a pin  10   a , with the result that the armature  30  may be mounted about a pin  10   a  with the possibility of pivoting, as represented by the double arrows F 4  in  FIG. 2 . The bore  301  of each armature  30  is made in an end  302  of this armature. 
   At its opposite end  303 , the armature  30  is in a body  31  made of an material, such as synthetic material and, more specifically, a material. The body  31  forms a catch  311  for retaining a mobile hook  13  in the vicinity of its position of top dead center. The body  31  is also provided with a heel  312  for centering with respect to a spring  32  exerting on the body  31  an effort or force F 5  tending to cause the lever  16  to pivot towards the outside of the box  10 . This effort tends to cause the catch  311  to penetrate in the opening  216  of the blade  21  of an adjacent mobile hook, which makes it possible to retain such a mobile hook in an upper position. 
   The metallic armature  30  of a lever  16  makes it possible to control its pivoting thanks to the electromagnet  15 , a lever  16  being able to be displaced by the curved end  214  of a blade  21  and possibly maintained in position against the effort F 5  when the electromagnet  15  is activated. 
   The body  31  allows an efficient interaction, without metal/metal contact, of a retaining lever  16  with a mobile hook  13 . 
   The levers  16  are each provided with a deflector  161  projecting with respect to their principal part  16   a  in the direction of the median axis X 10 –X′ 10  of the box  10 , between its pivot axis  10   a  and a zone Z 1  in which the armature  30  can come into abutment against the electromagnet  15 . A second deflector  162  is provided between the zone Z 1  and the adjacent hook  13 . The deflectors  161  and  162  are mobile with the lever  16 , inside grooves  101  and  102  made in the body  10 , which allows them to isolate the zone Z 1  which thus forms a closed chamber protected against pollution, particularly the flock likely to be transported by a hook  13 . 
   Taking into account the positioning of the pins  10   a  on the box  10  and the geometry of the levers  16 , these levers extend solely downwardly from these fixed pins, which gives the mechanism  7  an improved compactness with respect to the mechanisms in which the lever extends on either side of its pivot axis, as described for example in EP-A-0 219 437. 
   Furthermore, the uprights  212  and  212 ′ of the blade  21  of a hook  13  slide in grooves  10   b  made over the height of the box  10 , as shown in  FIG. 2  where the cords  12  have been shown partially so that the grooves  10   b  are visible. In this way, guiding of a lever  13  with respect to the box  10  is effected precisely and with minimum wear. As is shown in  FIGS. 2A and 2B , each groove  10   b  of the box  10  is defined by two ribs  10   f  and  10   f ′ between which it extends, this allowing an efficient guiding of the upright  212  or  212 ′ that it receives. Each rib presents this shape of the bottom of the box  10  approximately as far as the location of the upper convex part of the catch  202  to the right in  FIG. 2  where the rib  10   f ′ is eliminated, while the rib  10   f  extends upwardly. The elimination of the outer edge  10   f ′ of the groove, i.e. the fact that it is open towards the outside of the box in the vicinity of the retaining lever  16 , allows the outward clearance of the blade  21 , in the direction of arrow F 7  in  FIG. 2B , when the blade  21  comes into abutment against the adjacent lever  16 , as shown to the left in  FIG. 2 , in order to exert an effort of levelling F 6 . 
   In practice, the bending of the blade  21  takes place at that part of the box  10  where the groove  10   b  has no outer edge, this part extending over a height H, between the position of the top of the catch  202  to the right in  FIG. 2  and the zone of interaction between the blade  21  and the lever  16  during levelling. 
   According to a variant of the invention (not shown), it is possible for the rib  10   f ′ which forms the outer edge of the groove  10   b  not to be eliminated over the height H but to deviate from the rib  10   f  in order to leave the blade  21  a sufficient clearance space. 
   In the form of embodiment shown and in the afore-mentioned variant, the widening or opening of the groove  10   b  towards the outside in the vicinity of the elements  15  and  16  aims at allowing the bending of the blade  21  in this zone. 
   In accordance with the technical teaching of FR-A-2 752 246, a stop  40 , elastically urged by a spring  41 , is mounted between the paths of slide or movement of two mobile hooks  13 , in abutment on studs  10   c  of the box  10 . This elastic stop  40  is intended to cooperate with a heel  205  made in the vicinity of the end  201  of each body  20 . Taking into account the respective positioning of the elements  205  and  40 , this interaction takes place when each mobile hook  13  arrives in the vicinity of its position of top dead center. This arrangement makes it possible to essentially overcome the forces of inertia and of friction of the mobile hooks, this facilitating reversal of movement and allowing the dimensioning of the harness and the mechanical drive elements, such as the knives  14  or the return springs  5 , to be optimised. 
   The curved end  214  of the blade  21  is also dimensioned so that it can come into abutment and exert an effort F 6  against a ramp  313  formed by the body  31  of each lever  16 . This momentary abutment of a hook  13  on a lever  16  allows the lever  16  to be levelled, i.e. made to abut on the electromagnet  15 , with elastic pre-loading due to the bending of the blade  21  which performs the function of the elastic tongue described in EP-A-0 219 437. The blade  21  therefore performs a function of levelling. 
   In the second form of embodiment of the invention shown in  FIG. 5 , elements similar to those of the first embodiment bear identical references. As previously, knives  14  make it possible selectively to displace mobile hooks  13  each comprising a body  20  made of synthetic material and an elastic metal blade  21  which essentially extends above the zone where it is fixed to this body. Retaining levers  16  are associated with an electromagnet  15 . 
   In this embodiment, the levers  16  are mounted to pivot about pins  10   a  fixed with respect to a box  10 . The technical teaching of EP-A-0 577 524 is applied here, insofar as the box  10  comprises partitions  10   d  making it possible to isolate the electromagnet  15  from the ambient atmosphere. Each lever  16  is mounted to pivot on a corresponding pin  10   a , as represented by the double arrow F 4  and comprises an armature  30  which extends on either side of the pin  10   a  on which it is mounted. More precisely, each armature  30  comprises a first arm  304  which extends upwardly from a central part  305  in which is made a circular bore  301  for receiving the pin  10   a . The arm  304  is intended to interact with the electromagnet  15  during its activation. The armature  30  also comprises an arm  306  which extends opposite the arm  304  with respect to the part  305 . This arm  306  is molded in a body  31  made of plastic material which forms a catch  311  intended to interact with an opening  216  of the blade  21  of a hook  13 . The body  31  also forms a ramp  313  for levelling the position of the lever  16  used during an interaction with the curved upper end  214  of a blade  21 . The blade  21  in that case exerts on the lever  16  an effort F 6  of displacement of the armature  30  towards the electromagnet  15 . 
   In order to isolate the electromagnet  15  efficiently, the partitions  10   d  of the box  10  are provided with O-rings  10   e  disposed in the vicinity of the outer surface  305   a , cylindrical with circular base, of the part  305 . In this way, independently of the orientation of a lever  16  about the axis  10   a , a satisfactory seal can be ensured. 
   In a variant embodiment, the partitions  10   d  may be provided with reduced clearance with respect to the surface  305   a , the seals  10   e  in that case being able to be eliminated, as the ends of the partitions  10   d  then constitute means for seal against dust. 
   In the third form of embodiment shown in  FIG. 6 , elements similar to those of the first embodiment bear identical references. As previously, hooks  13  each comprise a body  20  made of plastic material as well as a metal blade  21 , these elements being molded in one another in the lower part of the body  20 . A movement of relative clearance F 3  is possible between the body  20  and the blade  21  of each hook. The blade  21  of each hook may be retained in position by a catch  311  formed by a body  31  of a retaining lever  16  mounted to pivot about a pin  10   a  formed by a box  10 . 
   Each lever  16  comprises a metal armature  30  that interacts with an electromagnet  15  at a zone Z 1  in which the armature  30  may come into abutment against the electromagnet  15  against an elastic effort or force exerted by a spring  32  centered on a heel  312  of the body  31 . 
   As in the first form of embodiment, a deflector  161  is provided on each lever  16 , between the armature  30  and the pin  10   a  while a second deflector  162  is provided between the armature  30  and that part of the body  31  intended to interact with the blade  21  of a hook  13 . The deflector  162  of this third embodiment may move inside a groove  102  made in the box  10  between the positions respectively shown to the left and to the right of  FIG. 6 . This deflector  162  projects with respect to the principal part  16   a  of the lever  16  both in the direction of the median axis X 10 –X′ 0  of the box  10  and opposed thereto, with the result that the circulation of flock or of dust is prevented both between the lever  16  and the electromagnet  15  and between the lever  16  and the outer web  10   g  of the box  10 . 
   In addition, and as is more particularly visible in  FIG. 6A , the deflector  162  also projects perpendicularly to the plane of  FIG. 6  with respect to the principal part  16   a  of the lever  16 , this also avoiding pollution rising in the direction of the armature  30 . 
   Whatever the form of embodiment in question, the elastic blade  21  efficiently performs the functions of selection and of levelling, while it is not in contact with the adjacent knife  14 , the function of direct interaction with the knife devolving on the catch  202  of the body  20 . In the same way, the body  20 , through which the effort of traction exerted by the knife  14  transits, does not enter directly into contact with the selection device which comprises the elements  15  and  16 . 
   The characteristics of the different forms of embodiment described may be combined within the framework of the present invention. 
   The invention relates to two-position shed forming mechanisms used for weaving so-called “flat” fabrics, unlike three-position mechanisms used for carpets and velvets. However, the invention can be used within the scope of associating two-position mechanisms allowing a three- or four-position shed to be obtained, as described for example in EP-B-0 399 930 or FR-B-2 715 666.