EP0161010A1 - Process and apparatus for picking up flexible sheets, especially textiles, and device for picking up and feeding these sheets - Google Patents

Abstract

The invention relates to a method for gripping flexible layers arranged on a stack of layers, in order to separate one or more upper layers from the other layers of the stack. The method uses a needle (23) moving relative to a bearing surface (14a) provided with an openwork part (16). The movement of the needle (23) is carried out so that, during the movement of its end, said needle pushes the upper flexible layer towards the perforated part (16) and causes it to form a ripple in said perforated part; during the final phase of the movement, the needle crosses said undulation.

Description

The invention relates to a method and a device for gripping flexible layers, in particular textile, knitted, woven or other layers; it extends to a machine allowing the transfer of these layers from a stack or several stacks where said layers are stored in superimposed positions, to one or more other locations.

In the textile and hosiery industry, the automation of the work to be done on layers of fabrics or knits to make finished or semi-finished articles is currently stumbling over the serious difficulties involved in entering these layers, by unit or by well defined number, from stacks produced by cutting; indeed, these layers are most of the time extremely thin (thickness often less than a millimeter) and tend to adhere to each other, so that the grip and the separation of the upper layer or of a determined number of layers above a stack are extremely delicate execution operations (even when performed manually).

• - préhenseurs à bandes accrochantes du type "Velcro", présentant les défauts d'être d'application limitée à certains types de tricots (non opérant sur la majorité des tissus) et d'entraîner des difficultés de décrochage de la couche saisie,
• - préhenseurs adhésifs, qui fournissent une bonne préhension, mais entraînent des difficultés de décrochage analogues aux précédents,
• - préhenseurs à roulettes agissant par effet de coincement du tissu ou tricot et présentant le défaut de posséder un fonctionnement très aléatoire et de provoquer la création de plis profonds dans les couches sou-ples,
• - préhenseurs à aiguilles croisées.

At present, no device is entirely satisfactory for carrying out this work with a reliability compatible with an automated process. There are basically four types of grippers:

• - grippers with hooking bands of the "Velcro" type, having the drawbacks of being of application limited to certain types of knits (not operating on most fabrics) and of causing difficulties in detaching the gripped layer,
• - adhesive grippers, which provide good grip, but cause release problems similar to the previous ones,
• - grippers on wheels acting by the jamming effect of the fabric or knitting and having the defect of having a very random operation and cause the creation of deep folds in the flexible layers,
• - grippers with crossed needles.

A gripper of the latter type is described in the French patent application published under No. 2,468,531 and in the request for certificate of addition published under No. 2,482,064. The flexible layer is gripped by means of two needles which cross out of a casing in order to penetrate at an angle into one or more flexible layers of the stack: by the effect of their crossing, these needles have a retaining action of the layer or layers in which they are embedded. However, if such a device has a certain effectiveness for knitted fabrics or thick fabrics, it totally lacks reliability for knitted fabrics or fine fabrics (a few tenths of a millimeter); indeed, if for example only one layer is to be gripped, the needles which descend into the fabric must not penetrate into it beyond the thickness of a layer under penalty of gripping the lower layer: taking into account the flexibility and elasticity of the material, penetration of a few tenths of a millimeter is not enough to ensure correct grip despite the crossed position of the needles and it is very common for the fabric to come off accidentally during its transfer.

In addition, to peel off the lower layer which tends to adhere to the gripped layer, it is necessary in this type of device to operate with great care, taking into account the poor maintenance of the gripped layer. Under these conditions, the designers of this type of device have been led, as described in the above-mentioned request for a certificate of addition, to provide hollow needles which penetrate the fabric up to the immediate vicinity of the underside of the layer to be grabbed and send a jet of compressed air to the bottom layer, in order to peel it off without too much risk of unhooking the grabbed layer. Such takeoff proves ineffective in practice, however that the device for implementing such a method is relatively expensive (in particular, hollow needles are of a cost much higher than the cost of a needle. ordinary of similar dimensions).

Furthermore, it has been described in German patent No. 2,002,750 and in French patent No. 2,218,417 a technique for gripping pieces of fabric which uses a curved needle and consists in rotating the latter around its center of curvature so that said needle protrudes from a plate and enters the tissue which is perfectly immobilized, until it emerges therefrom on the same face at the end of its circular movement. When the pieces of fabric are stacked one above the other, it is obvious, as these patents recommend, that during its circular movement around its center of curvature, the needle must protrude from the plate to a depth less than the thickness of the layer to be gripped; if it were otherwise, the needle would also grasp the neighboring layer since it would penetrate into it. Under these conditions, only one fiber or a small number of fibers of the layer to be separated are gripped by the needle.

In the case of thin layers (a few tenths of a millimeter), - we then find the defect of crossed needle devices which ensure ineffective input whose reliability is not compatible with an automated work process. To the knowledge of the inventors, this type of technique using a single curved needle rotating around its center of curvature has never been used despite its relative seniority, probably because of this major drawback, which does not allow seizure and safe separation of a thin layer from other layers of a stack. In addition, it is likely that such a device must frequently lead to deterioration of the tissue by rupture of the few fibers trapped by the needle.

The present invention proposes to remedy the aforementioned faults of known gripping devices. It aims to provide a new gripping device in which the gripping is ensured by means of a needle, under conditions suitable for eliminating all the defects of known grippers and in particular of grippers with crossed needles and grippers with curved needles rotating around their center of curvature.

One objective of the invention is in particular to simultaneously obtain the three essential qualities for good operating reliability: secure grip of the layer or layers to be gripped, assured take-off of this layer or of these layers relative to the lower layers, safe release of this layer or these layers in order to deposit them.

Another objective is to achieve these results with a space-saving gripping device, of simple structure and of low cost.

Another objective of the invention, directly linked to the previous ones (reliability, low cost, reduced bulk) is to provide a machine for gripping and transferring textile pieces, allowing, by means of several grippers, to grip and transfer with excellent reliability, parts of all shapes and sizes.

• . réaliser une saisie ferme de.la couche supérieure de l'empilage afin de pouvoir la décoller des autres couches et la transférer sans risque de détachement,
• . éviter de saisir en même temps la couche du dessous qui ne pourrait alors plus être décollée,

paraissent incompatibles, en particulier lorsque l'on utilise un préhenseur à aiguille : ou bien l'on limite la pénétration de l'aiguille à une profondeur inférieure à l'épaisseur de la couche et, dans ce cas, la saisie de la couche, opérée sur une épaisseur très faible par quelques fibres seulement, est inefficace ; ou bien l'on amène l'aiguille à pénétrer plus profondément et l'on saisit les couches inférieures.One can realize the difficulty of achieving the objectives indicated above in the case of thin layers superimposed in stacking. Indeed, the two conditions consisting in:

• . make a firm grip on the upper layer of the stack so that it can be detached from the other layers and transferred without the risk of detachment,
• . avoid grabbing the bottom layer at the same time which could no longer be peeled off,

appear to be incompatible, in particular when using a needle gripper: either the penetration of the needle is limited to a depth less than the thickness of the layer and, in this case, the gripping of the layer, operated on a very small thickness by only a few fibers, is ineffective; or you bring the needle deeper and grab the lower layers.

The present invention solves the problem posed by this apparent incompatibility and aims a method and a needle device which is able both to allow a firm grip of one or more thin layers and an assured takeoff of the lower layer which must be left in place.

• . appliquer au-dessus d'au moins une zone de la couche souple supérieure de l'empilage, une surface d'appui pourvue d'une partie ajourée, jusqu'à amener cette surface en contact avec ladite couche, laquelle demeure libre au niveau de la partie ajourée,
• . puis déplacer une aiguille par rapport à ladite surface d'appui, de sorte que son extrémité pointue se déplace par rapport à ladite surface d'appui prise comme référence, sur une trajectoire-T comprenant successivement, d'abord, une portion initiale Ti partant de la surface d'appui et s'écartant de celle-ci, de façon à faire pénétrer ladite aiguille dans la couche souple, puis une portion de rebroussement Tr comportant un changement du sens du déplacement relatif de l'extrémité de l'aiguille par rapport à la surface d'appui, enfin une portion finale Tf se rapprochant de la surface d'appui et décalée par rapport à la portion initiale afin de ne pas coïncider avec celle-ci,
• . ensuite, engendrer un mouvement relatif d'écartement entre l'empilage et l'ensemble aiguille/ surface d'appui.

To this end, the method proposed by the invention is of the type comprising the following operations:

• . applying above at least one area of the upper flexible layer of the stack, a bearing surface provided with an openwork part, until bringing this surface into contact with said layer, which remains free at the level of the openwork part,
• . then move a needle relative to said bearing surface, so that its pointed end moves relative to said bearing surface taken as a reference, on a trajectory-T comprising successively, firstly, an initial portion Ti leaving from the bearing surface and moving away from it, so as to make said needle penetrate the flexible layer, then a cusp portion Tr comprising a change in the direction of relative movement of the end of the needle by relative to the bearing surface, finally a final portion Tf approaching the bearing surface and offset from the initial portion so as not to coincide with the latter,
• . then generate a relative spacing movement between the stack and the needle / bearing surface assembly.

In accordance with the present invention, the movement of the needle is carried out so that, during the movement of its pointed end along the initial portion Ti and the cusp portion Tr, said needle pushes the flexible layer towards the perforated part, and causes it to form a corrugation in said perforated part, the final portion Tf of the trajectory crossing said corrugation.

Such a method can be implemented using a curved needle with a concavity oriented in the same direction as that of the trajectory (T); but it can also be implemented using a needle of different shape, in particular rectilinear, partially rectilinear or forming an angle.

According to one embodiment of the method of the invention, the needle is positioned, during its movement along the initial portion (Ti) and the cusp portion (Tr), so that, in each point, the direction of the needle end (defined in the case of a needle curved by the tangent to said needle at its end) does not coincide with the tangent to the trajectory so as to ensure the aforementioned action thrust on the flexible layer. Preferably, the needle is positioned so that the direction of its end is located above the tangent to the trajectory in order to ensure, as will be better understood later, a pushing action tending to lift the layer flexible towards the perforated part of the bearing surface.

According to another mode of implementation which, preferably, is combined with the previous one, use is made of a needle having an end provided with at least one point and, upstream of the latter, a stopper adapted to come into stop against the flexible layer; this retainer ensures or considerably increases the pushing action on the fabric of the upper layer and notably generates or facilitates the formation of the ripple in the fabric. One can in particular use a needle having at its end two separate points: the retainer is then formed by the part of the needle located between the bases of said points.

Thus, the method of the invention leads to forming an undulation of the layer to be gripped inside the openwork part of the bearing surface, and to stitch this undulation in the manner of a stitch, crossing layer ; the fabric is trapped by the needle over its entire thickness and is, at the end of movement of the needle, pinched at its undulation between said needle and the bearing surface. In this way, the grip which is carried out by all the fibers with pinching of a small portion of the fabric, is extremely firm and the experiments have shown that the risks of detachment were negligible even in the case of the thinnest layers of fabric. .

In addition, as will be better understood below, the gripping of the fabric by pricking and pinching a ripple formed thereon is compatible with a displacement of the needle (relative to the bearing surface) such that the trajectory of its end is very flattened at its cusp portion (Tr); under these conditions, it is easy to adjust the height of this movement so that a single layer or a determined number of layers is entered.

In the preferential case of the use of a stop needle, this is advantageously associated with elastic means tending to move it away from the bearing surface, said needle being mounted so as to be able to retract on a low course toward the _support surface. In this way, it is not necessary to operate a very precise adjustment of the movement of the needle; in fact when the needle stopper bears against the fabric, the retraction ability of the latter automatically limits the height of movement of the needle point: it is thus possible to obtain without difficulty, even in the case of very thin layers, a displacement of the needle such that, after penetration, the cusp portion (Tr) of the trajectory (T) is located at a distance from the bearing surface, less than or equal to l thickness of the layer to be gripped or layers to be gripped. This avoids accidentally grabbing the lower layers.

• . le déplacement de l'aiguille par rapport à la surface d'appui est réalisé par un mouvement de rotation de ladite aiguille autour d'un axe, lequel est décalé transversalement par rapport au centre de courbure de l'aiguille dans le cas d'une aiguille courbe ; cet axe, situé à l'opposé des couches souples par rapport au plan de la surface d'appui, est lui-même animé d'un mouvement relatif de translation par rapport à la surface d'appui qui tend à le rapprocher de ce plan,
• . l'on applique la surface d'appui sur la couche souple supérieure de l'empilage par un mouvement relatif de rapprochement dudit empilage et de ladite surface d'appui, mouvement réalisé de sorte que, après contact, la pression de la surface d'appui sur l'empilage soit sensiblement constante et assez faible pour ne pas comprimer sensiblement la ou les couches souples,
• . à la fin de la portion finale (Tf) du déplacement de l'aiguille, on bloque cette dernière par rapport à la surface d'appui et on la garde bloquée pendant le mouvement relatif d'écartement entre l'empilage et l'ensemble aiguille/surface d'appui.

The method of the invention can in particular be implemented according to the following methods:

• . the displacement of the needle relative to the bearing surface is achieved by a rotational movement of said needle about an axis, which is offset transversely relative to the center of curvature of the needle in the case of a curved needle; this axis, located opposite the flexible layers relative to the plane of the bearing surface, is itself driven by a relative movement of translation relative to the bearing surface which tends to bring it closer to this plane ,
• . the bearing surface is applied to the upper flexible layer of the stack by a relative movement of bringing said stack and said surface closer together support, movement made so that, after contact, the pressure of the support surface on the stack is substantially constant and low enough not to significantly compress the flexible layer (s),
• . at the end of the final portion (Tf) of the movement of the needle, the latter is blocked relative to the bearing surface and it is kept blocked during the relative spacing movement between the stack and the needle assembly /bearing surface.

The gripping of the fabric carried out under the conditions described above provides firmness and security of support, which considerably facilitate the release of the lower layers.

It is in particular possible, once the layer (s) gripped, to move the needle / bearing surface assembly (against which the gripped layer (s) is firmly held) by several rapid back-and-forth movements in a substantially direction parallel to the plane of the bearing surface. These movements break the adhesion forces of the seized layers with respect to the immediately adjacent layer which remains stuck against the other layers of the stack.

It is also possible, and this process can be combined with the previous one, to blow air over the upper flexible layer in the direction tending to separate the latter from the plane of the bearing surface. This air blown outside the seized areas tends to give the seized layer the shape of a bowl pressing its bottom on the lower layers which allows or promotes takeoff. In addition, in particular in the case of very thin layers, the air passes through the captured layer or layers and establishes a take-off back pressure on the lower layers.

It should be noted that, given the very firm maintenance of the seized layer (s), this air blowing is carried out by simple nozzles arranged above the layers, without the need for hollow needles as in the case of the crossed needle process.

After the relative movement of spacing of the gripped layer relative to the stack, the detachment of this layer is obtained without difficulty, by subjecting each needle to a reverse displacement relative to its bearing surface, so as to bring back each of said needles in its initial position set back relative to the bearing surface. The layer or layers which are then no longer maintained move away by gravity from the bearing surfaces to fall at the desired location. The method of the invention is thus not subject to the release difficulties encountered by adhesive grippers and grippers with hanging strips.

The invention extends to means for implementing the above-mentioned method, comprising at least one head provided with a bearing surface provided with an openwork part, a needle associated with said head and movable relative to the latter and kinematic guide means of each needle relative to the corresponding head, imposing on the needle end a trajectory (T) (relative to the bearing surface taken as a reference) having an initial portion (Ti ), a cusp portion (Tr) and a final portion (Tf) as defined above, in order to have the shape of a C with a concavity oriented towards the bearing surface of the head.

According to a characteristic of the invention, the kinematic guide means are adapted to move the corresponding needle according to a movement such that the direction of the end of the needle is distinct from the tangent to the trajectory (T) at least on the initial portion (Ti) and the cusp portion (Tr) of this trajectory.

According to another characteristic preferably combined with the previous one, the needle has an end provided with at least one point and, upstream of the latter, a stop adapted to come into abutment against the flexible layer; in particular said needle advantageously comprises two separate points, the retainer being formed by the part situated between the bases of said points.

• . chaque tête possède une fine rainure, d'épaisseur légèrement supérieure à celle de l'aiguille, s'étendant dans un plan sensiblement perpendiculaire à la surface d'appui et coupant la partie ajourée de la tête,
• . les moyens de guidage cinématique sont adaptés pour imposer à l'aiguille une position initiale entièrement en retrait dans ladite rainure et une position finale en fin de mouvement, dans laquelle au moins la pointe de ladite aiguille est en retrait dans ladite rainure,
• . lesdits moyens de guidage cinématique sont adaptés de sorte que la portion finale (Tf) de la trajectoire de la pointe d'aiguille coupe le plan de la surface d'appui au niveau de ladite partie ajourée.

According to other characteristics of the invention, the device is produced so that:

• . each head has a fine groove, of thickness slightly greater than that of the needle, extending in a plane substantially perpendicular to the bearing surface and cutting the perforated part of the head,
• . the kinematic guide means are adapted to impose on the needle an initial position entirely recessed in said groove and a final position at the end of movement, in which at least the tip of said needle is recessed in said groove,
• . said kinematic guide means are adapted so that the final portion (Tf) of the trajectory of the needle tip intersects the plane of the bearing surface at said perforated part.

• . une biellette articulée, adaptée pour porter l'aiguille de sorte que, dans le cas préférentiel d'une aiguille courbe, la concavité de celle-ci soit orientée dans le même sens que la trajectoire (T),
• . un axe d'articulation de ladite biellette, porté par un support de façon que ledit axe soit décalé transversalement par rapport à la tête et dans le cas préférentiel d'une aiguille courbe soit situé du côté de la concavité de l'aiguille et décalé par rapport au centre de courbure de celle-ci, .
• . des moyens de guidage en translation adaptés pour autoriser un mouvement relatif de translation entre le support de l'axe d'articulation et la tête,
• . une lumière de guidage de l'aiguille ménagée dans un élément solidaire de la tête, ladite lumière étant traversée par l'aiguille et agencée de façon à imposer à celle-ci son déplacement selon la trajectoire (T) lorsque la tête et l'axe sont soumis au mouvement relatif de translation sus-évoqué,
• . des moyens élastiques associés à la biellette porte-aiguille de façon à solliciter celle-ci dans le sens de son écartement par rapport à la tête vers une position extrême de butée.

In a preferred embodiment, the kinematic guide means of each needle comprise:

• . an articulated link, adapted to carry the needle so that, in the preferential case of a curved needle, the concavity of the latter is oriented in the same direction as the trajectory (T),
• . an axis of articulation of said link, carried by a support so that said axis is offset transversely relative to the head and in the preferential case of a curved needle is located on the side of the concavity of the needle and offset by relative to the center of curvature thereof,.
• . means for guiding in translation adapted to allow relative movement of translation between the support of the articulation axis and the head,
• . a needle guide lumen formed in an element integral with the head, said lumen being passed through by the needle and arranged so as to impose on the latter its displacement along the path (T) when the head and the axis are subjected to the relative movement of translation mentioned above,
• . elastic means associated with the needle-holder link so as to urge the latter in the direction of its separation from the head towards an extreme stop position.

• . au moins un support d'empilage mobile,
• . un dispositif de préhension du type précédemment décrit, situé au-dessus dudit support d'empilage avec sa ou ses surfaces d'appui situées en regard dudit support, et,
• . des moyens d'entraînement du support d'empilage dans un mouvément ascendant vers le dispositif de préhension ou dans un mouvement descendant.

The invention finally extends to a machine for gripping and transferring flexible layers, by unit or by determined number; said machine essentially comprises:

• . at least one mobile stacking support,
• . a gripping device of the type described above, located above said stacking support with its support surface (s) located opposite said support, and,
• . means for driving the stacking support in an upward movement towards the gripping device or in a downward movement.

• . la figure 1 est une vue de face partiellement coupée par un plan vertical AA', d'un dispositif de préhension conforme à l'invention,
• . la figure 2 en est une vue de côté selon la flèche V,
• . les figures 3 et 4 en sont des coupes de détail respectivement selon BB' et CC',
• . les figures 5 et 6 sont des schémas montrant la tête du dispositif et son aiguille respectivement dans une position intermédiaire d'accrochage d'une couche et dans la position finale d'accrochage,
• . les figures 7a, 7b, 7c, 7d, 7e, 7f et 7g sont des schémas explicatifs à échelle très dilatée, montrant diverses phases de fonctionnement du dispositif,
• . la figure 8 schématise en perspective une machine de préhension et de transfert conforme à l'invention, en cours de-fonctionnement,
• . la figure 9 représente en variante, à échelle dilatée, une aiguille à deux pointes, susceptible d'équiper le dispositif notamment dans le cas de couches très minces,
• . les figures lOa, lOb et 10c sont des schémas explicatifs à échelle très dilatée dans le cas , d'une utilisation d'une aiguille à deux pointes, telle que représentée à la figure 9.

Other characteristics, objects and advantages of the invention will emerge from the description which follows with reference to the appended drawings, which present by way of nonlimiting example a preferred embodiment; on these drawings which form an integral part of this description:

• . FIG. 1 is a front view partially cut by a vertical plane AA ′, of a gripping device according to the invention,
• . FIG. 2 is a side view thereof according to arrow V,
• . FIGS. 3 and 4 are detailed sections thereof respectively along BB 'and CC',
• . FIGS. 5 and 6 are diagrams showing the head of the device and its needle respectively in an intermediate position for attaching a layer and in the final position for attaching,
• . FIGS. 7a, 7b, 7c, 7d, 7e, 7f and 7g are explanatory diagrams on a very expanded scale, showing various phases of operation of the device,
• . FIG. 8 schematizes in perspective a gripping and transfer machine according to the invention, during operation,
• . FIG. 9 shows a variant, on an expanded scale, of a needle with two points, capable of equipping the device, in particular in the case of very thin layers. thin,
• . FIGS. 10a, 10b and 10c are explanatory diagrams on a very expanded scale in the case of the use of a two-pointed needle, as shown in FIG. 9.

The gripping device shown by way of example in FIGS. 1 to 4 comprises a frame 1 which carries around a central region -la- several assemblies 2, the structure of which is described in detail below. The number of sets 2 and their distribution depend on the shape and dimensions of the textile pieces to be gripped (which will be designated below by "pieces of fabric" whatever their knitted, woven or other texture). For example, for small parts fitting into a trapezoid, intended in particular for the manufacture of briefs, these sets may be four in number, two by two opposite, so as to grip each part in the vicinity of an angle.

As will be seen below, the chassis 1 can be associated with transfer means, making it possible to drive it between several locations where the parts are to be grasped or deposited.

In its central region, the chassis 1 is equipped with air blowing means in a substantially vertical direction (or a secant direction relative to the horizontal plane). These means comprise a support 3 oriented downwards and pierced at its end with a channel 4 to which is connected a flexible air intake duct 5; the air emerges from the channel 4 through an orifice 4a oriented downwards.

Each set 2 comprises a plate 6 positioned in a roughly vertical plane; this plate is articulated by two needle screws such as 7 on two legs of the chassis 1 so as to be able to undergo relative to this chassis tilting movements of small amplitude, around a horizontal axis passing through the screws 7.

The plate 6 is associated with drive means adapted to drive it in rapid round-trip movements, in rotation around the screws 7.

In the example, these means consist, on the one hand, of a single-acting cylinder 8 having a movable projecting rod 8a which bears against the lower part of the plate 6, on the other hand, by a return spring 9 acting on the upper part of said plate. Supports 10 and 11 secured to the chassis 1 allow the mounting of these means in appropriate positions.

The plate 6 supports the body 12a of a double-acting pneumatic cylinder 12, by means of a lug 13 integral with said plate and forming an projection relative to the chassis 1. The body 12a of the cylinder is fixed on the lug 13 as shown in Figures 1 and 2, so that the movable rod 12b of said cylinder is directed downwards in a substantially vertical position.

The jack 12 is associated with a proximity sensor 26 of a type known per se (in particular magnetic) which detects the high position of its piston and then delivers a control signal, causing the latter to lock in this position.

Furthermore, in the lower part a gripping head 14 is screwed onto the end of the rod 12b of the pneumatic cylinder 12.

This head is formed by a cylinder portion with a horizontal lower base 14a, called to play the role of a support surface for the tissue to be grasped. Said head is partially split, by a fine groove 15 of thickness slightly greater than that of a puncture needle of the conventional type; this groove extends in a plane (vertical) substantially perpendicular to that of the support surface (horizontal) and opens along a diameter of said support surface.

In addition, the head 14 has an openwork part 16, in the example of circular section, which also opens onto the bearing surface 14a and extends on either side of the plane containing the groove 15. (In l 'example, this perforated part 16 is formed by the extension of a threaded hole which allows the head 14 to be screwed onto the jack rod 12b).

In addition, the head 14 carries a finger 27 which slides in an appropriate notch 6a of the plate 6, in order to avoid rotation of said head on itself (around its vertical axis) and to ensure guidance of that - ci during its vertical translational movement.

Furthermore, the plate 6 carries a support 17, which is fixed on the latter in a position offset transversely relative to the head 14; this support is fixed on the plate by means of a stud 18 and a tubular spacer 19, which allow it to be assigned a relative preset position relative to said plate.

This support 17 carries a hinge pin 20 about which a link 21 can pivot; this axis 20 offset transversely with respect to the axis of the head 14 is located above the bearing surface 14a.

Elastic means are associated with the link 21 and arranged to urge the latter in the direction of its spacing with respect to the head, towards an extreme position where it abuts against the support 17 (position of FIG. 1). In the example, these elastic means consist of one end 22a of a spring 22, which comes to bear on the link 21; this spring is wound around the tubular spacer 19 and its other end 22b is locked in a hole in the plate 6.

In addition, the link 21 is pierced with a lumen for the passage and fixing of a curved needle 23. This needle, of the conventional needle pricking type, comprises, opposite its point 23a, a heel 23b which is housed in the above-mentioned light of the link 21 and locked in the preset position by a pressure screw 24.

The means for positioning the needle (spacer 19, support 17, link 21 and heel fixing light 23b) are arranged so that (apart from the thicknesses) said needle is located in the plane of the groove 15 of the head and can move in this plane relative to the head, by rotation of the rod 21 about its axis 20; the concavity of said needle is oriented upwards and its center of curvature is located between the axis of articulation 20 and the vertical axis of the head, in a position closer to this vertical axis so as to be very much offset relative to axis 20.

In addition, the needle 23 passes through a guide lumen 25a formed in an element integral with the head (in the example a plate 25 fixed on the edge thereof in the preset position). This guide light 25a and the positioning means already mentioned impose at all times the relative position of the needle relative to the head and are adjusted so as to give it the movements which are detailed below.

When under the effect of a vertical thrust, the head 14 rises to its high retracted position, the needle comes into contact with the lower edge of the guide lumen 25a which causes it to pivot around the axis 20. The relative movement of the needle relative to the head is therefore the combination of a rotational movement around the axis 20 and a vertical translational movement. Figures 5 and 6 show respectively an intermediate position of the needle and its link relative to the head 14 and the final position of attachment of the fabric.

The combination of the above-mentioned movements leads the needle tip 23a to move on a path T as shown diagrammatically in FIG. 7b. This trajectory of the needle tip 23a is considered relative to the head, that is to say taking this head 14 as a reference.

• . d'une portion initiale Ti correspondant à la descente de l'aiguille vers le tissu (en déplacement relatif) et à sa pénétration,
• . d'une portion de rebroussement Tr au cours de laquelle l'angle de pénétration« passe d'une valeur positive à une valeur négative,
• . d'une portion finale Tf au cours de laquelle la pointe d'aiguille remonte vers la surface d'appui 14a de la tête jusqu'à couper celle-ci au niveau de la portion ajourée 16 et à venir en retrait dans la rainure 15 de l'autre côté de l'axe vertical` de la tête.

The path T, as imposed on the needle tip by the kinematic guide means described, has the shape of a C with concavity directed upwards; it is successively composed:

• . an initial portion Ti corresponding to the descent of the needle towards the tissue (in relative displacement) and to its penetration,
• . a reversal portion Tr during which the penetration angle “changes from a positive value to a negative value,
• . of a final portion Tf during which the needle point rises towards the bearing surface 14a of the head until cutting the latter at the level of the perforated portion 16 and coming back into the groove 15 of the other side of the vertical axis of the head.

In all positions, the needle is above the path T: the direction of its tip (tangent to the tip) is located above the tangent to the trajectory and makes an angle with the latter of the order of a few degrees at 20 °.

The diagrams in FIGS. 7a to 7g illustrate the relative movement of the needle relative to the head 14.

The needle 23 is positioned so as to be situated initially set back in the groove 15 as shown in FIG. 7a. The head is in the low position and the jack 12 which carries it is in the open air, which leaves the head free to rise with constant and low friction forces. The link 21 is in the extreme stop position and the needle is in contact with the upper edge of the guide light 25a.

In a first phase, the stacking symbolized at E in the diagrams, is caused to move upwards according to the arrows F in FIG. 7a, until its upper layer S comes into contact with the bearing surface 14a of the head.

At this instant, the latter is raised and tends to retract upwards under the thrust of the stack; the pressure of the bearing surface on the stack is substantially constant and low enough not to significantly compress the layers and in particular the upper layer (due to the constant friction forces and low value of the jack 12).

At the start of the retraction of the head, the needle has relative to said head a vertical downward relative movement until it comes to bear against the lower edge of the guide light 25a: its point then begins to move on the portion Ti of the trajectory until it comes into contact with the layer S as shown in FIG. 7b. In this phase of the start of movement, the spring 22 confers good flexibility on the movement of the needle and conditions a substantially constant penetration pressure of the needle.

At the instant of penetration of the needle into the tissue, the angle α of penetration (i.e. the angle defined by the direction of the end of the needle and the plane of the fabric) is between about 15 and 35 °, which guarantees correct penetration of the needle end through the fibers of the fabric.

This penetration angle 0 (is different from the angle (3 formed by the tangent to the trajectory Ti (α> β) at the same point, because the displacement of the point is not constituted by a rotation around the center of curvature of the needle; it follows that the movement of the needle is not limited to a rotating component, but includes a component in translation constituted by a sliding towards the axis of the head 14, slip which causes a push on the fabric towards this axis. In the case of a needle without retainer, the angle β formed by the tangent to the path T with the layer at the point of penetration is preferably substantially between 3 ° and 15 °, which ensures an effective push on the tissue from the start of penetration to form the ripple (in the case of a locking needle, the value of this angle is less essential, since, as will be seen below, the thrust exerted on the fabric by the retainer is extremely ef effective and sufficient in itself).

The progressive retraction movement of the head continues as the stack rises. The point of the needle having entered the tissue moves over the initial portion Ti of the trajectory, then over the cusp portion Tr (FIG. 7c); the fabric repelled during this movement in the direction of the arrow P forms a ripple of increasing height in the perforated part 16 of the head.

If only one layer of fabric is to be grasped, the means for holding and guiding the needle are adjusted so that the retraction portion Tr of the trajectory is located at a distance from the bearing surface 14a, less than or equal to the thickness of a layer.

If -n- layers are to be grasped, this adjustment is made so that said cusp portion Tr is located in the lowest layer to be grasped, that is to say at a distance greater than (n - 1) e and less than or equal to ne (where e is the thickness of a layer).

When the point of the needle turns to the end of the reversal portion Tr (FIG. 7d), the penetration angle is reversed and, due to the undulation of the fabric, the point comes out on the underside of layer S without risk of catching the layer below (since it always remains above the level thereof).

The lifting of the stack E continues as does the upward movement of the head (FIG. 7e); the tip of the needle then describes the final portion Tf of the trajectory, which rises relative to the bearing surface and cuts the plane of this surface at the level of the perforated part 16. The needle tip which came out of the fabric on the underside of layer S re-enters it at the level of the ripple. In addition, the assembly of the needle tends to fade upward in the groove 15 of the head.

FIG. 7f shows diagrammatically the final position of the needle when its tip reaches the end of the portion Tf of the trajectory. In this position, the needle tip is positioned recessed in the groove 15 of the head; in the example shown, the needle has come completely back into this groove. The fabric stitched right through, in two places, is perfectly blocked by the needle and the support surface without being able to slip and come off.

In this position, the proximity sensor 26 controls the pneumatic supply of the jack 12, which blocks the head in the high retracted position. The firmly held fabric is locked in this state and cannot come off regardless of the movements impressed on the head and the stresses exerted on it.

The stack E is then brought down and simultaneously the jack 8 is subjected to several pneumatic pulses which subject the plate and therefore the needle / head assembly, rapid movements back and forth in a direction substantially parallel to the plane of the support surface. In addition, air is blown in through the channel 4, the orifice 4a of which is in the immediate vicinity of the layer S when the head 14 is fully retracted in the high position.

These actions ensure an extremely "efficient concreting of the layer S with respect to the layer S _' situated immediately below it. It should be noted that the takeoff is obtained in a very safe manner even in the case of layers having a high tendency to adhere to each other: this is due to the effectiveness of the take-off actions described above, but also to the fact that significant adhesion forces then develop between the stack and the non-attached layer S ', forces which tend to retain this layer on the stack.

Once the layer S separated from the stack, the movements of the actuator 8 and the air blowing are stopped and the gripping device is moved to the desired location.

The pneumatic cylinder 12 is then controlled in the opposite direction to condition the descent of the head 14 relative to the plate 6. The needle 23 then undergoes a reverse movement and releases the layer of fabric (FIG. 7g). It should be noted that the presence of the spring 22 allows this movement to be carried out with all the necessary flexibility. At the end of the stroke, the needle returns to its initial position, set back with respect to the bearing surface.

Furthermore, FIG. 8 represents a machine for gripping and transferring layers, comprising a device of the type described above, equipped with four gripping assemblies 2.

This machine comprises a movable stacking support 28 (or several supports), located below and opposite one of the locations where the gripping device can be positioned. This stacking support is associated with a jack 29 making it possible to raise it towards the gripping device or to lower it again.

The gripping device is carried by transfer means adapted to be able to move it between one or more position (s) located opposite the stacking support (s) 28 and one or more other positions located above above places where the layers are to be deposited. In the example shown, these means are shown diagrammatically by a carriage 30 movable along guide rails 31 and a jack drive which we see the movable rod at 32; 18 gripping device is suspended from the carriage 30.

The automation of the gripping and transfer operations can be easily obtained by providing control means adapted to generate the course of the following cycle: lifting of the stacking support 28 towards the gripping device until contact with the latter. view of producing the retraction phase of its heads 14, lowering of said support with rapid back-and-forth movements of the plates 6 relative to the chassis 1 and air blowing, transfer of the gripping device to another position, driving the heads 14 to produce the return phase of the needles 23, return of the gripping device to the aforementioned stacking support or another stacking support.

Of course, other means of transfer can be provided. Likewise, all the movements indicated are relative movements of organs with respect to each other, and it is obvious that it is equivalent to move a first organ with respect to a second or, in the opposite direction, the second with respect to at first.

In addition, in the machine described above, where several assemblies 2 are mounted on the chassis 1 and are distributed around its central region in order to ensure gripping of the layers in several zones, it is preferable, during the phase takeoff, synchronize the control of the various cylinders 8 so as to subject the heads 14 to synchronized movements of separation or approximation relative to the central region.

This produces a series of tensions and relaxations of the gripped layer S, which further increase the effectiveness of its takeoff relative to the lower layer.

For this purpose, each assembly 2 is arranged so that the rods of the jacks 8 have a radial direction (direction extending from the assembly 2 towards the central region of the chassis) and that each needle is located in a tangential plane perpendicular to this direction. It should be noted that such a tangential position of the needles is very favorable for opposing any radial sliding. fabric during tension and relaxation

Furthermore, the gripping device can be equipped with a needle 33 as shown diagrammatically in FIG. 9. This needle has the same general shape as the needle 23, but has at its end two separate points 33a and 33b, which the example are formed by beaks with biased upper faces. These points define at their base a front face 33c acting as a retainer. The tips 33a and 33b can have a length of the order of 5/10 mm.

This type of needle combined with the kinematics described above gives a remarkable result in terms of gripping efficiency, in particular for very thin layers. It is thus possible to seize with a success rate of 100% fabrics of thickness equal to 3 / 10e of mm.

The diagrams in FIGS. 10a, 10b and 10c illustrate the gripping of a layer by means of such a needle.

The needle first enters the upper layer, in the same way as the needle 23 previously mentioned, and this, until its stop 33c comes into contact with the upper face of the layer (FIG. 10a).

Its penetration is then stopped by the stop 33c, and it pushes the tissue extremely efficiently towards the perforated part 16 of the head; it should be noted that a reaction force is then exerted on the needle which tends to retract upwards by causing the spring 22 to act (FIG. 10b). Thus, the trajectory of the needle tip is substantially more flattened than in the previous case, and the risks of accidentally grasping the layer below is negligible, despite the very small thickness of the fabric.

At the end of the movement, the undulation markedly more marked than in the previous case is firmly pinched between the retainer 33c and the opposite edge of the perforated part 16 (FIG. 10c). The gripping of the tissue is therefore carried out not only by pricking the tissue, but also by pinching the ripple: it has proven to be extremely safe experimentally, whatever the thickness of the tissue and its texture.

We have described above a gripping device and an automated machine for transferring pieces of fabric. The invention extends of course to the case of a manual device comprising a single head (or possibly a small number of heads) which would be applied manually against a stack in order to separate one or more upper layers. The jack 12 is then replaced by means for guiding the head in translation; the kinematic guide means of the needle remain similar to those described, the blocking of the head in the high retracted position being effected by a latching member, unlockable by hand; a low modulus spring may be provided to ensure the return of the head downwards and the reverse movement of the needle. The maintenance of such a device is carried out by a handle integral with the plate.

Such a very simple device facilitates in certain cases (materials having a strong tendency to adhere) the manual operation of gripping and separation of the layers.

Claims (34)

1 / - Method for gripping a layer or a defined number of layers of flexible material placed on a stack of layers, in order to separate said layer or layers (S) from the other layers of the stack (E), this process consisting: . to apply above at least one area of the upper flexible layer (S) of the stack, a bearing surface (14a) provided with an openwork part (16), until bringing this surface into contact with said layer (S) which remains free at the level of the perforated part (16), . then moving a needle (23) relative to said bearing surface so that its pointed end (23a) moves relative to said bearing surface taken as a reference, on a trajectory (T) successively comprising, first, an initial portion (Ti), starting from the support surface and moving away from it so as to make the needle penetrate the flexible layer (S), then, a cusp portion (Tr), comprising a change in the direction of relative movement of the needle tip relative to the bearing surface, finally, a final portion (Tf), approaching the bearing surface and offset from the initial portion in order to not to coincide with it, . then to generate a relative spacing movement between the stack (E) and the needle / bearing surface assembly,
said method being characterized in that the movement of the needle (23) is carried out so that, during the displacement of its end along the initial portion (Ti) and the cusp portion (Tr), said needle pushes the flexible layer (S) towards the perforated part (16) and causes it to form a corrugation in said perforated part, the final portion (Tf) of the path passing through said corrugation. 2 / - gripping method according to claim 1, characterized in that the needle is positioned, during its movement along the initial portion (Ti) and the cusp portion (Tr), so that, in each point, the direction of the needle at its end does not coincide with the tangent to the trajectory of so as to ensure the above-mentioned pushing action on the flexible layer in order to cause the latter to form the above-mentioned undulation. 3 / - Gripping method according to claim .2, characterized in that the needle is positioned during its movement so that its direction at its tip is located at each point of the trajectory, above the tangent to said trajectory in order to ensure a pushing action of the flexible layer by promoting the lifting thereof towards the perforated part (16) of the bearing surface (14a). 4 / - gripping method according to claim 3, characterized in that, at the start of the initial portion of the trajectory (Ti), the needle is caused to penetrate into the upper flexible layer (S) with an angle of penetration α substantially between 15 ° and 35 °, the displacement of the needle being then carried out so that the cusp portion (Tr) is located at a distance from the bearing surface (14a) less than or equal to the thickness of the flexible layer or layers to be gripped (S). 5 / - gripping method according to one of claims 2, 3 or 4, characterized in that the displacement of the needle (23) relative to the bearing surface (14a) is achieved by a rotational movement of said needle about an axis (20), itself driven in a relative translational movement relative to the bearing surface (14a), said axis being located opposite the flexible layers relative to the plane of the bearing surface and tending to approach this plane during the relative translational movement. 6 / - gripping method according to claim 5, wherein a curved needle is used with a concavity oriented in the same direction as that of the trajectory (T), characterized in that the displacement of the needle is carried out by a rotational movement around an axis (20) offset transversely relative to the center of curvature of said needle, said axis itself being driven by the relative movement of translation mentioned above. 7 / - gripping method according to one of claims 1, 2, 3, 4, 5 or 6, characterized in that one uses a needle having an end provided at least one point and, upstream of the latter, a stop adapted to come into abutment against the flexible layer in order to ensure or increase the pushing action thereon. 8 / - gripping method according to claim 7, characterized in that one uses a needle having, at its end, two separate points, the abovementioned stopper being formed by the part of the needle located between the bases of said points . 9 / - gripping method according to one of claims 7 or 8, characterized in that one uses a needle associated with elastic means tending to separate it from the bearing surface and mounted so as to be able to retract on a short stroke towards the bearing surface. 10 / - Gripping method according to one of claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, characterized in that the bearing surface (14a) is applied to the flexible layer upper (S) of the stack by a relative movement of bringing said stack and said bearing surface closer together, movement carried out so that, after contact, the pressure of the bearing surface on the stack is substantially constant and fairly weak so as not to compress the flexible layer (s) appreciably. 11 / - Gripping method according to one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, characterized in that, at the end of the final portion (Tf) of the movement of the needle, the latter is blocked relative to the bearing surface and it is kept blocked during the relative spacing movement between the stack and the needle / bearing surface assembly. 12 / - Gripping method according to claim 11, characterized in that, after blocking of the needle (23) relative to the bearing surface (14a), the needle / bearing surface assembly is moved in several rapid back and forth movements in a direction substantially parallel to the plane of the bearing surface. 13 / - gripping method according to one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, in which the flexible layer or layers are gripped, in more i seperate areas spread around a central region of these, by means of several needles each associated with a bearing surface, characterized in that the movements of the needles are made so that their trajectories (T) are located in roughly tangential planes. 14 / - gripping method according to claims 12 and 13 taken together, characterized in that the rapid back-and-forth movements of each needle / bearing surface assembly are carried out in a radial direction substantially perpendicular to the plane containing the trajectory of the needle in question, the movements of the various assemblies being synchronized so as to move away or approach simultaneously the central region of the flexible layer or layers (S) so as to stretch and relax said layer or layers. 15 / - Gripping method according to one of claims 13 or 14, characterized in that, after blocking of the needles (23) relative to their respective bearing surface (14a), air is blown into the central region of the upper flexible layer (S) in the direction tending to separate said layer from the plane of the bearing surfaces. 16 / - gripping method according to one of the preceding claims, in which, after the relative movement of spacing of the stack (E), the needle or bearing / bearing surface assemblies are brought above a location where the flexible layer (s) are to be deposited, characterized in that each needle (23) is subjected to a reverse movement relative to the corresponding bearing surface (14a) so as to bring each of said needles back into its initial position set back from the corresponding bearing surface. 17 / - Device for gripping layers of flexible material, comprising at least one head (14) provided with a bearing surface (14a) provided with an openwork part (16), a needle (23) associated with said head and movable relative to the latter and kinematic guide means of each needle (23) relative to the corresponding head (14), imposing on the needle end (23a) a trajectory (T) (relative to the bearing surface (14a) taken as a reference) having an initial portion (Ti), a cusp portion (Tr) and a final portion (Tf) and having the shape of a C with concavity oriented towards the bearing surface (14a) of the head, said device being characterized in that the kinematic guide means (12, 20, 21, 25a) are adapted to move the corresponding needle according to a movement such that the direction of the end of the needle is distinct from the tangent to the trajectory (T) at least over the initial portion (Ti) and the cusp portion (Tr) of this trajectory. 18 / - Device for gripping layers of flexible material, comprising at least one head (14) provided with a bearing surface (14a) provided with an openwork part (16), a needle (23) associated with said head and movable relative to the latter and kinematic guide means of each needle (23) relative to the corresponding head (14), imposing on the needle end (23a) a trajectory (T) (relative to the support surface (14a) taken as a reference) having an initial portion (Ti), a cusp portion (Tr) and a final portion (Tf) and having the shape of a C with a concavity oriented towards the support surface (14a) of the head, said device being characterized in that the needle has an end provided with at least one point (33a, 33b) and, upstream of the latter, a stop (33c) adapted to come in abutment against the flexible layer. 19 / - Device according to claim 18, characterized in that the needle has at its end, two points (33a, 33b) separated and a stopper (33c) formed by the part located between the bases of said points. 20 / - Gripping device according to one of claims 17, 18 or 19, characterized in that: . each head (14) has a fine groove (15), of thickness slightly greater than that of the needle (23), extending in a plane substantially perpendicular to the bearing surface (14a) and cutting the perforated part (16) of the head, . the kinematic guide means are adapted to impose on the needle (23) an initial position entirely recessed in said groove (15) and a final position at the end of the movement, in which at least the end (23a) of said needle is recessed in said groove. 21 / - gripping device according to claim 20, characterized in that the kinematic guide means are adapted so that the final portion (Tf) of the path of the needle end intersects the plane of the bearing surface at level of said perforated part (16). 22 / - Gripping device according to one of claims 17, 18, 19, 20 or 21, characterized in that the kinematic guide means of each needle comprise: . an articulated link (21), adapted to carry the needle (23), . an axis (20) of articulation of said link, carried by a support (17) so that said axis is offset transversely relative to the head (14), . translational guide means (12) adapted to allow relative translational movement between the support (17) of the hinge pin and the head (14), and . a lumen (25a) for guiding the needle formed in an element (25) integral with the head (14), said lumen (25a) being traversed by the needle and arranged so as to force it to move according to the trajectory (T) when the head (14) and the axis (20) are subjected to the above-mentioned relative movement of translation. 23 / - Gripping device according to claim 22, characterized in that elastic means (22) are associated with the needle holder rod (21) and arranged so as to urge the latter, in the direction of its spacing relative to at the head (14), towards an extreme stop position. 24 / - Gripping device according to one of claims 22 or 23, wherein the needle is a curved needle carried by the link (21) so that its concavity is oriented in the same direction as that of the trajectory (T ), characterized in that the axis (20) of articulation of said link is located on the side of the concavity of the needle and is offset transversely relative to the center of the latter. 25 / - Gripping device according to one of claims 22, 23 or 24, characterized in that: the head (14) is mounted movable in translation relative to a plate (6), the support (17) of the articulation axis is fixed on said plate, - means for driving and guiding in translation (12) are associated with the head (14) and suitable for: . in a retraction phase during which the needle end (23a) describes the trajectory (T), passively guiding the translation of the head (14), in a blocking phase, as said / secure a head blocking (14) in the retracted position relative to the plate (6), . in a return phase, drive the head (14) in a reverse translation movement from that of the retraction phase, movement during which the needle end (23a) describes the trajectory (T) in the opposite direction. 26 / - Gripping device according to claim 25, characterized in that the aforementioned drive and guide means consist of a pneumatic cylinder (12) associated with a sensor (26) adapted to detect the retracted position of the head ( 14) and order the blocking of said jack (12). 27 / - Gripping device according to one of claims 25 or 26, characterized in that: - the support (17) of the hinge pin (20) is fixed on the plate (6) in a preset relative position, - the needle (23) is fixed on its link (21) in a preset relative position. 28 / - Gripping device according to one of claims 25, 26 or 27, characterized in that each plate (6) is movably mounted on a chassis (1) so as to be able to undergo relative to said chassis, small movements amplitude parallel to the plane of the bearing surface (14a) of the head, said plate (6) being associated with drive means (8, 9) adapted to drive it in rapid return movements with respect to the chassis (1). 29 / - Gripping device according to claim 28, characterized in that several plates (6) each provided with their movable head (14) and needle (23) are mounted on the frame (1) and distributed around a central region (la) thereof, in order to ensure a grip in several areas of the flexible layer or layers. 30 / - Gripping device according to claim 29, characterized in that the drive means (8, 9) of the various plates relative to the frame (1) are adapted to be able to subject the heads (14) to synchronized movements d 'spacing or approximation relative to the central region (la) of the chassis. 31 / - Gripping device according to one of claims 29 or 30, characterized in that it comprises means (4, 5) for blowing air at the central region (la) of the chassis in a secant direction relative to the plane of the bearing surfaces (14a). 32 / - Gripping device according to one of claims 29, 30 or 31, characterized in that the various plates (6) are mounted on the frame (1) so that each needle (23) is located in a tangential plane relative to a center located in the central region (la) of the chassis. 33 / - Machine for gripping layers and transferring them by unit or by determined number, characterized in that it comprises: . at least one mobile stacking support (28), . a gripping device according to one of claims 17 to 32, located above said stacking support with its support surface (s) (14a) located opposite said support, and, . means (29) for driving the stacking support in an upward movement towards the gripping device or in a downward movement. 34 / - Machine according to claim 33, characterized in that its gripping device is carried by transfer means (30, 31, 32) adapted to be able to move said device between one or more position (s) located opposite the support (s) ) stacking (28) and one or more other positions located above locations where the layers are to be deposited, control means being provided to generate the course of the following cycle: lifting the stacking support (28) towards the gripping device until contact with it in order to produce the retraction phase of its heads (14), lowering of said support with rapid back-and-forth movements of the plates (6) relative to the chassis ( 1) and blowing air, transfer of the gripping device to another position, driving the heads (14) to produce the return phase of the needles (23), return of the gripping device to the aforementioned stacking support or another stacking support.

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