EP0468578B1 - Workpiece guiding device and automatic sewing procedure - Google Patents

Abstract

The invention relates to a process and a device for the automatic sewing of a piece of fabric along its edges. <??>The process is of the type in which a rotating member (12) orientable by pivoting about a vertical axis ZZ' is arranged so as to bear against the fabric upstream of the press foot in order to guide it and drive it upstream of the sewing zone. According to the invention, the rotating member (12) is driven in rotation by a roller (16) coming to bear against said member in its upper zone, through which the vertical pivot axis ZZ' passes, in such a way that the bearing of the roller against this member leaves the latter free to pivot, especially at a high frequency, about the axis ZZ', whatever the coefficient of friction between the roller and rotating member. <IMAGE>

Description

The invention relates to a device for guiding a piece of fabric parallel to a predefined reference line, constituted in particular by an edge of the fabric; it relates to a device equipping a sewing machine of the traditional type comprising in particular a book-carrying plate and a mechanism with claws for advancing the fabric, associated with at least one needle; thereafter this mechanism and its accessories will be designated by the expression "presser foot". The invention extends to an automatic fabric sewing process, implemented by means of a sewing machine equipped with such a guide device. It also extends to improved sewing machines equipped with one or more guide devices according to the invention.

In sewing, the operations of sewing pieces of fabric generally aim to sew two pieces together along one of their edges or to make a hem at the edge of a piece, or even to fix along one edge of 'a piece a ribbon, elastic, belt, etc ... Currently, these operations require the presence of an operator who guides the fabric in front of the needle so that the seam follows the desired line. In an attempt to achieve labor savings and productivity gains, guide systems have been proposed which move the fabric in the transverse direction in front of the needle in order to constantly bring the area to be sewn in front of the needle ; these systems generally comprise wheels or tracks on casters, arranged in the transverse direction upstream of the needle; these wheels or tracks are rotated in one direction or the other so as to be able to move the fabric transversely in both directions in order to make the appropriate position corrections. However, these systems are little used because they lead to imperfect seams and frequent faults; in fact, the fabric driven by the presser foot at the level of the needle and braked upstream of the latter by the guide system tends to roll on itself, crease or pucker so random, which is incompatible with obtaining a regular quality seam; this defect is particularly serious for stretch fabrics or "soft mesh" fabrics which it is impossible to sew with known systems; in the case of two pieces to be assembled edge to edge, it leads to offsets from one edge relative to the other and to assembly imperfections detrimental to the quality of the product produced. In addition, most of the existing systems can only be used for fabrics of defined thickness.

Furthermore, patents FR 2 585 683 and EU 0 216 644 describe a fabric guiding device which comprises a spherical wheel bearing against the fabric upstream of the presser foot and rotating in a single direction of rotation to ensure a drive and guiding the fabric in the sewing area; this spherical wheel is pivotally mounted about a vertical axis so as to be able to orient it according to different drive directions making it possible to bring the fabric back to the desired position. In the device covered by these patents, the spherical wheel is rotated by friction by a roller which comes to bear on one side thereof in the horizontal plane containing the axis of said wheel. As these patents explain (in particular page 6, line 32 to page 7, line 35 of patent FR 2 585 683), the drive roller of the spherical wheel rotates at constant speed and its arrangement relative to the wheel ( lateral support in the horizontal plane containing the axis of rotation of the wheel) ensures automatic modulation of the speed of rotation of said wheel when the latter changes orientation: in fact, the roller driven at constant speed of rotation ensures that level of contact a constant tangential speed of the wheel; when the latter takes an oblique orientation with respect to the roller (axes of the roller and of the wheel not parallel), the wheel driven in circles of smaller diameter rotates at greater speed. This effect is favorable because the wheel then drives the fabric at a higher resulting speed, the component of which along the drive direction of the presser foot is constant whatever the orientation of the wheel; this component can therefore be brought to coincide permanently with the drive speed of the presser foot by adjusting the roller rotation speed once and for all to an appropriate determined value.

However, such a system encounters a serious practical difficulty of implementation. To allow satisfactory drive of the spherical wheel by the roller, it is necessary that the surfaces of these members roll without sliding against each other and therefore have a sufficient coefficient of friction; when the spherical wheel pivots around the vertical axis to adopt another orientation, the support of the roller on this wheel describes a segment of large circle and this movement is transverse with respect to the roller (parallel to the axis of the roller and perpendicular at tangential speed), so that the friction of the two surfaces tends to oppose the movement. Under these conditions, the pivoting of the spherical wheel in order to modify its orientation requires the application of significant forces, must be slow in relation to the speeds of rotation of the roller and the wheel, and produce rapid wear of the surfaces which forces frequent changes of these organs.

Thus, the problem of automatic sewing in the clothing sector is currently not satisfactorily resolved and the need for an operator by sewing machine, an operator who is employed full time by this machine, constitutes an obstacle for balance workstations and increase productivity gains.

The present invention proposes to provide a solution to the above-mentioned problem. It relates to a method of guiding the fabric and an improved device for implementing the type having a member rotating in one direction, in particular a sphere, which is caused to pivot around a vertical axis in order to orient it in directions. different fabric drive. The subject of the invention is the mounting of one or more of these improved devices on a sewing machine of a type known per se (provided with a work-holding plate and a presser foot associated with at least one needle) in order to allow automatic sewing of pieces of fabric parallel to a predefined reference line, constituted in particular by an edge pieces. The invention applies regardless of the purpose of sewing: sewing a ribbon, a belt, an elastic band at the edge of the workpiece, sewing a hem (the machine being provided with a device classic fabric folding), sewing two pieces together (the machine is equipped with two guiding devices) ...

The objective of the invention is to allow obtaining a regular seam of good quality, whatever the fabric (in particular fine fabrics difficult to handle, stretch fabrics ...), and this, by eliminating the difficulties of implementation encountered by the device of the same type described in the aforementioned patents.

Another objective is to provide a simple structure guiding device, which, mounted on a traditional type sewing machine, allows automatic stitching on fabrics of any thickness.

• "pièce de tissu" : pièce en tissu ou en toute autre matière similaire susceptible d'être cousue,
• direction "longitudinale" : direction de la ligne de couture désirée,
• "direction générale longitudinale" : direction qui peut être angulairement décalée par rapport à ladite direction longitudinale d'un angle petit inférieur à 30°, mais dont l'orientation générale est longitudinale,
• direction "transversale" : direction perpendiculaire à la direction longitudinale,
• direction "verticale" : direction orthogonale à la nappe de tissu (ou à la plaque porte-ouvrage de la machine à coudre, qui porte le tissu),
• direction "horizontale" : direction parallèle à la nappe de tissu (ou à la plaque porte-ouvrage de la machine à coudre),
• "pied-presseur" : ensemble du mécanisme classique assurant le guidage et l'avance du tissu au niveau de l'aiguille.

Certain terms used subsequently in order to simplify the terminology and make the description clearer are defined below:

• "piece of fabric": piece of fabric or any other similar material capable of being sewn,
• "longitudinal" direction: direction of the desired seam line,
• "general longitudinal direction": direction which can be angularly offset with respect to said longitudinal direction by a small angle less than 30 °, but whose general orientation is longitudinal,
• "transverse" direction: direction perpendicular to the longitudinal direction,
• "vertical" direction: direction orthogonal to the sheet of fabric (or to the work-holding plate of the sewing machine, which carries the fabric),
• "horizontal" direction: direction parallel to the sheet of fabric (or to the work-holding plate of the sewing machine),
• "presser foot": assembly of the classic mechanism ensuring the guiding and advancing of the fabric at the needle.

The process targeted by the invention is of the type in which a rotating member, orientable by pivoting about a vertical axis, is disposed in abutment against the fabric upstream of the presser foot so as to guide and drive the fabric upstream of the sewing area; the method according to the present invention is characterized in that said rotating member is driven in rotation by a roller bearing against said member in its upper zone traversed by the vertical pivot axis so that the support of the roller against the the rotating member leaves the latter free to pivot about the vertical axis whatever the coefficient of friction between the roller and the rotating member.

In addition, according to another characteristic of the method, the roller is rotated at a variable speed depending on the orientation of the rotating member so that said rotating member generates a speed of movement of the fabric, the projection of which on the line of sewing is substantially equal to the speed of travel provided by the presser foot in the sewing area.

• un organe tournant d'entraînement du tissu agencé en amont du pied-presseur et libre en rotation autour d'un axe sensiblement horizontal de façon à pouvoir venir au contact du tissu par des génératrices d'entraînement situées dans un plan vertical,
• un actionneur de pivotement portant ledit organe tournant et adapté pour pouvoir faire pivoter celui-ci autour d'un axe vertical sécant à l'axe de rotation de façon à pouvoir orienter les génératrices d'entraînement suivant des directions d'entraînement différentes,
• un rouleau agencé le long d'un axe transversal horizontal et disposé en appui contre l'organe tournant en vue de pouvoir l'entraîner en rotation autour de son axe de rotation, par friction,
• un moteur d'entraînement en rotation du rouleau,
• un détecteur de la position transversale du tissu, agencé en amont du pied-presseur et associé à des moyens de génération d'un signal de position et à des moyens de commande adaptés pour commander l'actionneur de pivotement en fonction du signal de position.

The fabric guiding device targeted by the invention with a view to implementing the above-defined method comprises:

• a rotating fabric drive member arranged upstream of the presser foot and free to rotate about a substantially horizontal axis so as to be able to come into contact with the fabric by drive generators situated in a vertical plane,
• a pivoting actuator carrying said rotating member and adapted to be able to pivot the latter about a vertical axis intersecting with the axis of rotation so as to be able to orient the driving generators in different driving directions,
• a roller arranged along a horizontal transverse axis and placed in abutment against the rotating member so as to be able to drive it in rotation about its axis of rotation, by friction,
• a motor for driving the roller in rotation,
• a transverse position detector of the fabric, arranged upstream of the presser foot and associated with means for generating a position signal and with control means suitable for controlling the pivoting actuator as a function of the position signal.

According to the present invention, the roller is positioned above the rotating member so as to come into abutment with the upper zone of said rotating member opposite the zone of contact of said member with the tissue, the bearing zone of said roller with said rotating member being substantially situated on the vertical axis around which the pivoting of said rotating member takes place.

Thus in the invention, the fabric is longitudinally driven, permanently, upstream of the guide zone, and the position corrections are effected by appropriately orienting the direction of this longitudinal drive; the rotating member is rotated by the roller by friction in an area which does not undergo any displacement during the pivoting of this member, so that the essential friction between the two surfaces of said members has no appreciable influence on the implementation of pivoting which can be ensured without particular difficulties.

• . un détecteur d'orientation est associé à l'actionneur de pivotement (ou à l'organe tournant), ledit détecteur étant relié à des moyens de mise en forme de signal adaptés pour délivrer un signal représentatif de la direction d'entraînement des génératrices de l'organe tournant,
• . le moteur d'entraînement du rouleau est asservi à des moyens de commande recevant le signal issu des moyens de mise en forme précités, lesdits moyens de commande étant adaptés pour ajuster la vitesse de rotation du moteur en fonction de ce signal.

Furthermore, according to other characteristic features of the invention,

• . an orientation detector is associated with the pivoting actuator (or with the rotating member), said detector being connected to signal shaping means suitable for delivering a signal representative of the driving direction of the generators of the rotating member,
• . the roller drive motor is controlled by control means receiving the signal from the aforementioned shaping means, said control means being adapted to adjust the speed of rotation of the motor as a function of this signal.

It is thus possible, by modulating the speed of the roller, to ensure a movement of the fabric at the level of the rotating member, which corresponds to that generated in the sewing area by the presser foot, whatever the direction of drive of the rotating member, in order to spread any risk of wrinkling, puckering ... of the fabric.

• . le détecteur de position est un détecteur de présence ou d'absence de tissu, associé à des moyens de génération d'un signal de position à deux états représentatifs de l'absence ou de la présence de tissu,
• . l'actionneur de pivotement est un actionneur de pivotement alternatif, apte à amener l'organe tournant à pivoter alternativement entre deux positions extrêmes à fréquence supérieure à cinq pivotements par seconde, les génératrices d'entraînement présentant, dans les deux positions extrêmes, deux directions sensiblement symétriques par rapport à la direction parallèle à la direction d'entraînement du tissu par le pied-presseur,
• . les moyens de commande de l'actionneur de pivotement sont adaptés pour commander celui-ci alternativement d'une position vers l'autre à chaque changement d'état du signal de position,
• . le détecteur d'orientation est un détecteur de positions extrêmes, associé à l'actionneur de pivotement, les moyens de mise en forme étant adaptés pour délivrer un signal de position extrême lorsque ledit actionneur se trouve positionné dans l'une ou l'autre de ses positions extrêmes,
• . le moteur électrique d'entraînement du rouleau est du type possédant deux vitesses de rotation, l'une dite lente, l'autre dite rapide,
• . les moyens de commande associés au moteur sont adapté pour commander la rotation rapide du moteur en présence du signal de position extrême et la rotation lente en l'absence dudit signal.

According to a preferred embodiment allowing the execution of an automatic sewing of a piece of fabric along one of its edges (constituting the aforementioned reference line), the guide device according to the invention is produced as follows :

• . the position detector is a presence or absence detector of tissue, associated with means for generating a position signal with two states representative of the absence or presence of tissue,
• . the pivoting actuator is an alternating pivoting actuator, capable of causing the rotary member to pivot alternately between two extreme positions at a frequency greater than five pivotings per second, the drive generators having, in the two extreme positions, two directions substantially symmetrical with respect to the direction parallel to the direction in which the fabric is driven by the presser foot
• . the means for controlling the pivoting actuator are adapted to control it alternately from one position to the other each time the state of the position signal changes,
• . the orientation detector is an extreme position detector, associated with the pivoting actuator, the shaping means being adapted to deliver an extreme position signal when said actuator is positioned in one or the other of its extreme positions,
• . the electric motor for driving the roller is of the type having two speeds of rotation, one called slow, the other called fast,
• . the control means associated with the motor are adapted to control the rapid rotation of the motor in the presence of the extreme position signal and the slow rotation in the absence of said signal.

In such a device, the pivoting actuator which can be a rotary actuator, is controlled alternately between two opposite angular positions according to the state of the position signal. When the rotating member is placed in one or other of these positions extreme, it performs a correction on the fabric by introducing a transverse component in the running speed at its level; in addition, the roller is driven in this case at high speed by the drive motor (presence of the extreme position signal) so that the transverse component of the speed is not created to the detriment of the longitudinal component. When, on the contrary, the fabric is in a substantially correct position, the position signal changes state very quickly, and the rotary actuator, controlled at high frequency, oscillates between the aforementioned extreme positions. During these oscillations, the fabric is driven by the drive generators in a very rapid succession of zigzags of very small amplitude around a medium direction; it thus moves along a resulting direction parallel to the driving direction of the presser foot; in this case, the extreme position detector does not provide a signal and the roller is driven at low speed by the drive motor: the rotating member rotates more slowly, the slow speed of the roller being adjusted so that said rotating member then conditions a running speed of the fabric substantially equal to that generated by the presser foot. On the contrary, the rapid speed of the rotating member is adjusted to condition a resulting speed of movement of the fabric of the order of 1% to 5% greater than the slow speed, such that the projection of this rapid speed on the longitudinal plane is substantially equal to said slow speed. There is thus obtained by means of a very simple device a drive of the fabric upstream of the sewing area, which is at all times compatible with the drive generated by the presser foot.

It should be noted that the above described operation, involving alternating pivoting at high frequency, is authorized by the mode of drive of the rotary member according to the invention (support of the drive roller on the vertical axis around which the pivoting takes place); this operation is strictly incompatible with the drive described in the two aforementioned prior patents.

Furthermore, according to other features of the invention, the rotating member comprises a sphere of elastic material which is secured by a lateral cap of its surface on a support axis. This carrier axis is mounted on the actuator so as to pivot around the horizontal axis of rotation, which passes through the center of the sphere. The center of the sphere and the upper bearing zone of the roller on the sphere are substantially aligned on the vertical axis around which the alternating pivotings of said sphere take place. These provisions allow the rotating member to pass, without difficulty, the extra fabric thicknesses, without having to control the support pressure of this member (as is the case of the devices described in the above-mentioned patents).

In addition, according to another advantageous characteristic of the invention, the above-mentioned guiding device is carried by the movable ascending / descending member of a jack whose body is secured to the frame of the sewing machine, in view to allow the guide device to descend to the working position in front of the needle or to raise it to the high position so as to release the front of said needle. It is thus possible, before and after the sewing operation, to completely release the work-holding plate from the sewing machine in order to carry out the various operations of placing or removing the fabric.

The invention extends to the guiding device defined above as such, as well as to improved sewing machines equipped with at least one such guiding device.

• la figure 1 est une vue générale en perspective d'une machine à coudre équipée d'un dispositif de guidage en position de travail,
• la figure 2 est une vue analogue montrant le dispositif de guidage en position relevée,
• la figure 3 est un schéma synoptique montrant les organes du dispositif de guidage et leur agencement fonctionnel,
• les figures 4 et 5 sont des vues en perspective du dispositif de guidage montrant celui-ci en position de travail, respectivement pour l'une et l'autre des deux orientations extrêmes de son organe tournant d'entraînement,
• la figure 6 est une figure analogue aux deux précédentes mais dans laquelle l'organe tournant est dans une position moyenne,
• la figure 7 est une vue en élévation de côté selon la flèche V₁ du dispositif de guidage,
• la figure 8 en est une vue frontale selon la flèche V₂,
• les figures 9 et 10 en sont des coupes par des plans verticaux passant respectivement par l'axe de rotation XX' de l'organe tournant, et par un axe perpendiculaire AA',
• enfin, les figures 11, 12 et 13 sont des vues partielles en plan du dispositif, respectivement pour l'une et l'autre des orientations extrêmes de son organe tournant, et pour l'orientation moyenne de celui-ci.

The invention having been explained in its general form, other characteristics, objects and advantages will emerge from the description which follows with reference to the appended drawings which present, without limitation, an embodiment; on these drawings which form an integral part of this description:

• FIG. 1 is a general perspective view of a sewing machine equipped with a guide device in the working position,
• Figure 2 is a similar view showing the guidance device in the raised position,
• FIG. 3 is a block diagram showing the members of the guide device and their functional arrangement,
• FIGS. 4 and 5 are perspective views of the guide device showing the latter in the working position, respectively for one and the other of the two extreme orientations of its rotating drive member,
• FIG. 6 is a figure similar to the previous two but in which the rotating member is in a middle position,
• FIG. 7 is a side elevation view along the arrow V₁ of the guide device,
• FIG. 8 is a front view thereof according to the arrow V₂,
• FIGS. 9 and 10 are sections thereof through vertical planes passing respectively through the axis of rotation XX ′ of the rotating member, and through a perpendicular axis AA ′,
• finally, FIGS. 11, 12 and 13 are partial plan views of the device, respectively for one and the other of the extreme orientations of its rotating member, and for the average orientation of the latter.

The guide device 1 shown in Figures 1 to 13 is mounted on a sewing machine 2 of the type with head on the left; conventionally, this machine comprises a frame 3, a work-holding plate 4, a presser foot 5 associated with a needle 6 with their conventional drive kinematics (feed mechanism with claws, etc.), means of distribution of the threads. The example referred to relates to the sewing of an elastic band of belt E at the edge of a piece of fabric and the machine is provided with conventional means for feeding and guiding this elastic ribbon towards the sewing area (not shown). In the left head sewing machine used, the presser foot 5 is arranged in the vicinity of an angle of the work-holding plate 4; this angle is delimited by a rounded edge Ra and by an edge Rb perpendicular to the previous one (parallel to the line of sewing).

The guide device according to the present invention is intended to guide the piece of fabric which rests on the work-holding plate 4 so as to allow a seam to be produced parallel to the edge of the fabric without the aid of an operator.

This guide device is carried by a pneumatic cylinder 7 whose body 7a is secured by means of a part 8 on the frame 2 of the machine and whose movable rod 7b is secured at its end to a support bracket 9 of the device guide. The jack 7 is arranged with a slight inclination relative to the vertical so as to be able to move the guide device between a working position (FIG. 1) where it is located just in front of the presser foot 5 and the needle 6 of the machine, and a raised position (Figure 2) where the front of these members is fully cleared. The movement of the jack is guided by rods 23 which allow the guide device to undergo perfect translation without angular movement. In the low position, the guide device is placed in front of the presser foot 5 in the vicinity of the aforementioned angle of the work-holding plate 4.

In the example, the presser foot 5 is attached to a cable 10 (which can best be seen in FIG. 7) which passes through a lumen made in the support bracket 9 and has at its upper free end a stud which automatically raises the presser foot when the guide device reaches its high position.

In addition, the machine is equipped with an optical detector of the presence of the fabric 11, capturing the light reflected by a small plate 11a located near the presser foot 5 (towards the inside of the fabric, that is to say near edge Rb); in the event of tissue appearing at its level, this detector controls the operation of the jack 7 and the descent of the guide device towards its working position; when the fabric disappears, it controls the lifting of the jack 7. In addition, a proximity sensor (not visible) equips the jack 7 in order to detect the instant when the rod reaches its lower deployed position corresponding to the position of job of the guide device. This sensor controls the start of the sewing machine when the guide device reaches this working position; it also controls the starting of the rotation drive means of the rotary member of this device and that of its alternating pivoting actuator.

• un organe tournant 12 comprenant une sphère en matière élastique qui est portée par une équerre mobile 13 et qui, en position de travail, est agencée en amont du pied-presseur 5 de façon à venir au contact du tissu par des génératrices d'entraînement (formant une bande de roulement BR symbolisée en traits discontinus sur les figures), ce contact s'effectuant au niveau du bord arrondi Ra de la plaque porte-ouvrage, au voisinage immédiat de l'autre bord Rb,
• un actionneur dit de pivotement alternatif 14 comprenant un vérin rotatif dont le corps 14a est fixé sur l'équerre-support 9 et dont la tige 14b porte l'équerre mobile 13 de façon à pouvoir faire pivoter la sphère 12 entre deux positions extrêmes, dans lesquelles les génératrices d'entraînement BR présentent deux directions différentes (dont on a représenté la trace en D₁ et D₂ sur la plaquette porte-ouvrage),
• des moyens d'entraînement en rotation de la sphère 12 comprenant un moteur électrique d'entraînement 15 et un rouleau 16 disposé en appui contre la surface de la sphère 12,
• un détecteur optique 17 agencé en amont du pied-presseur 5 avec un décalage transversal par rapport à celui-ci vers l'intérieur de la plaque porte-ouvrage en vue de détecter à ce niveau la présence ou l'absence de tissu, ce détecteur étant associé à un circuit 18 de mise en forme et d'amplification engendrant un signal électrique de position à deux états S_p qui asservit un distributeur électropneumatique 19 commandant le vérin rotatif 14,
• un détecteur de positions extrêmes 24 associé au vérin rotatif 14 et constitué par deux capteurs de proximité 24a, 24b qui sont situés en regard de butées de fin de course 14c et 14d du vérin rotatif en vue de délivrer un signal lorsque ces butées sont situées en face des capteurs (cette position correspondant aux deux positions angulaires extrêmes de la tige de vérin rotatif et donc de la sphère 12 portée par celle-ci).

As illustrated in the figures, the guide device essentially comprises the following five functional assemblies:

• a rotating member 12 comprising a sphere of elastic material which is carried by a movable bracket 13 and which, in the working position, is arranged upstream of the presser foot 5 so as to come into contact with the fabric by drive generators ( forming a tread BR symbolized in broken lines in the figures), this contact being made at the rounded edge Ra of the work-holding plate, in the immediate vicinity of the other edge Rb,
• a so-called alternating pivoting actuator 14 comprising a rotary actuator whose body 14a is fixed on the support bracket 9 and whose rod 14b carries the movable bracket 13 so as to be able to rotate the sphere 12 between two extreme positions, in which the BR drive generators have two different directions (the trace of which has been shown in D₁ and D₂ on the book holder plate),
• means for rotating the sphere 12 comprising an electric drive motor 15 and a roller 16 placed in abutment against the surface of the sphere 12,
• an optical detector 17 arranged upstream of the presser foot 5 with a transverse offset with respect to the latter towards the interior of the work-holding plate in order to detect at this level the presence or absence of tissue, this detector being associated with a circuit 18 for shaping and amplification generating an electrical position signal with two states S _p which controls an electropneumatic distributor 19 controlling the rotary actuator 14,
• an extreme position detector 24 associated with the rotary actuator 14 and constituted by two sensors proximity 24a, 24b which are located opposite end-of-travel stops 14c and 14d of the rotary actuator in order to deliver a signal when these stops are located opposite the sensors (this position corresponding to the two extreme angular positions of the actuator rod rotating and therefore of the sphere 12 carried by it).

The specific, structural and functional characteristics of these various assemblies are detailed below.

The sphere 12 which may be a hollow rubber ball is transversely offset with respect to the presser foot 5 so as to come into contact with the fabric in an area closer to the edge Rb than the presser foot. This sphere is bonded by a lateral cap of its surface on a substantially horizontal carrier axis 21, which revolves in a light of the movable bracket 13 so that said sphere is free to rotate around an axis XX 'passing through its center O.

The movable bracket 13 is fixed to the rod 14b of the rotary actuator 14 so that the extension of the vertical axis YY 'of said rod passes through the center O of the sphere. Thus, the rotations imposed by the rotary actuator changes the orientation of the axis XX 'around which the sphere rotates without changing the spatial position thereof.

The sphere 12 is arranged vertically above the rounded edge Ra of the work-holding plate 4, so that its center (O) is slightly offset towards the outside of said plate as illustrated in FIGS. 7 and 10; the sphere and the rounded edge have in the contact zone a common tangent Tc inclined with respect to the horizontal. Thus the fabric is entrained by the sphere at the level of the fold which it forms in line with the rounded edge Ra; at this fold, it benefits from a greater stiffness, which contributes to reducing the risks of gathering, even in the case of very light fabrics.

Blowing means 27 are provided below the rounded edge Ra of the work-holding plate in order to detach the fabric from the vertical edge of said plate and thus to put it in a better position to be driven by the sphere 12.

In addition, the work-holding plate 4 preferably comprises a small rounded flank 28 situated below the edge Rb in the vicinity of the sphere 12. This guiding of the fabric further improves the conditions of entrainment of the latter by the sphere 12 .

The rotary actuator 14 is a pneumatic actuator of known type, with adjustable angular amplitude; its low inertia allows it to change position at high frequency greater than five swivels per second and up to ten to fifteen swivels per second. This cylinder comprises end stops 14c and 14d which make it possible to adjust its pivoting amplitude to a value 2 α of the order of 20 ° to 30 °, in particular to a value of the order of 24 °. As already indicated, these stops serve to detect the instants when the rotary actuator reaches one or the other of its extreme angular positions (thanks to proximity sensors 24a, 24b). In an angular position, the axis of rotation XX 'of the sphere is offset by an angle α = 12 ° relative to the transverse direction (Figures 3, 4 and 11), while in the other angular position, this axis of rotation XX ′ is offset symmetrically with respect to said transverse direction by an equal angle (FIGS. 5 and 12). Thus, in the first position, the drive generators BR of the sphere has a direction D₁ angularly offset towards the inside of the fabric by the angle α relative to the longitudinal direction so that the rotation of the sphere ensures a drive longitudinal of the fabric with a transverse minority component directed towards the inside of the fabric (Figure 11); in the second position, the drive generators BR has a direction D₂ angularly offset towards the edge B of the fabric of the angle α and the rotation of the sphere ensures a longitudinal drive with a transverse minority component directed towards the edge (FIG. 12 ).

The roller 16 for driving in rotation of the sphere is located above the sphere 12 along a horizontal transverse axis ZZ 'so as to come into abutment with the upper zone of said sphere (upper pole Su thereof). ci) opposite the lower contact area of the sphere with the fabric. This upper area Su of contact between the roller 16 and the sphere 12 is located on the vertical axis YY 'passing through the center O, around which the sphere is made to pivot alternately by the rotary actuator 14. This area Su does not does not move during these pivotings so that, whatever the drive friction of the roller on the sphere, the contact of the latter does not hinder the execution of the pivotings.

The roller 16 is carried by the motor shaft 22 of the electric motor 15, a motor shaft located above the carrier axis of the sphere 12. For this purpose, the motor 15 is fixed to the rear of the bracket -support 9 and its motor shaft 22 passes through a hole in the movable bracket 13.

The detector 17 is a conventional type optical detector, capturing the light reflected by a plate 17a carried by the work-holding plate 4. Preferably, the optical detector (17) is associated with means for adjusting its transverse position in to allow the position of the seam to be adjusted relative to the edge of the fabric. In the longitudinal direction, the detector 17 is arranged between the presser foot 5 and the rotating sphere 12, which corresponds to the optimal guiding efficiency.

The optical information delivered by the detector 17 is transformed by a cell into an electrical signal which is processed in the circuit 18 to send a position signal S _p to the electropneumatic distributor 19 associated with the rotary actuator 14. In the presence of tissue, the signal S _p has a state, called state 1, corresponding to the position of the sphere 12 for which its drive generators have the direction D₁: the fabric is driven longitudinally with a tendency to slide transversely in the opposite direction from its edge (figure 11); the detector plate 17a which was covered by the fabric is exposed. The detector 17 then detects an absence of tissue and the signal S _p goes into its other state, called state 2, corresponding to the position of the sphere 12 in which its drive generators have the direction D₂: the tissue is always driven longitudinally but with a tendency to slip transversely towards its edge (figure 12). Thus, by pivoting the axis of rotation XX 'of the sphere at each change of state of the position signal S _p , the fabric is guided so that its edge passes substantially above the plate 17a, c' that is to say remains at a substantially constant transverse distance from the presser foot 5.

When the signal S _p changes state very quickly (edge of the fabric directly above the plate 17a), the rotary actuator 14 biased on one side and on the other at high frequency oscillates between the aforementioned extreme positions: Figures 6 and 13 illustrate these alternative pivotings which can reach a high frequency (greater than 5 hertz). During this oscillation, the drive generators BR of the sphere 12 drive the fabric in a resulting direction Dc parallel to the seam line. The extreme position detector 24 then does not deliver any signal.

The sensors 24a, 24b of this extreme position detector 24 are connected to signal shaping means 25, which, from the received signal, generates a signal Pe with two states (for example state 1 in the event of detection of extreme stable position and state 0 otherwise corresponding to an oscillation between the extreme positions). This signal is delivered to control means 26 to which the drive fitter 15 of the roller 16 is slaved. This motor is a two-speed electric motor, one slow capable, for example, of rotating the sphere 12 at 100 revolutions / minute, the other faster able to rotate it at 103 revolutions / minute. The control means 26 condition the rapid rotation when the signal Pe is representative of an extreme position and the slow speed otherwise.

The guide device according to the invention therefore drives the fabric upstream of the sewing area in a generally longitudinal direction and guides it permanently by creating a transverse component if necessary in order to obtain a seam parallel to its edge; this drive cooperates with that of the presser foot to eliminate the risks of wrinkling, puckering, etc. In FIGS. 11, 12, the edge of the fabric is symbolized in B, in C the seam line to be made and, as already indicated, in D _1, D₂ the directions of fabric drive by the sphere 12, when the latter is in its opposite extreme positions; these drive directions D₁ and D₂ are symmetrical with respect to the longitudinal direction Dc (the latter being parallel to the drive direction of the presser foot). In Figure 13, we have diagrammed the sphere oscillating between its extreme positions (the mean driving direction being the direction Dc).

When the drive directions D₁ and D₂ are angularly oblique with respect to the longitudinal direction (Figures 11 and 12), the drive speed Vr of the fabric is greater (fast motor speed) so that the component V1 along of the longitudinal direction remains equal to the speed V 'corresponding to the slow speed (Figure 13), at which the fabric is driven when the average direction of drive coincides with the longitudinal direction.

Furthermore, when the piece to be sewn reaches the end of the seam and its end edge exceeds the sphere 12 (it is no longer entrained by it), the fabric is guided by an elastic tongue 29 which is disposed in the transverse direction between the sphere 12 and the presser foot 5 as shown in the figures; this tab in elastic support on the fabric avoids a transverse sliding of the latter at the end of sewing. This tongue 29 can be movable vertically and controlled so as to descend against the fabric only at the end of the seam when the end of the fabric arrives near the sphere 12.

The device described above can be used in any application where a seam is to be made along a fabric edge in order to automate this operation. If several sheets of fabric are to be sewn, a guide device is provided to guide each sheet.

Claims (16)

1. Fabric guiding device for a sewing machine having a work-support plate (4) and a fabric-entraining presser foot (5), said presser foot being associated with at least one needle (6), with a view to making it possible to effect automatic sewing of the fabric parallel to a predefined reference line, said guiding device comprising :

   - a rotating fabric-entraining unit (12) arranged upstream of pressure foot (5) and free to rotate about a substantially horizontal axis (XX') so as to be capable of making contact with the fabric along entraining generators (BR) located in a vertical plane,

   - a pivoting drive (14) bearing said rotating unit (12) and so designed as to be capable of causing the latter to pivot about a vertical axis (YY') intersecting axis of rotation (XX') so as to be able to orientate entraining generators (BR) in different entrainment directions (D₁, D₂),

   - a roller (16) arranged on a horizontal transverse axis (ZZ') and placed so as to abut the rotating unit in order to be able to drive the latter by friction so as to rotate about axis (XX'),

   - a motor (15) for driving roller (16) in rotation,

   - a transverse fabric position detector (17) arranged upstream of presser foot (5) and associated with means (18) for generating a position signal (Sp) as well as control means (19) so designed as to control the pivoting drive as a function of position signal (Sp),

   said guiding device being characterised in that roller (16) is positioned above rotating unit (12) so as to abut upper zone (Su) of said rotating unit opposite fabric-contact zone (Si) of said unit, whereby abutment zone (Su) between said roller and said rotating unit is substantially situated on vertical axis (YY') about which alternate pivoting of said rotating unit takes place.
2. Device according to Claim 1, characterised in that :

   . an orientation detector (24) is associated with pivoting drive (14) (or with rotating unit (12)), said detector being connected with signal-shaping means (25) so designed as to deliver a signal (Pe) representative of the entrainment direction of generators (BR) of the rotating unit,

   . motor (15) for driving roller (16) is controlled by control means (26) receiving the signal (Pe) which emanates from the afore-mentioned shaping means (25), said control means being so designed as to adjust the rotary speed of motor (15) as a function of said signal.
3. Device according to Claim 2 making it possible to effect automatic sewing of a piece of fabric along one of its edges constituting the afore-mentioned reference line, characterised in that

   . position detector (17) is a detector indicating the presence or absence of fabric and associated with means for generating a position signal (Sp) with two states representative of the absence or presence of fabric,

   . pivoting drive (14) is a drive for alternate pivoting capable of causing the rotating unit to pivot alternately between two end positions at a frequency higher than five pivotal movements per second, whereby the entrainment generators assume, in the two end positions, two directions (D₁, D₂) substantially symmetrical in relation to direction (Dc) which is parallel to the direction in which the fabric is entrained by the presser foot,

   . control means (19) of drive (14) are so designed as to cause the latter to move alternately from one position to the other whenever the state of position signal (Sp) changes,

   . orientation detector (24) is the detector of end positions (24a, 24b) associated with pivoting drive (14), shaping means (25) being so designed as to deliver an end-position signal (Pe) whenever said drive is in one or the other of its end positions,

   . electric motor (15) for driving roller (16) is of the type having two rotary speeds, one of which is said to be the slow speed while the other is said to be the fast speed,

   . control means (26) associated with motor (15) are so designed as to bring about, in the presence of end position signal (Pc), fast rotation of the motor, and in the absence of said signal slow rotation thereof.
4. Device according to Claim 3, characterised in that motor (15) and its control means (26) are so designed as to ensure that the slow rotary speed of rotating device (12) gives rise to a fabric conveying speed substantially equal to that brought about by the presser foot and that the fast speed of said rotating unit (12) gives rise to a conveying speed about 1% to 5% higher than the afore-mentioned speed.
5. Device according to one of Claims 1, 2, 3 or 4, characterised in that rotating unit (12) comprises a sphere of elastic material secured by a lateral cap of its surface to support shaft (21), said support shaft being mounted on drive (14) so as to rotate about a horizontal axis (XX') passing through centre (O) of sphere (12), said centre (O) of sphere (12) and upper abutment zone (Su) between roller (16) and sphere (12) being substantially aligned on vertical axis (YY') about which alternate pivotal movement of said sphere takes place.
6. Device according to Claim 5, characterised in that the alternating pivoting drive comprises a rotary actuator (14) with a substantially vertical rod (14b) and an angle piece (13) secured to said rod and supporting support shaft (21) of the sphere, said angle piece having an opening in order to enable passage of a drive shaft (22) bearing entrainment roller (16), said drive shaft (22) being arranged above support shaft (21) of the sphere.
7. Device according to Claim 6, characterised in that rotary actuator (14) is an actuator with an angular amplitude which can be adjusted to a value 2 a of the order of 20° to 30°, said actuator having a low inertia enabling it to achieve a pivoting frequency higher than 5 Hertz.
8. Device according to one of Claims 5, 6 or 7, characterised in that elastic material sphere (12) constituting said rotating unit is arranged upstream of presser foot (5) perpendicular to a rounded edge (Ra) of work-support plate (4), centre (O) of said sphere being offset towards the outside of said plate so that said sphere and said rounded edge present, within the zone of contact, a common tangent (Tc) inclined in relation to the horizontal.
9. Device according to Claim 8, characterised in that it comprises blowing means (27) located below rounded edge (Ra) of work-support plate (4) with a view to detaching the fabric from the vertical side of said plate.
10. Device according to one of Claims 8 or 9, in which detector (17) is an optical detector of the presence or absence of fabric, characterised in that presser foot (5) is arranged in the proximity of an angle of the work-support plate, said angle being delimited by the aforementioned rounded edge perpendicular to which is located sphere (12) and by an edge perpendicular to the above which is parallel to the sewing line, optical detector (17) of the presence or absence of fabric being situated towards the inside of work-support plate (4) in the proximity of said presser foot (5).
11. Device according to one of Claims 1 to 10, characterised in that it comprises an elastic tongue (29) arranged in the transverse direction between rotating unit (12) and presser foot (5) with a view to abutting on the fabric and preventing transverse sliding of the latter at the end of the sewing operation.
12. Device according to one of Claims 1 to 11, characterised in that it is carried by the mobile ascending and descending element of an actuator (7), the body of which is secured to frame (3) of the sewing machine so that said device can be lowered into a working position in front of the needle or raised to a high position in order to disengage the front from said needle.
13. Guiding device according to one of Claims 1 to 12 by way of equipment of a sewing machine of the type with its head on the left.
14. Process for automatic sewing of a piece of fabric by means of a sewing machine equipped with a device according to one of Claims 1 to 13, in which a rotating unit (12) capable of orientation by pivoting movements about a vertical axis (ZZ') is arranged so as to abut the fabric upstream of the presser foot in order to guide and entrain the fabric upstream of the sewing zone, said process being characterised in that said rotating unit (12) is driven in rotation by roller (16) abutting said unit in its upper zone (Su) through which passes the vertical pivoting axis (ZZ') so that abutment between roller (16) and rotating unit (12) allows the latter to pivot about axis (ZZ') whatever the frictional coefficient between the roller and the rotating unit.
15. Process according to Claim 14, characterised in that roller (16) is driven in rotation at a speed depending on the orientation of rotating unit (12) so that said rotating unit induces a fabric conveying speed the projection of which on the sewing line is substantially equal to the conveying speed ensured by presser foot (5) in the sewing zone.
16. Process according to one of Claims 14 or 15, characterised in that rotating unit (12) is orientated by alternating pivotal movements between two angular end positions.

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