EP0359707A1 - Device for regulating the tension of a longitudinally moving thread, and the use of such a device - Google Patents

Abstract

This device comprises three plates (10a, 11 and 10b) in pairwise contact via yarn-clamping surfaces and subjected to the action of a mechanism applying these plates against each other with a force of adjustable intensity. Each of the clamping surfaces of the plates has two indentations defining two pairs of lips. Guiding means (12a, 12b) impose, on the length of yarn passing through the device, a trajectory such that this yarn enters between the clamping surfaces of the plates via one of the lips and leaves them via the other. …<IMAGE>…

Description

Sewing machines are known which include, upstream of the sewing needle, a device for adjusting the tension of the sewing thread comprising at least two substantially flat plates applied against each other and between which this thread passes, a manually controlled device making it possible to clamp these plates, and therefore the wire, with an intensity force characteristic of the desired tension at least on the portion of wire extending downstream of the plates.

However, such devices are not entirely satisfactory, the wire naturally tending to come out little by little between the plates, until completely leaving the device in question, which then becomes inoperative. This displacement of the wire is due to the fact that, even though the thickness of such a wire is generally very small, of the order of a few tenths of mm to 1 mm for example, under the action of the clamping force at which they are subject, the plates come to bear, on the one hand between them, at a point distant from the wire, and, on the other hand individually, on the wire itself. It follows that a sort of "wedge" effect is created on this wire, resulting in a force tending to push the wire in the direction opposite to the mutual support zone of the plates. When this force is greater than the friction action of the plates on the wire due to the tightening of these, the wire moves between the plates until it is ejected.

Among the arrangements proposed to try to obviate this conventional type of drawback, there is that disclosed by Singer US Pat. No. 4,123,984 which proposes cutting the edge of the plates by two indentations arranged so that each of them, belonging to a given plate, covers a portion of a homologous indentation belonging to the other plate, in a relative angular position of the plates, the pairs of indentations thus superimposed forming, on the edge of the assembly of the two plates, of them distinct and concave lips. In this device, the wire is guided so that it enters between the plates through one of the lips, preferably near one end of the lip in question, and that it leaves the device at a distance from the second lip.

This device is really satisfactory, on the one hand, only for certain types and dimensions of the thread and, on the other hand and above all, only in the case of sewing simple patterns, that is to say not requiring , for their formation, a high density of thread per unit area, the fabric being sewn should not, moreover, not be too thick. Indeed if, during its passage in the area of the plates close to their first lip, the trajectory of the wire is very controlled for the reasons mentioned in the American patent US 4 123 984, this wire is more and more abandoned to it -even as it subsequently penetrates between the plates so that the "wedge" effect mentioned above quickly becomes predominant and the wire here also acquires a natural tendency to escape from the device.

The present invention relates to an adjustment device of the above type but without the drawback noted and whose essential characteristics are the subject of claim 1.

Like that described in US Pat. No. 4,123,984, this device finds a particularly advantageous and efficient use in sewing machines, even if they are of the purely mechanical, electromechanical or electronic type, with microprocessor or not.

• La figure 1 est une élévation latérale, avec arrachement et section partiels, d'une machine à coudre, montrant la localisation du dispositif selon l'invention;
• La figure 2 est une coupe selon II-II de la figure 1, à plus grande échelle;
• La figure 3 est une vue d'un détail de la figure 1, à plus grand échelle.
• Les figures 4a et 4b sont des vues en plan de deux élé­ments apparaissant sur la figure 3;
• Les figures 5a et 5b illustrent, comparativement, une particularité du fonctionnement du dispositif selon l'inven­tion et d'un dispositif traditionnel.

The accompanying drawings illustrate, by way of example, an embodiment of the device of the present invention and of its practical mode of use in a sewing machine:

• Figure 1 is a side elevation, with cutaway and partial section, of a sewing machine, showing the location of the device according to the invention;
• Figure 2 is a section on II-II of Figure 1, on a larger scale;
• Figure 3 is a view of a detail of Figure 1, on a larger scale.
• Figures 4a and 4b are plan views of two elements shown in Figure 3;
• Figures 5a and 5b illustrate, comparatively, a feature of the operation of the device according to the invention and a traditional device.

The sewing machine shown in FIG. 1 comprises a lower arm 1, a column 2 carrying an upper arm 3 extending above the arm 1 and ending in a sewing head 4.

Traditionally, the arm 1 comprises the mechanism for driving the fabric and the control device for the loop sensor, both not shown.

The head 4 of the machine has a presser foot 5, a needle bar 6 with a needle 6 is fastened to the free end of the bar 6. The head 4 also carries a wire guide 7 and a device 8 for adjusting of the tension of the thread 9 which, delivered during sewing, from a spool, not shown, passes through the thread guide 7 and then passes through this device to reach the needle 6 a .

The device 8 comprises an assembly of three plates 10a, 11a and 10b (Figure 2) which are slidably mounted on two parallel rods, 12a and 12b, between an element 13 integral with the head 4 of the machine, and a rod support 14 in contact, at its right end, with the left face of the plate 10 b . The rod 14 is slidably mounted in a corresponding opening 15 of a support 16 integral with the head 4 and to which the rods 12a and 12b above are fixed. The left end, in the drawing, of the rod 14 is subjected to the action of a lever 17, articulated in 17a, which develops, on this rod, a force whose intensity can be varied by manual action exerted on a clamping device 18 of which 19 represents a control chicken (Figures 1 and 2). The variation in the angular position of this chicken therefore produces a more or less pronounced tightening of the plates 10 a , 11 and 10 b . The operating principle of this part of the device is well known to those skilled in the art since it is found as it is, in particular in the Elna 5000, Elna 6000 and Elna 7000 sewing machines placed on the market by the company TAVARO SA in Geneva, Switzerland).

It is thanks to this possibility of clamping the plates that the device illustrated makes it possible to adjust the tension of the thread intended for the needle of the machine.

Note that this device can be used both when the machine will be called upon to work with a single needle and with a double needle. We know in fact that, in the latter case, it is necessary to regulate the tension of two separate threads, emanating from two separate spools and each intended for one of the two needle stems that a needle has double. In this hypothesis, one of the wires will be passed, for example, between the plates 10a and 11 and, the other, between the plate 11 and the plate 10b.

The description which follows only refers to the case where the sewing machine is called upon to operate with a single needle, the thread being clamped between the plates 10a and 11. The structure of the assembly of the three plates 10a, 11 and 10b being symmetrical with respect to the central plate 11, it is obvious that everything which will be described with reference to the pair of plates 10a and 11 will also concern, mutatis mutandis, this same plate 11 and the plate 10b.

As can be seen in FIG. 4b, the plate 10 a is in the form of a flat metal plate, comprising a rectilinear fold 20 intended to delimit, with the plate 11, a slot for introducing the wire, and the surface has three projecting portions 21, 22a and 22b, obtained by stamping for example, and exceeding the surface of the plate, as well as two pairs of openings, 23a and 23b, for the first pair of these openings, respectively 24a and 24b, for the second.

The protruding portion 21 is planar and has a general shape of a cross, the edges of the arms of which include a connecting section 21a of rounded profile, of identical radius of curvature for each pair of arms, each section forming an indentation opening in the immediate vicinity. an opening 23a, or 23b, respectively 24a and 24b.

It will be noted that the projecting portion 21 has arms of the same length and that these openings are located, two ^ [two, on axes of transverse symmetry of the cross, on either side of it.

For each pair of openings, one, 23a, respectively 24a, has a slightly elongated shape, the other, 23b, respectively 24b, being of circular shape. This difference in shape is chosen such to give some play to allow easy passage of the rods 12a and 12b, even if their spacing is not strictly constant.

The projecting portions 22a and 22b, of circular shape, are arranged in such a way that their respective center is located on the axis of transverse symmetry of the projecting portion 21, axis passing through the openings 24a and 24b, for the portion 22a, and through the openings 23a and 23b, for the portion 22b.

The structure which has just been described is found exactly in the plate 10b. We will therefore refer to the description above to know the particularities of the latter.

As seen in the drawing (Figure 2), the plate 11 is mounted between the plates 10a and 10b.

It comprises, on each of its faces, a projecting and flat portion 25, which is obtained by stamping the plate, for that appearing on its obverse, and which, on the reverse, is formed by addition, for example by brazing in the hollow produced by the stamping, of a plate not shown, of shape corresponding to that of the portion 25, this plate projecting from the surface of the plate, as is the case for the projecting portion 25 appearing on the second side of this plate.

The projecting portion 25 has an elongated part, of generally triangular shape, 25a, with a rounded top, the radius of curvature of which corresponds substantially to that of the projecting portions 22a and 22b of the plates 10a and 10b, and a more enlarged part, 25b, of which the edge is attached to the edge of the part 25a by two rounded sections 25c forming corresponding indentations. The radius of curvature of these sections corresponds substantially to that of each indentation 21a between each pair of arms of the raw projecting portion ciform 21 of plates 10a and 10b. On either side of this projecting portion 25, the plate 11 has an opening 26a, respectively 26b, whose shape and spacing correspond to those of the pairs of openings 23a, respectively 23b, or 24a respectively 25b of the plates 10 a , and 10b. The center of the openings 26a and 26b is located on a common axis which is perpendicular to the longitudinal axis of the portion 25, at equal distance, and on either side thereof.

Note also that the general dimensions of the projecting portion 25, the profile of its edges and its position relative to the openings 26a and 26b are chosen such that, in the assembled position of the plates 10a, 11 and 10b, the rounded parts 25c of the protruding portion 25 of the plate 11, and of the counterpart of this portion protruding on the other face of the latter are located at the right of part of the length of the indentations facing the openings 24a and 24b of the plate 10a, respectively at the openings 23a and 23b of the plate 10b.

In addition, the projecting portion 25 rests, by its end portion 25a, on the projecting portion 22a of the plate 10a. It is the same with regard to the plate 10b, the projecting portion 22b of which forms a support for the homologous extremal part of the part 25a above, belonging to the projecting portion corresponding, on the other face of the plate, to the serving 25.

As seen in Figures 1 and 3, in the operating position of the sewing machine, the thread 9 passes between the plates 10a and 11, and is stretched between the rods 12a and 12b and in contact with the projecting portions 21 and 25 turntables. The wire is clamped between these plates under the action of the rod 14 (FIG. 2) according to the pressure exerted on it by the lever 17.

The edge of the indentations appearing on one as on the other face of the plate 11 and that of the indentations of the plates 10a and 10b covering the first edge above thus delimit two pairs of lips between which the wire 9 passes as well when it enters between the pair of plates concerned only when it leaves it.

As indicated in US Pat. No. 4,123,984, the fact of cutting, according to a rounded profile, the edge of the clamping surfaces of the plates of the device described therein and of forcing the wire to penetrate between these surfaces at through the lips thus delimited, at one end of these, results in the portion of the wire penetrating at all times between these lips, by the appearance of a thrust arising from the decomposition into two vectors of the tensile force axial exerted on the wire, this thrust being oriented tangentially to the profile of the indentations and in the centripetal direction and therefore having to prevent the wire from leaving the device.

According to this patent, it was intentionally that we chose to penetrate the wire between the plates at the end of the two lips which they delimit so that the above thrust is of maximum value and therefore that the wire retention between the plates is guaranteed even under extreme machine operating conditions.

As can be seen in the drawing and as follows from the description, the device according to the invention does not meet this latter condition since the wire enters the first pair of lips of each pair of plates 10a and 11, respectively 11 and 10b , and leaves the second, through a central portion of each pair of lips and not at the end of these. It follows that the wire is obviously also subjected to the action of a centripetal thrust of the same kind and for the same reasons as those mentioned above but of intensity much lower than it would have been if the wire , as in the cited patent, had passed between these lips at a point much more distant from their central portion.

Despite this, experience has shown that the device described was particularly effective since, even under the extreme operating conditions mentioned above, the section of wire crossing at all times the space between the clamping surfaces of the plates did not never removed from the ideal trajectory, which is that in which the wire would occupy a taut position between the rods 12a and 12b, by more than a few tens of mm.

This unexpected result is first of all the fact that, Contrary to what is recommended by US Pat. No. 4,123,984, the wire enters and leaves the tightening zone of the device through two pairs of lips in contact with which it is subjected to the action of a centripetal thrust tending to l prevent from leaving this space: the portion of wire passing through said space is therefore practically held at its two ends.

In addition, given the shape given to the clamping surfaces lining the plates 11, 10a and 10b and their position relative to the path followed by the wire, upstream and downstream of the device, it can be seen that if, by hypothesis , the portion of wire passing through the clamping space of each pair of plates tended to be pushed back in the centrifugal direction, this portion would tend to move over part of this clamping surface of greater length and would therefore be subjected to a force of superior friction from where an obstacle naturally limiting the possibilities of "migration" of the wire in the centripetal direction. On the contrary, the wire tends to place itself on a portion of the clamping surface offering the least resistance to its passage: in this case the ideal position should theoretically coincide with the axis of transverse symmetry of the projecting portion cruciform 21 (fig. 3).

To these two technical measures allowing the good cited result to be obtained, it should be mentioned that obtained by the mutual implementation of the projecting portions 22a and 22b of the plates 10a and 10b and of the end 25a of the portion 25 of the plate 11. For this, reference is made to FIGS. 5a and 5b: the first of these shows, in longitudinal section along VV of FIG. 3, the position occupied by the various plates of the device according to the invention, when a wire 9 is engaged between the plates 10a and 11. The second illustrates a similar situation in the case of a device of known structure, for example from US Pat. No. 4,123,984.

We see, in the first case (Figure 5a), that by the presence of the wire 9 between the plates, the plate 10a occupies a slightly tilted position relative to the plate 11. For a wire having 0.4 mm in diameter, l 'tilt angle α is around 2 °.

In the second case (FIG. 5b), the angle β of the plate 10 * relative to the plate 11 * is much greater since it is of the order of 2 ° 48 ′. This means that, in the present case, the thread 9 will be much easier to escape from the space comprised between the plates, thereby implying obtaining a poor quality seam due to the irregularities of tension of which the thread is the object.

This difference in behavior of the two described tightening devices is due to the fact that, in the device according to the invention, the possible tilting of the external plates, 10a or 10b, of the device is limited by mutual support of the projecting portion 22a or 22b and of part 25a of the projecting portion 25 of the plate 11 or of their counterparts appearing on the second face of the latter. Consequently, the force R acting on the wire as a result of the "wedge" effect to which it is subjected is less than the homologous force R₁ existing in the case of the device of FIG. 5b.

It goes without saying that the device described could comprise only one pair of plates (10a, 10b) in particular in the case of a machine having only the possibility of sewing with a single thread and not with two. However, it will be noted that, even in this case, the angle α to which reference has been made with reference to FIG. 5a, will be of value similar to that cited above: indeed, this result remains acquired since, at image of what has been described, the plates will then be in mutual contact by their respective projecting portions 22a and 22b, and 22b and 22a.

As a variant and, under the same conditions above, it would also be possible to use only a pair of plates of structure corresponding to that of the plate 11 described and the upper part of which would be bent so as to obtain a groove in the shape of a "V" at the top of the assembly of the plates, groove intended to facilitate the introduction of the wire between the plates.

Claims (10)

1. Device for adjusting the tension of a longitudinally movable wire, comprising at least two adjacent plates, applied one against the other and between which this wire passes, means making it possible to clamp these plates, and therefore the wire, with an intensity force characteristic of the desired tension, device in which the facing faces of the plates each have at least one wire clamping surface called to cooperate with at least one surface homologous to the other plate, the edge of these surfaces being cut by at least two indentations arranged so that each indentation of the clamping surface of one plate covers at least a portion of a homologous indentation of the clamping surface of the other plate at least in a relative angular position plates, the pairs of indentations thus superimposed delimiting, on the edge of the clamping surfaces of the plates, two distinct and concave lips, means being designed to maintain the plates in said angular position, characterized by guide means imposing, on the portion of wire passing through the device at all times, a path such that this wire enters between the clamping surfaces of the plates by one from said lips and out through the other. 2. Device according to claim 1, wherein said guide means comprise at least two support members for the wire, characterized in that one of the members faces the first of said lips and the other to the second. 3. Device according to claim 2, characterized in that said support members are arranged at least partly in the concavity delimited by the corresponding lips. 4. Device according to claim 1, characterized in that the clamping surface of each plate protrudes in the central part thereof. 5. Device according to claim 1, characterized in that each plate has at least two openings of identical size and spacing from plate to plate, and is slidably mounted on two rods each passing through a determined opening, the relative position of the openings of each plate and indentations of their respective clamping surface being chosen so as to obtain said superposition of homologous indentations of the clamping surfaces of the plates, the rods and the openings constituting said means for angular positioning of the plates. 6. Device according to claims2 3 to 5, characterized in that said support members are constituted by the portion of said rods between the plates. 7. Device according to claim 6, characterized in that, on its face comprising the clamping surface, one of the plates has at least one bearing surface placed in position distant from said clamping surface and substantially equidistant from said openings, and in that the clamping surface of the second plate has an extent such that it rests at least in part on said bearing surface in the clamped position of said plates. 8. Device according to claim 6, characterized in that the clamping surface of the first plate is in the general shape of a cross, the edges of the arms of which have a rounded profile section, with the same radius of curvature, extending at least near their intersection, this junction section of each pair of arms constituting said indentation, by the fact that this plate has two pairs of openings each made in a portion of the plate located between two adjacent arms of the clamping surface nearby immediately of said junction section of their edges, and by the fact that this first plate comprises two bearing surfaces, one of which is crossed by a geometric axis passing simultaneously through a first pair of openings made between two pairs of opposite arms pro cruciform wire of the clamping surface, the other occupying a position symmetrical to the first and being located in the axis passing through the second of said pairs of openings. 9. Device according to claim 8, characterized in that the clamping surface of the second plate extends longitudinally and symmetrically between the openings, along a geometric axis also distant from them, at least a portion of the edge of this surface forming two indentations each opening near one of said openings, in the direction thereof. 10. Use of the device according to one of claims 1 to 9 in a sewing machine.

Images