Device for forming the leno heald weave in weaving looms

Abstract

 A device for forming the leno heald weave in a weaving loom, of the type in which two warp yarns or two groups of warp yarns are controlled by corresponding yarn guide elements (5) so as to perform an alternate opening and closing movement of the shed and switching of the mutual lateral position with respect to the fabric being formed. The yarn guide elements (5) are fixed to a flexible conveying member (1) arranged in a closed ring along an oval path and controlled, by an electric motor (M), so as to perform alternate movements along said path.

Description

[0001] The present invention relates to a device for forming the leno heald weave in weaving looms and in particular to a device of this type which is entirely independent of the central drive system of the loom.

[0002] As is known to persons skilled in the art, the term "leno heald weave" is understood as referring to a particular method of weaving which is performed along the edge of the piece of fabric being woven in order to fix firmly the weft yarns and prevent fraying of the fabric. Basically the leno heald weave consists in controlling a pair of warp yarns-the two outermost ones or a certain number of the outermost yarns divided into two groups - independently of the other warp yarns, using devices of various types which allow, in addition to normal closing and opening of the shed, also lateral displacement of the yarns, such that the outermost yarn (or group of yarns) becomes the inner one and vice versa, therefore resulting in twisting of said yarns on top of one another. The object of this operation is obviously that of achieving a gripping of the weft yarn which is much tighter than that which is possible with the normal arrangement of warp yarns.

[0003] The aforementioned twisting of the outer warp yarns, in view of the continuity of the warp yarns themselves, obviously cannot always be performed in the same direction, but must be periodically reversed, after each insertion of the weft or after a certain number of insertions of the weft, so that the overall number of right-hand and left-hand twists is on average the same.

[0004] Initially, the leno heald weave was obtained by controlling the outer warp yarns used for this weave by means of the pair of heald frames operating in "cloth-weaving" mode (i.e. with reversal of the mutual position with each weft insertion). The weave was formed by means of a group of two healds connected by a mechanical device (the so-called "half link") inserted into said pair of frames and apt to produce, with each opening of the shed, alternate switching of the two warp yarns controlled by said healds between an innermost position and an outermost position. However, in the case where the pair of frames operating in cloth-weaving mode was not present on the loom because the fabric being woven did not envisage that particular type of weave, it was nevertheless necessary to provide a pair of heald frames specifically intended for the leno heald weave, resulting in an undesirable increase in the overall thickness of the frame set.

[0005] In order to overcome this drawback, it was then proposed in the sector to use special devices arranged along the edge of the loom in the vicinity of the weft insertion line and comprising - on a smaller scale in view of the greater closeness to the shed - only the mechanism consisting of the pair of healds and the half link which controls the two warp yarns intended to form the leno heald weave. Obviously it was necessary to provide a pair of said devices for each piece of fabric being woven, the devices being located along the edges of the fabric to be provided with the leno heald weave. A particular type of said device is described, for example, in EP-A-393,467.

[0006] In both these devices of the conventional type, the direction of reversal in position of the two groups of warp yarns necessarily changes each time the shed is opened such that it is only possible to obtain a leno heald weave in which twisting of the yarns - right and respectively left one - alternates each time the weft is inserted; i.e. it is not possible, using these conventional devices, to form weaves in which the same twisting direction is repeated identically and alternately for a predetermined successive number of wefts inserted, as is instead desirable for certain particular types of fabrics.

[0007] Another limitation of the conventional devices described above for formation of the leno heald weave arises from the fact that said devices are directly controlled by the central drive system of the loom. The exact time wherein formation of the weave takes place is therefore dependent on the transmission lay-out and cannot be modified easily and rapidly, as instead would often be required with a variation in the woven article.

[0008] More recently, therefore, devices for forming the leno heald weave have been introduced onto the market, where operation is obtained using electric motors of the stepping type or the brushless type equipped with encoder which are exclusively intended for these devices and which can therefore be programmed as required electronically in a manner which is entirely independent of the central drive system of the loom, so as to be able to produce the desired law of motion of the groups of warp yarns intended to form the leno heald weave.

[0009] The devices of this type also have a different mechanical design of the warp yarn guide elements, which no longer perform the linear alternating movement typical of the devices previously described, but an alternate rotational movement which, as a result of the co-operation with the independent motor, is apt to allow execution of a plurality of twists of the warp yarns all in the same direction, followed by a similar series of twists all in the opposite direction.

[0010] With the devices for the leno heald weave of the rotational type mentioned above, it is also possible to achieve the advantage of a considerable simplification in the transmission of the movement which must no longer comprise a step involving conversion from rotational movement to alternating movement and is therefore very more compact. Examples of devices of this type are disclosed in EP-A-674,031 and EP-A-873,439.

[0011] As mentioned above, the motion law of said devices and therefore of the motors operating them - is controlled electronically by a program which allows modification, as desired, of both the moment of crossing of the warp yarns - and therefore gripping of the weft yarn - and the duration of the opening phase. In connection with the latter point it has been found to be necessary, at least in modern high-speed looms, to introduce an actual stoppage phase in the opening movement of the warp yarns intended to form the leno heald weave, so as to ensure complete opening of the associated shed for the whole period of time necessary for insertion of the weft.

[0012] In the devices described above there is therefore the need to modify continuously the motion law of the electric drive motor, in order to achieve the abovementioned stoppage plate, with the consequence that the electronic part of the device necessary for obtaining this motion law is very complex and therefore, ultimately, excessively costly with respect to the benefit of the performance provided.

[0013] This high cost has hitherto prevented adequate development of this new type of device for the leno heald weave, with the result, therefore, that it has not been possible to fully exploit all the new and interesting possibilities described above. The object of the present invention is therefore to provide a device for forming the leno heald weave, of the type independently controlled by an electric motor, for example a stepping motor or brushless motor with encoder, wherein it is possible to obtain a stoppage during the phase of complete opening of the shed, independently of electronic control of said motor, so as to allow a simpler electronic control and therefore a more cost-effective construction of the device itself.

[0014] This object is achieved, according to the present invention, by means of a device for forming the leno heald weave in a weaving loom, of the type in which two warp yarns or two groups of warp yarns are controlled by corresponding yarn guide elements so as to perform an alternate opening and closing movement of the shed and switching of the mutual lateral position with respect to the fabric being formed, characterized in that said yarn guide elements are fixed to a flexible conveying member arranged in a closed ring along an oval path and controlled by motor means so as to perform alternate movements along said path according to a pre-set motion law.

[0015] Further features and advantages of the present invention will emerge, however, more clearly from the following description of certain preferred embodiments thereof, illustrated in the accompanying drawings, in which:

[0016] Fig. 1A is a side elevation view of a first embodiment of the device for forming the leno heald weave according to the present invention, mounted on a weaving loom, the latter being schematically represented in the drawing by the sley and the reed in two different working positions;

[0017] Fig. 1B is a plan view of the device shown in Fig. 1A;

[0018] Figs. 2A and 2B are, respectively, an axonometric view and a front elevation view of the device shown in Fig. 1A;

[0019] Fig. 3 is a view, similar to that shown in Fig. 1A, which shows schematically a variation of the first embodiment of the device according to the present invention;

[0020] Fig. 4 shows an axonometric view of a second embodiment of the device for forming the leno heald weave according to the present invention;

[0021] Fig. 5 is a side elevation view of the device according to Fig. 4, devoid of the motor means and associated transmission, which illustrates the substantial absence of drawing of the warp yarns during operation of the device according to Fig. 2A;

[0022] Fig. 6A is a schematic front elevation view of a third embodiment of the device for forming the leno heald weave according to the present invention; and

[0023] Fig. 6B is a side elevation view of the device according to Fig. 6A.

[0024] In a first embodiment, illustrated in Figs. 1A, 1B, 2A and 2B, the device for forming the leno heald weave according to the present invention consists of a closed-ring flexible belt mounted on a pair of pulleys 2, the respective parallel shafts of which are pivotably mounted on a support bracket 3. The belt 1 therefore assumes an oval configuration, where this term, here and below, is to be understood as meaning both a configuration which comprises two rectilinear sections radiused at the ends by semi-circles, as in the embodiment illustrated here, and a configuration which is of a generally elliptical, even irregular, type.

[0025] The bracket 3, to which the pulleys 2 are fixed, is in turn supported as a cantilever by a tube 4 projecting from a box 5, fixed to the loom, which box houses an actuating motor M for the device. In this way, the bracket 3 is arranged laterally with respect to the set of frames Q, in the vicinity of the mouth of the shed B. In order to illustrate more clearly the spatial arrangement of the device, in Fig. 1A alone the sley C and the reed P are also shown schematically.

[0026] Yarn guide elements 5 are fixed, in mutually facing positions, to the belt I, and the two warp yarns O with which the leno heald weave is performed are caused to pass through an end eyelet 5a thereof. The yarn guide elements 5 may be in the form of straight rods and be made of an elastic and flexible material such that, during their rotation about the pulleys 2, they flex sufficiently, owing to the increased tension of the warp yarns, to keep their yarn eyelet 5a in an approximately constant position substantially coinciding with the centre of rotation of the pulley 2. The same result may be all the same obtained with rigid yarn guide elements which are L-shaped or arc-shaped, as shown for the yarn guide elements 15 in the second embodiment of the device according to the present invention, illustrated in Figs. 4 and 5.

[0027] The actuating motor M is, for example, a stepping motor or a brushless motor equipped with encoder and is connected to one of the pulleys 2, more precisely the bottom one in the drawings, so as to drive the same in alternate rotational movements, by means of a drive spindle 6 haused inside the tube 4. The spindle 6 may be continuous, as in the embodiment illustrated in Figs. 1 and 2, or interrupted by a flexible coupling 7, as in the variant illustrated in Fig. 3.

[0028] One of the innovative features of the device according to the invention is in fact that of having very small lateral dimensions, both when arranged - as in the embodiment illustrated - with the axes of the pulleys 2 parallel to the warp yarns and in an arrangement rotated through 90°, where said axes are instead perpendicular to the warp yarns. As a result of these small lateral dimensions, it is possible to position the device in the immediate vicinity of the area occupied by the set of heald frames Q, with significant advantages both for the manufacturer of the loom, who has fewer difficulties when installing the device on the loom, and for the weaver who benefits from the fact that the warp yarns intended for the leno heald weave are very close to the warp yarns moved by the heald frames Q and therefore intended for formation of the fabric.

[0029] Since the lateral dimensions of the motor M are greater than those of the device according to the invention, the presence of the coupling 7 allows the motor to be arranged in a position which is laterally offset with respect to the device according to the invention which may thus be arranged even closer to the fabric being formed; moreover, the tube 4 has a length sufficient to allow the motor M to be arranged in a zone which is fairly far from that of the shed, this latter zone being already particularly crowded by the various devices intended for insertion and control of the weft.

[0030] The pulley 2 which is not operated by the motor M is an idle pulley which acts solely for supporting and tensioning the belt 1. As mentioned, the motor M imparts to the pulley 2 and therefore to the belt 1 alternate rotational movements which, owing to,the presence of the yarn guide elements 5, are converted into opening and closing movements of the warp yarns O intended to form the leno heald weave and, at the same time, into an alternate lateral overlapping movement thereof which allows the desired twisting effect of said warp yarns to be achieved.

[0031] The warp yarns O are preferably passed "through" the device according to the invention, inside a slot 8 formed in the central part of the device itself and protected by a yarn protection rim 9 suitably formed or lined with special materials - as are also the yarn guide elements 5 - in order to reduce the friction on the warp yarns and the abrasion on the device itself.

[0032] In order to be able to control exactly the position of the yarn guide elements 5, finally, it is necessary either for the movement of the belt 1 to be synchronized with that of the motor M or for the instantaneous position of the belt 1 to be constantly controlled. The first condition may be achieved in a fairly simple manner, using pulleys 2 and belt 1 of the toothed type; the second condition may also be obtained easily, using suitably arranged position sensors-well-known per se - for example Hall-effect sensors.

[0033] From the description above, it should be obvious how the device according to the present invention has fully achieved the predefined object. In fact, using an oval-pattern flexible belt for operation of the yarn guide elements 5 makes it possible to obtain - only thanks to the abovementioned geometrical arrangement - a beneficial stoppage phase in the movement of the warp yarns O intended for formation of the leno heald weave, during rotation of the yarn guide 5 around the pulleys 2. During this rotation, in fact, owing to the flexibility of the yarn guide elements 5 or their L-shaped or arc-shaped configuration, the position of the eyelet 5a of the yarn guide elements 5, with respect to a vertical direction, is almost constant and there are therefore no substantial variations in the opening of the shed. Moreover, by providing the diameter of the pulleys 2 with suitable dimensions, it is possible to obtain an opening and closing movement of the shed which is almost synchronized with the desired stoppage phases, making only slight corrections to the motion law resulting only from the geometry of the device and from a constant-speed rotation of the motor M. The electronics for controlling the motor M may therefore be considerably simplified, achieving the desired reductions in cost of the device.

[0034] Preferably, the electronic control system of the motor M consists of a digital system which continuously provides the speed and angular position values of the motor M, i.e. the pre-set motion law thereof, supplying this data to a processor controlling the motor M. Said processor detects, by means of an encoder, the real values relative to the movement of the motor M and corrects any errors with respect to the values supplied by the digital system by means of a closed-ring control system. The abovementioned digital system is moreover kept constantly in synchronism with the main motor of the loom by means of an electronic system which is commonly called an "electric axis" which continuously detects, by means of another encoder, the main movement of the loom.

[0035] In addition to achieving the main object of the invention, it has already been stated how the particular geometry of the device, which is characterized by reduced dimensions widthwise and depthwise, results in significant advantages during installation of the device, which may in fact be inserted without particular problems in the immediate lateral vicinity of the heald frames Q, either along the right-hand or left-hand edge of the shed - or in possible intermediate positions of the shed, if simultaneous weaving of several pieces of fabric is performed - and also in a front or transverse position with respect to the weaver (axes of the pulleys 2 parallel or perpendicular to the warp yarns), depending on the requirements and circumstances.

[0036] Another significant advantage of the device according to the invention is finally that of making it easy to achieve substantially constant drawing of the warp yarns O intended for formation of the leno heald weave. Owing, in fact, to the presence of the guide slot 8 and the elastic nature or the L-shaped or arc-shaped configuration of the yarn guide elements 5, the warp yarns O do not undergo any additional drawing during the stoppage phase which occurs at the maximum opening of the shed, during the "outer" semi-rotational movement of said yarn guide elements. During this phase, in fact, the eyelet 5a of the yarn guide elements 5 is approximately aligned with the centre of rotation of the pulleys 2 and therefore the overall length of the warp yarns O, and in particular of the warp yarn section lying between the yarn protection rim 9 of the slot 8 and said eyelet 5a is substantially constant.

[0037] Drawing of the warp yarns may also be kept constant during the position switch-over of the warp yarns O, i.e. when the yarn guide elements 5 are positioned in a central position of the device, by envisaging that the yarn-protection rim 9 - instead of lying in a plane as illustrated in the drawings - has an arched or tunnel-like shape, with the part which is more projecting, and therefore most distant from the slot 8, being arranged in a central position and projecting beyond the level of the eyelets 5a. In this way, the rim 9 forces the warp yarns O to follow a path which is longer the closer they are situated to the centre of the device and therefore to the theoretical minimum drawing position. By suitably designing the profile of the rim 9 it is therefore possible to ensure that the individual sections of the warp yarns O, in all the different positions defined by the yarn guide elements 5 fixed to the belt 1, have an overall length which is substantially constant, for each displacement of the belt by a particular amount.

[0038] This result of constant drawing of the warp yarns independently of the degree of opening of the shed - which is a fairly interesting feature for obtaining a tight and constant weave for the weft - is obtained in an even simpler and more reliable manner with the second embodiment of the device according to the present invention, illustrated in Figs. 4 and 5.

[0039] In this embodiment, two pairs of pulleys 12/12' are envisaged, each pair being keyed on a same shaft parallel to that of the other pair of pulleys. The pulleys 12 support a belt 11 and the pulleys 12' a belt 11', both belts being provided with yarn guide elements 15, 15', all in a manner which is perfectly similar to that already described with regard to the first embodiment.

[0040] The belts 11 and 11' are moved in synchronism by a single motor M, for example by means of a toothed-belt drive 13 which is coupled externally to the belt 11 and illustrated only schematically in Fig. 4. The belts 11 and 11' are reciprocally phase-displaced so that when the yarn guide elements 15 of the belt 11 are faced at their minimum mutual distance in the central zone of the belt, the yarn guide elements 15' of the belt 11' are opposed each other at the maximum mutual distance at the opposite ends of the belt 11', and vice versa. In other words, the position of the yarn guide elements 15 on the belt 11 is offset by 180° with respect to the position of the yarn guide elements 15' on the belt 11'.

[0041] Each of the two warp yarns O intended to form the leno heald weave is passed through a respective yarn guide element 15, a common central hole 18 and a respective yarn guide element 15'. In this way it is possible to achieve perfect control of drawing of the warp yarns O, since, when the drawing action imparted for example by the pair of yarn guide elements 15 increases, that imparted by the pair of yarn guide elements 15' decreases, such that the overall drawing of the warp yarns or, in other words, the length of their travel in any position of the belts 11, 11' is substantially constant. Measurements carried on the device above described have in fact shown that the length of the travel of the warp yarns, in any position of the belts 11 and 11', is constant; the theoretical maximum variation, having a fairly limited practical importance, is in fact equal to ± 1 mm.

[0042] Finally, Figs. 6A and 6B show, in a schematic manner, a third embodiment in which the oval path of the belt supporting the yarn guide elements is no longer obtained by means of two pulleys, but by means of a track 22 inside which a belt 21 is inserted.

[0043] The belt 21 is made to perform an alternate rotational movement by a motor M via a toothed drive belt 23 which is coupled with a corresponding external toothing of the belt 21. In order to reduce the friction of the belt 21 on the track 22, the periphery of the latter may be delimited by idle rollers instead of a rigid profile.

[0044] The present invention has been described with reference to particular embodiments thereof, which illustrate preferred applications, but it is obvious that the scope of protection of the invention is not limited to these embodiments, but also comprises all the possible variants thereof, within the competence of a person skilled in the art, provided that they are comprised within the definitions given in the accompanying claims.

Claims

1. Device for forming the leno heald weave in a weaving loom, of the type in which two warp yarns or two groups of warp yarns are controlled by corresponding yarn guide elements so as to perform an alternate opening and closing movement of the shed and switching of the mutual lateral position with respect to the fabric being formed, characterized in that said yarn guide elements are fixed to a flexible conveying member arranged in a closed ring along an oval path and controlled by motor means so as to perform alternate movements along said path according to a pre-set motion law.

2. Device as in Claim 1, wherein said flexible conveying member is a belt supported by two pulleys with parallel axes, at least one of which is caused to rotate by said motor means.

3. Device as in Claim 1 or 2, wherein said motor means consist of a stepping motor or a brushless motor with encoder.

4. Device as in Claim 2 or 3, wherein the motion transmission between said motor and said belt is of the synchronous type.

5. Device as in Claim 4, wherein said belt and said pulleys are of the toothed type.

6. Device as in Claim 4, wherein the position of said belt is controlled by sensor devices.

7. Device as in any one of the preceding claims, wherein said yarn guide elements are fixed to said belt in opposite positions.

8. Device as in Claim 7, wherein said yarn guide elements are rigid and have an L-shaped or arc-shaped configuration turning towards the inside of the device so that their eyelets move approximately in correspondence of the rotation centre of said pulleys.

9. Device as in Claim 7, wherein said yarn guide elements are flexible and elastic and have a rectilinear configuration when they are not under strain.

10. Device as in any one of the preceding claims, comprising moreover a central hole or slot, formed between said pulleys, for allowing the warp yarns to pass through the device.

11. Device as in Claim 10, wherein said slot comprises a yarn protection rim projecting from the slot and having an arc-shaped or tunnel-like configuration, the more projecting portion thereof being positioned in correspondence of the central part of the slot.

12. Device as in any one of Claims 2 to 11, comprising moreover a second belt/pulley set, wherein the pulleys of the second set are coaxial to and rotatable with the pulleys of the first set, and wherein the yarn guide elements of the first belt are arranged offset by 180° with respect to the yarn guide elements of the second belt.

13. Device as in Claim 1, wherein said flexible conveying member consists of a belt, at least partially slidable along an oval track, and caused to rotate by a drive belt with coupled toothing, controlled by said motor means.

14. Device as in Claim 13), wherein the periphery of said track is delimited by idle rollers.

15. Device as in any one of the preceding claims, wherein said oval path is an elliptical path.

16. Device as in any one of the preceding claims, wherein said oval path is a path formed by two parallel rectilinear sections radiused at the ends by semi-circles.

17. Device as in any one of the preceding claims, wherein said motor means are controlled by a digitally operated electronic system.

18. Device as in Claim 17, wherein said digital control system continuously supplies, to a processor unit controlling said motor, the information on the speed rates and on the angular position values of the motor itself.

19. Device as in Claim 18, wherein said processor unit detects, by means of an encoder, the real values of the motor drive mechanism and corrects any errors, with respect to the values supplied by the digital system, by means of a closed-ring control system.

20. Device as in Claim 17, wherein said digital control system is kept in synchronism, by means of an "electric axis", with the main drive mechanism of the loom.

Drawing