EP1724383B1

EP1724383B1 - Carrying gripper for weaving looms with (anti-loop) device to avoid anticipated weft gripping

Info

Publication number: EP1724383B1
Application number: EP05425330A
Authority: EP
Inventors: Roberto Lebbolo; Silvano Testa
Original assignee: Promatech SpA
Current assignee: Promatech SpA
Priority date: 2005-05-17
Filing date: 2005-05-17
Publication date: 2008-12-31
Anticipated expiration: 2025-05-17
Also published as: CN1865562A; ES2318443T3; EP1724383A1; ATE419416T1; TW200706716A; DE602005012062D1; CN1865562B; KR20060119770A; US20060260709A1; TWI350864B

Abstract

Carrying gripper for weaving looms, of the type wherein a channel (5) is formed behind the gripper tip head (4), arranged on a substantially vertical plane parallel to the direction of the waiting weft threads, for weft thread entry in an inner area of the gripper and towards the elastic weft-gripping means (8, 9). The inlet (7) of said elastic gripping means is arranged on the bottom of said channel (5) and immediately downstream thereof, and a weft thread deflector (6) is arranged sideways to said inlet (7), on the opposite side with respect to the weft thread end connected to the fabric being woven. The deflector (6) delays entry of the weft thread in said gripping means (8, 9), thereby preventing advance gripping of thin wefts.

Description

The present invention refers to a carrying gripper for weaving looms, and particularly to a gripper of this type equipped with a device to avoid anticipated gripping of the weft.
As is well known to people skilled in the field, during weaving of the weft thread (or of the different weft threads, in the case of weaving with wefts of a different type or colour), after the weft thread is inserted and beaten by the reed against the fabric, said weft thread is not cut off from the same fabric, but remains joined thereto until such thread is again selected by the weaving machine for a new insertion. Following selection, the weft thread is then stretched - between the point where it is joined to the fabric (with the possible presence of a deflector if the weft threads to be woven are many and hence some wefts remain inactive for many successive loom strokes) and the corresponding weft feeder - according to an oblique line which crosses the insertion path of the carrying gripper, in order to be gripped by said gripper and then conveyed through the shed.
After the weft thread has been gripped by the gripper, and while the gripper enters the shed, a cutting device intervenes which cuts off the weft thread end still joined to the fabric, thereby allowing correct insertion of such thread into the shed. The exact instant when weft thread cutting is performed must therefore be adjusted with extreme precision; as a matter of fact, it is necessary for the cut to occur at the exact time when the weft thread has been gripped enough by the elastic gripping means of the carrying gripper so as to prevent it from slipping off the gripper in the first half of the shed, but not so much as to impair weft exchange with the drawing gripper in the middle of the shed.
Of course, the criticalness of the instant in which cutting of the weft thread being inserted occurs is the higher, the smaller the count of the handled weft. As a matter of fact, in this case, if weft cutting occurs with delay, it is easier for a thin weft to deeply enter the elastic gripping means of the carrying gripper which consequently impart on the same a high retention strength at the time of weft exchange. Since tensile strength of a thin weft is obviously rather small, it easily occurs that such strength is smaller than the above-mentioned retention strength, so that at the time of weft exchange with the drawing gripper, breaking of the weft thread is inevitably caused.
As a result, grippers especially intended for work with thin wefts have been designed and proposed, wherein the shape and elastic strength of the elastic retention means are thoroughly designed and adjusted in order to try and reduce to a minimum the above-mentioned inconveniences, however, without having achieved a fully satisfactory solution yet. The inconveniences detected in the weaving of thin wefts, as outlined above, keep occurring, although to a smaller extent, even with this type of gripper. This type of approach further causes a disadvantage to the weaver, who has to proceed to the replacement of the grippers whenever he weaves an item with thin wefts and, besides, it does not even allow to face the problem when items are woven which comprise wefts having different counts.
Precisely starting from the consideration that the inconvenience of weft breakage at the time of exchange or, viceversa, of an insufficiently steady grip of the weft thread by the carrying gripper, occur to a certain extent also in grippers especially designed for thin weft insertion, the Applicant has conducted intensive studies on the weft thread gripping mechanism to try and determine the nature of the causes originating the above-mentioned problems.
At the end of such studies, the Applicant could finally ascertain that one of the main causes determining the gripping defects discussed above consists in the occasional irregular pattern of the weft thread in the cutting area. In fact, the weft thread portion between the gripper and the fabric - i.e. precisely the portion wherein weft thread cutting later occurs before insertion of said thread into the shed - upon contact with the gripper does not always stay well taut along the oblique line as it had originally arranged itself, particularly when the weft is thin, but it is subject to the formation of randomly shaped and positioned loops.
The forming of such loops depends on the fact that the weft, precisely due to its thinness, upon the first contact with the carrying gripper quickly wedges itself among the elastic gripping means of the gripper, locking itself in advance among the same. That moderate sliding of the weft thread on the front edge of said means is thereby prevented, which sliding is essential for the weft thread to keep in a taut condition, in the portion between the fabric and the carrying gripper, between the instant of the first contact with the carrying gripper - when the arrangement of such thread is oblique to the fabric - and the instant of cutting, when such thread portion is substantially parallel to the fabric and hence its length has obviously decreased.
The Applicant could therefore detect that it is precisely due to the formation of such loops that the above-discussed gripping irregularities occur. As a matter of fact, since loop positioning is fully random, as it depends on the dynamic reaction of the thread to the impact of the carrying gripper against said thread, there follows that the cutting instant is moved backward or forward, compared to the theoretically-calculated one, depending on whether the loop arranges the weft thread on the cutting means in a more advanced or more retracted position over the theoretical rectilinear position of the weft thread on the basis of which the cutting instant has been calculated.
As a result, if cutting occurs before the desired time, gripping has an insufficient retention strength and the weft thread may be lost by the carrying gripper before such gripper arrives at the weft exchange area. If, on the contrary, cutting occurs after the theoretically-calculated ideal instant, gripping carries on with excessive wedging of the weft thread, so as to determine a thread retention strength which exceeds its own tensile strength and hence its breakage at the time of exchange with the drawing gripper.
It is hence an object of the present invention to provide a gripper which solves this problem, removing the phenomenon of advanced weft thread gripping, especially in the case of very thin wefts, and of the consequent formation of a loop by the weft thread in the portion thereof comprised between the gripper and the fabric being woven. For this reason, the device of the invention is also called "anti-loop" device, in short, in the present description.
Another object of the present invention is to provide a gripper of the above-mentioned type, which allows to handle simultaneously both thin and thicker wefts, thereby eliminating the need to change gripper upon variation of the woven item and also allowing the weaving of items having varying wefts.
According to the present invention, such objects are achieved by a carrying gripper for weaving looms, of the type wherein behind the gripper tip head a channel is formed for weft thread insertion into an inner area of the gripper and towards the elastic weft gripping means, said channel lying on a substantially vertical plane parallel to the direction of the waiting weft threads, the inlet of said elastic gripping means being arranged on the bottom of said channel and immediately downstream thereof, characterised in that it further comprises a weft thread deflector arranged sideways of said inlet of the elastic gripping means and on the opposite side in respect of the weft thread end joined to the fabric being woven, said deflector being apt to delay weft thread entry into said gripping means.
Further features and advantages of the present invention will in any case be clearer from the following description of a preferred embodiment of the same, wherein:

fig. 1 is a side elevation view (weft feeders side) of a carrying gripper equipped with an anti-loop device according to the present invention;
fig. 2 is a side elevation view (woven fabric side) of the carrying gripper of fig. 1;
fig. 3 is a top plan view of the gripper of fig. 1;
fig. 4 is a cross-section view according to line IV-IV offig. 1 or of fig. 2; and
fig. 5 is a front view of the gripper of fig. 1

In the gripper according to the preferred embodiment illustrated here, the weft thread deflector which makes up the anti-loop device of the present invention has been advantageously associated with a mobile device defining the back wall of the weft thread entry channel, which device was previously developed by the same Applicant ( EP-A-1256644 ). Such device has various functions, in addition to that of forming the weft thread entry channel, and particularly of allowing channel width adjustment so as to allow to use the same gripper with threads having a different count; to hinder the further sliding of the weft thread on the back of the gripper, at the end of the sliding action on the gripper tip head, thereby preventing any problem of missed weft thread gripping inside the gripper; and finally of reducing the risk of warp yarns becoming entangled on the body of the gripper when sliding on the gripper back. The structure of such device will be briefly recalled in the following to facilitate understanding of the later description of the anti-loop device which is the subject of the invention.
The known device defining the back wall of the weft thread entry channel is clearly illustrated in the drawings and particularly in figs. 2 and 3. It consists of an elongated metallic element 1, fitted to a side wall of the gripper body by screws 2 which cooperate with eyelets 3 formed on a rear portion 1p of element 1, substantially planar and parallel to the longitudinal axis of the gripper. The major axis of eyelets 3 is also parallel to the longitudinal axis of the gripper, so that, by loosening screws 2, it is possible to move element 1 parallel to said longitudinal axis of the gripper by a distance indeed equal to the length of eyelets 3.
The front portion la of element 1, itself planar, is angled to the rear portion 1p, so as to be parallel to the rear edge 4p of gripper tip head 4. Thereby, between element 1 and gripper tip head 4, a constant-width channel 5 is formed, which lies on a substantially vertical plane and is inclined in respect of the longitudinal axis of the gripper, so as to be parallel to the waiting weft thread.
In the known construction reported above, the anti-loop device of the present invention consists of a weft thread deflector 6, which develops longitudinally at the bottom of weft thread entry channel 5, starting from an area in the proximity of the inlet 7 of elastic weft thread gripping means 8, 9 and towards the rear part of the gripper. In other words, deflector 6 is arranged so that the weft thread starts resting on the surface thereof as soon as it arrives at the bottom of entry channel 5 and comes near gripping means inlet 7. The resting of the weft thread on deflector 6 delays the entry of said thread in the gripping means and hence still allows modest sliding of the thread on inlet 7 during the further gripper advancement, so as to allow the weft thread to be perfectly taut, with no loop formation, and adequately retained within gripping means 8, 9 when it meets the cutting means.
In the gripper of the embodiment illustrated in the drawings and described here, deflector 6 is formed integrally with device 1 defining the rear wall of the weft entry channel, of which it makes up a side extension. The end part of such extension, which indeed makes up the resting surface of the weft thread sliding on the same, is inclined sideways and downwards, as is clearly visible in the cross-section of fig. 4, by an angle between 0 and 90° and preferably between 50 and 80°. Deflector 6 further has a wide radiussing area at the front connecting it with the front portion la of device 1, so as to offer continuous and steady support to the weft thread.
The extent of the support imparted by deflector 6 to the weft thread and consequently the extent of the delay with which said weft thread is inserted in gripping means 8, 9 can hence be modulated at pleasure by simply varying the inclination of the deflector to the vertical plane - the delay being null when the angle is 0° and being greatest when the angle is 90°, i.e. the resting surface of the deflector is substantially horizontal - and further making the connection between portion la of device 1 and deflector 6 more or less smooth.
It has been said earlier that deflector 6 develops longitudinally at the bottom of weft thread entry channel 5. More precisely, the free lower edge of deflector 6 - i.e. the edge from which the weft thread frees itself at the end of the "resting" action on the deflector - must be exactly at the height of inlet 7 of elastic gripping means 8, 9 of the weft thread.
By manufacturing deflector 6 integrally with device 1, the remarkable advantage is obtained that when device 1 is moved in order to vary the width of weft thread entry channel 5, anti-loop device 6 is consequently also moved in a way perfectly suited to its function. As a matter of fact, since elastic gripping means 8, 9 are fixed, it is obvious that when device 1 is moved back in order to weave with higher-count threads, the front edge of deflector 6 also moves arranging itself in a position closer to inlet 7 of the gripping means and hence the "resting" effect of the weft thread shows later and to a limited extent. However, this corresponds exactly to the gripping requirements of a higher-count weft thread which must be fastened to the gripper by a tighter gripping action; in this case it is hence correct for the delayed action of the anti-loop device to be weaker.
From the preceding description it is evident how the anti-loop device of the present invention has fully achieved the objects of the invention. As a matter of fact, thanks to the presence of deflector 6, a short delay is imparted to the gripping action, which allows to fully avoid the phenomenon of loop formation in the portion of weft thread between the gripper and the fabric being woven, i.e. precisely in the area where the cutting means operate. Thereby, the exact instant in which to perform the weft thread cut can be adjusted in an accurate and repeatable manner, providing correct weft thread gripping which does not originate advance loss of the weft thread by the carrying gripper, nor weft thread breakages at the time of weft thread exchange with the drawing gripper. Moreover, by manufacturing deflector 6 integrally with device 1, which defines the rear wall of weft thread entry channel 5, not only size adjustment of channel 5 to the count of the weft being woven is obtained, by moving device 1, but also a simultaneous effective adjustment of the "delay" effect of thread gripping, heightening such effect for thin wefts and viceversa.
The present invention has been described with special reference to a preferred embodiment of the same, but it is clear that the scope of protection of the invention also comprises the possible numerous variants of the same within the reach of a person skilled in the field - for example as far as concerns the shape of deflector 6 or the way in which such deflector is fastened to the gripper - provided they fall within the definitions of the invention provided in the attached claims.

Claims

A carrying gripper for weaving looms, of the type wherein behind the gripper tip head (4) a channel (5) is formed for weft thread insertion into an inner area of the gripper and towards the elastic weft gripping means (8, 9), said channel lying on a substantially vertical plane parallel to the direction of the waiting weft threads, the inlet (7) of said elastic gripping means being arranged on the bottom of said channel (5) and immediately downstream thereof, characterised in that it further comprises a weft thread deflector (6) arranged sideways to said inlet (7) of the elastic gripping means (8, 9) and on the opposite side in respect of the weft thread end joined to the fabric being woven, said deflector (6) being apt to delay weft thread entry into said gripping means (8, 9).
The carrying gripper for weaving looms as in claim 1), wherein said deflector (6) consists of an element fastened to the gripper or formed integrally therewith, which develops in the longitudinal direction of the gripper and has a resting surface for the weft thread.
The carrying gripper for weaving looms as in claim 2), wherein the weft thread resting surface formed on said deflector (6) is radiussed at the front to the back wall of the weft thread entry channel (5).
The carrying gripper for weaving looms as in claim 2), wherein the weft thread resting surface formed on said deflector (6) has an inclination to a vertical plane between 0° and 90°.
The carrying gripper for weaving looms as in claim 2), wherein the weft thread resting surface formed on said deflector (6) has an inclination to a vertical plane between 50° and 80°.
The carrying gripper for weaving looms as in claim 2), wherein the free lower edge of said deflector (6) is arranged at the same height as the inlet (7) to the elastic weft thread gripping means (8, 9).
The carrying gripper for weaving looms as in any one of the preceding claims, wherein said gripper further comprises a mobile device (1) defining the back wall of the weft thread entry channel (5), characterised in that said deflector (6) is formed integrally with said device (1) and is mobile therewith.