GB1559763A

GB1559763A - Loom having a thread tensioner

Info

Publication number: GB1559763A
Application number: GB9386/78A
Authority: GB
Original assignee: Lindauer Dornier GmbH
Current assignee: Lindauer Dornier GmbH
Priority date: 1977-03-10
Filing date: 1978-03-09
Publication date: 1980-01-23
Also published as: FR2383112B1; DE2710368A1; DE2710368B2; CH628935A5; IT1107133B; DE2710368C3; BE864779A; IT7867508A0; FR2383112A1

Abstract

In weaving machines, in which the weft thread (21) is drawn off intermittently from supply bobbins (V) arranged outside the shed and is shot into the shed by gripper members (G), a thread-tension device (S) is arranged between the supply bobbin (V) and the thread brake (B). By means of this thread-tension device (S), not only is the weft thread (21) fed under slight tension to the gripper member (G), but loop formation or twisting of the weft thread (21) between the supply bobbin (V) and thread brake (B) is also prevented. The thread-tension device (S) consists of a rotating drum (7) and of an annular brush (11) arranged freely displaceably on the latter. The thread (21) runs between the drum (7) and brush (11); the loose thread strand coming from the supply bobbin (V) is thereby wound as a loop on to the drum (7) and is drawn off from there during the next weft shoot-in. <IMAGE>

Description

(54) LOOM HAVING A THREAD TENSIONER (71) We, LINDAUER DORNIER GESELLSCHAFT m.b.H., a German limited liability company, of D-8990 Lindau/ Bodensee, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a loom having a thread tensioner.

In a loom, the weft thread which is to be inserted is withdrawn, weft for weft, from large supply spools mounted on a separate frame outside the loom. It is inherent in the nature of weft insertion that the thread is alternately drawn off at high speed and required to return to rest at frequent intervals. Due to inertia, however, the portion of thread withdrawn from the spool cannot be arrested instantly. Although a thread brake is normally installed between the supply spool and the weft insertion device to steady the thread and produce some tension in it to ensure that it will be gripped by the weft insertion device (for example a gripper), such a thread brake can at the earliest grip the weft thread at some point behind the thread guide of the spool frame (viewed in the direction of movement of the thread), so that the portion of thread extending from the spool to the thread guide is unchecked and remains without tension.

This loose piece of thread tends to become twisted and tangled, to an extent varying with the material and the twist already in the thread, and this may subsequently cause trouble in the process of weft insertion.

It is an object of the invention to reduce this disadvantage and ensure that the thread runs smoothly. According to the invention, there is provided a loom having a thread tensioner, in which weft thread is withdrawn intermittently from a supply spool, wherein an annular brush is arranged on a rotatable drum which has a smooth surface, the brush loosely encircling the drum and being axially displaceable within a limited range, the thread running over the surface of the drum underneath the brush, and wherein the loom has a first stationary thread guide which delivers the thread to the drum substantially in the axial direction and is arranged between the supply spool and the drum, and a second stationary thread guide which carries the thread forward substantially in the axial direction and is arranged downstream of the drum. The thread runs over the surface of the drum underneath the brush between the two thread guides. The light pressure applied by the brush forms the loose piece of thread into a loop on the drum, and so tensions the thread. The bristles of the brush are preferably arranged slightly obliquely to the direction of rotation of the drum. The second thread guide may be arranged at a distance from the axis of rotation of the drum which is smaller than the radius of the drum.

An embodiment of the invention will now be described by way of example with reference to the accompanying diagrammatic drawing, in which: Figure 1 represents schematically the arrangement of a thread tensioner on a loom; Figure 2 is a side elevation of the thread tensioner; Figure 3 is an end elevation of the thread tensioner seen in the axial direction and from the right of Figure 2; and Figure 4 is a top plan of the thread tensioner.

The structure and arrangement of the loom and the thread tensioner will first be described in outline with reference to Figure 1. A weft thread 21 runs from a supply spool V to a thread tensioner S through a thread guide 15. From the tensioner S, the weft thread is carried through a second thread guide 17 to a thread brake B and thence to a weft insertion device, which is indicated as a gripper rod G. The delivery of thread to the tensioner S and its subsequent movement are substantially in the axial direction of the tensioner. The thread brake B is constantly adjusted to a given value. Without the thread tensioner S, the slack length of weft thread between the spool V and brake B would be liable to twisting. A drum 7 with an annular brush 11 thereon is indicated schematically as a component of the thread tensioner. These parts will now be described in more detail.

Figure 2 is a highly simplified representation of the thread tensioner S. A shaft 5 of the drum 7 is mounted on supports 3 fixed on a base plate or supporting arm 1. The drive for the drum is indicated by way of example as a belt drive and represented by a pulley 9. The smooth-surfaced drum 7 is mounted on the shaft 5. It is encircled by the annular brush 11 which lies loosely against the surface of the drum 7 and is also freely displaceable thereon in the axial direction within limits which are set by fixed members, in the form in this embodiment of rings 13 fixed to the baseplate 1 by supports 14.

Instead of rings, other fixed abutments for example stirrups could be provided.

The first thread guide 15 is to the left of the drum 7. in the direction towards the supply spool. This guide 15 may be mounted (as shown) on one of the supports 3, or on the baseplate 1. A second thread guide 17, which is also stationary, is arranged to the right of the drum 7. The radial distance b of the first thread guide 15 from the axis of rotation 8 is at least equal to or slightly greater than the radius r of the drum 7. This is to ensure that the thread will not be pulled over the edge of the drum 7. The same purpose may also be achieved by shifting the outlet of the thread guide 15 so far fowards in the axial direction that it is still above the cylindrical surface of the drum 7, as shown in Figures 2 and 4. The thread 21 is then carried forwards on the surface of the drum underneath the bristles of the brush 11 and is taken up by the second thread guide 17 at the other end of the drum 7. This second thread guide 17 is placed in a position such that the thread 21 is led over the edge 7' of the drum 7 in the direction indicated by the arrow. For this purpose. the distance a of the thread guide 17 from the axis 8 is smaller than the radius r, The edge 7' of the drum is rounded off and polished to prevent damage to the thread.

Referring to Figure 3, the drum 7 is surrounded by the rings 13 which are fixed to the baseplate 1 by the supports 14. In this Figure one ring is seen, partly broken away to show the arrangement of the annular brush 11. The bristles 12, which loosely touch the surface of the drum, are shown over part of the circumference of the brush 11. Preferably the bristles are arranged slightly obliquely to the direction of rotation of the drum 7 indicated by the arrow. The position of the second thread guide 17 is indicated in broken lines.

Operation of the thread tensioner will now be explained with reference to Figures 2 and 4. When the thread tensioner is at rest, the weft thread 21 passes in the direction of the arrow through the first thread guide 15 to the surface of the drum 7 and then runs under the annular brush 11 over the surface of the drum to the second thread guide 17. Due to the thread tension, the thread 21 takes the shortest path between the two guides 15 and 17. So long as the weft thread is being drawn off the supply spool and inserted into the shed by the weft insertion device G, it is always under tension. This is not significantly altered by the rotation of the drum 7 because the drum has a smooth surface and because the pressure applied by the brush is very light due to the oblique position of the bristles in relation to the direction of rotation of the drum. As soon as weft insertion stops and the thread tension drops, either at a transfer of weft thread or at the end of weft thread insertion on the outside of the loom, the unbraked portion of weft thread between the supply spool and the brake continues to unwind due to the moving masses and is dragged over part of the circumference of the drum by the light pressure exerted by the brush so that it forms a loop on the drum, substantiallv as indicated by the continuous lines on the drum in Figures 1, 2 and 4. The loose length of thread between the spool and the brake is thus put under sufficient tension to prevent twisting of the thread but at the same time no more thread is withdrawn from the spool in spite of the thread tension.

As soon as the loop of loose thread has been wound over the drum 7, it is fixed in position by the brush 11 in spite of the continued rotation of the drum 7, the thread being thus deflected by the annular brush 11 before it reaches the second thread guide 17. As soon as the weft thread 21 is withdrawn to the right of the second thread guide 17 during the next weft thread insertion, the portion of thread on the drum is stretched so that it returns to the position indicated by the broken line 22, regardless of the continued rotation of the drum 7. The extent of deflection of the thread on the drum always corresponds to the length of the loop formed at the given moment by the influence of inertia. The thread deflection on the drum 7 adjusts itself automatically and the thread tension remains the same after each withdrawal of thread.

The size or length of the loop of thread on the drum is of minor significance. The loop can be smoothly withdrawn from the drum during the next weft insertion. This will certainly take place if the dimensions of the drum, i.e. its radius, is sufficient to ensure that even the longest loop of thread which may occur in practice will be wound over less than half the circumference of the drum. However, the thread could be wound several times around the drum provided care is taken to ensure that when weft insertion is resumed, the rate at which the thread is withdrawn by the weft insertion device G is greater than the circumferential velocity of the drum.

WHAT WE CLAIM IS: 1. A loom having a thread tensioner in which weft thread is withdrawn intermittently from a supply spool. wherein an annular brush is arranged on a rotatable drum which has a smooth surface, the brush loosely encircling the drum and being axially displaceable within a limited range, the thread running over the suface of the drum underneath the brush and wherein the loom has a first stationary thread guide which delivers the thread to the drum substantially in the axial direction and is arranged between the supply spool and the drum, and a second stationary thread guide which carries the thread forward substantially in the axial direction and is arranged downstream of the drum.

2. A loom according to claim 1 wherein the fist thread guide is arranged at a distance (b) from the axis of rotation of the drum greater than the radius (r) of the drum.

3. A loom according to claim 2 wherein the drum extends axially beyond the outlet of the first thread guide.

4. A loom according to any preceding claim wherein the second thread guide is arranged at a distance (a) from the axis of rotation of the drum smaller than the radius (r) of the drum.

5. A loom according to any preceding claim wherein the range of displacement of the brush is limited by fixed members, for example stirrups or rings, which at least partially surround the drum.

6. A loom according to any preceding claim wherein the edge of the drum is rounded off and polished at the end where the thread leaves the drum.

7. A loom according to any preceding claim wherein the bristles of the brush are arranged slightly obliquely to the direction of rotation of the drum.

8. A loom constructed and arranged substantially as herein described and shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The size or length of the loop of thread on the drum is of minor significance. The loop can be smoothly withdrawn from the drum during the next weft insertion. This will certainly take place if the dimensions of the drum, i.e. its radius, is sufficient to ensure that even the longest loop of thread which may occur in practice will be wound over less than half the circumference of the drum. However, the thread could be wound several times around the drum provided care is taken to ensure that when weft insertion is resumed, the rate at which the thread is withdrawn by the weft insertion device G is greater than the circumferential velocity of the drum. WHAT WE CLAIM IS:

1. A loom having a thread tensioner in which weft thread is withdrawn intermittently from a supply spool. wherein an annular brush is arranged on a rotatable drum which has a smooth surface, the brush loosely encircling the drum and being axially displaceable within a limited range, the thread running over the suface of the drum underneath the brush and wherein the loom has a first stationary thread guide which delivers the thread to the drum substantially in the axial direction and is arranged between the supply spool and the drum, and a second stationary thread guide which carries the thread forward substantially in the axial direction and is arranged downstream of the drum.