The present invention refers to a yam holding device for yam feeding systems in looms. The ya holding device may, however, also be applied in other types of systems where thread-like products or other elongated objects shall in a similar way intermittently be held with a pinch jaw over the product or object. The yam holding device in accordance with the invention refers to an improvement of a known yam holding device of a type which is elaborated upon in more detail in the ingress to the patent claim 1.

PRIOR ART In automated looms the feeding of yam and alternation between different yarns between wefts takes place completely automatically, whereby the yam which is to be feed into the warp can be cut and held before the next warp alternation and feeding into the warp. In high speed looms the traditional shuttle has also been replaced by systems which shoot the yam into the warp with air or water, so- called shuttle-less looms. These shuttle-less systems can incorporate a so-called water jet nozzle to which the yam is fed, and where the water jet nozzle shoots out a small water droplet which with high speed takes the yam with it through the warp to the other side of the weave. Alternatively it is possible to use air nozzles, where a first main nozzle and a slave nozzle shoot the yam into the warp. The yam shall in these systems be able to be drawn out with minimum possible resistance and with high speed, at the same time as the yam must be able to held secure in connection with its cutting and between subsequent wefts. The present invention relates to this purpose of holding the yarn.

Yam refers in this paper to all types of yarns which are used in weaving. These yarns can be manufactured of natural materials such as cotton, wool, linen, or jute, etc. or artificial materials such as polyester, etc. or different mixtures between natural materials and artificial materials. The yams can be of the single thread type or twined multiple thread yarns with circular, oval or flat shaped cross sections.

A previously know yam holding device has been manufactured with special steel plates in the pinch which grips the ya , since the yam which passes through the pincher exposes the pinching surfaces to severe wear. The ya holding device opens the pincher by only a fraction of a millimetre, up to several millimetres, and since considerable quantities of yam can be feed at high speed through the narrow gap in the open pincher the surfaces in the pincher can be exposed to a high degree of wear. With a view to increasing the durability of the pinching surfaces in the yam holding device the pinching surfaces in certain yam holding devices have been provided with ceramic plates. Even in these yam holding devices with ceramic plates there is considerable wear on the plates since they

most often pinch over the same place, which implies that gradually the yam wears down a depression across the plates where the yam runs.

A version of yam holding device with gripping plates manufactured of special steel is shown in Fig. 1, where rotating round special steel plates are used in the yam holding device's pincher, which implies that the plates can rotate and change the pinching surfaces for the line of wear running across the plates. The plates index forward new pinching surfaces as the yam is fed forward in the pincher. These yam holding devices with round special steel plates also ensure improved wear resistance than what can be achieved with yam holding devices with fixed ceramic plates, in that new pinch surfaces on the opening of the yam holding device can be indexed forward for exposure to wear from the yarn. The ya holding device in Fig. 1 is an electro mechanical yam holding device with a response which is adjusted to looms of the high speed type, primarily shuttle-less looms. The yam holding device consists of an electro magnetic coil 17 which activates an anchor 7, on which anchor 7 via a pull rod 6 one of the plates 3 is arranged which as an electro magnet can activate pinching over the yam 2. The grip plate 3, hereafter called active grip plate, is circular with a centre hole which is entered on the pull rod 6 from its opposite end to the anchor end, and held in a fixed axial position to the pull rod between an projection on the pull rod and lock nut 5, which lock nut is similarly entered on the pull rod 6 from the threaded end opposite the anchor end. The second pinching grip plate 4 over the yam, hereafter called passive grip plate, is also circular with a centre hole 10, which centre hole runs freely to a certain tolerance on the pull rod 6. The passive grip plate 4 is housed on a round pull rod mounted circular centring washer 11, the axial contact surface of which to the passive grip plate 4 is bowl shaped. In that the passive grip plate's contact surface to the centre washer 11 is in a corresponding way bowl shaped, the passive grip plate 4 can be made self-correcting in terms of parallelism with the active grip plate's 3 interactive pinching surface. The yam holding device 1 consists of a mounting flange 13 with mounting hole 13' for mounting on a bracket on the loom. In Fig. 1 this mounting flange is arranged between a fixed wear washer 12 on the flange, against which the centring washer 11 lies, and the electro magnet housing 15. The housing 15 houses in the conventional manner a coil 17 wound round a bobbin concentric with the pull rod and anchor 7. The yam holding device functions in such a way that when the coil is supplied with voltage the anchor 7 is drawn to an anchor stroke 18, whereby the yam holding device's active grip plate 3 is actuated away from the passive grip plate 4 and opens the pincher between the plates. When the voltage is switched off a return spring 8 shoots out on a flange 7' on the anchor 7 so that the active grip plate 3 pinches the yam 2 to the passive grip plate 4. In that the plates 3 and 4 can rotate round the yam holding device's axial line CC the pinching surfaces over the ya will continuously change, which can be seen in Fig. 2 where the grip plate 4 is

shown in a view seen from the section 11-11 indicated in Fig. 1. The yam 2 passes over the grip plate in the direction of feed, designated FEED in the figures. In that the grip plate can rotate, in the direction ROT, round the axis CC, the grip plate's contact line to the yam is continuously changed. The friction of the yam tends to rotate the grip plate in the direction ROT, and lines A, B and C indicate the contact lines which, for example, are achieved at the third, second and immediately preceeding pinching event respectively of the yam. The wear will in this way be evenly distributed over the plates. The active grip plate 3 is in the preferred version locked on the pull rod 6, but when the pull rod 6 together with the grip plate 3 and anchor 7 constitute in the housing round the centre axis CC a free-rotating unit, the active grip plate will also be able to rotate with this unit and continuously change the contact line to the yam 2.

A disadvantage with this type of yam holding device is that the passive grip plate is not fixed axially in the direction of the centre axis CC, which implies that the passive grip plate tends adhere at the active grip plate on the movement of the active grip plate to open the pincher. This causes the passive grip plate 4 to lift and interfere with the feeding of the yam between the plates 3 and 4, which can cause the yam to be exposed to braking forces which can break the yarn. In shuttle-less looms the undesired braking force on the yam can imply that the ya is not shot completely into the warp, whereby the weaving is incomplete and can stop.

Another disadvantage is that the passive grip plate as a result of its large radius of the bowl form in the contact surfaces between the passive grip plate 4 and centring washer 11 is given an irregular behaviour, when the yam feed over the passive grip plate's pinching surface tends to shoot the passive grip plate radially in the yam's direction of feed, FEED, on the opening and closing of the pincher when the grip plates are not parallel. With each pinch the passive grip plate 4 will return to the radial position which gives parallelism with the active grip plate, which causes noise and interference to the yam feeding. A further disadvantage is that the yam holding device can only be mounted so that the centre axis CC is vertical, with the active grip plate above. Other directions of mounting would imply that the passive plate would follow the active grip plate and interfere with the yam feeding.

PURPOSE OF THE INVENTION The purpose of the invention is to achieve an improved yam holding device which has all the advantages which a yam holding device with circular rotating grip plates has in terms of wear resistance and self-correction of the parallelism between the gripping surfaces over the yarn, but where a yam holding device in accordance with the invention reduces interference to the yam feeding through the yam holding device. A further purpose is that with the yam holding device in question receives a quieter gripping function with a prolonged service-life of the component parts, where lateral movement in the

direction of the yam feeding and axial movement across the direction of yam feeding are reduced on at least the grip plate which is self-adjusting for the parallel setting in relation to the other interactive grip plate.

A ftirther purpose is that the yam holding device should be able to be fitted so that a centre axis CC can assume any angle in a vertical plane transverse to the direction of the yam feeding, without the passive grip plate interfering with the yam feeding

SHORT DESCRIPTION OF THE INVENTION The yam holding device in accordance with the invention is distinguished by the characteristic part of claim 1.

By means of a yam holding device in accordance with the invention it is possible for the circular free-rotating grip plate to achieve a considerably prolonged service-life for a reliable yam gripping function, where at the same time interference to the yam feeding is reduced to a minimum.

Other characteristics and advantages of the invention are made clear in the other characteristic parts of the claims of the patent, and in the subsequent description of exemplified designs. The description of the design examples are made with reference to the figures indicated in the following list of figures.

LIST OF FIGURES

Fig. 1 shows a previously known yam holding device which by way of introduction was described in the section prior art:

Fig. 2 shows a view seen in the section Il-π in Fig. 1 of how the yam continuously changes the contact line to the fixed pinching circular grip plates over the yam in the this type of yam holding device.

Fig. 3 shows a yam holding device in accordance with the invention. Fig.4 shows a schematic view of a yam feeding system for a loom with a ya holding device arranged in a yam feeding system.

DESCRIPTION OF DESIGN EXAMPLE

Fig. 3 shows a design example of the yam holding device in accordance with the invention where the anchor, the pull rod and the active grip plate are disengaged in relation to other parts which are seen in a section through the ya holding device. The parts which correspond with parts in the yam

holding device shown in Fig. 1 have in Fig. 3 been given the same reference numbers. The yam holding device's housing 15 and the electro magnet 16, 17 arranged in the housing are basically identical with the housing and electro magnet in Fig. 1.

The anchor 7 and the thus related pull rod 6 actuate the movable active grip plate 3 in the corresponding manner as in Fig. 1 , i.e. that when the electro magnet is activated the active grip plate 3 is moved away in the axial direction CC of the pull rod to release the yam which is pinched between the passive grip plate 4 and the active grip plate 3 when the electro magnet is deactivated.

In the yam holding device in the invention the passive grip plate 4 is arranged in a semi spherical shaped holder 22. The cross-sectional surface on the holder 22 is unconventionally completely blackened with a view to increasing the clarity in the figure. The convex surface on the semi spherically shaped holder 22 is directed away from the passive grip plate. The semi spherical holder 22 has a concave and a convex surface where in the semi spherical holder arranged grip plate 4 lies like a lid over the holder's concave surface. The passive grip plate 4 is held round its outer periphery to the semi spherically shaped holder's 22 outer periphery by means of an anchor element 25. The anchor element 25 is in the shown design a form lock where a groove which runs along the semi spherically shaped holder's outer edges is mounted over a corresponding phase of the passive grip plate's outer periphery. The semi spherically shaped holder is appropriately manufactured of a polymer material of low- friction type, e.g. Teflon, which material has a certain limited flexibility which permits holder 22 and its groove to be pulled over the passive grip plate's chamfered outer periphery. The semi spherically shaped holder 22 is housed with its convex surface, in relation to the housing 15 fixed bearing washer 21 which has a corresponding concave bearing surface to which the holder's convex surface is in contact. The bearing surfaces between the holder 22 and the bearing washer 21 are convex and concave respectively with a radius R in relation to the pull rod's centre axis CC. The holder 22 can thereby adjust itself so that parallelism is achieved in the contact surfaces between the active grip plate 3 and the passive grip plate 4 arranged at the housing. The bearing washer 21 can be fixed to the mounting flange 13 arranged on the housing by means of gluing, welding or screwing on a threaded extension 24 of the anchor element 18, which extension is arranged concentrically round the pull rod 6.

The holder 22 is attached to the bearing washer with a lock ring 24 which is in contact with a concave surface in the semi spherically shaped holder 22. The lock ring 24 is preferably screwed on the threaded extension 24 of the anchor element and its clamping pressure against the holder 22 is regulated by means of the torque on the lock ring. The lock ring 23 is, however, only tightened sufficiently so that the tolerance between the lock ring and the holder's 22 inner concave surface is

minimised and the flexibility in the bearing surfaces between the holder 22 and the bearing washer is retained. After tightening of the lock element this is fixed in position in that the lock element's 23 internal thread is locked by means of locking agent to the external thread on the extruding projection 24 from the housing. For example, it is possible to use a locking liquid of the LOCTJTE type or the like. Alternatively locking can be achieved with a lock screw applied to the thread

The bearing surfaces between holder 22 and bearing washer 21 have a constant curvature with radius R and its centre of curvature should preferably lie in the pull rod's centre axis CC and in the passive grip plate's 4 plane. The passive grip plate 4 then takes up the forces which it is exposed to by the ya 2 fed through the gap. With the yam holding device in Fig. 1 an unstable lateral movement is achieved on the passive grip plate since the large radius on its contact surface implies that the passing yam tends to the lift the passive grip plate in the direction of the yam feeding, FEED. Similarly the holder's concave surface has a constant radius of curvature (R) where the centre of curvature coincide with the pull rod's centre axis (CC) and the grip plate's 4 plane arranged in the holder, and the lock element's (23) contact surface to the holder's concave surface has a convex surface corresponding to the holder's concave surface.

The semi spherically shaped holder 22 is in Fig. 3 mounted on the extended part of the anchor element and is provided with a sufficient tolerance between its mounting hole and the extended part of the anchor element in order to facilitate adjustment of parallelism between the plates 3, 4.

A yam feeding system for a shuttle-less loom 47 is shown in Fig.4 schematically with a yam holding device 34 arranged in the yam feeding system. Only one yam feeding system is shown in the figure. In automated looms there are often a number of parallel yam feeding systems, whereby replacement of yam with for example other colours can be made during the weaving between different successive wefts. Via a yam hopper 31, also designated fournisseur, the yam 2 is fed via a yam control funnel 32 and a yam guide 33 to the yam holding device 34. The yam is led after the yam holding device 34 on to a second yam guide 35 and on to a water jet nozzle 36. The water jet nozzle 36 then shoots the yam 2 into the warp between the threads in the warp which are lifted, hereafter designed top warp 39, and the threads in the warp which are lowered, hereafter designated bottom warp 40. The yam 2 is shot in between the top and bottom warps 39, 40 by means of a small water droplet which at high pressure is shot from the water jet nozzle taking the yam 2 with it Pressurised water is applied to the water jet nozzle from a pressure source P via an adjustable valve V. The valve V opens very quickly and only a small water droplet leaves the nozzle 36 and pulls the yam 2. With a cutting unit 37 the yam can be cut after it has been fed in the warp. The cutting unit can be provided with a cutting edge or alternatively hot wires can bum off the ya ,

which is often used for weaving with polyester yam. The cutting unit 37 is preferably arranged close to the warp or weave 38 with a view to minimising the yam spillage.

The yam feeding system is monitored by a control unit 41 which can be reprogrammed with a portable hand terminal 42 for adjustment to different types of yarns as a result of the weight of the yam, etc.

For example, heavier or more rigid yams require a larger water droplet or higher pressure in able to pull the ya through the warp.

The control unit 41 regulates the different unit functions, via control signal lines 50, 51, 52, 53 connected to the yam hopper 31, the yam holding device 34, the water jet nozzle's control valve V and cutting unit 37. The synchronisation of the units 31 , 34, V and 37 to the loom 47 takes place on the basis of input signals on a line 59 from for example a sensor 45 which detects the rotation of the loom's feeder rollers 44 and therefore the length of the finished weave, in combination with other input signal lines 58 from sensors 46 arranged on the loom 47.

As indicated above the holder 22 is preferably manufactured of a polymer material, while the lock ring 23 and bearing washer 21 are manufactured for example of an aluminium alloy. The choice of material is governed by the requirement of low friction and retained flexibility in the contact surfaces between the holder and bearing washer 21 / lock ring 23, and the requirement during longer periods of operation to retain a given tolerance between the holder's and the bearing washer's interactive bearing surfaces. In another version the holder 22 may instead be manufactured of aluminium, while the lock ring 23 and bearing washer 21 are manufactured of polymer material.

The invention may within the scope of the patent claims be modified in a number of ways. The free- rotating circular grip plates 3, 4 may for example be coated with ceramic material, or alternatively the grip plates in their entirety may be manufactured of ceramic material. The most important aspect is that the grip plates retain their free-rotating characteristics in order to enable continuous replacement of the yam's line of wear on the grip surfaces.

The lock ring 23 in the preferred version may also be replaced with a different design which ensures that the holder does not follow on when the active grip plate is actuated to open The holder 22 in Fig. 3 may, for example, in its lower part be provided with a sleeve arranged concentrically with the pull rod directed out from the holder's convex surface, which sleeve has a radial outward directed collar which grips in a radial groove arranged internally in the bearing washer's 21 inlet for the pull rod 6.

The ya holding device may also be modified in such a way that both grip plates are housed in their own semi spherical holder if improved and greater reliability in the parallel adjustment is required. If, for example, a holder should jam then it is possible for the other holder to achieve the requisite parallelism. This implies, however, a disadvantage in terms of the response of the yam holding device. It is often the case that the moving parts in the yam holding device which are actuated to open the pincher are designed with the lowest possible weight, which implies that the yam holding device in Fig. 3 is to be preferred. In Rg. 3 only the anchor 7, the pull rod 6 and the grip plate 3 arranged on the pull rod are actuated, which gives a low weight for the moving parts and quick response when the electro magnet is activated or deactivated to open or close. With the version shown in Rg. 3a, response is achieved of a magnitude of 3 milliseconds, which is a prerequisite to achieve a high speed off weaving and quicker yam feeding.

In a further version it is possible for both grip plates to be flexible, and actuated by the same or each by their own pull rod with attendant electro magnet. In other applications the servo element may also be of another type than the electro magnet, for example hydraulic or pneumatic cylinders.