YARN FEEDING DEVICE

Abstract: A yarn feeding device 1 comprises a rotatable drum 4, a yarn-braking unit 12 through which the yarn is guided at a certain wrapping angle, and a moveable detector element 14 lying against the yarn for surveying the tension thereof and for detecting a possible yarn breakage. For enhancing the dynamic behaviour of the detecting element and for reducing erroneous fault indication as generated by the detector element 14, said detector element 14 is tensioned against the yarn such that the wrapping angle of the yarn passing the yarn-braking unit 12 is increased when the yarn tension decreases.

Description: The present invention relates to a yarn feeding device for feeding a yarn from a supply spool to a textile machine, said feeding device having a rotatable drum, a yarn-braking unit arranged between said supply spool and said rotatable drum, through which yarn-braking unit the yarn is guided at a certain wrapping angle, and a movable detector element arranged between said yarn-braking unit and said rotatable drum, said detector element lying against said yarn for surveying the tension of the yarn and for detecting a possible yarn-breakage. Yarn feeding devices of the above-indicated kind are used for positively feeding a yarn, for example, to a knitting station of a circular knitting machine. The rotatable drum is driven in synchronism with the operation of the circular knitting machine. Thus, the yarn supply to the knitting station also takes place in synchronism with the operation of the knitting machine. The yarn detector element usually has the form of a pivotable detector arm lying against a portion of the yarn between the yarn-­ braking unit and the rotatable drum. As long as no yarn breakage occurs and the yearn has its normal tension, the detector element has a first position. In case a yarn-­ breakage occurs or the tension of yarn falls essentially below the normal tension level, the detector element pivots around its axis and thereby operates a switch which is usually connected to a stop-motion-relay for terminating the operation of the knitting machine. A prior art yarn feeding device of the above-mentioned kind is, for example, previously known from the references GB-A-2 026 554 and GB-A-2 027 456. At the prior art yarn feeding device as known from the first-mentioned reference, the detector element has the form of a pivotable sensing arm arranged between the yarn-braking unit in the form of a disc-brake and said rotatable drum. A yarn-guiding hook fixedly secured to the yarn feeding device is arranged between the detector arm or sensing arm and the rotatable drum so as to define a surveyed portion of the yarn between the disc-brake and the guiding hook. The sensing arm lies against the yarn due to its own weight. In case of a yarn-breakage, the sensing arm or detector arm of the prior art feeding device pivots downwardly and thereby actuates the stop-motion-relay which, in turn, immediately interrupts the operation of the circular knitting machine. Although yarn feeding devices of this type have proven to be reliable when processing normal yarns, problems occurred when feeding so-called "lively" yarns to the knitting machine. "Lively" yarns are, for example, twisted yarns which show a peculiar lively behaviour when feeding them. It has turned out that undesirable vibrations of the detector arm may occur during the feeding of these "lively" yarns resulting in an erroneous operation of the stop-motion-relay actuated by the detector arm although the average tension of the yarn has not fallen for a longer period of time below a critical value and although no yarn-breakage has occurred. In other words, the detector arm of the prior art yarn feeding device erroneously actuates a switch associated thereto, causing a fault indication, although no fault which is detrimental to the operation of the knitting machine, has occurred. US-C-3 937 417 discloses a yarn tensioning apparatus for generating a generally uniform output tension level of the yarn leaving the apparatus. It comprises an input roller, an output roller, a friction pin and a friction nose lying against the friction pin, which friction nose is pivotably arranged in the yarn tensioning apparatus. The pivotable friction nose is adapted for compensating for varying yarn tensions by increasing or decreasing the wrapping angle of the year with regard to the friction pin. In view of the above prior art, the present invention is based on the object to accomplish a yarn feeding device of the above-indicated kind having an improved reliability in detecting feeding faults like insufficient yarn tension or yarn-breakage whilst preventing erroneous fault detections. This object is achieved by a yarn feeding device in accordance with the prior art portion of claim 1, having the features indicated in the characterising portion thereof. In accordance with the present invention, the detector element fulfills two tasks at the same time, namely the surveying of the tension of the yarn or the detection of possible yarn-breakage and a dynamic controlling of the break force which is exerted by the yarn-braking unit on the yarn guided through it. The detector element compensates for a reduction in the yarn tension by increasing the wrapping angle of the yarn passing the yarn-braking unit. It has turned out that this unique double-function of the detector element of the claimed yarn feeding device guarantees an optimal dynamic behaviour of the detector element and of the yarn even when processing a so-called "lively" yarn. In addition, the claimed yarn feeding device accomplishes an essentially constant yarn tension in the yarn fed to the rotatable drum, which prevents the yarn from losing contact with the braking unit, which problem occurred at the prior art yarn feeding device. Advantageous details of the yarn feeding device in accordance with the present invention are defined in the respective subclaims. Hereinafter, a preferred embodiment of the yarn feeding device in accordance with the present invention will be described in more detail with reference to the enclosed drawings, in which: Fig. 1 shows a side view of a yarn feeding device; Fig. 2 shows a side view on a detector element of the yarn feeding device in accordance with Fig. 1; Fig. 3 shows a top view of the detector element as shown in Fig. 2; Fig. 4 is a detail of the yarn feeding device as shown in Fig. 1 in case of a reduced yarn tension, and Fig. 5 shows a top view of the feeding device in accordance with Fig. 1. A yarn feeding device 1 has a housing 2 defining a mounting recess 3 adapted for receiving a support ring of a circular knitting machine (not shown here) to which support ring the housing 2 of the yarn feeding device can be attached. A rotatable drum 4 is journalled with regard to the housing by means of roller bearings 5 for pivotably journalling a rotatable shaft 6 which is secured to the rotatable drum 4. The shaft 6 supports a drive wheel 7 which is driven in synchronism with the operation of the circular knitting machine (not shown here) by means of a drive belt (not shown) which engages the driving wheel 7. The yarn Y withdrawn from a supply spool (not shown here) passes an input guiding eyelet 8 fixedly secured to the housing 2 and a guiding hook 9 which is also fixedly mounted to the housing 2. Thereinafter, the yarn Y passes between the two discs and a non-rotatable brake shaft 11 of a disc brake 12 and runs over a detector arm 13 of a detector element 14 for detecting a yarn-breakage and for detecting a reduction in the tension of the yarn. Thereinafter, the yarn passes a horizontal guiding pin 15 attached to the housing 2 which also generates a certain friction which favourably damps the movement of the yarn Y before it reaches the rotatable drum 4. A few turns of the yarn Y are wound around the rotatable drum 4. The yarn leaving the drum runs through an output guiding eyelet 16 before it reaches a knitting station (not shown) of the circular knitting machine. The detector element 14 is journalled at its knee at the right-hand end thereof. An upright portion 18 is engaged by a spring 17 exerting a force on said upright portion 18 which tends to pivot the detector element 14 in a clockwise direction. Hence, the arm 13 of the detector element 14 abuts against the yarn Y in an upward direction and, thus, tends to displace the yarn between the braking unit 12 and the horizontal guiding pin 15 such that the wrapping angle of the yarn passing the discs 10 and the shaft 11 of the braking unit 12 is increased. In case a yarn-breakage occurs, the detector element 14 pivots in the clockwise direction. Hence, the upright portion 18 of the detector element 14 closes a switch 19 formed by contacts located at the upright portion 18 and the housing 2 which, in turn, actuates a stop-motion-­ relay (not shown) for terminating the operation of the circular knitting machine. As shown in detail at Figs. 2 and 3, the yarn detector element 14 is journalled at a support bearing 20 secured to the housing 2. The upright portion 18 is pre-tensioned by a leg 21 of the spring 17 which is held by a support pin 22 and which rests with its second leg 23 against an abutment pin 24. Fig. 4 shows a detail of the side view of the yarn feeding device in accordance with Fig. 1 at a reduced yarn tension. If the tension of the yarn coming from the spool decreases, the detection element 14 pivots in the clockwise direction and thereby moves its detector arm 13 in an upward direction. Hence, the wrapping angle of the yarn around the shaft 11 of the disc brake 12 increases, so that the yarn braking force exerted by the disc brake on the yarn Y is increased accordingly. Hence, changes in the yarn tension coming from the supply spool are essentially compensated for when leaving the disc brake 12. This tension compensation minimises vibrations of the detector element 13 when processing so-called "lively" yarn. Therefore, the tendency of erroneously generating a fault indication by actuating the stop-motion-relay in case of short-time occurrences which are not detriment­ al to the operation of the knitting machine is essentially reduced when compared to the tendency of generating erroneous fault-indications in the prior art yarn feeding device. Fig. 5 shows a top view on the yarn feeding device in accordance with Fig. 1. For obtaining a desirable tangential feeding of the yarn to the drum 4, the disc brake 12 is arranged in an inclined position with regard to the horizontal axis of the feeding device 1. The detector element 14 of the preferred embodiment has the form of a bow or bracket which is pivotably journalled at one end and which includes the detector arm 13 at the opposite end thereof. However, the detector element may also have the form of any suitable element which is adapted for lying against the yarn under a load for tensioning the yarn such that the wrapping angle of the yarn passing the braking unit is increased by the detector element when the yarn tension decreases. Preferably, the yarn-braking unit has the form of a disc brake having a fixed shaft 11 and two discs 10. Alternatively, any braking unit having a braking force depending on the wrapping angle of the yarn can be used instead of a disc brake.

Claims: 1. Yarn feeding device (1) for feeding a yarn from a supply spool to a textile machine having a rotatable drum (4), a yarn-braking unit (12) arranged between said supply spool and said rotatable drum (4), through which yarn-braking unit (12) the yarn is guided at a certain wrapping angle, and a movable detector element (14) arranged between said yarn-braking unit (12) and said rotatable drum (4), said detector element (14) lying against said yarn for surveying the tension of the yarn and for detecting a possible yarn-breakage,characterised in that said detector element (14) is tensioned against said yarn for being moved at a decreasing yarn tension and for correspondingly displacing said yarn between said braking unit (12) and said rotatable drum (4) such that said wrapping angle of said yarn passing said yarn-braking unit (12) is increased. 2. Yarn feeding device as claimed in claim 1,characterised in that said braking unit comprises a disc brake (12). 3. Yarn feeding device as claimed in claims 1 or 2,characterised in that a yarn guiding eyelet (8) arranged between said supply spool and said braking unit (12) and, a guiding pin (15) arranged between said detector element (14) and said rotatable drum (4). 4. Yarn feeding device as claimed in one of the claims 1 to 3,characterised in that said detector element (14) is tensioned by a spring. 5. Yarn feeding device as claimed in one of the claims 1 to 4,characterised in that said detector element (14) has the form of a bow or bracket which is journalled with regard to a housing (2) of said yarn feeding device (1) at one end thereof and which forms a detector arm (13) at the opposite end thereof.

Inventors: JACOBSSON, KURT ARNE GUNNAR
Applicants: AKTIEBOLAGET IRO
Application year: 1986
Main classification: D04B15
IPC codes: D04B15