Two wheel device for positve feeding of yarn to knitting machine
FIELD OF THE INVENTION 
     The present invention relates to a device for the positive feeding of yarn to a knitting machine, preferably a circular knitting machine, for knitting pieces of goods with a ready-made-up length, in which every knitted piece has portions with a different stitch length or knitting structure. 
     BACKGROUND OF THE INVENTION 
     The invention is based on a device which has a yarn feeding wheel which is freely journalled on a fixed shaft in the device, and a feeding tape synchronously driven by the knitting machine, which tape is adapted to run over a part of the periphery of said yarn feeding wheel with a desired speed. A yarn control element associated with the yarn feeding wheel is also arranged to bring the yarn into engagement with the yarn feeding wheel and the yarn feeding tape, co-acting therewith for the positive feeding of the yarn to the knitting place with said desired speed and also to guide the yarn out of this engagement into a position outside the feeding tape on the yarn feeding wheel to interrupt the positive feeding thereof. 
     In the case of knitting pieces of goods with ready-made-up lengths, and also in other connections, there is a requirement for being able to positively feed a yarn in one and the same knitting system with at least two different speeds during the various parts of the knitting cycle for such goods. For example, an instance can be mentioned where one knits a &#34;pullover&#34;, where the short, lower-most section in the form of a &#34;waist rib&#34; should be knitted with a first positive yarn speed for generating a first portion in the goods with a first stitch size and character. Immediately thereafter, the long breast and belly section (&#34;body section&#34;) is to be knitted with a second, positive yarn speed for generating a second portion in the goods with a second stitch size and character. This case is described in detail in the British Patent Specification No. 1.246.625 (Hosiery and Allied Trade Research Association, Nottingham), which also shows a yarn feeding device consisting of so-called &#34;nip rollers&#34; which enables the desired positive feeding of a yarn with two different speeds in one and the same knitting system during various parts of the knitting cycle. 
     GB-A-2 109 825 already discloses a device for the positive feeding of yarn to a knitting machine. The prior art device comprises two feeding wheels of different diameter which are caused to rotate at different rotational speeds. A number of turns of the yarn to be fed to the knitting machine are wound around the second wheel and a cone and further around the first wheel where the yarn is engaged by the feeding tape. Depending on the yarn tension, the yarn comes into and out of engagement with the feeding tape. Hence, the tension of the yarn can be controlled as desired. However, this prior art apparatus is not adapted for carrying out a positive feeding of the yarn at two different, clearly defined, speeds. 
     The object of the present invention is to accomplish a yarn feeding device adapted for a selective positive feeding of the yarn at different speeds having a less complicated structure than that of the prior art devices. 
     In accordance with the present invention, this object is achieved by a device. 
     A further object of the present invention is to ensure a permanently correct positioning of the feeding tapes on the two yarn feeding wheels, namely that the feeding tape on the respective yarn feeding wheel should always run over the wheel at its edge remote from the crossing between the two wheels. According to one embodiment of the invention, this object is accomplished by the rotation axes of the two yarn feeding wheels forming a small, acute angle, with each axis being inclined at a smaller angle from a line perpendicular, to the normal planes of movement for the two feeding tapes. This geometrical relationship is preferably accomplished by the journalling position for the further yarn feeding wheel on the fixed shaft consisting of a hub portion, the centre axis of which forms a small acute, &#34;positive&#34; angle to the centre line of the fixed shaft. The first yarn feeding wheel is journalled on a hub portion concentrically arranged with the centre line of the fixed shaft. Moreover, the whole yarn feeding device is arranged to be mounted on a support ring extending horizontally above the knitting machine and parallel to the feeding tapes in a conventional manner such that the centre line of the fixed shaft on which the two yarn feeding wheels are journalled, forms a small, acute, &#34;negative&#34; angle absolute relative to a line perpendicular to the normal planes of movement for the two feeding tapes. The &#34;negative&#34; angle has a smaller absolute valve than said &#34;positive&#34; angle. 
     Another object of the present invention is to facilitate the alteration of the speed of the yarn. Therefore, according to the invention, the device has, in one embodiment, an annular guiding flange fixed to the rim of the first yarn feeding wheel facing the further yarn feeding wheel and extending axially out over a small piece of the further yarn feeding wheel, which flange is adapted to enable the smooth sliding of the yarn over it from its position on the first yarn feeding wheel into a position on the further yarn feeding wheel, and vice versa. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the device according to the invention is described below with reference to the drawings, wherein 
     FIGS. 1 and 2 show two different views of this embodiment; 
     FIG. 3 shows the same embodiment where vital parts in the device are shown in longitudinal sections; 
     FIG. 4 shows the actuation means for the yarn control element in a more detailed form. 
    
    
     DETAILED DESCRIPTION 
     As shown at FIGS. 1 and 2, a knitting machine has a support ring 1 known per se, which is arranged to carry a number of identical yarn feeding devices. The respective feeding devices are located above the respective knitting places or yarn intakes of the circular knitting machine (not shown here), whereby said number corresponds to the number of knitting systems in the machine. Every yarn feeding device has a hook-formed attachment part 2a on the housing 2 which is intended for fitting the device to the support ring 1 in which a lock screw 3 is arranged for fixing the yarn feeding device on the support ring 1. On said support ring 1 a flat, electrical cable 4 comprising five electrical conductors which are principally the same as is shown in the Applicant&#39;s own European Patent Application No. 821101173.0 (publication No. 78 550) are connected to an electrical, preferably micro-processor-based control unit centrally arranged in the knitting machine. Two of the said conductors (not shown here) are connections connected to respective one of two electro-magnets EM 1  and EM 2  fixed in the housing 2 of the yarn feeding device, which electro-magnets are more closely shown in FIG. 4. 
     In supporting plate 5 projecting from the housing 2 a vertical, fixed (unrotatable) shaft 6 is attached. A first yarn feeding wheel FW 1  is by means of a ball bearing 7 (see FIG. 3) pivotably journalled on a hub portion 8 on the shaft 6 concentrically arranged with the centre line 6&#39; of the shaft 6. A further yarn feeding wheel FW 2  via a further ball-bearing 9 is rotatably journalled on a second hub portion 10 on the shaft 6, whereby the centre line 10&#39; of said second hub portion 10 forms a 2° angle to the centre line 6&#39; of the shaft 6. 
     First and second feeding tapes FT 1 , FT 2  are arranged to run over a part of the periphery of the respective yarn feeding wheels with first and second different linear speed v 1 , v 2 , synchronous with the drive of the knitting machine. Said speeds correspond to the positive feed speeds with which a yarn Y 1 ,2 from a yarn supply spool is, according to the present invention, fed by means of the yarn feeding device down to the working needles in the knitting machine as mentioned above so as to knit the &#34;waist rib portion&#34; or the &#34;belly and breast section&#34; in the pullover. The feeding tapes FT 1  and FT 2  are driven from the drive system of the knitting machine via a respective so-called quality adjustment pulley with an adjustable drive diameter in order to achieve the desired speeds v 1 , v 2  synchronous with the needle cylinder speed. 
     At point P in the housing 2 in the yarn feeding device, a yarn guiding arm 11 is pivotally journalled, which has a horizontal bearing part 11a and a guiding part 11b essentially perpendicular thereto which, at its free end, carries a yarn guiding eyelet 11c for guiding the position of the in-coming yarn Y 1 ,2 in the yarn feeding device. 
     The yarn guiding arm 11 is an arrangement of two electro-magnets EM 1  and EM 2  and a common return spring RS adapted to be able to take one of three possible positions through a control command from the above-mentioned, preferably a micro-processor-based electronic control unit, centrally arranged in the knitting machine via two of the conductors in the flat cable 4. 
     When none of the electro-magnets are actuated, the yarn guiding arm 11 will take the &#34;neutral position&#34; shown in FIGS. 1, 2 and 4 through the influence of the return spring RS. The yarn Y 1 ,2 running through the yarn guiding eyelet 11c will be in a position outside the feeding tape FT 1  on the yarn feeding wheel FW 1  in which it will not be subject to any positive feed. The working needles in the machine will, themselves, pull the yarn Y 1 ,2 from the yarn supply spool via the wheel FW 1  rotating with the speed v 1 . 
     During actuation of the lower electro-magnet EM 1 , the yarn guiding arm 11 will pivot in a clockwise direction under the influence of the movement of the armature 12 so that the yarn Y 1 ,2 comes into engagement between the feeding tape FT 1  and the yarn feeding wheel FW 1 , whereby the yarn Y 1 ,2 will be subjected to positive feeding with the speed v 1  of the feeding tape FT 1 . 
     During de-actuation of the lower electro-magnet EM 1  and directly following actuation of the upper electro-magnet EM 2 , the yarn guiding arm 11 swivels in an anti-clockwise direction, whereby the yarn Y 1 ,2 leaves its engagement between the feeding tape FT 1  and the wheel FW 1  via its &#34;neutral position&#34; shown in the Figures. This is utilized for making the first course of stitches in the goods to be knitted and, during adjustment and re-adjustment work in the machine, the yarn is moved over, under the influence of the movement of the armature 13 into an analogous engagement below the further feeding tape FT 2  so that, instead, the yarn Y 1 ,2 will be subjected to positive feeding with the speed v 2  of the feeding tape FT 2 . 
     By means of an annular guiding flange 14 attached to the lower rim of the wheel FW 1  and preferably made of highly polished aluminium, which flange extends axially out over a small piece of the wheel FW 2 , the wandering of the yarn Y 1 ,2 from the one yarn feeding wheel to the other, and vice versa, will be facilitated. 
     When the yarn is drivingly engaged between the tape FT 1  and the wheel FW 1 , then the yarn guiding eyelet 11c will be in its uppermost position (that is, displaced upwardly from the neutral position shown in FIG. 2). However, when the yarn is to be fed by the other feeding wheel FW 2 , then the arm 11 is pivotally swung downwardly so that the yarn guiding eyelet 11c is moved downwardly through the neutral position into a lowermost position wherein it is disposed adjacent but spaced radially outwardly from the wheel FW 2 . During this downward movement of the eyelet 11c the yarn is moved downwardly out from beneath the tape FT 1  and is slidably moved downwardly across the guiding flange 14 into engagement with the lower feeding wheel FW 2 , whereupon the yarn is engaged between the tape FT 2  and the wheel FW 2 . This downward displacement of the yarn is facilitated by the beveled or chamfered surface provided adjacent the upper edge of the annular guiding flange 14. 
     When the yarn is to be again moved upwardly for re-engagement with the top feed wheel FW 1 , the eyelet 11c is shifted upwardly through the neutral position back into its uppermost position, and this results in a portion of yarn extending from the eyelet 11c downwardly in inclined relationship across the edge of the guiding flange 14 into engagement between the driving tape FT 2  and the wheel FW 2 . Due to the fact that the eyelet 11c is spaced radially outwardly a substantial distance from both the wheels and the guiding flange 14, and is also displaced circumferentially from the point where the tapes engage the respective wheels, this hence enables the yarn portion which extends downstream from the eyelet 11c to readily pass upwardly over the flange 14 when the eyelet 11c is moved upwardly. These relationships, coupled with the movement of the tape FT 2  and the associated movement of the wheel FW 2  facilitate the upward movement of the yarn out of engagement with the tape FT 2  so that the yarn can again be displaced upwardly by the upward movement of the eyelet 11c for engagement between the tape FT 1  and the wheel FW 1 . 
     As is apparent from FIG. 2, the whole yarn feeding device is mounted such with its attachment portion 2a onto the support ring 1, with which the two feeding tapes FT 1  and FT 2  are adapted to run parallel by means of the previously mentioned quality wheels and guiding-rollers (not shown here). The centre line 6&#39; of the fixed shaft 6 in the device forms a 1° &#34;negative&#34; angle to the normal of the planes of movement for the two feeding tapes. Due to this, it will be ensured that the feeding tape FT 1  always runs over the wheel FW 1  adjacent its upper rim. As a consequence of said &#34;inclined&#34; mounting of the yarn feeding device on the support ring 1 and the previously mentioned angle of 2° between the centre line 10&#39; of the hub portion 10 on the wheel FW 2  and also to the centre line 6&#39; of the fixed shaft 6, said centre line 10&#39; will form a 1° &#34;positive&#34; angle normal to the planes of movement for the two feeding tapes through which it is analogously ensured that the feeding tape FT 2  will always run over the wheel FW 2  adjacent its lower rim. 
     The yarn feeding device comprises fixed guiding eyelets 15a, 15b and 15c for the yarn and a pivotally journalled yarn tensioning arm 16 which is also used for sensing the position of the yarn and for detecting a yarn breakage condition. The pivotable yarn tensioning arm 16 is known per se in the art. 
     In the embodiment of the invention shown in the drawings, the yarn feeding device also comprises a third yarn feeding wheel FW 3  which, like the wheel FW 1 , is concentrically journalled on the fixed shaft 6. The wheel FW 3 , with respect to the present invention, is irrelevant and, therefore, not described in more detail, co-acts with a feeding tape FT 3  for the positive feeding of another yarn Y 3  which, during certain parts of the knitting cycle, is utilized as strengthening thread, as in the above-described case, during the initial phase of knitting the &#34;waist-rib&#34; in the goods.