The invention relates to a method for removing a yarn wrapped around a ^" buffer and for winding the yarn into a package, and an apparatus for applying this method.

To minimise the chance of yarn breakage during winding, the tension in the yarn, as removed from the buffer, should be kept constant. Practice showed however that small variations in the yarn tension occur due to yarn shrinkage, an increasing diameter of the yarn package, certainly in the case of a spool with- a.. irect, motor drive _r ..s-l±pping. o . the—spααl.if- ,winding roll is used to drive the spool, differences in path length occurring during winding through the oscillating motion of the yarn to obtain a uniformly wound yarn package, and pattern or ribboning distortions.

The present invention has for its object to provide a method as set forth in the opening paragraph, whereby the yarn tension is kept constant. According to the invention, the method as described above, is characterised in that the transverse displacement, which is developed to compensate for tension variations and which is imparted to the yarn through being removed from the buffer in a continuously changing position due to differences in the speed at which the yarn is removed from the buffer with respect to the speed at which it is fed to the buffer, is converted into a control signal by a sensing unit, which control signal is applied to a regulating means to vary the winding speed of the yarn in such a way that said continuously changing position is kept within fixed limits. That is, tension variations in the yarn are compensated by the buffer, while the amount of yarn around the buffer is kept within fixed limits through the speed regulation performed. The invention is therefore directed to speed regulation performed under constant tension and not to tension regulation.

The invention and its advantages will now be described

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in detail with reference to the accompanying figures, of which:

Fig. 1 is a block diagram of the speed regulation circuit according to the invention; and

Fig. 2 illustrates an embodiment of the apparatus, in which the method according to the invention may be applied.

The input quantity of the speed regulation ciruuit in Fig. 1 is the speed V. at which a yarn is applied to a buffer and the output quantity of this circuit is the speed V at which this yarn is removed from the buffer. If these speeds are not constantly adapted to each other, tension variations will occur in the yarn; these variations may give rise to yarn breakage unless they can be compensated for. This compensation is accomplished here by means of a yarn buffer .101. As soon as the speed at which the yarn is removed from buffer 101 is greater than that at which it is applied to this buffer, the amount of yarn on the buffer is reduced, while in the reverse case the amount of yarn around the buffer is increased. These changes in the amount of yarn around the buffer imply a transverse displa¬ cement of the yarn; in particular, with a substantially constant yarn feed rate, the yarn will be removed from a changing position on the buffer. Since the yarn is removed from the buffer under a constant tension, the transverse displacement of the yarn, due to the abovementioned differences in the feed and removal rates, compensates any differences in tension in the yarn. The yarn buffer 101 thus converts a speed difference ΔV under constant yarn tension into a transverse displacement ΔR. If the above speed differences remain or even increase, the amount of yarn around the buffer will decrease to zero or increase to excess; both of these situations will give rise to yarn breakage. The amount of yarn around the- buffer should therefore be kept within certain limits; with a substantially constant yarn feed rate, this can be achieved by keeping the transverse displace¬ ment imparted to the yarn within fixed limits. To this effect a sensing unit 102 converts the transverse displacement of the yarn into a control signal ΔTT, applied to a regulating means 105 to vary the speed at which the yarn is removed in such a way that the subsequent change in ΔV keeps the transverse displace¬ ment within fixed limits.

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The above speed regulation performed under constant. ■ yarn tension may be applied continuously or discretely. With a continuous speed regulation the magnitude of the control signal Δϋ ^" will be determined by the magnitude of the transverse dis- placement of the yarn, while this control signal will act on the regulating means 103 to adapt the rate of removal V to the feed rate Y.. If the rate of feeding the yarn to the buffer is constant, the rate of removal will have been fully adapted to this constant feed rate after a short settling period, were it not for the fact that variations in tension, compensated by transverse displacements of the yarn, occur constantly, the cause of which variations being, apart from yarn shrinkage, the winding system employed. With a continuous regulation there¬ fore, the rate of removal will constantly be varied even after the settling period.

With a discrete speed regulation the sensing unit 102 responds to two positions assumed by the yarn during its trans¬ verse displacement. The control signal supplied by unit 102 determines the instances at which the yarn assumes the two positions and acts on the regulating means 103 to control the rate of removal between two values. With a continuous regulation the rate of removal may be varied at random in a given range, whereas with a discrete regulation this rate can assume only two values, while at the most the frequency at which the rate of removal is changed between these two values is subject to change. If in its transverse displacement the yarn reaches the position in which a maximum amount of yarn is wrapped around the buffer, the rate of removal assumes its maximum value, and if in its subsequent transverse displacement it reaches the position in which a minimum amount of yarn is wrapped around the buffer, this rate assumes its minimum value.

The rate of removal, as referred to in the foregoing, is identical to the winding speed, since the yarn is removed by the yarn winding means. The winding may be accomplished in two ways, viz. through winding the yarn directly on a motor-driven spool and through employing a motor-driven winding roll which in turn drives the spool, whereby the yarn is passed over the

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winding roll or through the grooves in the winding roll to wind it onto the spool. In the first case, the winding speed of the yarn is determined by the rotational speed of the spool, and in the second case by the peripheral speed of the winding roll. The influence of the thickness of the yarn package on the spool asserts itself particularly in the first case. With continuous regulation the rotational speed of the spool is decreased as th thickness of the package is increased. With a discrete regula¬ tion, the rotational speed is maintained between two values; this is however accompanied with the requirement that the tensi variations in the yarn be compensated by the transverse displac ment. Therefore, the thickness of.the yarn package may not be so great that the path ^' length between the limiting positions of the transverse displacement of the yarn is not sufficient to compensate for the increase in the yarn tension.

In the embodiment described below a winding roll is used; the tension variations then occurring through yarn shrinkage, slipping of the spool on the surface of the winding roll and differences in path length arising during winding may be fully compensated merely by the application of the method herein described. This is applicable to both cylindrical and conical winding' spools.

With continuous regulation the design of the yarn buf 101 may be identical to that used with a discrete regulation; this will be described with reference to Fig. 2. The sensing unit 102 should however be of a different design for a continuous and a discrete regulation. With a continuous regulation the magnitude of the transverse displacement may be converted in the sensing unit into a corresponding control signal, for example by having this displacement to effect a change in a dielectric, the magnitude of which change being determined by measuring the capacity. With a discrete regulatio the monitoring of the instances at which the yarn assumes the two fixed positions during its transverse displacement may be realised by recording interruptions in two small light beams; another method will be described with reference to Fig. 2. With continuous regulation a motor driven by the control signal

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is simply used for the regulating means -103; with a -discrete regulation, see the description with reference to Fig. 2.

Fig. 2 illustrates an embodiment of an apparatus for the application of the method according to the invention. The yarn buff-er here employed consists of a rotating cylinder 204 with a shaft 205, whose axis makes a small angle with that of the cylinder 204 in order to keep the yarn windings around the whole of the cylinder and the shaft separate.

The combination of cylinder 204 and shaft 205 is hereinafter denoted by buffer 204 _» 205 for the sake of simplicity. A yarn 207 is passed through an opening in the shield 206 which is fitted around buffer 204,205. After wrapping a few turns of yarn around the buffer, yarn 207 -β removed from the buffer and is wound onto spool 209 via winding roll 208. The rate at which the yarn is wound onto the spool is determined by the peripheral speed of winding roll 208.

In the present embodiment of the apparatus for applying the method according to the invention, the sensing unit consists of a reciprocating mechanism 211 movable between two positions. The reciprocating mechanism removes the yarn from a point on the buffer, which point changes continuously between two points corresponding with the above two positions. An increase of the tension in the yarn 207 passed from buffer 204,205 to the winding roll 208 is compensated through the yarn loosing its contact with buffer 204,205 sooner and experiencing a corresponding transverse displacement. With this action the reciprocating mechanism 211 moves to the position denoted by A. When the reciprocating mechanism has reached position A, the rotational speed of winding roll 208 will be slightly decreased as will be shown after. The result thereof is a reduction in the tension in yarn 207 passed to winding roll 208. This reduction is however compensated through the yarn maintaining longer contact with buffer 204,205 and experiencing a corresponding transverse displacement, and the yarn is wound further around buffer 204,205. With this action the reciprocating mechanism 211 moves to the position denoted by B. When the reciprocating mechanism has reached position B, the rotational speed of winding roll 208

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will be slightly increased. The result is that the tension in the yarn passed from buffer 204 _» 205 to winding roll 208 is kept constant. Hence, in the case in question, this result is reached through the peripheral speed of the winding roll assuming values above and below the value of the speed at which the yarn is fed to buffer 204,205. The yarn is removed from buffer 204,205 at a point moving between the two points which correspond with positions A and B of the reciprocating mechanism 211. As will be seen hereinafter, these two points are adjustable by hand. Because of the fact that these points are adjustable, ring 212 mounted to buffer 204*205 should preferably contain a hairy yarn guide 213 provided fully around ring 212. With this provision it is possible to remove the yarn from buffer 204,205 in all positions under the required constant tension.

According to the invention the regulating means further comprises a transmission mechanism, consisting of a relay circuit 214 _> a pneumatic control mechanism 215 _» a driving pulley 216 and a pulley 217 driven by pulley 21β and coupled to winding roll 208. The relay circuit 214 is coupled to the reciprocating mechanism 211, and each time this mechanism reaches either position A or position B the relay circuit delivers a signal representative of this positipn, which signal is applied to the pneumatic control mechanism 215. In the embodiment in question control mechanism 215 comprises a solenoid valve 218, a piston 219 with piston rod 220 and a pulley system 221. Pulley system 221 is connected with a rod 222 to driving pulley 216 and is capable of performing a reciprocating motion about the axis of pulley 216. The pulley 216 drives pulley system 221 through a belt 223 _» the pulley system in turn drives, via a belt 224 _» pulley 217 coupled to winding roll 208. Because of the reciprocating motion of pulley system 221, it is possible to change the distance between this pulley system and pulley 217. For this purpose, pulley 217 is provided with a belt groove with a variable depth. If the distance between pulley system

221 and pulley 217 is slightly increased, belt 224 will follow the peripheral of pulley 217 with a smaller radius; if the

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distance between pulley system 221 and pulley 217 is slightly decreased, belt 224 will follow the peripheral of the pulley 217 with a larger radius, i.e. through varying the distance between pulley system 221 and pulley 217 the transmission ratio between pulleys 216 and 217 is changed accordingly. This change should of course be very small and, hence, the subsequent displacement imparted to pulley system 221 as well. When reciprocating mechanism 211 reaches position B, the relay circuit 214 is actuated, operating solenoid valve 218 to force air into the cylinder of piston 219. Consequently, through piston rod 220 the distance between pulley system 221 and pulley 217 is slight¬ ly increased, thereby slightly raising the rotational speed of winding roll 208. When reciprocating mechanism 211 then reaches position A, the air supply via solenoid valve 218 is shut off, and the motion of piston rod 220 slightly decreases the distance between pulley system 221 and pulley 217, thereby slightly lowering the rotational speed of winding roll 208.

As stated before, the positional interval in which the yarn looses- its contact with buffer 204,205 is adjustable. This is realised with an eccentric bearing-mounted shaft 225 _» whose position is adjustable by hand. Winding roll 208 is rotatably attached to this shaft. A displacement of eccentric shaft 225 results in a positional change of the pulley system 221 with respect to the winding roll 208 and hence imparts a change in the transmission ratio. The values between which the rotatio¬ nal speed of winding roll 208 is varied can therefore be shifted slightly to both sides; this is also accompanied with a shift in the positional interval in which the yarn is removed from buffer 204,205» for example to two positions symmetrical with respect to the normal.

To initiate the process to which the yarn is subjected, the yarn must be wrapped a few turns around buffer 204,205. It may be that this yarn is of a foreign type, the socalled piecing yarn, not forming part of the yarn package. The piecing yarn should subsequently be extracted. The apparatus thereto comprises a counter 22β, a second pneumatic control mechanism 227 and a lever mechanism 228. The pneumatic control mechanism 227

consists of the solenoid valve 22 _» a piston 230 with piston rod 231. The number of turns of yarn to be applied around buff 204*205 corresponds with a certain winding time, selected with counter 226. During the winding time this counter actuates the solenoid valve 229 to force air into the cylinder of piston 23 Through the piston rod 231 the lever mechanism is then brought into the position, whereby roller 232 forming part of the leve mechanism 228 comes into contact with. roller 233 coupled to th drive pulley 216 and whereby roller 210, also forming part of the lever mechanism 228 is released from winding roll 208. In this position the yarn passed over winding roll 208 is taken along and extracted with the aid of extraction means 234« The rate at which this process is accomplished is determined by th peripheral speed of roller 233 _* This speed is considerably low than that of winding roll 208. That is, the speed at which the yarn is fed to buffer 204,205 is considerably greater than the speed at which the yam is removed from the buffer. The result is that the yarn is wound around buffer 204,205 until the leve mechanism reverses to the position whereby roller 210 makes contact with winding roll 208 and roller 232 is disengaged fro roller 233. This reversal of the lever mechanism is realised through the actuation of solenoid valve 229, shutting off the air supply to the cylinder of- piston 230 after the expiration the selected winding time. On the reversal of lever mechanism to the latter position, the peripheral speed of winding roll 2 again determines the speed at which the yarn is removed from t buffer 204,205. The yarn can subsequently be wound on spool 20

To wind a yarn on a spool, it is customary to use a winding roll, which is provided with grooves to obtain a unifo distribution of the yarn on the spool. It is known that the use of such winding rolls cause uneven patches in the yarn package during winding. These uneven patches may be prevented by regul ly lifting the spool off the winding roll for a brief moment, causing the rotational motion of the spool to lag slightly behi that of the winding roll. The speed regulation in question, removing the continuously running yarn under a constant tensio from the buffer, enables to lift the spool for a moment.

The apparatus thereto comprises a third pneumatic control mechanism 235 and a second lever mechanism 236. Each time the air supply to the piston 219 is shut off, an air surge (air- relief pulsation) is delivered from this piston, via valve 218, • to an ^" air-operated ~slide valve 2 forming"part" ^_ σ pneumatic control mechanism 235 _* The latter control mechanism further comprises a piston 238 with a piston rod 239. An air surge is supplied to piston 238 via slide valve 237f this air surge moves piston rod 239 a little to lift spool 209 off winding roll 208 for a short moment through the lever mechanism 236.