GB2078792A

GB2078792A - Yarn Control in Textile Machines

Info

Publication number: GB2078792A
Application number: GB8119929A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-06-27
Filing date: 1981-06-29
Publication date: 1982-01-13

Abstract

Yarn supply in textile machines is controlled by selectively applying a sustained restraint to the yarn on a reduction in yarn demand. The sustained restraint can be a yarn gripper or a displaceable yarn guide. When a yarn supply includes means to drive yarn into a textile machine such as a continuously driven wheel 10, a yarn slack detector, 20, 21, 22, 23, is provided to operate a yarn gripper 31, 32 to restrain the supply of yarn while reduced demand results in slack yarn. The yarn gripper may be operated directly by the detector or through a timing element 27, such as a monostable, which can extend the time for which the yarn is gripped or control the re-application of the gripping action. A compensatory control for a yarn feeder in a flat knitting machine is also disclosed which prevents slack in "floating" regions outside the knitting width. <IMAGE>

Description

SPECIFICATION Yarn Control in Textile Machines This invention relates to yarn control in textile machines.

In textile machines yarn is moved from a supply, which may be a package of yarn or some other form, to be formed into a textile. Generally the yarn is drawn from the supply by the action of the machine forming the yarn into the textile.

However the textile forming action is cyclic and at some instants in time yarn is not drawn from the supply, at other instants yarn is drawn at high speed and at further instants surplus yarn has to be drawn back from the machine to prevent damage such as tangling. To control yarn supply various types of spring-loaded tensioners are used e.g. light pivotted arms with feed eyes and bias springs, weighted jockey pulleys and friction devices such as spring-biassed cymbal tensioners.

These all have drawbacks such as non-linear action, friction and drag and the possibility of stretching or breaking fine or weak yarn.

UKPS 1475887 describes an element for controlling the feed of yarn which provides drive to supply yarn when the tension is high, i.e. a machine is calling for yarn supply, and reduces contact with the yarn when tension is low. The drive enables the supply of accurately measured amounts of yarn, even in excess of that which the machine could draw-in in the conventional manner. This excess is most useful in avoiding residual tensions in textiles. The provision of a weight-biassed arm associated with the element is also described in the above specification. This arm assists in the taking up of slack from surplus yarn drawn back as mentioned above.

While effective in improving in the yarn control of textile machines, for example circular and straight bed knitting machines, the problem of slack from surplus yarn can still arise particularly when slack is created very quickly as in the case with modern high-speed machines. The weightbiassed arm can be lengthened to increase the length taken up but this increases the load on the yarn during feed-in. If the arm is spring-biassed the spring load increases the burden on the yarn and it is in fact in wrong sense. The burden of the spring is greatest when the tension is highest and falls as the slack increases so the spring-bias weakens at the critical point. The spring strength for a large arm movement and therefore large take-up of slack, as is needed for modern highspeed machines, places too high a load on the yarn during normal supply. This can damage or break fine yarns.

It is an object of the invention to provide improved control of yarn slack in textile machines.

According to the invention there is provided an arrangement to control yarn slack in a textile machine yarn supply including means selectively operable to exert a sustained restraint on yarn in said supply and means to operate said restraint exerting means to restrict increase in yarn slack on a reduction in yarn demand.

The means to exert sustained restraint may be a yarn gripper. The means to exert sustained restraint may be means drivable to extend a yarn slack loop at least as quickly as slack is formed.

Both these means may be used in tandem with one another.

According to one aspect of the invention there is provided an arrangement to control yarn slack including drive means to start to forward yarn in response to yarn demand engaging yarn with the drive means and cease to forward yarn with cessation of yarn demand reducing said engagement and further including a yarn slack detector downstream of the drive means and a selectively operable yarn gripper upstream of the drive means connected in a control loop operable by the slack detector on the detection of slack yarn downstream of the drive means to cause the gripper to grip yarn and restrain the yarn against forward movement.

Preferably the yarn is restrained for at least a minimum period of time on said detection of slack. Additionally the control loop may include timing means to time a period of time.

Conveniently the control loop may include an electromechanical slack detector and yarn gripper and an electronic timing means. The slack detector may include a bias means to set the detected degree of slack. The bias means may be magnetic in action. The electronic timing means may include a monostable timing element to time an interval on the detection of slack. The electronic timing means may include a switching element whose switching action is delayed beyond the end of the detection of slack by the controlled decay of charge in an RC circuit.

The yarn gripper may be a solenoid operated cymbal tensioner.

According to another aspect of the invention there is provided an arrangement for a flat-bed textile machine to control yarn slack including for a yarn feeder a yarn guide to form a yarn loop and means to move the yarn guide at half the velocity of the feeder over a part of the bed used for textile production and further means to move the yarn guide at the velocity of the feeder over a part of the bed beyond that used for actual textile production but traversed by the feeder in such production, whereby the change in velocity of the guide extends the yarn loop to control slack.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows in schematic form a yarn control arrangement embodying the invention, Figure 2 shows a circuit arrangement for a timing means of the embodiment of Figure 1, Figure 3 shows an alternative circuit arrangement for a timing means of the embodiment of Figure 1, Figure 4 shows the yarn feed end of a flat-bed knitting machine with three yarn control arrangements embodying the invention, Figure 5 shows a yarn path length control arrangement usable with the yarn feed control arrangements described herein to control yarn slack in textile machines.

Referring to Figure 1 this shows a yarn control arrangement suitable for a flat-bed knitting machine. Figure 4 shows how several, e.g. three, such arrangements may be used on such a machine.

The arrangements illustrated make use of a yarn drive element as described in UKPS 1475887, and specifically the spoked form of circumferentially grooved or pinned wheel shown in Figure 7 thereof (also shown in USPS 4052245). Clearly other forms and types of drive element that provide yarn drive may be used in other embodiments of the present invention.

The yarn drive element is indicated at 10 in Figure 1, a number of similar elements are indicated at 100,101,102 in Figure 4. The elements are mounted to be fast on a shaft 11.

The shaft 11 is driven, by means not shown, in the direction of arrow C to rotate the elements 10,100,101,102. Shaft 11 may be supported by a suitable bearing or other means in a support 201. Support 201 can be mounted on a knitting machine, indicated at 200 Figure 4, to position the yarn drive element or elements in an appropriate position in the yarn supply of the knitting machine. Shaft 11 is driven at a steady speed related to the operating speed of the associated knitting machine to provide positive feed to meet the maximum demand of the machine for yarn. An arm 12 with a terminal yarn guide 13 is pivotted, e.g. around the shaft axis of element 10, to swing against the tension of yarn passing through guide 13.

A mounting plate 1 6 for other parts of the arrangement is supported on rods 14 and 15 close to element 10. A further yarn guide 2 f is provided on arm 20, which is pivotted at 22 on plate 1 6 and is described later in more detail.

Yarn from a supply not shown, such as a yarn package, is fed to element 10 via a cymbal device, 31, 32, described later, to pass part way around element 10, through guides 13 and 21 and on to the knitting machine yarn feeder (not shown) in the sense of the arrows A and B. Guides 13 and 21 are in the plane of the yarn drive element. A stop 28 limits the movement of guide 21 under yarn tension. As yarn tension increases arm 12 moves towards the broken line position 12' and the wrap of the yarn on element 10 tightens. The positive drive of the element on the yarn draws yarn from the supply through open or separated cymbals 31, 32 and feeds the yarn to the machine.As yarn demand slackens, e.g. in the "float" part of the machine carriage stroke, the yarn tension falls and the weight of arm 12 pulls the arm down towards the full line position, or beyond it, disengaging the yarn from the positive drive and taking up yarn slack to the extent that the arm is able.

Besides the limited length of slack that the arm 12 can take up the ability of arm 12 to take up slack quickly is limited. The arm moves under gravity and therefore has a set maximum possible speed of movement. The rate at which slack can be taken up is thus limited and if the limited response is not fast enough the positive drive can cause over-supply of yarn with risk of tangling, loss of guidance and other problems especially as the element 10 can supply yarn at at least 1000 feet per minute during machine operation.

Arm 20 is part of a yarn slack detector. The arm 20 is a light element of metal or plastic, pivotted at 22 to mounting plate 16. A magnetic: bias element 24, such as a piece of ECLIPSE (RTM) ferrite based magnetic strip, is supported on adjuster screw 25 to bias arm 20, and guide " 21, away from stop 28. The bias is quite small and generally the yarn tension to overcome bias and hold guide 21 on stop 28 is much less than the tension exerted by the weight of arm 12. For example if the tension exerted by arm 12 is about 8 grams the tension to hold guide 21 on stop 28 is about 3 grams. The bias on arm 20 may be augmented by a bob weight 26 if desired. Clearly arm 20 must be formed of, or carry, material capable of being attracted to the magnetic bias element 24 in at least the region of element 24.

Conveniently arm 20 is of steel wire or strip as this is also electrically conductive. An electrical contact 23 is insulatingly supported near to arm 20 to make electrical connection thereto when the guide moves off stop 28 on the appropriate reduction of yarn tension. An electrical connection is made to arm 20, conveniently at pivot 22.

Electrical leads are connected to contact 23 and arm 20 so that the arrangement can provide a make and break switch action in an external circuit. As shown the switch breaks the circuit when the tension rises and makes the circuit when the tension falls but the reverse sense of operation can readily be obtained by rearranging the elements if required.

The slack detector thus formed is effective to make the external circuit when the yarn slackens at such a rate that the fall of arm 12 cannot maintain a yarn tension to overcome the bias of element 24 on arm 20, allowing the guide 21 to move off stop 28 and arm 20 to make electrical connection with contact 23.

On the detection of slack by the slack detector the making of the external circuit operates a yarn gripper 30 to restrain the yarn and stop the feed of yarn 1 7 from the supply to the textile machine.

The yarn gripper acts by closing together cymbals 31,32.

In one embodiment of the invention the external circuit includes a semi-conductor arrangement, such as a transistor amplifier, connected with a power supply at D, to operate the yarn gripper 30, which is now described. The cymbal device 31,32 is mounted on a shaft 33 which is movable by the action of a coil 34, when electrically energised, to clamp the cymbals together on the yarn 1 7 passing between them and stop the yarn supply.

Conveniently the yarn gripper has a frame 32, attached in any suitable manner to plate 16, which supports the coil 34 and shaft 33 which is, or is attached to, the armature for coil 34. A nonmagnetic shim 35 is included in the magnetic circuit of the coil and armature to ensure easy release of the gripping action when the coil is deenergised. A spring, not shown, may be included to assist in the release action. The gripper may be produced by adaptation of a commercially available electromagnetic actuator such as that available as series 429 from Pye Electrodevices Ltd., England.

In the illustrated embodiments the circuit including the slack detector and yarn gripper also includes a timing device, indicated at reference 27, to determine a period of time for which the gripper grips the yarn. Clearly in the absence of the timing device the gripper is only effective for as long as the yarn has enought slack to enable the bias on arm 20 to move the arm to reach contact 23. The components can however be arranged to produce a certain minimum period of gripping, e.g. by the mechanical and electromagnetic inertia of the solenoid on release.

The addition of the timing device enables the operation of the slack detector to cause the gripper to operate in various more complicated ways, e.g. for a chosen period from its actuation, or to remain operated for a chosen period after the slack detector has ceased to detect slack, or to be inhibited from re-operation for a set period.

Figure 2 shows a timing device based on a single transistor and a resistor-capacitor (RC) circuit to maintain the gripper operated for a set period after the slack detector has ceased to detect slack yarn. The transistor TR1, which is of the BC461 type, has the coil 34 in the emitter circuit to the positive supply terminal with a parallel diode Dl to protect the transistor against coil-induced switching transients. The collector is connected to the negative supply terminal. The base potential is determined by a network of the yarn slack detector 5, identified as switch S1, in series with a resistor R2, connected between the base and the negative supply terminal and a capacitor C1 in parallel with resistor R1 connected between the base and the positive supply terminal.When switch S 1 is open transistorTR1 is biassed to the OFF condition and coil 34 is not energised. On closing switch S1 transistor TR 1 is biassed to the ON condition by the potential divider of resistors R1 and R2 and coil 34 is energised operating the yarn gripper 30.

Capacitor C1 is charged via resistor R2 to close to the negative supply voltage. When switch S1 opens again the negative charge on capacitor C1 maintains the transistor in the ON condition with gripper 30 operated for a period until capacitor C1 is discharged, via resistor Tri, to a low enough potential to allow the transistor to switch OFF and the gripper to release. The period of maintained operation is set by choice of capacitor C1 and resistor R1 Times, in order of 0.5 seconds to 2 seconds, are chosen to suit a particular situation.

Typically C1 is 100 microfarads and R1 is 2200 ohms while R2 is 22 ohms.

One use of the circuit in Figure 2 is in a yarn control arrangement on a circular knitting machine. Here switch S1 is a proprietary stop motion magnetically biassed switch with the bias adjusted to suit the yarn tension to be detected as "slack". This switch is used in place of the slack detector elements shown in Figure 1. Reference 120 and 123 indicate the moving arm and fixed contact respectively. The proprietary switch is of the P.l.F. type originating from Japan.

Figure 3 shows another circuit by which a different timing action is provided. Similar references are used in Figures 1,2, and 3 for similar items. The circuit in Figure 3 is based on an integrated circuit time delay generator IC1, such as the "555" series, in which the time delay is set by external components R4 and C3 in wellknown manner. The slack detector switch at S2 is arranged to switch the d.c. level at the input terminal 2 of IC1 effectively to the negative supply when slack is detected.

This action starts the timing of an interval, set by C3 R4 during which output 3 of IC1 causes transistor TR2 to switch to the ON state and energise coil 34 of yarn gripper 30. At the end of the interval transistor TR2 switches OFF and the gripper 30 no longer grips the yarn. If at the end of the interval switch S2 is again "made" to indicate slack yarn the timing restarts and the gripper is re-applied. Resistor R6 and capacitor C4 reduce the effects of contact flutter in switch S2 and prevent re-start of timing when switch S2 opens.Resistor R5 provides the "off" bias for IC1 and capacitor C2 provides a high-frequency bypass to ground for IC1. If necessary a further transistor, not shown, can be introduced between terminal 3 of IC1 and the base of transistor TR2 to improve the switching drive to TR2. Typical component values are shown on the Figure. The reset connection (terminal 4 of IC 1) is not used.

While suitable slack detectors have been referred to above clearly other appropriate types, e.g. using optoelectronic devices, will be readily apparent to those skilled in the art.

Typically, for V-Bed knitting machine, the yarn gripper is operated for an interval of about 0.5 seconds or longer.

While the actual tensions and timing intervals should be chosen to be appropriate for the textile machine to which the invention is applied some actual values are now given.

On a V-bed knitting machine the arm 12 has a weight of 12 to 14 grams and the normal supply tension is about 10 grams. The arm 20 is arranged to have a dead-weight of about 1.5 grams and the magnetic bias is adjusted to balance the arm so that a yarn tension of more than about 3 grams keeps guide 21 on stop 28 and the arm away from contact 23. At less than 3 grams the arm can move to touch contact 23, which is spaced at about 0.001 inch (0.025 mm) from arm 20. The magnetic material 24 is not touched by the arm during switching movement.

The dead weight of the arm can be raised to about 3 grams if required by the bob weight 26.

The yarn gripping action is controlled by the form of circuit 27 shown in Figure 3, and is usually only started by a very rapid fall in yarn tension and then ensures that the yarn "slips" on the positive drive 10 for a set interval. This provides a "backup" for the action of arm 12 which may not be needed even in every cycle but is ready to act, for example at the end of the yarn drawing phase, when tension can fall rapidly.

On a circular machine similar tensions exist and the arm 20 is again adjusted to operate at about 2 to3 grams. However here the gripping action is controlled by the form of circuit 27 shown in Figure 2 to ensure yarn gripping for as long as slack is detected and a short while more, the discharge delay, to match the pattern of yarn tension changes in such machines, which can include times when yarn demand fluctuates rapidly. Typically the slack detector causes the gripper to act for up to 3 to 4 seconds with about 1 second of delayed release.

The yarn gripper coil 34 operates at a current of some 200mA on 12 to 15 volts d.c. The shim 35 is some 0.001 inch (0.025 mm) thick to ensure quick release by the magnetic circuit.

UKPS 1476253 describes a flat-bed knitting machine yarn feed arrangement to maintain a constant yarn path length from a delivery point, such as a yarn package, to the knitting. In an embodiment illustrated in figure 2 of UKPS 1476253 the arrangement provides for a conventional knitting machine, 10, a satellite carriage 30 carrying a loose pulley 34 and a flexible substantially inextensible element 36 passing round pulley 34 and connected between a fixed point 40 and a fixing to the yarn feeder 22 at 38. The yarn is fed to the feeder through guide 32 on the satellite carriage 30. Satellite carriage 30 is subject to a tensator spring.As described in UKPS 1476253 the effect of the arrangement when knitting over part CD of needle bed 14 is to move guide 32 at half the speed of feeder 22 to compensate for the different relative yarn speeds during the to and fro motions of the feeder driven by carriage 12.

Conventional knitting machines had previously been provided with a light, spring-loaded arm such as item 1 5 to take-up the slack yarn resulting from such speed differentials. However such devices are not linear in their action, exerting the greatest burden on the yarn when there is no slack and the least burden when the slack is fully taken-up, which is the reverse of the desirable arrangement.

The arrangements described generally and specifically in UKPS 1476253 have provided an efficient and effective solution to the yarn path length problem described therein.

However in machine knitting it is frequently necessary, especially when using several different yarns and feeders, for the feeders to move over a stroke larger than the actual knitting width CD.

Such extra stroke parts are indicated diagrammatically at EC(25) and DF(26) in Figure 5 of the accompanying drawings. In this drawing the same reference numerals are used for similar items as those used in Figure 2 of UKPS 1476253.

The extra stroke parts 25 and 26 are for "floating" the yarn. "Floating" occurs after the yarn has been "laid-in" along the needles and covers the period when the needles move to knit 'the fabric. Some yarn is drawn in by the knitting action but generally, on balance, the yarn tension is reduced by the onward movement of the feeder. Conventionally the tensioner 1 5 would take-up some of the resulting slack but its action is far from perfect, as mentioned above.

Figure 5 shows an arrangement to improve yarn control during "floating". It is shown in conjunction with satellite carriage described earlier. The fixing of element 36 to the yarn feeder 22 is modified by attaching the element 36 to spring loaded pulley 51. This is arranged to wind element 36 around the pulley 51 when slack occurs. A similar spring loaded pulley 52 is provided for a flexible, substantially inextensible, elongate element 53 fixed at one end of the pulley 52 and at the other to satellite carriage 30 at 54.

Both pulleys 51 and 52 are mounted on a support 50 which is secured to yarn feeder 22 e.g. by a bracket 55. Spring 37, which may again be in the form of a spring loaded pulley acts between carriage 30 and a fixed point. The path of element 36 is as before, that is it ensures a constant yarn path length during "laying in" movement of the feeder between points C and D. Consider now the arrangement at the position shown in Figure 5 of the drawings and with carriage 12 driving the feeder 22 beyond position C toward E. Spring 37 will have drawn satellite carriage 30 to the limit in direction F to E and will be maintaining a tension on carriage 30. Element 36 will be fully deployed while element 53 will be partly wound-up on pulley 52. Continued movement of carriage 12 moves feeder 22 over "float" part C to E of the feeder stroke.Pulley 51 starts to wind-up element 36 and pulley 52 continues to wind element 53 as yarn carrier 22 is driven towards stopped satellite carriage 30 at the speed of carriage 12.

The yarn 1 6 slides through feeder 22 without altering the path length to the point C. Any yarn required can still be obtained but the yarn does not become slack and permit a variation in tension. When the carriage 12 has driven the feeder 22 to position E the drive is disengaged and the feeder remains at rest while the carriage reverses and the knitting action occurs. When the carriage again picks-up feeder 22, at E, initially pulleys 51 and 52 allow elements 36 and 53 to unwind, under the tension of spring 37 while the feeder moves at carriage speed and satellite carriage 30 is at rest again avoiding slack yarn.

When element 36 is fully deployed, at C, satellite carriage 30 is drawn along, against spring 37, at half carriage speed maintaining a constant yarn path length. Element 53 continues to be unwound from pulley 52. Element 53 is of such a length that when feeder 22 reaches point D the element is fully deployed and satellite carriage 30 is then drawn along, through element 53, at carriage speed. Slack in element 36 is wound on pulley 51. The now-equal speeds of satellite carriage 30 and feeder 22 would provide slack yarn by shortening the yarn path but for the simultaneous creation of an extra limb in the yarn path by the movement of feeder 22 beyond point D towards point F. This extra limb, shown dotted at 22', avoids the creation of slack as it ensures the maintainance of the constant yarn path length.

The yarn carrier stops at point F with element 53 fully deployed, element 36 partly wound and spring 37 extended. On the movement of carriage 1 2 back from B towards A the described cycle continues in a readily seen manner and begins again at point C. The lengths for elements 36 and 53 for any piece of knitting and float sizes are easily set from the knowledge of distances EC and CD.

Reference 60 indicates the position of a control arrangement such as is shown in Figures 1 or 4 if this is to be used as well.

The techniques described can be readily applied to textile machines having overstrokes beyond textilesize to maintain constant yarn path length and thereby stabilise tension and improve textile quality by providing more uniform yarn control. The need for over-large take-back wires is also reduced or eliminated. The sustained restraint is only applied to the yarn when yarn demand reduces so that the burden of a conventional yarn tensioner, as described above, is no longer applied to the yarn while demand is high. In this way wear and damage to yarn, and unevenness of tension in finished products, is avoided or reduced. The techniques are described with reference to certain types of knitting machine by way of example and those skilled in the art will be aware of any adaptations to apply to them to other types of knitting machines to achieve the control of yarn slack described.

Claims

1. An arrangement to control yarn slack in a textile machine yarn supply including means selectively operable to exert a sustained restraint on yarn in said supply and means to operate said restraint exerting means to restrict increase in yarn slack on a reduction in yarn demand.

2. An arrangement according to Claim 1 in which the means to exert the sustained restraint includes a selectively operable yarn gripper.

3. An arrangement according to Claim 1 in which the means to exert the sustained restraint includes means drivable to extend a yarn slack loop at least as quickly as slack is formed.

4. A system control yarn slack including an arrangement according to Claim 2 and an arrangement according to Claim 3 in tandem.

5. An arrangement according to Claim 2 including drive means to start to forward yarn in response to yarn demand engaging yarn with the drive means and cease to forward yarn with cessation of yarn demand reducing said engagement and further including a yarn slack detector downstream of the drive means and a selectively operable yarn gripper upstream of the drive means connected in a control loop operable by the slack detector on the detection of slack yarn downstream of the drive means to cause the gripper to grip yarn and restrain the yarn against forward movement.

6. An arrangement according to Claim 2 or Claim 4 or Claim 5 in which yarn is restrained for at least a minimum period of time.

7. An arrangement according to Claim 5 or Claim 6 when dependent on Claim 5 in which the control loop includes a timing means.

8. An arrangement according to Claim 5 or Claim 6 or Claim 7 in which the slack detector is an electromechanical device.

9. An arrangement according to Claim 5 or any claim dependent thereon in which the control loop includes an electronic timing means.

1 0. An arrangement according to Claim 5 or any claim dependent thereon in which the slack detector includes a bias means settable to determine the degree of slack at which the detector operates.

11. An arrangement according to Claim 10 in which the bias means is magnetic in action.

12. An arrangement according to Claim 9 in which the electronic timing means includes a monostable timing element startable to time an interval on the detection of slack.

1 3. An arrangement according to Claim 7 in which the timing means includes a switching element and a resistor/capacitor circuit to delay the action of the switching element beyond the end of the detection of slack by the controlled decay of charge in the circuit.

14. An arrangement according to Claim 2 or any dependent claim in which the yarn gripper is a solenoid operated cymbal tensioner.

1 5. An arrangement according to Claim 3 for a flat bed textile machine including for a yarn feeder a yarn guide to form a yarn loop and means to move the yarn guide at half the velocity of the feeder over a part of the bed used for textile production and further means to move the yarn guide at the velocity of the feeder over a part of the bed beyond that used for textile production but traversed by the feeder in such production whereby the change of velocity of the guide extends the yarn loop to control slack.

1 6. An arrangement according to Claim 1 5 in which the further means includes a flexible inextensible element fitted on a spring-reel to wind-up and deploy the element and connected between the guide and feeder to cause said change of velocity on fully deploying the element from the reel.

1 7. An arrangement to control yarn slack substantially as herein described with reference to the accompanying drawings.