GB2178070A - Open-end yarn piecer - Google Patents

Abstract

Apparatus for piecing a rotor spinning machine having a plurality of spinning stations, each of which includes a rotor unit (10) package forming means (14) to form a package of yarn produced at the unit, a nip roll pair (12) for withdrawing yarn from the unit and feeding it to said package forming means (14), feed means (30) selectively operable to feed fibers to said unit for spinning into yarn and drive means operable to drive the rotor unit (10) at a selected operating speed and to drive the package forming means, nip roll pair and feed means at respective speeds each in a selected relationship to said operating speed. Withdrawal of yarn (18) after piecing with a fiber ring in the rotor is effected by re-engaging previously separated withdrawal rolls on the rotor spinning machine. Feeding of the seed yarn back to the rotor and initiation of withdrawal of the seed yarn and newly spun yarn pieced thereto can be effected while the spinning unit is operating at a predetermined constant speed, preferably at or near the selected normal operating speed for the spinning unit. During the piecing operation a member 100 carrying guides 102, 104 are moved across to pick up a length of yarn L running to an end seeking nozzle 90. Member 100 is then withdrawn with the yarn to place the yarn in a predetermined position and orientation such that a threading up guide 120 movable along a track 122 can pick-up the yarn and thread it up in preparation for the next step in the piecing operation. <IMAGE>

Description

SPECIFICATION Open-end yarn piecer The present invention relatesto methods and apparatusforpiecing a rotorspinning machineofthe type (hereinafter referred to as "type described") comprising a plurality of spinning stations, each including a rotor unit, package forming means to form a package of yarn produced at the unit, a nip roll pairforwithdrawing yarn from the unit and feeding it to said package forming means, feed means selectively operable to feed fibers to said unit for spinning into yarn and drive means operableto drive the rotor unit at a selected operating speed and to drive the packageforming means, nip roll pair and feed means at respective speeds each in a selected relationship to said operating speed.

Rotor spinning machines of the type described are now extremely well-known in the rotorspinning art.

By way of example only, details of such machines can be obtained from United States Patent Specification No.3375649.

At present, the majority of the rotorspinning machines in commercial use are operated by manual attendance. In particular, start-up ofthe machine, doffing of packages and repair ofthread breaks are dealt witch by hand. In each ofthese operations, a so called "piecing" operation is required; that is, a previously spun "seed" yarn must be backfed into the rotor spinning unit to join or "piece" with a ring of fibers formed in the rotor, the seed yarn then being withdrawn from the spinning unit and bringing with it newly spun yarn formed in the rotor.

With increasing rotor speeds, particularly speeds substantially in excess of 50'000 RPM, manual piecing becomes increasingly difficult. Since commercial rotor speeds are now approaching the 80 to 90'000 RPM region, it is becoming imperative to provide at least mechanised piecing assistance and preferably fully mechanised, or automated, machine attendance.

Acommercial rotor spinning machine comprises a large number (usually approx 200) spinning stations.

For economic reasons, it is preferred notto provide individual piecing means at each of these stations, but instead to provide a travelling piecing apparatus movable from station to station and capable of performing a piecing operation at any selected station.

One example of a travelling piecing apparatus of a kind referred to above is shown in United States Patent Specification No.4041684. Said specification shows a piecing apparatus with a means for separating the nip roll pairon a station to be serviced and forthreading a seed yarn (a broken yarn end on the yarn package at the station) with the separated nip rolls before backfeeding the seed yarn the seed yarn into the spinning unit. Subsequent withdrawal ofthe seed yarn and newly formed yarn pieced thereto-is effected by re-engaging the nip roll pair. However, so far as present applications are aware, the company owning US-Patent 4041684 has not produced a commercial apparatus in accordance with the patent.

Instead, the system offered by that company on the market involves withdrawal of seed and newly spun yarn from the rotor spinning unitvia a withdrawl path passing through the piecing apparatus and by means of a withdrawal unit specifically provided for this purpose in the travelling piecing apparatus. All of the commercially available systems known to the present applicants also involve use of a special yarn withdrawal unit on the travelling piecing apparatus.

After completion oftheyarn piecing operation, therefore, control ofthe withdrawal operation has to be passed backfrom the piecing apparatus to the machine -this substantially complicates operation of both the travelling piecing apparatus and the machine.

Furthermore, several commercial piecing systems presently available depend upon piecing at a rotor speed which is substantially lowerthanthe normal operating speed of the rotor, e.g. a piecing speed of approx. 40'000 RPM in comparison with a normal operating speed in the region 70 to 80'000 RPM. By way of example only, details of a "lowspeed piecing" technique can be seen from US Patent Specification 4012116. The low speed piecing technique renders certain factors less critical to the success ofthe piecing operation. However, it also brings certain complications which will be explained in detail below inthecourseofexplanationoftheillustrated embodiments of the present invention and by way of contrast with the relatively straightforward technique enabled by this invention.

Present invention In the present invention, withdrawal of yarn after piecing with a fiber ring in the rotor is effected by re-engaging previously separated withdrawal rolls on the rotorspinning machine, as is known from the US Patent referred to above. Feeding of the seed yarn back to the rotor and initiation of withdrawal ofthe seed yarn and newly spun yarn pieced thereto can be effected whilethe spinning unit is operating ata predetermined constant speed, preferably at or near to selected normal operating speed forthe spinning unit. Thus, if the machine is set to drive its spinning units at, say, 80'000 RPM, the pieci ng operation is preferably carried out while the spinning unit is operating atornearto80'000RPM.

A predetermined time period is defined at the expiry of which withdrawal of seed yarn is commenced. By adjusting the backfeed of seed yarn relative to said predetermined time period,the duration of a "rest period" is determined. During this rest period, the end of the seed yarn is in the rotor groove and twist is transferred from the seed yarn to fibers in the groove. By control of the rest period, twist transference to the fibers is controlled.

Furtherfeatures of the invention will be apparent from the description of the drawings, in which Figure lisa diagrammatic side elevation of one spinning station of a rotor spinning machine ofthe type described, the diagram showing the relations of the parts of the station and co-operation thereofwith a travelling yarn piecer, Figure2is a speed vs time diagram for use in explanation of the piecing technique ofthe invention, the speed scale (vertical axis) being differentforthe rotor speed and yarn speed diagrams, Figure 3is a more detailed side elevation, also diagrammatic, of the package forming means of a spinning station and co-operation thereofwiththe piecer, the spinning station being on the opposite machine side relative to that shown in Figure 1, Figure 4 is a view in the direction of arrow A in Figure 3 and Figure 4A is a detail of part of Figure 4, Figure 5is a diagrammatic side elevation of the path of movement of a yarn threading element of a piecer accordign to the invention and Figure 5A is a detail of part of Figure 5, Figure s 6-9 i nclusive are diagrammatic side elevations of successive yarns paths adopted by a seed yarn during preliminary stages of a piecing operation according to the invention, Figure lOis a diagrammatic representation of a yarn reserve release device for a piecer according to the invention, Figure ii is a diagrammatic representation of a nip roll pair of a machine of the type described and co-operationthereofwith roll separating meansfora piecer according to the invention, Figure 12is a block diagram of a timing meansfora piecer according to the invention, Figure 13 is a plan view of the floor portion of a rotor showing an arrangement of markings adapting the rotorfor use with the piecer of Figure 1, and Figure 14 is a diagrammatic representation of a yarn clamping device suitable for use in a piecer according to the invention.

In the description of the drawings and in the claims the terms "upstream" and "downstream" are used.

Theseterms relate directions and positionstothe direction of travel ofthe yarn out ofthe spinning unit tothepackageforming means during normal spinning operation, that is, in Figure 1 "downstream" is upwards relative to the Figure since the package forming means is located above the spinning unit.

Description ofthe drawings The principles involved in the present invention will first be described with reference to Figures 1 and 2.

Mechanisms for putting those principles into effect will then be described with reference to the other drawings. Figures 1 and 2 are diagrammatic only and are in no way intended to represent exactly either a practical machine design or an exact piecing sequence.

Thefull linediagram in Figure1 illustrates in side elevation one spinning station of an open-end spinning machine. There would be many such stations arranged side by side in a practical machine, nowadays commonly up to 100 stations per machine side.

The dotted line illustration in Figure 1 represents a piecing apparatus which normally travels to and fro past the spinning stations but which can be stopped in alignmentwith a selected station in order to perform a piecing operation as will be outlined. The dotted line illustrations in Figure 1 also show certain modified positions of the elements ofthe spinning station and of the thread path during a piecing operation.

The illustrated spinning station comprises a spinning unit indicated generally bythe numeral 10, a yarn withdrawing means indicated generally by the numeral 12 and a package forming means indicated generally by the numeral 14. In normal operation of the spinning station, a sliver 16 of staplefiberis drawn into the unit and is converted therein to a yarn 18. The yarn is withdrawn from unit 10 by means of the withdrawal means 12 and isforwarded to the package forming means 14 at which it is wound into a package 20.

The spinning unit 10 is of a type very well known in the rotor spinning art. Details can be omitted. The general type of spinning unit involved can be seen from US Patent Specifications 3511045 and 4009562.

Figure 1 shows the outline of a unit housing 22 which is pivotally mounted on a tube 24 which extends over the full length ofone machine side being fixed in the machine frame and common to all spinning stations on the one machine side. Extending through the bore oftube 24 is a worm gear 26 also extending along a complete machine side.

At each spinning station there is a drive shaft coupling (not shown) to the worm gear 26 which therefore drives the input side of a clutch 28. The output side of clutch 28 is coupled to a knurled feed roller30.

Feed roller 30 draws the sliver 16 into the spinning unit and presents the sliver to an opening roller 32 having pins orteeth to comb individual fibers out of the presented sliver end. The fibers extracted from the sliver are forwarded by an airstream to a rotor 34.

Opening roller 32 is driven by a whorl 36 projecting from the underside of the housing 22so as to be engageable with a drive belt (not shown) common to all ofthe spinning stations.

Rotor 34 is carried bywayofa bearing unit38 on a carrier40 which is pivotally connected to the housing 22. Figure 1 shows the parts in their normal operating disposition in which housing 22 is latched in an "upright" disposition and carrier 40 holds the axis of rotor 34 substantially horizontal. Housing 22 can be unlatched and tilted forwardly (that is, in an anticlockwise direction) on its pivot mounting on tube 24 and carrier 40 can simultaneously pivot rearwardly (in a clockwise direction) on its pivotal connection with housing 22. In this manner, the rotor unit (34,38, 40) can be separated from the fibre feed system (30, 32) for ready access to the interior of the rotor.

The air stream which draws fibers from the opening roller 32 to the rotor 34 is created by a vacuum applied to the housing 22 for example as indicated at 42. A feed and guidetube (notshown) leadsthe fiber- carrying air stream from the opening roll through a rotor cover (not shown) into the rotor interior where the fibers are separated from the carrying air by centrifugal force and are laid as a fiber ring in the so called "rotor groove" atthe maximum interior diameter of the rotor. The air escapes over the rotor rim and is removed by the suction system (not shown). Forfurther detail of these arrangements see US Patent3481129.

The formed yarn is withdrawn from the rotor via a withdrawal tube 44 which extends at its upstream end through a withdrawal nozzle 46 mounted in the rotor cover. After leaving the withdrawal tube 44, the yarn passes a pivotable monitor 48. This monitor is also of a well known type comprising a lever pivoted to swing on an arc which intersects the normal yarn path. The lever is biased towards one position on its arc and is maintained spaced from that position by the normally running yarn. If yarn breaks, orthe yarn tension drops severely, the lever is pivoted under its bias to close a switch indicating a fault condition. Such a monitor is shown, for example, in US Patent No.3404524.

From monitor 48, the yarn passes to the withdrawal means 12 which comprises a guide 50, a drive roller 52 and a pressure roll 54. Guide 50 reciprocates the yarn over a slight traverse axially ofthe withdrawal rollers 52,54 to avoid persistent wear at one location ofthose rollers. The primary withdrawal function is performed atthe nip normally formed between the rollers 52 and 54. Roller52 extends along the complete side ofthe machine, being common to all stations. It is driven in a clockwise direction about its own axis, as indicated by the arrow in Figure 1.At each spinning station there is a respective pressure roller 54 mounted by a carrier arm on a rod 56 extending the full length ofthe machine side.The carrier arm is pivotable on the rod 56 to movethe roller 54from the full line position to the dotted line position. During normal operation, the roller 54 is in its full line position in which it engages roller 52to form a nip therebetween. The yarn 18 is withdrawn from the spinning unit by means ofthis nip and the drive on the roller 52. The withdrawal speed is determined by the speed of rotation of the roller 52.

The package forming means 14 comprises afixed guide 58, a traversable guide 60 and a drive roller 62.

Guide 60 is traversed (by means not shown) axially of the package 20. The latter normally rests in frictional engagement with the roller 62 which extends along a full machine side and is common to all spinning stations. Roller62 is driven to rotate clockwise as viewed in Figure 1 about its own longitudinal axis, thereby rotating the package in a anti-clockwise direction. The traverse motion of the guide 60 enables formation of a cross-wound package. The portion of guide 58 which contacts the yarn is formed to even out yarn length variation which would otherwise occur during the traverse motion. This general arrangement is also very well known in the art.

Package 20 is formed on a bobbin tube 64 carried between a pair of arms of a package cradle. Only one arm 66 can be seen in Figure 1. The arms are pivotable together about a pivot mounting 68 on the machine frame, part ofwhich is shown at 70.

In the event of a thread-breakwhich may be due to a fault our may be deliberately induced (for example at completion of winding of a package of a predetermined size or when cleaning ofthe spinning unit loins due), the thread break signal issued bythe monitor 48 causes operation of a mechanism (not shown) to lift the package 20 to the position illustrated in dotted lines in which it is clear of roller 62. The latter continues in rotation to drive the packages at the other spinning stations, but rotation ofthe package ceases at the station with the broken thread. The thread break signal also opens the clutch 28, so that feed of sliver 16 also ceases. The drive to the gear 26, whorl 36, rotor 34, withdrawal roll 52, and traverse guide 60 continues.

A call signal is also issued to cause the automatic piecer 72 to stop in alignment with the illustrated station. When it is correctly registered with the station, piecer 72 carries out a piecing operation which basically involves finding the broken thread end on the package 20 and feeding it back down the withdrawal tube 44to rejoin that end with a newly formed ring offibers in the rotor groove. As soon as the backfed yarn has formed an effective join with the fiber ring in a rotor, withdrawal ofthe newlyformed yarn must be restarted.As is well known in the art, and widely documented in the relevant literature over the last ten years, control ofthethreeoperations (yarn backfeed, fiber feed and yarn withdrawal) is critical and extremely difficultto achieve at least with rotor speeds substantially higherthan 50'000 RPM.

Accordingly, in all currently available automatic piecing devices, steps have been taken to modify the normal spinning conditions for the purposes ofthe piecing operation. For example, in all commercailly available piecing devices, the yarn path between the spinning unit and the package is diverted to pass through the piecing device, and the yarn must be passed back to the machine at the completion of a successful piecing operation.In certain systems, piecing is effected at a rotor speed which is lowerthan the normal operating speed, usually during acceleration of the rotortowards its normal operating speed. Despite these measures, the piecings, orjoins, obtained from the currently available devices do not always meet the requirements of the further processing industries, and the piecing is frequently cut out and replaced buy a knot or a splice after spinning at the spinning unit has been sucessfully restarted.

All of the above steps complicate the system and make it more expensive. In the system now to be described, piecing is effected under conditions approaching as closely as possible to those which occur during the normal spinning operation.

The dotted lines extending between the piecing device 72 in Figure 1 and the spinning station in that Figure indicate the main points at which the piecing device intervenes in the spinning station to effect piecing. Thus, the piecertakes over control of the position of the package 20 relative to the friction roller 62 as indicated by line 74joining the piecerto package holder arm 66. The piecer can be provided with a suitable leverforthis purpose. The piecer also lifts pressure roller 54 away from drive roller 52 and moves into the dotted line position as indicated bythe line 76 joining the piecerto that position. Again, the piecer can be provided with a suitable lever forthis purpose.

Thepiecerfurtherformsayarn reserve which is a defined length of yarn, the length of the reserve heing equal to the distance through which the yarn end will move in the last stage of the piecing operation in orderto bring it into contact with the fiber ring in the rotor groove. Forth is purpose, the piecer locates a reserve forming device 78 adjacent the exit end ofthe withdrawal tu be 44. The piecer may have a device for sensing the speed of rotation of the rotor. The device is indicated by the dotted line 80 in Figure 1 and a suitable arrangement will be described below. The piecer also has a means (indicated by the dotted line 82) for controlling operation of the clutch 28.

The piecer 72 is also provided with certain elements which have not been shown in Figure 1. In particular, there is a means forfinding the broken thread end on the package 20 and a device for threading the found yarn along thethread path indicated by dotted line between package 20 and the exit end ofthe withdrawal tube 44. It will be noted, in particular, that the yarn is threaded between the separated nip rollers 52,54 and into the reverse forming device 78. There is also a device which forms a prepared end ontheyarn and a device for performing a preliminary backfeed operation in which this prepared yarn end is inserted into the downstream end ofthe withdrawal tube 44 and is drawn by the suction on that tube to a position at or near the upstream end of the nozzle 46.Thus, the final backfeed phase which is performed underthe control ofthe reserve device 78, carries this yarn end from the nozzle 46 into the rotorgroove.

The piecerfurther includes a rotor cleaning device.

The device will not be described in the present application but can be formed, for example, in accordance with our Swiss Patent Application No.

3631/82. Cleaning ofthe rotor is performed simultaneouslywith the end seeking operation. In orderto perform the cleaning operation, the spinning unit must be opened in order to provide access to the rotor interior, and the rotor must be braked to a standstill. The dotted line yarn path shown in Figure 1 and the location ofthe yarn end within the nozzle 46 are established after reclosing the spinning unit following completion ofthe cleaning operation.At thattime, also, drive will be reestablished with the rotor, which will begin to accelerate towards its normal operating speed.

Piece 72 also includes a control means 84 which controls all functions of the piecer according to a predetermined sequencing program. Certain aspects of the program will be described in further detail with reference to the more detailed mechanisms.

However, particular attention will first be paid to the final stage ofthe piecing operation, in which a) a ring of fibers of controlled dimensions is formed in the rotor groove by operation of clutch 28, b) the prepared yarn end is fed back from the nozzle 46 to join with this fiber ring by operation ofthe reserve device 78, and c) withdrawal of newly formed yarn is restarted by return of roller 54 into re-engagement with roller 52 to form the withdrawal nip.

The timing of the commencement offiberfeed in relation to the other operations has been extensively dealt with in the literature and will not be covered again here. Reference can be made for example to US Patent Specification 4102116. Briefly, the aim of fiber feed control is to achieve a fiber ring of appropriate dimensions so that the piecing is neither too thick nor too thin in relation to the normal yarn count. In general, this is a matter of timing of the operation of clutch 28 in relation to the other two operations which will be discussed in additional detail with reference to Figure 2.

In the graph of Figure 2thevertical axis represents speed and the horizontal axis represents time. The line R represents the speed of the rotor, and the line Y represents the speed of the yarn end/piecing. The scale of the diagram is differentforthe rotorspeed and the yarn speed, since only the principle is of importance and absolute speed values are irrelevant.

At the left hand side ofthe diagram of Figure 2the rotor is assumed to be reconnected with its drive after the cleaning operation. The rotor speed then follows an acceleration curve which will be dependent upon the overall design ofthe system and which will be inevitably subject to minor variations from one station to another because of manufacturing and assemblytolerances. After the rotor has reached its normal operating speed N, the control 84 provides a startsignaltostartthefinal piecing stage. The issuanceofthestartsignal is dependent upon the completion ofthe preliminary piecing operations referred to above which will normally last longer than the acceleration time of the rotor R.

The control 84 now defines a predetermined timeT during which the formation of the fiber ring, the back-feed oftheyarn end and joining of the yarn to the fiber ring can occur. At the expiry ofthis timeT, the roller 54 has again engaged the roller 52 so that withdrawal of yarn from the spinning unit is commenced.

In accordance with the feedback operation indicated bythefull line Y shown in Figure 2, backfeed is assumed to be initiated as soon as the start signal is issued. As indicated by the dotted line, there can be a delay between the start signal and initiation of backfeed. Device 78 is operated to provide a controlled backfeed such that the yarn is continually tensioned along its length during the backfeed operation and so that the yarn end arrives in the groove with a slight time advance relative to the start of yarn withdrawal. For the backfeed operation indicated byfull line in Figure 2, the corresponding time advance is indicated att. The time advance may be greater or less depending upon delay in initiation of the backfeed.

Considernowthe motion oftheyarn end between the upstream end of nozzle 46 and the rotor groove.

Astheyarn end entersthe rotorsystem,theyarn begins to rotate about the nozzle axis with the rotor and the yarn end is drawn out by centrifugal force towards the rotor groove. Rolling of the yarn around the internal surface of the nozzle 46 increases the already available twist in the yarn. When the yarn end reaches the groove and begins to mix with the fibers therein, the yarn twist beginsto collectthe fibersfrom the groove and joins them intotheyarn. In orderto form a good join between the backfed yarn end and the fibers, a predetermined quantity of twist must be transferred from the backfed yarn to the newly forming yarn in the rotor groove. If the degree of twist transference is too low, the strength of the join will be inadequate and the yarn will breakwhenwithdrawal is attempted. If an attempt is made to transfertoo much twistto the piecing, then a yarn breakwilloccur due to "overtwist" either ofthe backfed yarn or ofthe piecing. The degree of twist transference to the piecing. The degee of twist transference to the piecing is dependent upon two factors, namely a) the amount oftwist present in the backfed yarn when it arrives in the rotor groove, and b)furthertwist imparted to the backfed yarn while theyarn end is present in the rotor groove and forming the join.

Factor a) is dependent upon the backfeed speed in relation to the rotor speed and factor b) is dependent upon the length ofthe advance referred to above, that isthedurationofthe"rest" period during whichthe yarn end remains in the groovewaitingforyarn withdrawal to begin. In principle, the degree oftwist transference can be controlled by controlling both factors a) and b) above, but we prefer to applythe main control via factor b) (that is by adjustment ofthe rest period) and to hold factor a) constant (that isto maintain constant backfeed speed for all piecing operations). Also, in principle, it would be possible to detect the completion of the backfeed movement and then to measure out a defined rest period.However, the rest period required in practice is of extremely small duration (up to 10 millisecs.) and it is impractical to initiate the mechanical operations involved in yarn withdrawal within the very short time available after sensing of completion ofthe backfeed movement.

For the above reasons, it is preferred to definethe initiation of withdrawal by reference to the start signal and to define the duration ofthe rest period by reference to the delay (or lack of it) between the start signal and the initiation of the backfeed movement.

The required duration ofthe rest period will depend upon the operating circumstances, and in particular upon the rotor speed and yarn count. A heavieryarn count will require greater twist transference and thus a longer rest period.

Closing ofthe clutch 28 is also preferably effected by referenceto the same start signal. Closing ofthe clutch must be effected at a stage of the piecing sequence such that a fiber ring ofthe required dimensions is available in the groove during the rest period to join with the yarn end. The actual stage of the sequence atwhich i nitiation of fiber feed must be effected will depend upon many factors including the mechanical design of the system and the yarn count.

Frequently, fiberfeed must be commenced before start of the backfeed movement and the total time T mustthen be settableto allow for an initial "feed delay" following the start signal, plus the time required for the backfeed movement plus the required rest period.

Approximately simultaneously with restart of yarn withdrawal, package 20 is returned to contact with the drive roll 62 so that packaging of yarn can be re-commenced. There will be substantial differences in the rate at which yarn is taken up by the package immediately after the latter contacts the drive roller 62 depending upon the surface conditions ofthe package, and its size (weight). Accordingly, in orderto take up temporary excess yarn length between the nip rolls 52,54 and the package 20, a suction storage device of a known type may be brought into association with the yarn path between the nip rollers and the package. There will thus be substantial yarn tension variations between the nip rolls and the package, but these have no undesirable influences on the spinning operation because the nip rolls isolate these tension variations from the spinning unit 10.

More detailed examples of mechanisms enabling the piecing operation outlined above will now be described with reference to the remaining figures. In those figures, parts identical with parts shown in Figure 1 are indicated by same reference numerals.

All figures are still diagrammatic, however.

Figures 3 and 4showthe packageforming means 14 and somefurtherdetails of its association with the piecer 72. In the side elevation of Figure 3 it can be seen that control of the positioning of the package 20 is taken over from the spinning machine by a lever86 on the piecer. Lever 86 acts on the outer end region of arm 66 and the piecer lever 86 is pivotable by a piston and cylinder unit 88 about a pivot mounting on the piecer from a starting position indicated by the dotted line 86A.

The package lift-off mechanism on the machine always lifts the package 20 through a predetermined distance H away from the friction roll 62 regardless of the size ofthe package (packages of totally different size are indicated by the full line and the dotted line circles 20 in Figure 3). The anglethrough which lever 86 must traverse from its starting position 86A in orderto reach the lever 66 is therefore dependent upon the size of the package when thethreadbreak occurred. This angular position ofthe arm 86 at the time itengagesthe arm 66 is registered and is maintained bythe piecer during the subsequentend seeking operation.

If arm 86 has to be moved slightly beyond this initial engagement position (for example, to enable release ofthe package lift mechanism on the machine) then the arm 86 is brought back to its initial engagement position in time for commencement of the end seeking operation.Thus,the "underside" of the package is at a designed spacing from thefriction roller 62 regardless of the package size.

Ayarn end seeking nozzle 90 can be moved to the position indicated in full lines in Figure 3 in which a mouthpiece on the nozzle is located in close association with the underside of the package.

Suction is applied to the nozzle 90 via a flexible connection with suction 91, and a broken yarn end on the package is drawn into the nozzle. Successful finding of the yarn is registered if necessary by a light beam emitted across the nozzle interior and interrupted by a found yarn end. lfthe yarn end sensor associated with the nozzle has not sensed the yarn therein after a predeterminedtimedelay following initiation oftheyarn seeking operation, then the control 84terminates both the yarn seeking operation and the piecing operation and the station is accounted faulty. The station can be "marked" in a suitable manner so that service personnel can attend to the defect. The piecer can proceed to service other stations.

Assuming thatthe yarn end isfound, nozzle 90 is moved away from the package 20 towards the dotted line position shown in Figure 3,thereb" creating a length Lofyarn which will be accessible toa threading device to be further descriu-ed ,.elbow.

During theyarn seeking operationandthe subsequent threading operation, package 20 is rotated in the reverse direction by means of a roller 92 engaging the upper side of the package. Roller 92 is carried by a lever 94 pivotably mounted on the piecer 72, and an appropriate controllable drive means (not shown) is provided to rotate the roller.

Figure 4 shows the package 20 viewed from the direction ofthe piecer 72 and from above. The suction nozzle is assumed to be withdrawn from the package so that the yarn length L has been created, butthe orientation ofthis yarn length L relative to the central line C ofthe spinning station is completely uncontrolled immediately after the withdrawal ofthe suction nozzle. Accordingly, a yarn centering mechanism 96 is used to bring the yarn length L into the full line disposition indicated on Figure 4.

Mechanism 96 comprises a carrier bar 98 which is reciprocable at right angles to the centre line C ofthe spinning station. Bar98 carries a cantilever rod 100 which carries two thread guide elements 102, 104 respectively. Guide 102 has a yarn receiving slot 106 and guide 104 has a yarn receiving slot 108.

Mechanism 96 is illustrated in Figure 4 in its start position immediately afterwithdrawal of nozzle 90.

Completion of nozzle withdrawal is indicated by suitable sensor which triggers movement of bar 98to the right as viewed in Figure 4from its starting position. The extent of the rightward movement of bar 98 is sufficient to traverse slot 106 of guide 102 across the yarn length L, whereeverthat yarn length may happen to be lying following the seeking operation.

As seen in Figure 4A in which the guide 102 is viewed in elevation from the direction of the package 20, the leading edge 110 ofthe guide 102 during this outward movement from the starting position is formed as a guide edge to directthethread downwardly and over a lower-lip 112 into the slot 106.

The otherside of the slot 106, and the trailing edge of the guide 102, is formed by a downwardly projecting finger 11 4, which projects slightly below the lip 112to ensurethatthethread is guided into the slot 106.

Guide 104 is formed similarlyto guide 102, butthe guide slot 108 of guide 104 leads the guide slot 106 of the guide 102 during the outward movement by a small distanced. Since the stroke of the outward movement of bar 98 is sufficient to sweep the trailing slot 106 across the yarn length L, the yarn length is located in both slots 106 and 108 on the completion of the outward stroke. The bar 98 now begins a return stroke (to the left as viewed in Figure 4) towards its starting position.This return stroke is, however, interrupted when thefinger 1 of the guide 102 is located in alignment with a recess 116 provided in the upwardlyfacing surface ofthe guide member 58 of the machine. Bar 98 is now pivoted slightly about its own longitudinal axisso asto bring thetips of parts 112 and 114 into the recess 116; accordingly, as viewed longitudinally ofthe yarn length L, the slot 106 is closed by the upwardly facing surface of guide member 58 and the yarn length L is effectively guided bythis "closed" slot 106 without any risk of jamming oftheyarn between thefinger 1 14and the surface of the guide member 58 or escape of the yarn between the lip 112 and the surface ofthe guide member 58.

The yarn length L still remains, however, in the slot 108 ofthe second guide 104and because of the relative dispositions ofthe slots 106, 108 at this stage, the yarn length L intersects the centre line C at a slight angle as indicated in Figure 4. The portion oftheyarn length Liying between the guides 102 and 104 is therefore accessibleto guide slot 118 (Figure 5A) of a threading pin 120 which is moved along athreading path 122 (Figure 5) suchthatthe slot 118travels along the centre line C ofthe spinning station.The pin 120 rises along the rearward portion (piecer side) of its path 122 between the guide 104 and the bar98, reaches a peak P on its path slightlythereafter and begins its downward travel by intersecting the yarn length Latthe point X.

In continuing its downward travel aftertaking up the yarn length, pin 120 sweeps out the forward portion (rnachine side) of its illustrated path 122. In doing so, the pin 120 passes between the drive roller 52 and the raised pressure roller 54, through an array ofthread guides (further described below) in the reserve forming device 78, past a yarn clamp 124 and around an abrading roller 126. After passing the point X, pin 120 carrieswith ityarn which is being continuously delivered bythe reverse rotation of package 20 referred to above. The yarn length extending between pin 120 and package 20 is carried by the pin along the path 122 lying on the centre line C (Figure 4).This yarn is therefore laid by the pin 120 on a yarn path Z 1 (Figure 6) contacting the roller 54, passing through the reserve forming devices 78, passing through the clamp 124, passing around the abrading roller 126 and extending to the nozzle 90.

During the movement of the pin 120 around its path 122 (Figure 5), diverting means (notshown) diverts the yarn extending between the pin and the nozzle 90 so thatthis diverted yarn is not laid along the path Z but is continually taken up by the suction nozzle.

The details ofthe mounting and moving meansfor carrying pin 120 around its path 122 have not been shown in the drawings. Pin 122 is cantilevered from its mounting means so thatslotll8is provided ajdacent its free end. The pin 120 can thus project freely into the spaces between rollers 52,54 and within the reserve device 78. The moving means can be a lever system operated from suitable cam plates 123 as is well known in the art of production of automatic yarn piecing devices.

Figure 6 - 9 inclusive show the series of mutations oftheyarn path following completion ofthe threading operation. In Figure 6, immediately after laying of the yarn on abrading roller 126, the pressure roll 54 is relatively widely spaced from the drive roll 52, the reserve device 78 is in a " receiving " condition and the clamp 124 is still open sothattheyarn can continue to pass to the suction nozzle. A sensing system (not shown) senses completion of one circuit of the path 122 by pin 120, whereupon reverse rotation ofthe package 20 is terminated, roller 54is brought to a position close to but still spaced from roller 52, reserve device 78 is adjusted to its "end preparation" condition and clamp 124 is closed.This givestheyarn path Z2 shown in Figure 7 with the yarn still extending beyond the abrading roller 126 along the dotted line portion of the path.

Reserve device 78 changes from its receiving to its end preparation condition by means of a rightward shiftofayarn guide 130 relative to a pairofyarn guides 128,132 so that a loop ofthread is formed between the guide pair 128,132.

With the yarn still on its Z 2 path, a second yarn clamp 134 (Figure 7 - 9) is moved to a position immediately downstream from the rollers 52,54 and clampsthethread. For reasons which will be explained later, this second clamp is brought as close as possibletothe rollers 52,54. Simultaneously, the abrading roller 126 is driven into rotation anti-clockwise as viewed in Figure 7 and cuts the yarn leaving a tail 136 of an accurately defined length extending from the clamp 124. The portion oftheyarn not held by the clamp 124 is taken up bythe suction nozzle 90. There is now an accurately defined length of yarn between the clamp 134 and the free end ofthe tail 136.The action of brading roller 126 is such asto form a "prepared" yarn end which is particularly suitable for eventual joining with the fiber ring in the rotor. Such rollers are already well known in the art and will not be described in detail - see for example US Specification 3934394.

Clamp 124 is carried bya lever 138 (Figure 5) which is pivotally mounted in the piecer 72. After completion oftheyarn end preparation step, lever 138 is pivoted on its mounting to bring clamp 124to a position immediately above the exit opening from withdrawal tube 44(Figure 8). During this movement of clamp 124, the relative positions of guides 128,130 and 132 in reserve device 78 are adjusted continually to maintain the length ofthread between the clamps 134and 124tautand undersubstantiallyconstantor atleastcontrolledtension.Atthecompletion ofthis movement, the yarn lies on the path Z 3 shown in Figure 8 with a tail 136 lying within the mouth of withdrawal tube 44.No attempt has been made in these Figures to represent accurately the geometry of this system required to produce the effect described.

The diagrams merely illustrate the pinciples involved.

The geometry of movements ofthe guides 128,130 and 132 inordertocompensateforthepivotal movement ofthe clamp 124can be developed from the stated requirement of control oftheyarn length between the clamps 124 and 134.

Clamp 124 is now released and lever 138 is pivoted back to its previous position shown in Figure 5.

Simultaneously, guide 128 is withdrawn from the yarn path, guide 130 is moved to the left relative to its position shown in Figure 8 and guide 132 is moved to the right relative to its position shown in Figure 8. The yarn is thus drawn along the withdrawal tube 44 underthe effect of the suction in the rotor housing. At the completion ofthis movement, the yarn lies on path Z4(Figure 9, and also Figure 1 )with a loop of yarn of defined length remaining between the guides 130 and 132 and the prepared yarn end lying atthe upstream end of the withdrawal nozzle 46 (Figure 1). It remains, therefore, to release the thread reserve defined bythe guides 130 and 132 and to return pressure roll 54 into engagement with roller 52 as already described with reference to Figure 1.

The movements described with reference to Figure 3 - 9 inclusive can be controlled conveniently by a set of rotatable cam plates and levers controlled by suitable cam followers, the plates being rotated as a set.

Such systems have been commonly used in the design of automatic piecers currently available and are not believed to require detailed description here.

The movement described with reference to Figure 2 are not, however, controlled by cam plates but by triggerable mechanisms. A suitable mechanism for the reserve device 78 is shown in Figure 10.

Guide 132 is carried by a rod 138 coupled with a piston 140 in a cylinder 142. A second rod 144 projects from the other side of piston 140. Piston 144 can be latched in its illustrated position by a latch element 146 releasable by a relase mechanism 148 upon receipt of a predetermined signal. Piston 140 adopts the illustrated position and is latched therein at the completion ofthe preliminary operations, that is when theyarn is on path Z4shown in Figure 9 and Figure 1. Piston 140 is pressurized via air inlet 150 to cylinder 142. Port 152 is vented. Upon release ofthe latch 146 bythe mechanism 148, piston 140 (and therefore guide 132) are urged to the right as viewed in Figure 10 at a speed which is controllable by adjustmentofthe pressure applied at the inlet 150.

Cylinder 142 is movable by the cam platesforthe preliminary piecing operations.

As shown in Figure 11, exactly the same principle is applicable in the case ofthe return movement ofthe roller 54. As indicated diagrammatically at 154, a strong bias is normally applied by means of a suitable spring acting between the carrier rod 56 (see also Figure 1 )for roller 54 and the cantilever arm 156 which carries the roller at its free end. This bias urges roller 54towards its nip position with roller 52. The free end of arm 156 is also provided with an abutment surfacel58which is engaged inthe "ready" condition of Figure 9 buy a latch 160 having an associated release mechanism 162 responsive to a release signal which, as will be described, is related to the start signal referred to above in description of Figure 2.The rotatable cam which moves roller 54 awayfrom roller52to its threading position (Figure 6) and back to its ready position (Figure7 and Figure 11) also acts via a lever 159 (dotted lines Figure 11) upon the surface 158, but the lever is arranged to move away from that surface when the arm 156 reaches its ready position (Figure 11). The latch 160 retainsthe arm 156 in the ready position, however, until the release signal is received.

Figure 12showsa part ofthe control 84designed for producing the release signals. The Figure is in the form of a block diagram, block PC representing a programmable controller. When the programmable controller has received signals on inputs (indicated generally but without reference numc. .- showing thatthe piecer is in the ready condition, controller PC sends an output to clock CL which then provides output pulses at a predetermined iate ro Wàsn or counters CF, CB and CW. Each of these counters is individually settable to provide a respective output signal when it reaches its respective set count. The output signal from counter CF is vied to a mechanism operating clutch 28to cause Op. a.,or, u, feed roller 30 and feed of fibers into the rotor. The output of counter is fed to the release mechanism 148 to release the yarn reserve device 78 and the output of counter CW is fed to the release mechanism 162to releasethe roll carrier arm 156.

Itwill berealisedfromtheabovethatthetiming means constituted bythe clock and counters in Figure 12 does not determine alone the period Tshown in Figure 2. That period is dependent also on the mechanical performance particularly of the trigger mechanisms and the bearing by which arm 156 is mounted upon rod 56. There is only one reserve mechanism (78) associated with the piecer 72 and its performance can be made reproduceable and can be maintained by adequate maintenance and periodic checks. However, there is one pressure roll 54 and carrier arm 156 for each individual spinning station, and a certain amount of variation in the performance ofthese units must be anticipated.There will therefore inevitably be at least some minor variation in the period Tfrom position to position, but by careful attention to the bearing mechanism, the variability can be maintained within tolerable limits.

As described above with reference to Figure 2, backfeed ofthe yarn is completed before withdrawal of newly spun yarn is begun. It is importantthata controlled length of backfed yarn should penetrate into or overlap with the fibers in the rotor groove in orderto ensure adequatetwisttransference from the yarn to those fibers. ltisthusimportanttoprovidea carefully controlled length of yarn from the clamp 134 (Figure 9) to the prepared yarn end. Furthermore, the location of clamp 134 as close as possible to, but downstream from, the nip rolls 52,54 helps to minimize this defined yarn length.This in turn assi'sts in reducing variabilitywhich might be introduced due to variable stretchability of different yarn types. Some stretching oftheyarn must be anticipated. The effect ofthe centrifugal force during the final stage ofthe piecing operation (and hencefora given yarn stretchability, the absolute degree of stretching of the backfed yarn) will be less for a yarn clamped immediately downstream ofthe nip rollsthanfora yarn which is permitted to extend freely back to the package 20.Clamp 134 cannot, however, be located upstream from the nip rolls 52, 54 because there it tends to interefere with exact performance ofthefinal piecing stage as described with reference to Figure 2, and such interference is highly undesirable.

Clamp 134 is released automatically by linkage (not shown) to the return movement of the nip roll to forward yarn to the package 20. As already descrbed with reference to Figure 1, package 20 is simultaneously returned to the friction roll 52. The temporary yarn store described above with reference to Figure 1 can be operated bythe set of rotatable cam plates also referred to above. Although not shown in the drawings, the store can be brought against the yarn path Z 4 downstream from the clamp 134.

Suitable temporary stores, preferably in the form of a suction tube with an open end immediately adjacent theyarn path are alreadywell known in the art,seefor example US Specification 4223518.

Further devices, not already described above, can also be incorporated in the piecer or operated by it.

For example, ayarn quality tester can be mounted on the piecerso hasto be broughtagainsttheyarn path by the cam plates referred to above to test the quality of a piecing. If the quality detected is unacceptable, the programmable controller PC can be arranged to induce a thread break so that the piecing operation is repeated. The system can be programmed to provide a predetermined numberofrepeats, and ifthe quality is still unacceptable, the spinning station can be marked as defective and the piecer can terminate its piecing attempts, moving on to service another station. It is common practice to associate a yarn lubricating device with the pressure roll mounting 156.The piecer can be provided with a suitable lever to move this waxing device out of the operating range ofthe piecing system. Similarly, if a spinning station includes yarn tension compensation means (for example, as commonly provided where conical packages are to be formed), the piecer can also be adapted to temporarily move aside the tension compensatorto avoid its interfering with the piecing operation.

A rotor speed sensing system may be used to check rotor speed. The system can be of a known type with a lighttransmitting tube passing through the rotor housing and permittingthe piecer72tosend a light beam through the tube to be reflected from a rotating surface, and to receive a reflected light beam. The rotating surface is provided with suitable markings modulating the reflected beam, and the piecer 72 is provided with a receiver sensitive to the moduiated beam. Such a system is shown,forexample, in the DE specification (Offen leg u ngsch rift) 2610575.

In the systems currently used it is normal practice to apply the relevant markings to a part rotating in synchronism with the rotor rather than to the rotor itself. This is not very convenient for a so called "direct bearing" rotorwhere the rotor itself is generally the only part readily accessible. A convenient location to provide the required markings on the rotor itself is on the rotor "floor" facing the open end ofthe rotor and spaced radially inwardly from the rotor groove.In Figure 13,forexample, 164 represents the rotor rim, 166 is the floor of the rotor visiblethrough the open rotor side, 168 is a hub by means ofwhich the rotor is connected to its drive shaft and 170 is an annular ring of markings suitable for using the speed sensing system referred to above.

As illustrated, the ring 170 is divided into 8 equianagular segments which are alternately light-reflecting and non-light-reflecting. The contrast is conveniently produced by first treating the floor 166 ofthe rotor to provide it with a reflective surface, for example, byfine polishing and/or application of a suitable coating. The non-reflective portions are then produced by selectively etching or eroding the surface to destroy its light reflecting properties preferably by converting itto a light diffusing surface.

Such marking gives good contrast and an unambiguous speed signal without being detrimentaltothetechnologyofthespinning operation.

The principles which have been outlined above are based upon recognition ofthe fact that currently available piecing systems have experienced difficulty in achieving close control of the piecing operation, particularly in ts final phase. Without close control of this phase, it is impossible to obtain a piecing reliably at rotor speeds in excess of 40-50-'000 RPM. In order to improve the success rate, the current systems have altered the background conditions in onewayor another. Such alteration of the background conditions inevitably introduces complication and expense, but in many instances it also makes the required degree of control over the final piecing phase even more difficult to achieve.For example, in a "slow speed piecing" system in which yarn withdrawal is triggered at a speed below normal and on the acceleration curve of the rotor, additional variability is introduced duetovariabilityoftherotor acceleration curve from spinning station to spinning station. The piecing operation should place a controlled quantity oftwist in the piecing, and since the twist level is directly related to the rotor speed, uncontrollablevariation of the rotor speed during the piecing operation makes the desired control virtually impossible.

Furthermore, low speed piecing (whether it is effected on the rotor acceleration curve or at a predetermined constant speed which is lowerthan the normal operating speed) introduces complication in matching the fiber feed and the withdrawal speed to the rotor speed as the rotor accelerates from its piecing speed to its normal operating speed after a successful piecing operation. The failure of such matching results in production of a substantial length of yarn having a totally different character from the yarn produced at normal rotor speed. The matching process necessitates, however, direct intervention of the piecer in control ofthe relevent spinning station to control its operating characteristics during the acceleration phase.Furthermore, it is extremely difficultto match the withdrawal speed to the increasing rotorspeedwhileusingthewithdrawal system ofthespinning station itself; forthis reason the currently available systems all use an initial withdrawal path passing through a substitute withdrawal system in the piecer. The disadvantage of this arrangement is, however, thattheyarn must subsequently be returned from the piecerwithdrawal system to the spinning station withdrawal system, which introduces further problems.

Another approach which has been adopted is to abandon attempts to produce a carefully controlled piecing and to attempt merelyto obtain a piecing which enables extraction of newly formed yarn from the spinning unit. The piecing itself can then be cut outoftheyarn before winding up thereof on the package. The piecing is replaced by a knot or a splicing, the yarn being temporarily stored to enable this operation and the timing ofthe knotting/splicing operation therefore being less critical. The addition of the knotter/splicer clearly complicates the piecer construction and makes it more expensive.

In contrast, the principles described with reference to Figure 2 enable as many features as possible to be held constant, reducing variability in the piecing process. The rotor speed is held constant during the piecing operation, preferably at the normal operating speed so that no subsequent matching of feed and withdrawal speeds has to be effected during a rotor acceleration phase. The performance ofthe backfeed system is also held constant. The length ofyarn backfed can also be held constant despite variation in the rotor diameter. The prepared yarn end should not penetrate the rotor space, that is it should not leave the withdrawal nozzle before the start of the final piecing phase.The yarn end can, however, be withdrawn from the nozzle end by a suitable amount when a rotorofsmallerdiameterthan the maximum designed rotor diameter is in use. Maintenance of these constant conditions enables the piecerto obtain close control over the final piecing phase and also enables the piecer to use the withdrawal system ofthespinning station, despite minorvariabilityfrom station to station.

The system is not limited to details ofthe mechanisms shown in the Figures. Nor is it limited to dealing with piecing of a broken end which has wound up on a package. Upon starting up of a machine, orafterdoffing of a full package, it may be necessary for the piecerto restart the spinning operation when there is no yarn already available at the spinning station itself. Forthis purpose, the piecer can carry an auxiliary yarn package (171, Figure 4) from which yarn can bedrawnforinsertionintothe spinning unit to piece with a fiber ring formed in the rotor of the unit. The auxiliary yarn can then be transferred to a bobbin tube inserted in the package cradle ofthe spinning station, and the auxiliary yarn can be separated from the piecer so thatfurther take-up is effected by the station.Such systems have been proposed, for example, in Swiss Specification 606533. In Figure 4, the dotted line illustration to the right ofthe main diagram shows a means for introducing the auxiliaryyarn to the threading system. 172 is a yarn feed means drawing yarn from the auxiliary supply. 174 is a yarn manipulating meanswhich includesayarntake-upmeans,for example a suction nozzle. By bringing the mouthpiece of the suction nozzle close to the feed means 172, the suction nozzle can be madetotake-up yarn from thefeed means.Then,by drawing the suction nozzle away from the feed means 172 to the position shown, an accessible length of thread 176 chain-dotted line) is produced.The stroke ofthe bar 98 of centering mechanism 96 is made long enough to sweep guides 102, 104 across this thread length 176.

On its return stroke, mechanism 96 draws the auxiliaryyarn in to the "threading position" already described in relation to a broken end and indicated at Lin Figure 4. Suction is simultaneously applied to nozzle 90 ata level suffcientto draw a loop ofauxiliary yarn (indicated in dotted lines at 176A) into the nozzle between forwarding means 172 and guide 104.

Threading ofauxiliaryyarn into the piecing system is identical to threading of a broken end; however, a knife (not shown) in forwarding means 172 is operated simultaneouslywith the abrading roller, so that the loop of th read drawn into the nozzle is ta ken up thereby.

Forwarding means 172 preferably includes both a positiveforwarding means (e.g. a driven rollerpairj and an-airstream to directthe yarn end tithe nozzle in means 174. Package 171 is replaceably supported on a carrier 169 mounted in the tender and enabling required withdrawal of yarn from the package. The forwarding means is operated to forward thread from package 171 untiltheyarn has been clamped by clamp 124. The suction nozzle in means 174 draws yarn continuously, but is of course ineffective to move the thread while either of clamps 124, 134 is effective.

As soon asyarnwithdrawalfromthespinning unit commences, manipulating device 174 is moved by means (notshown)to connecttheyarnto a bobbin tube in the wind-up system. Devices to enable this are known in the art, and will not be described here. A novel deviceforthis purpose is described in our co-pending British PatentApplication No. (entitled "Bobbin Inserting Device" and filed on 20th May 1983),the disclosure of which is hereby incorporated in the present specification by reference. However, the present invention is not limited to use in conjunction with the system disclosed in that co-pending application.

Control of movements ofthe means 174 and ofthe centering mechanism 196 is effected by the cam set 123 referred to above. Control ofthe application of suction and ofthe knife in the forwarding means 174 is effected by controller 84.

Thus the auxiliary seed yarn is introduced to the main piecing system at the most convenient stage thereof, namely immediately prior to the threading step. Mechanism 96 and nozzle 90 can be considered as arranged to present an accessible length of seed yarn to the threading element, and the manipulating means 174 brings the auxiliaryseedyarn into operative relationship with this presenting means.

The clamping means 124 and 134 can beof substantially similar construction, each preferably being arranged to apply a controlled clampng pressure to the yarn. The basic principles of a suitable clamp construction are shown in Figure 14. A carrier part 173 carries a pivotally mounted clamping element 175. Adogleg lever 177 is pivotally mounted on the carrier 173 at 179. One leg of the lever carries a clamping element 180 having a surface adapted to co-operate with the clamping element 175. The other leg of the lever is pivotally connected to an operating rod 182 operable by a cam followerfrom the cam set (forclamp 134 also from the nip roll release).Element 175 has a tail portion 184 and the element is biased (by means not shown) so that the tail portion retains contact with the dog-leg lever 177 as the latter is pivoted to open the clamp (illustrated condition). The yarn is guided to a position between the clamping elements by a centering slot 186 with the clamp open.

Lever 177 is then pivoted anti-clockwise as viewed in Figure 14 on its mounting 179, and element 175 is pivoted clockwise on its mounting because ofthe contact of tail 184with lever 177. The clamping elements come into contact at the line 188 in Figure 14 so that the yarn is clamped between the rounded surfaces of the elements 175,180. Itis released by reverse pivotal movement of the dog-leg lever on the fixed carrier 173.

Initiation offiberfeed may be effected by closing a reed switch operable to energize/de-energize an electromagnetically operated clutch 28. The reed switch may be under the control of the yarn monitor 48 and the piecer may be provided with meansto operate the yarn monitor despite the absence of a yarn during the piecing operation. Operation ofthe yarn monitor is, however, preferably effected in a contact-free manner; the principles of such operation are well known, see for example US Specification 4091606. Accordingly, detailed description is omitted in this Specification.

The position of the lever 66 atthe time of contact with lever 86 (Figure 3) on the piecer can be registered as follows. Lever 86 carries at its free end a proximity swtich (not shown) which indicates contact of lever 86 with lever 66. Operation of the proximity switch operatesaclamp (notshown) insidethe unit88to registerthe position of lever 66. However, the clamp (and hence levers 86 and 66 now associated therewith) is movable through a short stroke in the cylinder, sufficient to release the machine lift-off system. The clamp then travels in reverse through its additional stroke, returning arm 66 to the registered position.

Where it is considered necessary to piece at "low speed" (i.e. at a speed substantially below the normal operating speed), the starting signal for starting the final stage of the piecing operation may be triggered by reference to sensed rotor speed instead of merely by referenceto completion of preliminary operations.

The control means therefore responds to the condition ofthe spinning unit (as represented by rotor speed or completion of preparation operations on the unit) to issue the start sig na I .

Means may be provided to reduce rotor speed from normal tothe desired level-preferablybycancelling rotor drive for a brief period. Rotor speed is preferably as near constant as possible during the final piecing stages. Yarn withdrawal is preferably timed in relationtothestartsignal.

Claims (8)

1. Atravelling piecing apparatusfora machineof the type described comprising means forforming an accessible length of seed yarn in a predetermined zone, yarn guide means and moving meanstherefor operable to sweep the guide means across said zone andto locate the guide means in a predetermined position after said sweep so that said accessible length of seed yarn is held in a predetermined orientation.

2. Apparatus as claimed in claim 1 wherein said guide means comprises two guide elements adapted to holdtheyarn at respective locations spaced in a direction normal to the direction of movement of the guide means.

3. Apparatus as claimed in claim 2wherein said elements are adapted to hold the yarn inclined to said normal.

4. Apparatus as claimed in claim 3 wherein each elementcomprisesyarn retaining means, said retaining means being spaced in the direction of movement of the guide means.

5. Atravelling piecing apparatus for a machine of the type described comprising, means to receive an auxiliary supply of seed yarn, forwarding means operable to forward yarn from said supply when the latter is present, threading means operable to thread seed yarn provided by a broken end with piecing means operable by the apparatus, and yarn manipulating means operable to take yarn from said forwarding means and present itto said threading means for co-operation therewith.

6. Apparatus as claimed in claim wherein said threading means comprises yarn presenting means for providing an accessible length of seed yarn to a threading element and said manipulating means is operable to bring said auxiliary seed yarn into co-operative relationship with said presenting means.

7. Apparatus as claimed in claim 6wherein said yarn presenting means includes a suction operated yarn end finder and an aligning meansforaligning a found end, said manipulating means being operable to bring the auxiliary seed yarn into co-operative relationship with the aligning means and the aligning means being operable to bring the auxiliary seed yarn into co-operative relationship with the end finder.

8. Apparatus as claimed in claim 7 comprising means selectively operableto cutthe auxiliary seed yarn between the yarn forwarding means and the end finder.