Abstract:
The invention relates to a thread clamping device for lower winding threads on spindles of a ring spinning frame or ring twisting frame. A clamping sleeve is provided between a clamping ring and a radially protruding flange on the spindle which can be axially displaced between a clamping position, which is defined by the position on the clamping ring, and an open position. The clamping sleeve is associated with an actuation device for the axial displacement thereof, which co-operates with radially extending means on the clamping sleeve. The clamping sleeves are associated with elements for fixing the position thereof at least in the clamping position. The aim of the invention is to introduce lower windings into the clamping gap and to improve the removal thereof from the clamping gap. As a result, the actuation elements and/or the radially protruding means are maintained on the clamping sleeve in a radially, elastically touching manner in relation to each spindle axis and are provided with rising sloping surfaces which are radially effective in both relative directions of movement.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a yarn clamping device for underwinding yarns on spindles of a ring spinning or ring twisting machine wherein a clamping ring and at a distance therebelow a radially protruding collar are provided on the spindle under an underwinding crown; wherein an axially displaceable clamping sleeve is located between the clamping ring and the collar on the spindle; wherein the clamping sleeve can be displaced by means of an actuating device between a clamping position defined by the contact against the clamping ring and an open position defined by the contact against the collar for opening or closing a clamping cleft; and wherein the clamping sleeve is equipped with radially extending means for the operation of the actuating elements of the actuating device and with elements for fixing the position of the clamping sleeve at least in the closed position. 
     A similar kind of device is already known by publication EP 1 218 577 B1. The clamping sleeve is equipped with permanent magnets which, in order to secure the closed position, fix the clamping sleeve on the clamping ring below the underwinding crown. If the clamping cleft is to be opened, the clamping sleeve will move to the lower, open position by means of an actuating device which acts on a radially protruding collar of the clamping sleeve by means of actuating elements, thereby overcoming the magnetic forces. In the open position magnetic forces of the magnets integrated into the clamping sleeve will in turn become active and will hold the clamping sleeve on the lower collar of the spindle. The actuating device is not described in detail in publication EP 1 218 577 B1. 
     Common actuating devices for adjusting the clamping sleeve are described, among others, in publication EP 0 775 769 B1. Actuating means which act on radially protruding means of the clamping sleeve via levers and transport the clamping sleeve into the positions required by the functioning of the system are mounted on parts that are firmly fixed to the machine frame. These known devices share the feature that the actuating devices act on one side and/or eccentrically on the clamping sleeves. This eccentric action requires long guides of the clamping sleeves along the spindle axles. Therefore, a limitation of the spindle speed is quite often also required. Another disadvantage is the high amount of additionally required structural outlay for these devices, which is also shown by the devices described in the publications EP 587 526 A1 and DE 199 04 793 C1. 
     Publication EP 462 467 B1 also discloses an actuating device which uses a ring rail on its way to the underwinding position for moving the clamping sleeve from the closed position to the open position. For each spindle the ring rail is equipped in the region of each spindle on its lower side with a projecting part which presses on the radially protruding collar of the clamping sleeve when the ring rail is approaching the underwinding position. This action compresses an axially acting pressure spring which is called “retroactive element” to the maximum width of the clamping cleft, thus opening the clamping cleft for the insertion of the underwinding yarn spiral. Except during this described procedure, the spring constantly keeps the clamping sleeve in the closed position, which is also called “working position”. During the short opening of the clamping cleft the yarn end still held in the cleft is released and the new underwinding yarn spiral is inserted almost simultaneously. The spindles run at very low speed during this opening procedure, because the underwinding should show a yarn loop of less than 360°. Ejecting and removing the yarn ends from the clamping cleft overlaps to a certain extent with the application of the new underwinding yarn spiral and is therefore not reliable. Frequent machine standstills for cleaning are the result. 
     Publication DE 196 28 826 A1 describes a yarn clamping device with a clamping sleeve which slides vertically displaceably on the shaft of the spindle wharve. A pressure spring, which is supported on the lower side of the wharve collar, presses the front surface of the clamping sleeve upwards against the clamping ring and closes the clamping cleft. Between an upper ring-shaped surface inclined inwards and downwards on the clamping sleeve, there are ball-shaped centrifugal elements with a relatively small diameter of max. 3 mm, which are located in the clamping position with their upper vertex a short distance from the lower side of the clamping ring. The centrifugal elements are guided in radial grooves of the clamping ring which are open underneath. 
     When the cop spinning process is finished, the ring rail lowers. The yarn guided by the traveler of the spinning ring is inserted at slowly decreasing spindle speed, approx. 5000/min, into the clamping cleft which is to be kept open by the centrifugal elements. If the spindle falls below this speed, the spring will close the clamping cleft, because it has to generate the complete clamping force for the underwound yarn upon cop change. 
     During the following start of yarn spinning for the new bobbin or cop, the centrifugal elements guided on the clamping ring move outwards due to the rotation of the spindle. They only open the clamping cleft after having reached approx. 5000 spindle rpm and also only to a small extent. 
     Therefore, this device is highly disadvantageous. The pressure spring, which has to apply the complete clamping force for the underwindings in the state of highest extension, can be overcome by the centrifugal elements only at high speeds. This means that also the underwinding process has to take place at these high speeds. The large mass of spindles and drawing sections, however, does not allow a sudden standstill out of this speed range, which would be absolutely necessary for limiting the looping of the underwinding to 270° up to a max. of 360°. 
     The consequence is that at relatively low speed the underwinding yarn is deposited only in the wedge-shaped area in front of the already closed clamping cleft and thus it is not sufficiently clamped. This considerably disrupts cop change. The spinning of the new cop is not effected with the required reliability. 
     If, in contrary, the underwinding yarn is inserted at a speed of more than 5000/min and clamped in the clamping cleft, clearly more than one winding will be deposited in the clamping cleft and several spirals will regularly be wound on the clamping sleeve. Removing these additional spirals from the clamping cleft and from the clamping sleeve creates considerable problems. In most cases the start of winding the new tube is also hindered. Yarn breakages and losses of production are the result. 
     The publications DE 197 46 819 A1 and DE 198 07 740 A1 disclose devices for clamping the underwindings during the bobbin change and for releasing the underwindings to be removed. These devices dispense with a clamping sleeve which can be displaced by means of actuating elements. Instead of the clamping sleeve, this system uses an elastic O-Ring for clamping which, due to the centrifugal force, is supported at high spindle speeds on the inner side of a ring at a distance from the clamping surface on the spindle and thus opens the clamping cleft. Such a design is unsatisfactory because the underwinding threads can only be inserted into the wedge-shaped clamping cleft which is closed at low speeds. Also a specific control of the delivery speed during this phase does not lead to a satisfactory safety of the clamping procedure during cop change. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is to propose an actuating device for a yarn clamping device equipped with a clamping sleeve which allows the reliable removal of the yarn waste from the clamping cleft and the reliable and safe clamping of a new underwinding thread with a circumference angle smaller than 360° until the winding procedure for the newly placed tube has begun. 
     This object is achieved by a yarn clamping device for underwinding yarns on spindles of a ring spinning or ring twisting machine wherein a clamping ring and at a distance therebelow a radially protruding collar are provided on the spindle under an underwinding crown; wherein an axially displaceable clamping sleeve is located between the clamping ring and the collar on the spindle; wherein the clamping sleeve can be displaced by means of an actuating device between a clamping position defined by the contact against the clamping ring and an open position defined by the contact against the collar for opening or closing a clamping cleft; and wherein the clamping sleeve is equipped with outwardly radially protruding means for the operation of the actuating elements of the actuating device and with elements for fixing the position of the clamping sleeve at least in the clamping position and for the application of a clamping force; wherein the actuating elements and the radially protruding means are held together elastically on the clamping sleeve radially to the spindle axles via angular surfaces; and wherein the direction of action of the actuating elements relative to the clamping sleeve can be switched over in such a way that, depending on the programme of the spinning machine, with increasing RPM the open position and at decreasing RPM the clamping position can be activated. 
     The combined non-positive and partly positive clutch between the actuating elements and the clamping sleeve allows the forces of the clamping sleeve on the clamping ring resp. on the collar of the spindle during the opening procedure to be reliably overcome. The actuating elements release the additional fixing between clamping sleeve and clamping ring and push the clamping sleeve into the open position. Opening of the clamping cleft happens at an especially favourable moment, i.e. at the end of the first downwardly directed ring rail lift at a relatively low speed and it remains open during the complete cop spinning procedure. Throwing off of the yarn waste is done during a long period of time at high spindle speeds. In addition, this procedure is supported by repeated blowing and suction processes on the open clamping cleft by means of the conventional travelling cleaner. 
     During the preparation phase for the cop change, the underwinding thread can be inserted in the still open clamping cleft, which is completely free from yarn waste, at an especially low speed, e.g. lower than 2000/min. Once the underwinding is finished, the actuating element, after having changed the direction of action on the clamping sleeve and after having jumped downwards over the radially protruding elements of the clamping sleeve, pulls the clamping sleeve upwards into the clamping position. After having reached this position, the actuating elements again jump over the radially protruding elements of the clamping sleeve and the clamping force required for carrying out the cop change is taken over by the means for fixing the clamping sleeve in the clamping position. 
     The essence of the claimed invention consists of the fact that the underwinding thread is placed at low spindle speed into a clamping cleft which is reliably free from yarn waste and sufficiently open. 
     According to an especially useful design of the invention the actuating elements are located on the ring rail; the radially protruding means on the clamping sleeve and/or the actuating elements have radially effective angular surfaces in both relative directions of motion; and the effective movement of the ring rail for closing the clamping cleft is bigger than the maximum width of the clamping cleft. The ring rail is especially suitable for receiving the actuating elements, as they are directly involved in the formation of the underwinding thread. Only a modification of the cycle of motion is required. 
     According to a favourable design variant of the invention, the actuating elements of each spindle consist of a group of radially moveable, resilient actuating elements which are arranged around the spindle axle on the lower surface of the ring rail and which elastically cooperate with the radially protruding means of the clamping sleeve. This design of the actuating elements avoids a one-sided or eccentrical load on the spindles. 
     A simple design of the actuating elements is achieved by the fact that the angular surfaces are part of the actuating elements. 
     The object of this invention is also achieved in a surprisingly easy way by a yarn clamping device for underwinding yarns on spindles of a ring spinning or ring twisting machine, wherein on the spindle below an underwinding crown a clamping ring and at a distance therebelow a radially protruding collar are provided; wherein an axially displaceable clamping sleeve is located between the clamping ring and the collar on the spindle; wherein the clamping sleeve can be displaced by means of an actuating device between a clamping position defined by the contact against the clamping ring and an open position defined by the contact against the collar for opening or closing a clamping cleft; and wherein the clamping sleeve is equipped with radially extending means for the operation of the actuating elements of the actuating device and with elements for fixing the position of the clamping sleeve at least in the clamping position by applying a clamping force; wherein the yarn clamping device is characterized in that the actuating devices are located on the spindles; and the actuating elements consist of centrifugal elements which slide in guides which are radially oriented with respect to the spindle axle and participate in the rotation of the spindle; which cooperate with angular surfaces or conical ring surfaces on the spindle or on the clamping sleeve; and which act against spring elements which, on the one hand, are supported by the collar of the spindle and, on the other hand, press the clamping sleeve into the clamping position. 
     The combination of the centrifugal elements acting against the spring and the elements for fixing the clamping sleeve in the clamping position allows the use of a very weak spring as it does not have to provide the necessary clamping force for the cop change. The underwinding procedure can also be executed at very low speeds and with a reliably opened and cleaned clamping cleft. It is possible to limit the winding yarn to a circumference angle of less than 360° without abruptly stopping the machine. 
     According to an example of the invention, the guides of the centrifugal elements are located on the clamping sleeve and the angular surfaces or conical ring surface are located on the collar of the spindle. 
     According to another alternative design of the invention, the guides of the centrifugal elements are located on the collar of the spindle and the angular surfaces or the conical ring surface are located on the clamping sleeve. The advantage of this design is the very compact design and low risk of fouling. It is moreover advantageous when the elements for fixing the clamping sleeve and for applying a clamping force are permanent magnets which are integrated in the clamping sleeve. 
     In accordance with a preferred embodiment of the invention, the elements for fixing the position of the clamping sleeve and applying a clamping force in the clamping position or for fixing the position of the clamping sleeve in the open position are formed by radially acting spring push buttons in the shaft of the spindle in cooperation with fixing grooves on the inner surface of the clamping sleeve, whereby the fixing grooves have a mutual spacing in the axial direction that is at most equivalent to the width of the open clamping cleft. 
     The use of permanent magnets which are integrated in the clamping sleeve as elements for the fixing of the clamping sleeve and the application of a clamping force allows designing a structurally simple and functionally very reliable embodiment for the fixing of the clamping sleeve at least in the clamping position to be provided. The magnets produce a reliably high clamping force in the clamping position. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The invention shall be explained in more detail below with reference to some exemplary embodiments. The corresponding drawings show 
         FIG. 1  a cross section of the middle part of the spindle with its relation to the ring rail; 
         FIG. 2  the action of the clamping sleeve controlled by the ring rail during the cop building cycle in six successive phases a) to f); 
         FIG. 3  an embodiment with ball-shaped actuating elements; 
         FIG. 4  an embodiment in which the radially protruding means on the clamping sleeve consist of elastically supported balls; 
         FIG. 5  an embodiment in which radially resilient leaf springs are provided on the clamping sleeve; 
         FIG. 6  a schematic top view of the drawing according to  FIG. 3 ; 
         FIG. 7  a variant in which the actuating elements are made of a sleeve of synthetic material, the surface lines of which are slotted from the free, lower end. 
         FIG. 8   a , b, c three positions of a variant (a) underwinding, b) clamping, c) spinning) in which the clamping sleeve is allocated mechanical elements for the fixing in the end positions; 
         FIG. 9   a , b, c three positions of another alternative of the invention in which the actuating elements are centrifugal elements which rotate together with the spindle; 
         FIG. 10   a, b  two positions of a variant in which the centrifugal elements are ball-shaped and guided on parts of the collar of the spindle; and 
         FIG. 11  a successfully tested clamping device according to the principle of  FIG. 10   a  and  FIG. 10   b  in a view on the basis of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the middle part of spindle  1  of a ring spinning machine in a simplified cross section drawing. The support (not shown) of spindle  1  firmly connected with the machine frame shows, starting from the bottom, wharve  14 . The sleeve guided thereabove on shaft  16  forms collar  13 , of which the upper fore-part limits the path of clamping sleeve  2  at the lower end. At the upper end, the path of the clamping sleeve  2  is limited by clamping ring  12  which is firmly connected to underwinding crown  11  and shaft  16 . 
     The lower end of tube  51  for cop  5  to be wound is placed on the top end of shaft  16 . Other upwardly extending guiding elements for the tube are not shown. 
     Clamping sleeve  2  is equipped with magnets  21  which can fix clamping sleeve  2  on clamping ring  12  in the clamping position A or on collar  13  in the open position B. The way in which this is done is described in more detail in publication EP 1 218 577 B1. 
     The position change of clamping sleeve  2  from the open position B to the clamping position A and vice versa requires in any case additional adjustment means which release the fixing in one position and move the clamping sleeve into the range of activity of the other fixing elements. 
       FIG. 1  shows clamping sleeve  2  in the open position B. In the area of clamping cleft C underwinding zone  15  is emphasized on the surface of shaft  16 . 
     Ring rail  3  in the phase of  FIG. 1  is lowered in underwinding position. Traveller  32  moves on spin ring  31  at the level of clamping cleft C and underwinding zone  15  and forms the underwinding spirals with the thread. The underwinding encircles shaft  16  of spindle  1  by less than 360°. 
     In the bore on ring rail  3 , through which spindle  1  extends, actuating device  4  for each spindle  1  is inserted from below. Its holding ring  40  extends with its hook-shaped elements through said bores of ring rail  3 . 
     Leaf-like springs  411  adjoin the holding ring  40  towards the bottom; on their downwardly directed free end there are angular surfaces  412 ,  413  directed inwards for the radially outwardly directed means resp. collar  22  of clamping sleeve  2 . 
     The functioning of ring rail  3  with actuating device  4  and clamping sleeve  2  is shown in  FIG. 2  in several phases a) to f). Phase a) shows that a new sleeve  51  has just been placed. Spindle  1  is starting to rotate again. Ring rail  3  is lifted to form the first layer and tensions the yarn held in the closed clamping cleft C as far as the first upper winding of the first yarn layer of the new bobbin  5 . 
     In the following phase b) ring rail  3  is lowered to finish the first double yarn layer. It leads fixing element  43  which is firmly connected to it to a ball  222  (cf.  FIG. 4 ) radially guided in clamping sleeve  2 . The angular surface  2221  effective on the surface of this ball  222  is caught by actuating element  43  and moves clamping sleeve  2  downwards into the area where the force of magnets  21  and the inherent mass of clamping sleeve  2  moves clamping sleeve  2  further into the open position B. Clamping cleft C is then open. 
     This state is also maintained in phases c) and d). The yarn waste within clamping cleft C is torn at high speed at underwinding crown  11  and thrown off. The yarn waste will be removed by means of a blowing and/or suction device (not shown). In fact, the whole cop winding cycle can be used for this procedure. 
     After the winding of cop  5  is finished, phase e), ring rail  3  lowers into the underwinding position. Traveller  32  of spin ring  31  leads yarn  6  around underwinding zone  15  into the still open clamping cleft C and forms underwinding  61 . Actuating element  43  overcomes, by means of the resistance of collar  13  in the open position of clamping sleeve  2 , the ball  222 , which is resilient in a radially inwards direction, of clamping sleeve  2  and positions itself below the resilient ball  222 . 
     As soon as underwinding  61  is finished, delivery section and spindles  1  are stopped. Ring rail  3  moves upwards again. Actuating element  43  positions itself on the lower angular surface  2222  of ball  222  and lifts clamping sleeve  2  by overcoming the magnetic force between clamping sleeve  2  and collar  13 . Clamping sleeve  2  moves into the clamping position A and fixes the underwindings  61  by the action of the magnets  21  in clamping cleft C. 
     Cop change can be carried out. When removing cop  5  the yarn is torn or cut between clamping cleft C and cop  5 . This process starts again with phase a) after cop change has been completed. 
       FIGS. 3 to 7  show other embodiments of the elastic actuating elements and radially protruding means on clamping sleeve  2 . 
       FIG. 3  and  FIG. 6  show a clamping sleeve  2  with rigid collar  221 . Actuating element  42  has, on its holding ring  40 ′, radially directed bores  421 , which are tapered inwards. The taper forms a stopper for ball  422 . Annular spring  423 , which is guided in a circumferential groove of holding ring  40 ′, holds three of these balls  422  which are located at a mutual spacing of 120° elastically inwards on the mentioned stoppers. The parts of ball  422  protruding from the inner side of the bores  421  form the angular surfaces  412 ′ and  413 ′. This embodiment guarantees a high functional safety and allows a simple exchange of the balls  422  which are subject to wear. 
     In  FIG. 4 , actuating element  43  is stably fixed to ring rail  3 . The radially resilient ball  222  is pressed from inside to outside to the stoppers by annular spring  23 . The characteristics of this design are similar to those as described in  FIG. 3  with the limitation that the labour for exchanging the balls  222  is slightly higher. 
     The device as per  FIG. 5  is similar to the one as per  FIG. 4 . Also in this case the actuating element  43  is stable and has a rigid collar  431  directed to the inside. Actuating element  43  is firmly connected with ring rail  3 . The function of the ball  222  is carried out by an angularly bent leaf spring  251  which is fixed in a groove  25  of clamping sleeve  2 . The angular surfaces  2511  and  1512  are formed on leaf spring  251 . The vertex  2513  in between is very narrow and guarantees a safe movement of clamping sleeve  2  in all phases. 
       FIG. 7  shows another preferred embodiment. Clamping sleeve  2  has a fixed collar  221 ′. Actuating element  41 ′ is made in one piece as a sleeve and includes the functions and elements of the holding ring  40  and the springs  411 . Sleeve  41 ′ is preferably a part made from synthetic material. The section directed downwards which carries out the functions of spring  411 , is slotted along surface lines, so that the shell segments can spring individually. On their lower end, the shell segments form the angular surfaces  412 ,  413  and vertex  414 . Depending on the characteristics of the synthetic material of sleeve  41 ′, two or more shell segments are formed as springs  411  on the circumference of sleeve  41 ′. 
     Apart from these described embodiments, additional advantageous alternatives are possible within the context of the present invention. For example, instead of the balls  222  or  422  also the spring push buttons known in specialist fields as “Novibraknöpfe” (Novibra buttons) can be used. In the following text, these parts will be called spring push buttons ( 17 ). 
     In the case of these spring push buttons, a unit consisting of three elements (sleeve/spring/bowl), instead of the balls, bowl-shaped calotte shell segments are pressed against the actuating element  43  ( FIG. 4 ) or against the collar  221  of clamping sleeve  2  by means of spiral springs. 
     Instead of balls or bowls made of steel, also other materials, e.g. synthetic materials, can be used. 
     Publication EP 1 218 577 B1 described that, by means of certain arrangements of magnets in clamping sleeve  2  and in collar  13  when twisting the clamping sleeve  2  with respect to the collar  13 , an axial shifting of clamping sleeve  2  will be achieved. In the described embodiment magnetic poles with different polarity and attracting action are located opposite to each other at closed clamping position within the clamping cleft. When the actuating device touches the collar  221  of clamping sleeve  2 , it brakes first of all the clamping sleeve  2 . Clamping sleeve  2  twists against spindle  1 . With this, the poles in the clamping cleft of same polarity are initially opposing one another and repelling each other. Clamping sleeve  2  is pushed downwards in the direction of open position B. At the same time poles of different polarity are approaching each other at the bottom between clamping sleeve  2  and collar  13 . These are attracting each other and support the movement of clamping sleeve  2  into the open position B. Afterwards the poles of different polarity stabilize the open position B. 
     If the ring rail  3  is brought into the underwinding position, the actuating element  41  jumps over collar  221  of clamping sleeve  2 . The underwinding yarn which has in the meantime been inserted is clamped into clamping cleft C at the next upward movement of ring rail  3  when spindles  1  and delivery section are stopped. Between clamping sleeve  2  and clamping ring  12  poles of different polarity approach each other. Thereby they initiate a turning of clamping sleeve  2  with respect to spindle  1 . Clamping sleeve  2  and clamping ring  12  realign themselves in circumferential direction. The necessary clamping force for the underwinding yarn spirals can be generated. 
     In this case, upon opening of clamping cleft C the actuating element  4  of ring rail  3  does not execute a direct adjusting motion between clamping position A and open position B, but only transmits a braking impulse which allows the magnets to change the position of the clamping sleeve  2 . 
       FIGS. 8   a ,  8   b ,  8   c  show another alternative of the device of the invention. Instead of the magnets  21  described in relation to  FIG. 1 , the already described spring push buttons  17  are used for fixing the clamping sleeve  2 ′ in the clamping position A resp. in the open position B. Spring push buttons  17  are radially inserted in the shafts  16  of spindle  1 . The ball segments of ball  171  protruding outwards or the protruding segments of the bowls or calotte shells (not shown) grip elastically into the fixing grooves  27  resp.  28  and fix the position of clamping sleeve  2 ′ in the clamping position A or in the open position B. 
     This kind of fixing of the clamping sleeve  2 ′ allows the use of so-called O-rings  26  in the clamping area. The hoop  261  which embraces the O-ring  26  externally and partly from the top allows, due to its shape and configuration, space for the radial extension of the elastic O-ring  26  so that it can additionally fix the underwinding spirals in the clamping position A as shown in  FIG. 8   b . When the ring rail  3  reaches the underwinding position after cop winding, as shown in  FIG. 8   a , the spring of the actuating element  41  jumps over the collar  221  of clamping sleeve  2 ′ and positions itself below collar  221 . 
     The spring push button  17  is located in the fixing groove  27  and still secures the open position B. 
     In the position according to  FIG. 8   b  the ring rail  3  has lifted itself into the position required for the cop change. The spring of actuating element  41  has firstly displaced the clamping sleeve  2 ′ into clamping position A. The spring push button  17  now secures the position of the clamping sleeve  2 ′ by locking it in fixing groove  28 . 
     When continuing to move upwards, the spring of actuating element  41  overcomes the collar  221  of clamping sleeve  2 ′ and leaves the area of movement of clamping sleeve  2 ′. 
     After having finished the first yarn layer, the ring rail  3  with the actuating element  41  hits the collar  221  from above and displaces the clamping sleeve  2 ′ into a position in which it is shifted into the open position by the spring push button  17  in cooperation with fixing groove  27  and is fixed there. 
       FIGS. 9   a ,  9   b ,  9   c  show another solution for the object to be achieved according to this invention. As shown in  FIG. 1 , an actuating bush  18  is mounted axially non-displaceably and torsionally rigid on spindle  1  in the area of the collar  13 . The upwardly directed walls overlap the lower area of the clamping sleeve  2 ″ on the outside and form an inwardly and downwardly directed angular surface  181 . 
     The radially protruding means  22 ′ of clamping sleeve  2 ″are equipped with radial guides in which the radially freely moving centrifugal elements  29  are inserted. The outer upper edge of these centrifugal elements  29  is in contact with the angular surface  181  when the spindle  1  is rotating. 
     There are magnets  21 ′ inserted, in clamping sleeve  2 ″, the poles of which are directed towards the clamping cleft C. They assist the clamping pressure when they are close to the clamping ring  12 . Clamping sleeve  2 ″ is supported with its lower end on spring elements  131  which, in turn, are supported in bores of the actuating bush  18 . These spring elements  131  keep clamping sleeve  2 ″, during standstill of the spindle at a low clamping pressure, in clamping position A. The magnets  21 ′ provide the necessary clamping force which allows the tearing off of the yarn as shown in  FIG. 9   b.    
     The functioning of the device as per  FIG. 9  is the following. When the spindle speed has lowered to approx. 2000 rpm, the traveller  32  leads the thread into the underwinding area. Clamping cleft C is open. It can take up the underwinding yarn in an exactly defined length without problems. 
     If the spindle is stopped, as shown in  FIG. 9   b , the force generated by the centrifugal elements  29  on the angular surface  181  is reduced. The spring elements  131  displace clamping sleeve  2 ″ into clamping position A. The magnets  21 ′ provide the necessary clamping force. The cop change can take place. The yarn between cop and clamping cleft C is torn or cut. 
     As soon as the spinning process is started on the new cop, the spindle speed increases. The centrifugal elements  29  are pressed to the angular surfaces  181  and push clamping sleeve  2 ″ against the direction of action of spring  131  downwards into the open position B. Clamping sleeve  2 ″ remains in this position until the next cop change begins, starting with a decrease of the spindle speed. There is sufficient time left to throw off and remove the yarn waste from the open clamping cleft C. 
     The device according to  FIGS. 10   a  and  10   b  shows an embodiment in which balls  134  are used as centrifugal elements. They are guided in bores  135  radially directed outwards and upwards in collar  13 ′ of spindle  1 . 
     The clamping sleeve  2 ′″ overlaps this part of the collar  13 ′ on the spindle and forms on the inside a conical ring surface  20  directed inwards and downwards. The upper part of clamping sleeve  2 ′″ is positively guided on the spindle and can freely move in axial direction between open position B and clamping position A. In this area of the clamping sleeve  2 ′″ magnets  21 ′ are arranged which work together with the clamping ring  12  of the spindle. 
     A pressure spring  132  is supported at the bottom on the collar  13 ′ of the spindle and at the top on the clamping sleeve  2 ″′. The spring is designed in such a way that it can push the clamping sleeve  2 ′ as far as clamping position A. The required clamping force for the underwound threads is mainly provided by the magnet  21 ′. 
       FIG. 10   a  shows the device in clamping position A. During standstill of the spindles and at relatively low spindle speeds (below 5000/min), the balls  134  serving as centrifugal elements are not capable of opening the clamping cleft C, i.e. cannot overcome the adhesive force provided by the magnets  21 ′ and the force of pressure spring  132 . During the spinning process, at speeds above approx. 5000/min. the balls  134  can, assisted by the inherent weight of the clamping sleeve  2 ′″, firstly by overcoming the adhesive force of the magnets  21 ′ and against the action of the rather small spring  132 , move downwards. Clamping cleft C opens and clamping sleeve  2 ′″ assumes the open position B as shown in  FIG. 10   b.    
     After having finished bobbin  5 , ring rail  3  is lowered into the underwinding position and the speed of spindles  1  is reduced to approx. 2000/min. At around this low speed the centrifugal force of the balls  134  can still safely overcome the low force of the pressure spring  132  and can reliably keep the clamping cleft C open. At this speed the underwinding yarn can be produced in a manner limited to less than 360°. 
     This low speed also makes it possible to further slow down the spindle and the delivery speed of the drafting system in an appropriate time almost synchronously to zero; without increasing the underwinding yarn to an unacceptable extent. 
     Due to the decreasing centrifugal forces of the balls  134 , the spring  132  can guide the clamping sleeve  2 ″′ into clamping position A again. When the clamping cleft is closing, the magnet  21 ′ generates the main portion of the clamping force needed for an error-free cop change. 
     The magnets  21 ′ should be e.g. designed in such a way that the holding force exerted by them at almost closed clamping cleft C is higher than the difference of the pressure force of the spring elements  132  between open position B and clamping position A. 
       FIG. 11  shows a clamping device built according to the principle of  FIGS. 10   a  and  10   b  in a view analogue to  FIG. 1 . 
     Instead of the springs  132  a single spring  132 ′ takes over the movement of the clamping sleeve  2 ″″ into clamping position A. The simple construction design of clamping sleeve  2 ″″ and the hidden actuating elements, consisting of collar  13 ′, ball-shaped centrifugal elements  134 , ring surface  20  and the spring  132 ″, can be clearly seen. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Spindle 
           10  Spindle axle 
           11  Underwinding crown 
           12  Clamping ring 
           13 ,  13 ′,  13 ″ Collar 
           131  Spring element 
           132 ,  132 ′ Spring/spring element 
           134  Ball/centrifugal element 
           135  Ball guide 
           14  Wharve 
           15  Underwinding zone 
           16  Shaft 
           17  Spring push button 
           171  Ball 
           172  Spring 
           18  Actuating bus 
           181  Angular surface 
           2 ,  2 ′,  2 ″,  2 ′″,  2 ″″ Clamping sleeve 
           20  Ring area, conical 
           21 ,  21 ′ Magnets 
           22  Radially protruding means 
           221 ,  221 ′ Collar 
           222  Ball 
           2221  Angular surface 
           2222  Angular surface 
           23  Annular spring 
           24  Bore 
           25  Groove 
           251  Leaf spring 
           2511  Angular surface 
           2512  Angular surface 
           2513  Vertex 
           26  O-ring 
           261  Hoop 
           27  Fixing groove (open position) 
           28  Fixing groove (clamping position) 
           29  Centrifugal elements 
           3  Ring rail 
           31  Spin ring 
           32  Traveller 
           4  Actuating device 
           40 ,  40 ′ Holding ring 
           41  Actuating element 
           41 ′ Actuating element, sleeve 
           411  Spring 
           412 ,  412 ′ Angular surface 
           413 ,  413 ′ Angular surface 
           414  Vertex 
           42  Actuating element 
           421  Bore 
           422  Ball 
           423  Annular spring 
           43 ,  43 ′ Actuating element 
           431 ,  431 ′ Collar, inner side 
           5  Cop 
           51  Tube 
           52  First layer 
           6  Yarn 
           61  Underwinding 
         A Clamping position 
         B Open position 
         C Clamping cleft 
         N North pole 
         S South pole