Abstract:
A method for operating the winding heads of a bobbin winding machine each of which respectively has a yarn tension sensor connected to a work station computer for detecting the actual tension in a yarn traveling from a delivery bobbin to a take-up bobbin, a yarn tensioner for regulating the yarn tension, a splicing device for automatic connection of yarn ends following a yarn break and/or a yarn cleaning cut, and a delivery bobbin changing device. After a splicing of the broken or cut yarn ends, the actual yarn tension is detected by the yarn tension sensor, and the detected value is compared in the work station computer with a threshold value which, if exceeded, results in actuation of the delivery bobbin changing device to provide a fresh delivery bobbin.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to a method for operating a work station of a bobbin winding machine, typically for rewinding a yarn from a delivery bobbin onto a take-up bobbin. More particularly, the invention relates to such a method wherein the bobbin winding machine has a yarn tension sensor connected to a control device for monitoring the tension of the yarn traveling from the delivery bobbin to the take-up bobbin, a yarn tensioner for regulating the yarn tension, a splicing device for the automatic connection of the yarn end of the delivery bobbin (bottom yarn) with the yarn end of the take-up bobbin (top yarn) following a yarn break or a yarn cleaning cut, and a bobbin exchange device for exchanging delivery bobbins which cannot be further unwound. 
     BACKGROUND OF THE INVENTION 
     A bobbin winding machine designed as a cheese-producing textile machine is known, for example, from German Patent Publication DE 196 50 932 A1. Such so-called automatic cheese winders have a plurality of work stations designed as winding heads, which are usually arranged next to each other in the longitudinal extent of the bobbin winding machine. It is known to assign a separate work station computer to each winding head for operating, monitoring and controlling the bobbin winding machine. In this case, the individual work station computers are connected via a machine bus with a central control unit of the bobbin winding machine. 
     As a rule, such automatic cheese winders have a logistic device in the form of a bobbin and tube transport system. Delivery bobbins, e.g., so-called spinning cops, or respectively empty cop tubes circulate, standing upright on the arbors of transport disks, travel on this bobbin and tube transport system. 
     Such bobbin winding machines also have a service unit in the form of a cheese changer, which automatically services the work stations. The cheese changer transfers finished take-up bobbins from the creel of the work station to a transport device which extends the length of the machine to convey the cheeses to a transfer station arranged at the end of the machine. The service unit subsequently inserts a fresh empty tube into the creel of the respective work station. 
     During the rewinding of the yarn from a delivery bobbin to a take-up bobbin, it is known to monitor the running yarn, e.g., by means of a yarn tension sensor, and to keep the yarn tension at a predetermined level by means of a yarn tensioner. This means that an essentially constant yarn tension is set by means of the yarn tensioner in order to assure the uniform winding of the yarn on the take-up bobbin in this manner. 
     It is known from German Patent Publication DE 41 29 803 A1 to detect the actual yarn tension of the running yarn by means of a yarn tension sensor. A control signal for the yarn tensioner is made available by means of a yarn tension measurement performed by this yarn tension sensor on the running yarn which, in accordance with the control signal, then exerts a more or less large braking effect on the running yarn. In this manner, it is assured that the yarn is wound at a defined tension on the take-up bobbin. 
     It is furthermore known in the course of the rewinding process to guide the running yarn through a so-called yarn cleaner. This yarn cleaner traces the running yarn to detect irregularities, for example thickened or thin places. If such irregularities are detected, a yarn cut is triggered by the yarn cleaner. In the process the running yarn is cut below the faulty place, creating two cut yarn ends which may be referred to as a bottom yarn and a top yarn. The top yarn having the faulty place initially runs up on the cheese, since the latter cannot be abruptly braked to a stop because of its relatively great centrifugal mass. 
     With a controlled yarn cleaning cut, the bottom yarn is usually held in the yarn tensioner and can be transferred by means of a so-called gripper tube into a splicing device, wherein the end of the bottom yarn is connected with the end of the top yarn, which is retrieved from the cheese surface by means of a pivotably seated suction nozzle. 
     It is moreover known to equip the bobbin winding machines with a so-called bottom yarn sensor, which detects the presence of the bottom yarn, since the presence of the bottom yarn is absolutely necessary for the successful performance of a yarn connection. 
     As already explained above, in the course of an intended yarn cut because of a detected irregularity in the yarn, the bottom yarn as a rule is held by the yarn tensioner so that the bottom yarn sensor thereof, which is arranged upstream as viewed in the traveling direction of the yarn, can detect the presence of a bottom yarn. 
     However, operational states can also occur in the course of the operation of the bobbin winding machine which are caused by a yarn break or the exhaustion of the delivery bobbin, for example. In case of a yarn break, a search for the top yarn and the bottom yarn is performed by the splicing device, and they are automatically reconnected with each other analogously to the connection of the bottom yarn and the top yarn in case of an intended yarn cut. If the delivery bobbin has run out, or if the yarn breaks below the yarn tensioner, the absence of a bottom yarn in detected by the bottom yarn sensor. In such a case, a delivery bobbin changing device is automatically activated by the work station computer of the winding head, which makes sure that the empty cop tube or the spinning cop (as the case may be), which can no longer be unwound because of the lack of a bottom yarn, is exchanged for a fresh delivery bobbin. 
     It is also possible for hook formations of the yarn and/or loop formations to occur at the delivery bobbin, in particular in connection with a yarn break above the yarn tensioner. As a result, although the bottom yarn sensor detects the presence of a bottom yarn, these hooked yarns or loops can prevent the respective winding head from operating automatically in spite of several repetitions of the yarn connecting process. 
     In case of a hooked yarn and/or loop formation at the delivery bobbin, a yarn break will immediately occur again after the restart of the winding head. In this connection, it is disadvantageous, among other things, that a loss of time occurs because of the repeated connecting and breaking of the yarn, which results in a loss of productivity of the respective winding head. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to provide a method of operating a bobbin winding machine of the type described above, by means of which the productivity of the work stations, i.e., the winding heads, is increased. 
     Basically, the present invention concerns a method for operating a work station of a bobbin winding machine wherein a yarn is rewound from a delivery bobbin onto a take-up bobbin, wherein the bobbin winding machine utilizes a yarn tension sensor connected to a control device for monitoring the tension of the yarn traveling from the delivery bobbin to the take-up bobbin, a yarn tensioner for regulating the yarn tension, a splicing device for the automatic connection of the yarn end of the delivery bobbin (bottom yarn) with the yarn end of the take-up bobbin (top yarn) following a yarn break or a yarn cleaning cut, and a bobbin exchange device for exchanging delivery bobbins which cannot be further unwound. 
     In accordance with the invention, the intended objective is attained by a method wherein the yarn tension is tested by the yarn tension sensor, for example after the connection of the top yarn with the bottom yarn has been performed following a yarn break, to determine whether the actual tension value lies above a predeterminable set value for the yarn tension making it possible to directly detect whether a threshold value has been exceeded indicating an error which cannot be automatically repaired, whereby the change of the delivery bobbin can be immediately initiated. Thus, if the actual value measured by the yarn tension sensor exceeds the predeterminable threshold value, it is possible to draw the conclusion that the yarn is hooked, for example, on the delivery bobbin, has formed a loop, or is otherwise subject to a retaining force acting on the yarn in the opposite direction of the force of yarn withdrawal from the delivery bobbin which can be predicted to lead to a renewed yarn break. It is therefore obvious that every further attempt to connect the bottom yarn with the top yarn would be unsuccessful, because a yarn break will again occur thereafter. The correction of this trouble is only possible by exchanging the delivery bobbin. Because this can be immediately detected, it is possible to trigger an appropriate signal via a work station computer of the winding head, so that the delivery bobbin exchange is directly initiated. 
     The productivity of this winding head is therefore increased, since the time for the repeated locating (via aspiration) of the top yarn on the take-up bobbin and the time for the repeated connection of the bottom yarn and the top yarn, as well as the renewed detection of the yarn break, can be avoided and saved. Avoiding repeated yarn connecting attempts which are useless from the start furthermore has a positive effect on the quality of the wound take-up bobbin, since at each yarn connecting attempt the suction nozzle is pivoted onto the cheese surface for picking up the top yarn, which leads to a loosening of the already wound-up yarn layers. 
     In a preferred embodiment of the invention, it is provided that the predeterminable threshold value, which is compared with the actual value, is stored in a memory unit of the work station computer. It is particularly preferred if this preset value is mutually predetermined for all winding heads of at least one bobbin winding machine by a central computer unit. In this manner, it is possible in a simple manner to variably preset the set value as a function of the yarn to be rewound, for example in relation to its strength properties, material strength and the like. Thus, the predeterminable set values can be changed in respect to the actually wound yarn. This results in a very universal use of the method of the invention. It is furthermore provided in a preferred embodiment of the invention that the predeterminable threshold value can be changed during the operation of the winding head as a function of the operating parameters of the winding head. In this manner, it is possible to optimally adapt the set values to the actual conditions, for example as a function of an amount of yarn already unwound from the delivery bobbin, or changes in the ambient temperature which, for example, have an effect on the tear resistance of the yarn to be wound. To this extent it is possible to assuredly detect by means of the method of the invention whether an occurring yarn break actually is an unrepairable hook or loop formation of the yarn or the like. 
     Further aspects, advantages, features and preferred embodiments of the invention will be explained and understood in greater detail in the following disclosure of an exemplary embodiment, with reference to the associated drawings. 
    
    
     DETAILED DESCRIPTION OF THE DRAWING 
     The sole drawing FIGURE represents a schematic lateral elevational view of a winding head of a winding machine in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawing FIGURE represents a lateral view of a winding head, identified by  10 , of a cheese-producing textile machine  1 . Such textile machines, known as automatic cheese winders, have a plurality of winding heads  10 , arranged in alignment next to one another, on which delivery bobbins  12  (hereinafter also called spinning cops) are rewound into large volume take-up bobbins  14  (hereinafter also called cheeses). In this case, the spinning cops  12  arrive at the individual winding heads  10  via a transport installation  16 . As is known, the transport installation  16  includes a plurality of transport tracks, not further identified in detail, on which spinning cops  12  or empty tubes  18 , which are placed on transport plates  20 , are transported. 
     A yarn  22  is drawn off a spinning cop  12 , which is in the winding position I. From the spinning cop  12 , the yarn  22  passes in the yarn traveling direction  24  on its way to the cheese  14  first through a bottom yarn sensor  28 , which is connected via a signal line  30  with a work station computer  32 . By means of this bottom yarn sensor  28 , it is determined, for example following a yarn break or a controlled cleaning cut, whether a bottom yarn  34  is even present, prior to initiating a search for the top yarn. 
     A yarn tensioner  36  is arranged above the bottom yarn sensor  28 . The yarn tensioner  36  includes brake pads, not represented in detail, whose contact pressure which is exerted on the traveling yarn  22  can be controlled by the work station computer  32  via a signal line  38 . 
     A yarn end connecting device  40 , which for example is designed as a pneumatic splicer, is arranged outside of the regular path of the yarn. The splicing device  40  is also connected with the work station computer  32  via a signal line  42 . 
     A yarn cleaner  44  is arranged in the following course of the yarn travel for detecting yarn faults. The quality of the traveling yarn is continuously monitored by means of the yarn cleaner  44 . Signals from the yarn cleaner  44  are supplied via a signal line  48  to the work station computer  32  for evaluation. When a yarn fault appears, a cutting device  52  is actuated by the work station computer  32  via a signal line  50 , and the yarn  22  is cut. A yarn tension sensor  54 , as well as a paraffin application device  46  are also arranged downstream of the yarn cleaner  44  in the yarn traveling direction  24 . In this case, the yarn tension sensor  54  is also connected with the work station computer  32  via a signal line  56 . The yarn tension of the traveling yarn  22  is continuously monitored during regular winding operations and the yarn tensioner  36  is controlled via the work station computer  32  as a function of the signals delivered by the yarn tension sensor  54 . Thus, the brake pads of the yarn tensioner  36  apply a contact pressure to the yarn  22  which assures that an essentially constant yarn tension is applied to the traveling yarn  22 , which assures a uniform packing density of the finished cheese  14 . 
     After the paraffin application device  46 , a deflection device  58  follows in the yarn traveling direction, from which the yarn  22  travels onto a winding drum  60 , e.g., a so-called grooved drum, which provides a traversing placement of the yarn  22  onto the bobbin  14 , in accordance with the particular winding type called “random winding”. 
     The cheese  14  is rotatably seated on a tube, not shown in detail, on a pivotably seated creel  64 , and rests with its exterior circumference against the winding drum  60 , which is individually driven by a motor, and which in turn drives the cheese by means of its frictional peripheral contact. 
     The winding head  10  furthermore contains a suction nozzle  66 , as well as a gripper tube  68 . In this case, the gripper tube  68  is used for grasping the bottom yarn  34  from the spinning cop  12 , which in case of a controlled yarn cleaning cut or a yarn break is held above the yarn tensioner, as a rule in the yarn tensioner  36 . The gripper tube  68  is pivotable around an axis of rotation  72  along the movement path  74 , drawn in dashed lines, and is connected to a central vacuum supply  76  of the bobbin winding machine, which is connected with a vacuum source  78 . Pivoting of the gripper tube  68  is performed by means of a drive device, known per se and therefore not shown in detail, triggered by a signal supplied by the work station computer  32 . 
     The suction nozzle  66  is used for grasping the top yarn  80  from its disposition wound onto the cheese  14 . For this purpose, the suction nozzle  66  can be pivoted around a pivot pin  82  such that its mouth  84  moves over a movement path  86 . The suction nozzle  66  is also connected with the vacuum supply  76 . The pivot movement of the suction nozzle  66  is triggered via the work station computer  32  by controlling a drive device, known per se and not represented, preferably a cam disk package. 
     The winding head  10  contains further mechanical, electrical and pneumatic components, which need not be explained in greater detail in the present description. 
     The winding head  10  represented in the drawings has the following functions. If the yarn  22  breaks in the course of rewinding of the spinning cop  12  from the rewinding position I onto the cheese  14  or the yarn  22  is cut by the yarn cutting device  52  as a result of an appropriate error signal from the yarn cleaner  44 , the yarn tension prevailing at the yarn tension sensor  54  abruptly changes. In addition, the dynamic yarn signal provided by the yarn cleaner  44  is lacking. 
     Thereupon the work station computer  32  triggers the following actions. The creel  64  is immediately lifted off the winding drum  60  by means of a drive device, not represented, and in this manner the yarn end traveling onto the circumferential surface of the cheese  14  (i.e., the top yarn) is prevented from being pressed onto the cheese  14  by the winding drum  60  in such a way that it can no longer be picked up later by the suction nozzle  66 . Moreover, the cheese is braked to a standstill by means of a winding brake (not represented). 
     In addition, the bottom yarn sensor  28  determines whether there is a bottom yarn  34 . 
     Thus, through an appropriate signal, the bottom yarn sensor  28  immediately signals whether or not there is a bottom yarn  34  at all. If such a signal from the bottom yarn sensor  28  is missing, this indicates that either the spinning cop  12  has been exhausted, or that the bottom yarn  34  cannot be picked up by the gripper tube  68 . 
     In either case, the yarn connecting process is interrupted by the work station computer  32  and a so-called cop changing operation is immediately triggered, i.e. the spinning cop in the winding position I or the empty cop tube is automatically exchanged for a fresh spinning cop  12 . 
     With a positive signal from the bottom yarn sensor  28 , a yarn connecting process is then started. Initially the gripper tube  68  is controlled in such a way that it mouth moves into the traveling path of the yarn  22  and grasps the bottom yarn  34 . Thereafter, the gripper tube  68  is pivoted along the movement path  74 , so that the grasped bottom yarn  34  is inserted into the splicing device. 
     The top yarn pickup is started thereafter, or simultaneously. To this end, the mouth  84  of the suction nozzle  66  is pivoted against the circumference of the cheese  14  and the winding drum  60  is driven opposite the winding direction, so that the cheese  14  is turned backward. Because of the vacuum prevailing at the mouth  84  of the suction nozzle  66 , the top yarn  80  is picked up from the surface of the cheese  14  and, if required, is cleaned by a yarn cutting and sensor device (not represented) arranged inside the suction nozzle  66 , i.e. the faulty yarn piece of the top yarn is cut off. Thereafter, the yarn nozzle  66  is pivoted downward along the movement path  86 , so that the top yarn  80  is also inserted into the splicing device  40 . 
     In the process, the top yarn  80  is brought into contact with the yarn tension sensor  54  by the suction nozzle  66 , and is also threaded into the yarn cleaner  44 . Subsequently the splicing device  40  is actuated via the control line  42  to twist the bottom yarn  34  together with the top yarn  80 . 
     Thereafter, the creel  64  is lowered again via the work station computer  32 , so that the cheese  14  comes into contact with the winding drum  60 . In this manner, the winding process of the yarn  22  is continued. The yarn tension thereby created is immediately detected by the yarn tension sensor  54  and appropriate signals are forwarded through the signal line  56  to the work station computer  32 . The signals provided by the yarn tension sensor  54  are continuously compared in the work station computer  32  with a preset value stored in the memory unit  90  which represents a threshold value predetermined as a maximum tension value which should be permissible for a yarn which is not hooked or looped or will otherwise be problematic to resume winding. This preset value of the yarn tension can be predetermined either for each winding head  10  or for all winding heads  10  of a bobbin winding machine  1 . The set value can be a function of a quality characteristic, material strength, type of material or the like of the yarn  22  to be wound. This preset value can either be permanently stored in the memory element  90 , for example for various yarns  22 , or it is centrally preset by means of a central computer unit  94 , which is connected with the work station computer  32  by means of a machine bus  92  as schematically indicated. The work station computer  32  includes a comparator  96 , which compares the predetermined set value with the actual signal which is supplied by the yarn tension sensor  54  immediately following the restart of the winding process. If the detected actual value exceeds the predetermined threshold value, which precedes a subsequent yarn break, this is automatically interpreted by the work station computer  32  as an error which cannot be repaired, for example hookformation of the yarn  22  at the spinning cop  12 , a loop or like problem. 
     In this case, the work station computer  32  prevents further connecting attempts, which are useless from the start, and immediately initiates a delivery bobbin change. An exchange of the respective spinning cop  12  can be immediately initiated because of the direct detection of a yarn break which cannot be repaired, at least not automatically, for example caused by hooking or looping of the yarn  22  on the spinning cop  12 . A following spinning cop  12 , which is made available by the transport installation  16 , therefore can be immediately transferred into the unwinding position, and its bottom yarn  34  can be connected with the top yarn  80  in a known manner. 
     As a whole, the method of the present invention not only leads to an improvement in the efficiency of the individual winding heads  10  of the bobbin winding machine  1 , and thus to an increase in productivity of the textile machine, but also to an increase in the quality of the cheeses because of the overall lower stress of the cheese surfaces. 
     It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents therein.