Title of Invention

METHOD FOR MONITORING THE APPLICATION OF PARAFFIN ON A RUNNING YARN

Abstract

In order to improve the running and sliding properties of the yarn during its further processing, in particular for machine- knitting and knitting, it is waxed during rewinding in bobbin winding machines by passing it along a paraffin body. When the paraffin body is used up without this being noticed, the unwaxed yarn can cause yarn breaks or even needle breakages, which leads to production errors or lost production. It is therefore proposed to monitor the slippage at the winding stations where, to prevent pattern windings, the drive of the friction drum is switched on and off at intervals in such a way, that acceleration phases with slippage between the friction drum and the bobbin and slippage- free run-out phase follow each other. If the slippage decreases in successive acceleration phases and remains at a low level, while the drive output of the friction drum remains unchanged, this is considered to be an outage of the paraffin application.

Full Text

METHOD FOR MONITORING THE APPLICATION OF PARAFFIN ON A RUNNING YARN FIELD OF THE INVENTION The invention relates to a method for monitoring the application of paraffin to a running yarn at a winding station of a cheese-producing textile machine. BACKGROUND OF THE INVENTION It might be necessary to reduce the coefficient of friction of the yarn in connection with processing it. A known method for doing this is the application of paraffin. The running and sliding properties, in particular for machine-knitting and knitting, are considerably improved by the paraffin particles applied to the yam. The application of paraffin takes place, for example, on bobbin winding machines during the rewinding of the yarn from cops to cheeses. In the process, the yam is brought into contact with a paraffin body, which is used up by removal of the paraffin. When a paraffin body is used up, or its contact with the yarn is interrupted, but not detected, the unwaxed yarn can cause yam breaks during subsequent processing, or even needle breakage of a knitting machine, which leads to production errors or lost production. Therefore various methods and devices have already been proposed, which make monitoring of the paraffin application to the yam possible. Most methods are based on monitoring the paraffin body itself and signaling when it is detected that it is used up. It is disadvantageous here that the contact of the paraffin body with the yarn can also be disrupted if the paraffin body is not used up, but only being jammed or dirty. A method and a device are described in German Patent Publication DE 195 47 870 Al, by means of which the result of waxing can be checked. To this end heat sensors arc arranged in the course of the yarn before and behind the paraffin application device, which are charged with sliding friction by the running yarn. Each increase in friction exceeding a defined value is interpreted as a defect in the paraffin application device, which results in switching of the respective bobbin. Additional sensors are required for the known method and the known device, whose employment as a rule is not anticipated in a bobbin winding machine. It is therefore necessary to adapt the signal processing to these sensors. OBJECT AND SUMMARY OF THE INVENTION It is the object of the present invention to perform the monitoring of the paraffin application to a running yam by means which are already employed for monitoring the ongoing winding operation. This object is attained with the aid of the characterizing features of claim 1. Advantageous embodiments of the method are claimed in the dependent claims. If the friction drum and the bobbin run at the same angular speed, or if the angular speeds have a definite ratio, for example 1 :1.5, which causes strong patterns, the layers of yarn are placed on top of each other. Because of this the reversing points are also located on top of each other. This leads to the unwanted formation of bulges on the surface of the bobbin, so-called pattern windings. The build-up of pattern windings can be effectively reduced by a changing slippage between the friction drum and the bobbin. Changing slippage can be generated by the acceleration in intervals of the friction drum. With an unchanged drive output, the slippage changes with the increase in the bobbin diameter and therefore increasing mass of the bobbin. In accordance with the invention it is only assumed that the paraffin application has failed when the deposit shift on the surface of the cheese noticeably changes during successive acceleration phases of the cheese. The drive of the bobbin takes place by friction by means of the friction drum. When the friction drum is accelerated, based on the slippage, the circumferential speed of the bobbin lags more or less behind the circumferential speed of the friction drum. Pattern disruption is effected by means of this slippage. The frictional force, and therefore the drive moments on the bobbin are functions of bobbin-technological parameters, such as contact pressure compensation, type of yarn, mass of the bobbin, yarn preparation, etc. Sensors are applied to the friction drum as well as to the holder of the cheese in the winding frame, by means of which the angle of rotation, and therefore the angular speed, or respectively the length of the rotation period, of the two rotating bodies is continuously determined. Customarily this is used for detecting the diameter of the cheese, which continuously changes during the bobbin travel. Within the scope of the invention, these sensors are also employed for monitoring the paraffin application. Here, the invention is based on the knowledge that if the paraffin application fails, the yarn, which increasingly covers the surface of the cheese because of the traversing lift, significantly changes the frictional behavior of the cheese surface after already a short time. If the paraffin application stops in the course of a bobbin travel, the change in the frictional behavior of the bobbin travel can be easily detected. But since the frictional behavior of the bobbin surface formed by a waxed yarn is normally known as a function of the winding station, the batch and the winding parameters, at the latest after the batch has been running for a while, it is also possible after a cheese change to detect that the frictional behavior of the cheese surface is outside of expected values. To prevent an extended unwaxed length of yarn from collecting on the cheese, it is provided in accordance with the invention to immediately stop the winding station after the loss of paraffin application has been detected. But it would also be possible, however with incurring losses, to finish the winding of the cheese and to subsequently remove it as an off-standard bobbin. It is useful to emit a signal by which the operator is called when the winding station is stopped. The operator can then initiate appropriate steps for restoring the correct application of paraffin. If, in regard to the further processing of the yarn wound on the cheese, there should be the requirement of avoiding even short yarn sections lacking paraffin, after stopping the winding station it is possible to draw off the unwaxed yarn section from the reversely rotating cheese by means of the suction nozzle, or even by hand. The absolute size of the slippage between the friction drum and the bobbin occurring during the acceleration phases during pattern disruption is a very essential measurement for determining the frictional behavior of the cheese on the friction drum. The slippage between the cheese and the friction drum is determined and evaluated as a value which is proportional to the coefficient of friction after friction drum. It can be determined by the evaluation of the angular velocities, or respectively lengths of the rotation periods, of the friction drum and the cheese. However, to determine this slippage, the bobbin diameter, which continuously changes in the course of the cheese travel, must be calculated in a known manner and in the way already explained above. This calculation cannot be performed during the acceleration phases, since during this time a false diameter would be determined because of the slippage. For this reason, the diameter of the bobbin is calculated in the acceleration-free run-out phases, and the course of increase of the bobbin diameter for the acceleration phase is precalculated based on the previous values. The size of the slippage in the slippage phases can be quantitatively determined from the difference between the bobbin diameter distorted by the slippage and the actual value of the bobbin diameter. If then the slippage decreases in sequential acceleration phases, while the drive output remains unchanged, and remains on a low level, in accordance with the invention this is a signal that no paraffin was applied to the yarn. The coefficient of friction, and therefore the frictional force, have increased. This increase can be noted so clearly that its association with the paraffin application is easily possible. If in addition the detected frictional force, which is transmitted by means of the drive moment from the friction drum to the bobbin, is included in the evaluation, statements regarding the frictional behavior of the surface of the cheeses can be made even more distinctly. If in the slippage-free run-out phases of the two rotating bodies their deceleration within the scope of the pattern interruption is additionally determined, losses due to friction, inertia and convection, as well as load moments, the latter caused for example by the yam tensile force of the yarn being wound, can be determined. But these are also present in the acceleration phases. It is possible to determine parameters in this way which have no connection at all with the frictional behavior of the surface of the cheese on the friction drum. By means of this, the lack of paraffin application becomes noticeable even faster and clearer. Most of all it is possible by means of this to differentiate the position of the function of the frictional force as a function of the slippage clearly in accordance with the criteria of paraffin application/no paraffin application already at the start of the bobbin travel. If a sensor for the tensile force of the yarn is provided at the winding station, its yield values, which constitute the load moment of the two rotating bodies, can alternatively be included in the evaluation. By means of this it is at least prevented that fluctuations of the tensile yarn force distort the result of the slip determination. The deposit shift, which corresponds to the displacement of a reversing point of the yarn deposit on a circumferential line on the bobbin in respect to the preceding reversing point, is determined as a function of the slippage and is used for evaluating the frictional behavior of the surface of the cheese on the friction drum. Not only is the respectively absolute slippage size included in the evaluation by determining the deposit shift, but also the result of the slippage, so that the slippage course, including the length of the slippage, is determined. The inclusion of this additional dimension also leads to more significant deviations, in this case in the function of the deposit shift as a function of the slippage, in contrast to an isolated consideration of the slippage. An improvement of the ability to make a statement regarding the paraffin application can also be achieved in that a reference value is determined by averaging the frictional behavior of the cheeses at several winding stations, from which a certain measurement of a deviation is defined as the lack of paraffin application. The invention will be explained in greater detail by means of exemplary embodiments. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig. 1 represents a winding arrangement with an evaluation device for determining slippage; Fig. 2 represents the structure of an evaluation device in a block circuit diagram; Fig 3 shows a diagram as a small portion of a bobbin travel for explaining the present invention; Fig. 4 is a diagram of the slippage occurring between a friction drum and a bobbin during the portion of the bobbin travel in Fig. 3, wherein the slippage is scaled to the diameter of the bobbin; Fig. 5 represents the course of the diameter in an acceleration run-out diagram of a conical bobbin; Fig. 6 represents the equalized run-out process of a conical bobbin; Fig. 7 shows a diagram wherein the relative deposit shift has been applied over the slippage, respectively for a waxed and an unwaxed yarn, and Fig. 8 shows a diagram wherein the frictional force has been applied over the slippage, respectively for a waxed and an unwaxed yarn. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The winding device, in particular the winding device of a winding station of a bobbin winding machine, represented only schematically in Fig. 1, has a friction drum 10 driven by means of a drive motor 11. The friction drum 10 is provided with a reverse thread groove 12, so that it is simultaneously used as a traversing device for a yarn 15, which is running in the direction of the arrows over a sensor 13 for the tensile force of the yarn through a yam eye 14. The yarn 15 is wound onto a bobbin tube 16 as a random wound bobbin, so that a so-called cheese 17 is created. Since the invention is applicable both to the production of cylindrical cheeses as well as to the production of conical cheeses, a cylindrical cheese 17 is represented in Fig. 1, and a conical cheese 17 in Fig. 2. If in what follows mention is made of a bobbin radius or bobbin diameter, in connection with a conical cheese 17 the neutral diameter or the so-called driving diameter is meant. The bobbin tube 17 is held by means of two bobbin plates 18,19, which respectively engage the open ends of the tube 16 in a frictionally connected manner by means of a cone 20,21. The bobbin plates 18,19, which rotate with the tube 16, and therefore with the bobbin 17, are seated in a bobbin frame, not represented, which is pivotable around an axis which is parallel with the shaft 22 of the friction drum 10. A sensor 23 which, for example, is designed as an angle encoder, is associated with the shaft 22 of the friction drum 10. The angular speed, the period length or the rpm of a friction drum are detected by means of this sensor 23. A sensor 24, which is also designed as an angle encoder, is associated with the bobbin plate 16. The respective measured values of the bobbin 17 are detected by means of this sensor. The signals of the sensors 23 and 24 are detected in a control and evaluation device 25. To prevent pattern windings in the course of the production of the bobbin 17, a so-called pattern disruption is performed, during which slippage between the friction drum 10 and the bobbin 17 is intermittently generated. This is achieved in that the drive motor 11 of the friction drum 10 is altematingly switched on and off. If, after the drive motor 11 having been shut off, the rpm of the friction drum 10 fall below a predetermined value, the drive motor 11 is switched on again, by means of which the friction drum 10 is accelerated up to maximum rpm. Thereafter the drive motor 11 is switched off again, after which the process is repeated. Because of the mass inertia of the bobbin, a slippage between the friction drum 10 and the cylindrical bobbin 11 is created during the acceleration of the friction drum 10. Starting from the bobbin tube 16, which initially is seated empty against the friction drum 10, the radius or diameter of the bobbin increases because of the yarn 15 wound thereon, until the bobbin 17 has reached its maximum radius or diameter. The bobbin radius r,p can be calculated, based on the signals of the sensors 23,24, in accordance with the following equation: The following meanings apply here: arp angular speed of the bobbin afw angular speed of the friction drum rsp radius of the bobbin rfw radius of the friction drum. If this calculation is continuously performed at short time intervals, for example at time intervals of 0.1 s, a curve results such as is represented in Fig. 3 as a diameter (2 x rsp) over the time. Fig. 3 shows a diameter increase of approximately 0.75 mm in the range of a bobbin diameter of approximately 155.15 to approximately 155.9 mm during a time of approximately 17 seconds. The lower sections of this curve correspond to the run-out phases in which the drive motor 11 of the friction drum 10 is switched off, so that in case of a cylindrical bobbin geometry the friction drum 10 and the bobbin 17 run tree of slippage. Therefore the mentioned equation can be applied in these run-out phases 30, so that the course of the curve represented in the run- out phases 30 corresponds to the actual course of the increase of the bobbin radius rsp, or here of the diameter. In the acceleration phases 31 located between the run-out phases 30, the bobbin 17 has a lower circumferential speed than the friction drum 10. There, the calculation of the bobbin radius rsp or of the bobbin diameter leads, by means of the mentioned equation, to a fictitious bobbin diameter or bobbin radius, which is distorted by the occurring slippage. Because of the slippage, an increase in the bobbin radius or bobbin diameter is calculated by means of the above equation, which is larger than the actual course of increase of the bobbin diameter in the acceleration phase 31. vsp = (l-S)xvtr applies to the bobbin speed, S here represents the slippage. The drum speed vtr and the bobbin radius rsp can be provided as known values in the winding process. Therefore: asp x tsp = (1 - S) x vtr, In the acceleration phases, the bobbin radius is calculated as a so-called distorted bobbin radius: asp, s _ 0 means: on the condition that the slippage = 0. Therefore, the following relationship results for the slippage between the drum and the bobbin: Taking into account the course of the increase of the bobbin radius or the bobbin diameter calculated from the measured values in one or several of the previous run-out phases 30, the (actual) course of the increase of the bobbin radius or the bobbin diameter can be precalculated for the respectively following acceleration phase in the form of a time-varied compensatory straight line 32. The difference between the (distorted) bobbin radius or diameter calculated from the signals of the sensors 23,24 in the acceleration phases 31, and the precalculated course of the increase of the bobbin diameter in accordance with the compensatory straight line 32 in the acceleration phases 31 is a measurement of the slippage which actually occurred in the acceleration phases 31. This slippage has been applied in Fig. 4 in percent over the time, scaled to the diameter of the bobbin 17. With conical cheeses the driven diameter in which the circumferential speeds of the friction drum and the cheese coincide, changes fictitiously during acceleration, as can be seen in Fig. 5. A fictitious diameter increase 40 takes place. Starting from this time 41, an exclusively slippage- encumbered drive takes place. The bobbin diameter calculated during the acceleration phase (diameter increase 40) is distorted, and during the phase 42 of the slippage-encumbered drive is approximately constant. After switching off the friction drum, the titious diameter again meets the bobbin at the point 43, and a real, driven diameter wanders, proportional to the sinking rpm of the friction drum, on the bobbin from the large diameter in the direction toward the small diameter. This is the so-called run-out phase 44. Towards the end of the run-out phase 44 the driven diameter reaches a so-called neutral diameter zone based on the acceleration-free drive, in which an achieved diameter of the conical cheese can respectively be calculated. Reaching the neutral zone depends on several influence factors, for example on the flexing work, the conicity of the bobbin, and the friction between the drum and the bobbin, which has a disturbing effect on the diameter determination. The course of the curve shows a chronological run-in or settling process. The settling process is not usable for determining the diameter of a cheese, since here the distorted diameter does not coincide with the neutral bobbin diameter. However, since it is already necessary to have an actual bobbin diameter available in a short time for the next acceleration phase, this settling process must be equalized. This takes place by inserting prior knowledge of the course of the run-in into the neutral zone. If it is assumed that the above mentioned influence factors do not change during a disruption cycle, it must be assumed that the previous disruption cycles have a similar course as the actual one. By means of this knowledge it is possible to prepare a model course of the actual run-in behavior. Once this model course has been found, it is possible to calculate a prediction of the neutral cone diameter at any point in time of the run-in phase. The calculation of a compensation polynomial of the nth degree offers itself as a model process. Once the model parameters (polynomial coefficients) of the last n run-in cycles have been calculated, it is possible, simultaneously with the actual run-in phase, to determine a modeled run-in phase. To this end it is necessary to average the n sets of parameters of the run- in cycles, and a simultaneous course must be produced. If the measured distorted diameter value is divided by the corresponding model diameter value, an equalized diameter course is obtained. This course is corrected by the amount of the actually valid cone diameter. The integration of several run-in cycles into the model run-out is recommended, since it must be assumed that by means of this occurring differences between different run-out cycles can be averaged out. This method is represented in Fig. 6. Based on the run-outs (n - 2) and (n -1), a model run-out is calculated for the run-out (n) and is simultaneously carried along. At the same time the determined distorted diameter course ,s divided by the model diameter course, which results in an equalized diameter course in the run-out phase. The calculation of the time-variant compensatory straight line 32 and the slippage can take place, for example, in accordance with an evaluation device explained in Fig. 2. The period lengths measured by the sensors 23,24, and therefore also the angular speed of the bobbin, asp, and of the friction drum, afw, are introduced into a quotient former 33. Since the radius rfw of the friction drum 10 is constant, the quotient afw, to afw, is already representative of the bobbin radius tsp so that a multiplication by the radius rfw of the friction drum 10 can be omitted. However, this value cannot yet be used for a slippage determination, since it is a function of the diameter. Therefore this value is entered into a linear filter 34, for example a Kalman filter, into which the angular speed asp, of the bobbin 17 or 17 in Fig. 1, and the angular speed afw, of the friction drum are also entered. The diameter values or, in the case of the conical cheese the calculated equalized course, are only made available to the filter in the run-out phases of the pattern disruption. This linear filter 34 constitutes the time-variant compensatory straight line 32. The calculati a of the compensation radii takes place in the slippage-free phases. In the acceleration phases the compensatory straight line is continued, based on its predetermined increase. This compensatory straight line 32 is entered, together with the signal of the quotient former 33, into a subtraction device 35, which then shows the slippage which is independent of the rpm and independent of the diameter, i.e the sippage, which is independent of the state of the winding process. The slippage s determined in this manner constitutes the basis which is independent of the diameter for the calculation of the deposit shift. The following applies for the speed of the bobbin: The difference distance on the bobbin surface generated by the sippage is calculated as E1 wherein t3 - t1, represents the length of time to be examined. In the case of discreted slippage and speed courses, with -t as the scanning time, the following applies : E2 The value -1 is the deposit shift. To formulate from this a statement regarding the yarn deposit on the bobbin surface can be done by using the length of a double lift on the bobbin surface as an aid. This length is drum-specific and Is calculated as 1Trommet = 2xggx2xXx rTrommet, wherein gg is the drum pitch number (number of drum revolutions for one deposit ift on the bobbin surface). If the shift is related to a double lift, the relative shift in percent results E3: Since no further manipution mechanisms are available for the shift formation, only the acceleration of the friction drum can generate the sfppage required for pattern disruption and therefore the shift. Based on the fact that the drive moment is always the same in every disruption cycle independently of the motor operating point, the size of the shift during a bobbin travel also provides information regarding the size of the actually present sippage. If in the course of a bobbin travel after every disruption cycle, i.e the sequence of accelerations of the bobbin and its non-driven run-out, the values for the slippage and the shift are entered as dots in a diagram, tightly limited clouds of dots are created, whose position and orientation provide Information regarding the quality of the respective disruption cycle, and thus of the slippage. A representation of the state of the disruption cycles results. The cloud of dots also wanders with the increasing diameter of the bobbin. Since a waxed yarn has different frictional properties than an unwaxed yarn, the sippage occurring In the course of winding these yarns Is different, and accordingly also the deposit shift. This can be clearly seen in the slippage - deposit shift diagram represented in Fig. 7. A cloud of dots recorded during a bobbin travel of an unwaxed yarn clearly differs in regard to its position, extent and course from a cloud of dots which was recorded during the bobbin travel of a waxed yarn. A prerequisite for this comparison is that, besides the preparation, the setting parameters are the same during the two bobbin travels. The absolute position of the cloud of dots can be compared over the entire machine or batch, i.e. between many individual units. Because of this, deviations pointing to reduced or lacking paraffin application can be detected even quicker and better. Cylindrical bobbins of yarn of the same yarn count were wound at the same winding speeds. An average contact pressure compensation was set and a yarn tensile strength of 30 cN prevailed. The cloud of dots of the unwaxed yam extends in an area of little deposit shift and slippage, approximately up to 3.5% relative deposit shift at 1.5% of slippage, while the cloud of dots of the waxed yarn, clearly distinguished from the previous cloud, extends from approximately 4% of relative deposit shift and 1.5% slippage up to 8% of relative deposit shift and over 2.5% of slippage. A slippage-shift diagram makes it possible to clearly distinguish the waxed and unwaxed state of a yam by the position of the slippage-shift points alone. Slippage and frictional force also have a proportional connection. Therefore, a decrease of the slippage can be detected over the course of the frictional force. The frictional force can be calculated from the drive moment acting on the bobbin. During the acceleration phase of the pattern disruption, the following drive moment acts on the bobbin: This moment causes an rpm increase of the bobbin within a defined time interval. The following applies here:/ E4 . In the area of the run-out phase of the drum and bobbin, the friction moment mKeib = 0, and the bobbin rpm are reduced because of the loss and load moments acting on the system. Since in this phase the system is without any further external influences, these moments can be calculated by means of the courses of the angular speed. An uncoupling of the moment determination between the rotating bodies of bobbin and drum is performed by means of the calculation of the corresponding yields. Therefore the following applies to the loss and load yield detected in the run-out of the pattern disruption: E5 While there is no possibility of measuring the loss yield of the drum-bobbin system with the available measuring devices, the sum of the drive loss yield and the load yield as a result of the yam tension force can be explicitly determined. The determination of the fnctional and convection losses of the drum drive can be performed with the aid of run-out curves. Since the winding speed, and therefore the angular speed of the drum during the winding operation, vary only by the set pattern disruption lift (for example between V 1.5% to V 6%), the determination of this loss yield is only meaningful in the operational range. For this reason a model statement can be selected which takes into consideration the run-out increase of the drum speed in the area of the production speed. Therefore the following applies: JTrommet is the dnim inertia. The measurement of the increase of -aTrommet /-t can be performed during the normal production operation without a noticeable production loss. Following each winding process interruption, the drum drive needs to be uncoupled (lifting of the cheese) from the bobbin and switched off for only a short time. After the initial increase has been measured, the drum operation can be actively braked in order not to permit the creation of unnecessary production losses. Since this loss moment is constant during a bobbin travel, it is only necessary to perform the run- out measurements after each process-related interruption of the winding process. The determination of the drive output is performed by means of the measured acceleration moments of the drum and bobbin. Taking into consideration the equation the result of the calculation of the total drive output during the acceleration-free phases therefore is: E8 In order to be able to perform a more accurate localization of the characteristics of the climed of points, and therefore of the process properties, it is possible to determine and process the center and scattering of the cloud of points by means of this representation. The effect of the paraffin application can be clearly seen in Fig. 8. Without having to perform a localization of the cloud of points, it is possible by means of the rise of the cloud of points in the slippage-frichonal force diagram alone to detect the quality of the paraffin application. With the unwaxed yan the rise of the cloud of points is 4.2 N/%, that of the waxed yarn 0.63 N/%. The method in accordance with the invention for monitoring the paraffin application can be considered to be very dependable since the preparation of the yarn, i.e. the paraffin application, has a direct effect on the friction number T of the friction drive. If a yarn tensile strength sensor 13 is provided at the winding station, it can have a connection with the evaluation device 25, so that the changes in yarn tensile strength can be taken into account when determining the slippage. One of the most essential influence facters which have no relation to the coefficient of friction of the cheese, is eliminated by means of the We Claim: 1. Method for monitoring the application of paraffin to a traveling yarn (15) at a winding station of a textile machine producing cross- wound bobbins (17), at which textile machine the cross-wound bobbin is driven at its periphery by a friction drum (10), the drive of the friction drum being switched on and off at intervals to avoid pattern windings in such a way that acceleration phases (31) with slippage between the friction drum and bobbin and slippage-free run-out phases (30) follow one another, characterized in that the friction behaviour of the surface of the cross-wound bobbin (17) on the friction drum (10) is monitored during bobbin travel, in that for this purpose values proportional to the coefficient of friction are determined and evaluated by continuous detection of the angular velocities (Wsp, Wfw) of the friction drum and the cross-wound bobbin, in that these values are compared with the expected course over the bobbin travel and in that significant deviations from this course are evaluated as a loss of the application of paraffin. 2. The method as claimed in claim 1, wherein the said winding station is stopped when a loss of paraffin application has been detected, a signal for the operator is additionally generated. 3. The method as claimed in one of claims 1 to 2, wherein the said slippage between the cheese and the friction drum is determined and evaluated as a value which is proportional to the coefficient of friction. 4. The method as claimed in claim 3, wherein the said friction drum transmits drive moment to the bobbin, said drive moment determines the frictional force, which is detected as a function of the slippage and used for evaluating the frictional behavior of the surface of the cheese. 5. The method as claimed in claim 4, wherein during the slippage-free run-out phase loss and load moments acting on the drive system of the friction drum and the cheese are measured and taken into consideration in the determination of the frictional force. 6. The method as claimed in claim 4, wherein the said yarn tensile force is measured, and the slippage value is corrected by changes in the yarn tensile strength during the bobbin travel. 7. The method as claimed in claim 4, wherein the said frictional behavior of the surface of the cheese on the friction drum is evaluated by using the deposit shift, which corresponds to the displacement of a reversing point of the yarn deposit on a circumferential line on the bobbin in respect to the preceding reversing point, is determined as a function of the slippage. 8. The method as claimed in one of claims 1 to 8, wherein the said frictional behavior of the surface of the cheeses on the friction drums of a predeterminable number of winding stations of the bobbin winding machine is averaged and is used as the basis for comparing the frictional behavior at. each individual winding station. In order to improve the running and sliding properties of the yarn during its further processing, in particular for machine- knitting and knitting, it is waxed during rewinding in bobbin winding machines by passing it along a paraffin body. When the paraffin body is used up without this being noticed, the unwaxed yarn can cause yarn breaks or even needle breakages, which leads to production errors or lost production. It is therefore proposed to monitor the slippage at the winding stations where, to prevent pattern windings, the drive of the friction drum is switched on and off at intervals in such a way, that acceleration phases with slippage between the friction drum and the bobbin and slippage- free run-out phase follow each other. If the slippage decreases in successive acceleration phases and remains at a low level, while the drive output of the friction drum remains unchanged, this is considered to be an outage of the paraffin application.

Documents:

2101-cal-1998-granted-abstract.pdf

2101-cal-1998-granted-claims.pdf

2101-cal-1998-granted-correspondence.pdf

2101-cal-1998-granted-description (complete).pdf

2101-cal-1998-granted-drawings.pdf

2101-cal-1998-granted-examination report.pdf

2101-cal-1998-granted-form 1.pdf

2101-cal-1998-granted-form 2.pdf

2101-cal-1998-granted-form 3.pdf

2101-cal-1998-granted-form 5.pdf

2101-cal-1998-granted-pa.pdf

2101-cal-1998-granted-reply to examination report.pdf

2101-cal-1998-granted-specification.pdf