Spinning-mill preparing machine with a control apparatus

Abstract

A method is suggested for operating a spinning-mill preparing machine (1) with a control apparatus (20), especially a draw frame, card or combing machine, in which a running fiber structure (FV) is conducted through a measuring area (26, 26′,33) of a measuring apparatus (25, 25′, 32) and a measuring signal (S(t); Sa(t), Se(t)) is generated that represents the length-specific mass (M) of the fiber structure (FV) located in the measuring area (26, 26′,33), in which a corrected measuring signal (SK(t); SKa(t), SKe(t)) is generated in that a correction value (K0, K1, K2; Ka, Ke) is added to the measuring signal (S(t); Sa(t), Se(t)), and in which the determination of the correction value (K0, K1, K2; Ka, Ke) takes place by the following steps controlled by the control apparatus (20) of the spinning-mill preparing machine (1): The fiber structure (FV) is removed from the measuring area (26, 26′,33) by pneumatic and/or mechanical means (27, 13,14; 28), Then, an empty measuring is performed, and The correction value (K0, K1, K2; Ka, Ke) is calculated in that the empty measuring value obtained in this manner (SL0, SL1, SL2) is subtracted from a theoretical value (SLSoll) of the measuring signal (S(t); Sa(t), Se(t)) which value is predefined for an empty measuring.

Description

The present invention relates to a method for operating a spinning-mill preparing machine with a control apparatus, especially a draw frame, card or combing machine, in which a running fiber structure is conducted through a measuring area of a measuring apparatus and a measuring signal is generated that represents the length-specific mass of the sliver located in the measuring area. The present invention also concerns a spinning-mill preparing machine, especially a draw frame, card or combing machine, with a control apparatus and at least one measuring apparatus for generating a measuring signal that represents the length-specific mass of a fiber structure conducted through the measuring area of the measuring apparatus.

In a short-staple spinning mill at first a rather long fiber structure is produced from raw fibers that have a length of a few centimeters in several process steps. The raw fibers can consist of cotton, various artificial fibers or of a mixture of the same.

In a process for the manufacture of yarn that is customary at the present a closed fiber structure is manufactured by a card from fed raw fibers. In the card an areal fiber structure, a so-called fiber fleece, is produced at first that is then combined to a strand-shaped fiber structure, generally called a sliver. This sliver is evened out further by following draw frames and optionally by combing machines. The sliver produced in this manner is finally fed to a spinning machine for producing a twisted yarn.

The quality of the spun yarn depends in particular on the uniformity of the fed sliver. Therefore, spinning-mill preparing machines are provided with apparatuses for evening out and monitoring the uniformity of the fiber structure. Such apparatuses for evening out or monitoring the quality are connected to sensors that detect the length-specific mass of the sliver. The length-specific mass of a fiber fleece or of a sliver is indicated in the dimension of mass per unit of length and is at the same time a measure for the thickness of the fiber structure at a certain location.

It has been known for some time that the mass and the thickness of a running fiber structure can be detected by mechanical scanning systems. Furthermore, contactless sensors have been suggested that operate, e.g., according to a capacitive measuring process, an irradiation process, a reflection process or according to a resonance process.

Independently of the measuring principle, sensors for detecting the sliver mass and/or sliver thickness have a characteristic curve that describes the connection between the mass of the fed sliver or fiber fleece and between a generated output signal. It is known in order to monitor the observance of a defined theoretical characteristic curve of a mechanical scanning system that a plurality of measuring gauges of different but known thicknesses can be fed to the particular scanning system. Such gauges are also designated as check gauges. The thickness of the different check gauges is distributed over the measuring area of the sensor. In as far as differences are determined between the actual output signal and the particular theoretical output signal of the sensor the sensor is manually readjusted.

However, such a compensating method can not be used in the case of sensors operating in a contactless manner. It is also hardly possible to compensate a contactless sensor by feeding fiber structures with a defined mass since the latter can not be manufactured with the required accuracy. Furthermore, drafts conditioned by the manipulation and due to the loose inner cohesion of a fiber structure can not be avoided, so that the fed fiber structure would change its length-specific mass during a compensation procedure. It is therefore necessary as a rule in order to compensate a contactless sensor to check a fiber structure measured by the sensor subsequently in the lab and then adapt the sensor manually, for which several iteration steps are normally necessary.

Such manual methods for compensating a sensor for detecting the fiber structure thickness in a spinning-mill preparing machine require a lot of time and are therefore only performed in practice upon the occurrence of serious quality deviations in the manufactured fiber structure.

Deviations of measurement of a sensor that are located in the interval between two such steps for sensor compensation can not be detected in this manner and consequently also not be corrected. In particular, short-term fluctuations in the environmental conditions such as, e.g., variations in temperature or changes in the air humidity result in measuring errors that result on the one hand in a deterioration of the action of the evening-out apparatuses and on the other hand in unsatisfactory quality data. However, even other error sources are problematic such as, e.g., mechanical wear or contamination of the sensor.

The present invention has the goal of eliminating the described problems in conjunction with the detection of the sliver mass or thickness in a running fiber structure in a spinning-mill preparing machine.

This goal is achieved with a method for operating a spinning-mill preparing machine as well as with a spinning-mill preparing machine with the features of the independent claims.

In a method in accordance with the invention a correction of the measuring signal of the measuring apparatus takes place in that a correction value is added to the measuring signal and that the determination of the correction value takes place by following steps controlled by the control apparatus of the spinning machine. At first, the fiber structure is removed from the measuring area by pneumatic and/or mechanical means. In other words, the measuring area and the fiber structure are separated from one another spatially in such a manner that the fiber structure to be actually measured no longer influences the measuring signal. Then, an empty measuring is carried out and the correction value calculated in that the empty measured value of the measuring signal obtained by the empty measuring is subtracted from a predefined theoretical value of the measuring signal. In the method of the invention the complicated feeding of fiber structure specimens with a defined mass can be completely eliminated. The method can also be carried out in a few seconds.

The measuring area of a measuring apparatus is that spatial area in which the mass of the fiber structure is detected by the particular measuring method. The concept “measuring area” is therefore to be abstractly understood. It is of no significance whether the measuring area is defined physically or conceptually.

Once a correction value has been determined, it is used for correcting the measuring signal until a new correction value is determined. As a consequence of the low amount of time involved, the determination of new correction values can take place in relatively short time intervals. The correction value can assume positive or negative values and the proper sign of the addition to the measuring signal is to be observed. The suggested method can be used in continuous or discrete measuring methods. It is also of no consequence whether the measuring signal is present in digital or in analog form. The predefined theoretical value of the measuring signal in an empty measuring can be taken from the theoretical characteristic curve of the measuring apparatus or determined in a phase prior to operation.

The fiber structure can be removed from the measuring device in an especially simple manner for performing an empty measuring if a measuring device is used whose measuring area transverse to the longitudinal direction of the running fiber structure is open at least on one side. The fiber structure can then be removed from the measuring area by moving the fiber structure relative to the measuring area or the measuring area relative to the fiber structure transversely to the direction of movement of the fiber structure.

In this instance it is advantageous if the measuring area is moved and the fiber structure left in its original position. This can avoid an erroneous drafting of the sensitive fiber structure. The measuring area can be moved here in a straight line and/or in a curved line.

However, it is also conceivable to remove the fiber structure from the measuring area with a movable fiber structure guidance means, e.g., with a roller, hook, eyelet or a grasper.

It is also possible to remove the fiber structure from the measuring area by separating it upstream from the measuring area and by drawing the downstream section of the fiber structure out of the measuring area.

The determination of a new correction value preferably takes place when a deviation of quality is determined in the produced fiber structure by an automatic quality detection system associated with the spinning-mill preparing machine. The determination of a new correction value can take place for a sensor that supplies measuring signals directly to the quality detection system as well as for any other sensor.

The determination of a new correction value is advantageously initiated regularly after the passage of a certain time span. This takes place without an operational intervention automatically by the control apparatus. Likewise, the determination of a new correction value can be initiated regularly after a certain length of the fiber structure running through. In both instances a regular correction of the measuring signal of the measuring apparatus is ensured.

The fiber structure is frequently deposited in a spinning can at the discharge of a spinning-mill preparing machine. Filled cans must be regularly replaced by empty cans. It is appropriate in this instance to control the empty measuring for determining the correction value by the control apparatus in such a manner that it takes place regularly during a can replacement. The determination of the correction value can take place at each can replacement or, e.g., at each second or third can replacement.

Furthermore, it is possible that the determination of a correction value is automatically initiated alternatively or additionally immediately after the turning on the spinning-mill preparing machine by the control apparatus. In this instance the determination of a new correction value takes place independently of whether a can replacement is necessary or not. Changes in the environmental conditions such as, e.g., the temperature, that occurred during the service life of the spinning-mill preparing machine are therefore directly taken into consideration. The regular new determination can nevertheless continue to be carried out during a can replacement.

It is advantageously provided that the determination of a new correction value is initiated, even outside of any regular new determination of the correction value provided, by the control apparatus when the corrected measuring signal reaches a set threshold value. In this instance in particular an upper and a lower threshold value can be defined. In this instance a reaching or even a dropping below the upper boundary value as well as a reaching or a dropping below the lower boundary value result in a new determination of the correction value. If the old and the new correction values do not differ substantially from one another, this indicates an actual change of the mass of the fiber structure. Otherwise, a change in the measuring behavior of the measuring apparatus is obviously present.

The presetting of threshold values that can be defined absolutely or relatively can be checked automatically to see whether unusually high or unusually low values of the corrected measuring signal are based on an actual increase or decrease of the mass of the fiber structure or, e.g., on a change (drift) of the measuring behavior of the measuring apparatus. In the former instance a warning notice can then be emitted so that the operator is made aware of the unusual deviation of the mass of the fiber structure. If necessary, an interruption of the manufacture can also take place in order to prevent unnecessary waste. In the latter instance the drift of the measuring apparatus is automatically corrected by the new correction value.

It can also be provided that a new determination of the correction value is initiated by the control apparatus when the corrected measuring signal rises or falls by more than a set amount within a certain time span. The plausibility of such unusual measured values can also be automatically checked in this instance. If necessary, the already mentioned measures can be initiated.

It can be additionally or alternatively provided that the determination of the correction value is initiated by an operator action. Thus, the determination of a correction value is also possible outside of the provided cycles if, e.g., there is justified doubt about the correct functioning of the measuring apparatus. The determination of the correction value itself then takes place without additional input of the operator by the control apparatus of the spinning-mill preparing machine.

It is especially advantageous if the fiber structure is threaded into the measuring area after the empty measuring by pneumatic and/or mechanical means controlled by the control apparatus and is supplied to a pulling-off means controlled by the control apparatus and arranged downstream from the measuring area. The pulling-off means can be, e.g., a pair of pulling-off rollers. In this instance the manual threading in of the fiber structure is eliminated after an empty measuring.

It is especially advantageous if the manufacture of the spinning-mill preparing machine is automatically started after the threading in and supplying to the pulling-off means. In this manner interruptions of manufacture can be reduced to a minimum.

It is furthermore advantageous if the measuring area is cleaned after the removal of the fiber structure and before the empty measuring. This can prevent influences of contamination on the measuring signal. Contaminations frequently consist of accumulations of particles of fibers or of dirt. The cleaning of the measuring area is advantageously controlled by the control apparatus of the spinning-mill preparing machine.

The measuring area can be cleaned by a fluid, e.g., by compressed or suction air and/or by mechanical cleaning means.

A warning notice is preferably emitted and/or the spinning-mill preparing machine brought to a standstill if the determined correction value exceeds a predefined threshold value. This is appropriate since especially large deviations between the theoretical value and the actual value in an empty measuring indicate an especially strong contamination and/or a defective functioning of the spinning-mill preparing machine. A warning notice puts the user in the position of reacting appropriately. A stopping of the spinning-mill preparing machine prevents unnecessary waste.

In principle, the measuring signal can be generated using any known physical method. However, a mechanical scanning method, a capacitive measuring method, an irradiation method, a reflection method and/or a resonance method is/are preferably used for generating the measuring signal. The performing of a resonance method using microwaves is especially preferred since in this manner the mass and/or thickness of the fiber structure can be measured independently of the material moisture.

In an advantageous embodiment the running fiber structure is conducted through a measuring area of a measuring apparatus arranged at the inlet of the spinning-mill preparing machine and through a measuring area of another measuring apparatus arranged at the outlet of the spinning-mill preparing machine and the measuring signal of the measuring apparatus at the inlet is corrected by a correction value and the measuring signal of the measuring apparatus at the outlet is corrected by another correction value. As a result thereof, very accurate measured values can be made available for the regulation (open-loop and/or closed-loop control) of the spinning-mill preparing machine or for the quality monitoring.

It is appropriate that the measuring apparatus arranged at the inlet is compensated if unusual measuring results occur in the measuring apparatus at the outlet. This is especially valid if the corrected measuring signal of the measuring apparatus arranged at the outlet reaches or exceeds a predefined upper threshold value or predefined lower threshold value, or if the corrected measuring signal of the measuring apparatus arranged at the outlet rises or falls by more than a fixed amount within a certain time span, or if the further correction value reaches or exceeds a fixed maximum correction value or a minimum correction value.

It is especially advantageous if the determination of a new further correction value for correcting the measuring signal of the measuring apparatus at the outlet is initiated automatically by the control apparatus if the corrected measuring signal of the measuring apparatus arranged at the outlet reaches or exceeds a predefined upper threshold value or a predefined lower threshold value, or if the corrected measuring signal of the measuring apparatus arranged at the outlet rises or falls by more than a fixed amount within a certain time span, or if the previous further correction value reaches or exceeds a fixed maximum correction value or a minimum correction value.

If the newly determined further correction value deviates from the previous further correction value by less than a predetermined amount, this indicates a defective functioning of the regulation in front of the measuring apparatus at the outlet. In this instance the determination of a new correction value for correcting the measuring signal of the measuring apparatus at the inlet is automatically initiated by control apparatus 20. To the extent that the defective functioning of the regulation was based on a defective correction value of the measuring apparatus at the inlet, it is now corrected. Otherwise, e.g., an alarm can be released.

A spinning-mill preparing machine in accordance with the invention comprises a correction member for the addition of a correction value to the measuring signal. In this instance the control apparatus of the spinning-mill preparing machine is designed to control a method for determining the correction value using at least one empty measuring. This can eliminate a manual compensation of the measuring apparatus of the spinning-mill preparing machine.

Means for removing the fiber structure from the measuring area are advantageously present that can be controlled by the control apparatus. This can eliminate even the manual removal of the fiber structure.

If the measuring area is open at least on one side transversely to the longitudinal direction of the fiber structure the means for removing the fiber structure can advantageously be designed in such a manner that a relative movement is possible between the fiber structure and the measuring area transversely to the direction of movement of the fiber structure. This can avoid a separating of the fiber structure.

However, if the measuring area is closed on all sides so that it surrounds the fiber structure on all sides the means for removing the fiber structure can be designed in such a manner that the fiber structure can be separated upstream from the measuring area, for which pull-off means, e.g., calender rollers are provided for drawing the downstream section of the fiber structure out of the measuring area. For example, means comprising cutting or tearing tools can be provided for separating the fiber structure. Alternatively, a thin area can be produced in the fiber structure by an appropriate controlling of the roller pairs of a draw frame located in front, which thin area would result in a separation of the fiber structure. It is immaterial in this instance whether the roller pairs are driven via a regulating transmission by a common motor or by individual drives. It is possible in both instances to separate the fiber structure by differences in speed between the roller pairs. Likewise, the separation can take place in that the draw frame located in front is entirely stopped while maintaining the clamping of the fiber structure but the pull-off means continues to be driven.

It is especially advantageous if the control apparatus is designed for automatically initiating the determination of the correction value. This initiation regularly takes place in an advantageous manner after the expiration of a certain time span or after a certain amount or length of the fiber structure running through.

The control apparatus can also be designed to initiate the determination of a correction value after the spinning-mill preparing machine has been turned on.

If a depositing can is arranged downstream from the measuring apparatus the control apparatus can be designed to initiate the determination of the new correction value during a can replacement.

The spinning-mill preparing machine is advantageously designed to automatically initiate the determination of the correction value when the corrected measuring value reaches a fixed a threshold value.

The spinning-mill preparing machine can also be designed in such a manner that it automatically initiates the determination of the correction value if the corrected measuring signal rises or falls by more than a set amount within a certain time span.

If the control apparatus is connected to an operating element it is advantageous if the control apparatus is designed to initiate the determination of the corrected value after an operator action. An operator-initiated new determination of the correction value can also be performed, e.g., during the filling of a can that is, when no can replacement is taking place.

Furthermore, it is preferred that pneumatic and/or mechanical means for threading in the fiber structure and controlled by the control apparatus is present in the measuring area, which control apparatus is designed to automatically initiate the threading in after an empty measuring. The threading in brings about a feed of the fiber structure to a pull-off means controlled by the control apparatus and arranged downstream relative to the measuring area. It can be, e.g., a pair of calender rollers.

The control apparatus is advantageously designed to independently start the production after the threading in and the feeding of the fiber structure to the pull-off means.

It can additionally be provided that means controllable by the control apparatus is provided for cleaning the measuring area with mechanical cleaning agent or a fluid supplied under pressure, preferably by compressed or suction air. The control apparatus is designed in this instance to automatically initiate a cleaning procedure.

Furthermore, the control apparatus can be designed to control the emitting of a warning notice, e.g., by an output device connected to the control apparatus and/or to initiate a cutoff of the spinning-mill preparing machine if the correction value exceeds a predefined value.

The measuring apparatus is advantageously designed to carry out a mechanical scanning process, a capacitive measuring process, an irradiation process, a reflection process and/or a resonance process.

Other advantages of the invention are described in the following exemplary embodiments.

FIG. 1 shows a sketch of a draw frame in accordance with the state of the art.

FIG. 2 shows a sketched partial view of a draw frame in accordance with the invention.

FIG. 3 shows a detailed view of an alternative embodiment.

FIG. 4 shows a presentation of an uncorrected measuring signal and of a corrected measuring signal over the course of time.

FIG. 1 shows draft frame 1 as an example for a spinning-mill preparing machine in accordance with the state of the art. However, the invention also relates to other spinning-mill preparing machines, in particular cards or combing machines to the extent that they comprise a control apparatus 20 and at least one measuring apparatus 25, 25′, 32 for generating a measuring signal S(t) representing the length-specific mass of a fiber structure conducted through a measuring area 26, 26′, 33 of the measuring apparatus.

Six individual slivers FB are fed adjacent to each other to schematically shown draw frame 1. Slivers FB are shown from above whereas draw frame 1 is shown as such in a lateral view. Funnel 12 is arranged at the input to draw frame 1 and compresses slivers FB to a single fiber structure FV. After having run through a first measuring apparatus that generates a measuring signal S_e(t) representing the length-specific mass of fiber structure FV that was conducted through it, the now compressed fiber structure FV is conducted into draw frame 4 forming the core piece of the draw frame.

Draw frame 4 comprises entrance roller pair 5a, 5b, middle roller pair 6a, 6b and exit or also delivery roller pair 7a, 7b that rotate with a circumferential speed that is increased in this sequence. As a result of these different circumferential speeds of the roller pairs, fiber structure FV, that is spread out like a fleece in the draw frame, is drafted according to the ratio of the circumferential speeds.

Entrance roller pair 5a, 5b and middle roller pair 6a, 6b form the so-called pre-drafting field, and middle roller pair 6a, 6b and delivery roller pair 7a, 7b the so-called main drafting field. In unregulated draw frames both the pre-draft and the main draft are constant during the drafting procedure. On the other hand, in regulated draw frames a compensatory regulation of fluctuations in the mass of the fiber composite takes place by changing the draft height. In this instance the main draft is usually changeable since the main draft is as a rule greater that the pre-draft, so that a more accurate compensatory regulation of variations in thickness of the fiber structure can take place.

Pressure rod 8 additionally arranged in the main draft field deflects fiber structure FV and thus ensures a better guidance of the fibers. The drafted fiber structure FV is then deflected with the aid of upper deflection roller 9 and fed to sliver forming apparatus 10. Sliver forming apparatus 10 is designed as funnel 10 and serves to compress the fiber fleece to a unified sliver. Measuring apparatus 25 is arranged at the output of funnel 10 and comprises measuring area 26 in which the mass of fiber structure FV that was conducted through it is detected. This mass and/or thickness is converted into a measuring signal 5a(t) by sensor electronics (not shown).

Measured fiber structure FV is pulled off by calander roller pair 13, 14 and fed to depositing can 24. Depositing can 24 comprises rotary plate 17 rotating about its vertical axis of plane and with sliver conduit 16 for depositing fiber structure FV into can 18. Can 18 itself is moved by means (not shown) in the case of a square can translatorily and in the case of a round can rotationally relative to stationary rotary plate 17. As a result thereof, the entire inner area of can 18 can be filled with deposited fiber structure FV. Once a can 18 has been completely filled it can be replaced with an empty can manually by an operator or by can replacement device 19 (shown only schematically).

Draw frame 1 comprises control apparatus 20 that controls in particular the speed of the roller pairs of draw frame 4. To this end it acts on the drives (not shown) of the roller pairs. Likewise, control apparatus 20 acts on roller pair 2, 3 at the entrance of the draw frame, on the calender roller pair 13, 14 at the exit of the draw frame and on the speed of rotary plate 17 of depositing can 24. Furthermore, control apparatus 20 can be designed to control can replacement apparatus 19. As is customary, control apparatus 20 is connected to operating apparatus 22, e.g., a keyboard, and to output unit 23, e.g., a viewing screen.

In addition, draw frame 1 comprises quality monitoring system 21 designed to monitor the quality of the fiber structure produced.

The first measuring apparatus 32 comprises measuring area 33 and two scanning disks 2, 3 of which scanning disk 2 is designed to be stationary and scanning disk 3 is pressed with pressure against scanning disk 2 and can be deflected vertically to its axis of rotation. The deflections of scanning disk 3 are a measure for the mass of fiber structure FV. The deflection is produced e.g., with an inductive sensor (not shown) that generates measuring signal S_e(t). Measuring signal S_e(t) is then taken from control apparatus 20 for changing the pre-draft and/or the main draft of draw frame 4. This can stabilize fluctuations of the mass of the fiber structure. Such a method is also designated as open-loop control of the draw frame.

Measuring apparatus 25 at the outlet of draw frame 4 comprises measuring area 26 through which fiber structure FV is conducted and measured in a contactless manner. The using of a contactless sensor is especially advantageous here since the speed of the running fiber structure at the outlet of the draw frame is by nature clearly greater than at its entrance side. Measuring signal S_a(t), that is generated by measuring apparatus 25 by sensor electronics (not shown) is evaluated by quality detection system 21. In particular, the average thickness of the sliver and the non-uniform areas remaining in the fiber structure are detected. If the quality of the exiting fiber structure does not meet the requirements, e.g., a signal can be transferred from quality detection apparatus 21 to control 20 and the machine can be stopped. Also, a report to the operator can be made, e.g., via output unit 23.

Measuring signal S_a(t) of measuring apparatus 25 at the outlet of draw frame 4 is frequently also directly transmitted to control apparatus 20. Thus, e.g., the spinning-mill preparing machine can be cut off autonomously by control apparatus 20 on account of deficient quality. It is also conceivable that measuring signal S_a(t) can be used to control the draft of draw frame 4. The closed-loop control realized in this manner is particularly suitable for stabilizing long-term deviations in the direction of the theoretical value.

On the whole, an optimal stabilization of fluctuations of the running fiber structure is only possible if the measuring signals S(t) of measuring apparatuses 32, 25 used for this are sufficiently accurate. Also, an expressive determination of quality is only possible with a correspondingly accurate measuring signal S_a(t) of measuring apparatus 25.

Measuring apparatuses of spinning-mill preparing machines are therefore compensated or adjusted in complicated manual methods. To this end check gauges with known thicknesses are manually presented in mechanically scanning measuring apparatuses and the measuring signals S(t) compared with the theoretical value in accordance with the theoretical characteristic curve of the particular measuring apparatus. This customarily takes place with a plurality of check gauges with different thicknesses that cover the entire measuring area of the particular measuring apparatus. After such measuring series have been manually performed the particular measuring apparatus is then compensated or readjusted. In contactless measuring systems measuring results of the measuring apparatus are subsequently checked in the laboratory. In the case of deviations the sensor characteristic is changed in iterative steps until an appropriate coincidence of the measured results of the sensor and of the results measured in the laboratory occurs.

Such compensating methods can only be carried out at relatively large time intervals on account of the relatively high cost. However, influencing magnitudes on measuring signal S(t) that rapidly change in time can therefore not be detected and falsifications occurring as a result thereof cannot be corrected. Falsifications of measuring signal S(t) produced by a change of temperature of the measuring apparatus can be cited here. Also, falsifications of the measured results can take place due to contamination adhering in the measuring apparatus. Falsifications of the measured results due to temperature influences or contamination emerge in a more or less pronounced manner in all known measuring methods.

FIG. 2 shows part of a draft frame 1 in which measuring signal S_a(t) of measuring apparatus 25 arranged at the exit as well as measuring signal S_e(t) of measuring apparatus 32 arranged at the entrance are corrected in a manner in accordance with the invention. However, the invention could just as well be realized exclusively at the entrance or exclusively at the exit of the draw frame.

The invention will first be explained in detail using the example of measuring apparatus 25 arranged at the exit. Measuring apparatus 25 detects the mass of fiber structure FV running through in the manner already described and generates a measuring signal S_a(t) from it. This measuring signal S_a(t) is fed to correction member 31_a. Correction member 31_a is formed for the addition of a correction value K_a to measuring signal S_a(t). Corrected measuring signal SK_a(t) generated in this manner can be used in the manner already described for carrying out a closed-loop control by control apparatus 20 as well as for detecting the quality of the fiber structure by quality detection apparatus 21. Correction value K_a is determined by a method that is completely controlled by control apparatus 20.

In the example shown, correction value K_a is calculated by control apparatus 20 and mediated to correction member 31_a. Alternatively, correction member 31_a could be designed to independently calculate correction value K_a. It is also possible to integrate correction member 31_a into control apparatus 20. Correction value K_a is determined by an empty measuring and used for correcting measuring signal S_a(t) until a new value K_a is determined. The determination of a new correction value K_a takes place upon the occurrence of a predetermined condition by control 20. Such a condition can be an operator action on input unit 22, the expiration of a certain time or a certain length of fiber structure FV conducted through measuring apparatus 25. The determination of a new correction value K_a advantageously takes place during a necessary can replacement.

When can 18 located under rotary plate 17 is full, control apparatus 20 initiates the replacement of spinning can 18 by can replacement apparatus 19 provided for this purpose. At the same time a separation of the fiber structure takes place by means 27 for separating the fiber structure and controlled by control apparatus 20. Means 27 is designed and arranged in such a manner that the separation of fiber structure FV takes place upstream from measuring apparatus 25. Means 27 for separating the fiber structure can comprise, e.g., cutting or tearing tools. Alternatively, a thin area could be produced in the fiber structure by appropriately regulating the roller pairs of draw frame 4, which would result in a separation of the fiber structure. Likewise, the separation can take place in that draw frame 4 is entirely stopped while maintaining the clamping of fiber structure FV but calender roller pair 13, 14 continues to be driven. The only important factor is that the separation takes place upstream from measuring area 26.

After the separation the fiber structure consists of an upstream section FV_ab and of a downstream section FV_zu. Calender roller pair 13, 14 is now controlled in such a manner by control 20 that downstream section FV_ab of the fiber structure is completely removed from measuring area 26 of measuring apparatus 25. At the same time the transport of the upstream section of fiber structure FV_zu is interrupted by control apparatus 20. Measuring area 26 of measuring apparatus 25, that has now been emptied, can now be cleaned with the aid of means 30 for cleaning the measuring area. Means 30 for cleaning measuring area 26 can be controlled by control apparatus 20. The actual cleaning of measuring area 26 takes place by blowing in compressed air, which is indicated by the arrow in dotted lines. Means 30 could alternatively or additionally be designed for cleaning measuring area 26 by suction air and/or by mechanical means.

An empty measurement takes place after the cleaning of measuring area 26 during which empty measuring value SL₀ is compared with theoretical value SL_soll. Correction value K is determined by subtracting instantaneous value SL₀ of measuring signal S_a(t) from given theoretical value SL_soll. If necessary, even several empty measurements could be carried out successively during which the particular results for determining correction value K_a could be averaged.

The threading in of the front end of the upstream section of fiber structure FV into measuring area 26 of measuring apparatus 25 takes place after the empty measurement. To this end control apparatus 20 transmits control impulses to pneumatic threading-in means 29. At the same time control commands to the rollers of draw frame 4 occur, so that the upstream section of the fiber structure is transported further. The threading of the fiber structure into measuring area 26 takes place by the controlled emission of impulses of compressed air into funnel 10, which is indicated by the arrow in dotted lines. The threading-in could also take place by suction air or a combination of suction air and compressed air.

The compressed air flow generated by threading-in apparatus 29 and the formation of measuring area 26 and its relative arrangement to calender roller pair 13, 15 bring it about that the front end of fiber structure FV, which has now been threaded in, can be grasped and pulled off by calender roller pair 13, 14. Calender roller pair 13, 14 is arranged for its part in such a manner relative to rotary plate 17 that fiber structure FV that is now running is automatically introduced into sliver conduit 16.

The described method can be carried out within the time span that is required in any case for an automatic can replacement. It can therefore be performed several times daily or even several times hourly without limiting the productivity of the draw frame. Falsifications of measuring signal S_a(t) of measuring apparatus 25, e.g., due to contamination, temperature influences or to environmental influences can be rapidly corrected. It is not necessary to differentiate between the various disturbing influences. Although the method for operating the spinning-mill preparing machine is preferably carried out completely automatically, it can also be used in principle if the spinning-mill preparing machine does not have an automatic can replacement device 19 available. Thus, it can be provided that the full can is removed by an operator and replaced by an empty can. In this instance the threading in of the separated fiber structure and the resumption of production take place only after an operator action in order to prevent a sliver from being produced without an available spinning can.

Measuring signal S_e(t) of measuring apparatus 32 arranged at the inlet of draw frame 1 is corrected in an analogous manner. At first, it is transmitted to correction member 31_e and converted there into a corrected measuring signal SK_e(t) by the addition of correction value K_e determined by control apparatus 20. The determination of correction value K_e takes place as described above in the example of measuring apparatus 25 arranged at the outlet of draw frame 1 on the basis of at least one empty measurement. Means for cleaning measuring area 33 and means for removing sliver FV from measuring area 33 of measuring apparatus 32 are not shown but could be provided at the entrance.

When the corrected measuring signal SK_a(t) of measuring apparatus 25 arranged at the outlet reaches or exceeds a predefined upper threshold value SW₀ or a predefined lower threshold value SW_u, the determination of a new correction value K_a is automatically initiated by control apparatus 20. This can also take place if measuring signal SK_a(t) rises or falls by a certain value within a certain time span. If the new correction value K_a does not differ substantially from the previous correction value K_a this indicates an actual increase or decrease of the mass of fiber structure FV. In addition, a certain difference can be determined between the new and the previous correction value K_a and when it is maintained, an actual increase or decrease of the mass of fiber structure FV is assumed. If the set difference is exceeded there is obviously a drift relative to the measuring characteristic of measuring apparatus 25 that is then compensated by the new correction value K_a.

In case of an actual change of the mass of fiber structure FV the regulating of the draw frame does not function satisfactorily. The cause of this can be a drift of the measuring characteristic of measuring apparatus 32 arranged at the entrance since its measuring signals S_e(t) are used to regulate the draft of draw frame 4. Therefore, the determination of a new correction value K_e for measuring apparatus 32 arranged at the entrance of draw frame 1 is initiated by control apparatus 20. To the extent that the new and the old correction values K_e substantially coincide, there is obviously another disturbance and a warning notice can be emitted or the machine can be stopped in order to avoid unnecessary waste. However, if the old and the new correction values K_a sufficiently differ, the operation of the machine is restarted. In this instance too a minimal difference can be set in order to distinguish the cited instances. Finally, the observance of the given threshold values is again monitored by measuring apparatus 25 arranged at the outlet and by control apparatus 20 and a warning notice or a production stop initiated if necessary.

FIG. 3 shows an alternative arrangement for removing fiber structure FV out of measuring area 26′, that is open to its left side and can be arranged, e.g., at the outlet of a draw frame 1 (FIG. 2). Measuring area 26′ is supported in such a manner that it can be shifted transversely to the running direction of fiber structure FV. Measuring area 26′ can be moved to the right with the aid of means 28 controlled by control apparatus 20 (FIG. 2) in order to remove fiber structure FV from measuring area 26 in order to carry out an empty measuring. This straight-line shift is indicated by the double arrow. However, the movement of the measuring area can also take place in principle in a curved line, e.g., as a pivoting motion.

The measuring area could also be arranged to be stationary and the fiber structure could be pivoted out laterally from the measuring area by controllable grippers, hooks, eyelets or the like. It is not necessary in measuring apparatus 25′ according to FIG. 3 to separate fiber structure FV in order to perform an empty measuring.

In the position of measuring area 26 shown an empty measuring can be carried out as described. Means 28 for carrying out the relative movement between fiber structure FV and measuring area 26 is also controlled by control apparatus 20. Means 28 for removing the fiber structure from the measuring area is designed at the same time as a means for threading in the fiber composite into measuring area 26 after an empty measuring. During this time measuring area 26 is moved back to the left into its initial position (see FIG. 2). In order to carry out a movement of measuring area 26 means 28 for removing and threading in fiber structure FV into the measuring area comprises a pneumatic and/or mechanical drive.

FIG. 4 shows a typical course in time of measuring signal S(t) and of corrected measuring signal SK(t) when carrying out the method of the invention. At a time t₀ the spinning-mill preparing machine is turned on by its main switch. Since no fiber structure is being transported through the measuring area yet, measuring signal S(t) assumes the course of a horizontal straight line at first. At time t₁ an empty measuring is automatically performed. Since the value S(t₀) corresponds to theoretical value SL_soll of an empty measuring, a correction value K₀ with value 0 is determined at first.

At time t₂ the production of the spinning-mill preparing machine is begun. A fiber structure FV with the average and uniform sliver mass SB is conducted through measuring area 26 of measuring apparatus 25. Measuring signal S(t) has a wave form in this area due to the variations of mass present in running fiber structure FV. In an ideal measuring apparatus 25 the measuring signal S(t) would oscillate around value SB. However, measuring signal S(t) of real sensor 25 present increasingly deviates upward from line SB in the course of time. The cause for this can be grounded, e.g., in a temperature rise of the measuring apparatus conditioned by the operation or in increasing contamination of the measuring apparatus.

At time t₃ a first can replacement KW₁ is initiated. Measuring signal S(t) falls to a value SL₁ after the fiber structure was removed from measuring area 26. At time t₄ a new empty measuring takes place. However, the measured value SL₁ obtained in this manner deviates up from the theoretical value of an empty measuring SL_soll. Therefore, a new correction value K₁ equal to SL_soll−SL₁ is calculated. This new correction value K₁ is added at time t₅ with the proper sign to measuring signal S(t). The corrected measuring signal SK(t) therefore deviates from time t₅ downward from measuring signal S(t) by value K₁.

At time t₆ the production is restarted. In this second production phase the corrected measuring signal SK(t) deviates downward from measuring signal S(t) at each point in time by correction value K₁. Due to the further increase of disturbing influences, measuring signal S(t) and corrected measuring signal SK(t) increasingly deviate up from value SB, that corresponds to the average sliver weight. A second can replacement KW₂ takes place in time window t₇ to t₁₀. A new empty measuring is carried out at time t₈, wherewith a new correction value K₂ is calculated. This new correction value K₂ is added from time t₉ to measuring signal S(t). As a consequence thereof, corrected measuring signal SK(t) is moved closer to its theoretical line during the resumption of production at time t₁₀.

A lower threshold value SW_u and an upper threshold value SW_o are determined for the corrected measuring signal. If one of the two threshold values SW_u, SW_o is reached or exceeded, which is not shown in FIG. 4, an empty measuring would take place in order to determine a new correction value independently of the can replacements KW₁, KW₂.

FIG. 4 serves to basically explain the operating method of the invention for a spinning-mill preparing machine. The courses shown for measuring signal S(t) and for corrected measuring signal SK(t) are not shown true-to-scale. Note concerning the course in time that that in a real production operation the ratio of the time of a can replacement and of a production phase is distinctly higher. In the exemplary instance shown, measuring signal S(t) migrates upward from its theoretical value. However, even those instances can be corrected with the method in which the measuring signal S(t) deviates downward from the value SB. Only the detection of the value K with the proper sign as well as its addition with a proper sign to measuring signal S(t) is essential here.

The present invention is not limited to the exemplary embodiments shown and described but rather modifications are possible at any time within the scope of the patent claims. For example, it can be provided that several empty measurings (that are then to be averaged or weighted) are carried out in order to determine a correction value.

Claims

1. A method for operating a spinning-mill preparing machine (1) with a control apparatus (20), especially a draw frame, card or combing machine, in which a running fiber structure (FV) is conducted through a measuring area (26, 26′,33) of a measuring apparatus (25, 25′, 32) and a measuring signal (S(t); Sa(t), Se(t)) is generated that represents the length-specific mass (M) of the fiber structure (FV) located in the measuring area (26, 26′,33), characterized in that a corrected measuring signal (SK(t); SKe(t), SKa(t)) is generated in that a correction value (K0, K1, K2; Ka, Ke) is added to the measuring signal (S(t); Sa(t), Se(t)) and that the determination of the correction value (K0, K1, K2; Ka, Ke) takes place by the following steps controlled by the control apparatus (20) of the spinning-mill preparing machine (1):

The fiber structure (FV) is removed from the measuring area (26, 26′,33) by pneumatic and/or mechanical means (27,13,14; 28),

Then, an empty measuring is performed, and

The correction value (K0, K1, K2; Ka, Ke) is calculated in that the empty measuring value obtained in this manner (SL0, SL1, SL2) is subtracted from a theoretical value (SLsoll) of the measuring signal (S(t); Sa(t), Se(t)) which value is predefined for an empty measuring.

2-39. (canceled)