EP0678601A2 - Controlled draw frame - Google Patents

Abstract

In the chain of fibre processing stages, where each stage affects the character of the final prod. the characteristics of the material are set at an intermediate stage where subsequent stages cannot be controlled. At the intermediate stage, signals are generated to represent fixed elements of the character of the intermediate prod. which can be related at the working of the previous stages. Pref. the signals from the intermediate stage are used to correct the working of at least one previous stage. One signal represents the short fibre portion in the material delivered by the combing stage, whcih can be used to correct and adjust the complete process line. A guide signal from the drawing unit is used to correct the sections where the material is prepd. for drawing. <IMAGE>

Description

The invention relates to the use of regulating drafting systems, i.e. Drafting systems in which the draft can be controlled or regulated in order to even out fluctuations in mass in a fiber structure. Such drafting systems are often used in so-called regulating lines in short fiber spinning, but can also be used on cards, combing machines and combing preparation machines in short fiber spinning. The same principles are of course also suitable for use in long-staple spinning.

The principles of control technology have been used in regulating drafting systems for several decades. This has made it possible to continuously improve the quality of the fiber assemblies processed (provided this quality is determined solely by the uniformity of the mass per unit length).

As a last measure before final spinning, fiber bundles are often subjected to a draft in a regulating drafting system in order to improve the uniformity of the bandage before feeding into the final spinning process.

At least the last regulating drafting device or the last uniformity regulation before spinning is intended as a control center, specifically for the uniformity of the intermediate products from the processing stages preceding and supplying the corresponding processing stage.

In the conventional spinning mill, the route of the second passage serves as the stage which protects the final spinning stage from fluctuations in the uniformity of the preparation machines (blowroom, carding and combing).

Over the same period, intensive efforts have been made to clearly define the term "quality" in relation to the uniformity of the fiber structure. These efforts have led to generally accepted test procedures with the consistent availability of suitable test equipment.

With the help of the technology previously used together with a quality-oriented organization of the spinning mill, it is now possible for every spinning mill to avoid or correct most (relatively coarse) errors and to produce fiber assemblies of good average quality.

Because of continuously increasing quality requirements, it is now necessary to increase this good quality level again. However, this leads to a technical area where it is no longer sufficient, the basic principles of control technology or the basic principles of statistical quality control to be used in the spinning mill. In order to achieve a further significant quality improvement, it is now necessary to take a closer look at the more intimate interactions of the measuring principles, control and regulation principles used, drive systems, distortion forces and material properties. It is always necessary to keep in mind the principles of uniformity testing for fiber associations that have already been established by standards.

Quality control in the spinning mill is nowadays largely carried out in the laboratory ("off line"). For this purpose, samples are taken from the processing line, carried to the laboratory and checked. The test results are intended to enable conclusions to be drawn about the setting of the machines or the adaptation of the material to be processed to the requirements for the desired end product. The world's leading manufacturer of test equipment is Zellweger, Uster, Switzerland. This company's application manual, entitled "Uniformity Check", is approximately 230 pages long and describes at least six different test criteria that provide different information for assessing the uniformity of a fiber structure (namely the diagram, imperfections or rare errors, the spectogram, the mean factor and the length variation curve).

In the laboratory (off-line procedure) there is time to analyze the different information, to make a suitable interpretation of the different results and to determine the corresponding conclusions. If you try such methods in To use normal operation "on line", where corrective interventions should be made in the process on the basis of the measured values that have just been determined, it is hardly surprising that there is a great risk of a mistake or a fallacy.

The previous suggestions for a more precise inspection of the products in the company ("on line") are not aimed at enabling an intervention in the processing, but rather to trigger an alarm, for the acquisition of operational data or for the analysis of a process (eg US 4,758,968), so that a closer examination by the staff takes place or the staff can carry out targeted maintenance work. A system according to DE-PS 32 37 371 belongs to this category, according to which a yarn produced by the nozzle spinning process is checked in operation both with respect to the spectrogram and with regard to the Uster value (unevenness coefficient). This identifies faults in the drafting system of the jet spinning machine itself, which can lead to the replacement of the defective parts. This procedure does not allow conclusions to be drawn about the running behavior of the preparation stages.

A proposal for monitoring a route can be found in EP 340 756. According to a first variant of this proposal, limit values for a signal supplied by the outlet measuring element are to be determined, an alarm being triggered or the machine being switched off when a limit value is exceeded. In this case, the product (the fiber structure supplied) should be checked by the personnel. Depending on the results of this Checks should be concluded for measurement errors or control errors.

A second variant of the same proposal provides for the determination of limit values for the actuating signal determining the delay, the triggering of an alarm or the switching off of the machine likewise taking place when a limit value is exceeded. In this case, the sliver should be checked by the staff, depending on the test results for errors in the infeed measuring system or in the production of the sliver material (i.e. in the processing machines in front of this drafting system).

Monitoring the measurement signal from the outlet measurement system can convey certain information about malfunctions. However, this measure alone is certainly not enough to achieve a significant improvement in quality. The monitoring of the control signal proposed in EP 340 756 has hardly any advantages in combination with an alarm or when the machine is switched off. By the time the personnel checked the defective fiber bundle, it had long been processed (corrected) by the drafting system, so that important information regarding the error is no longer available. Because the surveillance is set to react only to a short-term (possibly rare) "outlier", the piece of the sliver fiber association to be examined by the staff probably does not contain a corresponding "event", so that the risk of a fallacy arises again. The investigation does not take place in the company but "off-line".

It is the object of this invention to further develop the regulating drafting system in such a way that the interactions which are decisive for its function can be taken into account better than in the past.

The invention provides a regulating drafting device for fiber bundles, which is equipped with at least one warping field, a controllable or regulatable drive system for determining the warping height in said warping field, a programmable controller for the drive system and at least one sensor for determining the fiber mass passing through per unit length at a measuring point is. The drafting system is characterized in that a warp-determining signal is stored in a memory of the control system over a certain period and information for adapting the drafting system and / or for assessing the quality of the fiber bundles is obtained from the stored values.

The information mentioned includes e.g. the CV value of the fiber bundle, the spectogram of the fiber bundle and / or the length variation curve of the fiber bundle. The controller preferably comprises a digital signal processor e.g. the model 56001 from Motorola.

The delay-determined signal can be an output signal from a sensor or an actuating signal for the drive system. Is a signal "Defining default" in the sense of this invention if it exerts an indirect or direct influence on the default, even if other signals also exert such an influence.

The information can be obtained by said controller and / or by a process control system, in the latter case the stored values are preferably conveyed to the process control system via the controller, e.g. according to our Swiss patent application No. 1025 / 91-2 dated April 5, 1991. Such information can only be obtained by the controller itself if this controller comprises a digital signal processor or a device with a similar or better computing power.

The sensor is preferably suitable for following short-wave mass fluctuations. In order to process such signals using digital technology, it is necessary to digitize them, which is done by periodic sampling. According to the preferred embodiment of the control system, the sampling rate is selected to be higher than 2000 Hz, preferably in the range 2500 to 3500 Hz. Such a signal can be processed in the processor according to the Fast Fourier Transform method in order to enable spectral analysis.

The sampling rate of the control preferably remains constant; the speed of the material passing through is changeable. The controller is preferably also provided with a sensor which reacts to the speed at which the material runs in, so that the control (despite the constant sampling rate) can perform a corrective action per incoming length unit. Appropriate storage means are provided.

This preferred embodiment has the advantage that the information is obtained from signals which are also used to control the correction interventions, which increases the uniformity of the information content of the various signals.

For the same or similar considerations, the operator support provided on the basis of the signals obtained according to this invention is provided via the operator interface (operator consoles or operator panels) of the machines concerned, as described in the aforementioned PCT patent application PCT / CH 91/0097 is. In order to limit the length of this description, the operating support will not be treated as such here. The remarks of PCT / CH 91/0097 are included in this description by this reference.

The signals obtained by this invention can be linked to a material flow tracking system in order to enable or provide a fault diagnosis. A suitable material flow tracking is described in DE-A-40 24 307 dated July 31, 1990, but this invention is not restricted to use in such a combination.

The regulating drafting system can be used as the last stage before spinning that the results of the previous stages are checked here via the process control system and, if necessary, interventions in the preceding stages are initiated.

The invention is described using an exemplary embodiment. 1 shows a schematic representation of a regulating drafting system.

Figure 1 shows a schematic representation of an embodiment of the route according to our European patent application No. 0 411 379.

In the system according to FIG. 1, several fiber tapes 215.1-215.6, in the example six of them, are combined next to each other to form a loose fleece and are guided through several roller systems 201-206. Because the circumferential speed of the rollers increases in two stages in the direction of transport of the fiber material, the latter is pre-drawn over the first stage (pre-drafting) and further drawn over the second to the desired cross-section (main drafting).

The fleece emerging from the route is thinner than the fleece of the fed tapes 215.1 - 215.6 and correspondingly longer. Because the warping processes can be regulated as a function of the cross-section of the fed tapes, the tapes or the fleece are made more uniform as they pass through the line, i.e. the cross-section of the emerging fleece is more uniform than the cross-section of the fed fleece or tapes . The present route has a pre-default area 211 and a main delay area 212.

The belts 215.1-215.6 are fed into the line by two systems 201 and 202 of conveyor rollers. A first system 201 consists, for example, of two rollers 201.1 and 201.2 between which the fed belts 215.1-215.6, which are combined to form a loose fleece, are transported. A roller system 202 follows in the transport direction of the belts, which here consists of an active conveyor roller 202.1 and two passive conveyor rollers 202.2, 202.3. During the feeding through the roller systems 201 and 202, the fed tapes 215.1-215.6 are brought together to form a fleece 216. The peripheral speeds V₁ and V₂ (= V _in ) of all rollers of the two roller systems 201 and 202 of the feed are the same size, so that the thickness of the fleece 216 corresponds essentially to the thickness of the fed tapes 215.1-215.6.

The two roller systems 201 and 202 of the feed are followed in the transport direction of the nonwoven 16 by a third system 203 of pre-drawing rollers 203.1 and 203.2, between which the nonwoven is transported further. The peripheral speed V₃ of the pre-drafting rollers is higher than that of the inlet rollers V _1.2 , so that the fleece 216 is stretched in the pre-drafting area 211 between the intake rollers 202 and the pre-drafting rollers 203, its cross section being reduced. At the same time, a pre-drawn fleece 217 is created from the loose fleece 216 of the fed tapes. A further system 204 follows from the pre-drawing rollers 203 an active conveyor roller 204.1 and two passive conveyor rollers 204.2, 204.3 for further transport of the fleece. The peripheral speed V₄ of the conveyor rollers 204 for further transport is the same as V₃ of the pre-drawing rollers 203.

The roller system for further transport 204 is followed by a fifth system 205 of main drafting rollers 205.1 and 205.2 in the transport direction of the fleece 217. The main drafting rollers in turn have a higher surface speed V₅ than the preceding transport rollers, so that the pre-drawn fleece 217 between the transport rollers 204 and the main drafting rollers 205 in the main drafting area 212 is further drawn to the finished drawn fleece, the fleece being brought together via a funnel T to form a belt .

Between a pair 206 of outlet rollers 206.1, 206.2, the circumferential speed V = (= V _out ) of which is the same as that of the preceding main drafting rollers (V das), the finished stretched strip is led away from the draw frame and placed, for example, in rotating cans 213.

The roller systems 201.2 and 204 are driven by a first servo motor 207.1, preferably via toothed belts. The pre-drawing rollers 203 are mechanically coupled to the roller system 204, whereby the translation can be adjustable or a setpoint can be specified. The gear (not visible in the figure) determines the ratio of the peripheral speeds of the feed rollers (V _in ) and the peripheral speed V₃ of the pre-drafting rollers 203.1, 203.2, hence the pre-drafting ratio.

The roller systems 205 and 206 are in turn driven by a servo motor 207.2. The inlet rollers 201.1, 201.2 can also be driven by the first servo motor 207.1 or optionally by an independent motor 207.3. The two servomotors 207.1 and 207.2 each have their own controller 208.1 and 208.2. The regulation takes place via a closed control loop 208.a, 208.b or 208.c, 208.d. In addition, the actual value of one servo motor can be transmitted to the other servo motor in one or both directions via a control connection 208.e so that everyone can react accordingly to deviations from the other.

The mass or a quantity proportional to the mass, e.g. the cross section of the fed tapes 215.1 - 215.6 measured by an inlet measuring element 209.1. At the exit of the line, the cross section of the emerging strip 216 is then measured by an outlet measuring element 209.2.

A central computer unit 210 transmits an initial setting of the target size for the first drive via 210.a to the first controller 208.1. The measured variables of the two measuring elements 209.1, 209.2 are continuously transmitted to the central computer unit via the connections 209.a and 209.b during the stretching process. From these measurement results and from the target value for the cross section of the emerging belt 218, the setpoint for the servo motor 208.2 is determined in the central computer unit and any other elements. This setpoint is continuously given to the second controller 208.2 via 210.b. With the help of this control system (the "main control"), fluctuations in the cross-section of the fed strips 215.1-215.6 can be compensated for by appropriate control of the main drafting process or the strip can be made more uniform.

The lower part of FIG. 1 now shows the adaptation of this system to this invention in its third aspect. In a first embodiment, the central control 210 of the machine itself is assigned a memory 220, where the or certain signals of the drafting system control system are stored for evaluation. If the operating speed of the central processor in the controller 210 is high enough, such a high sampling rate can be selected that a spectrogram of the input signal (from sensor 209.1), the output signal (from sensor 209.2) and / or the control signals (to motors 207.1 and / or 207.2 emitted signals) can be obtained.

A drafting system control according to FIG. 1 is normally designed not to carry out a control intervention in the material (a change in the material processing) continuously, but rather after a certain interval. The duration of this interval is preferably not chosen to be constant, but is adapted to the running-in speed in such a way that the interventions each at the end of a predetermined fleece length. For this purpose, the arrangement shown can be supplemented by determining the running-in speed, for example, on the roller group 202, and using it to control the processing operations. Storage means (not shown) are then necessary in the draft control system in order to store the control signals and to activate them at the right time.

However, the values contained in the memory 220 are not evaluated as a function of the running-in speed but according to the time. In a spectral analysis, the time functions are then converted into frequency functions using the Fast Fourier Transform method. The time required for this depends on the computing speed of the processor and the number of frequencies (or frequency ranges) that should be examined individually. For an adequate analysis of a template material, preferably at least 1024 individual frequency ranges are to be examined.

Such an evaluation requires a considerable computing or storage capacity in the machine itself. In many cases this may not be present, so that the analysis must be relocated to a process control computer PLR. For this purpose, a data bus DB can be provided and the controller 210 can be provided with an interface SNM to this data bus, the computer PLR also comprising an interface SNR to the data bus.

In the process control computer, neither the computing speed nor the storage capacity will normally limit the desired analysis - a prerequisite for this analysis is to ensure that the process control computer has access to the "raw data" of the relevant sensors, e.g. as shown in the aforementioned Swiss patent applications Nos. 189/91 and 1025/91. The statements after these applications are also included in the present description by this reference.

However, the aforementioned "raw data" are not to be understood as the actual output signals of the appropriate sensors, but these signals can be processed by the machine control (at least for the transfer to the process control computer). It is important that the essential information content for the intended analysis is maintained.

Claims (2)

Regulating drafting system for fiber bundles with at least one draft zone (212), a controllable or regulable drive system for determining the amount of draft in said draft field, a programmable controller (210) for the drive system and at least one sensor (209.1) for determining the continuous fiber mass per unit length on one Measuring point is equipped, characterized in that a warp-determining signal is stored for a predetermined period in a memory (220) of the controller (210) and information from the stored values for adapting the drafting system and / or for assessing the quality of the fiber bundles (215.1 to 215.6) can be obtained. Regulating drafting system according to claim 1, characterized in that the information for assessing the quality of the fiber bundles (215.1 to 215.6) is used to influence the control of a processing stage upstream of the regulating drafting arrangement.

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