EP3495542B1 - Warp knitting machine, method for monitoring the quality of a warp knit and system therefore - Google Patents

Description

The invention relates to a warp knitting machine with a knitting area in which the warp knitting machine produces a knitted fabric during a knitting process, with a thread feed area in which warp threads run during operation of the warp knitting machine before they are subjected to the knitting process in the knitting area, and with a system for monitoring a Goods quality of the knitted goods produced, the system for monitoring the quality of the knitted goods produced having an optical scanning device and a data processing unit, and the data processing unit being set up to generate an evaluation signal relating to the quality of the knitted goods.

Warp knitting machines have knitting tools that process the warp threads in a knitting process into a textile material, a so-called knitted fabric. This takes place in a knitting area of the warp knitting machine. The warp threads pass through a thread feed area beforehand. The knitted fabric is produced by a loop-forming process. Warp knitting machines have several bars, a plurality of knitting tools being arranged on each bar. Since a large number of knitting tools can be moved simultaneously by means of a bar, a large number of loops are formed at the same time during the knitting process. Herein lies is the reason for the particularly high production output of warp knitting machines.

Systems for monitoring the quality of a knitted fabric produced are known from the prior art. So shows the DE 37 33 791 C2 a system that monitors the quality of a knitted fabric by means of an optical scanning device. The optical scanning device is aimed at the knitted fabric produced. In this way, faults in the goods can be detected. In the edge area of the knitted fabric, however, it is very difficult to reliably identify errors in the formation of the loop by means of image processing methods. This is due, among other things, to the fact that the edge area of the knitted fabric often has an irregular, frayed structure and tends to curl up. The knitted fabric produced also has a spring-in behavior, that is to say it becomes increasingly narrow in the direction of a fabric winding device of the warp knitting machine. This also makes error detection more difficult. In particular, thread breaks can therefore not be reliably detected.

In order to reliably detect thread breaks in the edge area of the knitted fabric, drop stirrups are occasionally used in warp knitting machines. During operation, each drop bracket rests against a single thread in the thread feed area. If the thread breaks, the drop stirrup assigned to it can lower, which triggers an error signal. Since each warp thread is assigned its own drop bracket, this approach is structurally very complex.

It is also known to arrange a light barrier in front of the effective area. A system with a light barrier is out of the DE 34 01 582 A1 known. When in the knitting process a The warp thread breaks, then it is usually thrown out of the effective area and passes a monitoring area of the light barrier. However, not all thread breakage errors can be detected by means of the light barrier, since not every broken warp thread necessarily passes through the monitoring area of the light barrier. In addition, a fan should be provided during operation of the light barrier in order to blow the warp threads out of the thread feed area in the direction of the light barrier.

All of the systems described above are often used in combination. Nevertheless, even then, certain operating errors cannot be recognized. If, for example, a warp thread is intermeshed incorrectly in the edge area of the knitted fabric, this is not noticeable, since the thread does not break. In the event of a meshing fault, a warp thread is hooked into a stitch to which it is not assigned according to the laying plan.

The invention is therefore based on the object of providing a warp knitting machine that reliably detects knitting errors such as thread breaks and interlacing errors, but also other quality deficits in the knitted fabric produced.

The object is achieved by providing a warp knitting machine of the type described at the outset, in which the optical scanning device is arranged so that it can capture a moving image of at least one warp thread in the thread feed area, the data processing unit being set up to determine a thread running speed from the moving image to determine at least one warp thread, the thread running speed in one Evaluate evaluation step and generate the evaluation signal as a function of an evaluation result of the evaluation step.

According to the invention, the thread running speed is evaluated. The thread running speed is sometimes also referred to as the thread delivery speed. It describes the speed at which the warp thread is moved in the direction of the knitting area. The thread running speed can also be negative for a short time in special cases. By evaluating the thread running speed of the warp thread, it is possible to determine types of defects such as thread breaks, interlacing defects, but also other quality restrictions such as a drop in tension in the knitted fabric produced. The errors can be detected early so that the machine can be stopped quickly in the event of an error. The evaluation is only made possible by the fact that the optical scanning device is aimed at the warp threads in the thread feed area instead of on the knitted fabric produced. Alternative means of error detection such as drop bars or light barriers can be completely omitted. A large number of errors, which previously could only be found by observing the finished knitted fabric, can also be recognized by evaluating the thread running speed of the warp threads.

If the thread running speed of a warp thread drops sharply, for example, it can be assumed that there is a thread break. If the thread running speed of a warp thread drops slightly, this may be due to the fact that the warp thread was incorrectly intermeshed. Incorrect meshing can also lead to an unexpected increase in the thread running speed.

Often, once incorrectly performed meshing continues over several rows of stitches, the thread running speed of the warp thread permanently deviates from an expected thread running speed. According to a possible embodiment of the invention, it is possible for the data processing unit to classify the quality of the knitted fabric as defective if the thread running speed of a warp thread deviates from a previously measured average thread running speed of the warp thread. According to the invention, it is also possible to evaluate the thread running speed of several warp threads.

The optical scanning device preferably detects the warp threads in an area of the warp knitting machine which is arranged directly in front of the knitting area. The optical scanning device is preferably a camera or a moving image camera. According to one possible embodiment of the invention, the camera can be a line camera. Alternatively, a laser scanning system can be provided for optical scanning of the warp yarn.

The data processing unit is responsible for assessing the quality of the knitted fabric. The assessment can be carried out in different ways depending on the embodiment of the invention. It is thus possible according to the invention for a quality measure to be output with the evaluation signal. On the basis of the quality index, an operator can decide whether it is necessary to stop the warp knitting machine in order to make corrections. According to the invention, the quality measure can be output at regular intervals. Alternatively, it can be provided that the Evaluation signal is only output if the quality falls below a predefined quality threshold. According to the invention, it is also possible for the warp knitting machine to be set up in such a way that it stops the knitting process when the quality falls below a predefined quality threshold.

In the evaluation step, the data processing unit is preferably set up to compare a time profile of the thread running speed of the at least one warp thread in the thread feed area with a movement profile stored in the data processing unit. The course of the thread running speed over time reflects the measured thread running speed of the warp thread during operation at different points in time.

The movement profile reflects a desired course of the thread running speed of the warp thread over time. The desired course of the thread running speed over time can have been determined by a measurement or else have been calculated. Too great a deviation of the course of the thread running speed over time from the movement profile indicates poor quality of the knitted fabric or a fabric defect. According to the invention, the data processing unit can be designed in such a way that it generates an evaluation result that indicates a reduced quality of the knitted fabric or a defect in the fabric if a difference between the temporal course of the thread running speed and the stored movement profile exceeds a predefined limit value at one or more times . According to the invention, a separate movement profile can be stored for different warp threads.

It is preferred if the data processing unit uses a synchronization signal from the warp knitting machine in order to compare the movement profile with the actually measured temporal course of the movement speed of the warp thread. The knitting process is a cyclical process. Thus, for example, the synchronization signal can always be generated when this process starts again. The synchronization signal can be determined by means of a measurement at different points on the warp knitting machine, but a measurement is preferably carried out on the main shaft. The main shaft is a drive shaft arranged in a machine bed of the warp knitting machine, which drives the bars of the warp knitting machine.

It is advantageous if the data processing unit is set up to receive patterning information via a data interface or an input means of the warp knitting machine, to calculate the movement profile from the patterning information and to store the movement profile in the data processing unit. Thus, according to the invention, a desired pattern can be entered via an input means such as a keyboard or a touchscreen. However, the patterning information can also be transmitted to the data processing unit via a data interface, for example a network interface or a reader for a data carrier.

The patterning information defines how guide bars of the warp knitting machine should move during operation. The movement of the guide bars determines the pattern created in the knitted fabric during the knitting process. From the patterning information, the data processing unit calculates a time-dependent warp thread consumption and thus also a time-dependent thread running speed of the warp threads. This results in an ideal movement profile that is stored in the data processing unit.

The data processing unit is preferably set up to learn the movement profile of the at least one warp thread by analyzing the moving image of the at least one warp thread and to store the movement profile in the data processing unit. This is preferably done in such a way that the thread running speed of the at least one warp thread is determined during a complete pattern laying cycle. This results in the movement profile. According to the invention, measurements can be made and averaged over several pattern laying cycles in order to obtain the movement profile.

According to a particular embodiment of the invention, the data processing unit is set up to evaluate a speed difference between two warp threads in the evaluation step. For this purpose, a speed of a first warp thread and a speed of a second warp thread are measured in the thread feed area. The speed difference is calculated from this. According to embodiments of the invention, the procedure can be as follows: If the speed difference exceeds a predefined limit value, then this indicates a reduction in quality or a defect in the goods, and a An evaluation result is generated that indicates a reduced quality of the knitted fabric or a fabric defect.

According to a further embodiment of the invention, speed differences of several pairs of warp threads are determined by the data processing unit. According to the invention, the resulting speed differences can be averaged or added. In a subsequent step, the data processing unit determines according to the invention whether the result of the averaging or the addition exceeds a predefined limit value.

In the evaluation step, the data processing unit is preferably set up to filter out an interference spectrum from a time profile of the thread running speed of the at least one warp thread, to isolate at least one frequency peak from the interference spectrum and to compare a frequency and / or an amplitude of the at least one frequency peak with reference data. Measurements have shown that the course of the thread running speed of the warp thread over time is not exclusively dependent on the pattern of the knitted fabric. Vibrations in components of the warp knitting machine can have a strong influence on the thread running speed of the warp threads. The action of the knitting tools - which are themselves subject to vibrations - on the warp threads influences the course of the thread running speed over time.

The quality of the knitted fabric can be determined by analyzing the frequencies that occur. According to the invention, an interference spectrum is filtered out from the course of the thread running speed over time. This can be done, for example, by means of a Fourier analysis or in another suitable manner respectively. The interference spectrum includes frequencies that typically lead to product defects. The interference spectrum differs from machine to machine and can be determined by measurements. Individual frequency peaks are isolated from the interference spectrum and then compared with reference data. The reference data describe properties of at least one frequency peak that is typical for the occurrence of a specific product defect. If there is sufficient correspondence between the reference data and an isolated frequency peak, then the data processing unit generates an evaluation signal which indicates a defect in the knitted fabric or a reduced quality of the knitted fabric.

The invention also relates to a method for checking the quality of a knitted fabric in a warp knitting machine. The method has the following steps: acquisition of a moving image of at least one warp thread in a thread feed area of the warp knitting machine, determination of a thread running speed of at least one warp thread in the thread feed area, evaluation of the thread running speed in an evaluation step and generation of an evaluation signal relating to the quality of the knitted fabric as a function of one Evaluation result of the evaluation step. This method can be applied to the warp knitting machine described above.

In the evaluation step, a time profile of the thread running speed of the at least one warp thread in the thread feed area is preferably compared with a movement profile. It is advantageous if the movement profile is calculated from pattern design information before the evaluation step. Alternatively, it can However, before the evaluation step, the movement profile can also be learned by analyzing the moving image of the at least one warp thread.

According to the invention, a speed difference between two warp threads can be evaluated in the evaluation step. However, it is also advantageous if, in the evaluation step, an interference spectrum is filtered out from the temporal course of the movement speed of the at least one warp thread, at least one frequency peak is isolated from the interference spectrum and a frequency and / or an amplitude of the at least one frequency peak is compared with reference data.

The invention also relates to a system for monitoring the quality of a knitted fabric produced by a warp knitting machine, the system for monitoring the quality of the knitted fabric having an optical scanning device and a data processing unit, and the data processing unit being set up to issue an evaluation signal relating to the quality of the fabric to produce the knitted fabric. This system can be used in the warp knitting machine according to the invention. According to the invention, the optical scanning device is provided in this system to capture a moving image of at least one warp thread in a thread feed area of the warp knitting machine and the data processing unit is set up to determine a thread running speed of the at least one warp thread from the moving image, to evaluate the thread running speed in an evaluation step and to generate the evaluation signal as a function of an evaluation result of the evaluation step. The data processing unit of the system for monitoring the quality of the goods is preferably set up to evaluate a speed difference between two warp threads in the evaluation step in order to determine the evaluation result. It is also advantageous if the data processing unit is set up in the evaluation step to filter out an interference spectrum from a time profile of the thread running speed of the at least one warp thread, to isolate at least one frequency peak from the interference spectrum and to include a frequency and / or an amplitude of the at least one frequency peak Compare reference data.

• Fig. 1 eine Kettenwirkmaschine mit einem System zur Überwachung einer Warenqualität einer Wirkware,
• Fig. 2 ein Zeit-Geschwindigkeit-Diagramm mit einem gemessenen zeitlichen Verlauf einer Fadenlaufgeschwindigkeit eines Kettfadens und mit einem vordefinierten Bewegungsprofil und
• Fig. 3 ein Frequenzdiagramm mit eine gemessenen Frequenzspitze bei einem zeitlichen Verlauf einer Fadenlaufgeschwindigkeit eines Kettfadens und mit einer Referenzspitze.

The drawings represent preferred embodiments of the invention.

• Fig. 1 a warp knitting machine with a system for monitoring the quality of a knitted fabric,
• Fig. 2 a time-speed diagram with a measured time profile of a thread running speed of a warp thread and with a predefined movement profile and
• Fig. 3 a frequency diagram with a measured frequency peak in the course of a thread running speed of a warp thread over time and with a reference peak.

Fig. 1 shows a warp knitting machine 1 with a system for monitoring a fabric quality of a knitted fabric 2. The warp knitting machine 1 has a thread feed area 3 in which warp threads 4 run when the warp knitting machine is in operation before they are subjected to a knitting process. In a knitting area 5 of the warp knitting machine 1, the knitted fabric 2 is fastened to bars 6 by knitting tools are generated. The warp knitting machine 1 has three optical scanning devices 7, which are moving image cameras. The optical scanning devices 7 are directed at the warp threads 4. When the warp knitting machine 1 is in operation, the warp threads 4 have a variable thread running speed. The optical scanning device 7 records a moving image of the warp threads 4 and forwards this to a data processing unit (not shown). The data processing unit analyzes the moving image and derives an evaluation result relating to the quality of the knitted fabric 2 from the thread running speeds of the warp threads 4. The data processing unit then outputs the evaluation result via an evaluation signal.

Fig. 2 shows a time-speed diagram 8 with a movement profile curve 9 of a warp thread and with a movement profile curve 10. The time-speed diagram 8 has a time axis 11 and a speed axis 12. The movement curve 9 shows a measured thread running speed of the warp thread at different times. The movement curve 9 is represented by a dotted line. The movement profile curve 10 reproduces a temporal course of the thread running speed which is to be expected from the warp thread when the warp knitting machine is operating correctly. The movement profile curve 10 is represented by a dashed line. The data processing unit of the warp knitting machine determines a difference between the movement profile curve 9 and the movement profile curve 10. If the difference is too great, the data processing unit outputs an evaluation signal which informs the warp knitting machine that a defective knitted fabric is produced. The warp knitting machine then stops the knitting process.

Fig. 3 shows a frequency diagram 13 with a frequency peak 14 and with a reference peak 15. The frequency diagram 13 has a frequency axis 16 and an amplitude axis 17. The frequency peak 14 was determined from a measured time profile of a thread running speed of a warp thread. The frequency peak 14 is represented by a dotted line. The reference point 15 is expected when there is a certain type of defect in the warp knitting machine. The reference tip 15 is represented by a dashed line. The frequency peak 14 is compared with the reference peak 15 by the data processing unit of the warp knitting machine. If a frequency and an amplitude of the frequency peak 14 and the reference peak 15 deviate only slightly, the data processing unit outputs an evaluation signal which informs the warp knitting machine that a defective knitted fabric is being produced. The warp knitting machine then stops the knitting process.

B E Z U G S Z E I C H E N L I S T E

1. 1. Warp knitting machine
2. 2. Knitwear
3. 3. Thread feed area
4. 4. Warp thread
5. 5. Effective range
6. 6. Barre
7. 7. Optical scanning device
8. 8. Time-speed diagram
9. 9. Movement curve
10. 10. Motion profile curve
11. 11. Timeline
12. 12. Speed axis
13. 13. Frequency diagram
14. 14. Frequency peak
15. 15. Reference tip
16. 16. Frequency axis
17. 17. Amplitude axis

Claims (15)

1. Warp knitting machine (1) with a knitting area (5) in which the warp knitting machine (1) produces a warp knit (2) during a knitting process, with a yarn feed area (3) in which warp yarns (4) run during operation of the warp knitting machine (1) before they are subjected to the knitting process in the knitting area (5), and with a system for monitoring a fabric quality of the produced warp knit (2), wherein the system for monitoring the fabric quality of the produced warp knit (2) has an optical scanning device (7) and a data processing unit, and wherein the data processing unit is configured to produce an evaluation signal relating to the fabric quality of the warp knit (2), characterised in that the optical scanning device (7) is arranged in such a way that it can capture a moving image of at least one warp yarn (4) in the yarn feed area (3), the data processing unit being configured to determine a yarn running speed of the at least one warp yarn (4) from the moving image, to evaluate the yarn running speed in an evaluation step and to produce the evaluation signal as a function of an evaluation result of the evaluation step.
2. Warp knitting machine (1) according to claim 1, characterised in that the data processing unit is adapted to compare, during the evaluation step, a behaviour of the yarn running speed of the at least one warp yarn (4) in the yarn feed area (3) over time with a movement profile stored in the data processing unit.
3. Warp knitting machine (1) according to claim 2, characterised in that the data processing unit is adapted to receive patterning information via a data interface or an input means of the warp knitting machine (1), to calculate the movement profile from the patterning information and to store the movement profile in the data processing unit.
4. Warp knitting machine (1) according to claim 2, characterised in that the data processing unit is adapted to learn the movement profile of the at least one warp yarn (4) by analysis of the moving image of the at least one warp yarn (4) and to store the movement profile in the data processing unit.
5. Warp knitting machine (1) according to claim 1, characterised in that the data processing unit is adapted to evaluate, during the evaluation step, a speed difference between two warp threads (4).
6. Warp knitting machine (1) according to claim 1, characterised in that the data processing unit is adapted to filter out, during the evaluation step, an interference spectrum from a behaviour of the yarn running speed of the at least one warp yarn (4) over time, to isolate at least one frequency peak (14) from the interference spectrum and to compare a frequency and/or an amplitude of the at least one frequency peak (14) with reference data.
7. Method for monitoring a quality of a warp knit (2) in a warp knitting machine (1), comprising the steps:

   - detecting a moving image of at least one warp yarn (4) in a yarn feed area (3) of the warp knitting machine (1),

   - determining a yarn running speed of at least one warp yarn (4),

   - evaluating the yarn running speed in an evaluation step,

   - producing an evaluation signal relating to the quality of the warp knit (2) as a function of an evaluation result of the evaluation step.
8. Method according to claim 7, characterised in that, in the evaluation step, a behaviour of the yarn running speed of the at least one warp yarn in the yarn feed area (3) over time is compared with a movement profile.
9. Method according to claim 8, characterised in that, before the evaluation step, the movement profile is calculated from patterning information.
10. Method according to claim 8, characterised in that, before the evaluation step, the movement profile is learned by analysis of the moving image of the at least one warp yarn (4).
11. Method according to claim 7, characterised in that in the evaluation step a speed difference between two warp yarns (4) is evaluated.
12. Method according to claim 7, characterised in that, in the evaluation step, an interference spectrum is filtered out of a behaviour of the yarn running speed of the at least one warp yarn (4) over time, at least one frequency peak (14) is isolated from the interference spectrum and a frequency and/or an amplitude of the at least one frequency peak (14) is compared with reference data.
13. System for monitoring a fabric quality of a warp knit (2) produced by a warp knitting machine (1), the system for monitoring the fabric quality of the warp knit (2) having an optical scanning device (7) and a data processing unit, and the data processing unit being adapted to produce an evaluation signal relating to the fabric quality of the warp knit (2), characterised in that the optical scanning device (7) is provided for the purpose of capturing a moving image of at least one warp yarn (4) in a yarn feed area (3) of the warp knitting machine (1), and wherein the data processing unit is adapted to determine a yarn running speed of the at least one warp yarn (4) from the moving image, to evaluate the yarn running speed in an evaluation step and to produce the evaluation signal as a function of an evaluation result of the evaluation step.
14. System according to claim 13, characterised in that the data processing unit is adapted to evaluate, in the evaluation step, a speed difference between two warp threads (4).
15. System according to claim 13, characterised in that the data processing unit is adapted, during the evaluation step, to filter out an interference spectrum from a behaviour of the yarn running speed of the at least one warp yarn (4) over time, to isolate at least one frequency peak (14) from the interference spectrum and to compare a frequency and/or an amplitude of the at least one frequency peak (14) with reference data.

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