EP1570255A1

EP1570255A1 - Method and device for evaluating defects in textile structures

Info

Publication number: EP1570255A1
Application number: EP03757617A
Authority: EP
Inventors: Rolf Leuenberger
Original assignee: Uster Technologies AG
Current assignee: Uster Technologies AG
Priority date: 2002-11-06
Filing date: 2003-11-03
Publication date: 2005-09-07
Also published as: US20060251295A1; CN1708682A; JP2006504965A; WO2004042379A1

Abstract

The invention relates to a method for identifying defects in a textile structure (2), whereby signals are derived from the textile structure and are processed at least with pre-determined parameters. The invention also relates to a device (3) for identifying defects in a textile structure, said device comprising a sensor, a processing unit and an input/output unit. The processing unit is connected to the sensor and to the input/output unit and is embodied and arranged in such a way as to process signals detected by the sensor on the textile structure, at least with pre-determined parameters, and produces an output signal which indicates the defect in the textile structure. In order to adapt parameters of the method and the device for identifying defects in a textile structure to a determined textile structure subjected to a defect identification process, in an especially simple and rapid manner, a fixed data carrier (26) of the pre-determined parameters is subjected to the action of a sensor and a sensor is embodied and arranged in such a way as to read the pre-determined parameters of the fixed data carrier.

Description

METHOD AND DEVICE FOR ASSESSING ERRORS IN TEXTILES

FABRICS

The invention relates to a method and a device for assessing defects in textile fabrics.

From WO00 / 06823 a method and a device are known which allow a repeatable and unambiguous assessment of faults in textile fabrics. An image of a flat structure is generated, at least two representations of defects in the flat structure appearing in the image, which are different in terms of length and contrast or intensity of the defect. Based on these representations, the admissibility and inadmissibility of an error in the fabric is decided on the basis of the visual impression. For this purpose, a table or matrix-like arrangement of representations of errors of different types is created. An image of the flawless fabric is used as the background. Sensitivity curves built into the image can serve as an additional aid in distinguishing impermissible errors from admissible errors.

From a technical point of view, this method or this device can lead to an unnecessary flood of recorded data if all possible errors that can be classified are recorded. This hinders a rapid assessment of the errors and leads to an unnecessarily generous design of the elements from which the device is to consist.

It is therefore an object of the invention to provide a method and a device for assessing defects in fabrics which allow a rapid and uniform assessment of the errors in different types of fabrics and thus also enable the quality of different types of fabrics to be compared with one another.

This is achieved by forming a classification matrix for the errors on the basis of two selected parameters, dividing the classification matrix into fields at the class boundaries and values of two parameters, such as the extent and intensity of the errors, determining the class boundaries. In addition, the classification matrix is divided into at least two areas, for example for permissible and impermissible errors. The defects in the fabric are to be recorded according to a known method and values for the two aforementioned parameters are to be determined. The detected errors are assigned to the fields or classes in the classification matrix according to the values of the parameters measured for them.

It is thus proposed in particular to choose a classification scheme or a classification matrix in which pixels and defects of a fabric represented by pixels can be ordered or classified according to their intensity and extent. In this case, values for the intensity along an axis are to be plotted in an area which is independent of an existing fabric and can apply to all possible fabrics. The zero point of this axis or the lower limit of this area can optionally be set so that irregularities in the image cannot be considered errors in very homogeneous flat structures. Between this zero point and an upper limit, which depends on the relevant fabric to be examined, image points are to be recorded which, for example, belong to the normal tissue structure in the case of a tissue. Events with intensity values above this limit are either only counted, or are evaluated as errors that are unacceptable from a predeterminable intensity. Pixels that do not reach the limit, for example, are no longer processed and therefore do not burden the system. This limit is calculated for light pixels and dark pixels separately in a learning step, namely from a group of the brightest pixels for dark fabrics and a group of the darkest pixels for light fabrics or from the brightest and darkest pixels in the same fabric, e.g. a fabric always has 50% gray pixels.

The advantages achieved by the invention can be seen in particular in the fact that the defects in the textile fabrics can be assessed independently of properties that can change from fabrics to fabrics and thus usually complicate or falsify the assessment. In this way, all errors are recorded according to the same specifications. The detection of non-disturbing defects is automatically adapted to the existing textile fabric. In addition, the method according to the invention makes it possible to automate the evaluation of tested fabrics and to have them carried out without human intervention. 0716

The invention is explained in more detail below using an example and with reference to the accompanying drawings. Show it:

1 shows a representation of a classification matrix.

2 shows a schematic representation of a textile fabric with defects,

Figure 3 illustrates another classification matrix

Fig. 4 shows an example of a fine fabric

Fig. 5 shows an example of a coarser fabric

6 shows a simplified detail from a flat structure,

Fig. 7 is a schematic representation of gray or color values and

8 shows a three-dimensional representation of a helpful function.

1 shows a first example of a classification matrix 1 for two parameters from a flat structure, for which values along axes 2 and 3 are to be plotted. Such parameters are, for example, the length and the intensity of an error in the textile fabric. Values for the length are, for example, between 10 ^"1 and 10 ⁴ mm. Values for the intensity of the error are, for example, between 0 or X% and 100%. Vertical lines 4 to 8 and horizontal lines 9 to 15, which form class boundaries, the classification matrix 1 divided into fields or classes A comparatively thick stair line 16 further divides the classification matrix 1 into a lower area 17 and an upper area 18. Individual errors 19 to 23 are also entered in the classification matrix 1 and shown schematically in such a way that they show errors, for example, as they belong in the class in question The stair line 16, for example, represents an upper limit for an area 17 in which there are permissible errors.

2 shows an example of a textile fabric, such as, for example, a fabric 24 which has defects. The errors shown schematically here are also entered in the classes of the classification matrix 1 and, if already shown there, are provided with the same reference numerals 19-23. Since this is supposed to be a fabric, it can be expected that most of the errors will be noticeable in the direction of the warp threads or the direction of the weft threads. Therefore, they are approximately at right angles to each other. A further error 25 relates here, for example, to a plurality of warp threads lying next to one another or concerns an undesired inclusion in the fabric, which is why it is relatively wide. In the case of a knitted fabric, however, it can be expected that the most frequent errors have a different direction to one another, not shown here. This then depends on the type of weave or structure chosen for the knitted fabric. In the case of so-called "non-wovens", the errors are predominantly oriented arbitrarily. FIG. 3 shows a further example of a classification matrix 26, the fields or classes 27 of which may have unequal sizes or dimensions. A stair line 28 also divides the classification matrix into a lower area 29 and an upper area 30. The lower area 29 is obviously larger than the lower area 17 of FIG. 1, which is due to the higher stair line 28. This means that this classification matrix 26 is provided for a flat structure which, for example, consists of thicker yarn and which may additionally also have less tight bonds between the yarns than is the case for the flat structure for which the classification matrix 1 is intended. Accordingly, in comparison to FIG. 1, events with higher intensity values are also classified below the stair line 28, since such events are not to be assessed as errors in the roughly structured fabric.

Fig. 4 shows an example of fine fabrics, while Fig. 5 shows an example of a comparatively coarse fabrics. The same errors are built into both figures. A comparison of the two figures shows that the errors in FIG. 4 are more noticeable than in FIG. 5 and that certain errors that can be found immediately in FIG. 4 can no longer be seen in FIG. 5. This applies in particular to errors that are in the left half of the picture.

6 shows a detail 31 from a flat structure with a so-called camera line 32. The camera line 32 corresponds to that part of the flat structure that a camera that covers the flat structure records. The camera line 32 comprises a number of lines 33 - 36, each of which consists of a row of pixels, such as e.g. Pixels 37, 38 exist, which are shown here greatly enlarged and shown schematically. The camera line 32 is the electronic image of a section of the flat structure, this section already being divided into pixels with associated gray or color values.

FIG. 7 shows a schematic representation of a stage in the processing that can take place on the basis of the captured camera line 32. For each camera line 32, the gray or color values of the captured pixels 37, 38 etc. are to be applied in an orderly manner according to their intensity or brightness. This results in a representation with a horizontal axis 39, along which a position is provided for each captured pixel and a vertical axis 40 for values of the intensity or brightness of the pixels. These pixels are recorded according to their intensity or brightness or the size of the values for the intensity or brightness. So the brightest or least intense colored pixels on the left and the darkest or most colored pixels on the right. An average value 48 is represented by a broken line.

8 shows an illustration of a method with which a measure of the visually perceptible intensity of the error can be determined from the measurable quantities such as error width and contrast of the error. 8 shows a conical surface 42 in a three-dimensional space, which is represented by horizontal axes 43, 44 and a vertical axis 45. Along the axis 43 are values for the contrast in percent, along the axis 44 are values for the width of an error in mm and along the axis 45 values for the intensity of the error are also given in percent. Based on the measured width of an error and the determined contrast of the error, the intensity of an error can be determined with this representation, as will be explained below. The intensity is a measure of how much an error is noticed by the viewer when viewing the flat fabric. A high intensity error is more disturbing to the viewer than a low intensity error. A high-intensity error can be recognized much faster and it reduces the value of a fabric much more. We are talking here about the intensity because it should summarize the effect of the contrast and the width of an error. This makes it easier to compare errors of different widths and with different contrast levels. This also results in massive data reduction.

The mode of operation of the invention can be explained in two parts, namely firstly the formation of a suitable classification matrix and secondly the classification of the errors recorded in the fabric using this classification matrix.

First, the formation of a classification matrix or a classification scheme according to FIGS. 1 and 3 will now be described. First, a horizontal axis 2 is specified, along which values for the lengths of possible defects are recorded, as can generally be expected for a flat fabric or textile fabric. Such values can be between a tenth of a millimeter and several meters. A vertical axis 3 is then specified for values of the intensity from 0 or X% - 100%. Then you have to decide how many classes you want to have. This results in the number of lines 4 to 15. However, it is recommended to use a single and always the same classification matrix for all fabrics to be assessed. This makes it much easier to compare the effects of the errors in different fabrics. In a further step it is a matter of defining the lower and the upper region 17, 18 or 29, 30, which is due to the shape and the position of the stair line 16, 28 as well as the assignment of a basic value corresponding to 0 or X% for the lower limit or the position of axis 2. Since every field or class of the classification matrix 1 stands for a group of possible errors, it is now a matter of deciding which errors or events will have a disruptive effect on a given fabric due to their length and intensity, and which errors are tolerable and therefore only bare as events without effect. It is known that a given error, for example in the flat structure according to FIG. 5, cannot be recognized at all, but that it should have a disruptive effect in the flat structure according to FIG. 4. There are also events that consist of particularly clear irregularities in the fabric, but which cannot be considered errors. The staircase line 16, 28 or the upper limit of the areas 17, 29 must take these circumstances into account.

To distinguish tolerable errors from intolerable errors, you can choose different approaches. The simplest procedure would be to form a larger number of reference errors and to consider, compare and possibly classify each of these errors against the background of the given and to be assessed real fabric, and thereby subjectively decide which errors do not bother or which bugs certainly disturb , If you have as many reference errors as fields or classes in the classification matrix 1, you can use the above-mentioned subjective comparison to directly determine those classes whose errors interfere or not. This then results in a boundary line between classes of disturbing errors and classes of non-disturbing errors and this is the stair line 16, 28. Since fine, flat structures also show smaller, less contrasting faults, the stair line 16 according to FIG. 1 is lower than the stair line 28 according to Fig. 3, which is provided for more structured fabrics such as shown in FIG. 5.

Another, more complex and precise way of automatically determining the upper limit or stair line 16, 28 can be done as follows. First a minimum intensity has to be defined, which is assigned to the lowest intensity class (eg 0 or X%). This limit must be set so low that even weak defects can be detected in very homogeneous fabrics. Since the intensity coincides approximately with the gray-scale value of the pixels in the case of small, punctiform errors, the intensity scale can be aligned with the gray-scale range of the existing pixels. The intensity scale can be, for example, between +/- 64.128, 256 etc., depending on the number of bits used in the calculation. The intensity is assigned 100% to the maximum gray value, which corresponds to 64, 128 or 256, for example. A value of 5% of this can be useful as a minimum intensity. This can be used, for example, to prevent the lower limit for very homogeneous tissues from being reduced to such an extent that normal irregularities in the image lead to pseudo errors. Now that a scaling for the values of the intensity and the length of the errors has been determined, the stair lines 16, 28 are to be determined such that only a few events in the fault-free tissue image are recognized as so conspicuous that they exceed the stair line and are counted. The stair line 16, 28 must be determined for an existing fabric. You can do this as follows.

1) For example, a camera captures the flat structure and images it in pixels in the camera line 32. The pixels recorded by the camera are assigned intensity or brightness values according to the predefined scale. From a representative set of pixels from an error-free section of the fabric, these values are to be recorded in order of their size or stored in a memory, as illustrated in FIG. 7. This can also be done, for example, by determining an average of the gray values of the pixels in the column for each column 46, 47, etc. in the camera line 32, only the mean values being ordered and stored. Thus, there is only one pixel pattern with pixels per camera line 32, the values of which are arranged as indicated above.

2) A group 51 (FIG. 7) with pixels is then formed, this group comprising those pixels which have the highest or the lowest intensity or brightness, or which have the greatest positive or negative deviation from the mean value 48 (FIG. 7) exhibit. This group can comprise, for example, 10, 15, 20 or another number of pixels, the pixels with the lowest intensity for dark fabrics and the pixels with the highest intensity for bright fabrics. A value in a group 51 can be taken as the upper limit for areas 17, 29.

3) From group 51, the median value of the brightness, the intensity or the deviation can also be determined for the upper limit. This median value can then indicate a value for the intensity for the stair line 16, 28 in its central region with regard to the length of the errors. It applies to rather long mistakes. If one starts from the deviation, this must be related to the mean value 48 in order to obtain a value for the stair line 16, 28. However, this median value still has to be converted into a% value that matches the scaling on axis 3

4) A further step is desirable for the stair line in the area of short errors. In known methods for the detection of defects in textile fabrics, such as are known from WO98 / 08080 and must also be used in this context, experience has shown that short defects are evaluated differently than longer defects. This is given by the device or the method with which the image points are recorded and which can have special properties which lead to such a differentiated treatment of errors. It is therefore appropriate to provide a correction that increases the value for the stair line 16, 28 for short errors. The properties mentioned can be represented by a characteristic such as can be represented by curve 49 in FIG. 3. Such a characteristic, as represented by curve 49, is either already known or has to be determined by tests with the given device. If it is assumed that the above-mentioned method determines values for the stair line 28 that apply to the right half on axis 2, curve 49 indicates how far the stair line in the left half of FIG. 3 is would increase. It applies that fields or classes in which curve 49 falls should fall as a whole below the stair line 28. This also takes into account the easily understandable fact that short defects in the fabric are more likely to be hidden by the structure of the fabric, so that such short errors must be noticed by a stronger contrast to the fabric in order to be recognizable.

In order to find a measure and also a scaling for the intensity of a pixel or error, it can be assumed, for example, that the intensity in this case is influenced by the width and contrast of an error. FIG. 8 shows one possibility of how the intensity could be determined from the width and the contrast with the aid of a model. The model is represented and thus predefined by the surface of a cone, that is to say the cone surface 42, on which values for the intensity lie. From the value for the width of an error, which is given by the number of pixels, and from the contrast, which is determined from the brightness values of the pixels, a value for the intensity can now be found by looking at the values for width and contrast applies the relevant axes 44, 43 and then erects a perpendicular at the intersection in the plane of the two axes 43, 44. The intersection point 52 of this perpendicular with the conical surface 42 gives the desired intensity, which is given by the height of the conical surface 42 above the plane.

Once the classification matrix 1, 26 has been defined with the stair line 16, 28, it is then a matter of recognizing the errors in a given flat structure and classifying them according to the classification matrix. For this purpose, a method is used, for example, as described in WO98 / 08080. Each camera line is represented by its pixels and it is now possible to store these pixels in the classification matrix 1, 26 according to their intensity or brightness. Since new camera lines are constantly being scanned, there can be several assignments for certain fields or classes in succession, so that these can also be counted, a count value being able to be entered in the class in question. The stair lines 16, 28 thus represent limits that depend on the fabric or knitted fabric presented. Pixels in the fabric that do not reach these limits are ignored by the system for processing them. Pixels that are above these limits do not necessarily have to indicate errors. However, they indicate particularly clear irregularities. From a textile point of view, these can also be interesting and therefore it can make sense to count them as events. For such reasons, the classification matrix can therefore even have three zones. The lowest zone, like the areas 17 and 29, extend from the lowest intensity limit or axis 2 to the stair lines 16, 28. Above that is a zone of mere event counting and the error zone is even higher. The areas 18, 30 are subdivided by the user as desired, while the stair lines 16, 28 can be determined automatically. Fig. 3 shows with a further staircase line 50 such a division into three zones.

Claims

claims:

1. A method for assessing defects in textile fabrics, characterized in that two parameters are selected for the assessment, that a classification matrix (1, 26) is formed, in which values of the parameters determine class limits and class limits (4 - 19) the classification matrix Divide into fields so that the classification matrix is further divided into at least two areas (17, 18 or 29, 30) by determining an average value for pixels from the error-free flat structure for one parameter and depending on a group of pixels with the greatest deviation of the parameter to the mean, a boundary between two areas is determined, that the division into at least two areas takes place along the class boundaries, that values in the fabric are recorded from pixels (37, 38) that represent them, and the values according to the two selected parameters be classified in the classification matrix and that pixels that are in one area are classified into the classification matrix, indicate a possible error in the fabric.

2. The method according to claim 1, characterized in that the intensity of the pixels and their extent is recorded as a parameter, the extent being brought about by a plurality of adjacent pixels.

3. The method according to claim 2, characterized in that the length is measured as the extent, which is formed by several adjacent pixels of similar, but different from a reference value intensity.

4. The method according to claim 1, characterized in that the area for possible errors is further divided into a first area for permissible errors and a second area for inadmissible errors.

5. The method according to claim 1, characterized in that the boundary between the two areas is determined automatically.

6. The method according to claim 5, characterized in that the automatic determination of the upper limit is carried out with the aid of holiness or intensity values which are recorded and ordered according to size, the upper limit being a value which is defined in a group (51 ), which is formed by a predetermined number of the most extreme values.

7. The method according to claim 6, characterized in that within the group the median value of the holiness or intensity values is determined as the upper limit.

8. The method according to claim 5, characterized in that the upper limit is changed for a value range of the one parameter.