EP0420867A1

EP0420867A1 - Process and sewing machine for stitching layers of fabric together to ensure pattern matching

Info

Publication number: EP0420867A1
Application number: EP89906357A
Authority: EP
Inventors: Heribert Geisselmann; Manfred Frank; Fritz Jehle; Erich Willenbacher
Original assignee: GM Pfaff AG
Current assignee: GM Pfaff AG
Priority date: 1988-06-06
Filing date: 1989-05-26
Publication date: 1991-04-10
Also published as: US5103749A; ES2016023A6; WO1989012126A1; JPH04504962A; BR8907470A

Abstract

N'importe quel type de dessin sur chacune de deux nappes de tissu est reconnu par une caméra et les nappes de tissu sont orientées de sorte que les dessins se chevauchent dans les sens transversal et longitudinal. Les effets des fluctuations dues à la vitesse et des limitations dues aux dessins sont réduites pendant la production du signal. Des images bidimensionnelles des deux nappes de tissu (7, 8) sont produites par des caméras matricielles (39, 45) pendant une pause de transport. Le degré de chevauchement des dessins des nappes de tissu est déterminé par analyse d'intercorrelation bidimensionnelle des points d'image disposés en lignes et en colonnes, les valeurs de correction d'orientation étant dérivées de ce degré. La distance entre les bords des nappes de tissu est mesurée au moyen d'une section séparée des détecteurs matriciels, déterminée en fonction de l'évaluation. Les données relatives à la distance des bords sont utilisées pour régler la nappe inférieure du tissu (8) en continu et la nappe supérieure de tissu (7) suivant les besoins, en fonction de la distance. En s'accommodant de légères imprécisions et en limitant les opérations de calcul uniquement aux régions étudiées, on peut considérablement réduire la durée totale de calcul.Any type of design on each of two webs of fabric is recognized by a camera and the webs of fabric are oriented so that the designs overlap in the transverse and longitudinal directions. The effects of speed fluctuations and design limitations are reduced during signal generation. Two-dimensional images of the two webs of fabric (7, 8) are produced by matrix cameras (39, 45) during a transport pause. The degree of overlap in the patterns of the fabric webs is determined by two-dimensional cross-correlation analysis of the image points arranged in rows and columns, the orientation correction values being derived from this degree. The distance between the edges of the fabric webs is measured by means of a separate section of the matrix detectors, determined based on the evaluation. The edge distance data is used to adjust the lower fabric web (8) continuously and the upper fabric web (7) as needed, depending on the distance. By accommodating slight inaccuracies and limiting the computation operations only to the regions studied, the total computation time can be considerably reduced.

Description

description

Process and sewing machine for sewing fabric layers according to the pattern

The invention relates to a method and a sewing machine according to the preamble of claims 1 and 5, respectively.

DE-OS 37 38 893 is a

Pattern alignment device known for a sewing machine, the operation of which corresponds to the preamble of method claim 1. The known device allows two to be the same

Sew the surface structure or the fabric layer with the same pattern according to the pattern. If this is a check pattern, for example, pattern lines of one layer of fabric running across the seam line should be aligned with the corresponding pattern lines of the other layer of fabric, and pattern lines of one layer of fabric running parallel to the seam line should have the same lateral distance to the seam line as the corresponding pattern lines of the other layer of fabric to have.

As a prerequisite for an alignment of pattern lines running parallel to the seam line, one of the fabric layers must first be aligned to a predetermined edge distance from the stitch formation point. For this purpose, an edge sensor is provided which measures the distance between the

Fabric layer edge determined. If the actual distance value deviates from the nominal distance value, the alignment means of the corresponding edge guiding device is acted on in such a way that the nominal-actual value deviation is eliminated. The other layer of material is now aligned according to the pattern based on the data obtained in the cross-correlation analysis via a possible transverse offset with the help of the other alignment means of the edge guiding device.

The known pattern alignment device is primarily used for forming the center back seam on jackets, since the perfect appearance of this seam is a very important quality criterion when assessing the overall quality of these garments. It is very important that the pattern lines of the left and right parts run absolutely flush with each other and that the lengthways pattern lines are at exactly the same distance from the seam line. Because of the larger width of the jacket in the shoulder area, however, it follows that pattern lines otherwise aligned parallel to the seam line in this area are under one acute angle to the seam line. With certain patterns in which the longitudinal pattern lines are at a mutual distance that exceeds the width of the surface sensor, it can now occur in the shoulder area that the oblique longitudinal lines migrate sideways out of the measuring field of the surface sensor, so that no longitudinal lines can be detected for a certain time and thus no signal depicting the transverse distance of the longitudinal lines can be obtained. Although it would be possible to use appropriately sized area sensors to avoid this situation, such area sensors are extraordinarily expensive.

The invention is therefore based on the object of providing a method and a sewing machine for stitching layers of fabric according to the pattern, which enables the simple processing of such patterns in which longitudinal pattern lines or structural elements have a comparatively large mutual distance to have. The object is achieved by the features specified in the characterizing part of claims 1 and 5.

To quickly determine whether longitudinal pattern lines or structural elements can be recognized by the area sensors, according to the Claims 2 and 3 simplify the arithmetic operation to be carried out after each shift of the mask image by standardizing an arithmetic parameter that is always to be recalculated and restrict the time-consuming exact arithmetic method required for the exact determination of the degree of coverage of the two layers of material to the image area of interest in each case, whereby the overall arithmetic time for the cross-correlation analysis is considerably reduced becomes.

By means of the parabolic approximation method specified in claim 4, the mutual offset of the two layers of material which may be present can be determined very precisely even with relatively large pixels.

The reduction in the total computing time for the cross-correlation analysis not only serves to quickly determine whether longitudinal pattern lines are recognizable and can be used for the cross-adjustment of the layers of fabric to be sewn together, but also serves to increase the sewing speed while still accurately determining and correcting a possible pattern offset .

From the claims relating to the design of the sewing machine, in particular the measure according to claim 6 is to be emphasized, according to which the edge scanning sensor is a component of the area sensor of the corresponding matrix camera. In this way, it is not necessary to use a separate sensor for edge scanning.

The invention is explained with reference to an embodiment shown in the drawing. Show it:

Figure 1 is a side view of the sewing machine with two matrix cameras.

Fig. 2 is a block diagram of the

Signal processing device;

3 shows a representation of the image format of the search image and the mask image;

Fig. 4 shows the location of an entire

Image field, consisting of an area for structure comparison and an area for edge measurement, with respect to the assigned fabric layer.

The sewing machine shown only partially in Fig. 1 has a base plate (1) and a head (2). In the head (2) is the usual presser foot (3) The presser bar (4) and the needle bar (5), the thread-guiding needle (6) of which works with a gripper (not shown). The sewing machine has an upper fabric pusher (9) and a lower fabric pusher (10) for advancing two layers of fabric (7, 8) to be joined together.

The lower fabric pusher (10) is received by a carrier (11), the fork-shaped end of which engages around an eccentric (12) which is arranged on a shaft (13) mounted in the base plate (1) and the fabric pusher (10) per stitch-forming process issued a lifting movement. The other end of the carrier (11) is connected to a crank (14) which is fastened on a shaft (15) which is also mounted in the base plate (1).

The shaft (15) is driven by an adjustable drive mechanism, not shown, which, like that shown in DE-PS 33 46 163 in FIG. 3

Drive mechanism for the shaft also designated there (15) is constructed and works in the same way.

The presser bar (4) is provided at its lower end with a crossbar (16) which carries a pin (17). A handlebar (18) is mounted on the pin (17) and is articulated to the upper fabric slide (9) by means of a joint pin (19). This is constantly pressed downwards by a spring-loaded ball (20) and receives its lifting movement from a lever (21) pivotably mounted on the crossbar (16), the free end of which engages under a roller (22) carried by two lateral bearing webs of the upper fabric slide (9) . The other end of the lever (21) is over an intermediate link (23) is connected to an angle lever (24).

The angle lever (24) is connected to an eccentric drive, not shown, which corresponds to the eccentric drive shown in DE-PS 33 46 163 in FIG Fabric slide (9) is used.

An intermediate link (25), which is connected to a rocker arm (27) by a pivot pin (26), acts on the pin (19) to drive the upper fabric slide (9). The rocker arm (27) is connected to a drive mechanism, not shown, which, like the drive mechanism shown in DE-PS 33 46 163 in FIG. 3, is constructed for the rocker arm designated there (58) and functions in the same way.

In order to be able to change the feed size of the upper fabric slide (9) relative to the feed size of the lower fabric slide (10), a schematically illustrated actuating device (28) is provided which, like the actuating device (80), is constructed from DE-PS 33 46 163 and accordingly contains, among other things, a stepper motor, not shown here.

In front of the presser foot (3) there is a layer of fabric (7, 8) separated from one another by an intermediate plate (29) for guiding the edges

Edge guide device (30) is provided which corresponds to the guide device disclosed in DE-GM 85 16 184 and designated there with (6). The edge guide device (30) accordingly has an upper one Guide wheel (31) and a lower guide wheel (32). Both guide wheels (31, 32) carry a plurality of freely rotatable rollers 33 arranged transversely to the wheel plane on the circumferential side of their wheel bodies. The upper guide wheel (31) is connected to a stepper motor (35) via a toothed belt drive (34). The lower guide wheel (32) is connected to a stepping motor (37) via a toothed belt drive (36).

A CCD matrix camera (39) and a lighting device (40) are arranged on a carrier (38) attached to the front of the head (2).

Arranged below a glass plate (42) in front of the stitch formation point in the stitch plate (41) is an optical fiber bundle (43) which is surrounded by an optical fiber bundle (44) insulated from it. The inner light guide bundle (43) is connected to a CCD matrix camera (45) and the outer light guide bundle (44) to an annular lighting device (46-). Beneath the glass plate (42) there is an optic (not shown) which enables targeted illumination of the measuring surface and which in turn images this on the end face of the inner light guide bundle (43).

The matrix camera (39) is connected to an image memory (47) (FIG. 2) for the recording of digital image data. In terms of address, the image memory (47) is divided into two sections of different sizes, the larger of which is connected to a correlation module (48) and the smaller is connected to an edge evaluation module (49). The matrix camera (45) has an image memory (50) for recording digital image data connected. Like the image memory (47), the image memory (50) is divided into two sections of different addresses, the larger of which is connected to the correlation module (48) and the smaller to the edge evaluation module (49).

The correlation module (48) and the edge evaluation module (49) are connected to an offset correction module (51). A control module (52) is connected to the offset correction module (51)

Stepper motor control circuit (53) and corresponding lines (54, 55, 56) are connected to the stepper motor (not shown) of the actuating device (28) and the two stepper motors (35, 37) of the edge guide device (30). The image memories (47, 50), the

Modules (48, 49, 51) and (52) and the control circuit (53) form a signal processing device (57).

functionality

The image field (F) on the respective fabric layer (7) or (8) that can be detected by the matrix cameras (39, 45) is approximately 45 × 15 mm, this area being a pixel format of 0.44 × 0.44 mm Matrix field of 104 columns × 32 rows gives a total of 3328 pixels. 4, the two image fields (F) are divided into two functionally different areas, with the pattern offset of the two layers of fabric (7th in a section (A) consisting of 85 columns (Sp) and 32 rows (Z) (FIG. 3) , 8) across and parallel to

Feed direction (V) and in a section (B) consisting of 19 columns and also 32 rows, the position of the edge (K) of the respective fabric layer (7) or (8) adjacent to the seam (N) to be produced with respect to the needle (6) is determined. In the individual cells of the CCD sensors, not shown, each assigned to a pixel of the image fields (F), charge carriers are released in a known manner by the incident photons, the number of which corresponds to the image brightness at the respective pixels. The charge carriers are converted into 1-byte digital image data in a circuit part of each camera in a likewise known manner, the brightness of each pixel being represented by a numerical value between 0 and 255.

For the pattern offset detection of the two layers of fabric (7, 8), the image of the lower matrix camera (45) designated as mask image (M) is shifted row by row and column over the image of the upper matrix camera (39) designated as search image (S). So that the mask image (M) does not protrude beyond the edge of the search image (S), the mask image (M) is chosen to be smaller than the search image (S) corresponding to the section (A) in proportion to the displacement area.

The range of displacement depends on the maximum allowable pattern offset before performing pattern alignment. With a permissible pattern offset of - 1.5 mm, the shift range is 10 pixels lengthways and crossways. Since there are 11 different cover states in a shift by 10 pixels in each shift direction (starting position + 10 shifts) and also for increasing the accuracy between the

Function values are interpolated and the field is expanded by a function value at each limit, a field of 13 × 13 function values is finally obtained. The mask image (M) is thus chosen in comparison to the search image (S) in the row and column direction by 12 pixels each.

The similarity of two functions representing the pattern or surface structure of the two layers of material (7, 8) can be calculated in an exact manner by the two-dimensional standardized cross-correlation function KKF.

The KKF coefficient (p) is calculated as follows

p = cross correlation coefficient, range of values (-1, ..., +1)

Sij = gray value of a pixel from image 1 (search image) Mij = gray value of a pixel from image 2 (mask image) = mean value from search image section = Mean value of the mask image ij = rows, column running variable in image coordinates

The KKF coefficient is a measure of the similarity of the compared functions and has a value that is in the range (-1, ..., +1). The following applies:

p = +1: greatest possible similarity p = 0: no similarity P = -1: greatest possible "inverse" similarity

In a standard procedure, the KKF coefficient is calculated for every possible offset within the offset range. This gives you one two-dimensional function with the two orthogonal displacement values as variables. This function shows a maximum in the area of greatest agreement between the two images. The height of the maximum is a measure of the degree of similarity.

When using the standardized KKF, the following terms must be calculated for each exact shift after each shift:

To evaluate an entire pair of images, 13 × 13 = 169 KKF coefficients must be determined. As the gray value (Sij) of the pixels of the search image (S) is multiplied by the gray value (Mij) of the pixels of the mask image (M) in rows and columns when calculating each KKF coefficient and the aforementioned terms are also to be calculated over 700,000 arithmetic operations for the KKF analysis of an entire pair of images. When using an arithmetic unit that is clocked at 20 MHz, this results in a computing time of approx. 37 ms. Since in addition to the pure computing time about 5 ms for the actual recording and data transmission from the camera to the evaluation system and about 10 ms for the calculation of the manipulated variables, there is a total time of over 50 ms. Such a comparatively long time can only be represented in slow-running sewing machines.

For use with sewing machines with a speed of 6000 min ^-1 , the computing time must be reduced considerably. For this purpose, while accepting a slightly reduced accuracy, the term (1) is not calculated from every search image section in which the

Pattern comparison is carried out. Instead, the mean value of the entire search image (S) is determined only once and the result is used for each shifting step.

To further reduce the computing time, terms (4) and (5) are only calculated for those shifts in which the KKF reaches maximum values, since the quality of these maxima is only of interest if the patterns are assigned. To determine the non-standardized maximum values, the KKF sum is formed after each shift of the mask image (M) by only calculating the term in the numerator of the equation for determining the KKF coefficient. The KKF sums are then sorted by size, which determines their non-normalized maximum values. Since the KKF sums give high values for light fabrics or sample sections and low values for dark fabrics or sample sections, the maximum values of the KKF sums do not yet provide any information about the actual similarity of the functions or the actual location of a sample offset. After calculating the normalized KKF coefficients for the maximum function value, the degree of similarity of the two material samples is known and the decision can be made as to whether the measured value is used to control the offset. However, since the time-consuming calculation is only used for a pronounced maximum or a few outstanding maxima, this measure can reduce the computing time to about a third. In this way, the simplified two-dimensional KKF analysis can also be used for high-speed sewing machines with a speed of 6000 min, if one picture is taken by the matrix cameras (39, 45) in every third transport break of the fabric layers (7, 8).

A parabolic approximation method is used for the exact determination of the geometric position of the greatest similarity with the help of the KKF sums adjacent to the maximum value of the KKF sums, whereby the exact position of the greatest similarity results from the base point of the arithmetically formed parabolas.

The geometrical position of the greatest similarity of the KKF also forms a measure of the possible mutual offset of the pattern or surface structure course of the two layers of material (7, 8) that exists transversely and in the feed direction (V). This measure is transferred from the correlation module (48) to the offset correction module (51).

The gray value difference between the layers of fabric (7, 8) and the intermediate plate (29) is determined from the sections (B) of the image fields (F), the total values of the image columns (Sp) running parallel to the feed direction (V) being evaluated. Since the If the geometrical position of the image columns (Sp) is clearly defined, the current position of the edge (K) of each fabric layer (7, 8) can be easily recognized from the number of uncovered image columns (Sp). The distance dimension of the edges (K) to the needle (6) determined in this way is also input into the offset correction module (51) by the edge evaluation module (49).

The pattern offset data and the edge spacing data are then processed in the offset correction module (51) in such a way that correction data for maintaining a predetermined edge spacing of the lower layer of fabric (8) and for eliminating a possible pattern offset between the two fabric layers (7, 8) are formed. The correction data are then processed in the control module (52) and the stepper motor control circuit (53) into control data for the stepper motors (35, 37) and the stepper motor (not shown) of the actuating device (28). While the

Edge alignment of the lower fabric layer (8) by the stepper motor (37) and the guide wheel (32), the pattern-oriented alignment of the upper fabric layer (7) relative to the lower fabric layer (8) in the feed direction (V) is carried out by the adjusting device (28) and the upper fabric pusher (9) and transversely to the feed direction (V) through the stepper motor (35) and the guide wheel (31).

As long as the matrix cameras (39, 45) in

If the direction of feed (V) or structures or pattern lines are recognized, the edge spacing of the upper layer of fabric (7) is irrelevant for the alignment of the upper layer of fabric (7), since this is due both to the correction data obtained in the KKF analysis transversely as well as parallel to the feed direction (V) in the direction relative to the lower fabric layer (8). It can happen that the upper layer of fabric (7) with a pattern match with the lower layer of fabric (8) another

Edge distance than the lower fabric layer (8) adjusted to a predetermined edge distance.

If structures or pattern lines running in the feed direction (V) are temporarily not recognized, the edge spacing of the upper layer of fabric (7) formed during the last pattern adjustment serves as a setpoint for an edge distance control of the upper ones until the next detection of structures or pattern lines running in the feed direction (V) Fabric layer.

Since, due to the alignment movements carried out after the first KKF analysis to reduce an existing pattern offset, the size of the offset at the time of the next exposure by the matrix cameras (39, 45) will actually be reduced and not increased, a further reduction in the computing time can be achieved by taking the Knowledge from the previous KKF analysis can be achieved by restricting the arithmetic operations for determining the KKF sums to the area immediately adjacent to the previously calculated offset value.

Claims

1.Procedure for two-dimensional stitching together of two layers of fabric having the same surface structure by means of an automatic sewing machine with a sewing machine with an upper and a lower feed means, the feed sizes of which can be changed relative to one another by at least one adjusting device, with an edge guide device assigned to the two layers of fabric and working transversely to the feed direction , whose alignment movement can be carried out by first and second alignment means, with at least one edge sensor for determining the lateral distance of the edge of the fabric adjacent to the seam to be produced from one of the fabric layers to the stitch formation point of the sewing machine, the distance value determined being compared with a predefinable setpoint distance value and the corresponding alignment means corresponding to the deviation the edge guiding device is acted upon, each with a surface sensor for each layer of material and a signal processing device, the vo n Each layer of fabric is generated from image points arranged in rows and columns of flat sections of the surface, digital image data is determined by two-dimensional cross-correlation analysis of the digital image data of the search image and the mask image to be shifted in rows and columns and determines the mutual offset of any structural elements of the two layers of fabric and depending on them the size of the longitudinal offset of the adjusting device and depending on the size of the

Cross offset applied to the other alignment means of the edge guide device, characterized in that the lateral distance of the the adjacent edge of each of the two layers of fabric to be produced to the stitch formation point of the sewing machine is determined and, if temporary structural elements are not recognized, the pattern-oriented alignment of the fabric layer, which has not been oriented in relation to the feed direction since then, is interrupted and this is then also adjusted in relation to the edge, the prior to the change the distance from the pattern to the edge-related alignment of this fabric layer edge to the stitch formation point of the sewing machine is used as the setpoint distance.

2. The method according to claim 1, characterized in that, in particular for the rapid determination of whether longitudinal structural elements are recognizable, a simplified normalized cross-correlation function is calculated by determining the mean S of the entire search image only once and the result being used in each arithmetic shift step .

3. The method according to claim 2, characterized in that before the first shift and after each row or column shift of the mask image, the corresponding digital image data of the individual pixels of the search and mask image are multiplied and the products are added to cross-correlation sums which the maximum value is calculated and only from this the cross-correlation coefficient determining the quality of this maximum is calculated.

4. The method according to claim 2 or 3, characterized in that with a relatively roughly sampled cross-correlation function, the accuracy in determining the geometric Position of the maximum is increased by means of parabolic approximation.

5. Sewing machine for performing the method according to claim 1, wherein each fabric layer is one of the

Sewing machine controlled, connected to an image memory matrix camera is assigned with an area sensor, characterized in that for determining the lateral distance of the edge (K) adjacent to the seam (N) to be produced, both fabric layers (7, 8) to the stitch formation point (6) each have an edge scanning sensor is provided.

6. Sewing machine according to claim 5, characterized in that the edge scanning sensors

Are part of the area sensor of the corresponding matrix camera (39; 45).