DE4037854A1 - Sewing machine optical monitor - comprises line camera used to scan lines of points across fabric direction of movement - Google Patents

Abstract

The optical sensor system, to monitor the fabric passing through a sewing machine, uses a sensor (40) which is limited to scanning a line of points across the direction (V) of fabric (10) movement during sewing. A scanning control system (51-54) repeatedly reads the light values of the points in the line, at time intervals corresponding to equal lengths of fabric movement. The line scanning duration is shorter than the scanning intervals. A memory (50) stores the picture signals for a given number (k) of line scans in succession. ADVANTAGE - The system is a low cost assembly, which occupies less room, and requires less data processing.

Description

The invention relates to a device for optically scanning a Sewing material during its processing in the sewing operation of a sewing machine, according to the preamble of claim 1

Automatic control of a sewing machine often requires Devices for scanning the material during its movement in order the sewing mode or the feed depending on the position of the sewing material influence. So-called edge detectors are generally known generally with a simple transmitted light or reflex light barrier have a single photocell, the output signal of the Appearance of a leading or trailing edge of the material changes suddenly, what can be used to emit an edge sensing signal. Something more complicated scanning devices are required in the so-called "pattern-correct" sewing together of two pieces of sewing material, where applicable, the the two patterned pieces always in relation to each other during sewing to keep the patterns aligned. At Fabrics that only cross or diagonally to the direction of the seam have oriented sample components, it is sufficient to Pattern offset only in the direction of the seam and correct if necessary. Two separate ones are used for this Photoelectric sensors, each one at least in the direction of the seam narrowly limited area of the piece of sewing material assigned to it was observed and provides an electrical output signal, which is accordingly the pattern-related fluctuations in the overall brightness of the respective Observation area changes when the sewing pieces are in the sewing direction be transported. Individual periods of the two Sensor signals, each of at least one repeat length of the pattern  correspond to the determination of a possible sample offset compared with each other, e.g. B. forming the Cross-correlation function, as known from DE 33 46 163 C1, for what temporary storage of a plurality of successive ones Values of the two sensor signals is required.

If a pattern offset not only in the direction of the seam, but also across to determine and correct what is in checkered Pattern or in the presence of parallel to the direction of the seam trending pattern components is often desired, one two-dimensional scanning of the sewing material takes place. This is it known from DE 37 38 893 A1 and DE 39 17 120 A1, to use two-dimensional image sensors, e.g. B. CCD matrix cameras, each a two-dimensional image section of the material level capture and each an image signal similar to a television signal produce. The comparative analysis of the two image signals for Determination of the pattern offset in two mutually orthogonal In this state of the art, directions are given with the help of two-dimensional cross-correlation function of both image signals.

Another case where it would be beneficial to have a two-dimensional one This is to capture a section of the material level edge-parallel sewing for curved edges or corners of the Sewing goods. Here it is important to change the direction of the edge in good time detect. So it is z. B. in the production of double seams a two-needle machine necessary, the fabric edge course behind one expected corner in advance to recognize the last stitch lengths the corner accordingly.

The known use of two-dimensional image sensors or Two-dimensional sensor matrices have various disadvantages. Such Sensor devices are not only relatively expensive, they require due to its areal expansion also a lot of space, in particular if they are arranged touching and therefore the same Extent as the image section to be captured must have. After all, the amount of data is two-dimensional  Processing sensors very large. The cost of Space requirements and the amount of data to be processed contribute to Total expenditure of the optical scanning device at.

The object of the present invention is to determine the total outlay for optical scanning of a two-dimensional image section of the Reduce the material surface. This object is achieved according to the invention solved by the characterizing features of claim 1.

The solution according to the invention comes with a "one-dimensional" sensor which is arranged transversely to the feed direction of the sewing machine, while the scanning in the perpendicular dimension of the Image section by successively querying this one-dimensional sensor takes place during the feed movement, and at intervals that correspond to equidistant feed lengths. By storing the image signals of a predetermined number consecutive sensor queries are stored Overall image signal that contains the image content of a two-dimensional Reproduces image section of the material surface.

There are several ways to keep the equidistance successive one-dimensional scans (line queries) with regard to the material surface. If in the feed direction only a low image resolution corresponding to a stitch length only one is required during each stitch period Line query, the equidistance by simple Phase synchronization with the arm shaft rotation of the sewing machine can be ensured.

If the image resolution in the feed direction is to be higher, then it must Several line queries are carried out during each stitch period, which are marked with the material feed are to be synchronized. In one embodiment of the Invention according to claim 3, this synchronization is based on of increments of arm shaft rotation. The material is fed but not with a constant rate within a period Speed, but is made up of a transport phase and a  Standstill or rest phase together. In one embodiment of the Invention according to claim 4 is therefore only the line query activated during the respective transport phase, namely in Line spacing, each a given number of increments correspond to the arm shaft rotation. Here, however, remains Not taking into account the fact that the Feed speed is not constant throughout, but on Gradually increases at the beginning and gradually decreases at the end. This can be too a slight disturbance in the equidistance of the successive Perform line queries, but this is tolerable in many cases. If you do not want to accept this disturbance, you can do it in one further embodiment according to claim 5, the line queries restrict the (middle) part of the transport phase in which the feed rate is constant. However, this remains the equidistance is only maintained within each stitch period, so that this Measure should preferably only be used if the one to be recorded Image section of the material surface in the feed direction is not larger is the feed length of said part of the transport phase. At larger image sections that go over several stitch lengths the line queries preferably according to claim 6 at specifically selected angular positions of the arm shaft, each correspond to equidistant feed lengths. This can happen that the line queries with appropriately selected count values of arm wave incremental pulses.

An alternative according to claim 7 is that Line queries with incremental pulses of the feed movement of the Synchronize sewing material directly measuring motion measuring device.

Further refinements of the invention, relating to the formation of the optical sensor device and the storage device are in Subclaims 8 to 16 marked.

The scanning device according to the invention can be used in conjunction with a second, similar scanning device, one Signal processing device and a transport control device  the pattern offset of two superimposed ones is used for this Sewing pieces in a sewing machine both lengthways and crossways to Determine the direction of the seam and correct it if necessary in order to sew the two pieces of material "according to the pattern". The characteristics of advantageous embodiments of a related combination listed in claims 17 to 23. To determine the Pattern offsets in the two orthogonal directions can either two one-dimensional cross-correlation functions are used (Claims 18 and 19), or a two-dimensional Cross-correlation function (claim 20).

Scanning devices according to the invention can also be used in combination with Corresponding evaluation circuits serve to close the edges of the material capture if such edges are within the observed two-dimensional image section appear. In this regard Further developments of the invention are in claims 24 to 26 described.

The invention is explained in more detail below with reference to drawings:

Fig. 1 shows the diagram of a scanning device according to the invention;

Fig. 2 shows the principle of a memory matrix with numerical values and graphical representations of the mean values of the matrix columns and rows;

Fig. 3 illustrates the use of scanning devices according to the invention in sewing according to the pattern;

Fig. 4 shows a graphic representation of the sewing material transport depending on the arm shaft rotation of the sewing machine.

In FIG. 1, the top view of a section of a patterned fabric 10 is shown on the left, which is moved in the direction of arrow V in a sewing machine in order to form a seam 21 parallel to the fabric edge 11 by means of a sewing needle piercing at point 20 . The parts of the sewing machine involved here, such as the sewing needle, presser foot, feed devices and throat plate, are not shown in FIG. 1 for reasons of clarity. The patterning of the fabric 10 in the example shown consists of evenly spaced dark longitudinal strips 13 parallel to the seam direction and of equally spaced dark transverse strips 14 perpendicular to the sewing direction. The areas 16 between the strips are light, and the areas 15 at the crossing points of the strips are darker than the strips 13 and 14 .

For many reasons, which have already been mentioned above, it may be desirable to determine the relative position of the pattern and / or the fabric edges with respect to the seam 21 to be formed or the piercing point 20 of the sewing needle, both in the feed direction V and transversely thereto. For this purpose, it is necessary to scan the fabric 10 areally within a two-dimensional image section, as indicated by the dashed frame 30 in FIG. 1. So far, two-dimensional image sensors have been used for this, that is to say arrangements which have a two-dimensional grid of image-receiving elements, onto which the entire image section 30 is imaged at once.

In the present case, only a one-dimensional photoelectric sensor is used to scan the image section 30 , which only detects a row of points which is transverse to the feed direction V. In Fig. 1, this sensor 40 is schematically represented by a transverse row or row of a number n discrete light receiving elements 40 _j (with j from 1 to n), which lie on the surface of the fabric 10 and by a likewise line-shaped light source, which is extends congruently with the sensor line below the fabric 10 (and therefore cannot be seen in FIG. 1), through which fabric 10 is irradiated. The consequence of this is that each light receiving element 40 j supplies an electrical output variable which corresponds to the material brightness at the relevant location. The light receiving elements located outside the fabric edge 11 receive most of the light since they are not shadowed by parts of the fabric 10 from the light source, so that the output size of these elements is maximum.

In FIG. 2, a memory device 50 is shown, and form a matrix of individual memory cells, the n columns (corresponding to the number of light receiving elements in the line sensor 40) and k lines in the form. A scanning control device, which is not shown in FIG. 1 and is described further below in connection with FIG. 3, ensures that the output variables of the light receiving elements 40 _{j of} the line sensor 40 are queried and written into a line of the matrix memory 50 . This inscription is preferably carried out in such a way that the output variable of the first light receiving element 40 _{1 is written} into the first memory cell of a row, the output variable of the second light receiving element 40 ₂ is written into the second cell of the row, etc., up to the nth light receiving element, the Output variable is written in the nth cell of the row.

These "line queries" are repeated at certain time intervals in the course of the sewing operation. Said time intervals are selected so that the same feed length of the material movement in the feed direction V is always measured from one line query to the next. The results of successive line queries are written into successive memory cell lines of the matrix memory 50 , so that after k successive line queries, the memory contains the image content of a two-dimensional image section, the transverse dimension of the width of the line sensor 40 and the longitudinal dimension (in the seam or feed direction) of the product kd _v corresponds to, where d _{v is} the feed length between successive line queries.

Fig. 1 shows the position of the fabric 10 in the fourth line query in the course of scanning of the image section 30 of the fabric surface. The first query took place when the upper edge of the cutout 30 was still at the level of the line sensor 40 . Accordingly, the first line of the memory matrix contains the values of n adjacent picture elements (pixels) along the upper edge of the cutout 30 . The pixel values are entered in the memory cell matrix shown within the memory device 50 as numerical values. It is arbitrarily assumed that the darkest pattern areas 15 each deliver the lowest pixel values 2 at the crossing points of the strips, while the less dark parts of the strips 13 and 14 each give the pixel value 4, the light areas 16 each the pixel value 6 and the areas outside the Fabric edges each deliver the highest pixel value 8. Intermediate values arise wherever a light receiving element of the sensor line simultaneously detects parts of different bright areas due to its finite spatial extent.

In the third last line scan, the material 10 has moved so far in the feed direction V, that is to say the image section 30 has moved so far upwards in FIG. 1 that the end edge 12 of the material 10 has exceeded the line sensor 40 and thus all the pixels of this line scan have the highest value 8. This also applies to the following second last line query and the k-th query, in which the lower edge of the image section 30 lies at the level of the line sensor 40 .

It can be seen from the numerical values within the memory cell matrix that these values represent a true image of the brightness distribution within the image section 30 after a storage cycle of k queries. This stored image information can be processed in a variety of ways in order to analyze the spatial position and orientation of certain features of the image and thus of the fabric 10 and to control the operation of the sewing machine accordingly, for example for sewing in accordance with the pattern or for parallel sewing or also for switching off the sewing operation upon arrival of the end edge of the fabric.

As already indicated, a scanning control device ensures that successive line queries take place after the same feed lengths of the material movement, ie are "equidistant" with respect to the material surface. How this aquidistance can be ensured is explained below with reference to FIGS . 3 and 4.

Fig. 3 shows various mechanical and electronic devices in a sewing machine, which cooperate in operation to sew pieces of sewing material according to the pattern. In the case shown, the one piece of sewing material corresponds to the fabric 10 , as shown in plan view in FIG. 1. In the middle of FIG. 3, this substance 10 and also the line sensor 40 lying above it can be seen in a sectional view, which corresponds approximately to the line III-III of FIG. 1.

Coming from the right, the fabric 10 arrives at an intermediate plate 41 , in which there is an illuminating device 42 , which is arranged at the same height as the line sensor 40 and shines through the fabric 10 in the direction of the light receiving surface of this line sensor. The lighting device 42 has an upper and a lower flat optical fiber strand 43 , 43 a arranged in the intermediate plate 41 . The optical fiber strands 43 , 43 a connected to a light source (not shown) end at a transparent reflex line 44 arranged in the intermediate plate 41 and extending transversely to the feed direction V. The end of the reflex line 44 opposite the optical fiber strands 43 , 43 a is forked in a V-shape, the surfaces 45 , 45 a running at an angle of 90 ° to one another being mirrored and the light emerging from the optical fiber strands 43 , 43 a perpendicularly upward or forward down.

The individual light receiving elements of the line sensor 40 form a line perpendicular to the drawing plane of FIG. 3. Further to the left is the sewing needle 71 of the machine, which is moved up and down by the main drive shaft (arm shaft) around the fabric 10 and an underlying fabric 10 a periodically pierce and in the process entangle an upper thread carried along with a lower thread guided below the two fabrics. The thread guide is not shown in FIG. 3 for reasons of clarity. Every time the needle 71 has moved out of the fabrics 10 , 10 a again, two fabric pushers 73 , 73 a come into action in order to shift the fabrics a predetermined distance to the left in the feed direction V. A presser foot 72 ensures that the two fabrics 10 , 10 a are held down on the needle plate 70 , which is provided with recesses for reaching through the parts of the lower fabric slide 73 a and with a stitch hole for the needle 71 to pass through.

During the sewing operation described, the fabric 10 intermittently moves with its pattern in the feed direction V over the intermediate plate 41 . In order to obtain an image of a two-dimensional section of the fabric surface that is as true to scale as possible, the line sensor 40 must provide individual images of equidistant line areas of the fabric surface. This means that the successive line queries must be synchronized with the material movement. For this purpose, a synchronization device 54 is provided which, at certain intervals, applies line synchronization pulses H to a synchronous input 46 of the line sensor 40 , whereupon the sensor delivers the output signals of the individual light receiving elements in rapid succession at its signal output 47 . The line sensor 40 can be a CCD line camera, the photosensitive CCD charge storage cells of which are temporarily activated for the duration of a certain exposure or integration time, in order to then read out the stored charge values sequentially with the aid of a relatively high-frequency clock signal T.

Since the fabric pushers 73 , 73 a are driven by the arm shaft, the feed movement of the fabric is normally synchronized with the arm shaft rotation. Normally, it can be assumed that the fabric is always moved by the same amount in the course of the sewing operation within each rotation period of the arm shaft. The required equidistance of the successive line queries can thus be achieved if the synchronizing pulse H is generated at a predetermined angular position of the arm shaft, for. B. whenever the needle is at bottom dead center and the fabric is stationary. Corresponding position sensors are installed in many sewing machines and can therefore be used directly as a synchronizing device 54 for generating the line synchronizing pulses H.

With the synchronization method described above, however, only a relatively coarse image resolution in the feed direction is possible. If the image resolution is to be higher, then several line queries must occur during each arm shaft rotation, the times of which can be derived from the output pulses A of an incremental encoder 60 on the arm shaft. Since the relationship between the angular steps (increments) of the arm shaft rotation and the material feed is not linear, the output pulses of such an incremental encoder cannot be used directly or continuously to generate "equidistant" line synchronizing pulses H.

Fig. 4 shows the feed movement of the fabric as a function of the arm shaft angle of rotation over a revolution period. The zero point of the abscissa is arbitrarily assumed to be the arm shaft position at which the material slide starts to work. The ordinate represents the transport path of the material, divided into eight equal lengths d _v . It can be seen that the feed rate, ie the steepness of the curve, initially increases gradually, then remains constant for a certain time and then gradually decreases again to zero. This "transport phase" extends over about two thirds of a full arm shaft rotation, during the last third a "rest phase" passes in which the fabric does not move.

One way of obtaining the line synchronizing pulses H is to use the pulses A of the arm wave incremental encoder 60 (or a frequency-divided version of these pulses) as line synchronizing pulses H only during the transport phase. The pulses appearing during the rest phase are simply blanked out, which can be done with the aid of a gate circuit in the synchronizing device 54 , the switching on and off of which can be controlled by corresponding position detectors on the arm shaft. In this case, the equidistance of the line queries is not perfect everywhere, because the transport speed is not constant everywhere even during the transport phase. Because of the smaller slope of the curve shown in FIG. 4 at the beginning and at the end of the transport phase, the line spacing of the scanning becomes somewhat smaller at the relevant points than in the middle of the transport phase. However, it has been found that this equidistance disturbance can be tolerated in many cases.

It is also possible to generate line synchronizing pulses H only those arm wave incremental pulses (direct or in frequency-divided version) to be used during the middle Part of the transportation phase will be delivered where the Feed rate is pretty constant. However, this is likely Measure only be useful if the whole to be recorded Image section in the feed direction is not larger than that Feed length within the constant speed interval.

A very good equidistance of successive line queries for an image section, which can also go over several arm shaft rotation periods (stitch periods), is obtained if each line query is assigned to a selected angular position of the arm shaft, these angular positions being selected so that their distances are equal to the feed lengths d _{v of} the substance. For this purpose, an arm shaft incremental encoder which has a relatively high resolution and a counter which counts the successive incremental pulses of each arm shaft revolution are preferably used. The output of the counter is applied to a decoder programmed to predetermined counts corresponding to the selected angular positions mentioned. Whenever one of these count values appears, a line sync pulse H is emitted. To illustrate this procedure, the increments of the arm shaft rotation are also entered along the abscissa in FIG. 4, which in the case shown range from 0 to 127 (that is, 128 = 2 ⁷ increments per arm shaft rotation). If you want to carry out eight equidistant line queries per revolution period, corresponding to the eight equally spaced feed lengths d _v along the ordinate, the incremental pulse count values for the individual queries are found as abscissa values of the relevant points on the transport curve. In the case of FIG. 4, the successive line inquiries No. 1 to No. 8 are therefore to be carried out for the incremental pulse count values 15, 24, 32, 40, 48, 56, 65 and 80.

Another alternative is to derive the line sync pulses H from a motion sensor that detects the actual feed motion of the fabric. Such a motion meter can be a so-called "pole wheel" rolling on the fabric surface, as shown in dashed lines at 61 in FIG. 3. An incremental encoder monitoring the rotation of the pole wheel can give corresponding incremental pulses B to the synchronizing device 54 (as indicated by the dashed line B), which then delivers the line synchronizing pulses H directly or with frequency division from these pulses.

The pixel values read out from the line sensor 40 after each line synchronization pulse H are preferably fed to an analog / digital converter 51 , which is also controlled by the high-frequency clock signal T, and from there they arrive at the matrix memory 50 via a write control circuit 52 . The write control circuit 52 uses the line synchronizing pulses H, which are fed to it via a suitably dimensioned delay element 53 , and the high-frequency clock pulses T to ensure that the pixel values of each line scan are written into successive matrix lines of the memory 50 . After k line queries, z. B. a memory content, as shown in FIG. 2 by the numerical values within the matrix of the memory 50 .

A processing device 55 can use a microprocessor (not shown here) to analyze the memory content in order to find out certain features of the stored image and to determine their spatial position and orientation, so that the operation of the sewing machine, in particular as regards the guiding and joining of the materials 10 , 10 a concerns, can be controlled automatically. Fig. 3 illustrates as an example the special case of an automatic machine control for pattern-based sewing.

When sewing according to the pattern, it is important to guide the two superimposed fabrics 10 and 10 a so that their patterns are always in register with each other. As soon as a pattern offset in a certain direction is determined, the two substances are moved in the relevant direction relative to one another until this offset disappears. In order to correct a pattern offset in the feed direction, the upper and lower fabric slides 73 , 73 a are acted on by means of assigned actuators 77 , 77 a (e.g. stepper motors) in such a way that they provide a different feed of the two materials 10 , 10 a in the sense of a Reduce the pattern offset. To regulate a pattern offset transversely to the feed direction V, two guide wheels 74 , 74 a are provided, which engage the upper or lower fabric 10 or 10 a and can be rotated by means of associated actuators 75 , 75 a, which can also be stepper motors to move the fabrics across the feed direction. The guide wheels 74 , 74 a are provided on their circumference with freely rotatable sliding rollers 78 , 78 a, which allow the materials 10 and 10 a to slide freely in the feed direction V, as described in DE 39 17 120 A1. The actuating devices for the guide wheels 74 , 74 a and also the actuating mechanisms for the slider 73 , 73 a can also be designed as is known from said publication.

While the upper fabric 10 slides as described over the intermediate plate 41 provided with the lighting device 42 , the lower fabric 10 a is pulled between the underside of this intermediate plate and the surface of the needle plate 70 . As already described, the lighting device 42 is designed such that it also shines downwards in order to illuminate a second line sensor 40 a through the lower material 10 a, which can be configured in exactly the same way as the first line sensor 40 and the one line-shaped region of the lower one Fabric 10 a is detected, which corresponds in size, position and orientation to the area of the upper fabric 10 detected by the first line sensor 40 . The lower line sensor 40 a is controlled in the same way as the upper line sensor 40 with the aid of line synchronizing pulses H _a and with the aid of high-frequency clock pulses T in order to output the values of successive line queries via an A / D converter 51 a and a write control circuit 52 a to give second matrix memory 50 a. The elements 40 a to 53 a of the "lower" scanning device shown in FIG. 2 correspond in function and structure to the elements 40 to 53 of the "upper" scanning device, so that a repeated description is unnecessary.

If the two substances 10 and 10 a are aligned with one another in the desired manner so that the features (pattern components, edges) detected by the line sensors 40 , 40 a within the scanned image section 30 ( FIG. 1) are in register with one another, then the second or "lower" matrix memory 50 a after k line queries the same content as the first or "upper" matrix memory 50 . However, if the lower fabric 10 a is spatially offset from the upper fabric 10 , then the pixel values of the lower matrix memory 50 a are also offset in a corresponding manner from the pixel values of the upper matrix memory 50 . This offset can be calculated in the processing device 55 by comparative analysis of the memory contents.

The offset calculation is advantageously carried out using cross correlation functions. Such as B. from DE 37 38 893 A1 or DE 39 17 120 A1 known per se, a two-dimensional cross-correlation function (KKF) of the two memory contents can be formed with a two-dimensional displacement vector in order to search for the value of the displacement vector at which the KKF has an absolute maximum. From the displacement vector found and the known values for the line spacing (feed length per period of the line synchronizing pulses H) and for the pixel spacing within a line (spatial division of the light receiving elements of the line sensor), the two components for the pattern offset along and across the feed direction V can then be calculated . From these components, control signals L 1 , L 2 and Q 1 , Q 2 for the actuators 77 , 77 a and 75 , 75 a are determined in order to move the slider 73 , 73 a and the guide wheels 74 , 74 a to compensate for the longitudinal or to influence the transverse offset.

Instead of a two-dimensional cross-correlation function, two one-dimensional cross-correlation functions can also be used to determine the pattern offset. To determine the longitudinal offset, the cross-correlation function of the pixel values of a selected column of the one matrix memory can be formed with the pixel values of the corresponding column of the other matrix memory, with a displacement vector pointing in the column direction. The size of the displacement vector at which the KKF is at a maximum or exceeds a certain value indicates the measure of the pattern offset in the longitudinal direction and can be converted to generate the control signals L 1 and L 2 . In order to determine the transverse offset, the KKF of successive pixel values of a selected row of the one matrix memory can be formed with the pixel values of the corresponding row of the other matrix memory, with a displacement vector pointing in the row direction. The value of this displacement vector at which the KKF is at a maximum or exceeds a certain value is a measure of the offset transverse to the feed direction and can be converted to generate the control signals Q 1 and Q 2 .

In many cases, however, better results can be achieved if one forms the cross-correlation function of the row mean values to determine the longitudinal offset and the cross-correlation function of the column mean values to determine the cross offset. The row mean values are shown in FIG. 2 to the right of the matrix memory 50 both as numerical values and graphically. The column mean values are shown in FIG. 2 above the matrix memory 50 , likewise numerically and graphically. It can be seen that the line mean values have a well distinguishable waviness which is characteristic of the transverse stripes 14 of the pattern on the fabric 10 . These ripples would also be present if the crossover areas 15 of the pattern strips were just as bright as the strips themselves. For example, lines # 3, # 4, # 9, and # 10 all have the same uniform pixel values, as do columns # 5, # 6, # 10, and # 11. Cross-correlation functions along these lines and columns, respectively would be useful for pattern detection.

Compared to the formation of a two-dimensional cross-correlation function, the formation of two one-dimensional cross-correlation functions has the advantage of a far lower computing effort, so that the hardware of the processing device 55 can be reduced and / or the computing time can be reduced.

The following algorithm would apply to the two-dimensional KKF use:

The algorithm for the one-dimensional cross correlation function for Determining the transverse offset is:

and the algorithm for the one-dimensional cross-correlation function to determine the longitudinal offset is:

In the above equations:

P1, P2 each have a discrete pixel value in the first and second matrix memories,
S1, S2 in each case the mean value of a pixel column in the first or second matrix memory,
Z1, Z2 in each case the mean value of a pixel line in the first or second matrix memory,
M1, M2 each the mean value of all pixels within the relevant summation area in the first or second matrix memory,
j, i the run variables in the row or column direction
x, y the displacement parameters in the row or column direction,
a and b the limits of the summation range in the row direction,
c and d the limits of the summation range in the column direction.

The parameters a, b, c, d are preferably selected such that the widths (b-a) and (d-c) of the summation areas in the row and column directions at least the repeat length of the pattern in the relevant direction correspond, whereby it must of course be ensured that the areas are smaller than the total number n or k of columns or Lines. For the displacement parameter x, all (integer) Values from (1-a) to (n-b) can be selected for the displacement parameter y all (integer) values from (1-c) to (k-d).

Scanners of the type described here can also be used for purposes other than pattern sewing. So z. B. by analyzing the memory content also determine where the edges of the fabric and how they run. The column coordinate of the edge point in the relevant line can be determined for each line of the image section 30 by successively addressing the memory locations of the relevant line and comparing the pixel values read there with a threshold value in order to determine the address where the threshold value is crossed for the first time. An analogous procedure can also be used in the column direction. In the case of FIG. 2, the said threshold would have to be set to a value between 7 and 8. The address information evaluated in this way is also location information about the edge points, by means of which certain functions of the sewing machine can be controlled, for example for edge-parallel sewing or for so-called corner control.

The scanning device described can also be combined with a detection circuit which detects the arrival of the leading or trailing edge of the fabric at the scanning location in order to prepare certain functions (e.g. initialization of signal processing, initiation of adjustment processes, etc.) or the end of a seam . Such a detection circuit can, as shown in FIG. 3, contain an averager 57 which receives the pixel values of a complete line scan and forms the mean value therefrom. This mean value is compared in a threshold circuit 58 with a threshold value which is set in such a way that it lies between the range of pixel values resulting from the presence of material and the pixel values resulting from the absence of substance. Threshold circuit 58 generates an edge sensing signal K as soon as the pixel average of a line scan (or a predetermined portion thereof) crosses this threshold. In the illustrated as an example in Fig. 3 system for sewing to pattern the detection circuit 57, 58 either the upper or the lower sensing device may be associated. If desired, two detection devices can also be provided, one for each scanning device, in order to separately detect the edges of the two substances 10 and 10 a.

In addition to the embodiment of the scanning device described above, other configurations and developments are also possible. In the above description of the synchronizing device for the equidistant line interrogation, the fact has been neglected that the control devices, which serve to correct the pattern offset, have an additional influence on the transport movement of the fabrics when sewing according to the pattern. This influence naturally affects the equidistance of the line interrogation if the line synchronization pulses are derived from the arm shaft rotation. In most cases, however, this impairment is so small that it can be tolerated. If desired, the influence of the offset correction on the equidistance of the line queries can also be compensated for by modifying the operation of the synchronizing device 54 depending on the control signals L 1 and L 2 , which determine the mass transport in the feed direction. In general, more line queries must be carried out per arm shaft rotation if the feed length increases per arm shaft rotation. If a frequency divider is used to derive the line sync pulses, the number of line queries per arm shaft rotation can be modified by changing the division ratio of the frequency divider accordingly. If the synchronization device 54 works with a programmed set of selected incremental pulse count values, as was explained above with reference to FIG. 4, the influence of the offset correction can be compensated for by different sets of feed control signals L 1 and L 2 Assigned incremental pulse counts.

The line sensor (e.g. a CCD line camera), unlike in the case of FIG. 3, can be arranged at a greater distance from the surface of the material to be detected, with lens optics for imaging the line-shaped region of the surface of the material on the light-receiving elements of the line sensor or an optical fiber bundle can be used. Instead of the transmitted light scanning shown, a reflection light scanning can also be carried out by illuminating the material to be scanned from the same side on which the sensor is also arranged. A corresponding lighting device can be integrated in the sensor itself; in the case of scanning by means of an optical fiber bundle, the illumination can take place via a second optical fiber bundle which is embedded in the first bundle or lies parallel to it. These possibilities of reflected light scanning are shown and described, for example, in DE 33 46 163 C1. Finally, it is also possible to scan the line-shaped area of the fabric surface by a light spot traveling in the line direction and to observe it by means of a single light receiving element, the output signal of which then corresponds to a line scan each time the light spot passes.

It is also possible to use both types of lighting - i.e. the transmitted light Scanning and reflected light scanning - to be provided and each that type of lighting for carrying out a scanning process to select which of the substances currently being processed is most suitable, d. i.e. where the clearest signal values are generated will. The most suitable type of lighting can be selected either by the operator from personal experience or based on of instructions or during a sewing process previous measurement phase are carried out automatically, whereby successively obtained measurement signals with both types of lighting and these are then compared.

One as a storage device for the successive Row queries used matrix memory can also be of the type of Shift registers are operated, the pixel values of each Row queries are always written in the first matrix row and then the entire memory content is advanced by one line will return the first line for the next line query to clear. In this way you always get in the memory matrix a complete "continuous" image of the image section always up to date. However, this illustration be temporarily frozen if you do more complicated image analysis such as computing cross-correlation functions wants, whose computing time is longer than the time interval between the Row queries is.  

Since the image information contained in the matrix memory consists of discrete Pixel values, the spaced points of the sampled Image detail, it can increase the accuracy of the Image processing can be useful through interpolation processes Form intermediate values, so that one can process a larger one Column and row density and thus more continuous functions receives. Of course, in this case, those in the above increase Formulas (1), (2) and (3) used values n for the number of columns and k for the number of lines accordingly. To form the Cross-correlation function in the transverse direction according to the above formula (2) it suffices to interpolate between the column means perform, and for the cross-correlation function in the longitudinal direction according to formula (3) above, it is sufficient to interpolate between to perform adjacent row averages.

Claims (26)

1.Scanning device for optically scanning a sewing material during its processing in the sewing operation of a sewing machine to obtain image information which represents the image content of a two-dimensional image section of the material surface, with a photoelectric sensor device which has a predetermined field of view directed at the material surface and the light values of the inside scans points lying in this field of view in order to generate corresponding image signals, characterized in that the field of view of the sensor device (e.g. 40 ) is limited to a line of points which is transverse to the main feed direction (V) of the sewing material ( 10 ) during the sewing operation is that a scanning control device ( 51-54 ) is provided which repeatedly polls the light values of the points of the line at time intervals which correspond to the same feed lengths of the sewing material ( 10 ), the respective duration of a line query being short in comparison I at these time intervals, and that a memory device ( 50 ) is provided which stores the image signals of a predetermined number k of successive line queries. 2. Scanning device according to claim 1, characterized by a synchronizing device ( 54 ) which synchronizes the clock of the successive line queries with increments of the feed movement of the sewing material ( 10 ). 3. Scanning device according to claim 2, characterized in that the synchronizing device ( 54 ) derives line synchronizing pulses (H), which trigger line queries, from incremental pulses (A) of an arm shaft rotation of the sewing machine sensing incremental encoder ( 60 ). 4. Scanning device according to claim 3, characterized in that the synchronizing device ( 54 ) is activated only during the transport phase of the material feed in order to generate the line synchronizing pulses (H) during this time at intervals which are equal to a given number of incremental pulse periods. 5. Scanning device according to claim 4, characterized in that the synchronizing device ( 54 ) is activated only during each interval of the transport phase in which the feed rate is substantially constant. 6. Scanning device according to claim 3, characterized in that the synchronizing device ( 54 ) contains a counting device which counts the incremental pulses (A) over each arm shaft rotation in order to generate a line synchronizing pulse (H) for each of a number m of predetermined count values, the Count values are selected so that they correspond to m discrete angular positions of the arm shaft, between which the sewing material is moved by 1 / m of the feed length caused within the arm shaft revolution. 7. Scanning device according to claim 2, characterized in that the synchronizing device ( 54 ) synchronizes the clock of consecutive line queries with incremental pulses (B) of a movement measuring device ( 61 ) which directly measures the material movement. 8. Scanning device according to at least one of the preceding claims, characterized in that the sensor device has a CCD line camera ( 40 ), on the light receiving elements ( 40 j) of a line-shaped illuminated by an illumination device ( 42 ) extending transversely to the direction of advance of the plane of the sewing material ( 10 ) is shown. 9. Scanning device according to claim 8, characterized in that a lens system is provided for illustration.   10. Scanning device according to claim 8, characterized in that a bundle of light guides is provided for the illustration, the Light entry ends one line in close proximity to the material level form and to the individual light receiving elements of the Lead line scan. 11. Scanning device according to claim 8, characterized in that for imaging the light receiving elements ( 40 j) of the line camera ( 40 ) are arranged in close proximity to the material level. 12. Scanning device according to at least one of claims 8 to 11, characterized by such an arrangement of the lighting device ( 42 ) that it shines through the line-shaped region of the material level in the direction of the line camera ( 40 ). 13. Scanning device according to at least one of claims 10 to 12, characterized in that the lighting device ( 42 ) has a line-shaped light outlet which is arranged in close proximity and parallel to the area to be imaged of the material level. 14. Scanning device according to at least one of the preceding claims, characterized in that the memory device ( 50 ) has a matrix of memory cells which form k rows and n columns, and that a memory control circuit ( 52 ) is provided which in each case contains the image signals of successive row queries Inscribes the form of n pixel values in assigned memory cell rows of the matrix. 15. Scanning device according to at least one of claims 8 to 14, characterized in that each of the n columns of the memory matrix ( 50 ) is associated with a light receiving element ( 40 _j ) of the CCD line camera ( 40 ). 16. Scanning device according to claim 14 or 15, characterized by an A / D converter ( 51 ) which converts the image signal of each line scan into n digital pixel values. 17. Combination of two scanning devices ( 40-52 , 40 a- 52 a) according to at least one of claims 14 to 16 with a signal processing device ( 55 ) and one influencing the relative position of two superimposed patterned pieces of sewing material ( 10 , 10 a) in two mutually perpendicular directions Transport control device ( 75 , 75 a, 77 , 77 a), the first scanning device ( 40-52 ) for scanning an image section ( 30 ) of the first piece of sewing material ( 10 ) and the second scanning device ( 40 a- 52 a) for scanning an identical one Image section of the second piece of material to be sewn ( 10 a) is arranged and the signal processing device ( 55 ) reads the stored pixel values from the matrix memories ( 50 , 50 a) of the two scanning devices and determines by comparative analysis sizes which determine the two-dimensional offset of the patterns of the two pieces of material to be sewn Show row direction and column direction and in manipulated variables (L 1 , L 2 , Q 1 , Q 2 ) are converted, which are given to the transport control device ( 75 , 75 a, 77 , 77 a) in the sense of reducing the offset. 18. Combination according to claim 17, characterized in that the signal processing device ( 55 ) for determining the size indicating the pattern offset in the row direction, the coefficient of the cross-correlation function of the column mean values of the pixel values contained in the matrix memories ( 50 , 50 a) at different values of a displacement parameter in the row direction calculated and the displacement value at which the coefficient is maximum. 19. Combination according to claim 17 and / or 18, characterized in that the signal processing device ( 55 ) for determining the size indicating the pattern offset in the column direction, the coefficient of the cross-correlation function of the row mean values of the pixel values contained in the matrix memories ( 50 , 50 a) at different values of a displacement parameter in the column direction and calculates the displacement value at which the coefficient is maximum. 20. Combination according to claim 17, characterized in that the signal processing device ( 55 ) for determining the values indicating the pattern offset calculates the coefficient of the two-dimensional cross-correlation function of the pixel values contained in the two matrix memories at different displacement vectors and determines the components of the vector in which the coefficient is maximum. 21. Combination according to at least one of claims 17 to 20 in conjunction with at least one of claims 3 to 7, characterized in that the relationship between the arm wave incremental pulses (A) and the line synchronizing pulses (H) generated in the synchronizing device ( 54 ) is dependent of the manipulated variables (L 1 , L 2 , Q 1 , Q 2 ) given to the transport control device ( 75 , 75 a, 77 , 77 a) can be changed in order to maintain the equidistance of the line queries. 22. Combination according to at least one of claims 17 to 21, characterized in that the signal processing device ( 55 ) contains an interpolation device which forms additional intermediate values by interpolation in the row and / or column direction, and that the numbers n and k represent the additional intermediate values with include. 23. Combination according to at least one of claims 17 to 22, characterized in that for the sensor devices ( 40 , 40 a) of the two scanning devices ( 40-52 , 40 a- 52 a) a common lighting device ( 42 ) is provided, which in a flat plate ( 41 ) is accommodated between the pieces of sewing material ( 10 , 10 a) and the two sensor devices are irradiated through the pieces of sewing material assigned to them. 24. Combination according to at least one of claims 17 to 23, characterized in that the signal processing device ( 55 ) contains an evaluation circuit which identifies the row and column coordinates of those of the pixels read from the two matrix memories which identify the image of the edge line of the assigned workpiece ( 10 , 10 a) represent. 25. Combination of a scanning device (z. B. 40-52 ) according to at least one of claims 14 to 16 with an evaluation circuit (in 55 ) which reads the stored pixel values and thereby identifies the row and column coordinates of those pixels that the image of Represent the edge line of the sewing material ( 10 ). 26. Combination of an arrangement according to at least one of the preceding claims with a detection circuit ( 57 , 58 ) which generates an edge detection signal (K) when the mean value of the image signal of at least a predetermined part of a line query crosses a set threshold value, which is between the existing one Sewing material ( 10 ) resulting range of image signal amplitudes and the resulting image signal amplitude in the absence of sewing material.