EP3656907B1 - Device and method for monitoring the handling of a thread and sewing machine - Google Patents

Description

The present invention relates to a device for monitoring a thread wound on a spool.

It also relates to a sewing machine with a device for monitoring the unwinding of a thread wound on a spool.

Furthermore, the invention relates to a method for monitoring the unwinding of a thread wound on a spool.

Devices for monitoring the amount of thread wound on a spool, or the amount of remaining thread, and for determining the amount of thread used during sewing are used in sewing machines in order to be able to draw conclusions about errors in the stitch pattern. Sewing machines typically use upper and lower threads wound on spools to form a seam.

Due to factors such as material, machine settings, tolerances and wear in the machine, thread breakage, skipped stitches or false stitching can occur. False stitches are missing stitches in the seam pattern that are caused by an incorrect wrapping process between the upper thread and the lower thread. Too many skipped stitches within a seam pattern can lead to a considerable reduction in the tensile strength of the seam. False stitching is the partial or complete absence of the lower thread in the finished seam. The upper thread is held in the shape of the seam pattern by the material. A false stitched seam does not offer anywhere near the tensile strength of a correct seam. This is particularly the case with safety-relevant and load-bearing

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Skipped stitches and false stitches are not permitted in seams, which is why they must be reliably detected. Subsequent quality control using optical systems is not reliable and must therefore be carried out manually, which represents a considerable amount of work and underlines the need for seam or thread monitoring during the sewing process within the sewing machine.

Such monitoring is extremely difficult due to the available installation space on the sewing machine's gripper system and due to the oscillating movement of the spool carrying the thread in various gripper systems. State-of-the-art monitoring systems are only able to detect the rotation and direction of rotation of the spool as the thread is unwound during the sewing process. In the event of a thread breakage or an incorrect wrapping process of the upper and lower threads, the spool can come to a standstill or start a trembling/oscillating movement. This can be partially reliably detected by existing systems via the rotation and direction of rotation of the spool. Due to the weight of the spool and the thread wound onto it, the spool continues to rotate in the event of skipped stitches or certain types of false stitching, even though the thread required for the sewing process is not used. This case cannot be reliably detected by existing systems and may not be classified as faulty.

The JP 2010 252 847 A discloses a bobbin thread monitor with a bobbin, wherein a flange portion of the bobbin is made of a magnetic material. The CN 105 821 596 A 2 teaches a coil with flanges, wherein on the flange facing the sensor a

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Magnet unit is arranged. The DE 38 00 717 A1 discloses an apparatus and a method according to the preambles of claims 1 and 7.

The state of the art also includes residual thread monitoring using optical sensors. DE 2007 021 300 A1 A device for monitoring the remaining thread quantity of a thread wound on a spool is known, in which an optical sensor is used to detect when a certain area of the monitored spool is exposed by a thread. The thread must be wound accordingly beforehand so that after the monitored area, the desired amount of remaining thread is present on the spool. Aside from the necessarily specified type of winding of the thread on the spool, the problem with this device is the use of optical sensors, particularly light/dark sensors. Due to the sewing dust generated during the sewing process, the hook lubrication and compressed air that may be contaminated with water and oil, these become dirty and must be cleaned regularly.

It is therefore the object of the invention to propose a device that reliably allows the rotational movement and direction of the bobbin in a sewing machine to be determined and enables the thread consumption to be determined. It is also the object of the invention to propose a corresponding sewing machine and a method with which an exact thread consumption in a sewing machine can be reliably determined and which thus allows conclusions to be drawn about errors in the seam pattern.

The device task is solved by a device according to claim 1. The device according to the invention has field generating means that can be attached to the spool in a rotationally fixed manner to monitor the unwinding of a thread wound on a spool in a sewing machine in order to generate a field that can be sensed without contact. This enables reliable spool and thread monitoring without the need for error-prone optical measurements.

It is intended that it has detection means for detecting the contactless scannable field, wherein the detection means are designed to record changes in the contactless scannable field depending on a rotation angle of the coil. The detection means enable the Reliable determination of the rotation and direction of rotation of the spool. This allows the amount of thread used to be reliably determined.

Furthermore, the invention provides that the field generating means have a magnet, in particular a permanent magnet, and that the detection means comprise a magnetic field sensor. The use of magnetic fields advantageously replaces previous optical systems. Measuring the magnetic field using a magnetic field sensor is also significantly easier compared to optical systems - there is no need for a clear line of sight between the sensor and the coil, which is a problem due to the limited space in the area of the gripper system. No special optical markings, coloring or the like are necessary either. External scattered radiation is also negligible compared to optical systems. The field of a permanent magnet advantageously does not have to be generated, which means that errors are further reduced.

Furthermore, according to the invention, it is advantageously possible to detect a coil that has been inserted incorrectly using the magnetic field strength that can be determined using the magnetic field sensor, since this decreases significantly when the direction of insertion is incorrect. According to the invention, the insertion of a new coil is checked using the magnetic field sensor.

According to the invention, the north-south axis of the magnet is aligned perpendicular to the axis of symmetry of the coil. This means that when the magnet rotates around the axis of symmetry of the coil, comparably large field changes in the magnetic field occur even with small changes in the angle of rotation, which enables detection of even small changes in the angle of rotation. The north direction of the magnetic field can therefore be used within the scope of the invention to determine The angle of rotation of the bobbin can be clearly determined by the magnetic field sensor. In an embodiment of the invention, the direction of rotation can also be used to detect an incorrect winding direction of the bobbin thread.

According to a preferred embodiment of the invention, the magnet is designed as a bar magnet or diametrically magnetized, in particular as a diametrically magnetized hollow cylinder, wherein the magnet is arranged in particular within the coil. A diametrically magnetized hollow cylinder can advantageously be arranged within the coil in such a way that both have the same axis of symmetry and rotate about this axis when the coil rotates. This makes it particularly easy to calculate a change in the angle of rotation of the coil from the field change, since deformation due to different rotation geometries is advantageously eliminated.

When using a bar magnet, in an advantageous embodiment, this is embedded in one of the two front sides of the coil. In another embodiment of the invention, it is provided that it has evaluation means for evaluating field signals detectable by the detection means, wherein the evaluation means influence a rotation of the coil. The evaluation means calculate a rotation or direction of rotation of the coil with the help of a logic. With great advantage, they influence a rotation of the coil in such a way that, when appropriate measured values are reached, the rotation of the coil can be stopped without intermediate steps and the sewing process can be interrupted.

In a sewing machine according to the invention with a spool for a thread, the object of the invention is achieved by providing it with a device according to the invention. A sewing machine is proposed that enables reliable monitoring of the bobbin and thus also of the thread consumption without optical systems.

In an advantageous embodiment of the sewing machine according to the invention, it is provided that it has a further spool for a further thread and a further device according to the invention. This makes it possible to better monitor the seam pattern of the sewing machine, since typically two threads are used for a seam and seam errors sometimes only affect one thread.

According to a further embodiment of the sewing machine according to the invention, the spool is designed as a bobbin thread spool for winding a bobbin thread and the further spool is designed as a measuring wheel for guiding an upper thread. The upper thread runs as a continuous thread from a yarn cone from outside to the sewing machine. To measure the upper thread consumption, the upper thread runs over the measuring wheel. In this way, within the scope of the invention, a sewing process of a typical stitch pattern with upper and lower thread, such as a double lockstitch or lockstitch, can be monitored. This is particularly advantageous for sewing machines that are not equipped with a CNC control. In a special embodiment of the invention, it is possible to record upper thread consumption.

Furthermore, in an embodiment of the invention, it can be provided that the sewing machine is designed in such a way that the evaluation means are designed to determine a remaining thread length. The logic of the evaluation means is thus to determine the consumption of the thread wound onto the spool via the rotation, direction of rotation and angle of rotation of the spool. designed to be calculable. By precisely measuring the consumption and the maximum length of thread that can be wound on due to the dimensions of the spool, the available remaining length of thread on the spool can be determined at any time using the thread consumption of the bobbin thread.

To reliably detect thread consumption, it is necessary to use a correctly wound spool. The thread must be wound parallel to the spool. A complete layer of thread is always wound parallel to one another across the entire width of the spool before the next layer is started. This leads to a change in the unwinding radius of the spool that is predictable according to the Archimedean spiral.

By monitoring the upper and lower threads, it is possible according to the invention via the logic of the evaluation means to clearly detect thread breakage and false stitching in non-CNC-controlled sewing machines at the earliest after each stitch and at the latest after the seam has been completed, since here a delta in the consumption of the upper thread compared to the lower thread occurs.

In CNC-controlled sewing machines, the logic of the evaluation means in the embodiment of the invention is designed to calculate a theoretical consumption of the thread, in particular the upper and lower thread, based on the step size between the stitches and to use this for the evaluation. This means that a user is also able to recognize skipped stitches with great advantage when using the invention, since a delta occurs between the theoretical thread consumption and the measured thread consumption of the upper and lower thread.

In a further embodiment of the sewing machine according to the invention, it is provided that it has output means for outputting signals of the evaluation means. This makes it possible, with great advantage, that when the evaluation means detect a thread break, skipped stitch or false sewing, the output means can issue an error message to the operator. Within the scope of the invention, this advantageously makes it possible to safely remove the relevant component to be sewn from the production chain and assign it to the rejects. Furthermore, the output means enable the evaluation means to point out a necessary bobbin change in good time, thus preventing the start of a sewing process with, for example, too little bobbin thread, which would inevitably lead to a seam error.

The method task is solved by a method according to claim 7. In the method according to the invention for monitoring the unwinding of a thread wound on a spool in a sewing machine, field generating means for generating a contactless, scannable magnetic field are attached to the spool in a rotationally fixed manner, with the field being continuously measured. This makes it possible to determine the rotation of a spool, in particular the angle of rotation and the direction of rotation, directly and continuously, without having to draw conclusions about the rotation via optical marks or the like. The north-south axis of the magnet generating the magnetic field is aligned perpendicular to the axis of symmetry of the spool.

In a particularly advantageous embodiment of the method according to the invention, it is provided that a rotation angle and a rotation speed of the bobbin are continuously determined and evaluated, whereby an evaluation signal for influencing the rotation of the bobbin and a user output signal are generated. This enables the user of the method to take any necessary precautions, such as changing the bobbin or stopping the sewing process, in order to obtain a correct seam pattern.

Furthermore, according to another embodiment, it is provided that a consumption and/or a residual thread quantity of the thread wound onto the spool is determined. This allows comparisons to be carried out on the basis of calculated and measured thread lengths or on the basis of two measured thread lengths, which enables reliable control of the seam pattern.

Using the measured angle of rotation, the logic of the evaluation means according to the invention can determine the rotation, direction of rotation and thread consumption. To measure thread consumption, the logic initially assumes the largest possible unwinding radius of the spool after a spool change. During the first sewing process, the logic according to the invention compares the detected changes in the angle of rotation of the spool with the expected change in the angle of rotation depending on the largest possible unwinding radius in order to verify that the spool was completely full after insertion. Based on the completely filled spool, the logic according to the invention can calculate the thread used with a correction factor for the change in the unwinding radius caused by emptying the spool.

According to a further embodiment, it is provided that a further spool with a further thread wound on it is monitored in the sewing machine, wherein at least one further field generating means for generating a further contactlessly scannable magnetic field is attached to the further spool in a rotationally fixed manner, wherein the further magnetic field is continuously measured,
whereby the consumption of the thread wound onto the other spool is determined and compared with the consumption of the thread wound onto the spool. This allows the upper and lower thread consumption to be compared with each other and direct conclusions can be drawn about seam defects, which means that the component in question can be removed from the machine at the latest after completion of the seam in question. production chain. Within the scope of the invention, the additional spool can also be designed as a measuring wheel for guiding an upper thread. According to this design, the upper thread runs as if it were an endless thread from a yarn cone from outside to the sewing machine. To measure the upper thread consumption, the upper thread runs over the measuring wheel.

The present invention enables the monitoring of a thread wound on a spool in a sewing machine, in particular via a magnet embedded in the spool, which is detected according to the invention by a magnetic field sensor, which is connected to a logic and thus evaluated. This logic can thus determine the rotation, the direction of rotation, the angle of rotation and, via the angle of rotation, the consumption of the thread wound on the spool during a sewing process. By monitoring both a lower thread wound on the spool and an upper thread wound on another spool, upper and lower thread consumption can be determined at any time. Within the scope of the invention, the upper thread can alternatively or additionally also be fed as a quasi-endless thread from a yarn cone from outside via a measuring wheel to the sewing machine. In this case, the upper thread consumption is measured within the scope of the invention via the measuring wheel over which the upper thread runs. By comparing the used bobbin thread on the spool with the consumption of the upper thread and/or with the step width between the stitches on CNC sewing machines, the logic can monitor the sewing process in terms of thread breakage, skipped stitches or false stitches. In addition, due to the dimensions of the spool and thus the maximum length of thread that can be wound up, the available remaining length of thread on the spool can be determined at any time using the thread consumption of the bobbin thread.

The invention is described by way of example in a preferred embodiment with reference to a drawing, wherein further advantageous details can be taken from the figures of the drawing.

Functionally identical parts are provided with the same reference symbols.

Figur1 :

Darstellung einer mit einem runden Diametralmagneten versehenen erfindungsgemäßen Spule mit Magnetfeldlinien in einer geschnittenen Spulenkapsel;

Figur 2:

Darstellung einer geschnittenen, mit einem runden Diametralmagneten versehenen Spule nach der Erfindung;

Figur 3:

Darstellung eines mit einem runden Diametralmagneten versehenen Messrades mit Magnetfeldlinien zur Überwachung des Oberfadenverbrauchs;

Figur 4

schematische Darstellung der Funktionsweise der erfindungsgemäßen Vorrichtung anhand der Darstellung des Fadenverlaufs durch die Verbrauchsüberwachung.

The figures in the drawing show in detail:

Figure1 :

Representation of a coil according to the invention provided with a round diametrical magnet with magnetic field lines in a cut coil capsule;

Figure 2:

Representation of a sectioned coil provided with a round diametrical magnet according to the invention;

Figure 3:

Representation of a measuring wheel equipped with a round diametrical magnet with magnetic field lines for monitoring the upper thread consumption;

Figure 4

Schematic representation of the functioning of the device according to the invention based on the representation of the thread path through the consumption monitoring.

Figure 1 shows a coil 2 according to the invention provided with a round diametrical magnet 7 with magnetic field lines 14 in a cut coil capsule 15. The diametrical magnet 7 forms a field generating means 5 for generating a field 4 that can be sensed without contact. The diametrical magnet 7 is designed as a ring and is embedded in an end face 16 of the coil 2 in such a way that a north-south axis 11 of a magnetic field 14 generated by the diametrical magnet 7 is aligned perpendicular to an axis of symmetry 10 of the coil 2.

Figure 2 shows a sectioned coil 2 according to the invention, provided with a round diametrical magnet 7. The magnet 7 is designed as a rotationally symmetrical hollow body 9 and is embedded in an end face 16 of the coil 2. The axes of symmetry 10 of the magnet 7 and the coil 2 thus coincide and both components 2, 7 rotate about the same axis, namely the axis of symmetry 10, when the coil 2 rotates. This makes it easier to determine a change in the angle of rotation of the coil 2 from a measurement of the field change in the magnetic field 14.

Figure 3 shows a measuring wheel 17 provided with a round diametrical magnet 7 with field lines of a magnetic field 14. The measuring wheel 17 is referred to according to the invention as a (further) spool 2' or upper thread spool 20'. In one end face of the measuring wheel 17, which is used in particular for monitoring a further thread 3' or upper thread 30', a further field generating means 5', which generates a further, contactlessly scannable field 4', is embedded in the form of a ring-shaped magnet 7. In addition to the other design of the surface conditions of the spool body, the functioning of the monitoring of the rotation of the measuring wheel 17 to determine the consumption of a length of an upper thread 30' corresponds to the functioning of the Figures 1 and 2 devices shown.

Figure 4 shows a schematic representation of the functioning of the device according to the invention based on a representation of the thread path through the consumption monitoring. Here, a Figure 4 The seam produced by the sewing machine 1, which is only partially shown, is shown in the form of a double lockstitch 18. A material 19 lying on a needle plate 22 is sewn by means of a needle 24 of the sewing machine 1. For this purpose, an upper thread 30', which is on a needle plate lying above the material 19 in a needle stitch direction, is Yarn cone 21 is mounted, is connected to a bobbin thread 30 wound on a bobbin thread spool 20, which is mounted below the material 19 in the needle stitch direction, to form a seam. To connect the two threads 30, 30', a gripper 23 arranged on the bobbin thread spool 20 takes up the upper thread 30' and guides it around the lower thread 30 so that both threads 30, 30' are entwined. In order to detect errors in the double lockstitch in good time and to enable monitoring of the rotation of the bobbin thread spool 20 or the upper thread spool 20', magnets 7 are arranged on the bobbin and upper thread spools 20, 20' in such a way that they rotate equally when the respective spool 20, 20' rotates. At the same time, a magnetic field 14 (not shown) generated by the respective magnet 7 also moves and changes according to the respective angle of rotation. The magnetic field 14 of the magnet 7 embedded in the respective spool 20, 20' is detected according to the invention by a magnetic field sensor 8, with a magnetic field sensor 8 being arranged on both the lower thread spool 20 and the upper thread spool 20'. Both magnetic field sensors 8 are connected to a logic (not shown here) that evaluates the measured values of the magnetic field sensors 8 in such a way that it determines the angle of rotation and the direction of rotation of the spools 20, 20'. From this, the logic determines a thread consumption according to the invention.

The use of the device according to the invention for monitoring the upper thread 30' shown takes place in particular in such a way that the upper thread spool 20' is formed by a plastic-coated cylinder, in which the magnet 7 is inserted into the cylinder in a similar way to the implementation in the lower thread spool 20. According to the invention, the cylinder is rotatably mounted and attached to a sewing machine head within a feed of the upper thread 30'. The cylinder is wrapped with the upper thread 30' and rotated by the upper thread 30' in the sewing process. This rotation is also carried out via a magnetic field sensor 8 mounted there. Due to a fixed radius of the cylinder and the detected angle of rotation, the logic can determine the consumption of the upper thread 30' directly according to the invention. The consumption of the lower thread 30 is determined based on the measured values of the magnetic field sensor 8 on the lower thread spool 20. These measured values are calculated in the logic using the largest possible unwinding radius of the lower thread spool 20 and correction factors for this radius. This allows the consumption of the lower thread 30 to be calculated. By comparing the upper and lower thread consumption, a fault in the seam can be reliably detected in the sewing process with the sewing machine 1 shown.

LIST OF REFERENCE SYMBOLS

• 1 sewing machine
• 2 Coil
• 2' additional coil
• 3 threads
• 3' additional thread
• 4 Field generating agents
• 4' additional field generating means
• 5 Field
• 3' additional field
• 6 Detection means
• 7 Magnet
• 8 Magnetic field sensor
• 9 hollow cylinders
• 10 Axis of symmetry
• 11 North-South axis
• 12 Evaluation tools
• 13 Output media
• 14 magnetic field lines
• 15 Bobbin case
• 16 Front side
• 17 Measuring wheel
• 18 Lockstitch
• 19 Materials
• 20 Bobbin
• 20' upper thread spool
• 21 yarn cones
• 22 Needle plate
• 23 grippers
• 24 needle
• 30 bobbin thread
• 30' upper thread

Claims (10)

1. Device for monitoring the unwinding of a thread (3) wound on a spool (2) in a sewing machine (1), wherein it comprises field generating means (4) which can be attached to the spool (2) in a rotationally fixed manner for generating a contactlessly scannable field (5),

   and it comprises the detection means for detecting the contactlessly scannable field (5), wherein the detection means are designed to pick up changes in the contactlessly scannable field (5) as a function of an angle of rotation of the spool (2), wherein

   the detection means comprise a magnetic field sensor (8),

   characterised in that the field generating means (4) have a magnet (7), in particular a permanent magnet, which can be attached to the spool in such a way that its north-south axis (11) is aligned perpendicularly to the axis of symmetry (10) of the spool (2).
2. Device according to claim 1, characterised in that the magnet (7) is designed as a bar magnet or diametrically magnetised, in particular as a diametrically magnetised, hollow cylinder (9), the magnet (7) being arranged in particular inside the spool (2).
3. Sewing machine (1) with a spool (2) for a thread (3), characterised in that it is provided with a device according to one of claims 1 to 2.
4. Sewing machine (1) according to claim 3, characterised in that it has a further spool (2') for a further thread (3') and a further device according to claim 1 or 2.
5. Sewing machine (1) according to claim 4, characterised in that the spool (2) is designed as a lower thread spool (20) for winding up a lower thread (30) and in that the further spool (2') is designed as an upper thread spool (20') for winding up an upper thread (30').
6. Sewing machine according to one of claims 3 to 5, characterised in that it has evaluation means for evaluating field signals which can be detected by the detection means (6), the evaluation means being designed to determine a residual thread length.
7. Method for monitoring the unwinding of a thread (3) wound on a spool (2) in a sewing machine (1), wherein field generating means (4) for generating a contactlessly scannable magnetic field (5) are attached to the spool (2) in a rotationally fixed manner, wherein the magnetic field (5) is continuously measured, in order to record changes in the magnetic field as a function of an angle of rotation of the spool (2), characterised in that the north-south axis (11) of the magnet (7) generating the magnetic field (5) is aligned perpendicular to the axis of symmetry (10) of the spool (2).
8. Method according to claim 7, characterised in that a rotation angle and a rotation speed of the spool (2) are continuously determined and evaluated, an evaluation signal for influencing the rotation of the spool (2) and a user output signal being generated.
9. Method according to claim 7 or 8, characterised in that a consumption and/or a residual thread quantity of the thread (3) wound onto the spool (2) is determined.
10. Method according to claim 9, characterised in that a further spool (2') with wound-on further thread (3') is monitored in the sewing machine (1), wherein at least one further field generating means (4') for generating a further contactlessly scannable magnetic field (5') is attached to the further spool (2') in a rotationally fixed manner, wherein the further magnetic field (5') is continuously measured, wherein a consumption of the further thread (3') wound onto the further spool (2') is determined and compared with the consumption of the thread (3) wound onto the bobbin (2).

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