EP3656907A1 - Device and method for monitoring the handling of a thread and sewing machine - Google Patents

Abstract

In order to provide a device for monitoring the unwinding of a thread (3) wound on a bobbin (2) in a sewing machine (1), which reliably allows the rotational movement and direction of the bobbin to be determined in a sewing machine and which enables the determination of a thread consumption, It is proposed that it have field generating means (4) which can be attached in a rotationally fixed manner to the coil (2) for generating a contactlessly scannable field (5).

Description

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

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

The invention also relates to a method for monitoring the unwinding of a thread wound on a bobbin.

Devices for monitoring a thread quantity or residual thread quantity wound on a bobbin, as well as for determining the thread quantity consumed during sewing, are used in sewing machines in order to be able to draw conclusions about errors in the stitch pattern. Typically, upper and lower threads wound on bobbins in sewing machines are used to form a seam.

Due to the influencing factors such as material, machine settings, tolerances and wear in the machine, thread breakage, missing stitches or false sewing can occur. Missing stitches are missing stitches in the seam pattern that result from an incorrect looping process between the upper thread and the lower thread. Too many skipped stitches within a seam pattern can significantly reduce the tensile strength of the seam. False stitching is the partial or total absence of the lower thread in the finished seam. The upper thread is held by the material in the form of the seam pattern. A sham-stitched seam does not come close to the tensile strength of a correct seam. Especially for safety-relevant and load-bearing Seams are not allowed for false stitches and false stitching, which is why they must be reliably recognized. Subsequent quality control via optical systems is not reliable and must therefore be carried out manually, which represents a considerable effort and underlines the need for a seam or thread monitoring during the sewing process within the sewing machine.

Such monitoring is extremely difficult due to the available space on the hook system of the sewing machine and due to an oscillating movement of the bobbin carrying the thread in various hook systems. State-of-the-art monitoring systems are only able to detect the rotation and the direction of rotation of the bobbin during the unwinding of the thread in the sewing process. In the event of a thread break or an incorrect winding process of the upper and lower thread, the bobbin can come to a standstill or start to shake / oscillate. In some cases, this can be reliably detected by the systems using the rotation and direction of rotation of the coil. Due to the weight of the bobbin and the thread wound there, the bobbin continues to rotate in the event of skipped stitches or a certain type of false sewing, although the thread corresponding to the sewing process is not used up. This case cannot be reliably identified by existing systems and may be classified as not faulty.

Residual thread monitoring using optical sensors is also known from the prior art. So is from the DE 2007 021 300 A1 a device for monitoring a remaining amount of thread 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 exposure of the monitored area, the desired amount of remaining thread is available on the bobbin. The problem with this device, in addition to the necessarily prescribed type of winding of the thread on the bobbin, is the use of optical sensors, in particular light / dark sensors. Due to the sewing dust generated in the sewing process and the hook oil and any compressed air contaminated with water and oil, they get dirty and must be cleaned regularly.

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

The device object is achieved in a device according to the invention for monitoring the unwinding of a thread wound on a bobbin in a sewing machine in that it has field generating means which can be attached to the bobbin in a rotationally fixed manner to produce a contactlessly scannable field. This enables reliable bobbin and thread monitoring without the need for faulty optical measurements.

According to one embodiment of the invention, it is provided that it has detection means for detecting the contactlessly scannable field, the detection means being designed to accommodate changes in the contactlessly scannable field as a function of an angle of rotation of the coil. The detection means enable the reliable determination of the rotation and direction of rotation of the coil. From this, a used amount of thread can be reliably determined.

Furthermore, it is provided in an advantageous embodiment of the invention 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 has advantageously replaced previous optical systems. The measurement of 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. In addition, no special optical marks, coloring or the like are necessary. External scattered radiation is also negligible in comparison with optical systems. The field of a permanent magnet advantageously does not have to be generated, which results in a further error reduction.

Furthermore, according to the invention, it is advantageously possible to identify a wrongly inserted coil by means of the magnetic field strength that can be determined on the magnetic field sensor, since this decreases sharply due to an incorrect insertion direction. The insertion of a new coil is checked according to the invention via the magnetic field sensor.

In a further embodiment it is provided that a north-south axis of the magnet is aligned perpendicular to an axis of symmetry of the coil. This results in a comparatively large field change in the magnetic field when the magnet rotates about the axis of symmetry of the coil, even with small changes in the angle of rotation, which enables detection of even small changes in the angle of rotation. A determination of the north direction of the magnetic field is therefore within the scope of the invention the angle of rotation of the coil can be clearly determined by the magnetic field sensor. In an embodiment of the invention, a wrong winding direction of the lower thread can also be seen in the direction of rotation.

According to a further preferred embodiment of the invention, the magnet is designed as a bar magnet or diametrically magnetized, in particular as a diametrically magnetized hollow cylinder, the magnet being 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 means that a change in the angle of rotation of the coil can be calculated particularly easily from the change in field, since reshaping due to different rotational geometries is advantageously eliminated.

In an advantageous embodiment, when a bar magnet is used, it is embedded in one of the two end faces of the coil.

Another embodiment of the invention provides that it has evaluation means for evaluating field signals detectable by the detection means, the evaluation means influencing a rotation of the coil. The evaluation means calculate a rotation or direction of rotation of the coil using logic. They have a great advantage in influencing a rotation of the bobbin in such a way that, with appropriate measured values, the rotation of the bobbin can be stopped without intermediate steps and the sewing process can be interrupted.

In a sewing machine according to the invention with a bobbin for a thread, the object of the invention is achieved in that it is provided with a device according to the invention, the device preferably being attached to the bobbin in a rotationally fixed manner. So that's one Sewing machine proposed, in which a reliable monitoring of the bobbin and thus also the thread consumption is made possible without optical systems.

In an advantageous embodiment of the sewing machine according to the invention it is provided that it has a further bobbin for a further thread and a further device according to the invention, the further device preferably being attached to the further bobbin in a rotationally fixed manner. This makes it possible to better monitor the seam pattern of the sewing machine, since typically two threads are used for one seam and seam defects sometimes only concern one thread.

According to a further embodiment of the sewing machine according to the invention, it is provided that the bobbin is designed as a lower thread bobbin for winding up a lower thread and that the further bobbin is designed as a measuring wheel for guiding an upper thread. The upper thread runs almost as a continuous thread from a thread cone from outside to the sewing machine. The upper thread runs over the measuring wheel to measure the upper thread consumption. A sewing process of a typical stitch pattern with upper and lower threads, such as double lockstitch or lockstitch, can thus be monitored within the scope of the invention. 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 here to record an upper thread consumption.

Furthermore, it can be provided in an embodiment of the invention that the sewing machine is designed such that the evaluation means are designed to determine a remaining thread length. The logic of the evaluation means is thus a consumption of the thread wound on the bobbin via rotation, direction of rotation and angle of rotation of the bobbin designed predictable. Due to the precise measurement of the consumption and the maximum thread length to be wound due to the conditional dimensions of the bobbin, the available thread length on the bobbin can be determined at any time via the thread consumption of the lower thread.

The use of a properly wound bobbin is necessary for reliable detection of thread consumption. The thread must be wound on the bobbin in parallel. Here, a complete layer of thread is always spooled parallel to each other across the entire width of the bobbin before the next layer is started. This leads to a roll radius change of the spool predictable according to the Archimedean spiral.

By monitoring the upper and lower thread, it is possible according to the invention via the logic of the evaluation means, within the scope of the invention for sewing machines that are not CNC-controlled, thread breakage and false stitching to be clearly recognized at the earliest after each stitch and at the latest after completion of the seam, since this is where a Delta occurs in the consumption of the upper thread to the lower thread.

In the case of CNC-controlled automatic sewing machines, the logic of the evaluation means in one embodiment of the invention is designed to additionally calculate a theoretical consumption of the thread, in particular the upper and lower thread, via the step size between the punctures and to use it for evaluation. As a result, when the invention is used, a user is able to recognize skipped stitches with great advantage, since there is a delta 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 from the Has evaluation means. It is thus made possible with great advantage that when a thread break, miss stitch or a false sewing is determined by the evaluation means, the output means give the operator an error message. In the context of the invention, this advantageously makes it possible to safely remove the component to be sewn in question from the production chain and to assign it to the reject.

Furthermore, a timely reference of the evaluation means to a necessary bobbin change is made possible via the output means, which prevents the start of a sewing process with, for example, insufficient bobbin thread, which would inevitably lead to a seam defect.

The method is achieved in a method according to the invention for monitoring the unwinding of a thread wound on a bobbin in a sewing machine in that field generating means for generating a contactlessly scannable field, in particular a magnetic field, are attached to the bobbin in a rotationally fixed manner, the field being measured continuously. This makes it possible to determine the rotation of a coil, 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.

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 coil are continuously determined and evaluated, an evaluation signal for influencing the rotation of the coil and a user output signal being 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 appearance.

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

With 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 roll radius of the bobbin after changing the bobbin. During the first sewing process, the logic according to the invention compares the detected changes in the angle of rotation of the bobbin with the expected change in the angle of rotation as a function of the largest possible rolling radius in order to verify that the bobbin was completely filled after insertion. Starting from the completely filled bobbin, the logic according to the invention can calculate the thread used with a correction factor for the change in the unwinding radius by emptying the bobbin.

According to a further embodiment, it is provided that a further bobbin with another thread wound is monitored in the sewing machine, at least one further field generating means for generating a further contactlessly scannable field being attached to the further bobbin in a rotationally fixed manner, the further field being continuously measured, whereby a consumption of the thread wound on the further bobbin is determined and compared with the consumption of the thread wound on the bobbin. In particular, an upper and lower thread consumption can be compared with each other and conclusions can be drawn directly about seam defects, with which the component in question at the latest after completion of the seam in question Production chain can be pulled. In the context of the invention, the further bobbin can also be designed merely as a measuring wheel for guiding an upper thread. According to this embodiment, the upper thread runs as an endless thread from a yarn cone from outside to the sewing machine. The upper thread runs over the measuring wheel to measure the upper thread consumption.

The present invention enables the monitoring of a thread wound on a bobbin in a sewing machine, in particular via a magnet embedded in the bobbin, which is detected according to the invention by a magnetic field sensor, which is connected to a logic and is 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 bobbin during a sewing process. By monitoring both a lower thread wound on the bobbin and an upper thread wound on another bobbin, an upper and lower thread consumption can be determined at any time. In the context of the invention, the upper thread can alternatively or additionally be guided as a continuous thread from a yarn cone from outside via a measuring wheel to the sewing machine. In this case, the upper thread consumption is measured in the context of the invention via the measuring wheel over which the upper thread runs. By comparing the used lower thread on the bobbin with the consumption of the upper thread and / or with the step size between the stitches in CNC sewing machines, the logic can monitor the sewing process with regard to thread breakage, missing stitches or false stitching. In addition, due to the dimensions of the bobbin and thus a maximum thread length to be wound, the available remaining thread length on the bobbin can be determined at any time via the thread consumption of the lower thread.

The invention is described by way of example in a preferred embodiment with reference to a drawing, with further advantageous details being shown in the figures of the drawing.

Functionally identical parts are provided with the same reference numerals.

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:

Figure 1:

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

Figure 2:

Representation of a cut coil provided with a round diametral magnet according to the invention;

Figure 3:

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

Figure 4

schematic representation of the operation of the device according to the invention based on the representation of the thread course through the consumption monitoring.

Figure 1 shows a coil 2 according to the invention provided with a round diametral magnet 7 with magnetic field lines 14 in a cut bobbin case 15. The diametral magnet 7 forms a field generating means 5 for generating a contactlessly scannable field 4. The diametral magnet 7 is designed as a ring and is thus in an end face 16 of the coil 2, that a north-south axis 11 of a magnetic field 14 generated by the diametrical magnet 7 is oriented perpendicular to an axis of symmetry 10 of the coil 2.

Figure 2 shows a cut, with a round diametral magnet 7, another coil 2 according to the invention. The magnet 7 is designed as a rotationally symmetrical hollow body 9 and 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 when the coil 2 rotates about the same axis, namely the axis of symmetry 10. This is a determination of a change in the angle of rotation of the coil 2 from a measurement of the field change of the magnetic field 14 facilitated.

Figure 3 shows a measuring wheel 17 provided with a round diametrical magnet 7 with field lines of a magnetic field 14. According to the invention, the measuring wheel 17 is referred to as a (further) bobbin 2 'or upper thread bobbin 20'. In an end face of the measuring wheel 17, which is used in particular for monitoring a further thread 3 'or upper thread 30', there is a further field generating means 5 'which generates a further field 4' which can be scanned without contact, in the form of an annular magnet 7 let in. In addition to the other configuration of the surface conditions of the bobbin, the mode of operation of monitoring the rotation of the measuring wheel 17 for determining a consumption of a length of an upper thread 30 'is in agreement with the mode of operation shown in FIGS Figures 1 and 2nd shown devices match.

Figure 4 shows a schematic representation of the operation of the device according to the invention based on a representation of the thread course through the consumption monitoring. Here is one of one in the Figure 4 only partially shown sewing machine 1 shown in the form of a lockstitch 18 shown. 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 lies on top of the material 19 in a needle stitch direction Garnkone 21 is stored, connected to a lower thread 30 wound on a lower thread bobbin 20, which is stored in the needle stitch direction below the material 19, to form a seam. To connect the two threads 30, 30 ', a gripper 23 arranged on the lower thread spool 20 picks up the upper thread 30' and leads around the lower thread 30, so that both threads 30, 30 'are intertwined. In order to determine errors in the lockstitch in good time or to enable monitoring of the rotation of the lower thread bobbin 20 or the upper thread bobbin 20 ', magnets 7 are respectively arranged on the lower and upper thread bobbin 20, 20' in such a way that they rotate when the respective one Turn the spool 20, 20 'equally. Thus, a magnetic field 14, not shown, generated by the respective magnet 7 is simultaneously moved and changes in accordance with the respective angle of rotation. The magnetic field 14 of the magnet 7 embedded in the respective bobbin 20, 20 'is detected according to the invention by a magnetic field sensor 8, a magnetic field sensor 8 being arranged both on the lower thread bobbin 20 and on the upper thread bobbin 20'. Both magnetic field sensors 8 are connected to a logic, not shown here, which 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 coils 20, 20 ′ in each case. From this, the logic determines thread consumption according to the invention.

The device according to the invention for monitoring the upper thread 30 'shown is used in particular in such a way that the upper thread spool 20' is formed by a cylinder coated with plastic, in which the magnet 7 is inserted into the cylinder in a manner comparable to the implementation in the lower thread spool 20. According to the invention, the cylinder is rotatably mounted and is attached to a sewing machine upper part within a feed of the upper thread 30 '. The upper thread 30 'is wrapped around the cylinder and the upper thread 30' rotates it in the sewing process. This rotation is also about a magnetic field sensor 8 attached there is detected. By means of a fixed radius of the cylinder and the detected angle of rotation, the logic according to the invention can directly determine the consumption of the upper thread 30 '. The consumption of the lower thread 30 is determined on the basis of 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. The consumption of the lower thread 30 can thus be calculated. A comparison of the upper and lower thread consumption can reliably detect an error in the seam in the sewing process with the shown sewing machine 1.

REFERENCE SIGN LIST

1

sewing machine

2nd

Kitchen sink

2 '

another coil

3rd

thread

3 '

another thread

4th

Field generating means

4 '

another field generating agent

5

field

3 '

another field

6

Detection means

7

magnet

8th

Magnetic field sensor

9

Hollow cylinder

10th

Axis of symmetry

11

North-south axis

12

Evaluation means

13

Output means

14

Magnetic field lines

15

Bobbin case

16

Face

17th

Measuring wheel

18th

Lockstitch

19th

material

20th

Bobbin

20 '

Upper thread bobbin

21st

Yarn cone

22

Stitch plate

23

Gripper

24th

needle

30th

Bobbin thread

30 '

Upper thread

Claims (15)

Device for monitoring the unwinding of a thread (3) wound on a bobbin (2) in a sewing machine (1), characterized in that it has field generating means (4) which can be attached to the bobbin (2) in a rotationally fixed manner to produce a contactlessly scannable field (5) having. Device according to Claim 1, characterized in that it has detection means (6) for detecting the contactlessly scannable field (5), the detection means (6) for recording changes in the contactlessly scannable field (5) as a function of an angle of rotation of the coil (2 ) are designed. Device according to claim 1 or 2, characterized in that the field generating means (4) have a magnet (7), in particular a permanent magnet, and in that the detection means (6) comprise a magnetic field sensor (8). Apparatus according to claim 3, characterized in that a north-south axis (11) of the magnet (7) is oriented perpendicular to an axis of symmetry (10) of the coil (2). Device according to claim 3 or 4, characterized in that the magnet (7) is designed as a bar magnet or diametrically magnetized, in particular as a diametrically magnetized hollow cylinder (9), the magnet (7) being arranged in particular within the coil (2). Device according to one of claims 2 to 5, characterized in that it has evaluation means (12) for evaluating field signals detectable by the detection means (6), the evaluation means (12) influencing a rotation of the coil (2). Sewing machine (1) with a bobbin (2) for a thread (3), characterized in that it is provided with a device according to one of Claims 1 to 6, the device preferably being attached to the bobbin (2) in a rotationally fixed manner. Sewing machine (1) according to claim 7, characterized in that it has a further bobbin (2 ') for a further thread (3') and a further device according to claims 1 to 6, the further device preferably being rotationally fixed to the further bobbin ( 2) is attached. Sewing machine (1) according to claim 8, characterized in that the bobbin (2) is designed as a lower thread bobbin (20) for winding up a lower thread (30) and that the further bobbin (2 ') as an upper thread bobbin (20') for winding up an upper thread (30 ') is configured. Sewing machine according to claim 7, 8 or 9, characterized in that the evaluation means (12) are designed to determine a remaining thread length. Sewing machine according to one of claims 7 to 10, characterized in that it has output means (13) for outputting signals from the evaluation means (12). Method for monitoring the unwinding of a thread (3) wound on a spool (2) in a sewing machine (1), characterized in that field generating means (4) for generating a contactlessly scannable field ', in particular Magnetic field (5), rotatably attached to the coil (2), the field (5) is continuously measured. A method according to claim 12, characterized in that a rotation angle and a rotation speed of the coil (2) are continuously determined and evaluated, an evaluation signal for influencing the rotation of the coil (2) and a user output signal being generated. Method according to claim 12 or 13, characterized in that a consumption and / or a remaining thread quantity of the thread (3) wound on the bobbin (2) is determined. Method according to Claim 14, characterized in that a further bobbin (2 ') with a further wound thread (3') is monitored in the sewing machine (1), at least one further field generating means (4 ') for generating a further contactlessly scannable field ( 5 ') is attached in a rotationally fixed manner to the further bobbin (2'), the further field (5 ') being continuously measured, a consumption of the thread (3') wound on the further bobbin (2 ') being determined and with the Consumption of the thread (3) wound on the bobbin (2) is compared.

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