KR102372614B1 - Sensor assembly for a sewing machine - Google Patents

Abstract

The sensor assembly 28 is used for the sewing machine to identify mis-stitches. The light source is used to generate the detection light beam 30 . A sensor is used to detect the detection light beam 30 . The light source is aligned with respect to the sensor such that the detection light beam 30 is guided by the reflective section 31 of the component 32 of the sewing machine through which the thread passes during operation of the sewing machine. The evaluation unit is in signal communication with the sensor for time-resolved evaluation of the detection signal generated by the sensor. This results in a sensor assembly that can be used to identify mis-stitches.

Description

Sensor assembly for a sewing machine {SENSOR ASSEMBLY FOR A SEWING MACHINE}

The present invention relates to a sensor assembly for a sewing machine. The present invention also relates to a sewing machine comprising such a sensor assembly.

A sensor assembly for a sewing machine is known, for example, from EP 2 045 386 A1. US 4,569,298 describes an optical prewarning device for a sewing machine. DE 37 07 321 C1 describes a sewing machine with a thread monitor for bobbin threads. DE 41 16 638 A1 describes a device for identifying the thread remaining wound on the spool of a sewing machine. US 2003/0221601 A1 describes a sewing machine that monitors the rotation of the lower spool. DE 11 2005 002 785 T5 describes a lower thread feed device capable of identifying the remaining thread for a sewing machine. EP 1 700 941 A1 describes a sewing machine or embroidery machine comprising a device for determining the supply of thread on the lower spool.

It is an object of the present invention to develop a sensor assembly for a sewing machine that makes it possible to identify a mis-stitch.

This object is achieved by a sensor assembly for a sewing machine for identifying a miss-stitch according to the present invention, the sewing machine comprising:

- a light source for generating a detection light beam;

- a sensor for detecting the detection light beam;

- an evaluation unit in signal communication with the sensor for time resolved evaluation of the detection signal generated by the sensor;

- the light source is aligned with respect to the sensor so that the detection light beam is guided by a reflective section of a component of the sewing machine through which the thread passes during operation of the sewing machine and during the formation of stitches;

It has been recognized that according to the present invention it is possible to use the fact that during the formation of the stitch the thread is guided around the lower thread bobbin housing of the sewing machine and thus passes through the various sewing machine components in order to identify mis-stitches according to the present invention. . In the sensor assembly according to the invention, the thread passing through the section reflecting the detection light beam temporarily obstructs the detection light beam during stitch formation. This temporary disturbance can be detected by a sensor and evaluated by an evaluation unit to identify the mis-stitch. The evaluation unit measures whether or not the detection signal has changed as a result of the passage of the seal. If these changes are measured, it is evaluated that it is possible to ensure that sewing is not made without threads in an undesired manner. Mis-stitches are identified in another way. A reflective section may be provided on the lower spool housing itself. The reflective section can in particular be arranged in the region of the middle part of the lower spool housing. Alternatively, the reflective section may also be provided on other components of the sewing machine including at least one section through which the yarn is passed during sewing machine operation. An example of such a sewing machine component is the tip of a hook or gripper. In this case the region of the hook tip is preferably chosen as the reflective region touched by the thread.

Placing the sensor directly in the light path of the detection light beam results in a measure of the signal reduction by reduction of the reflection of the reflection detection light beam caused by the yarn sliding over it. The sensor thus measures the fundamental intensity of the reflected detection light beam, which is generally reduced during the passage of the seal and the resulting disturbance of the detection light beam. Alternatively, it is possible to arrange the sensor to measure the scattered detection light but not directly in the light path of the detection light beam. This takes advantage of the fact that the detection light is scattered differently by the sewing machine components, in particular the lower spool housing, and is generally less scattered than the upper thread it passes through. As soon as the thread runs through the detection light beam, ie, passes through the reflective section of the sewing machine component, scattered light is generated that can be measured by the sensor. In the case of scattered light measurements, zero measurements are possible for insignificant or low background signals.

In an embodiment of the evaluation, the evaluation unit is designed to form a moving average of the at least one detection signal generated within a time interval during the stitch formation period, which moving average may be compared with a predefined value. It can be used, for example, for drift measurement or for the detection of contamination. This signal may in particular be formed in phase synchronization with the stitch formation.

The formation of the plurality of detection signals at different time periods during the stitch formation period, wherein the evaluation unit is configured to form a moving average of the at least two detection signals generated at different time intervals during the stitch formation period, is an additional signal It allows comparison, which in turn improves the useful detection value.

Advantages of a sewing machine comprising a sensor assembly according to the present invention and a stitch forming tool in the form of a hook and needle rotating relative to a lower spool housing correspond to those already described above with reference to the sensor assembly.

A highly reflective embodiment in which the reflective section of the sewing machine component is designed to be highly reflective increases the sensitivity of detection. The reflective section may be designed to be polished. The reflective section may be designed to be flat. The reflective section can be designed to be concave and in particular to display the light source on the sensor.

The positioning of the gripper with the hook positioned relative to the light path of the detection light beam such that the hook in the fully rotating hook travel path does not obstruct the detection light beam, preventing the gripper from becoming an obstruction to detection by the sensor assembly .

The selection of the reflective section selected such that the reflective section of the sewing machine component is brushed by contact with the thread as the thread passes avoids contamination on the reflective section from affecting detection.

The arrangement in which the evaluation unit is in signal connection with a motor for driving at least one of the stitch forming tools provides a simple solution for taking into account the state of the stitch forming period during evaluation. In particular, phase-synchronized measurements are possible which increase the accuracy of the evaluation.

An alternative or additional sensor assembly for a sewing machine includes a light source for generating a detection light beam and a sensor for detecting the detection light beam. The light source is aligned with respect to the sensor such that the detection light beam is guided over the reflective section of the component of the sewing machine. The evaluation unit is in signal connection with the sensor and is used for time-independent evaluation of the detection signal generated by the sensor. The evaluation unit is designed to form a moving average of the at least one detection signal generated in time intervals during the stitch formation period. The degree of contamination in the sewing machine may be measured by such a sensor assembly.

When a sewing machine becomes dirty, for example due to contamination or lint deposited on the sewing machine during operation, the light guide properties in the detection light path deteriorate. This is used by the sensor assembly. The moving average may be compared to a reference value or a predefined value within the average unit. The reference value may be a false value of the detection signal in the case of optimal reflection of the detection light beam above the reflective section to the sensor. If the difference between the detection signal and the predefined value exceeds or falls below the error range, a fault signal, for example a “dirty” signal, may be emitted. The error range can be specified by defining a minimum allowable value for the detection signal. The fault signal may be an acoustic signal and/or may appear on the operation panel. Alternatively or in addition, it is possible to directly intervene in the operation of the sewing machine as a result of a fault signal, in particular to stop the sewing machine.

The sensor may be placed directly in the light path of the detection light beam. The advantages of this arrangement correspond to those already described above. An alternative arrangement in which the sensor is not placed directly in the light path of the detection light beam but is positioned to measure the scattered detection light is also possible.

a plurality of light source/sensor pairs, the sensor assembly comprising at least two pairs comprising a sensor each assigned by a light source and a detection light beam generated thereby, making it possible to compare the moving average values of the individual pairs within the evaluation unit do. This increases the accuracy of contamination detection.

Alternatively or in addition, a sensor assembly comprising a fixed frame light source for generating a detection light beam and a fixed frame sensor for detecting a detection light beam may be provided for identifying mis-stitches, wherein the light source comprises: and an evaluation unit arranged relative to the sensor such that the detection light beam is guided over at least one reflective section of the lower spool of the sewing machine, the evaluation unit being connected to the sensor by the signal for time-independent evaluation of the detection signal generated by the sensor; .

This takes advantage of the fact that the lower spool rotates when the lower thread is used during correct operation of a sewing machine equipped with the lower spool. This rotation is reliably detected by the sensor assembly. As long as the lower spool rotates, it always reflects the detection light beam using the reflective section when touched by the detection light beam. If the detection signal or the characteristic time change of the detection signal is not measured, this indicates that sewing is being performed without using the lower thread correctly, and an appropriate defect signal may be emitted.

The sensor may be placed directly in the light path of the detection light beam. The advantages already described above in connection with this direct arrangement are obtained. Alternatively an arrangement is possible in this case in which the sensor is not placed directly in the light path of the detection light beam but is positioned to measure the scattered detection light.

The evaluation unit may be designed to form a moving average of the at least one detection signal generated in the time period during the stitch formation period. The evaluation unit may alternatively or in addition be designed to form a moving average value of the at least two detection signals generated at different time intervals during the stitch formation period. The advantages of such an evaluation unit correspond to those already described above.

This additional sensor assembly may also be part of a sewing machine that includes a stitch forming tool in the form of a needle and a gripper that rotates around a lower spool housing. The advantages of such a sewing machine correspond to those already described above.

A plurality of reflective sections may be formed to reflect the detection light beam in a circumferential region around the spool in the casing wall.

The plurality of reflective sections increases the measurement accuracy of the sensor assembly, as many situations occur during a failed rotation that lead to a detection signal in which the detection light beam is reflected by the reflective section.

The plurality of reflective sections may be non-uniformly distributed around the spool in the circumferential direction. For example, three reflective sections may be disposed in a first quadrant in the top view of the spool, and two reflective sections may be disposed in a second adjacent quadrant in a circumferentially counterclockwise direction and again adjacent in a counterclockwise direction. A single reflective section may be disposed within the third quadrant. The direction of rotation of the failure may also be specified for evaluation. In the example described above, an evaluation sequence of “3/2/1” may mean that the failure is rotating clockwise. An inverse evaluation sequence “1/2/3” may mean that the failure is rotating counterclockwise. Alternatively or additionally, it is possible to determine the direction of rotation of the spool by means of various different dimensions of the reflective sections in the circumferential direction. For example, reflective sections uniformly distributed in the circumferential direction can be used, for example, with three different circumferential length extensions, wherein the three circumferential length extensions are arranged in a descending sequence of their extension lengths. It is then possible to determine the direction of rotation in a manner similar to that described above with respect to the case of non-uniform distribution in the circumferential direction.

The at least one reflective section can thus be designed in the spool casing wall such that the overall diameter of the spool is retained over the circumferential region of the at least one reflective section, in particular of the upper spool end wall or the upper spool cover. In this way it is possible to prevent the failing thread from leaving the failing area in an undesirable way at the circumferential point of the reflective section. The at least one reflective section may be designed such that, for example, the overall spool diameter is held up at an axial height of 0.5 mm. The reflective sections may be configured as a facet on the spool. The facets can be formed at low cost.

At least four reflective sections may be provided. The four reflective sections have proven particularly suitable for reliable detection. Also fewer or more than 4 reflective sections may be used, eg more than 6, more than 10 reflective sections, eg 12 or more reflective sections.

The evaluation unit may be in signal connection with a motor for driving in at least one of the stitch forming tools. The advantages of such an arrangement correspond to those already described above in relation to the evaluation unit. Interfering and/or defective signals may be filtered out during evaluation.

Exemplary embodiments of the present invention have been described in greater detail below with reference to the drawings.
1 is a front view of the sewing machine partially exposing details of the interior;
2 shows, in a much enlarged form, a perspective view of a cutout of the sewing machine in the region of the gripper with a plurality of sensor assemblies for recognizing in particular a miss-stitch in a much enlarged form;
Fig. 3 is a view similar to Fig. 2 with the further lower spool housing removed; and
FIG. 4 is a view similar to FIG. 2 showing examples of the arrangement of further embodiments of an inlace sensor assembly which may be used instead of an inlace sensor assembly in the design according to FIGS. 2 and 3 ;

The sewing machine 1 includes a base plate 2 having a stand 3 extending upwardly therefrom and an angled arm 4 . The angled arm 4 terminates at the head 5 . An arm shaft 6 driving a crank drive 7 having a seal lever 8 in the head 5 in the arm 4 is rotatably mounted. The crank drive 7 is drive-connected to a needle rod 9 mounted displaceably within the head 5 . The latter has a sewing needle 10 at its lower end. The sewing needle 10 may be moved up and down by a crank drive 7 . Here, the sewing needle 10 runs through the movement area. The sewing needle 10 guides the thread 13 supplied through the thread tensioning device and the thread lever 8 by the thread reel 12 at a glance.

On the base plate 2 is mounted a support plate 16 on which the sewing product 17 is placed. The support plate 16 has a fabric feed opening designated as a passageway for the fabric feed 19 . The fabric feed 19 has a stitch hole 20 for the passage of the sewing needle 10 . The fabric feed 19 is driven by a push and lift gear disposed below the base plate 2 .

Below the support plate 16 is arranged a hook or gripper 21 comprising a hook or gripper housing 22 with a casing-side hook or gripper tip 23 . The hook 21 is vertical after and thus has a vertical axis of rotation 24 that is orthogonal to the support plane of the support plate 16 .

The sewing needle 10 on one side and the gripper 21 on the other side are the stitch forming tools of the sewing machine 1 .

The gripper housing 22 is fixedly connected to a shaft coaxial with the rotation shaft 24 . This shaft is rotatably mounted in a bearing block 25 screwed to the base plate 2 . In the latter the drive shaft 26 is also mounted in connection with a gear drive arranged inside the bearing block 25 . The drive shaft 26 is connected to the arm shaft 6 on the drive side via a belt drive 27 .

2 and 3 show details of a plurality of sensor assemblies of the sewing machine 1 that can be used to detect a miss-stitch and at the same time detect contamination.

The first sensor assembly 28 is used to recognize mis-stitches in the form of enlacement control. The inlace sensor assembly 28 , which is configured as an upper thread miss-stitch sensor assembly, determines whether the needle thread 13 , ie the upper thread is being used in a desired manner in the seam forming process of the sewing machine 1 , and is controlled by the gripper tip 23 . It is detected whether the gripper 21 is being transported correctly to inlace it.

The inlace sensor assembly 28 has a light source/detection unit 29 secured to a frame next to the gripper housing 22 in the base plate housing. The inlace sensor assembly 28 includes a light source for generating a detection light beam 30 . A red LED or a red laser diode is used as the light source. Other light sources may also be used for the detection light source 30 . In addition, the light source/detection unit 29 has a sensor in the form of a photodiode for detecting the detection light beam 30 . The sensor is mounted next to the light source in a suitable housing mount of the light source/detection unit 29 . The sensor is designed as a single photodiode. Alternatively, the sensor can be designed as a local resolution sensor with a plurality of photodiodes, for example as a quadrant detector. The sensor can also be designed as a phototransistor or as a light sensitive component in general. In case it is designed as a local resolution sensor, the latter can be designed as a CCD sensor or a CMOS sensor.

The gripper 21 is arranged relative to the light path of the detection light beam 30 so that the gripper in the fully rotating gripper movement path does not obstruct the detection light beam 30 .

The light source of the inlace sensor assembly 28 is aligned with respect to the sensor of the inlace sensor assembly 28 so that the detection light beam 30 is passed by the needle thread 13 during sewing machine operation at the bottom of the sewing machine 1 . Guided over the reflective section 31 of the spool housing 32 . The gripper 21 rotates relative to the lower spool housing 32 .

When the reflective section 31 of the lower spool housing 32 is selected so that the needle thread 13 avoids and obstructs the detection light beam 30 , the reflective section 31 is contacted and brushed by the needle thread 13 . The needle thread 13 thus polishes the reflective section 31 and keeps the reflective section 31 free from contamination.

In the lower spool housing 32 , a spool 33a is mounted against the lower thread of the sewing machine 1 .

The inlace sensor assembly 28 also has an evaluation unit 33 schematically shown in FIG. 1 . The latter is in signal connection with the sensor of the inlace sensor assembly 28 . The evaluation unit 33 is used for time-independent evaluation of the detection signal generated by the sensor of the inlace sensor assembly 28 . The evaluation unit 33 measures whether the detection signal has changed due to the needle thread 13 passing through it. If a corresponding signal change is detected, it is ensured that no sewing was performed without the needle thread 13 in an undesired manner during the operation of the sewing machine 1 . If, during operation of the sewing machine 1, no change in the signal was measured by the evaluation unit 33 as a result of the passing needle thread 13 interfering with the detection light beam 30 within a predefined time period, the evaluation unit ( 33) emits a miss-stitch signal and the operation of the sewing machine 1 is automatically stopped by emitting an error signal or an error display.

The sensor of the inlace sensor assembly 28 is disposed directly in the light path of the detection light beam 30 . The signal reduction is in the needle thread 13 caused by a reduction in the reflection of the detection light beam 30 reflected by the evaluation unit 33 compared to the highly reflective reflective section 31 of the lower spool housing 32 . It is measured for obstruction of the optical path by

In an alternative, not shown embodiment of the inlace sensor assembly 28 , the sensor is arranged such that it measures the scattered detection light, ie, is not placed directly in the light path of the detection light beam 30 . The detection light is scattered differently by the lower spool housing and is generally less scattered than by the needle thread 13 passing through the reflective section 31 , and thus changes when the needle thread 13 passes through the reflective section. , in particular an increase in the detected detection light scattering signal is measured in this other embodiment of the inlace sensor assembly. In this case a zero measurement is possible for insignificant or very small background signals.

The evaluation unit 33 is designed to first form a moving average of the at least one detection signal generated in the time period during the stitch formation period. This moving average, which may represent, for example, an average of ten or more stitches, is compared in the evaluation unit 33 with a predefined value. If the moving average differs from the predefined value to a greater extent than the margin of error, the evaluation unit emits a "dirty" signal different from the "miss-stitch - no needle thread present" signal. A “contamination” signal can be provided, for example, by a change in the color of the signal light on the sewing machine 1, which is a green signal light when there is no dirt, which is first to yellow when it has a low level of contamination and then to a higher degree of contamination. When it has , it changes to red. Relying on the contamination signal emitted by the evaluation unit 33 also corresponds to, for example, by stopping the sewing machine 1 , by activating the gas rinsing device to wash components of the sewing machine 1 which are particularly likely to be dirty. means can be automatically controlled.

Alternatively or in addition, the evaluation unit 33 may be designed such that it forms a moving average of at least two detection signals generated at different time intervals during the stitch formation period. The evaluation is performed in phase synchronization with stitch formation, for example, one measurement signal is determined before the sewing needle 10 pierces the sewing product 17 and the second measurement signal is the sewing product 17 . It is determined after stabbing, and a moving average value is formed by different stitches by these two measurement signals. The plurality of detection signals generated in this way enables a comparison of the time curves of the two detection signals from which more information can be provided on the detection of contamination. Factors affecting the intensity of the detection signal that are not caused by contamination can be selected or suppressed more reliably in this way.

The contamination effect that can be detected by the inlace sensor 28 relates in particular to contamination of the light source and sensor or lint reaching other points in the light path of the detection light beam 30 , for example.

For phase synchronization, the evaluation unit 33 may be in signal connection with a motor for driving at least one stitch forming tool 10 , 21 , in particular a main drive of the sewing machine 1 .

Phase synchronization of detection can be used to accurately determine the detection signal when it is expected that the needle thread 13 will skim and thus interfere with the detection light beam 30 . In addition to detecting the upper thread miss-stitch, whether the stitch formation is operating correctly, i.e. the needle thread is operating at the correct time for the intended section of the lower spool housing that may affect the knot quality during seam formation and It is also possible to detect whether there is

Phase synchronization of detection can also be used to increase the reliability of the measurement. Inaccurate measurements can be prevented in this way.

Independently of the inlace sensor assembly 28, the sewing machine 1 may also include an additional contamination sensor assembly, not shown, which in principle has the same design as the inlace sensor assembly, but in this case different types of sewing machine components. The section is used as a reflective section corresponding to the reflective section 31 of the lower spool housing 32 . A contamination sensor assembly of this kind may comprise at least two pairs consisting of a light source and a sensor which is assigned via a detection light beam thus generated, i.e. two light sources/ depending in particular on the type of light source/detection unit 29 . detection units. These units can measure the contamination at different points of the sewing machine 1 via a detection light beam guide over the corresponding reflective section of the sewing machine component. By comparing the moving averages of the detection signals of the light source/detection unit generated in the evaluation unit 33 , the reliability and accuracy of the pollution measurement can be improved.

The sewing machine 1 also has a rotation monitoring sensor assembly 34 for monitoring the rotation of the spool 33a.

The rotation monitoring sensor assembly 34 is in principle designed to have the same structure as the light source/detection unit 29 and has a light source/detection unit 35 mounted to be fixed to a frame adjacent to the inlacing sensor assembly 28 . The light source/detection unit 35 of the rotation monitoring sensor assembly 34 includes a light source for generating a detection light beam 36 and a sensor for detecting the detection light beam 36 . The sensor of the rotation monitoring sensor assembly 34 is disposed directly in the light path of the detection light beam 36 .

The light source in the light source/detection unit 35 of the rotation monitoring sensor assembly 34 is a sensor such that the detection light beam 36 is guided over the reflective section 37 (see FIG. 3 ) of the lower spool 33a of the sewing machine 1 . are sorted against An evaluation unit 33 for time-independent evaluation of the detection signal generated by this sensor is in signal connection with the sensor of the rotation monitoring sensor assembly 34 .

The spool 33a has a plurality of reflective sections 37 around its circumference. The latter are formed as facets in circumferential sections around the spool 33a in the latter casing wall 38 . There are a total of six reflective sections 37 in the embodiment of the failure 33a shown in FIG. 3 . The latter are uniformly distributed circumferentially around the spool 33a, so that after the spool has turned 60° the adjacent reflective section 37 comes to the point of the current reflective section 37 according to FIG. 3 . Depending on the design of the spool 33a, two reflective sections 37, at least four reflective sections 37, more than four reflective sections 37, more than six, more than ten Many, or twelve reflective sections 37 or more reflective sections 37 may be provided. The reflective sections 37 each have the same circumferential length extension in the circumferential direction around the spool 33a.

In an alternative configuration of the reflective sections 37 , the latter have different circumferential length extensions in the circumferential direction around the spool 33a and/or are non-uniformly distributed in the circumferential direction around the spool 33a. In this arrangement of the reflective sections 37 it is possible to establish the direction of rotation of the failure 33a during evaluation of the detection signal. This can be used to detect a specific operating state of the sewing machine 1 .

In the embodiment shown in the figures the reflective sections 37 are designed in the upper spool wall which closes off the space for the lower thread not wound at the top, so that the spool 33a at the site of the individual reflective section 37 is There is a slight decrease in the overall diameter of Alternatively, the reflective sections 37 may be designed such that they run only for a portion of the total axial extension of the spool wall, so that for example the upper web still remains and the upper spool wall over its entire perimeter. It retains the overall spool diameter despite the inserted reflective sections 37 . A gap between the upper spool wall and the adjacent spool housing can then be avoided.

The at least one reflective section 37 can be designed to be highly reflective to the detection light beam 36 . The reflective section 37 may be designed flat or concave. The radius of curvature of the reflective section 37 in the case of a concave design can be selected such that the reflective section 37 displays the light source on the sensor of the light source/detection unit.

During operation of the sewing machine 1, the spool 33a rotates as a result of lower thread consumption. If one of the reflective sections 37 reflects the detection light of the rotation monitoring sensor assembly 34 in its sensor, this generates a sensor signal that the evaluation unit 33 can evaluate. The evaluation unit 33 thus detects whether the spool 33a is rotating and thus identifies that the spool 33a is still and the lower seal is not being used if no signal is present. The evaluation unit 33 in this case emits a signal "Mis-stitch - no lower seal present". At the same time, the evaluation unit 33 may automatically stop the operation of the sewing machine 1 .

The rotation monitoring sensor assembly 34 may be used to detect contamination as already described above.

The evaluation unit 33 thus forms a moving average of the detection signals. Alternatively or in addition, the evaluation unit 33 can form a moving average, in particular a phase-synchronized moving average, of the detection signals generated at time intervals at least during the stitch formation period.

The detection light of the corresponding sensor assembly may be guided through the window of the spool housing such that it is reflected by the outer casing wall 39 (see FIG. 3 ) of the central body of the spool 33a. The detection light emitted from the light source of this sensor assembly is detected after reflection from the casing wall 39 by an assigned sensor of this sensor assembly. This reflection only occurs when the spool is completely unraveled, ie when there is no more lower seal on the spool. In this way any remaining yarn can be identified by this sensor assembly.

In one variant of the inlace sensor assembly 28 , a reflective section for the detection light beam is formed on the gripper tip 23 of the gripper 21 . Measurements are then performed to see whether the reflective section has been passed by the needle thread during sewing machine operation. The function of the corresponding variant of the inlace sensor assembly corresponds to that already described above with respect to the inlace sensor assembly 28 .

FIG. 4 shows by way of example two further possible arrangements of an inlace sensor assembly that can be used instead of the arrangement according to FIGS. 2 and 3 . The arrangement of these two possible inlace sensor assemblies is denoted below by reference numerals 28a and 28b.

The inlace sensor assembly 28a is designed to intersect the reflective section for the detection light beam formed on the gripper tip 23 of the gripper 21 as already described above.

An alternative inlace sensor assembly 28b is designed to intersect the reflective section 40 on the lower spool housing 32 . Compared to the reflective section 31 used in the arrangement of the inlace sensor assembly 28 according to FIGS. 2 and 3 , the reflective section 40 from the point of view of the gripper 31 is spaced counterclockwise. The inlace sensor assembly 28b is used to measure whether the reflective section 40 has been passed by the needle thread in the sewing machine operation. The function of the inlace sensor assembly 28b otherwise corresponds to that already described above with respect to the inlace sensor assembly 28 .

Claims (11)

A sensor assembly for a sewing machine for identifying a mis-stitch, comprising:
a light source for generating a detection light beam;
a sensor for detecting the detection light beam;
an evaluation unit in signal communication with the sensor for time resolved evaluation of a detection signal generated by the sensor;
the light source is aligned with respect to the sensor such that the detection light beam is guided by a reflective section of a component of the sewing machine through which the thread passes during operation of the sewing machine and during the formation of stitches;
and the evaluation unit is designed to form a moving average of the at least one detection signal generated in time intervals during the stitch formation period. The method of claim 1,
wherein the sensor is disposed directly in the optical path of the detection light beam. delete 3. The method of claim 1 or 2,
sensor assembly, characterized in that the evaluation unit is configured to form a moving average of at least two detection signals generated at different time intervals during the stitch formation period. As a sewing machine,
The sensor assembly according to claim 1 or 2,
A sewing machine comprising a stitch formation tool in the form of a hook and needle rotating about a lower thread bobbin housing. delete 6. The method of claim 5,
The sewing machine, characterized in that the hook is disposed with respect to the optical path of the detection light beam so that the hook does not obstruct the detection light beam within the fully rotating hook movement path. 6. The method of claim 5,
and is selected to be brushed in contact with the thread as the reflective section of the sewing machine component passes. 6. The method of claim 5,
A sewing machine, characterized in that the evaluation unit is in signal connection with a motor for driving in at least one of the stitch forming tools. 3. The method of claim 1 or 2,
A sensor assembly, characterized in that the sensor assembly comprises at least two pairs of sensors each assigned by a light source and a detection light beam generated thereby. 3. The method of claim 1 or 2,
Sensor assembly, characterized in that the evaluation unit is designed such that a detection signal is formed in phase synchronization with the stitch formation.

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