EP1571248A1 - Sewing machine with needle thread control system - Google Patents

Abstract

The needle thread (17) on a sewing machine is taken from the moving thread guide arm to the needle through a tension transducer (21), which provides a continuous electrical tension signal to a micro-processor. The tension profile through a full rotation of the drive shaft is then compared with the profile to be expected with a correct stitch to provide a fault signal. The transducer (21) has an eyelet (26) at the end of a spring arm (23) that moves through the field of a permanent magnet (32). The movement is detected by a sensor (36), preferably a Hall generator.

Description

The invention relates to a sewing machine according to the preamble of the claim 1.

From US-PS 4,170,951 a sewing machine is known in which between the thread tensioning device and the thread lever, a thread tension detecting means is arranged. This device essentially consists from a downwardly open U-shaped deflection, in the strain gauges are mounted. The one of the thread tensioning device The next needle thread is deflected by more than 90 ° and then led to the thread lever, from where he essentially is guided straight to the needle. Depending on the needle thread tension are intended by the strain gauges of the needle thread tension corresponding electrical voltages are generated in be processed by a microprocessor, creating a miss can be recognized. The known embodiment is at least extraordinary inaccurate and therefore not reliable.

The invention is based on the object, a sewing machine of the generic type Art to design so that the detection of a missing stitch or a needle thread breakage reliably and with little effort is recognizable.

This object is achieved by the features in the characterizing part of claim 1 solved. By having a mis-stitch detection device arranged between the needle and the thread lever is, there is no distortion of the detection of the needle thread tension on, which takes place through the deflection in the thread lever. The dependent from the needle thread voltage generated voltage is over the entire circulation of the arm shaft with a predetermined electrical Target voltage compared. With a corresponding deviation becomes Signal triggered or, if necessary, the sewing machine stopped.

In particular, by the development according to claim 2 is achieved that deflection-related influences on the detection of the needle thread tension be completely excluded.

The development according to claim 3 gives a particularly advantageous embodiment a non-contact detection of the needle thread tension again, wherein the claims 4 to 7 advantageous developments of this purport.

Fig. 1

eine Nähmaschine in Seiten-Längs-Ansicht,

Fig. 2

eine Draufsicht auf eine Fehlstich-Erfassungs-Einrichtung in gegenüber Fig. 1 vergrößertem Maßstab,

Fig. 3

eine Seitenansicht der Fehlstich-Erfassungs-Einrichtung gemäß dem Sichtpfeil III in Fig. 2,

Fig. 4

zwei miteinander vernähte Nähgutteile im Schnitt,

Fig. 5

den Soll-Verlauf einer der Nadelfaden-Spannung entsprechenden elektrischen Spannung über der Drehwinkel-Stellung der Armwelle und

Fig. 6

eine Schemadarstellung der Signalverarbeitung.

Further features, advantages and details of the invention will become apparent from the following description of an embodiment with reference to the drawing. It shows:

Fig. 1

a sewing machine in side-longitudinal view,

Fig. 2

a plan view of a mis-stitch detection device in relation to FIG. 1 enlarged scale,

Fig. 3

2 is a side view of the mis-stitch detection device according to the viewing arrow III in FIG. 2, FIG.

Fig. 4

two sewing pieces sewed together on average,

Fig. 5

the desired course of the needle thread voltage corresponding voltage across the rotational angle position of the arm shaft and

Fig. 6

a schematic representation of the signal processing.

The sewing machine shown in Fig. 1 has in the usual way an upper Arm 1, a box-like base plate 2 and the arm 1 and the Base plate 2 on each end connecting stand 3, d. H. the Sewing machine is C-shaped. In the arm 1, an arm shaft 4 is mounted, at its lying outside of the arm 1 end of a handwheel. 5 carries and attached to the next to the handwheel 5, a rotary pulse transmitter 6 is. From the arm shaft 4 in the usual way the drive a Needle bar 7 with a needle 8 and a presser foot 9 derived.

In the base plate 2 is a vertical gripper 10 about a vertical axis eleventh rotatably mounted in a gripper bearing 12. The drive of the gripper 10 takes place arranged by means of one in the base plate 2 below the stator 3 Drive motor 13 via a gripper drive shaft 14. From this Shaft 14 and the arm shaft 4 is driven by a belt drive 15.

The arm 1 is also a likewise driven by the arm shaft 4 Thread lever 16 arranged for a needle thread 17. This needle thread 17 is from a thread supply, not shown, in a needle thread feeding direction 18 fed to the thread lever 16, via a Thread lever 16 - in relation to the feed direction 18 - upstream thread tensioning device 19. This is on a support plate attached to the arm 1 20 of ferritic material, for example steel, attached. Of the Needle thread 17 is on the thread tensioning device 19 and the thread lever 16 is fed to a mis-stitch detection means 21 and from there forwarded to the needle 8. The mis-stitch detection device 21 is also mounted on the support plate 20.

As is apparent from Figs. 2 and 3, the mis-stitch detection means 21 a mounted on the support plate 20 spring housing 22nd in which a leg spring 23 is held by a screw 24. The leg spring 23 protrudes through a substantially down and to the needle thread 17 side facing slot 25 of the Spring housing 22 from the latter down out. At her lower outside the housing 22 end carries the leg spring 23 a Thread eyelet 26. Above and below and in total laterally next to the Missing stitching means 21 are upper to the support plate 20 Thread guide 27 and a lower thread guide 28 mounted by the the coming of the thread lever 16 needle thread 17 without significant deflection is guided by the thread lever 16 to the needle 8. Between the two Thread guides 27, 28 he is through the eyelet 26 of the mis-stitch detection device 21 out, as shown in FIGS. 1 to 3 can be removed. in the Slot 25 is still a deflection pin 29 is arranged, via which the needle thread 17 at a return pivoting of the leg spring 23 with the thread eyelet 26 is deflected as shown in Fig. 2.

Below the spring housing 22 is a sensor housing 30 of a non-magnetizable material, in particular plastic, by means of Countersunk screws 31 attached to the support plate 20. In the housing 30 is a Permanent magnet 32 attached, in coincidence with the thread eyelet 26 and the adjacent region of the leg spring 23, the Steel, so a ferritic, that is magnetizable material. at Deflections of the eyelet 26 substantially transversely to the through the position the thread guides 27, 28 predetermined main direction 33 of the needle thread 17, the eyelet 26 moves in front of the permanent magnet 32, that is approximately transversely through its magnetic field, extending from its poles 34, 35 extends from. A pole 34 is the thread eye 26 facing and - as Fig. 3 reveals - closely adjacent.

In the sensor housing 30 is in addition to the magnet 32 a to changes the magnetic field responsive sensor 36, so usually one Hall generator, arranged. This sensor 36 is connected by means of a line 37 switched to an input of a controller 38. The controller 38 is still on connected to a power supply line 39 and has a Connecting line 40 to the pedal of the sewing machine, not shown on. Furthermore, the control via a rotary-pulse line 41 with the Rotary-pulse encoder 6 connected. Finally, the controller 38 with the Drive motor 13 connected via a control line 42. The controller 38 has in the usual way switch 43 and indicator lights 44.

The operation will be explained with reference to FIGS. 4 to 6:

By actuating the switch 43, the drive motor 13 is activated and the sewing machine by means of the pedal in operation. For example two sewing parts 45, 46 are sewn together. Fig. 4 shows three stitch positions in the Nähgutteilen 45, 46, namely - from left to right - a correct stitch 47, a missing stitch position 48 and again a correct stitch 49. In the middle between the two correct stitches 47, 49 so no stitch formation has taken place. This means that the Gripper tip 50 of the gripper 10, the needle thread 17 and the Needle thread loop not grasped and pulled out and around the one supply to lower thread 51 having, located in the gripper 10, not shown Coil has led. So it has no stitching between the needle thread 17 and only indicated in Fig. 4 lower thread 51 occurred.

As already indicated above, the eyelet 26 and the adjacent Area of the leg spring 23 during the sewing process in the magnetic field moved in front of the permanent magnet 32. When the needle thread 17 has its greatest tension, the needle thread 17 is in the area the mis-stitch detection device 21 in its most pronounced elongated position, which is indicated by dashed lines in Fig. 2. If he opposes it has its lowest thread tension, it is in its in Fig. 2 shown pulled position in which the leg spring 23 against a stop 52 of the spring housing 22 abuts. The needle thread 17 is therefore transverse to its predetermined by the thread guides 28, 29 Main direction in the form of a triangle pulled out. The greater the thread tension is, the more obtuse is this triangle, how vivid From Fig. 2 shows.

The sensor 36 outputs an electrical voltage U, which depends on the movement the leg spring 23 with eyelet 26 in the magnetic field of the magnet 32nd depends. As is apparent from Fig. 5, in which the sensor 36 to the controller 38 delivered voltage U over the rotation angle W of a full Rotation of the arm shaft 4 is shown, the output from the sensor 36 Voltage U1 greatest when the thread lever 16 is in his High position is when the thread tension in the needle thread 17 so on biggest one is. The tension decreases with the lowering of the thread lever 16 during the trick down to a very low value U2. This tension U2 is thus released when the needle thread 17 largely relaxed is and the leg spring 23 abuts against the stop 52. This Point is reached when the needle 8 through the workpieces 45, 46th pierced through and then moves back up. Now if the gripper tip 50 by the upward movement of the needle 8 formed needle thread loop engages the needle thread 17 again curious, d. H. the eyelet 26 is again from its position at the stop 52 - in Fig. 2 to the right - deflected, since the needle thread 17 due the increased tension is stretched. This leads to an increase the voltage U to a value U3. After dropping the needle thread loop from the gripper tip 50, the voltage drops back to the Value U2 from until the thread lever 16 is moved back up and the Needle thread tensioned until at the end of a turn of the arm shaft 4 and so that a full stroke of the needle 8 is back in its high position and so that the needle thread 17 is tensioned, causing the electrical voltage again increases to the value U1. The above-described voltage curve returns its target value.

As Fig. 6 can be removed, the output from the sensor 36 electrical Voltage together with those coming from the rotary pulse generator 6, the Angular position of the arm shaft 4 representing signals in the micro-processor 53 of the controller 38 processed. When shown in Fig. 5 History of the voltage U is given to the micro-processor 53 is the Stichbildung in order. The actual value of the voltage thus corresponds to the Target value. The micro-processor 53 is so far no signal. If on the other hand, the sensor 36 detects the intermediate rise of the voltage from U2 to U3 does not exist on the micro-processor 53, then this is a sign that the stitching did not take place. The actual value of the voltage corresponds So not the target value. In this case, the micro-processor gives 53 from a corresponding signal, so that then from the controller 38 of Drive motor 13 is stopped and, if necessary, the indicator light 44 lights up. If a breakage of the needle thread 17 takes place, then it sinks the voltage U of the sensor 36 continuously to the value U2 from what also leads to a stop of the sewing machine, because again a Deviation of the actual value of the voltage from the desired value is present.

Claims (7)

Sewing machine, with a needle (8) which can be driven up and down by an arm shaft (4) and to which a needle thread (17) can be fed in a needle thread feed direction (18), with a gripper (10) cooperating with the needle (8), with one of the needle (8) in needle thread feed direction (18) upstream, the needle thread (17) leading thread lever (16), with a thread tensioning device (19) arranged upstream of the thread lever (16) in the needle thread feed direction (18), with a mis-stitch detection device (21) for generating from the needle thread tension on the rotational angle position of the arm shaft (4) dependent electrical signals and with a micro-processor (53) for generating a control signal as a function of the electrical signals and a rotational angle position of the arm shaft (4) characterized in that the mis-stitch detection means (21) in the path of the needle thread (17) from the thread lever (16) to the needle (8) is arranged, and
in that means are provided for comparing the electrical voltage generated as a function of the needle thread tension with a predetermined desired voltage profile. Sewing machine according to claim 1, characterized in that the mis-stitch detection device (21) a the needle thread (17) leading, in response to the needle thread tension substantially transversely to the main direction (33) of the needle thread (17) elastically deflectable Has thread eye (26) and a deflection movement of the eyelet (26) detecting sensor (36). Sewing machine according to claim 2, characterized in that the thread eyelet (26) is associated with a permanent magnet (32) in whose magnetic field the eyelet (26) is movable, and
that the sensor detects (36) changes the magnetic field, and generates signals representing these changes. Sewing machine according to claim 2 or 3, characterized in that the thread eyelet (26) is formed on a leg spring (23). Sewing machine according to one of claims 2 to 4, characterized in that the sensor (36) is a Hall generator. Sewing machine according to claim 4 or 5, characterized in that the leg spring (23) is mounted with the eyelet (26) in a spring housing (22). Sewing machine according to one of claims 2 to 6, characterized in that the thread eye (26), the sensor (36) and the permanent magnet (32) are mounted on a common support plate (20).

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