EP0424395B1 - Thread stop-motion device - Google Patents

Abstract

In the case of known thread stop-motion devices, the thread is monitored at one point on its course. The device according to the invention, on the other hand, monitors the thread in various regions along its course and, if a defect arises during the passage of the thread through one of these regions, triggers a corresponding switching process. The thread stop-motion device (28) has first sensor units (13) in the region between the thread supply (10) and the corresponding tensioning device (19, 27) and second sensor units (22 and 26) in the region between said tensioning device and the corresponding stitch-forming element (17, 24) which, in the event of a thread defect, emit signals which, for the purpose of producing different switching operations, can be evaluated differently. The thread stop-motion device is used preferably in stitch-forming machines.

Description

The invention relates to a thread monitor according to the preamble of claim 1.

In sewing machines, the needle thread is generally monitored between the endless thread supply and the needle. The hook thread is monitored between the endless thread supply and the hook in multi-thread chainstitch sewing machines, and between the hook and the stitch formation point in double lockstitch sewing machines. After a thread fault occurs, the thread monitor emits a signal that triggers a reaction from the machine.

For example, a thread monitor for monitoring the needle thread is described in German utility model 69 13 073. For this purpose, a disc, which is set in rotation by the needle thread withdrawn from the thread supply and is interrupted in the edge region by radially extending slots, is monitored by a sensor device. As soon as one of the slots is aligned with the sensor device, a pulse is passed on to an electronic switch of a control circuit. If, after the needle thread breaks, the disc stops and the electronic switch no longer receives any pulses, the sewing machine is stopped.

From Japanese patent application 53-43 335 a thread monitor is known, the sensor device used to monitor the needle thread on one of the head attached to the sewing machine bracket.

The needle thread is passed through the monitoring area of the sensor device to the needle. As a result of the up and down movement of the needle bar during sewing, the needle thread is alternately deflected from its central position in mutually opposite directions, so that it executes a swinging movement perpendicular to the thread pull-off direction and traverses the monitoring area of the sensor device back and forth once per stitch. Failure to do so is indicated as a fault.

The invention specified in claim 1 has for its object to design a thread monitor of a stitch-forming machine so that it monitors the thread along the thread path at a plurality of points and controls the machine in the event of a thread fault so that one of the fault location depending on the fault location corresponding switching process is triggered on the machine.

This object is achieved in the arrangement according to the invention by the characterizing features of claim 1.

Here, for example, on multi-filament Chainstitch sewing machines monitor the needle and looper threads immediately after they have been withdrawn from the endless thread supply by the first sensor unit. This measure makes it possible to detect the end of the thread early, since a relatively large thread remnant remains between the sensor unit and the tensioning device assigned to the thread. After displaying the thread end or a thread break, it is therefore still possible to finish a seam with the size specified by the thread length without thread change with the required thread tension.

With needle thread there is the greatest risk of breakage in the area between the tensioning device and the needle, since it is most heavily loaded there. The resulting thread remainder to the needle is without tension, so that the seam formation is interrupted. In order to indicate this, the second sensor unit for monitoring the needle thread in the thread take-off direction is provided behind the tensioning device.

The hook thread in multi-thread chainstitch sewing machines between the tensioning device and the hook is most at risk from thread breakage. For this reason, the area in question is also equipped with the second sensor unit.

When using several sensor units monitoring the needle and / or the hook thread at different points on the machine, it proves advantageous to evaluate the signals of each sensor unit individually so that the machine is always operated in such a way that the damage caused by the thread fault is minimal.

If the thread fault occurs, for example, in the area of the first sensor unit, the measure according to claim 2 proves to be advantageous, since smaller seam pieces can also be produced without changing the thread. In order to obtain a reproducible, relatively precisely adjustable, processable thread length, the measure of claim 3 is advantageous. The measure according to claim 4 is applied when the processable thread length must always be constant.

If the thread fault occurs in the area of the second sensor unit, the machine is activated according to claim 5.

In claim 6, a measure is specified to implement the different evaluation of the signals with little technical effort.

The measure of claim 7 ensures that the thread is always monitored in areas in which it is already performed in the most appropriate manner for monitoring. Such areas are specified in claims 8 to 10.

Claim 11 is directed to a measure by which a sensor unit monitoring the bobbin thread of a lockstitch sewing machine can be linked to the thread monitor.

The thread can be monitored dynamically by the thread movement customary on sewing machines and described in the preamble of claim 12. When crossing the effective range of a sensor unit, the thread impulsively reduces the signal that otherwise reaches the receiver uniformly. This signal reduction is evaluated depending on the stitch formation. For this purpose, for example, a position transmitter monitoring the rotation of the main shaft and connected to the control device is provided, which, depending on the speed of the sewing machine, specifies the test interval in which the signal reduction must occur. A run of the test interval without a signal reduction is an indication that no thread has crossed the effective range of the sensor unit due to thread end or break.

Claim 13 specifies a possibility of how the sensor units for dynamic monitoring of the thread can be positioned relative to the latter. This version is also suitable for displaying skipped stitches. In this case, the transverse movements of the thread are considerably reduced because of the small thread withdrawal, so that this does not swing out of the effective range of the sensor unit. As a result, the signal reduction occurs continuously during the test interval predetermined by the position transmitter.

• Fig. 1 eine Nähmaschine in perspektivischer Darstellung,
• Fig. 2 eine vergrößert herausgezeichnete erste Sensoreinheit, in Fig. 1 strichpunktiert eingekreist,
• Fig. 3 eine vergrößert herausgezeichnete zweite Sensoreinheit nach dem Schnitt III-III der Fig. 1,
• Fig. 4 eine Sensoreinheit unterhalb der Stichplatte,
• Fig. 5 einen vereinfachten Schaltplan einer Steuervorrichtung,
• Fig. 6 ein weiteres Anwendungsbeispiel für eine Sensoreinheit unterhalb der Stichplatte.

The invention is explained with reference to exemplary embodiments shown in the drawing. It shows:

• 1 is a perspective view of a sewing machine,
• 2 shows an enlarged first sensor unit, circled in dash-dot lines in FIG. 1,
• 3 shows an enlarged second sensor unit according to section III-III of FIG. 1,
• 4 a sensor unit below the throat plate,
• 5 shows a simplified circuit diagram of a control device,
• Fig. 6 shows another application example for a sensor unit below the throat plate.

On the back of a multi-thread chain stitch sewing machine shown in Fig. 1, the housing (1) consists of a base plate (2) with a needle plate (3), a stand (4), an arm (5) and a head (6) , a thread supply stand (7) is arranged, on the vertical stand rod (8) of which a thread supply carrier (9) for receiving the thread supply (10) is attached. Above the thread supply (10) extends a holder (11) which is fastened to the stand rod (8) and has eyelets (12) for thread guidance.

A sensor unit (13) is accommodated on each eyelet (12) and is shown enlarged in FIG. 2. The sensor unit (13) has a photodiode (14) as a transmitter and a photodetector (15) as a receiver. The thread (F) (needle or looper thread) is in the directions shown through the area from the photodiode (14) to the photodetector (15) directional light barrier movable.

On the right side of the head (6) in FIG. 1, in which a needle bar (16) for receiving the needle (17) and a thread lever (18) are mounted and driven, there is a tensioning device (19) with a thread tightening spring (20 ) and a bracket (21) attached.

A sensor unit (22) (FIG. 3) is accommodated on the bracket (21), the structure of which corresponds to the sensor unit (13) with a photodiode and a photodetector. The needle thread (NF) can be moved in the manner shown in the area of the sensor unit (22) perpendicular to the head (6).

The needle thread (FIG. 1) drawn off from the thread supply (10) is via the associated eyelet (12), via thread guides, not shown, the tensioning device (19), the thread lever (18), the bracket (21) and one on the needle bar (16) trained thread eyelet (23) fed to the needle (17).

The gripper (24) (FIG. 4) mounted below the throat plate (3) has on its rear side a bracket (25) attached to the base plate (2) for thread guidance. A sensor unit (26) is accommodated on the bracket (25), the structure of which corresponds to the sensor units (13 and 22). The looper thread (GF) swings in the area of this sensor unit (26) perpendicular to the base plate (2).

The looper thread drawn from the thread supply (10) (FIG. 1) passes through the associated eyelet (12), a tensioning device (27) arranged on the stand (4), a plurality of thread guides and not shown reaches the gripper (24) via the bracket (25).

The sensor units (13, 22 and 26) together form a thread monitor (28) and are connected to a control device (29).

5 shows the elements required for the function of the control device (29) in a simplified circuit diagram. The control device (29) enables dynamic thread monitoring.

Each of the two sensor units (13) has a regulated voltage source, from the positive pole of which current flows to ground via the photodiode (14) and a resistor (30). Current also flows from the positive pole of the voltage source via the photo detector (15) designed as a phototransistor and a resistor (31) to ground.

The emitters of the photodetectors (15) are each connected to a capacitor (32) which is used to filter out direct currents caused by daylight and alternating currents caused by low frequency sewing light. The output of the capacitor (32) is connected via a negation element (33) and an amplifier (34) to an input (E1) of a counter (35). Together with the elements (32 to 34), the counter (35) forms a counting device (36).

To set the counter (35), a signal corresponding to the required maximum value can be fed to it via an input (E2). The maximum value can be preselected on a control panel (37) to which the input (E2) is connected. The maximum value preselected on the control panel (37) corresponds, for example, to one Number of stitches to be carried out by the sewing machine after a thread fault. The number of stitches specifies a thread length that can be processed until the sewing machine stops, which can also take the value zero. The sewing machine is designed in such a way that, for stitch numbers greater than zero, a change in the stitch length at a stitch regulator (S) which is known per se and is therefore only shown schematically causes the output of a signal assigned to the stitch length to the control panel (37). The control panel (37) then automatically adjusts the number of stitches to the new stitch length so that the processable thread length is retained.

A position sensor (39) monitoring the revolutions of the main shaft (38) is connected to an input (E3) of the counter (35). This has a photodiode (40) connected to the positive pole of a regulated voltage source, which is connected to ground via a resistor (41) and a photodetector (42) also connected to the positive pole and designed as a phototransistor, which is connected to ground via a resistor (43) is laid on. Provided in the light path between the photodiode (40) and the photodetector (42) is a disc (44) which is fixed on the main shaft (38) and is designed with a plurality of openings (45) for the passage of the light beams. With each pass, a pulse (P) is delivered to the input (E3) of the counter (35).

The outputs (A) of the counters (35) are connected via an OR gate (46) to a display element (47) which is connected to ground via a resistor (48). The output (A) is also with a shutdown device (49) of the drive motor (50) Sewing machine connected. The drive motor (50) drives the main shaft (38) via a V-belt (51).

A display element (52) is connected to each of the additional inputs (ZA) of the counters (35) and is connected to ground via a resistor (53).

The sensor unit (22) is connected to a counting device (54) and the sensor unit (26) is connected to a counting device (55). The design of the counting devices (54 and 55) corresponds to the described counting device (36), but their counters (56) have no additional output (ZA) compared to that of the counting device (36).

The counter devices (54 and 55) are connected via their counter outputs (A) to an OR gate (57), the output of which is connected to a display element (58). The display element (58) is connected to ground via a resistor (59). The shutdown device (49) of the drive motor (50) is also connected to the output of the OR gate (57).

The thread monitor works as follows:
The cyclical succession of tensioning and relaxing the needle and the looper thread in the rhythm of the thread retraction cause these to vibrate transversely to the thread take-off direction.

The sensor units (13) on the thread supply stand (7) are traversed up and down by the needle and the looper thread with each stitch as long as there is no thread end or break between the thread supply (10) and the eyelets (12) is present.

The light signal entering the photodetector (15) of each sensor unit (13) is interrupted in each of these passes. As a result, the otherwise conductive photodetector (15) is temporarily blocked and no current reaches the input of the negation element (33), so that its output outputs a signal with the potential "high", hereinafter referred to as signal (H). The signal (H) is passed on via the amplifier (34) to the input (E1) of the counter (35). The counter (35) is reset by the signal (H) to its initial position, the value zero.

The counter (35) then begins to sum the pulses arriving at the input (E3) from the position transmitter (39), a predeterminable number of signals corresponding to one revolution of the main shaft (38). As long as both loops (12) of the thread reel stand (7) have run through threads, the counter (35) is always reset to zero before it has reached the maximum value set on the control panel (37) and entered via input (E2).

If the signals (H) fail to appear due to breakage or end of the needle or looper thread, the relevant counter (35) counts up to the maximum value and outputs a signal (H) at its output (A) via the OR gate (46 ) to the display element (47) and to the shutdown device (49). As a result, the display element (47) is switched on and the switch-off device (49) is activated such that it prevents the drive motor (50) from restarting after the next stopping process.

The sensor units (13) are additionally provided for the detection of missing stitches. Since only a small needle or looper thread is pulled in the event of a missing stitch, the vibration introduced in the transverse direction is very low, so that the thread in question does not leave the effective range of the assigned sensor unit (13). As a result, there is always a signal (L) at the input of the negation element (33) and a signal (H) at its output and at the input (E1) of the counter (35), which prevents the counter (35) from counting up. At the same time, the pulses from the position sensor (39) arriving at the counter input (E3) are counted in a second counter part. If the number of pulses corresponding to a full revolution of the main shaft (38) is reached without an interruption of the signal (H) present at the counter input (E1), the counting device (36) gives a signal to switch on the display element (52) at its additional output (ZA). out.

The light path of the sensor unit (22) is interrupted twice by the needle thread swinging back and forth perpendicular to the head (6). The signals from the sensor unit (22) are transmitted to the counting device (54), in which they are evaluated in order to detect a thread break occurring behind the tensioning device (19) in the same way as the signals fed to the previously described counting device (36). After a thread break occurs, the counting device (54) outputs a signal (H) at its counter output (A) which, after passing through the OR gate (57), switches on the display element (58) and switches off the device (49) for immediately switching off the Drive motor (50) controls.

The sensor unit (26) on the bracket (25) is from the Crossing the hook thread once with each stitch going up and down. The resulting brief interruption of the signal entering the photodetector (15) serves to reset the counter of the counting device (55) to the initial value zero. This resetting takes place in the manner already described for the counting device (36).

If the looper thread behind the tensioning device (27) breaks, the thread end leading to the looper (24) is without tension, so that the looper thread no longer cyclically crosses the light barrier of the sensor unit (26). As a result, a signal (H) is output at the counter output (A) of the counting device (55), which switches on the display element (58) and at the same time activates the switch-off device (49) to stop the drive motor (50) immediately.

The bobbin thread (SF) on lockstitch sewing machines, as shown in FIG. 6, is guided along the front of the hook (60) and is deflected by it in a direction parallel to the hook axis during the rotational movement. A bracket (62) for thread guidance is attached to a bearing block (61) on the underside of the throat plate (3), on which a sensor unit (63) identical in structure to the sensor units (13, 22 and 26) is received. The light barrier of the sensor unit (63) runs parallel to the underside of the throat plate and perpendicular to the drawn cross-wise direction of the bobbin thread. To evaluate the signals, the sensor unit (63) is connected to the counting device (55) of the control device (29) instead of the sensor unit (26).

If the take-off is trouble-free, the bobbin thread traverses the Area of action of the sensor unit (63) swinging back and forth once per revolution of the gripper (60). The interruptions in the light barrier directed towards the photodetector (15) are evaluated in the manner already described by the counting device (55).

Claims (13)

1. Thread monitor for monitoring the thread on stitch-forming machines, such thread being feedable to the associated stitch-forming element from an endless thread supply via a tensioning means, characterised in that the thread monitor (28) includes first sensor units (13) between the thread supply (10) and the associated tensioning means (19, 27), and a second sensor units (22, 26) between each of the tensioning means (19, 27) and the stitch-forming element (17, 24), which is associated therewith, said sensor units releasing signals, which are variably evaluatable to produce different switching operations, in the event of a fault in the thread occurring.
2. Thread monitor according to claim 1, characterised in that the signals of the first sensor units (13) serve to stop the machine after a prescribable thread length has been utilised.
3. Thread monitor according to claims 1 and 2, characterised in that the thread length is prescribable by inputting a number of stitches associated therewith into the machine.
4. Thread monitor according to claims 1 to 3, characterised in that the number of stitches is automatically variable by the machine in dependence upon the set stitch length.
5. Thread monitor according to claim 1, characterised in that the machine is immediately stoppable by the signals which are released by the second sensor units (22 and 26).
6. Thread monitor according to claims 1, 2 or 5, characterised in that both sensor units (13 and 22, 26) are connected to a control means (29) which variably evaluates the signals.
7. Thread monitor according to one or more of claims 1 to 6, characterised in that each sensor unit (13, 22 and 26) is disposed in the region of a thread guiding member (12, 21 and 25).
8. Thread monitor according to one or more of claims 1 to 7, characterised in that one sensor unit (13) is disposed on a holder (11) of a thread supply support (7) in the region of an eyelet (12).
9. Thread monitor according to one or more of claims 1 to 8 on a sewing machine, characterised in that one sensor unit (22) is mounted on a bow-shaped clip (21), which is mounted on the head (6) in the region between the thread lever (18) and the needle (17).
10. Thread monitor according to one or more of claims 1 to 9 on a multi-threaded chain-stitch sewing machine, characterised in that one sensor unit (22) is accommodated in front of the gripper (24), when viewed with respect to the thread delivery direction, in the region of a yoke-shaped clip (25), which is mounted on the underside of the base plate (2).
11. Thread monitor according to claims 1 and 6 on a double lock-stitch sewing machine provided with a sensor unit which monitors the bobbin thread, characterised in that the sensor unit (63) and the two sensor units (13 and 22, 26) are connected to a common control means (29).
12. Thread monitor according to claim 1 for monitoring the thread which is displaced transversely relative to the thread delivery direction by the delivery of thread in synchronism with the stitch-formation, characterised in that the sensor units (13, 22 and 26) are disposed at locations of relatively large transverse movements of the thread, so that the thread pivots through the effective range of the sensor units (13, 22 and 26) at least once per stitch-forming cycle, thereby producing a signal.
13. Thread monitor according to claims 1 and 12, characterised in that the sensor units (13, 22 and 26) are each accommodated centrally between the two turning points of the thread, which pivots in the transverse direction, and their effective range is so dimensioned that, in its interference free state, the thread pivots out of said state alternately into directions which are opposed to one another.

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