EP0943713A2 - Yarn tension sensor with repeated adjustment - Google Patents

Abstract

The tension in the yarn (7) is measured by the force exerted on a guide peg (21). An actuator can move two further pegs (42,43) into the yarn path to lift the yarn off the measuring peg (21) to calibrate the zero position on the transducer. Independent claims are also included for the following: a) A yarn feeder for knitting machines with strongly variable yarn requirements, having a yarn delivery wheel (4) driven by a motor controlled by the claimed yarn tension sensor to provide constant feed tension. b) Analyzing the tension signal to detect periods when the tension can vary from the set value (e.g. during the carriage return on the knitting machine) and initiating the actuator to lift the yarn off the measuring peg, reset the zero and replace the yarn on the peg.

Description

The invention relates to a thread tension sensor, in particular for supplying elastic threads to knitting machines Thread delivery device for knitting machines and a method for Adjusting a thread tension sensor.

In many textile applications, in particular With knitting machines, it is often necessary to have one too Knitting points or other places to be supplied thread to keep under a constant tension. This is particularly so important for flat knitting machines that result from the back and forth movement of the Thread guide (slide) a very strong time fluctuating thread consumption. A corresponding one Thread delivery device must have the thread here with it in time deliver abruptly changing speed again and again. The thread tension changes, for example during, before or after the thread guide reverses movement, the mesh size of the knitted fabric changes, what its appearance, elasticity and quality impaired. Here in particular are the marginal areas of knitted fabrics made on flat knitting machines critical.

Special requirements must be placed on the constant voltage when supplying elastic threads (elastane) be, for example, in connection with others Threads are knitted together. To keep it constant the thread tension, it is necessary to keep this constant to monitor and the thread delivery quantity accordingly to regulate.

For this purpose, for example, from DE 195 37 215 A1 Thread delivery device for elastic yarns known for Use on flat knitting machines is provided. The Thread delivery device is used to supply elastane threads and has a thread delivery wheel driven by an electric motor on. The electric motor is controlled by a control loop controlled with the current thread tension a thread tension sensor detected. This has one pin that can be deflected transversely to the thread running direction, over which the thread is guided at an obtuse angle. The deflection of the pin corresponds to the thread tension and is detected by a suitable displacement sensor.

In addition, US Pat. No. 3,858,416 Thread delivery device for knitting machines known that also has a thread delivery wheel that is driven by a motor is driven. The engine is looped controlled the thread tension with a thread tension sensor detected. This has a deflectable Pen on which the thread runs.

DE 39 42 341 A1 describes a force sensor for Monitoring thread tension known in the case of a Sensor element is mounted on a spring parallelogram. The deflection of the sensor element is based on a a flexible body provided with variable resistance transmitted so that the deflection of the sensor element and thus the thread tension is electrically detectable.

The constant tension is particularly important when supplying elastic threads for the production of elastic knitted fabrics of great importance. Even the slightest fluctuations and especially propose long-term changes itself in a changing or changing Quality. Therefore, the thread tension also applies over long periods, i.e. Hours, days and months to keep stable away.

Knitting machines and thread delivery devices are becoming common used in workshops in which, not least due to the heat loss of the knitting machines, the temperature throughout the day and according to the duration that changes machines. This also changes Temperatures of the thread tension sensors, what despite possibly existing temperature compensation influences whose output signal can have. They can also be long term Dirt deposits for a change in the sensor output signal cause, for example, deposits the total weight on a pin to record the thread tension of the pen and thus the zero point shift the signal.

Proceeding from this, it is an object of the invention to Thread tension sensor to create a long-term stable Detection of the thread tension enables. Furthermore a thread delivery device is to be created that the Thread with a flat knitting machine, for example constant thread tension. After all it is Object of the invention, a method for operating a To create thread tension sensor when using it the sensor has a reliable long-term stable output signal delivers.

This task is done with a thread tension sensor with the features of claim 1, with a thread delivery device with the features of claim 17 and a method according to claim 22 solved.

The thread tension sensor according to the invention has except for its thread sensing element, which is used to measure thread tension is in contact with the thread, a thread take-up means on that is movably mounted. At least it points two different positions on each other differ in that the thread is in a calibration position is separated from the thread sensing element and in the Measuring position of the thread take-up means on the thread sensing element is present. It is therefore through targeted adjustment of the thread take-up means and / or the thread tension sensor possible, the thread arbitrarily from the thread sensing element take off so that it comes to its rest position. This is characterized by the fact that no force acts on the thread sensing element. The measuring device detects this position or state of the thread sensing element. Should be in the mechanical or electrical system the thread tension sensor has drifted, can this when lifting the thread from the thread sensing element recognized and recorded. For example, that Lifting the thread from the thread sensing element for zero adjustment of the thread tension sensor can be used. On this way, long-term offsets can be avoided, otherwise the output signal of the thread tension sensor would overlay. By detecting and Elimination of offset influences, for example by temperature drift or by deposits on the Thread sensing element could be caused in the long run generates a sensor output signal that is the thread tension reproduces zero-point errors. This enables the construction of a thread delivery device with high Long-term constant thread tension.

This is achieved by using the thread tension sensor repeated during the operation of the thread delivery device is calibrated, in particular by repeatedly performing a zero point adjustment is made. This is done by taking off / taking away of the thread from the thread tension sensor and Acquisition of the measured value reached with the thread lifted. The recorded measured value is the zero point for the after Replace the thread on the thread sensing element from the thread tension sensor detected.

In a first embodiment there are thread sensing elements and thread take-up means on opposite Arranged sides of the thread path. To measure this "pushes" Thread take-up means the thread to the thread sensing element; for calibrating it leaves the thread from the thread sensing element take off.

In a second embodiment there are thread sensing elements and thread take-up means on the same side arranged the thread path. To "calibrate" it Thread take-up means remove the thread from the thread sensing element path; for measuring it leaves the thread on the thread sensing element issue.

In both embodiments, one can first design the sensor can be moved while in a second design, the thread take-up element is movably mounted is.

The calibration or zero point adjustment process is preferably carried out when the thread delivery device provides no thread. During this period by zeroing induced or permitted thread tension fluctuations cannot interfere here of the knitwear produced. Alternatively it is possible to adjust the zero point with a short time Lifting the thread from the thread sensing element, if the thread moves slowly or his Movement speed currently does not change. In this Fall is the control device regulating the thread delivery briefly hidden, i.e. their output signal will be on the current value is clamped, the zero point adjustment carried out and after replacing the thread on the The thread loop sensor is activated again.

For the reliable detection of a sufficiently long Engine standstill becomes the control signal of the engine supervised. If an L-0 edge occurs, i.e. a clear one Transition of the control signal from a non-zero Value to zero, it is assumed that the engine has been deliberately stopped. For flat knitting machines is due to the special way of working after a deliberate stop of the delivery motor at the earliest after a given period of time, in the example of approximately 500 ms, with a restart of the motor count. The same applies to changes of feathers in stockings or Sock machines. A waiting time is now preferred waited for example of 20 ms and, if the control signal after this waiting time is still zero, the calibration process is allowed, which takes about a few 10 ms lasts. The calibration process is then carried out when it is allowed (released) and (as a second criterion) when requested. This is usually regular Time intervals the case. The time intervals can be shorter after switching on the machine (2 min.) and longer after running in (30 min.).

The thread tension sensor preferably has one Drive device assigned to thread take-up means, for example a pull magnet or another Drive (electric or pneumatic rotary, swivel or Linear drive) on by a calibration device can be activated and the thread take-up means drives such that this in its first thread of the thread-sensing element is transferred to the lifting position. Now the zero point adjustment can be carried out. Becomes If the drive device is deactivated, the thread take-up means arrives in its second position, in which the thread abuts the thread sensing element. Preferably that is Thread take-up means in this position from the thread separated, i.e. does not touch it. This will Measurement error due to friction of the thread on the thread take-up means eliminated. However, it is also possible the thread take-up device deliberately for thread guidance use. In the first version, the thread is either with the thread take-up means or with the thread sensing element engaged. In the second variant, the Thread always in contact with the thread take-up device, regardless of whether it is lifted off the thread sensing element is or not.

The thread take-up means is by, preferably two thread sensors adjacent to the thread sensing element educated. In the simplest case, these are pens that to the preferably also pin-shaped Extend the thread sensing element in parallel. It can eyelets can also be used. Both the pin of the thread sensing element as well as the pins of the thread take-up means extend transversely to the thread running direction, preferably at right angles to this. This ensures that even with relatively wide pens all thread positions are equal on the pen, so that the thread does not saw in a preferred location.

The thread sensing element of the thread tension sensor is preferably mounted on a spring parallelogram. The preferably pin-shaped thread sensing element is then in arranged at right angles to the spiral springs. Thereby one-sided clamping and storage of the Thread sensing element and it is a good measurement accuracy ensured.

The measuring device preferably has two displacement sensors on whose output signals change when deflected of the thread sensing element preferably in opposite directions to change. This enables offset suppression in the Evaluation circuit. This is preferably a differential generator circuit, through a bridge circuit or an operational amplifier or other equivalent Means can be formed.

The thread tension sensor according to the invention and the Thread delivery device according to the invention are for example to use a flat knitting machine, said Calibration or zero point adjustment process, for example when the thread guide changes direction or changes thread can be carried out. The thread guide moves For example, running away from the thread delivery device and stops at the end of its movement stroke to reverse the required thread delivery quantity, regardless of the respective Knitting pattern, briefly zero. A separate one Calibration circuit can detect this and the drive device activate briefly so that the thread of that Thread sensing element is lifted off and the adjusting one Measured value can be recorded as the zero point. Once this is done the calibration circuit deactivates the drive device, so that the thread is back on the thread sensing element is launched. The entire process can, if appropriate Design of the thread tension sensor and the drive device for the thread take-up means in some to be finished for a few 10 ms. The one when reversing direction the downtime of the thread guide is therefore sufficient to perform the calibration.

It is also possible to calibrate others Occasions with low thread speed or thread running speed associated with zero. For example, the thread delivery device at Standstill of the knitting machine in a standby or Standstill mode are operated. Will the thread delivery device led out of this state (switched on) the short-term calibration process can be carried out.

Fig. 1

ein Fadenliefergerät mit einem Fadenspannungssensor mit abgenommener Sensorabdeckung in einer perspektivischen Gesamtansicht,

Fig. 2

das Fadenliefergerät nach Fig. 1 in einer schematisierten Seitenansicht,

Fig. 3

den Fadenspannungssensor des Fadenliefergerätes nach Fig. 1 und 2 in einer vereinfachten Perspektivdarstellung und in einem anderen Maßstab,

Fig. 4

den Fadenspannungssensor nach Fig. 3 in einer Draufsicht,

Fig. 5

den Fadenspannungssensor nach Fig. 4 in einer schematisierten Prinzipdarstellung zur Veranschaulichung seines Funktionsprinzips,

Fig. 6

den Fadenspannungssensor nach Fig. 4 geschnitten entlang der Linie VI-VI,

Fig. 7

den Fadenspannungssensor nach Fig. 4 in einer schematisierten Vorderansicht,

Fig. 8

den Fadenspannungssensor nach Fig. 4 in einer Seitenansicht,

Fig. 9

eine elektrische Schaltung zur Signalverarbeitung der Ausgangssignale zweier als Wegaufnehmer dienender Hallsensoren und

Fig. 10

einen Ablaufplan zur Veranschaulichung des Verfahrens bei dem Nullabgleich des Fadenspannungssensors.

Further details of advantageous embodiments of the invention are the subject of dependent claims, the drawing and the associated description. An exemplary embodiment of the invention is illustrated in the drawing. Show it:

Fig. 1

a thread delivery device with a thread tension sensor with the sensor cover removed in an overall perspective view,

Fig. 2

1 in a schematic side view,

Fig. 3

1 and 2 in a simplified perspective view and on a different scale,

Fig. 4

3 in a plan view,

Fig. 5

4 in a schematic representation of the principle to illustrate its operating principle,

Fig. 6

4 cut along the line VI-VI,

Fig. 7

4 in a schematic front view,

Fig. 8

4 in a side view,

Fig. 9

an electrical circuit for signal processing of the output signals of two Hall sensors serving as displacement sensors and

Fig. 10

a flowchart to illustrate the method in the zero adjustment of the thread tension sensor.

Description:

In Fig. 1, a thread delivery device 1 is illustrated, whose housing 2 is a substantially flat one Front 3 has. There is a thread delivery wheel on this 4 and a thread tension sensor 5 are arranged. The housing 2 of the yarn delivery device, which is not shown with Means for attachment to a knitting machine, in particular a flat knitting machine, has an eyelet 6 for guidance in addition to the thread delivery wheel 4 one illustrated only by a section Thread 7 on. The eyelet 6 is made with an insert 8 Ceramic provided and with respect to an arrow 9 illustrated thread running direction in front of the thread feed wheel 4 arranged. At the opposite end of the Housing 2 is connected to a signal lamp 11 further eyelet 12 arranged with a ceramic insert 13.

In the thread path defined between the eyelets 6 and 12 13 serve the thread delivery wheel 4 of the needs Promotion and delivery of thread 7 and the thread tension sensor 5 monitoring the thread tension. A controls arranged in the housing 4 controls accordingly based on one of the thread tension sensor delivered signal one to drive the thread delivery wheel 4 serving engine.

The thread feed wheel 4 is preferably six or multi-winged and has several of one Hub 14 radially extending spokes 15, 16 on connected to each other at the ends by a web 17 are. One pair of spokes and one web 17 each define a wing 18. The wings 18 are uniform Angular distances arranged. The thread delivery wheel 4 therefore defines a polygonal outer circumference on which the thread 7 rests as a regular hexagon.

The thread tension sensor follows the thread feed wheel 4 5, the one serving as a thread sensing element 21 has. This extends across the thread 7, which is at an obtuse angle over the outer circumferential surface of the cylindrical pin 21 runs. As illustrated in FIG. 2, is the yarn feed wheel 4 about an axis of rotation 22 rotatable that is not parallel to one of the pin 21st defined longitudinal axis 23 is arranged. Through the Inclination of the yarn feed wheel 4 with respect to the Pin 21 and thus the thread 7 are used for the thread Leaving the thread delivery wheel 4 advantageous conditions reached. The thread is drawn off at a larger angle. This causes an exact detachment of the thread from the thread delivery wheel or other of the thread delivery wheel recorded thread turns. So much for the thread flow conditions regardless of the orientation of the pin 21 are, the thread 7 runs at an acute angle to an imaginary Level 24 from (Fig.2), for which the axis of rotation 22 Establishes normal direction. This is done through appropriate Positioning of the eyelet 12 reached.

The thread tension sensor 5 is in particular based on 3 to 5 to understand. The pin 21 is at the end mounted on a low-mass carrier 27 by two Kind of a spring parallelogram arranged leaf springs 28, 29 are held movably essentially in the longitudinal direction is. At the end, the carrier 27 projects with cylindrical ones Sections in damper pots or tubes 31, 32 that contain a more or less viscous liquid. Suppression, in particular, becomes more high-frequency Signal components reached, for example, due to the polygonal Outline of the yarn feed wheel 4 can occur.

The bending springs 28, 29 are at the ends of corresponding Recordings 33, 34 taken on a base 35 are attached. As can be seen from FIG. 7, with a total of four, preferably made of rubber Damper elements 36 mounted stationary. The base 35 is, as is apparent from Fig. 4, for example. By a U-shaped Yoke 35a formed.

A permanent magnet 37 is arranged on the carrier 27, whose magnetic field two in the immediate vicinity arranged Hall sensors 38, 39 reached and influenced. A slight relocation of the wearer 27 with respect to the base 35 is from the Hall sensors 38, 39 recorded.

A calibration device belongs to the thread tension sensor 5 40 with two serving as thread take-up means 41 Pins 42, 43 that are substantially parallel to each other the pin 21 are arranged. The pins 42, 43 are on a support frame 44 held with the pins 42, 43 movable across the pin 21 in the direction of arrow 45 is (Fig. 3, 4 and 5). The thread take-up means 41 is thereby in at least two different positions transferable. In a first position, which is shown in FIG is shown in broken lines, there are the pins 42, 43 in a position in which it takes the thread 7 from the pin 21 take off. In this position none of the thread 7 act outgoing forces on pin 21.

In a second position of the thread take-up device 41, shown in Figure 5 in thick solid lines the thread 7 lies solely on the pin 21, but not on the pins 42, 43 of the thread take-up means 41 on. The thread tension now causes a corresponding one Deflection of the pin 21 and thus a sensor output signal.

The thread take-up means 41 has a drive device 46 connected. For this purpose, the pins 42, 43 of a frame 47 is held which has a solenoid drive 48 embraces. Its magnetic coil 49 has one with the Frame 47 connected tie rod 51. The frame 47 is by means of corresponding guide means 52, for example in one Base plate 53 provided elongated holes 54 or the tie rod 51 can be moved in the direction of adjustment (arrow 45) stored.

To the thread take-up means 41 to its second, inactive Preload position is the frame over a Spring means 56 connected to the base plate 53. The Spring means 56 is preferably a leaf spring 57 which held at one end on the base plate 53 and with connected at its opposite end to the frame 47 is.

The only schematically indicated in Fig. 5 Hall sensors 38, 39 are on, as illustrated in FIG. 9 a measuring circuit 61 connected to outputs 62, 63 of the Hall sensors 38, 39 pending output signals processed. The Hall sensors 38, 39 are arranged that they send opposite signals. If the carrier 27 deflected in one direction, for example, increases the signal from the Hall sensor 38 while the of the Hall sensor 39 reduced. To evaluate this Signals is the measuring circuit 61 as a difference generator circuit trained and contains an operational amplifier 65. This works as a differential amplifier. The voltage gains are at the non-inverting and the inverting input among each other in terms of amount same, but different in sign. this will ensured by appropriate wiring.

In addition, TP1 and TP2 are connected upstream in low passes, to suppress higher frequency components of the sensor signals. So there is a time at the exit averaged and amplified value of the difference of the output signals of the Hall sensors 38, 39.

Due to the polygonal outline of the thread delivery wheel 4 and the direct guidance of the thread to the pin 21 without the thread 7 interposed therebetween changes periodically its angle on the pin 21. This caused Fluctuations in the sensor signal are caused by the low-pass characteristic the measuring circuit 61 filtered out.

A change in the installation position of the thread delivery device 1, deposits on the pin 21 and the brackets of the Magnet 37 or changes in temperature or drift of Hall sensors 38, 39 and temperature or Aging drift on the measuring circuit 61 can gradually to a change in the output signal at the output of the Lead measuring circuit 61. To such a zero point shift can be seen, the thread delivery device 1 with an automatic calibration or zero point adjustment circuit Mistake. This is with the solenoid 49 connected.

The thread delivery device 1 performs its adjustment as follows through:

It is initially assumed that one is not further shown knitting machine with the thread delivery device 1 is provided, does not work. The thread delivery device 1 is turned off, its electronic Circuit is active, however. It is in one Wait mode. To start up the knitting machine among other things the thread delivery device 1 is also activated. The calibration circuit briefly controls the solenoid 41, which attracts the armature 51. With that the Frame 47 pushed so far towards pin 21, that the pins 42, 43 pass the pin 21 and lift the thread 7 from the pin 21. The pin 21 is now free of thread forces and that of the measuring circuit 61 signal given in this state marks the Zero point, i.e. the thread tension is zero.

As soon as this value is recorded and registered, the excitation of the solenoid 49 is switched off, so that the Armature 51 drops and the frame 47 from the spring means 56 is returned to its retracted position. Here the thread 7 is placed on the pin 21 and the pins 42, 43 release the thread 7. Now from thread 7 force exerted on the pin 21 causes a displacement of the carrier 27, which is detected by the Hall sensors 38, 39 and displayed by the measuring circuit 61 as an output signal becomes. This signal serves as an actual value signal for a Control loop that controls the motor of the yarn feed wheel 4.

If thread consumption now occurs, the control loop controls the motor so that the thread delivery wheel 4 the necessary to keep the thread tension constant Thread quantity delivers.

Avoiding errors as a result of commissioning of the yarn feeder 1 occurring zero drifts can be effected by the described Calibration process is carried out frequently recurring. This is particularly possible in time windows in which the thread delivery wheel during the operation of the thread delivery device 1 4 and thus the thread 7 comes to a standstill. This state is, for example, by a corresponding one Controller output signal marked (motor control voltage equals zero). To capture such time windows the calibration circuit monitors the controller output signal. If there is such a time window, it will only a few or a few tens of milliseconds Calibration process triggered, i.e. the solenoid 49 will briefly excited and the zeroing of the measuring circuit 61 performed by the adjusting output signal is taken as the zero value.

In order to detect possible time windows, the process according to the flow diagram according to FIG. 10 first waits for a preset interval time t to be _compared. passes. The time t _equ. is the time interval in which a zero adjustment is to be carried out. It is between a few minutes and an hour. When the interval time has elapsed, the controller output signal is first checked to see if it goes to zero. Then it is checked whether it remains at zero for a given time, for example 20 ms. If this is the case, there is a time window and it is expected that the Fourni's motor has been consciously stopped and will remain stopped for a longer time (500 ms). The adjustment can be carried out during such a time window. The detection of the time window is preferably edge-triggered.

For a machine with intermittent thread consumption an automatic adjustment can be carried out when the slide or thread guide is reversed, with standstill the motor of the thread delivery wheel 4 goes hand in hand. Becomes a Such engine stop can be detected according to a predetermined an automatic comparison is carried out at variable times become. This way it is possible to do it yourself short-term and relatively fast drifts within of the overall system and harmless do.

One especially for machines with intermittent interruptions Thread consumption and elastic yarns provided Thread delivery device 1 has a thread tension sensor 5 on, which is provided with a calibration device 40. This lifts the thread 7 at times from one to the other Thread tension sensor 5 belonging to pin 21, in which this without affecting the operation of the thread delivery device 1 is possible. These are preferably time windows in which no thread delivery is required. Is the Thread 7 is lifted from the pin 21, a zero point adjustment carried out, with zero drift of the whole Sensor system including its measuring circuit 61st can be recorded and compensated.

Claims (26)

Thread tension sensor (1) for detecting the tension of a running thread (7), in particular for suppliers for the supply of elastic threads, in particular for knitting machines, with a thread sensing element (21) which is arranged in a thread path and which has a contact surface for the thread (7), with a measuring device (5) connected to the thread sensing element (21) for detecting the force exerted by the thread (7) on the thread sensing element (21), with a thread take-up means (41), which can at least be brought into contact with the thread or is in permanent contact with the thread, with an actuator device (48), by means of which the thread-sensing element (21) and the thread-receiving means (41) can be moved relative to one another between a calibration position and a measuring position such that the thread in the calibration position is not in contact with the thread-sensing element (21) and that the thread abuts the thread sensing element (21) in the measuring position. Thread tension sensor according to claim 1, characterized characterized in that the actuator device (48) specified direction of movement transverse to the thread is. Thread tension sensor according to claim 1, characterized characterized in that the thread take-up means (41) and the Thread sensing element (21) on a fixed same Side of the thread are arranged and that the thread receiving element (41) in the calibration position the thread of the thread sensing element (21) lifts and in the measuring position preferably does not rest on the thread, the thread abuts the thread sensing element (21). Thread tension sensor according to claim 1, characterized characterized in that the thread take-up means (41) and the Thread sensing element (21) on fixed opposite Sides of the thread are arranged and that the thread receiving element (41) in the calibration position the thread of the thread sensing element (21) and in the measuring position preferably attached to the thread in System with the thread sensing element (21) holds. Thread tension sensor according to claim 1, characterized characterized in that the actuator device (48) with the Thread take-up element (41) is connected to this the calibration position to the measuring position and back to move, and that the thread sensing element (21) essentially, i.e. arranged stationary up to its measuring path is. Thread tension sensor according to claim 1, characterized characterized in that the actuator device (48) with the Measuring device (5) is connected to this together with the thread sensing element (21) from the calibration position in to move the measurement position and back, and that that Thread take-up element (41) is arranged stationary. Thread tension sensor according to claim 5 or 6, characterized characterized in that the actuator device (48), is an electric linear drive (49, 51, 56). Thread tension sensor according to claim 1, characterized characterized in that the thread receiving means (41) by at least one, preferably two thread take-up (42, 43) is formed, which is adjacent to the thread sensing element (21) are arranged. Thread tension sensor according to claim 1, characterized characterized in that the thread sensing element (21) essentially movable and preferably transverse to the thread path is resiliently mounted, the measuring device (5) contains a displacement sensor device (38, 39). Thread tension sensor according to claim 1, characterized characterized in that the thread sensing element (21) by means of a spring parallelogram (28, 29) on a base (35) is stored, which also the displacement sensor device (38, 39) carries and the spring and / or damped mounted (36) is. Thread tension sensor according to claim 9, characterized characterized in that the displacement transducer device (38, 39) has two displacement sensors which are connected to a measuring circuit (61) are connected, which are preferably a difference former (65) contains the sensors at the inputs (+, -) the measuring device (5) are connected. Thread tension sensor according to claim 1, characterized characterized in that the thread sensing element (21) a cross to the direction of movement of the thread (7) arranged, preferably is made of ceramic pin, the Thread (7) is not guided with respect to the longitudinal direction of the pin is. Thread tension sensor according to claim 1, characterized characterized in that the thread take-up means (41) a calibration device (40) belongs to the setting a reference value of the measuring device (5) is provided is. Thread tension sensor according to claim 13, characterized characterized in that the calibration device (40) from a signal emitted by the machine can be activated is that indicates a state in which the thread (7) has a speed less than one is the specified limit. Thread tension sensor according to claim 14, characterized characterized that the limit is the thread speed Is zero. Thread tension sensor according to claim 1, characterized characterized in that a to the measuring device (61) Control device for keeping the thread tension constant is connected and that the control device one Has inactivation input, the control device their output signal does not change when at the inactivation input a corresponding signal has arrived is. Thread delivery device, in particular for elastic threads, in particular for knitting machines with strongly fluctuating thread consumption, such as flat knitting machines, with a thread delivery wheel (4) driven by an electric motor, with a control device for controlling the electric motor (4) in such a way that the required amount of thread is supplied and the thread tension is kept within predetermined limits, with a thread tension sensor (5) according to one of the preceding claims and with a calibration device (40) for the thread tension sensor (5) which can be activated by a calibration pulse, by means of which the thread take-up means (21) and the thread tension sensor can be transferred to the calibration position in relation to one another for the calibration of the thread tension sensor (5). Thread delivery device according to claim 17, characterized characterized in that the thread delivery wheel (4) has an axis of rotation (22), which in the normal direction to a Level (24) is arranged with which the running thread (7) includes an acute angle. Thread delivery device according to claim 18, characterized characterized in that the calibration device (40) from the thread speed is controlled. Thread delivery device according to claim 19, characterized characterized in that the calibration device (40) at least is inactive when the thread speed exceeds a limit. Thread delivery device according to claim 18, characterized characterized in that the calibration device (40) at Reversal of direction of the thread guide of a flat knitting machine or when changing threads in hosiery and sock machines or for other breaks in thread consumption of machines can be activated. Method for calibrating a thread tension sensor, in particular for zeroing the thread tension sensor, with the following steps: Detection of a signal which indicates a state in which the thread tension may briefly deviate from its nominal value Separating the thread from the thread tension sensor, Detecting the signal emitted by the thread tension sensor when the thread is lifted, Reinstall the thread on the thread tension sensor. A method according to claim 22, characterized in that the signal indicates a thread speed, which is less than a predetermined limit. A method according to claim 22, characterized in that the measured value recorded when the thread is lifted off as Zero value is taken. A method according to claim 22, characterized in that the calibration process with a flat knitting machine when reversing movement and / or starting is carried out. A method according to claim 22, characterized in that the calibration process with moving thread is carried out in a time window in which the thread speed is constant.

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