EP2092100B1 - Method and apparatus for needle monitoring - Google Patents

Abstract

The method according to the invention for monitoring needles of a knitting machine is based on dynamic fixing of the monitored time intervals between individual needle pulses. The time duration of at least one or more preceding time periods between individual signal pulses is taken as a measure of the time interval which is currently to be assessed. Dynamic fixing of the switching thresholds for generating the signal pulses can likewise be performed. In turn, the amplitude of preceding pulses is analysed, a trend is determined and the switching thresholds for generating the current signal pulse is stipulated from this trend. The pulses which are generated at all needle positions can be assessed by way of this method. If the needle cylinder is deliberately fitted only partially, individual needle positions can be indicated correspondingly and removed from the assessment. This results in a dependable, robust and reliable monitoring method.

Description

The invention relates to a method for monitoring needles on knitting machines and a corresponding device.

Knitting machines have a large number of knitting needles, which are subject to wear and in particular can break off. Often knitting machines, in particular circular knitting machines are used for the ongoing production of large quantities of goods. If a needle breaks, the result is a defect in the goods produced. There is produced rejects. However, needle breaks can occur again and again. It is therefore important to monitor the needles of the running knitting machine. For this purpose, various efforts have already been made.

The U.S. Patent 3,577,750 discloses a monitoring arrangement with an optical sensor in the form of a light barrier, run through the measuring path, the needle heads. The pulses generated during the passage of the needle heads through the light path of the light barrier are converted into rectangular pulses. The length of such a pulse is relatively large in intact needles, while it is significantly lower in broken needles. If the pulse length is shorter than expected, an alarm signal is given.

This monitoring method is based on the requirement of constant engine speed. If it is to be adjusted so sensitively that even needle bends or only fractures of parts of the hooks can be recognized, there are false alarms in case of speed fluctuations of the knitting machine.

The same applies to the from the DE-OS 1 915 362 apparent method. The hooks of the needles run through the focal point of a lens for optical needle monitoring. It is optically generated a signal containing a periodic component in which individual pulses are visible. When a needle is bent, a single pulse will appear a little earlier or a little later. As a result, the time interval to the one neighboring pulse is shortened and increased to the other neighboring pulse. If a needle is missing, the time interval between two successive pulses is doubled from the normal value. In this way, the monitoring of the needles is attributed to a time measurement. This is done, for example, by comparing the actual pulses obtained with a sequence of desired pulses, wherein an error signal is triggered when the actually obtained pulse deviates from the desired pulse.

Furthermore, the beats DD 274 455 A1 The needle monitoring ago by derived from the individual needles signal pulses and converted into digital signals. For each needle, a comparison is made between a stored and a current signal value. If the signals are outside a predetermined value range, an error signal is generated.

Next beats the DE-OS 20 40 515 To scan the needles with photoelectric probes and to check the number of resulting pulses. For this purpose, a preset counter is used, which is preset to the desired number of needles. He counts the needle pulses backwards. If the preselection counter does not reach the desired value (zero) after one or more machine revolutions, an alarm signal is generated.

The latter method is insensitive to variations in engine speed. Also, needle vibrations that shorten or lengthen the interval between successive needle pulses during one machine revolution can hardly result in machine shutdowns. However, the method is only applicable if the needle number of the machine is known. Also, a missing or bent needle is detected only after a complete machine revolution. In the worst case, multiple machine revolutions are required to capture. However, the goal is to capture errors as quickly as possible.

The DE 19 924 924 A1 discloses a method and an apparatus according to the preamble of claims 1 and 14.

On this basis, it is an object of the invention to provide an improved method for monitoring needles on knitting machines.

• Bei dem erfindungsgemäßen Verfahren werden durch optische Überwachung einzelne Signalimpulse immer dann erzeugt, wenn eine Nadel bzw. ein Haken durch das Sichtfeld des optischen Sensors wandert. Die Zeitabstände zwischen den einzelnen aufeinander folgenden Signalimpulsen werden registriert. Ist der Zeitabstand zwischen zwei aktuellen Signalimpulsen wesentlich größer oder wesentlich geringer als der Zeitabstand zwischen zwei zuvor aufgetretenen Nadelimpulsen wird ein Alarmsignal erzeugt. Mit anderen Worten - es wird überwacht, ob ein aktueller Zeitabstand nicht wesentlich größer oder kleiner ist, als einer (oder mehrere) der vorigen Zeitabstände. Die zeitliche Abweichung der Zeitabstände voneinander darf somit ein gewisses Grenzmaß nicht übersteigen. Zur Festlegung des Grenzmaßes können zwei Grenzfaktoren p_o und p_u festgelegt werden, die beispielsweise bei 1,2 bzw. 0,8 (d.h. 120% und 80%) liegen. Damit können Geschwindigkeitsschwankungen der Strickmaschine toleriert werden. Wird eine Strickmaschine beispielsweise langsam hochgefahren, ändern sich die Zeitabstände zwischen den Signalimpulsen, indem sie immer kleiner werden. Die Abnahme der Zeitabstände von Signalimpuls zu Signalimpuls ist jedoch relativ überschaubar und übersteigt meist das Maß von, z.B. 20% nicht. Bricht jedoch eine Nadel oder verbiegt sie sich stark, tritt bei jeder Drehzahl eine große Abweichung zwischen dem entsprechenden von der verbogenen Nadel hervorgerufenen Zeitabstand und dem vorigen Zeitabstand auf. Dies kann zur Generierung eines Alarmsignals genutzt werden. Bricht eine Nadel, wird erst durch die darauf folgende Nadel wieder ein Signalimpuls erzeugt. Durch den Ausfall eines Impulses ist somit ein Zeitabstand verdoppelt, was klar oberhalb der oben genannten, z.B. auf 20% Zeitabweichung festgelegten Grenze liegt.

This object is achieved by the method according to claim 1:

• In the method according to the invention, individual signal pulses are generated by optical monitoring whenever a needle or a hook moves through the field of view of the optical sensor. The time intervals between the individual successive signal pulses are registered. If the time interval between two current signal pulses is substantially greater or substantially less than the time interval between two previously occurring needle pulses, an alarm signal is generated. In other words, it is monitored whether a current time interval is not substantially greater or less than one (or more) of the previous time intervals. The temporal deviation of the time intervals from each other must therefore not exceed a certain limit. To fix the limit, two limit factors p _o and p _{u can be} defined, which are for example 1.2 and 0.8 (ie 120% and 80%). Thus, speed variations of the knitting machine can be tolerated. For example, when a knitting machine is started up slowly, the intervals between the signal pulses change as they become smaller and smaller. The decrease in the time intervals from signal pulse to signal pulse, however, is relatively manageable and usually does not exceed the level of, for example, 20%. However, if a needle breaks or bends strongly, a large deviation occurs at each rotational speed between the corresponding time interval caused by the bent needle and the previous interval. This can be used to generate an alarm signal. If a needle breaks, a signal pulse is generated only by the following needle. By the failure of a pulse is thus a time interval doubled, which is clearly above the above limit, for example, set to 20% time deviation limit.

Bent or broken needles are thus reliably detectable regardless of the insensitivity of the method according to the invention against fluctuations in speed. Furthermore, a failed needle is immediately detectable. There is no need to wait for a machine cycle.

The mentioned limit factors can be determined depending on the operating state of the knitting machine. For example, they can be changed when starting the machine by increasing the upper limit factor and decreasing the lower limit factor. This increases the permissible tolerance for the time intervals. In stationary operation, the differences between the two limiting factors can be reduced, which narrows the tolerance interval. This allows bent needles to be detected at a very early stage of their deformation and wear.

The cutoff factors can be set symmetrically (e.g., 0.8 and 1.2, which equals ± 20%) or also asymmetrically (e.g., 0.9 and 1.3, which equals -10% and + 30%, respectively).

It is further appropriate to register the number of signal pulses occurring per machine revolution, for example, to count. The number can be compared with a predetermined target number. If a deviation occurs, an alarm signal can be generated. It is also possible to generate the alarm signal only if the deviation persists over several machine revolutions.

Advantageously, the desired number is determined in a test run. It is neither necessary nor appropriate to register the signal pattern generated by the needles. The signal pattern may vary from cycle to cycle as a result of needle vibrations and as a result of the thread moving from the needles. However, it may not be the number of detected needles, i. the number of detected signal pulses varies, which is reliably monitored by the present method.

Further, in knitting machines which desirably have gaps in their needle sequence, it is convenient to register the number (i.e., the index) of the signal pulse thereby dropped. For this pulse of the signal sequence, the generation of an alarm signal is suppressed. In a sense, the alarm signal generator for this pulse is arbitrarily temporarily disabled.

It is expedient to detect not only the number of signal pulses detected per revolution but possibly also their amplitude. It can be displayed when needed. In this case, the amplitude for each pulse can be displayed individually, which is useful information for the setter when setting up the machine when the knitting cylinder turns very slowly. It is also possible to display only the highest and / or the lowest peak amplitude value of the signal pulses in a high-speed machine. Furthermore, it is possible to display a mean signal amplitude to signal to the operator whether the monitoring device is correctly positioned.

Due to the continuous amplitude detection, it is possible to set the switching thresholds for the signal conversion from the analog signal dynamically adapt to the digital signal. For example, an optionally weighted average of the average amplitude value of one or more preceding signal pulses can be used to form an average value to be expected for the next signal pulse. The lower trigger threshold for signal shaping can be determined by subtracting a fixed amount from this expected mean value. The upper trigger threshold for signal shaping can be determined by adding a fixed amount to the expected average.

The corresponding advantages apply to the device according to claim 14 for implementing the method.

Figur 1

ist eine Gruppe Nadeln einer Strickmaschine mit einer zugehörigen Überwachungseinrichtung aufs Äußerste schematisiert, veranschaulicht,

Figur 2

veranschaulicht eine Folge von Nadeln sowie die von ihnen abgeleiteten Impulse,

Figur 3

eine Folge von Nadeln mit einer gebrochenen Nadel sowie die daraus abgeleiteten Impulse,

Figur 4

eine Folge von Nadeln mit fehlenden Nadeln und die daraus abgeleiteten Impulse und

Figur 5

eine Folge von Nadeln und die von ihnen erzeugten Analogsignale.

In the drawing, an embodiment of the method according to the invention is illustrated. The description is limited to the explanation of essential aspects of the invention and other circumstances. Smaller modifications are possible. Not described details, the expert can be found in the usual way of the drawing, which complements the description of the figures. Show: In

FIG. 1

is a group of needles of a knitting machine with an associated monitoring device extremely schematized,

FIG. 2

illustrates a sequence of needles and the pulses derived from them,

FIG. 3

a sequence of needles with a broken needle and the pulses derived from it,

FIG. 4

a series of needles with missing needles and the derived impulses and

FIG. 5

a series of needles and the analog signals they produce.

In FIG. 1 is schematized to the extreme schematized a knitting machine 1 in the form of a circular knitting machine with needles 2 on a needle cylinder 3. The needles 2 is associated with an optical monitoring device 4, to which an optical head 5 and an evaluation device 6 belong. The head 5 is connected, for example via an optical fiber 6 to a light source 7 to send a light beam to the passing needles or their hooks or heads. The light beam can be light with a particular frequency, the light receiver is then set to this frequency, to avoid stray light interference. It is also possible to use pulsed and / or modulated light to avoid external light interference. Only the received light, which corresponds to the transmitted light, is then evaluated.

By using optical fibers and a head 5 having a front outer diameter of, for example, only 1 to 2 mm, it is possible to position the sensor in inaccessible places of the knitting machine. For example, it is possible to provide a sensor head in which the two optical fibers together have a diameter of only about 0.5 mm. This makes the monitored area very small. Even with very small needles, this ensures that only a single needle head is monitored.

Preferably, the sensor heads are brought very close to the needle heads. The distance is for example only 0.2 to 0.5 mm. This gives a high received signal strength.

In jacquard knitting machines, in which individual needles are optionally not fully extended, it is possible provide two sensors per needle. While the needle, when fully expelled, is detected by both sensors, if it is not completely expelled, the needle is only detected by the second slightly deeper sensor. This opens up the possibility of further evaluations of the function of the knitting machine.

In order to increase the reliability of the needle monitoring, it is possible, at the knitting machine another sensor at a distance of e.g. to provide ten needles on the circumference of the knitting machine. Other sensors may be provided at further intervals. Are e.g. If two sensors are provided, past which the needles pass in succession, it can be provided that the machine only stops if both sensors transmit the same error message one after the other.

• In Figur 2 ist eine Folge intakter Nadeln 2 veranschaulicht. Diese erzeugen an dem Kopf 5 ein Analogsignal AS, das beispielsweise aus der von dem Kopf 5 aufgenommenen Lichtintensität abgeleitet werden kann. Jeder Lichtreflex der Nadeln 2 erzeugt dann eine entsprechende Signalspitze. Diese wird durch einen Signalformer zu den weiter unten veranschaulichten Signalimpulsen S₁ bis S_n umgeformt. Die Zeitabstände T₁ bis T_n zwischen den einzelnen Signalimpulsen S₁ bis S_n sind, wenn der Strickzylinder 3 mit gleichmäßiger Drehzahl dreht und die Nadeln 2 vollkommen in Takt sind, untereinander vollständig gleich. Das Auswertegerät überwacht nun die Zeitabstände T₁ bis T_n fortwährend. Es qualifiziert einen empfangenen Signalimpuls S_i dann als einen gültigen Folgeimpuls S_i für einen vorangegangenen Signalimpuls S_i-1, wenn der Zeitabstand T_i im Wesentlichen so groß ist, wie der Zeitabstand T_i-1. Dies ist dann der Fall, wenn gilt: $${\mathrm{p}}_{\mathrm{u}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{<}{\mathrm{T}}_{\mathrm{i}}\mathrm{<}{\mathrm{p}}_{\mathrm{o}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{i}\mathrm{-}\mathrm{1}}$$
  
  
  wobei p_o und p_u einen unteren Grenzfaktor für eine untere Zeitdauerabweichung darstellt. Beispielsweise kann p_u 0,8 betragen. p_o kann 1,2 betragen. Damit gilt, dass der Zeitabstand T_i wenigstens 80% des Zeitabstands T_i-1 und höchstens 120% des Zeitabstands T_i-1 betragen kann.

The evaluation device 6 is connected via an optical fiber 9 to the head 5. The evaluation device 6 contains one or more displays 10 and one or more input means, for example in the form of a keypad 11. It also contains electronic processing means not further illustrated, for example in the form of hardware and software, one or more processors, signal formers and the like. as the person skilled in the art can provide to implement the functions described below:

• In FIG. 2 is a sequence of intact needles 2 illustrated. These generate at the head 5 an analog signal AS which can be derived, for example, from the light intensity received by the head 5. Each light reflection of the needles 2 then generates a corresponding signal tip. This is converted by a signal shaper to the signal pulses S ₁ to S _n illustrated below. The Time intervals T ₁ to T _n between the individual signal pulses S ₁ to S _n , when the knitting cylinder 3 rotates at a uniform speed and the needles 2 are perfectly in tact, completely identical to each other. The evaluation device now monitors the time intervals T ₁ to T _n continuously. It qualifies a received signal pulse S _{I is} then as a valid pulse sequence S _i for a preceding pulse signal S _i-1, when the time interval T _i is substantially as large as the time interval T _{i -1.} This is the case when: $${\mathrm{p}}_{\mathrm{u}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{<}{\mathrm{T}}_{\mathrm{i}}\mathrm{<}{\mathrm{p}}_{\mathrm{O}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{i}\mathrm{-}\mathrm{1}}$$
  
  
  where p _o and p _{u represents} a lower limit factor for a lower duration deviation. For example, p _u can be 0.8. p _o can be 1.2. Thus, the time interval T _{i can be} at least 80% of the time interval T _i-1 and at most 120% of the time interval T _i-1 .

If the above test is positive, ie every T _{i is} in the interval from 80% to 120% of T _i-1 , the signal pulse S _i qualifies as a valid signal pulse and no alarm signal is generated. This pulse is counted, for example.

However, if the signal pulse S _i lies outside the specified time interval, ie deviates by more than 20% from the previous time interval T _i-1 , it is not qualified as a valid signal pulse. Thus there is no valid pulse in the expected interval and an alarm signal is generated. A broken needle or a badly bent needle is thus detected immediately on her first pass in front of the head 5. To improve the reliability of the error detection, corresponding error signals can be derived from a plurality of sensors which are arranged at different points of the circumference of the knitting machine, wherein a valid error signal is only generated if all sensors for the same needle position generate an error signal.

If only a single sensor is used for monitoring, it can be provided that an alarm signal is only generated when the signal pulse that is outside the time window or repeats itself at the same position or needle position during the following machine revolution.

It should be noted that, instead of the time interval T _i-1 used for the comparison, it is also possible to use a different reference time value, which is calculated, for example, from a plurality of preceding time intervals. The calculation can be carried out, for example, by calculating an arithmetic mean, a weighted mean or another comparison value.

On the other hand, slow speed variations of the rotational speed of the knitting cylinder 3 can not lead to the generation of an alarm signal. The alarm signal can be displayed on the display 10 of the evaluation device 6. It is also possible to relay this alarm signal. For example, network connections can serve this purpose. It can also be passed to the knitting machine 1 to shut down this.

It will open FIG. 3 directed. This illustrates a needle sequence 2 'in which a needle 2a is partially damaged, eg broken off. The corresponding analog signal AS falls below an upper threshold in this case. A corresponding digital signal pulse is not generated. In FIG. 3 below, the correspondingly large gap between the signal pulses generated by the adjacent needles 2b, 2c is visible. Accordingly, the time interval T _{5 is} twice as large as the time interval T ₄ . This large deviation is no longer tolerated. The limit p _o is exceeded and an alarm signal is generated.

Beyond the monitoring of the individual pulses, it is possible to provide a counter in the evaluation unit 6, which counts the generated signal pulses S ₁ to S _n . The count can be redetermined for each revolution of the knitting cylinder 3. For this purpose, the evaluation device 6 may have a sensor, which is not further illustrated, or may be connected to such a sensor, which in each case delivers a pulse at each rotation of the needle cylinder 3 at a defined point. This can be one pulse per revolution or even several pulses per revolution of the knitting cylinder. If the number of pulses counted per revolution deviates from a desired number Z, an alarm signal can be generated. This can in turn be displayed on a display of the evaluation device 6 or forwarded for further processing in a network wired or wireless.

The desired number Z can be entered by the operator, for example via the keypad 11. However, it is also possible to start a learning mode of the evaluation device 6 via the keypad 11, in which the evaluation device 6 the Number of needles automatically detected. This can happen, for example, in a test run over one or more revolutions. The number of needles detected in the test run with an intact machine is then stored as a setpoint Z.

In some knitting machines, the needle cylinder 3 is not completely populated with needles or there are intentionally larger gaps between individual needles. In this case, the evaluation device 6 may be modified so that it interrupts the needle monitoring at the predetermined selected location. An illustration of the appropriate procedure is in FIG. 4 given. The sequence of needles 2 has two gaps L ₁ , L ₂ . In FIG. 4, the needles and the associated analog signals AS, as well as the signal pulses S, are designated merely by their index positions 1, 2, 3, etc. As can be seen, the needles are missing at the index positions 3 and 6. Accordingly, no signal pulses S are present at the index positions 3 and 6. The failure of these pulses would be in accordance with the FIG. 2 given description for the generation of alarm signals. However, this is avoided in an extended embodiment. The index positions at which no needles 2 are present, in the present embodiment, the index positions 3 and 6, are either entered via the keypad 11 in the evaluation device 6 or registered in the test run. The corresponding time interval extending from the signal pulse S ₂ to the signal pulse S ₄ is thus excluded from the test described above. The same applies to the time interval preceding the signal pulse S ₇ .

The evaluator described so far has several advantages. For one, it is insensitive to speed fluctuations of the knitting machine. On the other hand, it is largely insensitive to influences of the thread and needle vibrations. Furthermore, bent or broken needles can be reliably detected. It is not necessary to store an entire needle pattern. Irregular needle sequences can be monitored by pre-storing the positions of missing needles. This comes with very little storage space. Here, the fact is exploited that needles can be present on the knitting cylinder only according to the predetermined pitch. It is therefore sufficient to store the index position of non-existent needles in order to suppress generation of the alarm signal at this point.

In a further advantageous embodiment of the method, the amplitude of the signals generated by the sensor is monitored. This is based on FIG. 5 illustrated. The signal thresholds T1, Tb used for triggering these analog signals are calculated from the signal thresholds and signal average values Tm of preceding pulses. In this way, trends in long-wave signal amplitude fluctuations can be detected and rendered harmless. For example, the lower trigger limits Tl can be approximated by the two mean signal values Tm of the preceding pulses. This can be done by averaging, for example. For example, the averages of several previous pulses can be added by weight and divided by a factor. The lower trigger threshold for shaping the next pulse can be determined by subtracting a fixed amount from this expected average. The upper trigger threshold for signal shaping This next pulse can be determined by adding a fixed amount to the expected average. This results in a hysteresis method. The switching thresholds T1 and Th are thus set dynamically as a function of the signal amplitude of the preceding pulses. In a circulation of the knitting cylinder regularly occurring fluctuations of the signal amplitudes are thus made ineffective as a disturbance factor.

The inventive method for monitoring needles of a knitting machine is based on a dynamic definition of the monitored time intervals between individual needle pulses. The duration of at least one or more preceding periods between individual signal pulses is taken as a measure of the time interval currently to be evaluated. Likewise, a dynamic determination of the switching thresholds for generating the signal pulses can be made. Again, the amplitude of preceding pulses is analyzed, a trend is determined, and the switching thresholds for generating the current signal pulse are determined from this trend. This method can be used to evaluate the pulses generated at all needle positions. If the needle cylinder is intentionally only partially loaded, individual needle positions can be indexed accordingly and excluded from the evaluation. This provides a reliable robust and reliable monitoring method.

LIST OF REFERENCE NUMBERS

1

knitting machine

2

Needles, 2a, 2b, 2c

3

knitting cylinder

4

monitoring device

5

head

6

evaluation

7

optical fiber

8th

light source

9

optical fiber

10

display

11

keypad

Claims (14)

1. Method for monitoring needles on knitting machines, wherein a relative speed exists between the needles and an optical sensor and the needles move through the viewing field of the sensor, characterised in that
   in the method at least in some needles:

   a signal pulse (S₁, S₂, S₃, ... , S_n) is generated by means of the sensor every time a needle moves through its viewing field,

   the time interval (T₁, T₂, T₃, ... , T_n) between successive signal pulses (S₁, S₂, S₃, ... , S_n) is determined and a signal pulse (S_i) is only recorded as valid sequence pulse (S_i) of the preceding signal pulse (S_i-1) when the time interval (T_i) is less than the product (p_o·T_i-1) of an upper limit factor (p_o) and a reference time interval (T_i-1) and also greater than the product (p_u·T_i-1) of a lower limit factor (p_u) and the reference time interval (T_i-1).
2. Method according to claim 1, characterised in that the reference time interval is an earlier time interval (T_i-1).
3. Method according to claim 1, characterised in that the reference time interval is a reference value calculated from one or more earlier time intervals (T_¡-1 ... T_i-n).
4. Method according to claim 1, characterised in that the amplitude (A₁, A₂, A₃, ... , An) of the individual signal pulses (S₁, S₂, S₃, ... , S_n) is recorded.
5. Method according to claim 1, characterised in that variable trigger thresholds determined from the amplitudes (A₁, A₂, A₃, ... , A_n) are used to generate the signal pulses.
6. Method according to claim 1, characterised in that an alarm signal is generated when a signal pulse (S_i) lies outside a time window (ΔT₁ = p_u·T_¡-1 - p_o·T_i-1).
7. Method according to claim 1, characterised in that the number of signal pulses (S₁, S₂, S₃, ... , S_n) recorded per stroke or revolution of the knitting machine is compared with a desired value (Z) and an alarm signal is generated if a deviation occurs.
8. Method according to claim 7, characterised in that the desired number (Z) is determined in a test run.
9. Method according to claim 1, characterised in that empty positions where no needles are provided are determined in a test run.
10. Method according to claim 9 and 6, characterised in that the generation of an alarm signal is suppressed if the signal pulse is absent at an empty position and therefore does not occur within the time window (ΔT_i = p_u·T_i-1 - p_o·T_i-1).
11. Method according to claim 1, characterised in that execution of the method is interrupted during start-up of a knitting machine.
12. Method according to claim 1, characterised in that the number of signal pulses (S₁, S₂, S₃, ... , S_n) detected per revolution or stroke is represented on a display.
13. Method according to claim 1, characterised in that the amplitude (A₁, A₂, A₃, ... , A_n) of the respectively detected signal pulses (S₁, S₂, S₃, ... , S_n) is represented on a display.
14. Device for monitoring needles on knitting machines, wherein a relative speed exists between the needles and an optical sensor and the needles move through the viewing field of the sensor, characterised in that
    in the method at least in some needles:

    a signal pulse (S_1, S₂, S₃, ... , S_n) is generated by means of the sensor every time a needle moves through its viewing field,

    the time interval (T₁, T₂, T₃, ... , T_n) between successive signal pulses (S₁, S₂, S₃, ... , S_n) is determined and a signal pulse (S_i) is only recorded as valid sequence pulse (S_i) when the time interval (T_i) is less than the product (p_o·T_i-1) of an upper limit factor (p_o) and an earlier time interval (T_i-1) and also greater than the product (p_u·T_i-1) of a lower limit factor (p_u) and an earlier time interval (T_i-1).

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