WO1993021368A1

WO1993021368A1 - Moving profile detector, particularly for detecting damaged knitting machine needles

Info

Publication number: WO1993021368A1
Application number: PCT/IT1992/000038
Authority: WO
Inventors: Bruno Pirone
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-08
Filing date: 1992-04-08
Publication date: 1993-10-28
Anticipated expiration: 1994-10-08

Abstract

A moving profile detector, particularly for detecting damaged knitting machine needles, whereby an electrode (10), mounted in a fixed position facing the path of the needles (3) on a rotary drum, is so biased and sized as to produce a sequence of electric discharges, the frequency and amplitude of which are proportional to the distance between the needle (3) and the electrode (10). The electric discharges are picked up by a sensor connected to the electrode (10) and designed to emit an electric discharge signal, which is supplied to and processed by a damaged needle detecting unit, for emitting an alarm output signal whenever, on account of a broken or damaged needle, no discharges are produced between the electrode and the needle, or the frequency or amplitude of the discharge differs from predetermined reference values.

Description

MOVING PROFILE DETECTOR, PARTICULARLY FOR DETECTING DAMAGED KNITTING MACHINE NEEDLES

TECHNICAL FIELD The present invention relates to a moving profile detector, particularly for detecting damaged knitting machine needles.

BACKGROUND ART

Knitting machines comprise a fixed or movable drum supporting one or more numbers of needles, which move longitudinally for forming the stitches. The needles present a hooked end by which the yarn is hooked up and threaded through a previous stitch to form a new one; and a tongue hinged to the body of the needle and pivoting between two positions for correctly forming the stitch.

Breakage or damage to the hooked end or tongue therefore results in "dropped stitches", which must be detected immediately so as to stop the machine and change the needle with as little damage as possible to the work. For this purpose, various types of devices have been designed comprising a sensor next to the drum, and which either provide for detecting displacement of the sensor caused directly or indirectly by the passage of a damaged needle, or employ reflecting optical systems designed to produce a light beam. Neither of the above solutions, however, has proved entirely satisfactory, in that they are unreliable (optical systems in particular, despite complex compensating systems, are sensitive to ambient lighting conditions, which vary according to the weather or the time of day); must be set accurately to conform with varying operating conditions; fail to provide for rapid detection; remain ineffective for some time when the machine is started up again; and, being of complex design, are highly susceptible to breakdowns and expensive to produce.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a moving profile detector, particularly for detecting damaged circular or straight knitting machine needles, designed to supply a profile signal for immediately sounding an alarm and possibly also arresting the machine upon detection of a broken or damaged needle. According to the present invention, there is provided a moving profile detector, particularly for detecting damaged knitting machine needles, characterized by the fact that it comprises an electrode fitted facing and in a position of relative motion in relation to a surface, said electrode being biased to a high voltage in relation to said surface, so as to produce a series of electric discharges the frequency and amplitude of which are proportional to the distance between the electrode and said surface; and a sensor, connected to said electrode, for emitting an electric signal relative to said discharges.

BRIEF DESCRIPTION OF DRAWINGS A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Fig.l shows a schematic top plan view of a circular knitting machine; Fig.2 shows a side view of a needle being checked for damage to the hooked end;

Fig.s 3 to 5 show schematic top views of whole and broken needles during checking;

Fig.6 shows a circuit diagram of the device according to the present invention;

Fig.s 7a to 71 show time graphs of signals picked up at various points in the Fig.6 circuit;

Fig.8 shows an enlarged cross section of a detail on the device according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

In the accompanying drawings, the detector according to the present invention is illustrated as applied to a circular knitting machine 1 comprising a rotary drum 2 (Fig.l) fitted with a number of known equally-spaced peripheral needles indicated schematically by 3. As shown in Fig.2, each needle 3 presents an elongated body 4 (shown partially) having a hooked end or hook 5 and a tongue 6 pivoting on body 4 at 7, and is grounded as shown schematically at 8. During operation, one or more needles 3 may break or bend, breakage usually consisting in the hook 5 breaking off roughly at the point shown by the dot and dash line 9 in Fig.2, and bending normally consisting in the needle bending inwards or outwards of drum 2. Bending normally occurs between hinge point 7 and hook 5, as shown by way of example in Fig.2a, wherein the continuous and dotted lines show the needle bent towards and outwards of drum 2 (not shown) respectively. In the following description, therefore, the term "damaged" is intended to mean either a broken or bent needle.

As shown in the accompanying drawings, any damaged needles 3 are detected by providing an electrode 10 facing and in a position of relative motion in relation to needles 3, so as to detect the passage of one needle at a time, and by biasing the electrode to such a voltage as to produce a series of electric discharges between itself and needles 3 as these move past the electrode. The electric discharges are produced continuously one after the other, and present a roughly constant frequency and amplitude (power) when needles 3 moving past the electrode are undamaged. In the event of a damaged needle, however, the electric discharges, which in this case may even be absent, present a different frequency and/or amplitude. Any broken or bent needles may therefore be detected by detecting a variation in the discharges, thus enabling the machine to be stopped immediately.

In the example shown, electrode 10 (made of or at least covered with conductive ceramic or ferrite) is fitted to machine 1 on a level with hook 5 in a given operating position. (As shown in Fig.2, electrode 10 is preferably fitted facing needle 3 in the idle position, i.e. before or after forming the stitch, and with tongue 6 in the open position) .

Electrode 10 is so biased, designed and sized, and located at such a distance from hook 5 of needle 3 moving past it on drum 2 as to produce a number of discharges between itself and hook 5 for each undamaged needle 3.

More specifically, as shown in Fig.s 3 to 5, electrode 10 presents a flat front surface 96 blending continuously (at 97) with lateral surfaces 98, the width of front surface 96 being roughly equal to the distance a between adjacent needles 3.

Fig.3 shows a needle 3 with an undamaged hook 5 moving past electrode 10. In this case, the distance b between electrode 10 and needle 3 is minimum, and a series of electric discharges are produced, as shown schematically, between the electrode and the needle. Fig.4 shows two adjacent needles 3 and 3* moving respectively away from and towards electrode 10. As shown schematically, when both needles are undamaged, the maximum distance b., between electrode 10 and the nearest needle (which is maximum when the outgoing and incoming needles 3 and 3' are at the same distance from the electrode) is still sufficient to produce a discharge. Consequently, when all the needles 3 on drum 2 are undamaged, a.continuous, substantially regular sequence of discharges will be produced, visible externally in the form of a continuous spark.

Fig.5 shows a hookless needle 3" moving past electrode 10, in which case distance b, between the broken needle 3" and electrode 10, and distance b₃ between the electrode and the incoming (or outgoing) undamaged needle 3 are both too great to produce a discharge.

Similarly, in the case of a needle 3 bent inwards of the drum (as shown by the continuous line in Fig.2a) the distance between hook 5 and electrode 10 is again too great to produce a discharge; while hook 5 of a needle bent outwards of the drum passes so close to electrode 10 as to produce a lower-voltage, i.e. weaker, discharge as compared with that of an undamaged needle, and which may thus be detected.

The sequence, temporary absence or reduced power of the discharges (the latter two respectively indicating a broken or bent needle) are detected by an electric circuit 13 (Fig.6), which also provides for discriminating between broken/bent needles and any deliberately skipped, as frequently occurs, for producing a vertical cutting line in the work. If this were not so, the absence of a discharge corresponding to the skipped needle/s would result in the machine being stopped at each turn of the drum.

As shown in Fig.6, therefore, electrode 10 is connected by two resistors 11, 12 to electric circuit 13, which provides for indicating any irregularity in the discharges, cutting off supply to the motor of machine 1, and supplying the high voltage required for operating electrode 10. Circuit 13 is preferably mounted on a board at the top of machine 1, close to the yarn feed devices (not shown), and presents a connector (not shown in detail) at 17 from which extends a shielded cable 14 to electrode 10, as shown in detail with reference to Fig.8. The output of circuit 13 is connected by lead 16 to drive device 15 for powering the machine motor.

More specifically, circuit 13 comprises a known high negative direct voltage source 20 having a grounded terminal 21 (defining a first reference potential line), an output 22 for the high negative voltage to the electrode, and a potentiometer 23 adjustable manually for varying the output voltage, for example, between -3000V and -6000V. A powerful resistor 19 is provided between output 22 of source 20 and point 17, to safeguard the operator in the event of accidentally touching point 17.

Point 18 between resistors 11 and 12 (respectively 10 and 100 MΩ for producing rapid discharges alternating with longer charge periods) presents stray capacitances shown schematically by a condenser 24. Point 18 is also connected to a condenser 25, e.g. 5pF, the other terminal of which is connected to a grounded resistor 27 via a shielded wire 26 to the circuit 13 board; condenser 25 and resistor 27 constituting a discharge sensor for generating an electric signal indicating the presence or absence of electrical discharges.

The physical construction of this part of the circuit is shown in Fig.8, which shows wire 14 inside a shield 90; resistors 11 and 12 inside a shield 91 (e.g. of metal) to prevent interference; electrode 10 supported on a supporting body 92 (e.g. an elastic fork) for troublefree removal and replacement; and condenser 25 connected by one terminal to point 18 and by the other to wire 26, which, also enclosed in a shield 94, is fitted through a hole 93 in shield 91 and extends parallel to wire 14 as far as circuit 13.

As shown in Fig.6, point 28 between condenser 25 and resistor 27 is connected to the inverting input of two operational amplifiers 29 and 30 via respective resistors 31 and 32.

The non-inverting input of amplifier 29 is grounded via resistor 33, and its output is fed back to its inverting input via resistor 34. The output of amplifier 29 is connected to one terminal of a condenser 35, the other terminal of which is connected to the cathode of a diode 36, the anode of which is grounded. The cathode of diode 36 is also connected to the anode of a further diode 37, the cathode of which is connected to a terminal of a condenser 38 and resistor 39 constituting an RC filter. The cathode of diode 37 is also connected, via resistor 40, to the non-inverting input of an operational amplifier 41, the inverting input of which is connected to the cursor of a potentiometer 42 between a positive supply (+), defining a second reference potential line, and ground. The output of amplifier 41, which is fed back to its inverting input via resistor 43, is connected to the input of a storage element or FLIP-FLOP 44, and, via resistor 45 and Zener diode 46,.to the base terminal of an NPN transistor 47, the emitter terminal of which is grounded, and the collector terminal of which is connected to supply (+) via resistor 48. The collector of transistor 47 is also connected to the anode of a first LED 49 and to the cathode of a second LED 50 connected antiparallel between the collector of transistor 47 and the mid point between two resistors 51 and 52 series connected between supply (+) and ground.

Amplifier 30 also presents its non-inverting input grounded via resistor 55, and its output connected to one terminal of resistor 56. The other terminal of resistor 56 is connected to a first terminal of condenser 57, the other terminal of which is grounded, and which combines with resistor 56 to define a low-pass filter. The mid point between resistor 56 and condenser 57 is connected to one terminal of a potentiometer 58, the other terminal of which is grounded, and the cursor of which is connected to the non-inverting input of an operational amplifier 59. The inverting input of amplifier 59 is connected to a reference voltage at the mid point of a pair of resistors 60 and 61 series connected between supply (+) and ground. The output of amplifier 59 is connected to one input of a NAND circuit 62 and, via a condenser 63, to one input of a timing element 64 consisting, for example, of integrated circuit 555, and grounded and connected to the supply in known manner. The output of timer 64 is connected via resistor 65 to a further input of NAND circuit 62, which input is also connected to supply (+) via switch 66 and grounded via condenser 67. The output of circuit 62 is connected to a further input of storage element 44.

More specifically, storage element 44 comprises two cross-connected NAND circuits 70 and 71. That is, the inputs of circuit 70 are connected respectively to the outputs of amplifier 41, circuit 62 and circuit 71; while circuit 71 presents a first input connected to the output of circuit 70, and a second input grounded via a hand-operated switch 72 and connected to supply (+) via resistor 73. The output of circuit 70 is connected to - li ¬

the cathode of a LED 74, the anode of which is connected via resistor 75 to supply (+). Via resistor 76, the output of circuit 71 drives the base of an NPN transistor 77, the emitter of which is grounded, and the collector of which is connected to supply (+) via a . relay 78 having a parallel safety diode 79. Relay 78 comprises a grounded moving contact 80 normally connected to a fixed contact 81 in turn connected, via a parallel lamp 82 and resistor 83, to lead 16 connected to drive device 15 for disabling the motor of machine 1. Operation of the detector according to the present invention will be described with reference to Fig.s 7a-71.

At the end of the discharge, voltage s_ at point 18 is zero, so that needle 3 is disconnected electrically. Stray capacitance 24 and condenser 25 therefore begin charging via resistors 12 and 22 with a relatively high time constant, so that voltage s- decreases exponentially to roughly the voltage of source 20 (3000V in Fig.7a). During this period, the small charge current of condenser 25 flows through resistor 27, so that a low negative voltage (signal s_ in Fig.7b) is detectable at point 28. At the end of this period (T_), which depends on the high voltage supplied by source 20 and the distance between electrode 10 and needle 3, an electric discharge is produced electrically connecting electrode 10 and needle 3. In this phase, condensers 24 and 25 discharge via resistor 11 in time ₂ (which, due to the much smaller value of resistor 11 as compared with resistors 12 and 22, is much shorter than T-); the voltage at point 18 increases rapidly to zero; and resistor 27 is supplied with a current pulse to produce the voltage pulse shown in Fig.7b.

As already stated, the parameters of the detector according to the present invention (the distance between electrode 10 and needles 3; and the values of stray capacitances 24, condenser 25 and resistors 11 and 12) are so selected as to produce a number of discharges in the time (T₃ in Fig.7c) taken by each needle to move past electrode 10. For example, if drum 2 on the machine rotates at a speed of l turn/sec and is fitted with 5000 needles (so that the needles move past electrode 10 at a frequency of 5 kilocycles), the above parameters are so selected as to produce discharges at a frequency of a few tens of a kilocycle. Signal.s, therefore presents an uninterrupted sequence of pulses, as shown to a smaller time scale to the left in Fig.7c, until a broken or back-bent needle 3 moves past electrode 10. In this case, the distance between needle 3 and electrode 10 is such as to prevent the discharge from being produced; condensers 24 and 25 remain charged; the voltage at point 18 remains the same as the output voltage of source 20; and no current flows in resistor 27. Consequently, throughout the time (T₄ in Fig.7c) taken by the broken or bent needle to move past electrode 10, signal s» is zero. Signal s~ is sent to the inverting input of amplifier 29 by which it is inverted and amplified; is rectified and filtered by components 36-39 to obtain the mean value; and then supplied to amplifier 41 by which it is compared with a threshold value regulated by means of potentiometer 42. More specifically, the threshold value is so regulated as to be lower than the mean value at the non-inverting input of amplifier 41, during normal operation of the machine (with no damaged needles). In this case, the output of amplifier 41 is high; Zener diode 46 and transistor 47 are on; the collector of transistor 47 is low; and LED 50 (e.g. green) is on to show the circuit is operating properly. Conversely, if the distance of electrode 10 is badly adjusted, or the voltage supplied by source 20 is too low, the signal at the non-inverting input of amplifier 41 is lower than the threshold value at the inverting input; Zener diode 46 and transistor 47 are disabled; the collector of transistor 47 is high; and LED 49 (e.g. red) is on. The correct signal values may thus be obtained by regulating the high voltage by means of potentiometer 23 and adjusting the distance of electrode 10.

Signal s_ is also supplied to amplifier 30 by which it is inverted and amplified. More specifically, for normal signals, amplifier 30 is regulated so as to saturate and produce a constant amplitude signal s, (Fig.7d) which oscillates as long as the needles moving past the electrode are undamaged, but which maintains a constant maximum level in the event of a broken or bent-back needle.

Signal s_ is filtered by filter 56, 57 to produce signal s, (Fig.7e) which presents a low mean value if the needles moving past the electrode are undamaged, and a higher value in the event of a broken needle. Signal s., appropriately divided by potentiometer 58, is clipped by amplifier 59 and compared with a predetermined threshold to produce output signal s₅, which presents a low logic level for undamaged needles, and a high logic level for a broken one.

Signal s- is supplied to the input of NAND circuit 62 as well as to timer 64 which, on arrival of the trailing edge of the pulse generated by amplifier 59 (with a small delay due to components 65 and 67), supplies a high output signal s._g, as shown in Fig.s 7h and 7k, which show two cases in which a broken (or bent-back) needle is located a different distance from a missing needle. In both cases, detection of the missing needle on the drum is assumed to produce, at t., a pulse having a trailing edge at t. (Fig.s 7g and 7j). After a very short time interval (not shown) , timer 64 therefore supplies a high output signal, the duration of which is so selected as to be longer than half but shorter than a whole rotation period T₅ of drum 2. Output signal s_g of timer 64 therefore terminates at t„. In the interval t_Q-t₁ in which signal s_ presents a high pulse, the output of timer 64 is low, so that the output of circuit 62 is high. Moreover, if no damaged needles are detected in the interval t.-t,, as in the two cases shown in Fig.s 7g-71, the output of circuit 62 remains high due to the low output signal s^. Consequently, and thanks also to the high signal supplied under normal operating conditions by amplifier 41, signal s_ at the output of NAND circuit 70 of storage element 44 is low, so that diode 74 is on; the output of circuit 71 is high; transistor 77 is on; relay 78 is energized; moving contact 80 is open; and device 15 driving the motor thus operates normally.

If, as shown in Fig.s 7g-7i, a damaged needle is not even detected towards the end of period T₅, the output of circuit 62 remains high, thus enabling operation of the motor, and the next missing needle pulse (with a trailing edge at t₃) again results in a high signal s_g being produced by timer 64. In the event, however, of a damaged needle switching signal s_ to high at t₄, as shown in Fig.s 7g-7i, the resulting simultaneously high input signals s₅ and s_g of circuit 62 switch the output of circuit 62 to low; storage element 44 is switched; output signal s_? switches to high (Fig.7i), thus turning off LED 74 and switching the output of circuit 71 (supplied with signal s„ and a high signal via resistor 73) to low; transistor 77 is disabled, thus opening relay 78 and switching moving contact 80; and device 15 driving the motor is disabled, thus arresting machine 1.

The same applies when the damaged needle pulse of signal s₅ is received after output signal s_g of timer 64 switches to low, in which case, as shown in Fig.s 7J-71, the trailing edge of signal s_ at t₅ switches the output of timer 64 to high, and, until the next missing needle pulse is received (interval ^"^3) th^e output of circuit 62 remains, high so that the motor is kept running. At t₃, however, as both input signals s₅, s_g of circuit 62 are high, circuit 62 switches to stop the motor as described above.

The above operating principle also applies in the event of a needle bent outwards of drum 2, in which case a lower voltage discharge is produced, the amplitude (power) of signal s, is lower than under normal operating conditions, and the value of signal s₄ is such as to switch amplifier 59 to high.

When the work involves no missing needles, switch 66, when closed, provides for ensuring correct operation of the circuit by forcing signal s_g permanently to high. The pulses in signal s₅, which thus relate solely to damaged needles, therefore provide for switching NAND circuit 62 to low and so stopping the motor. Switch 72 provides for startup and adjusting the parameters of the device, such as the distance of electrode 10 and the output voltage of source 20. When closed, switch 72 grounds one input of circuit 71 (low logic level state) so that the output of circuit 71 remains high and relay 78 energized, regardless of the input signals of circuit 70.

INDUSTRIAL APPLICABILITY The advantages of the detector according to the present invention will be clear from the foregoing description. First of all, it provides for a high degree of reliability by being independent of the operating conditions of the machine, particularly ambient lighting. In the embodiment shown, reliability is further enhanced by basing detection of a broken or damaged needle on the absence or a reduction in the power of several discharges (by determining the mean value of the signal from sensor 25, 27 connected to the electrode), thus eliminating the possibility of errors caused by a random missing discharge or pulse. Furthermore, it provides for minimizing downtime and rejects by detecting any damaged needles in the space of one turn of the drum. The device according to the present invention can be set easily and quickly; is immediately operative following replacement of the needle and startup of the motor; and, by means of switch 66, can easily be adapted to work involving one or more or no missing needles. The device is extremely easy to assemble by simply requiring adjustment of the distance between electrode 10 and needles 3, which, with the assistance of LEDs 49, 50 and 74, involves no particular accuracy. The device is straightforward in design and, with no components directly contacting the needles, is subject to very little wear and therefore cheap to produce. To those skilled in the art it will be clear that changes may be made to the device as described and illustrated herein without, however, departing from the scope of the present invention.

In particular, though the embodiment shown provides for detecting a missing hook 5, the device may be employed, with no alterations required, for detecting breakage of tongue 6, in which case, electrode 10 need simply be mounted facing tongue 6 in a given operating position (e.g. in the open position shown in Fig.2). In addition, the device may also be applied to circular fixed-drum or straight knitting machines, in both of which cases, instead of being fixed as in the example shown, the electrode moves past the needles on a slide or similar conveying system. Finally, circuit 13 may present components other than those described herein, providing it is capable of detecting a variation in discharge frequency and amplitude.

Claims

1) - A moving profile detector, particularly for detecting damaged knitting machine needles, characterized by the fact that it comprises an electrode (10) fitted facing and in a position of relative motion in relation to a surface (3), said electrode (10) being biased to a high voltage in relation to said surface (3) , so as to produce a series of electric discharges the frequency and amplitude of which are proportional to the distance between the electrode (10) and said surface (3); and a sensor (25, 27), connected to said electrode (10), for emitting an electric signal (s₂) relative to said discharges. 2) - A detector as claimed in Claim 1, wherein the surface detected comprises a drum (2) fitted with a number of needles (3); characterized by the f ct that it comprises a damaged needle detecting unit (13) receiving said electric signal (s,) and generating an alarm output signal (s_) on detecting a variation in the frequency and/or amplitude of said electric discharges as compared with predetermined threshold values.

3) - A detector as claimed in claim 2, characterized by the fact that said electrode (10) is so biased and located at such a distance from said needles (3) as to produce a number of discharges between itself and each said needle (3) . 4) - A detector as claimed in Claim 3, characterized by the fact that said electrode (10) is so biased and located at such a distance from said needles (3) as to produce a substantially continuous sequence of electric discharges in the event of undamaged needles moving past the electrode.

5) - A detector as claimed in one of the foregoing Claims from 2 to 4, wherein said needles (3) are connected to a first reference potential line (ground); characterized by the fact that it comprises an adjustable high voltage source (20) connected to said electrode (10) via the interposition of resistive elements (11, 12, 19) and via a first conductor (14) connected capacitively (24) to said first reference potential line.

6) - A detector as claimed in Claim 5, characterized by the fact that said sensor comprises a condenser (25) and a resistor (27) series connected between said first conductor (14) and said reference potential line.

7) - A detector as claimed in Claim 6, characterized by the fact that the mid point (28) between said condenser (25) and said resistor (27) is connected to the input of said detecting unit (13) via a second conductor (26); said first and second conductors (14, 26) being shielded.

8) - A detector as claimed in one of the foregoing Claims from 2 to 7, characterized by the fact that said detecting unit (13) comprises low-pass filter means (56, 57) receiving said electric signal (s₂) generated by said sensor (25, 27) and designed to generate a substantially continuous output signal (s₄) varying in amplitude according to the presence or absence of electric discharges; comparing means (59) receiving said substantially continuous signal (s₄) and a threshold signal, and designed to generate an output pulse (s₅) having a predetermined logic state in the absence of discharges; and storage means (44) for generating an alarm signal (s_) and disabling the knitting machine (1) on receiving said pulse.

9) A detector as claimed in Claim 8, characterized by the fact that inverting and amplifying means (30) are provided upstream from said filter means (56, 57); and said pulse (s₅) is generated by said comparing means (59) upon said substantially continuous signal (s₄) exceeding said threshold signal.

10) - A detector as claimed in Claim 8, characterized by the fact that the output of said comparing means (59) is connected to a first input of a logic circuit (62) and to a timer (64) for generating a logic signal (s_g) delayed in relation to said pulse (s₅) and lasting from half to a whole period (T_) of the relative motion of said electrode (10) and said needles (3); the output of said timer (64) being connected to a second input of said logic circuit (62), the output of which is connected to said storage means (44). 11) - A detector as claimed in Claim 10, characterized by the fact that it comprises means (66) for disabling said timer (64); and control means (72) for forcibly enabling said storage means (44) regardless of the output of said logic circuit (62).

12) - A detector as claimed in Claim 12, characterized by the fact that said disabling means comprise a first switch (66) between said second input of said logic circuit (62) and a second reference potential line (+); and said control means comprise a second switch (72) between said first reference potential line and a switch input of said storage means (44).

13) - A detector as claimed in one of the foregoing Claims from 2 to 12, characterized by the fact that said detecting unit (13) comprises means (29, 31, 33-43, 45-52) for indicating normal operation of the detector; said means comprising inverting and amplifying means (29) input connected to said sensor (25, 27); rectifying and filtering means (35-38) connected to the output of said inverting and amplifying means; comparing means (41) input connected to said rectifying and filtering means and to a reference threshold signal; a switch (47) controlled by said comparing means; and two antiparallel-connected light emitting elements (49, 50) connected to said switch and designed to light up alternately. 14) - A detector as claimed in one of the foregoing Claims, characterized by the fact that said electrode (10) is fixed.

15) - A detector as claimed in one of the foregoing Claims, characterized by the fact that said electrode (10) presents a flat front surface (96) blending continuously (97) with lateral surfaces (98); the width of said front surface (96) being roughly equal to the distance (a) between two adjacent needles (3). 16) - A detector as claimed in one of the foregoing Claims from 2 to 15, wherein said needles (3) present a hooked end (5); characterized by the fact that said electrode (10) is mounted on a level with said hooked end (5) with said needles (3) in a predetermined operating position.

17) - A detector as claimed in one of the foregoing Claims from 2 to 16, wherein said needles (3) present a movable tongue (6); characterized by the fact that said electrode (10) is mounted on a level with said tongue (6) with said needles (3) and said tongues (6) in a predetermined operating position.

18) - A detector as claimed in one or more of the foregoing Claims, characterized by the fact that said electrode is made of and/or covered with conductive ceramic material.

19) - A moving profile detector, particularly for detecting damaged knitting machine needles, substantially as described and illustrated herein with reference to the accompanying drawings.