US 3905211 A
An apparatus for detecting faulty needles on an operating loom, particularly an operating hosiery loom. The apparatus comprises at least one magnetic detector, for example a Hall effect probe, mounted so that the needles of the loom pass successively in front of it during operation of the loom, and an associated electronic circuit for receiving signals from the or each detector, identifying those signals indicative of a defective needle, and providing a control signal for stopping the loom when such a signal is identified.
Description (OCR text may contain errors)
United States Patent [191 Raisin et al.
[4 1 Sept. 16, 1975 1 1 APPARATUS FOR DETECTING DEFECTS IN NEEDLES  lnventors: Jean-Pierre Raisin, Troyes; Bernard Helffer, Saint Andre les Vergers, bothof France  Assignee: Centre Technique Industriel dit:
Institut Textile de France, Boulogne sur Seine, France  Filed: June 13, 1974  Appl. N0.: 479,119
5/1972 MCAnhUrMQ. ..66/157 1/1974 Brose ..66/157 Primary Examiner-Louis K. Rimrodt Attorney, Agent, or FirmLewis H. Eslinger; Alvin Sinderbrand [5 7] ABSTRACT An apparatus for detecting faulty needles on an operating loom, particularly an operating hosiery loom. The apparatus comprises at least one magnetic detector, for example a Hall effect probe, mounted so that the needles of the loom pass successively in front of it during operation of the loom, and an associated electronic circuit for receiving signals from the or each detector, identifying those signals indicative of a defective needle, and providing a control signal for stopping the loom when such a signal is identified.
9 Claims, 2 Drawing Figures 5'6 79b 96 if 12 M Ma 18 20 39 I7 PATENTULSEP em 3 905.211
SHEET 1 [IF 2 PATENTEU SEP 1 61975 sum 2 05 2 mw mm mm APPARATUS FOR DETECTING DEFECTS IN NEEDLES The present invention relates to an apparatus for detecting defects in needles and relates more particularly to an apparatus which can detect defects in the needles of a hosiery loom throughout the entire operation of such a loom.
During knitting operations, the latch needles used on hosiery looms may deteriorate so that they are put out of use or damaged such that the knitted article produced comprises faults.
All hosiery looms at present in use are provided with inspection devices. These devices, which are very old, are generally mechanical feelers. They are able to detect needles whose latches are closed and additional thicknesses of knitting which form between the needle rows. in order to operate efficiently, it is necessary that these devices are regulated in an extremely accurate manner, which is generally difficult to carry out. Furthermore, they are unable to detect a needle whose hook is broken.
More recently, optical detectors have appeared. These detectors are sensitive only to the absence of a hook and thus may only be used to complement mechanical feelers. The operation of the electronic apparatus associated with these optical detectors and intended to detect this absence is based on the charging of a capacitor in the absence of a signal.
Still more recently. apparatus has appeared for detecting faulty needles on an operating hosiery loom, comprising at least one magnetic detector arranged such that all the needles pass in succession in front of the latter during their operating movement. An associated electronic circuit capable of transforming the signals received from said magnetic detector is provided which upon detection of a defect of a needle supplies a signal for controlling the stoppage of the loom.
These known magnetic detection devices have the drawback that the magnetic detectors used are constituted only by windings sensitive to the effect of induction. The low detection power, i.e., the low sensitivity of such detectors, necessitates the provision of an additional amplification stage before using the signals emitted by said detectors, and the location of the detectors as close as possible to the trajectory of passage of the needles, in other words at a distance less than approximately one-tenth mm. This distance is naturally difficult to maintain constantly along the entire length of passage of the various needles of the loom in front of the detectors.
Furthermore, even if the associated electronic circuits enable the detection of absences of signal owing to faults, such as the absence of a needle or a broken hook, they nevertheless do not enable the detection of signals having an amplitude greater than normal, such as those caused by the opening of the hook, the twisting of the needle towards the front, or the closure of the latch.
It is thus an object of the present invention to provide an apparatus which is capable of detecting practically all types of defects in the needles of a hosiery loom.
According to the present invention, there is provided an apparatus for detecting faulty needles on an operating loom, comprising at least one magnetic detector mounted in use so that the needles of the loom pass successively in front of it during operation of the loom,
and an associated electronic circuit for receiving signals from the or each detector, identifying those signals indicative of a defective needle, and providing a con trol signal for stopping the loom when such a signal is identified.
The magnetic detectors may be the detectors which are sold under the name of Hall effect probes, which detect and measure variations in the magnetic field caused in their vicinity by the passage of a needle. Other types of magnetic detectors may be used however, such as magneto-resistance detectors. These two types of detectors, Hall effect probes and magnetoresistance detectors, comprise thin rectangular plates of semi-conducting material. When Hall effect probes are subject to a magnetic field and traversed by a current at right-angles to said field, a voltage depending on said field and called a Hall voltage is produced between two electrodes located at right-angles to the direction of said current and to that of said magnetic field. Magneto-resistance detectors have a variable internal resistance depending on the magnetic field applied at right-angles to their major side.
Since these two types of detectors have a sensitivity of co-efficient of application which is much greater than that of conventional detectors comprising windings, their use makes it possible firstly to eliminate the previously indispensable amplifier stage and secondly to arrange them much further away from the trajectory of the needles, for example at a distance of several millimetres. In addition, the mounting of such detectors on existing machines is simplified in view of their miniaturization (dimensions: approximately 2mm 1mm X 1/10 mm).
The electronic circuit preferably comprises first and second circuits arranged in parallel, the first circuit comprising a first comparator for detecting faults which cause the appearance of a signal of an amplitude greater than normal and the second circuit comprising a second comparator and two monostables connected in series for detecting defects which cause the absence of a signal, the first comprator and the second monostable being connected to an OR gate which controls a delay trigger for providing a prolonged control signal for stopping the loom. The first comparator may comprise any equivalent system, for example a Schmitt trigger.
Finally, the connection of several of the detectors in a bridge makes it possible to eliminate background noise as well as various drawbacks such as interference and variations of an unpredictable nature which may be produced in all electronic components.
The signals emitted by the magnetic detectors during the passage of a needle in their immediate vicinity have very different characteristics depending on whether the needle is or is not defective, and the electronic circuit makes it possible to ensure the detection of a signal corresponding to any particular defect as soon as it appears, and to stop the loom immediately.
The apparatus of the present invention has the considerable advantage over optical systems of being completely insensitive to dust or powdery material which may be located in the vicinity of the needles.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 illustrates various types of defects which may occur in the needles of hosiery looms; and
FIG. 2 is a basic diagram of an apparatus according to the invention.
As shown in FIG. 1 the various defects which may occur in the heads of latch needles for hosiery looms, such a needle being shown in its normal form at 1 and comprising a hook 1a and a latch 11), may be regrouped in five major categories.
Each of these categories is symbolized by one of the five needles numbered 2 to 6, which illustrate the various defects encountered in a diagrammatic form.
Thus, the needle shown at 2 has a broken hook; the needle shown at 3 has an opened hook 3a, the needle shown at 4 has a broken latch 4b; the needle shown at 5 has a front part 50 which has been twisted; and the needle shown at 6 has a closed latch 6b.
Referring now to FIG. 2, the illustrated apparatus comprises a magnetic detector and an associated electronic circuit.
The magnetic detector is composed of two known magnetic detectors 7 sold under the name of Hall effect probes. A half-bridge connection of these probes has been adopted in this case, but other types of connection are naturally possible, for example a single probe or four probes connected as a bridge.
Each of the two Hall effect probes 7 is connected in series with a resistance 8 connected to earth 9.
The two probes 7 are supplied in a manner known per se at a constant voltage by a conventional stabilized supply 10 which is not shown.
The active surface of each probe has a width less than the depth of the needles to be detected. This width will be less than 50/100 mm. for looms of English gauge, equal to at the maximum for example, and should be less for looms of finer gauge.
Each magnetic detector is located in the path of the needle hooks at a point where the latter are located outside the range of any other ferrous member or member having magnetic properties. It is able to inspect the needles during their operating movement to form the stitch, or even during a first displacement prior to said movement. It may be mounted on an inspection door to which is fixed a cam ensuring, in this case, the partial ascent of all the needles, whatever their type if needles having different lengths or heels of different heights are used.
The electronic circuit is composed of two separate parts each assigned to the detection of certain of the types of defects described.
During the passage of the hook of a normal needle 1 in front of the magnetic detector, the detector emits a pseudo-sinusoidal signal 11 of given amplitude. If the needle which passes in front of the detector has one of the defects 3 (open hook), 5 (needle twisted at the front) or 6 (latch closed), then the detector is influenced by the modification of the resulting magnetic field surrounding it which is different from the normal, and due to this emits a pseudo-sinusoidal signal 12 of an ampltude clearly greater than that of the normal signal 11.
If the needle passing in front of the detector has the defect 2 (broken hook), the absence of the hook results in the magnetic field surrounding the detector being unmodified, and the detector emits no clear signal as shown at 13.
Finally, if the needle which passes in front of the detector has the defect 3 (broken latch), the needle is no longer able to knock-down the stitches which it collects. This results in an accumulation of stitches on its body, which causes the neighbouring needles to move forwards. During their forwards movement, these needles act on the detector like twisted needles (defect 5 and are consequently detected as described above.
Thus, all the above-mentioned defects are detected by the detector and identified either by the absence of a signal or the presence of a signal of too great an amplitude. Thus, the function of the associated electronic circuit is to detect these two types of irregularities and bring about the immediate stoppage of the loom if necessary. A first part of the electronic circuit, which carries out the detection of signals of too great an amplitude, comprises an electronic comparator 14. The comparator 14 receives the signals emitted by one of the Hall effect probes 7 of the magnetic detector at one of its two inputs 14a via a wire 15 which is connected to a wire 16 which joins the respective Hall effect probe 7 and series resistance 8.
The other input 14b of the electronic comparator 14 is connected by a connection 40 to a source of reference voltage 17. Thus, each time the comparator 14 re ceives a signal whose amplitude exceeds a threshold value regulated by the source 17, it emits a pulse 18.
This pulse is applied to an input 19a of an OR gate 19 by means of a wire 20 connected to the output 14c of the comparator 14.
The second part of the electronic circuit, which detects the absence of signals emitted by the magnetic detector, comprises a second electronic comparator 21, a first monostable 22 and a second monostable 23 connected in series. The monostable 23 is retriggerable so that its output may be held in its unstable state by a series of trigger pulses.
The second electronic comparator 21 has two inputs 21a, 21b connected by wires 25a, 25b to respective ones of the wires 16 which connect the Hall effect probes to their series resistances 8.
Thus, the second electronic comparator 21 continuously receives all the outputs of the magnetic detectors 7, including the normal signals 11, the signals of increased amplitude 12, and the null signals indicated at 13.
The electronic comparator 21 transforms the pseudo-sinusoidal signals 1 1 and 12, whose amplitudes vary, into square wave signals 24 of constant amplitude.
The first monostable 22, whose input 22a is connected by a wire 25 to the output 210 of the comparator 21, transforms the sequence of signals 24 into a train of pulses 26 of constant width, i.e., duration 26a and of the order of l millisecond. The frequency of these pulses 26 thus depends on the speed of the loom, since it is dependant upon the passage of the needles in front of the magnetic detectors.
The absence of a signal such as is indicated at 13 results in the sequence of signals 24 being broken by a gap as shown at 27 in FIG. 2, and by a break in the pulse train as shown diagrammatically at 28.
The retriggerable monostable 23 produces a pulse 29 when, at the end of a predetermined interval, a pulse has not been received at its input 23a. This time depends firstly on the adjustment of a R-C network comprising a capacitor 30 whose two terminals 30a and 30b are each connected to one of two other inputs 23b and 230 of the monostable 23 and an adjustable resistance 31 connected between one of the terminals 30b of the capacitor 30 and an electronic control member 32, and
secondly on the voltage applied to the adjustable resistance 31 by the control member 32. Since the frequency and consequently the period of the pulses is, as has been seen, dependent on the speed of the loom, it is necessary to vary the triggering time of the monostable 23. This is achieved by applying a voltage depending on the loom speed to the R-C network. This speeddependant voltage is obtained from pulses leaving the first monostable by means of the electronic control member whose input 32a is connected by a connection 33 to the output 22b of the first monostable and whose output 32b is connected by a connection 34 to the adjustable resistance 31 of the R-C network. Thus, since the triggering time of the monostable 23 is controlled by the speed of the loom, the detection of a break in the pulse train is independent of the speed of the loom. When a break in the pulse train occurs, the monostable 23 provides a pulse 29 on an output 23d of the monostable 23, which output is connected by a wire 35 to the second input 19b of the OR gate 19.
The capacitor 30 controlling the monostable 23 may be charged by a current obtained by any means so as to satisfy the desired conditions as regards its variations depending on the speed of the loom.
The OR" gate 19 thus receives pulses either from the first or from the second part of the electronic circuit and in both cases transmits a pulse 36 to a delay trigger 37 whose input 37a is connected by a wire 38 to the output 190 of said OR gate.
The function of this delay trigger 37 is to extend the output signal of the gate in order for it to have a sufficient duration to actuate loom stopping means (not shown), the necessary power being obtained by a mean power amplifier 39.
1. An apparatus for detecting faulty needles on an operating loom, comprising:
magnetic detecting means mounted so that the needles of the loom pass successively in front of it during operation of the loom, for producing signals of a normal amplitude when non-defective needles pass in front of it, signals of greater than normal amplitude when a first class of defective needles pass in front of it and signals of smaller than normal amplitude when a second class of defective needles pass in front of it;
a first electronic circuit connected to said magnetic detecting means for identifying signals of greater than normal amplitude indicative of a defective needle, and for providing a first control signal for stopping the loom when said defective needle is detected; and
a second electronic circuit connected to said magnetic detecting means for identifying signals of smaller than normal amplitude indicative of a defective needle, and for providing a second control signal for stopping the loom when said defective needle is detected, said second electronic circuit comprising means for producing a first output signal in response to signals which are not of smaller than normal amplitude, and for producing a second output signal in response to the absence of signals which are not of smaller than normal amplitude, during a time interval dependent on the operating speed of the loom.
2. An apparatus according to claim 1, wherein said first electronic circuit comprises a first comparator circuit having a first input connected to said magnetic detecting means and a second input connected to a source of reference voltage.
3. An apparatus according to claim 2 wherein said first comparator circuit includes a Schmitt trigger.
4. An apparatus according to claim 1 wherein said second electronic circuit comprises a second comparator circuit for producing first pulses having a recurrent frequency equal to the frequency of said signals which are not of smaller than normal amplitude, and monostable circuit means having a first input connected to said second comparator circuit and a second input connected to electronic control means, said monostable circuit means being retriggerable and said electronic control means supplying a voltage dependent on the speed of operation of the loom to said monostable circuit means for making the triggering time of said monostable circuit means dependent on the speed of operation of the loom.
5. An apparatus according to claim 4 wherein said second electronic circuit further comprises second monostable circuit means responsive to said first pulses for producing second pulses having a recurrent frequency equal to the frequency of said first pulses and having constant amplitude and time-width, said second pulses being supplied to said electronic control means.
6. An apparatus according to claim 1 further comprising an OR gate having a first input connected to said first electronic circuit for receiving said first control signal, a second input connected to said second electronic circuit for receiving said second control signal and an output connected to an output circuit for producing a control signal of at least predetermined duration for stopping the loom.
7. An apparatus according to claim 1 wherein said magnetic detecting means includes at least a Hall effect probe, the active surface of which has a width less than the depth of the needles to be detected.
8. An apparatus according to claim 7 wherein said magnetic detecting means includes a plurality of Hall effect probes connected as a bridge.
9. An apparatus according to claim 1 wherein said magnetic detecting means includes at least a magnetoresistance detector the active surface of which has a width less than the depth of the needles to be detected.