US3055200A

US3055200A - Fault finders

Info

Publication number: US3055200A
Application number: US51951A
Authority: US
Inventors: Meiners Carl Otto; Lessing Heinz Walter; Lessing Walter Benno
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-08-25
Filing date: 1960-08-25
Publication date: 1962-09-25
Anticipated expiration: 1979-09-25

Description

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b FE ttorne United States Patent Ofi 3,055,209 FAULT FMDERS Carl Otto Meiners, 40A Altenbergstrasse, Stuttgart, Germany; Heinz Walter Lessing and Walter Benno Lessing, both of 121 London Wall, London, England Filed Ang. 25, 1960, Ser. No. 51,951

4 Claims. (Cl. 66-166) This invention is a continuation-impart of our United States patent application Serial No. 702,174, filed December ll, 1957, and now Patent No. 2,991,639. It relates to inspection or iiaw-detecting apparatus, and especially such apparatus when used for the surveillance of travelling bands or webs of material, for example textile fabric, for the automatic detection of iiaws or discontinuities. The invention is particularly, though not exclusively, concerned with detecting faults in knitted fabric, especially the fabric produced by flat bar knitting machines including warp knitting machines such as Raschel and lace-lever machines.

The commonest fault occurring in the fabric produced on such textile machines is that due to a missing warp or a duplicated warp, or to a broken or bent needle. ln each case, the fault appears as a line in the fabric which goes on lengthening as the machine continues to operate. It is, therefore, important that `a stop motion or warning device be provided for stopping the machine or allowing it to be stopped as soon as possible after the fault has started to occur.

For this purpose, there can be used a photo-electric cell which is traversed across the fabric while the fabric is suitably illuminated, the signal from the cell being amplied as necessary and employed for controlling the stop motion or warning device of the machine, for example through a relay. The photo cell detects the change in transmitted or reliected light falling on it from the fabric that takes place due to the presence of a fault, and its output signal changes accordingly. ln such an arrangement, however, there is a practical limit to the speed at which the photo-cell can be mechanically traversed across the fabric. Consequently, a considerable time-as much perhaps as 8 seconds or even more-may elapse between successive scannings of a particular warp which, in that time, will have moved through a substantial length and have produced a fault of that length. The higher the speed of the machine, the longer may be the fault which can occur before remedial action is taken.

Another factor is the distance between the photo-cell and the fabric and between the photo-cell and the needles. If the traversing assembly is such that the scanning cell cannot be made to travel very close to the fabric and to the needles, it leads to an undesirable lack of sensitivity in the operation of the detecting cell and also to the detection of a fault only a substantial time after the fault has started to occur. This can be remedied by the provision of an optical system between the source of light and the fabric, and between the fabric and the photo-electric cell. However, that adds to the weight of the traversed assembly and to magnification of the difculty referred to above of moving the assembly at an acceptably high speed.

It is an object of the invention to provide an apparatus which is an improvement in these respects.

It is a further object to provide inspection or iiawdetecting apparatus, for the supervision by scanning of a given area or iield, comprising a plurality of photo-electric scanners mounted for movement transversely of the area or eld, the different scanners simultaneously traversing different parts of the surface or iield and each scanner receiving light reflected from or transmitted through a small portion of the surface or field at a time, and electrical connections provided from each scanner to a common signal channel whereby reaction'to a aw or discontinuity Patented Sept. 25, 1962 by any of the scanners produces a signal in the common channel for use in bringing about actuation of means such as a warning or stop motion device.

When the apparatus is for the detection of aws or discontinuities in a travelling band or web of material, for example textile fabric, a plurality of photo-electric scanners may be mounted for movement in unison close tothe web and transversely of the direction of travel thereof, the different scanners traversing different parts of the width of the web.

For any given speed of traverse, the time delay between' the instants at which each portion of the width of the web' is scanned is reduced substantially in inverse proportion to the number of scanners employed. For a knitting ma` o chine fault-tinder, four -scanners per seven feet of machine bed is found to be a useful number, although more orless can be used, if desired.

Each scanner may comprise a small photo-electric semiconductive device. This device can be a photo-transistor i.e. a light-sensitive triode, or a diode device of the kind` known as a photo-conductive cell and consisting of a backing plate bearing a layer of a photo-sensitive semi conductor material upon Which the incoming light is directly focussed.

To promote better understanding of the nature and objects of the invention, the following detailed description is given by way of example, reference being had to the accompanying diagrammatic drawings in which:

FIGURE 1 is a general view of a flat bar knitting ma-A chine with a fault-finder `according to the invention fitted,

FGURE 2 is a fragmentary elevation showing the fault finder as seen from the needle bed side, andv a mechanism for traversing it,

FIGURE 3 is `an elevation in section of the arrange-y ment of each scanner seen in the direction at right angles to the fabric travel,

IFIGURES 4A, 4B and 4C are diagrams Iof the electrical circuit connections,

FIGURE 5 is a diagram of means for preventingY curl of the edges of the fabric leaving the needles of the'knit` ting machine, y

FIGURE 6 is a general elevation, partly in section, of another form of fault-finder according to the invention, and

`FIGURES 7 and 8 are respectively a cross-sectional elevation of the fault-finder of FIGURE 6 to a larger scale, and a cross-sectional elevation of illuminating means to be used in association therewith.

In the iiat Vbar knitting machine 11 shownin FIGURE 1, the web 12 of knitted fabric issues from the needle bed 13 and is Wound on a horizontal take-up bearn`14. The fault-under fitted to the machine consists essentially of `a fixed assembly 1S and `a traversing assembly 16. The xed assembly 15 has a horizontalsupport bar 17 which is rigidly secured to the upper part of the machine 11 longitudinallyv thereof, and extending downwardly from the support bar are a number of spaced members 18 each having a roller guide 19 at its lower end. The traversing assembly comprises a horizontal'vrail Ztlwhich slides endwise in the guides 19 and is provided with depending tubular stems 21 vspaced at' equal intervals along its length and each carrying at its' lower end` a scanner head 22. v

ln FIGURE 2 an example of a'simple mechanism'for' reciprocating the rail 20 is shown. It consists of a mol tor 29 driving a crank 28v through a belt31 andV reduction gearing 32,'the crank being coupled to the end ofV the rail 2l) by a connecting rod '27. However, any suit# able reciprocating drive mechanism may be employed;

As the traversing assembly 16 of the fault-finder isy reciprocated, each scanning

head

2,2 surveys a dilierent portion of the width of the fabric web 12. Adjacent scan` ning heads operate over adjoining portions of the web width, so that the heads together keep the whole width of the web under surveillance while the reciprocating travel of the assembly 16 is substantially only that necessary to traverse each head over the individual fraction of the web width which it surveys, Preferably the portions of the web width surveyed lby adjacent scanning heads overlap slightly, i.e. the travel of the assembly 16 is just slightly more than the spacing distance of the heads 22.

Each scanning head 22 (FIGURE 3) comprises a tubular housing 23 screw-threaded to the lower end of the stem 21 and having an internal shoulder 24 upon which is a deck 25 carrying a photo-conductive diode cell 26. Electrical connections 33 for the cell 26 extend from the deck 25 and up inside the lstem 21. Below the cell 26 is an optical stop 34 having a slit aperture, and below that near the bottom end of the housing 23 is mounted a focusing lens 35. v

United to the bottom end of the housing 23 is an offset light-source housing 36 which accommodates a lamp 37 to co-operate with the photo-cell. Light from the lamp 37 passes through a slit aperture 38 at the lower end of the housing 36 and falls on the knitted fabric IZ which is travelling in the direction 4of the arrow. The photocell receives light reiiected from the fabric and from a much more reflective chromium plate strip mirror 39 @FIGURES 1 and 3) -placed below the fabric. It will be realised that when there is present in the view `of the scanning head a faultresulting, for example, from the absence of a warp thread, the quantity of light passing through the fabric and reflected to the photo-Cell by the mirror Alwill be greater, and this will change the current conducted by the cell and set up a fault detected signal.

Although in the embodiment illustrated the background to the fabric, i.e. the mirror, is more reliective than the fabric itself, so that aV fault of the kind described results in more light falling on the photo-cell, it will be understood that, as an alternative, the detection can be effected in the opposite manner, that is by eliminating the mirror and having the background less reflective than the fabric. Such a fault then causes a reduction in the light falling von the cell. Y Owing to the sensitivity of the photo-conductive 'cell only a low-power lamp is needed in the light-source housing 36. The lamp can, for example, be a standard l2 volt 0.1 amp. midget lamp of the kind used for illuminating instrument panels.v 'Ihe lamp has a terminal cap socket-assembly 40 to which exible supply leads 41 extend from an entry in the side of the st em 21.

'I'he electrical connections lfrom the photo-conductive cells 26 and the lamps 37 are carried up through the stems 21 into the rail 20 which is also hollow. From here they can Ibe taken to an amplifier and relay unit for controlling the operation of a machine stop motion vand/or operating a warning device. This control unit is preferably a stationary unit 42 (FIGURE 2) mounted on the knitting machine frame, and the leads from the reciprocating assembly 16 may be taken to it from the end of the rail 20 if desired, in the manner shown at 43. In addition to the signal ampliication effected at the unit 42, it is useful to provide preampliiication of each photo-cell signal before it is fed into the common signal channel to the main amplifier. Such individual preampliiication units can be transistor circuits, and can be'carried by the reciprocating assembly, for example on the rail 20.

FIGURES 4A, 4B and 4C show one way of laying out the electrical circuitry of the fault-finder, this layout being intended for the case in which the knitted fabric itself is more reiiective than its background, a mirror not being used.` i

power is supplied to the 4primary winding of a transformer 44 (FIGURE 4A) which has three

secondary windings

45, 46, 47. The secondary winding 45 feeds 4 through a rectifying network 48 and an R.C. iilter network 49 to deliver a rectified output of about l5 volts which is applied to the scanning head circuits via lines Si) and 51.

In 4the diagram, the circuits of four scanning heads are shown (FIGURE 4B). The four photo-conductive cells, indicated by the numerals l to 4, are biassed from the 15 volt line 50 through individual resistors S2, and are connected through capacitors S3 to the base electrodes of individual signal-amplifying transistors 54. Between the

l5 volt lines

50 and 51 there are connected in series potential-dividing resistors 55 and a tapped resistor 56. The collector electrodes of the transistors 54 are fed `from the junction point of the potential-dividing resistors 55 through individual load resistors 57, while the transistor base electrodes are -biassed from the tapping on the resistor S6 through individual resistors 58. The emitter electrodes of the transistors are connected to the ground line 51.

The separate outputs of the transistors S4 are fed through individual capacitors 59 and rectifying junction diodes 60 -to a common output channel 61 including a capacitor 62.

FiGURE 4C shows the main amplifier and relay unit. This unit Vis supplied with 300 volts rectified power from the transformer secondary 46 by way of a rectifying valve 63 and R.C. filter network 64 (FIGURE 4A), the output being

lon lines

65 and 66. Two stage amplification of the signal in channel 61 is provided by a conventionally-connected double-triode valve 67, and the ampliiied output is applied via a capacitor 68 to one stage 71 of a bi-stable double-triode switching valve 69 which has the energising winding 70 of a relay connected as part of the anode load of its other stage 72. The grid of each stage of the valve 69 is interconnected with the anode of the other stage, whereby variation in the signal applied -to the first stage 71 due to detection of a fault by any one of the four scanning heads brings about the biassing of the seco-nd normally nonconductive stage 72 to a conducting state and so operates the relay.

The relay has contacts working in an A.C. circuit supplied from the third transformer secondary 47 (FIG- URE 4A). This circuit can be connected to operate a machine'stop switch and light a red warning lamp. The relay remains energised until a manual switch 73 is operated, whereupon the second stage 72 of the valve 69 returns to its non-conducting state.

The circuitry shown in FIGURES 4A and 4C is intended to have astationary mounting on the knitting machine frame, while that of FIGURE 4B is intended to be borne by the traversing assembly 16. The resistor 52 and capacitor 53 individual to each scanning head can be disposed within the llower end of the corresponding stem 21, as shown in FIGURE 3.

The arrangement described enables each scanning head to be brought to a position one inch above the fabric and to scan the fabric at a point half an inch from the needles of the knitting machine. At any instant, each scanning head sees a small strip of fabric aboutone inch long in the direction of the warp threads and 1/50 inch wide, this strip falling within the local illumination afforded by the associated low-power lamp. These factors, coupled with the sensitivity characteristic of the photo-conductive cell, enable Ithe eifect of disturbing iniiuences, such as variations in general mill illumination, to be reduced to a minimum. It will be appreciated that the sensitivity of the apparatus must be so adjusted that it only reacts to sharp changes such as occur at a fault, and is not aifected by slow or small changes such as are produced by gradual variation in ambient light, specks of dust, differences in shade of the knitted fabric, and so forth.

The speed of traverse is limited by, among other considerations, the time taken by the photo-conductive cell to react. With four scanning heads operating over a seven foot width of fabric, a suitable speed is 2 feet per second.

Since, by the use of this apparatus, different portions of the fabric width are scanned simultaneously, the whole fabric Width is scanned in much less time than could be achieved by a single scanning head, the time taken decreasing in approximately inverse proportion to the number of scanners. Thus it becomes possible to reduce considerably the length of faults in the fabric.

The reflecting mirror, or such other contrasting background strip as may be provided if a mirror is not being used, should be long enough to allow for the widest fabric it is possible to produce on a particular knitting machine. This will mean that when something less than the widest fabric is being knitted the mirror or other background will project beyond `the fabric edges, and indeed it is advantageous to have a slight projection even with the Widest fabric. Spurious detection of a fault each time an end scanning head passes beyond the fabric margin can be prevented by placing over the projecting portions of the background blanking pieces made from the fabric being knitted or of a material simulating that fabric in appearance. This enables all widths of the fabric to be scanned right over the margins.

In FIGURE 3, the background reflector 39 is shown to have iianges 75 inturned above its upper edges, and the blanking pieces at the ends of the mirror can be inserted under these flanges and so retained in position. The same technique can be employed with a background strip than a reflector.

A diiiiculty that may be encountered in scanning the fabric arises from a tendency of the knitted fabric leaving the needles to pull in and curl at the margins. This can be overcome by providing means to stretch out or straighten the fabric at the margins, at least until it has passed beyond the scanners, one such means being illusstrated in FIGURE 5.

The device of FIGURE 5 comprises a pair of sheets or plates 111, 112 mounted on a bracket 113 in position to receive one margin of the cloth 11d as it leaves the needles 115. The edges 116 of the plates 111, 112 are met obliquely by the curled edge 117 of the cloth at an appropriate acute angle.

The two plates 111, 112 are spaced apart the requisite distance by a spacer 118 inserted between them. As the device illustrated is to be used on a machine fitted with the photo-cell fault-detector to be described in connection with FIGURES 6 and 7, the bottom plate 112 is formed with a channel or cutout 119 to allow passage of the scanning photo-cell right up to the edge of the cloth while keeping close to-it.

It will be understood that many modifications of the particular arrangement described above can be made without departing from the scope of the invention. Thus, germanium photo-transistors can be used in the scanning heads in place of the photo-conductive diodes.

Instead of having an individual lamp traversing with each scanning cell, there could be one light source for illuminating the whole width of the fabric. This could be in the form of a horizontal strip-light having a stationary mounting on the knitting machine or on the nontraversing frame of the fault-finder. Or another form of stationary light source or sources could be employed, such as lamps at intervals Ialong the machine bed. In certain applications, there may be enough light falling on the fabric from existing sources for fault-detection without the need for additional illumination associated with the fault-iinder.

It is not necessary that the light source or sources and the scanning cells be both on the same side of the fabric. 'They can be on opposite sides, with the scanners sensitive to light passing through the fabric instead of to the contrast of light-reflected from the fabric and its background. Any place where there is a fault in the fabric due, for example, to a broken warp thread will allow more light to pass through tothe appropriate detector cell.

While the scanning apparatus is shown Ias mounted over the fabric, it can instead be mounted underneath. Certain advantages `accrue from this in that the fault finder can, in general, be mounted more rigidly on the machine frame, and clear access to the needles is afforded to the machine operator. Such an arrangement is illustrated in FIGURES 6 and 7.

In the construction of FIGURES 6 and 7, four scanning heads 200 are mounted to travel to and fro in unison on a reciprocating frame structure 201 that slides on a fixed guide rod 202 mounted in endplates 210 on a stationary frame 203. .The reciprocating drive is imparted to the frame structure 201 by -an electrical motor 204- driving an Archimedean screw 2015 upon which is a travelling block 206. The block 206 fits around the screw and houses a rack member 207 having teeth to engage the screw and urged into engagement therewith by a spring 208. The block 206 is united to the reciprocating frame structure 201 by a plate 209. The screw 205 is mounted in bearings 211 on the stationary frame 203', and the motor 204 is mounted on a pedestal 212 on the frame 203 with its drive shaft 213 offset from the screw axis, the drive being taken through universal couplings at 214.

The assembly is housed in la casing 215 with a gap 216 along the top through which the scanners 200 protrude. 'Ihe fault-finder is mounted on the frame of the knitting machine immediately below the fabric issuing from the needles so that the fabric 217 passes` down close over the upper inclined surface 218 of the housing 215 and the scanning heads 200 scan the fabric close to the needles. Above the fabric are lamps 221 fitted in ta trough reiiector 219, andthe scanners detect any change in the amount of light passing through the knitted fabric due to the occurrence of a fault in the fabric. The lamp trough is mounted on the ends of the machine frame upon adjustable brackets for easy positioning, the mountings including vibration damping springs. The height of the trough above the cloth is not critical but eight to ten inches has been found convenient. The lamps can be, for example, 6 volt 6 watt festoon lamps, a large number, say 36 in a Seven foot' trough, being used, or alternatively they might be 2.4 volt watt double-ended tubular lamps of which, say, six to eight would be required for the same length trough. The lamps are chosen for thickness of filament so as to be robust enough to withstand vibration and they are underrun in use to prolong their Llife 'and to yield a red/ yellow light to which the photo-cells best respond.

Each scanning head has a slit 22d to admit light and comprises a photo-transistor 222 that performs the faultdetection, and 'a pre-amplifier transistor 223 By the use of transistors the sensing portions of the scanning heads are kept very small so that they can traverse in a path that lies within half an inch of the sinker bar and almost in contact with or actually touching the cloth.

To vary the sensitivity of the apparatus it is not necessary to adjust the transistor circuits but instead the amount of light thrown on the cloth by the overhead lamps can be easily varied by the Kadjustment of a rheostat 220 in the supply to the lamps. Sensitivity adjustment can be made necessary by an alteration in the thickness and/ or colour of the threads from which the cloth is being knitted, or by a change in Ithe stitch or pattern being knitted. It may also be lnecessary to vary the light from the lamps in accordance with changes in the general mill or ambient illumination falling on the machine. Such lighting adjustment can, for example, be effected `automatically for example by setting up a lightsensor 225 such `as a photoelectric cell which provides a signal for controlling the adjustment, for example thro-ugh an amplifier-servo-motor combination 226, of the rheostat 220. I

The apparatus has an electrical control unit providing 'i stabilised electrical supplies to the detecting heads and to the overhead lighting. The control unit receives signals from any of the detecting heads 280; these signals are amplified, and through a thyratron relay the machine is stopped when a fault is detected.

The arrangement of FIGS. 6 and 7 not only does not hinder the machine operatives view but also is of actual assistance to the operative in this respect. The lamps, being well above the cloth, cause no obstruction whatever but provide additional light where it is most needed.

The electrical arrangements are capable of considerable variation. Thus all the amplification and relay components may have a stationary mounting on the machine frame, or be traversed with the scanning assembly, as desired. In addition to individual amplifiers for the various scanner cells there may be individual relays also, either instead of, or feeding into, the relay in the common relay channel. Or a thyratron valve or valves may `be used instead of the common channel relay or the individual relays.

In a further electrical arrangement, a number of the scanning photo-cells can be connected into different arms of one or more bridge circuits, whereby a bridge is unbalanced upon detection of a fault by one of the cells.

While the particular fault-under described is for fitting to flat bar knitting machines, fault-detecting apparatus according to the invention can be put to many other uses. It can be employed on weft knitting machines and looms producing woven fabrics, and also for detecting flaws tion of faults or other discontinuities in a web of fabric f issuing therefrom, comprising a stationary guide frame fixed across the machine, scanning means mounted on the guide frame for travelling to and fro in a direction across the fabric, and lighting means illuminating the fabric as a whole, and wherein the scanning means comprises a photosensitive cell that receives light from a small portion of the fabric at a time and is sensitive to light variation due to the presence of a fault or the like in the fabric, electrical connections are provided from the photosensitive cell to a signal channel whereby reaction to a fault or the like by the cell produces a signal in said channel to bring about actuation of a Warning or stop motion device, and means is provided for adjusting the amount of light given on to the fabric by the lighting means so as to vary the sensitivity of the fault-detection apparatus as a whole.

2. A machine as claimed in claim l, wherein the lighting means comprises lamps in a trough reflector placed well above the fabric.

3. A textile machine having apparatus for the detection of faults or other discontinuities in a web of fabric issuing therefrom, comprising in combination a stationary guide frame fixed across the machine, scanning means mounted on the guide frame for travelling to and fro in a direction across the fabric, and lighting means illuminating the fabric as a whole, and wherein the scanning means comprises a photosensitive cell that receives light from a small portion of the fabric at a time and is sensitive to light variation due to the presence of a fault or the like in the fabric, electrical connections are provided from the photosensitive cell to a signal channel whereby reaction to a fault or the like by the cell produces a signal in said channel to lbring about actuation of a warning or stop motion device, and means is provided for adjusting the amount of light given on to the fabric by the lighting means so as to vary the sensitivity of the fault-detection apparatus as a whole, the combination further including at least one guide device for the web of fabric said device comprising two stationary guide members having opposed fiat surfaces spaced apart and substantially parallel to the fabric web which guide members are mounted on the machine at a position where an edge margin ofthe issuing fabric passes between said at surfaces thereby preventing curl of said edge margin where it is scanned.

4. A machine according to claim 3, wherein said guide members are constituted by parallel plates mounted with edges oblique to the oncoming edge margin of the web of fabric whereby said edge margin is constrained to a progressively increasing extent as the guide device is approached.

References Cited in the le of this patent UNITED STATES PATENTS 2,290,257 Stanley et al. July 21, 1942 2,421,092 Thomas May 27, 1947 2,578,889 Kennedy Dec. 18, 1951 2,859,603 Edelman et al. Oct. ll, 1958 2,991,639 Meiners et al. July 11, l96l