Method and apparatus for detecting yarns

Abstract

 A plurality of yarns 10 are scanned by a beam of radiation from an emitter 13. The emitter 13, together with a detector 14, is mounted on a carriage 11 which moves along a track 12. The detector 14 detects the effect that each yarn has on the radiation and this can be used to dedect if any of the yarns have significantly different properties from other yarns.

Description

[0001] The invention relates to the detection of yarns, and in particular to the detection, among a plurality of yarns arranged in a sheet, of any yarns having significantly different properties from other yarns in the sheet.

[0002] When preparing a warp sheet for use in weaving, a plurality of warp yarns are respectively wound from a plurality of bobbins on to a warp beam. As the yarns travel from the bobbins to the beam they travel along parallel paths, the yarns being arranged close together so that they form a flat sheet.

[0003] Occasionally a so-called "wrong end" may be included in the sheet. An operator may for example accidentally use a bobbin carrying a yarn which has different properties to the normal yarns and this fact may not readily be apparent visually. Thus the warp sheets may be formed, weaving may take place, and the mistake may only be noticed when the woven cloth is dyed, since the wrong end may react to the dye in a different manner to the other yarns. A length of cloth may thus be obtained which is visually unsatisfactory, and the cloth may have to be scrapped. It is therefore obviously desirable to have a means of detecting wrong ends in a warp sheet.

[0004] The invention provides a method of detecting if one or more of a plurality of yarns has different properties from other yarns of the plurality, characterised by the steps of scanning the yarns with a b6am of radiation, detecting the effect that each yarn has on the radiation, and comparing the results.

[0005] It is preferred that the radiation is electromagnetic radiation and the wavelength of the radiation will normally be outside the visual spectrum, since yarns that affect the visual spectrum can in any event often be detected as being odd ones out visually. The radiation may, for example, be in the infra-red or the ultra-violet range, but it is preferred that it is in the near infra-red range since emitters and detectors for this range are available readily and relatively cheaply.

[0006] The radiation may be provided by an emitter mounted on a carriage for travel over the yarns, the carriage including a detector to detect any radiation reflected by the yarns.

[0007] The detector may be connected to a microprocessor which is arranged to monitor the properties of the radiation reflected back by each yarn, calculate the mean and standard deviation for at least a group of the yarns, and provide means for identifying one or more yarns having properties which are significantly different from the mean.

[0008] Problems can also arise if one or more yarns are under significantly different tension to the majority of the yarns but it is not easy to detect this. However we have discovered that the method according to the invention can be used if the yarns are caused to move, for example using a stream of air or other gas. The extent to which the yarns move under a given stimulus is dependent on the tension, and the extent to which the yarns move affects the radiation reflected by the yarns.

[0009] Air or other gas can also be conveniently used to move the carriage.

[0010] The invention also provides apparatus for carrying out the method according to the invention, the apparatus comprising a carriage, and means for mounting the carriage for reciprocatory movement across a plurality of yarns extending in the same direction, characterised by a radiation transmitter mounted on the carriage for the transmission of a beam of radiation towards the yarns as the carriage moves over the yarns, and a radiation detector mounted on the carriage to scan the yarns as the carriage moves over the yarns and detect the radiation reflected from each yarn.

[0011] By way of example, specific embodiments of the invention will now be described, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic diagram illustrating the principle of the invention;

Figure 2 is a perspective view of a practical embodiment of the invention;

Figure 3 is a longitudinal cross-section through part of the carriage of the embodiment of Figure 2; and

Figure 4 is a transverse cross-section through the carriage of the embodiment of Figure 2 and through means for supporting the carriage.

[0012] Figure 1 shows four parallel warp yarns 10, each travelling from bobbins (not shown) to a warp beam. The four yarns are only shown to give a diagrammatic representation and it will be understood that in practice there may be several hundred such yarns arranged closely together to form a substantial flat sheet, as best shown in Figure 3_"

[0013] Mounted above the sheet is a carriage 11 arranged to travel along a track 12, the track being arranged horizontally above the yarns 10 and at right angles thereto. The carriage 11 can thus travel right across the warp sheet, passing over each yarn 10 in turn.

[0014] Mounted on the carriage 11 is an infra-red emitter 13 and infra-red detector 14.

[0015] As the carriage 11 passes over each yarn 10, the yarn reflects some of the infra-red radiation back to the detector 14 and the signal generated is fed to a microprocessor (not shown).

[0016] It has been found experimentally that different counts of yarn reflect different amounts of infra-red radiation and in some cases a different type of fibre in the yarn results in a different amount of reflected radiation. A table of results is given below for a series of experiments carried out using a gallium arsenide infra-red emitting diode and a silicon photo sensitive diode detector. The peak emission wavelength for the emitter was 940 nanometres whilst the detector was sensitive to radiation throughout the visible and into the infra-red region. The reflection intensity is given in arbitary units, 15.0 units representing the background value obtained in the absence of any yarn.

[0017] The tex given is for the single yarn.

[0018] The microprocessor has a memory for each yarn. Thus if there are 400 yarns in a sheet, the microprocessor will have at least 400 memories. The reflection reading for each yarn is stored in a separate memory and at the end of each scan the readings are examined by the microprocessor to determine if any of the yarns differs significantly from the average. There is a wide range of wellknown statistical methods which may be used for this examination. For example, in the case of very uniform yarns it would be sufficient simply to calculate the mean and standard deviation and select any individual readings which fell outside, say, plus or minus 4 standard deviations. The microprocessor can be arranged to operate a visual and/or audible alarm if there are any such non-average readings and the microprocessor can also be arranged to identify which yarns initiated these readings. The microprocessor may for example allocate to each yarn a number from 1 to 400, and the microprocessor can then indicate, for example on a digital readout, the numbers of those yarns which have produced a non-average reading.

[0019] In the case of yarns having properties which tend to vary naturally along the length of the yarn, it may be necessary to arrange for the microprocessor to register or otherwise record any ends falling outside, say, plus or minus 2 or 3 standard deviations and then see whether such suspect ends were still outside the predetermined tolerance on the next few succeeding scans. Any ends which are no longer outside the tolerance would probably be suspect only because of variation in their-properties along the length of the yarn. However any ends still outside the tolerance would almost certainly represent a wrong end having consistently different properties from the other ends.

[0020] The necessary calculations may be based on standard statistical procedures which could readily be programmed into the microprocessor. For example the analysis carried out by the microprocessor may utilise a Bartlett's test. This is a known statistical test for homogeneity of variance which is used to detect individual results which do not belong to the same statistical population as the rest of the results.

[0021] Turning now to Figures 2, 3 and 4, these illustrate a practical embodiment of the invention.

[0022] The embodiment is designed to scan a warp sheet consisting of several hundred parallel equally spaced threads 10 closely spaced apart over a width of substantially 1.4 metres, as shown in Figure 3. A few of the threads are shown in Figure 2 for the purposes of illustration.

[0023] The apparatus has a detector box 15 containing a light source 16 and two infra-red sensors 17. The detector box is fixed to a glider 16a which is supported on an air track comprising two hollow sections 17a having holes 18 drilled in their upper surfaces. The sections are pressurised to substantially 100 millibars from a blower via pipes 19.

[0024] When the glider reaches each end of the track a prong 20 on the glider strikes a reversing spring 21 so that the glider bounces back towards the other end. Only one prong and spring have been shown in Figure 2 for the sake of simplicity. There is very little friction involved in movement of the glider but the glider would eventually come to rest without some form of energy input. The movement is maintained by providing an air blast at each end. As the glider approaches each end of the track, a proximity switch 22 is actuated by a bar 23 mounted on the glider. This operates an air valve 24 via a time delay circuit which allows air from a pipe 25 to pass through one of the nozzles 26 and impinge on one of the targets 27 mounted on the glider. Each target is designed to give the maximum thrust by reversal of the air stream.

[0025] If the glider is travelling too fast then the actuating bar 12 will pass right over the proximity switch 11 and the timing circuit will be reset so that the air valve will open for a short period or not at all. The operating speed of the glider can therefore be fixed by suitable choice of spring rate and proximity switch position.

[0026] The detector is shown moving below the warp sheet and facing upwardly, but in some cases it is more convenient to mount the detector above the threads facing downwardly, although the principle of operation is exactly the same.

[0027] The detector box 15 is shown in more detail in Figures 3 and 4. The light source 16 is a quartz halogen incandescent bulb and the image of the filament is focused by a lens 28 on to the plane of the warp sheet 10. The image of ehch illuminated thread is focused by lenses 29 on to the two infra-red sensors 17. The peak wave lengths of the sensors vary according to the fibres which are most likely to be present in any particular installation but are normally between 900 and 2500 nanometres.

[0028] As the detector box passes each thread the output from the sensors will rise from a background level (e.g. zero) to a peak and then fall back to the background level. The outputs are converted to digital form and the peak values are detected in hardware or software and stored in temporary memory locations. The actual number of threads in the warp sheet is keyed into the micro processor before operation commences and at the end of each scan the number of threads "observed" is compared with this figure. If the number is correct then a cusum is calculated for each thread and for each detector and stored in the micro processor. Whenever the value of any cusum exceeds preset tolerances then the machine is stopped and the number of the faulty thread is displayed.

[0029] The detector box 15 also carries a minature air blower 30 which blows a vertical jet of air through the warp sheet 10 via a pipe 31. The air jet deflects the threads causing them to move from their normal position and the distance between the detector box and the warp sheet is such that the threads are in focus on deflected threads at normal thread tension. Thus if the tension differs from normal the thread will be deflected too little or too much by the air jet and will thus be out of focus. This will produce an output different:from normal which will be detected by the apparatus.

[0030] The invention is not restricted to the details of the foregoing embodiments. For instance it is not essential that infra-red radiation be used. It is however preferred that infra-red radiation is used, not only for the reasons already mentioned, but also because infra-red radiation is safe, easily produced, and easily detected electronically. It seems clear from experimental evidence that infra-red radiation is selectively absorbed by vibrational energy level in fibres. The energy levels and hence the wavelengths absorbed depend on molecular structure and an infra-red absorption spectrum can be used to identify fibres. The reflection of infra-red radiation from fibres in yarns is a complex phenomenon depending on the nature of the fibre surface, and the presence of additives such as delustrant, in addition to the molecular structure.

[0031] By a correct choice of wavelengths it is possible to distinguish a wide range of different yarns.

[0032] It has been found that the vibrational energy levels in the polymers commonly used as fibres give absorption peaks in the wave-length range 3000 nanometres to 15000 nanometres. The following table gives details:-

Infra-red absorption peaks

[0033] 

[0034] Not all of these wavelengths are usable since the atmosphere itself is strongly absorbing at certain wavelengths, for example because of water vapor, notably between 2400 nanometres and 3100 nanometres, 4200 to 4500 nanometres, and 5000 to 8000 nanometres.

[0035] There may be sufficient differences in reflective properties in the near infra-red range, around 940 nanometres, to produce satisfactory results. However it is desirable for more than one wavelength to be utilised, to increase the sensitivity of the device. With a single wave- length, effects may cancel out under certain conditions. For example if a yarn is thinner than its neighbours, but is also more reflective, it may produce the same amount of total reflected radiation as its neighbours. If however, there are two wavelengths, and the microprocessor is given two sets of data to work on, it is unlikely that the effects will cancel out at both wavelengths.

[0036] In the embodiment desired with reference to Figures 2 to 4, the source 16 emits radiation over a range of wavelengths and each detector 17 is sensitive to a different wavelength within the range.

[0037] If necessary however, there may be more than one emitter 11, each emitter being arranged to emit a different wavelength radiation, or even a different type of radiation. It may for example be possible to use one or more additional wavelengths in the middle and/or far infra-red ranges.

[0038] Any desired combination of numbers and types of sources and deflectors may be used.

[0039] Whilst the device described above is particularly suitable for detecting wrong ends in a warp sheet, the device may be used whenever it is desired to detect if one or more of a plurality of yarns are odd ones out with respect to other yarns. If for example a patterned warp sheet is being prepared, which is to comprise say, x black yarns followed by y white yarns followed by x black yarns again, and so on, to give a black and white striped warp sheet, it may for example be that the warp sheet is threaded up wrongly, so that there are perhaps x minus 1 or x plus 1 black threads in a group. If x is large, this fault might not be readily detectable by mere visual comparisons. However the microprocessor could be programmed with the knowledge that there should be x black yarns followed by y white yarns and so on, and the microprocessor could be arranged to process each group of black or white yarns separately. The microprocessor would then readily identify a white yarn which was in a position which should be occupied by a black yarn, and vice versa.

[0040] Furthermore, it is not essential for the invention to be used with yarns extending in a flat plane. It may for example be used in circular knitting, where a plurality of yarns converge radially inwardly and like the spokes of a wheel and then follow a parallel path, the parallel yarns defining a cylinder. With such an arrangement the carriage may be arranged to travel around a circular path to scan the yarns.

Claims

1. A method of detecting if one or more of a plurality of yarns has different properties from other yarns of the plurality, characterised by the steps of scanning the yarns with a beam of radiation, detecting the effect that each yarn has on the radiation, and comparing the results.

2. A method as claimed in Claim 1, in which the radiation is electromagnetic radiation.

3. A method as claimed in Claim 2, in which the wavelength of the radiation is outside the visible spectrum.

4. A method as claimed in Claim 3, in which the wavelength is in the ultra-voilet range.

5. A method as claimed in Claim 3, in which the wavelength is in the infra-red range.

6. A method as claimed in Claim 5, in which the wavelength is in the near infra-red range.

7. A method as claimed in any one of the preceding claims, in which the radiation is provided by an emitter mounted on a carriage for travel over the yarns, the carriage including a detector to detect any radiation reflected by the yarns.

8. A method as claimed in Claim 7, in which the detector is connected to a microprocessor which is arranged to monitor the properties of the radiation reflected back by each yarn, calculate a mean and standard deviation for at least a group of the yarns, and provide means for identifying one or more yarns having properties which are significantly different from the mean.

9. A method as claimed in any one of the preceding claims, in which the yarns are moved out of their normal position so that differences in tension can be detected, the extent to which the yarns move under a given stimulus being dependent on their tension.

10. A method as claimed in Claim 9, in which the yarns are moved by a stream of air or other gas.

11. A method as claimed in Claim 7 or Claim 8, and Claims 9 or 10 when dependent on Claim 7 or Claim 8, in which the carriage is moved by means of air or other gas.

12. Apparatus for carrying out the method claimed in any one of the preceding claims, the apparatus comprising a carriage, and means for mounting the carriage for reciprocating movement across a plurality of yarns extending in the same direction, characterised by a radiation transmitter mounted on the carriage for the transmission of a beam of radiation towards the yarms as the carriage moves over the yarns, and a radiation detector mounted on the carriage to scan the yarns as the carriage moves over the yarns and detect radiation reflected from each yarn.

13. Apparatus as claimed in Claim 12, in which the radiation is infra-red radiation.

14. Apparatus as claimed in Claim 12 or Claim 13, having a microprocessor which is arranged to monitor the properties of the radiation reflected back by each yarn.

15. Apparatus as claimed in any one of Claims 12 to 14, including means to move the yarns out of their normal position

16. Apparatus as claimed in Claim 15, in which the means to move the yarns comprise means to direct a stream of air or other gas over the yarns.

17. Apparatus as claimed in any one of Claims 12 to 16, including air or other gas operated means for moving the carriage.

Drawing