YARN QUALITY MONITORING METHOD AND APPARATUS

Abstract: A method of monitoring yarn quality in a yarn texturing process comprises measuring the velocity of the travelling yarn at two locations and comparing the measured velocities. At a first location the yarn tension is sufficient to draw out the crimp and at a second location the tension is lower such that the crimp is developed. Apparatus for performing this method comprises a measuring device (28) to measure the peripheral speed of a driving roller (26) which is part of a nip-feed device (21) serving to feed a crimped yarn (13) at the first location from a false twist device (20) to a secon heater (22) of a false twist texturing machine (10). At the second location between the second heater (22) and a third feed device (23) of the machine (10) is a second velocity measuring device (30) which comprises an inlet tube (31), an outlet tube (33) and two discs (34) of brass which form spaced measuring stations spaced by an insulating body (35). Signals proportional to the static electrical charge carried by the yarn (13) as it passes through the measuring device (30) are sent from the discs (34) to an amplifier (38) and calculating means (29), at which the speed of travel of the yarn (13) between the discs (34) is calculated.

Description: This invention relates to a yarn quality monitoring method, and apparatus for use in such method, and in particular to a method of and apparatus for on-line monitoring of the "crimp velocity" of textured yarn, which can be related to off-line "bulk level" or "crimp retraction" measurements. Bulk level or crimp retraction is a measure of the amount of crimp which has been put into the yarn by the texturing process. It can be measured conventionally by a test in which a hank of yarn, after preheating in air, is measured for length under a high load sufficient to pull out the crimp and again under a low load sufficient only to stabilise the fibres but retain the maximum crimp. The bulk level is then defined as the difference between the measured lengths expressed as a percentage of the first length. The above test is carried out on a crimped yarn, and if it is desired to measure the effect of varying the parameters controlling the crimping process, it is necessary to run a separate test for each parameter variation and measure the bulk level of each sample thus produced. In addition, although in test conditions yarn samples may be taken from the beginning, end and any number of intermediate stages of the run, this is not practicable when crimping yarn commercially, since the test is destructive of the samples taken. In consequence, it is not possible to check by the above method the consistency of the bulk level produced in a commercial crimping operation. An alternative test is known, for example as disclosed in Research Disclosure No. 120 (1974) pp48-50, in which the crimp frequency is determined by measurement of correlated periodic effects of the reflection of light from the surface of a crimped yarn as it passes between sets of forwarding rollers. The tests are performed at differing tension levels in the yarn under which the crimp is firstly developed and subsequently is pulled out. However, since the apparatus used is a laboratory instrument and the test is performed on a package of already crimped yarn, the disadvantages referred to above in relation to the previously described test apply also to this test. A similar test is disclosed in WP-A-8302665, with the same disadvantages. It is an object of the present invention to provide a method of, and apparatus for, determining, continuously throughout a commercial texturing operation, the quality of the textured yarn, in manner which can be related to the known off-line bulk tests. The invention provides a method of texturing a yarn and simultaneously monitoring the quality of a crimped yarn produced during the texturing process, comprising the steps of forwarding a yarn to a crimping device in a texturing zone and texturing the yarn in that zone to insert a crimp therein, measuring a first velocity of the crimped yarn whilst forwarding the crimped yarn through that zone from the crimping device under a first tension which is sufficient to draw out the crimp, forwarding the crimped yarn under a second stabilising tension which is insufficient to draw out the crimp, and measuring a second velocity of the crimped yarn whilst so forwarding it and calculating a crimp velocity value from the yarn velocity measurements. The method may comprise false-twist crimping the yarn prior to performing the velocity measuring steps, and may comprise drawing the yarn simultaneously with the false twist crimping thereof. The first velocity measurement may be effected by measuring the peripheral speed of a yarn feed device, which feed device is operable to feed the crimped yarn from the texturing zone to a subsequent processing region. In the subsequent processing region the crimped yarn may be wound onto a package or may be heated under the second tension prior to being wound onto a package. The second velocity measurement may be effected by detecting, at two spaced locations in the subsequent processing region, a parameter of the crimped yarn which moves with the yarn, and measuring the elapsed time between such detections. Preferably the second velocity measuring step comprises detecting at the two locations a static charge carried by the yarn. The invention also provides apparatus for texturing a yarn and simultaneously monitoring the quality of a crimped yarn produced during the texturing process comprising texturing means in a texturing zone operable to insert a crimp in the yarn, first forwarding and tensioning means operable to forward the crimped yarn through the texturing zone from the crimping means under a first tension sufficient to draw out the crimp therein, first velocity measuring means operable to measure the velocity of the crimped yarn whilst it is forwarded under the first tension, second forwarding and tensioning means operable to forward the crimped yarn under a second stabilising tension insufficient to draw out the crimp, second velocity measuring means operable to measure the velocity of the crimped yarn whilst it is forwarded under the second tension, and calculating means operable to calculate a crimp velocity value from the yarn velocity measurements. The apparatus may comprise false twist crimping apparatus, and the first forwarding and tensioning means may be operable to draw the yarn simultaneously with the false twist crimping thereof. The first forwarding and tensioning means may comprise a yarn feed device, which may be operable to feed the yarn from a crimping apparatus to a subsequent processing apparatus, and the first velocity measuring means may be operable to measure the peripheral speed of the feed device. The feed device may comprise a driving roller and a roller forming a nip therewith through which the yarn may pass. The subsequent processing apparatus may comprise package winding means, and may also comprise yarn heating means disposed upstream thereof. The second velocity measuring means may comprise detecting means operable to detect at two spaced locations of the subsequent processing apparatus a parameter of the yarn which moves with the yarn, and time measuring means operable to measure the elapsed time between such detections. Preferably the detecting means comprises a housing defining a path of travel of the yarn therethrough, a pair of measuring stations spaced along the yarn path within the housing, and at each measuring station, a sensor adapted to detect the presence of a static electrical charge on the yarn and to produce an electrical signal proportional to the value of such static electrical charge, wherein each sensor is electrically connected to an input of an amplifier and then to the calculating means, and the calculating means is operable to apply a delay to the signal from the first measuring station and to cross-correlate the delayed signal with the signal from the second measuring station. The invention also provides a false twist crimping machine having a plurality of yarn processing stations in which for each station there is an apparatus as defined above, wherein the calculating means (29) has signal store means (42) for each of a set of the yarn processing stations each to receive signals from a respective measuring means (30), and the calculating means (29) is operable to cross-correlate the signals from the spaced locations of a measuring means (30) at a first yarn processing station of the set simultaneously with receiving into a respective store of the calculating means the signals from at least one other measuring means (30) at an adjacent yarn processing station of the set and to repeat the operation in sequence for each of the yarn processing stations of the set. Four measuring means at adjacent yarn processing stations may be adapted to produce signals which are received simultaneously into the respective signal store means of the calculating means. One embodiment of apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which Fig 1 is a schematic end elevation of a false twist crimping machine embodying the apparatus of the invention. Fig 2 is a sectional elevation of a part of a machine similar to that of Fig 1, showing the second velocity measuring means. Fig 3 is a longitudinal section of the second velocity measuring means of Fig 2. Fig 4 is a sectional plan view on the line 4-4 of the second velocity measuring means of Fig 3. Fig 5 shows an arrangement of an amplifier of the velocity measuring means. Fig 6 and 7 show the arrangement of a signal store of the calculating means associated with consecutive machine positions, and Fig 8 shows a relationship between crimp velocity and bulk level. Referring now to Fig 1 there is shown a false twist crimping machine 10 comprising a creel 11 having several packages 12 thereon of uncrimped, undrawn or partially drawn, yarn. A yarn 13 is withdrawn from a package 12 by a first feed roller device 14 mounted on a support 15 of the creel 11. The yarn 13 is then passed over an upstanding primary heater 16 which is also mounted on the support 15. A guide arrangement 17 at the top of the heater 16 guides the yarn 13 to a cooling plate 18, which extends downwardly over the operator's aisle 19 to guide the yarn 13 to a false twist device 20. The false twist device 20 serves to insert twist into the yarn 13 extending thereto from the first feed roller device 14, and a second or intermediate feed roller device 21 serves to draw such length of yarn 13 simultaneously with twist insertion. The now crimped yarn 13 then passes through a subsequent processing region in which is provided a secondary heater 22, a third feed roller device 23 and a package winding apparatus 24. Apparatus as thus described is conventional for the production of set yarns. If however stretch yarns are required the aforementioned secondary heater 22 is omitted and the yarn 13 passes directly from the second feed roller device 21 to the package winding apparatus 24. In either case one or more yarn guides 25 may be provided before the winding apparatus 24. The yarn 13, as it arrives at the second feed roller device 21, is crimped but is under such a relatively high tension that the crimp is pulled out. Between the second feed roller device 21 and the yarn guide 25 the yarn 13 is crimped and is under a relatively low tension sufficient only to stabilise the fibres but such as to allow full crimp to be developed. If the yarn velocities in these two regions are measured as being V1 and V2 respectively, then the quantity is herein defined as the "crimp velocity" and can be shown to have a positive relationship to the bulk level or crimp retraction defined as where L1 and L2 are the lengths of the yarn under the same tension conditions when measured in an off-line test as previously described. The velocity V1 of the crimped yarn 13 as it arrives at the second feed device 21 is equal to the peripheral speed of that feed device. The feed device 21 comprises a driving roller 26 and a driven roller 27 forming with each other a nip through which the yarn 13 passes. A first velocity measuring device 28 of any conventional type is provided to measure the peripheral speed of the driving roller 26 and hence V1. A signal proportional to the speed V1 is sent by the measuring device 28 to a calculating means 29. A second velocity measuring device 30 is provided in the subsequent processing region between the second feed device 21 and the yarn guide 25. The measuring device 30 provides a signal which contains information from which the yarn velocity V2 in this region can be calculated, the signal being amplified by amplifier 38 and then also being transmitted to the calculating means 29. The calculating means 29 is operable to calculate the quantity which is by definition the crimp velocity. By this means the yarn quality can be continuously monitored throughout the texturing operation. In addition transient variations, which cannot be detected by the off-line static sampling methods, may be detected by the method of the present invention. Conveniently the second velocity measuring device 30 may be located between the secondary heater 22, if one is present, and the yarn guide 25 as shown in Fig 1. A similar arrangement is shown in Fig 2 in greater detail but with a slightly different machine layout. In this case the yarn guide 25 serves to turn the yarn 13 through 90° to direct it to the third feed roller device 23 in the manner and for the purpose described in GB patent no. 2147323. The second velocity measuring device 30 has an inlet tube 31, which may be attached to or be part of the inner tube 32 of secondary heater 22, and an outlet tube 33 which serves as an entry tube for the yarn guide 25. By this means threading of the yarn 13 through the device 30 may be effected simultaneously with the threading of the yarn 13 through the heater 22 and yarn guide 25 using a suction gun as is described in GB patent no. 2147323. The velocity measuring device 30 provides two measuring stations a fixed distance apart, for example 200mm. At each measuring station is located a disc 34 of a suitable electrically conducting material, such as brass, and each disc 34 is connected to a respective input A or B of the amplifier 38 and then to the calculating means 29. The discs 34 are separated by a body of an insulating material 35, eg ceramic, air, plastics material, the latter being a high temperature plastics material if the heater 22 is positioned adjacent the device 30, and are enclosed in an earthed, electrically conductive case 36 so as to form a screen against extraneous pick up of static electricity. As is more clearly seen in Figs 3 and 4 the discs 34 and insulation body 35 are provided with a central hole 37 through which the yarn 13 passes without contact from the inlet tube 31 to the outlet tube 33. As the yarn 13 passes each disc 34 a signal is transmitted from that disc 34 via amplifier 38 to the calculating means 29 proportional at any given instant to the quantity of static electrical charge carried by that part of the yarn 13 passing through the hole 37 of that disc 34 at that instant. The velocity measurement is based on the fact that the distribution of the static electrical charge value along the yarn 13 is random, and that the time taken for a charge value pattern detected at the first measuring station to be repeated at the second measuring station will enable the velocity of the yarn to be determined. The time taken is determined by applying a delay to the signal from the first measuring station and correlating the delayed signal with the signal from the second measuring station. The correlation will be a maximum when the two signals coincide, ie when the delay applied to the first signal is equal to the time taken for a given part of yarn 13 to travel between the two discs 34. The signals from the two discs 34 are fed to the inputs A-in and B-in of an amplifier 38 of the velocity measuring means 30, the amplifier 38 being shown in Fig 5. The amplifier 38 is a modified form of a standard high impedance, non-inverting, negative feedback operational amplifier. The modification comprises the provision of a leakage resistor 39 between each inputs A-in, B-in and the zero volt (earth) lead 40. The resistors 39 have a compromise value, for example 180 kΩ, which is low enough to give sufficient leakage to earth to provide an adequate signal from the feedback loop 41, but is high enough to prevent too much drainage of the signal at input A-in from the first measuring station and hence insufficient charge remaining to be carried to the second measuring station. The output signal from the amplifier 38 represents the voltage differences at the points 2-, 3+ and 5+, 6-, such voltage differences being amplified by a factor of 10. Correlation of the output signals A-out, B-out is performed in the calculating means 29 in conventional manner, leading to a calculation of the velocity V2 of the yarn 13 in its crimp developed condition in the subsequent processing region between the second feed device 21 and the yarn guide 25. The velocity V1 of the yarn 13 in its crimp pulled out condition is determined by the measuring device 28 as previously described, and the value of the crimp velocity, as determined by the relationship is calculated by the calculating means 29, noting that the crimp velocity has a direction opposite to the direction of yarn travel. In a conventional false-twist crimping machine, having for example 24 yarn processing stations per bay and 9 such bays, it is convenient to provide monitoring apparatus as above described for each bay instead of for each processing station, thereby reducing considerably the cost of providing such apparatus for the machine. However, if each yarn in a bay is monitored in succession the time lapse between successive monitorings of any one yarn would be such that many transient variations of crimp velocity could be missed. To overcome this problem an arrangement such as is shown in Figs 6 and 7 is used. Within the calculating means 29 there are provided signal stores 42, one for each yarn processing station 1 to 24 but only stores S1 to S6 corresponding to stations 1 to 6 being shown for clarity. Each store 42 is set to receive from its respective transducer T, 100 signals from amplifier output B in it each of four delay band widths of 4 ms in an overall delay band of from 4ms to 20ms. If, as previously mentioned, the spacing of the measuring stations is 200mm the overall delay band represents yarn throughput speeds of 3000m/min to 600m/min. Other measuring station spacings and/or other delay band widths may be used if desired. When all of the data from processing station number 1 has been loaded into S1, ie the signal from transducer T1 output A with all of the incremental delays from 4ms to 20ms, the signal from transducer T, output B and a 4ms bandwidth of signals from the store S1 spanning the delay corresponding with the speed of yarn throughput, are fed to a correlator C of the calculator 29, as shown in Fig 6. This reduces the correlation time to one quarter of that required if all of the information stored in S1 were to be fed to the correlator C. Whilst the correlation is being performed loading of data into the next four stores S2, S3, S4 and S5 takes place, each store's data being 4ms delay spaced from the adjacent store's data. In consequence, when the correlation of the data from store S1 has been performed, all of the necessary data will have been loaded into store S2 and correlation of the signal from transducer T2 output B and a 4 ms bandwidth of signals from stores S2 may be fed to the correlator C as shown in Fig 7. During the correlation of this data the loading of further data into stores S3, S4 and S5, and the loading of data into store S6 is carried out. This procedure is carried out for each processing station 1 to 24 in sequence. Since loading of four stores is performed simultaneously the time taken to complete the monitoring of all 24 processing stations is reduced to approximately one sixth of that which would be required if each store were to be loaded after the correlation of the data from the previous store had been effected. In consequence the risk of non-detection of transient variations in the crimp velocity of any one yarn is considerably reduced. Alternative embodiments of apparatus in accordance with the invention will be readily apparent to persons skilled in the art. For example, since there is a predetermined constant speed ratio between the intermediate feed roller device 21 and the third feed roller device 23, the peripheral speed of the third feed roller device 23 may be measured to determine V1 if desired. Also the second velocity measuring device 30 may be adapted to measure other parameters which are randomly distributed along, but travel with, the yarn 13, such as vibration, capacitance, reflectivity, temperature or the like. Also the velocity measuring device 30 may be located between the intermediate feed device 21 and the second heater 22, or within the second heater 22, if preferred. If no second heater 22 is provided, or as an alternative to the use of a suction gun for threading purposes, the case 36, insulating body 35 and discs 34 may be provided with a threading slot so that the yarn 13 may be introduced laterally into the velocity measuring device 30. Referring now to Fig 8 there is shown a typical relationship between crimp velocity as measured in accordance with this invention and final bulk level on crimp retraction as measured by an off-line test as previously described. In this case a textured 78f34 polyester yarn has been evaluated and the crimp velocity and crimp retraction are shown to vary in a corresponding manner with primary heater temperature.

Claims: A method of texturing a yarn and simultaneously monitoring the quality of a crimped yarn produced during the texturing process, characterised by the steps of forwarding a yarn to a crimping device in a texturing zone and texturing the yarn in that zone to insert a crimp therein, measuring a first velocity (V1) of the crimped yarn (13) whilst forwarding the crimped yarn (13) from the crimping device under a first tension which is sufficient to draw out the crimp, forwarding the crimped yarn (13) under a stabilising second tension which is insufficient to draw out the crimp, and measuring a second velocity (V2) of the crimped yarn (13) whilst so forwarding it and calculating a crimp velocity value (V1 - V2/V1) x 100) from the yarn velocity measurements. A method according to claim 1 characterised by feeding the crimped yarn from the texturing zone to a subsequent processing region and in that the second velocity measurement is effected by detecting, at two spaced locations in the subsequent processing region, a parameter of the crimped yarn which moves with the yarn (13), and measuring the elapsed time between such detections. A method according to claim 2 characterised in that the second velocity measuring step comprises detecting at the two locations a static charge carried by the yarn (13). Apparatus for texturing a yarn and simultaneously monitoring the quality of a crimped yarn produced during the texturing process according to claim 1 characterised by comprising texturing means in a texturing zone operable to insert a crimp in the yarn, first forwarding and tensioning means (21) operable to forward the crimped yarn (13) from the crimping means under a first tension sufficient to draw out the crimp therein, first velocity measuring means (28) operable to measure the velocity (V1) of the crimped yarn (13) whilst it is forwarded under the first tension, second forwarding and tensioning means (23) operable to forward the crimped yarn (13) under a second stabilising tension insufficient to draw out the crimp, second velocity measuring means (30) operable to measure the velocity (V2) of the crimped yarn (13) whilst it is forwarded under the second tension, and calculating means (29) operable to calculate a crimp velocity value (V1 - V2/V1) x 100) from the yarn velocity measurements. Apparatus according to claim 4 characterised in that said first forwarding and tensioning device (21) comprises a yarn feed device (26, 27), and in that the first velocity measuring means (28) is operable to measure the peripheral speed of the feed device (26). Apparatus according to claim 4 or claim 5 characterised by comprising a subsequent processing apparatus and in that said second velocity measuring means (30) comprises detecting means (34) operable to detect at two spaced locations of the subsequent processing apparatus a parameter of the yarn (13) which moves with the yarn (13), and time measuring means (29) operable to measure the elapsed time between such detections. Apparatus according to claim 6 wherein the detecting means (34) comprises a housing (36) defining a path (37) of travel of the yarn (13) therethrough, a pair of measuring stations spaced along the yarn path (37) within the housing (36), and at each measuring station, a sensor (34) adapted to detect the presence of a static electrical charge on the yarn (13) and to produce an electrical signal proportional to the value of such static electrical charge, characterised in that each sensor (34) is electrically connected to an input of an amplifier (38) and then to the calculating means (29), and in that the calculating means (29) is operable to apply a delay to the signal from the first measuring station and to cross-correlate the delayed signal with the signal from the second measuring station. A false twist crimping machine having a plurality of yarn processing stations and characterised in that for each station there is provided an apparatus according to claim 7, and in that the calculating means (29) has signal store means (42) for each of a set of the yarn processing stations, each to receive signals from a respective measuring means (30) wherein the calculating means (29) is operable to cross-correlate the signals from the spaced locations of a measuring means (30) at a first yarn processing station of the set simultaneously with receiving into a respective store of the calculating means the signals from at least one other measuring means (30) at an adjacent yarn processing station of the set and to repeat the operation in sequence for each of the yarn processing stations of the set. A false twist crimping machine according to claim 8 characterised in that four measuring means (30) at adjacent yarn processing stations are adapted to produce signals which are received simultaneously into the respective signal store means (42) of the calculating means (29).

Inventors: EATON, DAVID CHARLES
Applicants: RIETER SCRAGG LIMITED
Application year: 1987
Main classification: G01N33
IPC codes: G01N33, D02G1, B65H61