GB2538495A

GB2538495A - Method and device for monitoring oil borne by a thread

Info

Publication number: GB2538495A
Application number: GB1508240.7A
Authority: GB
Inventors: Charles Eaton David
Original assignee: Saurer Fibrevision Ltd
Current assignee: Saurer Fibrevision Ltd
Priority date: 2015-05-14
Filing date: 2015-05-14
Publication date: 2016-11-23
Also published as: WO2016180682A1; GB201508240D0

Abstract

A method of monitoring oil carried by a moving thread comprises illuminating the thread with light at a frequency which causes the oil to fluoresce and detecting light emitted from the moving thread by fluorescence. Light reflected from the thread may also be detected. A monitoring device has a light source 50 and a light sensor 54 arranged around thread passage 56. The sensor 54 is responsive to light at the frequencies of fluorescence of the oil and unresponsive to light at the frequencies emitted by the source 50. The output of the sensor is processed and calibrated to provide information about the oil borne by the thread. The device is used in manufacture and spinning of threads or yarn making possible real time monitoring of the oil without physical contact with the thread.

Description

METHOD AND DEVICE FOR MONITORING OIL BORNE BY A THREAD

The present invention relates to real time monitoring of oil borne by a thread.

During spinning of synthetic fibres it is commonly necessary to apply an oil to a thread. This oil serves as a lubricant for the thread as it passes through subsequent stages in its processing and can provide a route for earthing of static electricity, certain synthetic fibres being poor conductors. The nature of the oil and the quantity applied can also have an important bearing on the properties of the finished thread or yarn such as its take up of dye. A range of different oils is used depending on the type of fibre and its application, and the oils are variously referred to as "spin finish", "oil pick-up" and "finish on yarn" (FOY).

As an example of a well-known process for manufacture of synthetic fibres, Figure 1 represents in schematic form a fibre spinning machine suitable for manufacture of thread from materials including nylon, polyester, polyethylene and polypropylene. An extruder 10 supplies the relevant material in viscous liquid form via a metering pump 12 to a spin pack 14 which incorporates a spinneret -an extrusion tool typically having multiple small openings through which emerge continuous filaments 16. The filaments are cooled, in this example by quench air from a source 18, and brought together to form a thread 20. Oil is applied to the thread by a lubrication station 22. This application may be by spraying of the oil. Beyond the lubrication station 22 the thread is typically wound onto a drum (not shown).

The illustrated machine is for "melt spinning", in which solid polymer material is heated in a hopper 24 to form the liquid supplied to the extruder 10. However there is a range of different spinning processes including (by way of example and not limitation) dry spinning, wet spinning, gel spinning and electrospinning All of these are familiar to the skilled person, and so will not be described herein, but it must be understood that the present invention is not applicable only to melt spinning processes.

Because of the importance of the oil to the manufacturing process and to the properties of the finished product, it is desirable to measure the quantity of oil carried by the thread. This may for example be important in quality control, and in enabling proper set-up and adjustment of the spinning machine.

There are various techniques for analysing a static sample of thread. For example the oil from a sample may be dissolved in an organic solvent, and then quantified gravimetrically or by use of infra-red spectroscopy. Another approach to static testing relies on nuclear magnetic resonance imaging.

It is desirable however to monitor oil content on a real time basis, while spinning is underway.

This can for example enable faults in the process to be detected when they occur, enabling prompt remedial action, which is greatly preferable to their detection during periodic testing of the finished product, which may take place only after quantities of imperfect thread or yarn have been produced.

A known method of monitoring oil content in real time, developed by the present applicant, is based on continuous measurement of electrical conductivity of the thread, a property which varies with the quantity of oil it carries. In this technique the moving thread is passed over a pair of pins which are separated along the thread's length and by passing an electric current a measurement is made of the resistance between the pins. While effective, this method has the drawback of being reliant on contact with the fast moving thread passing through the spinning machine. This contact may affect the thread adversely and is not acceptable in certain processes.

In accordance with a first aspect of the present invention there is a method of monitoring oil carried by a moving thread, the method comprising illuminating the thread with light at a frequency which causes the oil to fluoresce, and detecting light emitted from the moving thread to provide information relating to the oil.

Preferably the method further comprises resolving the fluoresced, reflected and absorbed components of the optical signal.

The method according to the invention can be carried out without making physical contact with the thread, making it applicable for example to certain high value, delicate and safety-critical materials to which the electrical resistance method has not been applied.

Note that the term "thread" as used herein refers to any suitable fibrous material including a yarn and is not for example limited to a thread to be used for sewing. Note also that the term "oil" refers to any liquid applied to the thread, whether or not it includes hydrocarbons or functions as a lubricant.

In accordance with a second aspect of the present invention, there is a monitoring device for monitoring oil borne by a moving thread, the monitoring device comprising a housing having a through-going passage for receiving the moving thread, a light source which emits light at a frequency that causes the oil to fluoresce and which is arranged to illuminate the thread, and a light sensor arranged to receive and sense light fluorescently emitted by the oil bearing thread while the thread is in the through-going passage.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 is a schematic representation of a fibre spinning machine of known type; Figure 2 is a graph of experimentally measured spectra relating to samples of various oils; Figure 3 is a graph based on the same experimental data as Figure 2 but shows the difference between the spectrum measured with an oil sample present and the spectrum measured without an oil sample present, as will be explained further below; Figure 4 is a bar chart representing the effect of the oils on light intensity in the wavelength band from 400nm to SOOnm; Figure 5 is a plan view of a monitoring device embodying the present invention; Figure 6 is a section through the monitoring device in a longitudinal plane C-C indicated in Figure 5. The scale of Figure 6 is larger than that of Figure 5; Figure 7 is a graph of output of the monitoring device over time in a trial using a moving thread.

The present invention uses measurement of light emitted by fluorescence from oil carried by a thread to provide monitoring of the quantity of that oil. The embodiments described below also serve to measure light reflected from the thread, resolving the fluoresced and reflected components of the resultant signal.

It is known that stimulation of oil with light of suitable frequency causes it to fluoresce, emitting light of a frequency different from the stimulation frequency. Note that the word "light" as used herein is not limited to frequencies in the visible part of the spectrum but includes in particular ultra violet light. Aromatic hydrocarbons in oils are caused to fluoresce in the visible spectrum when stimulated with ultra violet light (although fluorescence is not limited to such molecules). For example stimulating certain oils with light in the ultra violet part of the spectrum (e.g. between 300 and 400 nm wavelength) causes them to fluoresce in the visible part, e.g. between 400 and 500nm.

Figure 2 represents spectroscopic data obtained in experiments conducted by the present applicant. In these experiments a pipette of borosilicate glass was placed in a spectroscope and illuminated with an LED (light emitting diode) light source whose emission spectrum was centred at 365nm with a frequency range of about 15nm to either side of that centre (i.e. 350nm to 380nm). Line 30 represents the measured spectrum when the pipette contained only air, and is seen to be peaked close to the source frequency of 365nm as might be expected. Other lines in the graph represent the results when a range of different oils (and also de-ionised water) were placed in the pipette. While three of the oils tested, indicated in Figure 2 by an arrow 34, show attenuation of the peak around the source frequency, other oils, indicated by arrow 32, show instead -in this particular test -a large increase in the excitation signal -i.e. a higher peak around the source frequency.

The effect of luminescence of the oil is better seen in Figure 3. This shows, to an enlarged scale and for the same selection of oils as Figure 2, the difference between the spectrum measured with the oil present and the spectrum measured with the empty pipette. That is, the empty pipette spectrum values have been subtracted from the values measured with the oil present. This graph shows that in each case there is an increase in frequencies in the 400nm -500nm range, attributed at least in part to fluorescence. Figure 4 represents the average signal increase of the light detected in the 400nm -500 nm wavelength band and makes it clear that all the oils tested show an increase in luminous intensity in this band. This effect is exploited by the present invention.

The monitoring device 40 represented in Figures 5 and 6 is for real time monitoring of the oil carried by a thread during its manufacture. Referring to Figure 1, the monitoring device 40 may for example be mounted in the position represented by an arrow 42, downstream of the lubrication station 22. It has a housing 44 with a though-going thread-passage 46 through which the moving thread passes in use. In operation the thread is typically drawn through the thread-passage 46 at considerable speed (which depends on the manufacturing process involved, but may for example be in the region of 60kph) without making contact with it. The thread-passage 46 has a laterally facing mouth 48 (see Figure 5) to enable the thread to be introduced into it.

A light source 50 is arranged to direct light onto the moving thread within the thread-passage 46. The frequency range of the light from the source is chosen to stimulate fluorescence of the oil. In the present embodiment the light source is an LED emitting in the ultra violet part of the spectrum. More specifically it emits in a narrow band of wavelengths around 365nm.

Other types of light source including diode lasers or lasers of other types could be substituted, but the LED is economical and raises no safety issues, and is capable of providing light in a chosen narrow frequency band. It is mounted in an illumination-passage 52 which communicates with the thread-passage 46 and is in this example inclined to it. The light source 50 incorporates a lens providing a directional beam directed toward a centre line of the thread-passage.

Also mounted in the housing 44 is a first light sensor 54 for detecting light emitted by fluorescence from the oiled thread. According to the present embodiment the first light sensor is a silicon photodiode but other types of light sensor could be substituted. An optical filter could be incorporated, to transmit only selected frequencies to the first light sensor 54.

The first light sensor 54 is intended to respond maximally to the fluorescent emission of the oiled thread and minimally to the light emitted from the source 50. To this end it is mounted in, and receives light through, an elongate detector-passage 56. Axes of both the illumination-passage 52 and the detector-passage 56 are indicated by dotted lines in Figure 6 and it can be seen that they intersect at the centre of the thread-passage 46 so that the first light sensor 54 observes the region of the thread which is maximally stimulated by the light source 50. To minimise the amount of light from the source 50 that reaches the first light sensor 54, the arrangement of the detector-passage 56 with respect to the illumination-passage 52 is such that there is no line of sight between the light source 50 and the first light sensor 54. Hence light cannot travel directly from the light source 50 to the first light sensor 54. In the illustrated embodiment this is because the axes of the illumination-passage 52 and of the detector-passage 56 form an acute angle. Other arrangements are possible in order to achieve this effect. Some of the light from the source 50 will be reflected from the internal walls of the thread-passage 46 or from the thread itself onto the first light sensor 54. To minimise this effect, the orientation of the detector-passage 56 is non-parallel with the expected angle of reflection of light from the source 50 -in the illustrated embodiment the detector-passage 56 is perpendicular to the thread-passage 46 while the illumination-passage 52 is inclined to it.

Also mounted in the detector-passage 56 is a bi-convex lens 58 serving to focus the received light onto the first light sensor 54.

A mirror 60 is arranged to reflect light emitted from the thread by fluorescence onto the first light sensor 54, and so to increase the proportion of the fluorescently generated light that is sensed. In the illustrated embodiment the mirror is at one end of a mirror-passage 62 whose other end communicates with the thread-passage 46. The mirror-passage 62 is on the opposite side of the thread-passage 46 from the detector-passage 56 but coaxial with it. A screw thread or other small scale shaping or roughening of the mirror-passage's internal wall serves to reduce reflection of light within the passage, reducing the amount of light from the source 50 that, by virtue of multiple reflections in the mirror-passage 62, is able to reach the first light sensor 54.

The illustrated monitoring device 40 incorporates a second light sensor 64 intended to respond to reflected light from the source 50. In the present embodiment this takes the form of a silicon photodiode, but again other forms of light sensor could be used, with or without an optical filter to select the required response frequency range. The second light sensor 64 is disposed in a receiver-passage 66 whose axis intersects that of the detector-passage 56 and is aligned with the expected principal angle of reflection of light from the source 50. That is, the inclination of the detector-passage 66 with respect to the axis of the thread-passage 46 is equal and opposite to the inclination of the illumination-passage 52 with respect to the thread-passage 46. In this way reflection of light by the thread onto the second light sensor 64 is expected to be maximised.

The ability of the first and second light sensors 54, 64 to discriminate between reflected light from the source 50 and light generated by fluorescence is not only a result of their physical arrangement, but also of their response frequencies. In fluorescence there is typically a difference between the stimulation frequency and the emission frequency. Hence the response frequency ranges of the first and second light sensors 54, 64 can be chosen to be different. The first light sensor 54 has a response frequency range chosen to include the fluorescent light, and so responds preferentially to that light. That is to say, the first light sensor 54 is responsive to the light generated by fluorescence and at least substantially unresponsive to light from the source 50.

The second light sensor 64 has a response frequency range chosen to include output frequencies of the light source 50 and so responds preferentially to that.

In the present embodiment the first light sensor 54 responds to wavelengths between 400 and 500nm. The second light sensor 64 responds to wavelengths between 300 and 400nm.

The graph forming Figure 7 represents results of a trial of the monitoring device using moving thread. On the vertical axis is the voltage output of the first light sensor 54, whose response band is centred at 450nm. Time is on the horizontal axis, the units being milliseconds. A thread was wound through the monitoring device at a speed of 120 metres per minute. Between 0 and 15 seconds (15000 milliseconds) oil was applied to the thread. Between 15 and 30 seconds no oil was applied. Line 70 represents the direct output of the first light sensor 54, which incorporates appreciable noise. Line 72 was generated by passing that signal through a first order low pass filter which in this example had a cut-off frequency of 1 Hertz. In a practical monitoring device this filter may be implemented either digitally or by means of an analogue circuit such as an RC circuit. Also shown in this graph at 74 is a high pass filtered version of the signal. Note that there is a marked change in the output of the first light sensor 54 when oil ceases to be delivered. This change takes the form of a reduction in the output signal, as expected.

Note also that the low pass filtered signal 72 varies in a roughly periodic manner while the oil is being applied. This is attributed to a periodic variation in the rate of application of oil due to the nature of the pump used to supply it. A gear pump is often used for this purpose and its output rises and falls during each revolution of its gears. The resultant modulation can be used to improve the ratio of signal to noise by filtering to select that part of the light sensor's output which is modulated at the relevant frequency. A combination of a low pass filter and a high pass filter can be used to define a suitable passband (practically of course these may be combined in a band-pass filter). The high pass filter's cut-off frequency is selected by reference to the pump used but a frequency of the order of 5 Hz has been found to be suitable in certain practical applications. The filter may be digitally implemented but very well-known analogue circuitry may instead be used. One example of a suitable band-pass filter is the RLC circuit, whose details will be well known to the skilled person and will not be described herein.

Other signal processing techniques may additionally or alternatively be applied. In particular a comparison may be made between the outputs of the first and second light sensors 54, 64 and the determination of oil quantity borne by the thread may be based upon that comparison. In this way factors such as change in light output level from the source 50 (e.g. due to deposit of oil within the monitoring device 40) may be allowed for.

Calibration may be carried out by comparing the outputs of the monitoring device 40 against oil content data from another source (e.g. from one of the static testing processes referred to above). Thus the monitoring device 40 may provide data from which a quantitative measurement can be made of the oil, e.g. in terms of milligrams of oil per metre of thread.

The above described embodiments are presented by way of example and not limitation.

Numerous variations are possible within the scope of the present invention. For example while the light source 50 is an LED in the embodiments, an alternative would be to use a laser. This could be a laser diode. While the source used in the embodiments has an emission spectrum centred at 365 nm, it is possible that a slightly shorter wavelength, in the region of 340nm, would produce stronger fluorescence. LEDs having suitable wavelengths are commercially available and could be adopted.

Claims

CLAIMS1. A method of monitoring oil carried by a moving thread, the method comprising illuminating the thread with light at a frequency which causes the oil to fluoresce, detecting light emitted from the moving thread by fluorescence to provide an output signal, and processing the output signal to provide information relating to the oil.
2. A method as claimed in claim 1 in which the thread is illuminated with light in the ultra violet part of the spectrum.
3. A method as claimed in claim 1 or claim 2 in which the detected light is in the visible part of the spectrum.
4. A method as claimed in any preceding claim in which the processing of the output signal includes low pass filtering.
5. A method as claimed in any preceding claim carried out in real time during spinning of a synthetic thread.
6. A method as claimed in claim 5 in which a pump is used to deliver the oil to the moving thread, the pump having an output which varies periodically and the output signal being filtered to select components modulated at the frequency of variation of the pump output.
7. A method as claimed in any preceding claim which further comprises detecting light reflected from the thread to provide a further output signal.
8. A monitoring device for monitoring oil borne by a moving thread, the monitoring device comprising a housing having a through-going passage for receiving the moving thread, a light source which emits light at a frequency that causes the oil to fluoresce and which is arranged to illuminate the thread, and a light sensor arranged to receive and sense light fluorescently emitted by the oil bearing thread while the thread is in the through-going passage.
9. A monitoring device as claimed in claim 8 in which the light source has an emission spectrum, the light sensor has a response spectrum, and the emission spectrum and the response spectrum are at least substantially non-overlapping.
10. A monitoring device as claimed in claim 8 or claim 9 in which the light sensor responds preferentially to light in a predetermined band which contains wavelengths longer than 400nm.
11. A monitoring device as claimed in any of claims 8 to 10 in which the light emitted by the source is at least substantially limited to frequencies below 400nm.
12. A monitoring device as claimed in any of claims 8 to 11 in which the light source is a narrowband source whose output spectrum is centred on a wavelength between 330 and 375 nm.
13. A monitoring device as claimed in any of claims 8 to 12 in which the arrangement of the light source and the light sensor is such that there is no line of sight from one to the other.
14. A monitoring device as claimed in any of claims 8 to 13 further comprising a reflector arranged to reflect light emitted from the oil bearing thread onto the light sensor.
15. A monitoring device as claimed in any of claims 8 to 15 comprising a second light sensor responsive to the light emitted by the light source and arranged to receive light reflected from the thread.
16. A monitoring device as claimed in any of claims 8 to 15 provided with a low pass filter arranged to filter an output of the light sensor.
17. A monitoring device as claimed in any of claims 8 to 15 provided with a filter which receives an output signal from the light sensor and selects frequency components of it in a filer passband which lies between 0.5 and 50 Hertz.
18. A fibre spinning machine provided with a monitoring device as claimed in any of claims 8 to 17.
19. A monitoring device substantially as herein described with reference to, and as illustrated in, accompanying Figures 5 and 6.
20. A method of monitoring oil borne by a moving thread substantially as herein described with reference to, and as illustrated in, accompanying Figures 2 to 7.