METHOD AND APPARATUS FOR DETECTING CONTAMINANTS IN TEXTILE MATERIAL

The invention relates to an apparatus and a method for detecting foreign substances in a textile material, in particular for detecting the presence of contaminants in particular in a flow of pieces like fibre chunks of the textile material or in a strand¬like material such as a yarn, sliver or roving as described in the preamble of the 5corresponding independent claims.

BACKGROUND OF THE INVENTION

WO .2007/010 325 discloses an apparatus and measurement method for detecting 10foreign substances in a strand-like textile material, comprising a visible light source and an infrared light source, and correspondingly, a visible light and an infrared light detector both measuring light reflected from the textile material and possibly from a contaminant in the material. A weighted difference of the two detector signals is determined. A contaminant is considered to be detected when this weighted difference exceeds a threshold value.

WO 03/008950 shows a device emitting light at two different wavelengths, and having a single light receiver. Since the dependency of reflection on wavelength differs according to material, the amount of total reflected light depends on the presence and the kind of contaminant material. In this manner, it should be possible to distinguish between different contaminants.

US 5,915,279 shows a measurement setup for detecting parameters of an object in general terms. A polychromatic light source emitting light of at least two different wavelengths, and a plurality of detectors for different colour bands are used. Methods for the statistical analysis of a plurality of parameters are described, e.g. light intensities detected at different wavelengths, and including time histories of
intensities in order to determine deviations. However, the resulting algorithms are complicated and too general to be immediately applicable.

EP 0 652 432 A1 discloses the use Of sensors for two wavelengths, with the optical arrangement ensuring that the light received by the sensors comes from exactly the same location of the yarn. The light received may lie in the infrared or near-infrared spectrum. From the detector signals corresponding to received intensities, a signal corresponding to a quotient (i.e. a difference of logarithms) is formed, in order to eliminate the influence of yarn diameter, structure etc.

GB 2461967 and GB 2461371 show the detection of plastic, such as polypropylene or polyethylene contaminants by means of simultaneously illuminating a textile material with UV light and with polarized light. A CCD colour camera observes the textile material. It is not sensitive to the polarized light or to UV light. Only when the polarisation is changed by a contaminant, when passing through the textile material,
or when fluorescence causes the UV light to be reflected in the visible spectrum, does the camera detect a signal and thus indicate the presence of a contaminant.

EP 0 545 129 B1 discloses the detection of polypropylene contaminants in laps of silk by comparing two camera images taken with polarised light and with light. The images are taken separately, such that the textile material must be stopped.

It is desirable to provide a contaminant detection method and apparatus which allow for a more detailed discrimination of contaminant types.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide an apparatus and a method for detecting foreign substances in a textile material which is simple in construction and detects the most difficult contaminants in the textile material. A further object is to deter¬mine the material of numerous types of contaminants. A further object of the inven¬tion is that the contaminant detection is suited for continuous, intermittent flow rates at varying volumes.

These and further objects are achieved by an apparatus and a method for detecting foreign substances in a textile material according to the corresponding independent claims.

The method thus is for detecting foreign substances in a textile material, in particular in a flow of pieces of the textile material or in a strand-like material such as a yarn, sliver or roving. The method uses at least one detection arrangement comprising a visible light source, an IR (infrared) light source and a UV (ultraviolet) light source, and at least one detector sensitive to light in the visible spectrum and the IR spectrum, the light sources being arranged to illuminate a portion of the textile material and the detector being arranged to measure light reflected from the textile material and to generate a corresponding detector signal, the method comprising the repeated execution of the steps of illuminating the same section of the textile material sequentially with at least two different illumination conditions, each illumination condition corresponding to one or more of the three light source emitting and the others not emitting (in other words, the light sources are used to emit light alone or in combination; that is, either only one of the light sources is active at a given instant, or only two or all three light sources are active at a given instant);

• measuring light reflected from and/or transmitted by the textile material by means of the at least one detector;

• determining, for each of the different illumination conditions, a corresponding detector signal;

• computing, from the resulting detector signals, secondary signals;

• from the detector signals and the secondary signals, detecting the presence of contaminants and, when a contaminant is detected, generating a signal that is indicative of the presence of a contaminant.

The light sources are arranged to illuminate a portion of the textile material as it is transported past the detection arrangement.

The term "contaminant" denotes foreign material, that should be removed from the base material, which typically is cotton. Contaminants may be of different types, mainly plastic or paper or others, such as colourless paper, seeds, jute, hair, strings, cloth etc.

The term "sequentially" indicates that the light sources are controlled to emit or not to emit light, giving rise to the different illumination conditions as a temporal sequence at essentially the same location along the textile material. In other words: the measurement is accomplished by observing the same section of the textile material, at essentially the same location. Therein, the switching rate between different illumination conditions preferably is so high that the distance travelled by the textile material does not substantially affect the detector signals. Alternatively, the step of illuminating the same section of the textile material sequentially is accomplished with more than one single detector or set of detectors that are placed at different locations along the transport direction of the textile material. Thereby, in the steps of computing the secondary detector signals and detecting the presence of contaminants, the time difference that the textile material takes to travel between the different locations is taken into account.

With two or more detection arrangements arranged along the textile material, and observing the textile material from different sides, the signal analysis and optionally the control of contaminant removal can be done independently, or by taking the material speed dependent time difference into account and combining the measurements. In the latter case, it becomes possible to combine information on the same contaminant seen from different sides.

In each case thus, the detector signals being analysed together represent observations of the same section of the textile material being transported past the detection arrangement(s), with the observations being made virtually at the same time, or at different times but then shifted relative to one another.
The signal that is indicative of the presence of a contaminant can optionally be used to activate a removal device. For example, if the material being observed is a flow of cotton chunks, then the removal device may be a blow-out device or a suction device. If the material is a yarn or the like, then the removal device may cut out the section containing the contaminant.

In one variant of the method, it comprises the further step of classifying the contaminants and generating a signal that is indicative of the type of a contaminant. This can be done by comparing the values of the signals with, for each signal, one or more different threshold values.

In one variant of the method, the step of illuminating the textile material comprises generating at least three different illumination conditions and determining, for each illumination condition, corresponding detector signals,, and preferably also the secondary signals.
In one variant of the method, it comprises

• determining, for each detector signal and secondary signal at least two corresponding bands in which the values of the signal can lie;

• determining, at a given instant in time, depending on which of their corresponding bands the values of the signals lie in, whether a contaminant Is present or not.

The bands can be defined by corresponding upper and/or lower limits, and determining whether a signal value lies in a given band can.be done by comparing the signal value with the limits. Relating a plurality of signals with their corresponding bands or limits can be done by first determining, for each signal, the band it lies in, and the comparing this combination of bands with stored combinations of bands, each stored combination corresponding to one or more types of contaminants. Alternatively, the comparison of signals with bands or limits can be done through a decision tree, comparing one signal after the other, thereby sequentially eliminating more and more combinations, until one is left, or no matching combination has been found, corresponding to no contaminant being present.

In one variant of the method, the different illumination conditions comprise

• visible light and UV light being emitted simultaneously, the resulting detector signal being labelled "Visible plus UV" signal henceforth;
and

• IR light and UV light being emitted simultaneously, the resulting detector signal being labelled "IR plus UV" signal henceforth.

In one variant of the method, the step of illuminating the textile material comprises using at least the four following different illumination conditions:

• UV light being emitted alone, the resulting detector signal being labelled "UV" signal henceforth;

• IR light being emitted alone, the resulting detector signal being labelled "IR" signal henceforth;

• visible light and UV light being emitted simultaneously; and

• IR light and UV light being emitted simultaneously.

In one variant of the method, the step of computing secondary signals comprises computing at least the following secondary signals:

• change (AUV) in "UV" signal with respect to uncontaminated textile material;

• difference between "Visible plus UV" signal and "IR plus UV" signal;

• ratio (AUV/AIR) of the change (AUV) in "UV" signal with respect to uncontaminated textile material to the change (AIR) in "IR" signal with respect to uncontaminated textile material.

In each case, reference values corresponding to the uncontaminated textile material or simply base material, can be determined by manual, off-line measurement, or by continuously calculating and updating a long term -average signal value, "long term" in this context means a configurable continuous moving average of the signals of the uncontaminated textile material based on material flow rates. The window size for the moving average may be, for example, equal to or larger than 50, 100, 200, 500 or
1000 data points. Standard signal analysis procedure such as outlier removal may be used.

In one variant of the method, the detection and classification of contaminants is done according to table 1.

In one variant of the method, the step of illuminating the textile material comprises using at least the three following different illumination conditions and corresponding detector signals:

• UV light being emitted alone, the resulting detector signal being labelled "UV" signal henceforth;

• IR light being emitted alone, the resulting detector signal being labelled "IR" signal henceforth;

• visible light being emitted alone, the resulting detector signal being labelled "VL" signal henceforth.

In one variant of the method, the step of computing secondary signals comprises computing at least the following secondary signals:

• change (AUV) in "UV" signal with respect to uncontaminated textile material;

• change (AIR) in "IR" signal with respect to uncontaminated textile material;

• change (AVL) in "VL" signal with respect to uncontaminated textile material;

• difference between "VL" signal and "IR" signal;

• ratio (AUV/AIR) of the change (AUV) in "UV" signal with respect to uncontaminated textile material to the change (AIR) in "IR" signal with respect to uncontaminated textile material.

In a further variant of the method, the step of computing secondary signals comprises computing, as secondary signal, the difference between "IR" signal and "UV" signal;

In one variant of the method, the detection and classification of contaminants is done according to table 2.

In one variant of the method, for all the different illumination conditions, a single detector is used to generate the detector signal, or using a set of two or more detectors having the same spectral sensitivity and operating in parallel to generate the detector signal.

In one variant of the method, the detector is sensitive to light both in the visible and in the IR range.

In one variant of the method, the step of illuminating the same section of the textile material sequentially is accomplished with a single detection arrangement.. This single detection arrangement operates by rapidly switching the light sources to create the different illumination conditions, with a switching frequency high enough to ensure that the textile material has not travelled a significant distance between the observations made under the different illumination conditions. In other words, it is the same section of the textile material that is observed by the detection arrangement under the sequential, different illumination conditions, and this happens at a single location along the path of the textile material. If the textile material is transported along a material flow duct, then this location is a single location along the duct. If the textile material is a strand-like material, then this location is a single location along the path of the strand-like material. The detector signals from this single detection arrangement are used to compute the secondary signals. It may well be, according to this variant, that there are two or more detection arrangements operating, at separate locations along the path of the textile material, observing, for example, the textile material from different sides. However, each of these detection arrangements can operate autonomously in the manner described and can compute secondary signals without taking detector signals from the other detection arrangements into account.

In another variant of the method, the step of illuminating the same section of the textile material sequentially is accomplished with at least two detection arrangements located at separate locations along the path of the textile material, and preferably observing the textile material from the same side. Herein, the detector signals from the at least two detection arrangements are combined in order to compute the secondary signals, taking into account the time the material takes to travel between the separate locations of the detection arrangements. So in-this variant, the temporal sequence of measurements corresponds to a spatial sequence of the measurement locations and of the detection arrangements.

The apparatus is for detecting foreign substances in a textile material, in particular in a flow of pieces of the textile material, or in a strand-like material such as a yarn, sliver or roving. The apparatus comprises at least one detection arrangement, the at least one detection arrangement comprising a visible light source, an IR (infrared) 1ight source and a UV (ultraviolet) light source, and at least one detector sensitive to light in the visible spectrum and the IR spectrum, the light sources being arranged to
illuminate a portion of the textile material and the detector being arranged to measure light reflected from the textile material and to generate a corresponding detector signal. In the apparatus the three light sources are arranged to illuminate the same section of the textile material and are controlled by a controller to do so sequentially with at least two different illumination conditions, each illumination condition corresponding to one or more of the three light sources emitting and the others not emitting;
the detector is arranged to measure light reflected and/or radiated from and/or transmitted by the textile material;

• the detector is arranged to determine, for each of the different illumination conditions,, a corresponding detector signal;

• a signal evaluation system is configured to compute, from the resulting detector signals, secondary signals;

• the signal evaluation system is configured to detect, from the secondary signals and the detector signals, the presence of contaminants and to generate, when the presence of a contaminant is detected,

a signal that is indicative of the presence of the contaminant.

Further embodiments are evident from the dependent patent claims. Features of the method claims may be combined with features of the apparatus claims and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings, in which:

Figure 1 schematically shows a material flow duct with detection arrangements; Figure 2-11 shows detector responses under three illumination conditions for different contaminants, and in particular for the contaminant being Figure2 plastic, white, fluorescent; Figure 3 plastic, white, non-fluorescent; Figure 4 plastic, coloured, fluorescent; Figure 5 plastic, coloured, non-fluorescent; Figure 6 plastic, transparent, fluorescent; Figure 7 plastic, transparent, non-fluorescent; Figure 8 paper, white, fluorescent; Figure 9 paper, white, non-fluorescent, Figure 10 other contaminants, fluorescent; Figure 11 other contaminants, non-fluorescent; Figure 12 shows generic signal bands and limits used in signal analysis.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION
Figure 1 schematically shows an apparatus for detecting contaminants in a textile material, which in this example are chunks of cotton. The textile material 1 is transported along a material flow duct 10. One or more detection arrangements 12 are arranged to detect contaminants 11 in the textile material 1 as it passes along the material flow duct 10. Each detection arrangement 12 comprises a first light source 2 for emitting visible light, a second light source 3 for emitting IR light in the infra red spectrum and a third light source 4 for emitting UV light in the Ultra violet spectrum. The three light sources are arranged in such a way that the textile material 1 is illuminated by the three light sources through a source optical arrangement 5. The source optical arrangement 5 as illustrated comprises separate lenses or lens systems for the different light sources, but in other embodiments one or more lenses or light focusing elements can be shared by one or more of the light sources. The amount and the spectral distribution of light reflected or radiated off the textile material 1 depends on the amount and spectral distribution of the light from the three light sources, and on the nature of the textile material 1 and any contaminants 11. This reflected / radiated light is collected through a detector optical arrangement 6 and passed to the detector 7. The detector optical arrangement 6 may share one or more optical elements with the source optical arrangement 5. A signal evaluation system 8 receives a raw signal from the detector 7. For each detector, the signal is representative of the light received by the detector 7. A controller 9 is arranged to control the light sources, for example, turning them on and off such that they illuminate the flow of textile material 1 alone or in combination, that is, at the same time. Preferably, the light sources are turned off by controlling their electric supply. However, other means such as electro-optic (liquid crystal) filters or shutters for controlling light transmission, mechanical shutters for blocking or transmitting light, or rotating mirrors or prisms can be used as well. Such rotating elements also may be used to scan across the width of a material flow duct. Any such other means controlling emission of light shall, in the following, also considered to be part of the light source. Each combination of particular light sources being emitting or non- emitting shall be called an illumination condition. The controller 9 indicates to the signal evaluation system 8 which light sources are active, and accordingly the signal evaluation system 8 determines different detector signals according to different illumination conditions. The signal evaluation system 8 is configured to analyse the different detector signals separately or in combination to determine the presence of contaminants in the textile material, and optionally to classify, the contaminant according to type.

A switching frequency for generating the different illumination conditions is preferably high enough such that the textile material 1 does not travel a significant distance between observations by the same detection arrangement 12 under different illumination conditions. Depending on the speed of the textile material 1 as it passes the detection arrangement 12, the switching frequency can be in the range of one kHz to one or more MHz. In an embodiment, the switching frequency lies in the range of kHz to 100 kHz.

The procedure comprising generating the different illumination conditions, measuring the detector signals, computing the secondary signals and detecting and optionally classifying contaminants etc. is repeated at sufficient measurement frequency according to the speed of the travelling textile material 1, for example at more than 100 Hz. In an embodiment, the measurement frequency lies in the range of 5 kHz to 25 kHz.

The measurement frequency typically equals the light switching frequency divided by the number of different illumination conditions per measurement.

In the embodiment shown, two separate detection arrangements 12 are arranged along the length of the material flow duct 10, observing the flow of cotton chunks 1 from opposing sides. In other embodiments, there is only one such detection arrangement 12, or there are more, e.g. distributed around the material flow duct 10.

The detection arrangements 12 shown are staggered along the length of the material flow duct 10 in order to avoid interference of the light sources and detectors. In other embodiments the detection arrangements 12 be located closer to one another or at essentially the same location along the material flow duct 10. In this case, the controllers 9 may be synchronised such that only the light sources of one of the detection arrangements 12 are emitting at any given time. Here and in general, the controllers 9 of separate detection arrangements 12 can be implemented as a single common controller. The same holds for the signal evaluation system 8.

Similar detection arrangements 12 for observing a strand-like textile material such as a yarn, sliver or roving etc, can be structured and operated in essentially the same manner as that of Figure 1. They will differ in the manner in which contaminants are removed from the flow of textile material 1, and preferably also differ in the source and detector optical arrangements 5, 6. For example, these optical arrangements may be focused on an object being observed, or may have a spread out, wider angle of emission or detection, respectively, consequently illuminating/observing an entire region e.g. of a material flow duct 10.

In the embodiment shown, there is one detector 7 in each detection arrangement 12, returning a single detector signal. There may, alternatively, be several physically separate detectors observing the textile material 1 from different viewpoints, giving the combined sensors a wider field of view. The signals of these separate sensors are combined either on the hardware level or later, after digitisation, thereby for example returning a single (combined) detector signal which then is processed in the same manner as the signal from the single detector 7.

In an embodiment, the detector 7 is sensitive to light both in the Infrared and visible range. Alternatively, separate sensors for the different ranges may be present, with their signals being combined. As a rule, IR light reflected off the textile material 1 remains in the IR range, visible light remains in the visible range, but UV light by fluorescence is returned as visible light.

The controller 9 and the signal evaluation system 8 are synchronised, such that the signal evaluation system 8 knows which illumination condition currently is in effect.

From this information the signal evaluation system 8, as the illumination conditions are brought about repeatedly at high frequency, separately collects detector signals associated with each of the repeatedly effected illumination conditions. This results in separate sequences of detector signals for each illumination conditions. Such signal sequences thus can be

- for illumination conditions in which only one source is emitting: "UV" signal, "IR" signal, "VL" (visible light) signal;

- for illumination conditions in which two sources are emitting, for example, "Visible plus UV" signal or "IR plus UV" signal.

From these sequences, secondary signals are computed. Such secondary signals are,
for example one or more of:

- change AUV in "UV" signal with respect to a base reference for this signal, (the base reference corresponding to the uncontaminated base textile material);

- change AIR in "IR" signal with respect to a base reference for this signal;

- change AVL in "VL" signal with respect to a base reference for this signal;

- difference between "VL" signal and "IR" signal;

- difference between "Visible plus UV" signal and "IR plus UV" signal;

- ratio AUV/AIRof AUVto AIR;

- difference between "IR" signal and "UV" signal.

The base reference for each of the signals is, for example, obtained by manual measurements or from a long term average of the respective signal.

It has been determined by experiment and analysis that certain choices of detector signals and secondary signals, and certain combinations of these signals, are particularly useful in detecting and optionally also classifying contaminants.

Major contaminant types are categorised below. In each case, a further differentiation can be made into categories corresponding to fluorescent and non-fluorescent material.

1. Plastics

a. white
b. coloured
c. transparent

2. Paper

a. white

3. Other types of contaminants (coloured or colourless)

a. paper
b. jute
c. hair
d. string
e. cloth
etc

The Figures 2-11 show the trajectory of three selected detector and secondary signals, the "UV" signal, the "IR plus UV" signal and the "Visible plus UV" signal. The following examples use these signals and also further signals not illustrated.

According to one embodiment, detector signals and secondary signals are correlated with the different contaminant types according to table 1. The table is structured as follows: Each row represents one of the types of contaminants listed above, subdivided into fluorescent and non-fluorescent categories. The first column references the Figure with exemplary signals corresponding to this type. The second and third column indicate the type and category. The remaining columns give, for the three signals used

- ΔUV,

- difference between "Visible plus UV" signal and "IR plus UV", and

- ratio ΔUV/ΔIR of ΔUV to ΔIR

criteria regarding the contaminant type and category of which hold for these signals. Each criterion is satisfied if the signal falls into a range of values corresponding to the criterion.

In order to simplify the explanation, the values for each of the signals are considered to fall into one of five different bands. For some of the signals, less bands are required, which can be described as the union of two or more of the five bands mentioned. The bands are defined around a base value, also called reference value, which can have a value of zero or another value. For each signal, the base value is the
average value of the signal for the uncontaminated textile material. The base value depends on the type of the signal and on any optional scaling, normalising, offset compensation etc. performed in determining the signal.

- tolerance band: values lie near the base value, within an upper tolerance limit and a lower tolerance limit around the base value.

- upper band: values lie above the tolerance band but are smaller than a top limit

- top band: values he above the top limit

- lower band: values lie below the tolerance band but are larger than a bottom limit

- bottom band: values lie below the bottom limit

For some cases, a further sub-band is defined:

- lower part of the upper band: values lie above the tolerance band but are smaller than a first top limit. This lower part of the upper band is thus separated from an upper part of the upper band by the "first top limit".

Figure 12 shows generic signal bands and limits used in signal analysis, as described above. For some of the signals, all of the bands and limits are used, for some, only a subset. The values of the limits (or threshold values) defining the different bands depend, of course, on the type of signal and on the material. That is, for each of the signals, the values for the limits usually are different. The limits can be determined by experiment as absolute values or as values relative to the base references and/or be
adapted according to measurements and updates of the base reference for the corresponding signals.
The limits are not necessarily symmetric relative to the base value or zero value.

It is evident that in order to determine whether a particular signal value lies within a particular band, this is done by comparing the signal value to the limits pertinent for the signal.

Based on table 1 or table 2, various embodiments may be realized which operate in a logically equivalent manner. That is, if for a particular row and with the signals considered, the signals all lie within the bands specified in that row, then that contaminant can be considered to be present.

In some cases, depending on the table used and on which signals are considered, it may not always be possible to differentiate between different types of contaminants.

For example, whereas the signals listed in table 1 do not allow to discriminate between white plastics and white paper, the signals listed in table 2 allow to do so.

Thus, in an embodiment, the signal AIR and optionally also the difference between VL and IR is used to distinguish white paper from white plastics.

If for none of the rows all signals lie within the bands specified in that row, then no contaminant has been detected.

In other words, table 1 can be expressed in words by stating that

- for the signal ΔUV, henceforth called S1, a top, upper, lower and bottom band are defined

- for the signal "difference between (VL+UV) and (IR+UV)", henceforth called S2, a top, lower part of an upper band, tolerance, lower and bottom band are defined;

- for the signal AUV/AIR, henceforth called S3, a top, upper, tolerance, and lower band are defined;

- a contaminant is detected if

• S1 lies in its top band AND S2 lies in its top band AND S3 lies in its top band (the contaminant being white fluorescing plastic or white fluorescing paper); OR

• SI lies in its lower or bottom band AND S2 lies in its top band AND S3 lies in its tolerance or lower band (the contaminant being white non-fluorescing plastic or white non-fluorescing paper); OR

• SI lies in its upper or top band AND S2 lies in its tolerance band AND S3 lies in its top band (the contaminant being coloured fluorescing plastic); OR

• etc. ...

... according to the remaining rows of table 1;

- otherwise, if none of the above conditions is satisfied, no contaminant is detected.

The comparison of signal values with limits according to the tables can be implemented in many different ways, for example by a microprocessor, a DSP (digital signal processor), a customizable integrated circuit such as an ASIC (application specific integrated circuit) or an FPGA (field programmable gate array),
an analog circuit, etc.

Table1

According to one embodiment, detector signals and secondary signals are used to detect the presence of contaminants and optionally classify the contaminants according to the different contaminant types according to table 1.

According to another embodiment, detector signals and secondary signals are used to detect the presence of contaminants and optionally classify the contaminants according to the different contaminant types according to table 2. In a first variant of this embodiment, only the signals ΔVL, ΔIR, ΔUV, difference between VL and IR and ΔUV/ΔIR are used. In another variant, the difference between IR and UV is used as well. For both variants, table 2 can be expressed in words in the same manner as done above for table 1.

Table 2

Note: the bands denoted "lower part of upper band, and below" and "tolerance and below" include all values below the bands named, including negative values, that is the tolerance, lower and bottom band.

In all embodiments, the use of multiple signals, that is, of detector signals and secon- dary signals, allows to compensate for variations in the textile material that, using fewer signals, would look the same as signal variations caused by contaminants. For example, using the IR signal in combination with the UV signal and/or the VL signal allows to differentiate between small contaminants and large cotton chunks or tufts.

The wavelength of visible light is considered to be from 390 nanometres (nm) to about 740 nm. The range of infrared light is considered to be from 700 nm or 740 nm to 1400 nm. The range of ultraviolet light is considered to be from 254 nm to 390 nm

While the invention has been described in present embodiments, it is distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practised within the scope of the claims.

When signals are described as being added, it is understood that the signals that are added are related to the raw sensor signals by a scale factor. This scale factor includes scaling by analog amplifiers, Analog to Digital converters, scaling of digitised signal values, etc. and can include a manually or automatically adjustable scaling factor that brings the signals being added into a comparable signal range.

Similarly, the intensity of the light sources 2, 3, 4 can be adjusted relative to one another in order to ensure that detector signal corresponding to illumination with one or more of the light sources lie in a comparable signal range.

LIST OF DESIGNATIONS

1 textile material 7 detector 2 visible light source 308 signal evaluation system 253 IR light source 9 controller 4 UV light source 10 material flow duct 5 source optical arrangement 11 contaminant
6detector optical arrangement 12 detection arrangement

PATENT CLAIMS

1. A method for detecting foreign substances in a textile material (1), in particular in a flow of pieces of the textile material or in a strand-like material such as a yarn, sliver or roving, the method using at least one detection arrangement (12), the at least one detection arrangement (12) comprising a visible light source (2), an ER. (infrared) light source (3) and a UV (ultraviolet) light source (4), and at least one detector (7) sensitive to light in the visible spectrum and the IR spectrum, the light sources being arranged to illuminate a portion of the textile material and the detector (7) being arranged to measure light reflected from the textile material (1) and to generate a corresponding detector signal, the method comprising repeatedly executing the steps of

• illuminating the same section of the textile material (1) sequentially with at least two different illumination conditions, each illumination condition corresponding to one or more of the three light sources
emitting and the others not emitting;

• measuring light reflected and/or radiated from and/or transmitted by the textile material (1) by means of the at least one detector (7);

• determining, for each of the different illumination conditions, a 20 corresponding detector signal;

• computing, from the resulting detector signals, secondary signals;

• from the detector signals and the secondary signals, detecting the presence of contaminants (11) and, when a contaminant is detected, generating a signal that is indicative of the presence of a contaminant (11).

2. The method of claim 1, comprising the further step of classifying a contaminant (11) and generating a signal that is indicative of the type of a contaminant (11).

The method of claim 1 or 2, wherein the step of illuminating the textile material (1) comprises generating at least three different illumination conditions and determining, for each illumination condition, corresponding detector signals.

The method of claim 1 or 2 or 3, comprising

• determining, for each detector signal and secondary signal at least two corresponding bands in which the values of the signal can lie;

• determining, at a given instant in time, depending on which of their corresponding bands the values of the signals lie in, whether a contaminant is present or not.

The method of one of the preceding claims, wherein the different illumination conditions comprise

• visible light and UV light being emitted simultaneously, the resulting , detector signal being labelled "Visible plus UV" signal henceforth; and

• IR light and UV light being emitted simultaneously, the resulting detector signal being labelled "IR plus UV" signal henceforth.

The method of claim 5, wherein the step of illuminating the textile material (1) comprises using at least the four following different illumination conditions:

• UV light being emitted alone, the resulting detector signal being labelled "UV" "signal henceforth;

• IR light being emitted alone, the resulting detector signal being labelled "IR" signal henceforth;

• visible light and UV light being emitted simultaneously; and

• IR light and UV light being emitted simultaneously.

The method of claim 6, wherein the step of computing secondary signals comprises computing at least the following secondary signals:

• change (AUV) in "UV" signal with respect to uncontaminated textile material;

• difference between "Visible plus UV" signal and "IR plus UV" signal;

• ratio (AUV/AIR) of the change (AUV) in "UV" signal with respect to uncontaminated textile material (1) to the change (AIR) in "IR" signal with respect to uncontaminated textile material (1).

8. The method of claim 7, wherein the detection and classification of contaminants
(11) is done according to table 1.

9. The method of one of claims 1 to 4, wherein the step of illuminating the textile material (1) comprises using at least the three following different illumination conditions and corresponding detector signals:

• UV light being emitted alone, the resulting detector signal being labelled "UV" signal henceforth;

• IR light being emitted alone, the resulting detector signal being labelled "IR" signal henceforth;

• visible light being emitted alone, the resulting detector signal being labelled "VL" signal henceforth.

10. The method of claim 9, wherein the step of computing secondary signals comprises computing at least the following secondary signals:

• change (AUV) in "UV" signal with respect to uncontaminated textile material;

• change (AIR) in "IR" signal with respect to uncontaminated textile material;

• change (AVL) in "VL" signal with respect to uncontaminated textile material;

• difference between "VL" signal and "IR" signal;

• ratio (AUV/AIR) of the change (AUV) in "UV" signal with respect to uncontaminated textile material to the change (AIR) in "IR" signal with respect to uncontaminated textile material.

11. The method of claim 10, wherein the step of computing secondary signals comprises computing at least the following additional secondary signal:

• difference between "IR" signal and "UV" signal.

12. The method of claim 10 or claim 11, wherein the detection and classification of contaminants (11) is done according to table 2.

13. The method of one of the preceding claims with, for all the different illumination conditions, using a single detector (7) to generate the detector signal, or using a set of two or more detectors (7) having the same spectral sensitivity and

operating in parallel to generate the detector signal.

14. The method of one of the preceding claims, wherein the detector (7) is sensitive to light in the visible and in the ER. range.

15. The method of one of the preceding claims, wherein the step of illuminating the same section of the textile material (1) sequentially is accomplished with a single detection arrangement (12).

16. An apparatus for detecting foreign substances in a textile material (1), in particular in a flow of pieces of the textile material, or in a strand-like material such as a yarn, sliver or roving, the apparatus comprising at least one detection arrangement (12), the at least one detection arrangement (12) comprising a visible light source (2), an IR (infrared) light source (3) and a UV (ultraviolet) light source (4), and at least one detector (7) sensitive to light in the visible spectrum and the IR spectrum, the light sources being arranged to illuminate a portion of the textile material and the detector (7) being arranged to measurelight reflected / radiated from the textile material (1) and to generate a
corresponding detector signal,

• the three light sources being arranged to illuminate the same section of the textile material (1) and being controlled by a controller (9) to do sosequentially with at least two different illumination conditions, each illumination condition corresponding to one or more of the three light sources emitting and the others not emitting;

• the detector (7) being arranged to measure light reflected and/or radiated from and/or transmitted by the textile material (1);

• the detector (7) being arranged to determine, for each of the different illumination conditions, a corresponding detector signal;

• a signal evaluation system (8) being configured to compute, from the resulting detector signals, secondary signals;

• the signal evaluation system (8) being configured to detect, from the secondary signals and the detector signals, the presence of contaminants (11) and to generate, when the presence of a
contaminant is detected, a signal that is indicative of the presence of the contaminant (11).