FIELD OF THE INVENTION

The present invention lies in the field of detecting contaminants in a raw fibre material, such as cotton fibers.

According to a first aspect, the present invention relates to a device and method of illuminating over the static and/or dynamic raw fibre material for detecting contaminants in the raw fibre material of a contamination cleaning device.

According to a second aspect, the invention relates to a device and method of detecting contaminants by a detector arrangement of a contamination cleaning device.

BACKGROUND OF THE INVENTION

Contaminants in a raw fibre material are highly dangerous in the textile manufacturing process. Problems due to contaminants like interference in process, poor fabric appearance, quality rejections etc. adds burden to any textile manufacturer.

Detecting contaminants are usually done in the spinning process either in cotton opening state or after yam is formed. Removing contaminants from yam is effective, but the yam waste is a major loss to spinners. Removing contaminants in cotton stage itself to a maximum extent is most preferable to achieve a profitable spinning. The removal contaminants in cotton stage usually takes place in the so-called blowroom of a spinning mill between a bale opener and a carding machine in terms of textile processing. For this, contamination cleaning devices, also called contamination sorters, are used in the blowroom of a spinning mill to detect the contamination during the flow of raw fibre material in the blowroom. Usually, a contamination cleaning device comprises a light source which illuminates the raw fibre material which is flowing through the contamination cleaning device, a detector to detect the contaminants by analysing the light reflected by the contaminant and received by the detector and as well an ejection module to eject the detected contaminants separately from the material flow. The ejected contaminants get collected in a separate collection zone. Detecting contaminants in raw fibre material, such as cotton flocks, is a challenging one due to the exposure of contaminants to the detecting module of the contamination cleaning device during the passage of the raw fibre material. Though many technologies are available for detecting contamination in raw fibre material, an efficient detection is needed to achieve the best detection efficiency.

Various light sources and detectors are available and being improved to achieve best detection efficiency of contaminants in raw fibre material. Due to high speed flow of the raw fibre material and the possibility of small sized contaminants, it is becoming a challenge to detect the contaminants in the raw fibre material. Detection of contaminants like white polypropylene and transparent Polypropylene is another challenge due to the colour of contaminants almost similar to the raw fibre material. Also due to the importance of contamination removal, the demand for best detection and ejection of contaminants is increasing. However, there is a continual improvement in the field of lighting arrangement for detecting the contaminants and in the field of detectors processing the received light signals for detecting contaminants. In this direction, further enhancement of the lighting arrangement and of the detector is done which is explained in the summary of the invention. SUMMARY OF THE INVENTION

The invention concerns a contamination detection device for detecting contaminants within a raw fibre material. The raw fibre material preferably are textile fibres. The textile fibres in particular are used to produce textile fabrics.

The raw fibre material in particular are cotton fibres. The cotton fibres can be present in the form of cotton flocks.

The contaminants can be parts of packing materials, such as plastic strings, threads, plastic films, Jute or fabrics.

The contamination detection device contains:

- a light source for illuminating the raw fibre material, and

- a detector arrangement with a sensor module for receiving and sensing the reflected light from the raw fibre material and a signal-processing unit for identifying contaminants based on the sensed reflected light.

A first aspect of the invention concerns the structure and functionality of the detector arrangement.

According to this aspect the detector arrangement contains light signal separators for separating parts of the electromagnetic spectrum of the received light.

The received light in particular is light which is reflected by the fibre material and the contaminants.

The received light in particular contains visible light. The received light can also contain infrared light. The detector arrangement can contain light signal separators for separating parts of the colour spectrum of the visible part of the received light.

The detector arrangement can contain at least one light signal separator for separating a or the infrared signal, such as short-wavelength infrared light (SWIR), of the received light.

The detector arrangement can contain a plurality, for example two light signal separators for separating spectral bands from the infrared light signal, in particular from the short-wavelength infrared light (SWIR) signal of the received light. The detector arrangement can also contain only one light signal separator for separating the infrared signal.

In particular, the detector arrangement contains a first light signal separator for separating a first primary colour from the visible part of the received light, a second light signal separator for separating a second primary colour from the visible part of the received light, a third light signal separator for separating a third primary colour from the visible part of the received light and, as the case may be, at least one, in particular one infra-red light signal separator for separating the infra-red light from the received light.

The separated colours and the separated infra-red light correspond to colour light signals and infra-red light signal, respectively. Basically, the received light also corresponds to a light signal.

In an embodiment, the first primary colour is red, the second primary colour is green and the third primary colour is blue. In other words, the separated colour signals correspond to the additive primary colors (RGB colour space). In another embodiment, the first primary colour is cyan, the second primary colour is magenta and the third primary colour is yellow. In other words, the separated colour signals correspond to the primary colors (CMY colour space). In particular, the light signal separators are arranged within the detector arrangement such that the separated colours and infrared light can be collected and directed to a sensor module, such as an image sensor.

The light signal separators, in particular for separating the primary colours of the visible part of the received light, in particular are optical signal separators, such as e.g. prism.

In front of the light signal separators at the entrance of the reflected light into the detector arrangement in particular an optical lens is arranged.

The optical lens can have a fixed focus.

The optical lens can be a (variable) focal lens. Accordingly, the detector arrangement can comprise a mechanism for adjusting the focus. The focal lens allows to adjust the detection area (within the raw fibre material).

The adjustment of the size of the detection area, e.g. the length of the detection area in transport direction of the fibre material, by changing the focus of the lens can be necessary when the transport speed of the fibre material is changed.

The detection area corresponds to a defined space from which the light which is reflected by the raw fibre material that is located in this space or transported through this space is received by the detector arrangement. The space of the detection area in particular contains a width, a length and a height. The raw fibre material can be a stream of fibre material which is moved in a main transport direction, e.g. in a transport duct, through the detection area and thus past the detector arrangement and in particular also past a lighting arrangement. In this case, the extension of the detection area parallel to the main transport direction can be 0.1 to 1 mm, in particular 0.25 to 0.6 mm. Depending on the transport speed of the fibre material, the extension can be longer with lower speed and shorter with higher speed, in order to always detect the same amount of fibre material per time unit.

The sensor module in particular comprises at least one electronic image sensor. The at least one electronic image sensor can be a charge-coupled device (CCD sensor). The at least one electronic image sensor can be an active-pixel sensor (CMOS sensor).

However, the sensor module can also comprise several image sensors of the same type or of different types.

The sensor module can comprise a common image sensor for the colour signals of the visible light.

In particular, the sensor module can comprise at least one additional image sensor for the at least one infra-red signal.

In particular, the image sensor contains a plurality of pixel fields, which are e. g. defined by photo diode.

The image sensor can be a colour sensor. As the colours of the received light beam already are separated before being directed to the image sensor, also a black and white sensor can be used.

Accordingly, the analysis of the received and separated light signals and the detection and classification of contaminants in particular is based on image processing. In particular, the sensor module, i.e. the at least one electronic image sensor is designed for converting the received separated colour and infrared signals, respectively, into pixel information for further image processing by means of the signal-processing unit.

The at least one electronic image sensor can be a linear image sensor or linear array sensor, respectively. In particular, the at least one electronic image sensor can be a line scan sensor. Usually, such an image sensor only contains a single row of pixel fields, such as photo diodes.

In particular, the sensor module can comprise at least one electronic image sensor, such as line scan sensor for the separated colour signals and an electronic image sensor, such as a line scan sensor, for the separated infrared light.

The detector arrangement in particular contains a camera, comprising the lens, the sensor module and as the case can be also the light signal separators. Furthermore, also the signal-processing unit can be arranged within the camera. In particular, the detector arrangement corresponds to a camera.

In a further development of the invention the contamination detection device is also designed for removing detected contaminants from the raw fibre material. Thus, the contamination detection device in particular corresponds to a contamination cleaning device or contamination sorter. Accordingly, the contamination detection device further contains an ejection module for removing detected contaminants from the raw fibre material.

The contamination detection device in particular contains a transparent fibre transport duct, in which a stream of raw fibre material can transported pneumatically in an aiidlow in a transport direction. The detector arrangement and the lighting arrangement in particular are arranged outside the fibre transport duct but next to the fibre transport duct. The detector arrangement and the lighting arrangement can be arranged on the same side of the fibre transport duct. The detector arrangement and the lighting arrangement can be arranged on opposite sides of the fibre transport duct with the fibre transport duct in between.

According to the first aspect, the light can be directly directed from the light source to the raw fibre material. By combining with the second aspect of the invention as described below, the light can be indirectly guided towards the raw fibre material via a suitable surface medium, such as e. g. a reflector. The reflector can be a mirror.

Further, the detector arrangement can receive the reflected light directly from the raw fibre material or contaminant. However, the detector arrangement can also receive the reflected light indirectly from the raw fibre material or contaminant via a suitable surface medium, such as a reflector, or light guides.

The contamination detection device can comprise a detector arrangement on each side of the transport duct which are located opposite to each other. The two detector arrangements can be located directly opposite to each other or opposite to each other with a lateral offset distance.

Such an arrangement has the advantage that contaminants within a detection area can be detected from two opposite sides of the transport duct. In other words, a better coverage of the detection area is achieved which improves the detection rate.

A second aspect of the invention concerns the structure and functionality of a lighting arrangement also called illumination system. The lighting arrangement contains at least one light source and in particular at least one reflector which is associated to the at least one light source.

The light source is for illuminating the raw fibre material within the detection area.

In particular, the lighting arrangement contains several light sources wherein in particular to each of the light sources a reflector is associated. The illumination can take place over a static or dynamic raw fibre material. A dynamic raw fibre material means e.g. a stream of raw fibre material which is moved/- transported through the detection area.

The illumination facilitates the detection of contaminants by the detector arrangement in comparison with only ambient light. Accordingly, better detection results are achieved. Furthermore, the light source allows to determine the most suitable electromagnetic spectrum for detecting contaminants.

According to this second aspect the light source is part of the above mentioned lighting arrangement. The lighting arrangement comprises a reflector which is associated to the light source for reflecting the light emitted by the light source into the raw fibre material.

The light source is arranged such that the emitted light is directed towards the reflector.

In particular, the light source and the reflector are part of a lighting module. Accordingly, the lighting arrangement can comprise several lighting modules.

The reflector in particular faces the raw fibre material and the fibre transport duct, respectively.

The reflector is designed and arranged for reflecting the incident light emitted by the light source towards the detection area located within the raw fibre material or within the fibre transport duct, respectively.

In particular, the reflector is designed and arranged for directing the incident light towards the detection area. In particular, the reflector is designed and arranged such that the reflected light converges towards the detection area. This allows a targeted or a selected illumination of the spacially limited detection area.

The use of a reflector allows a uniform distribution of the light across the spatial detection area, i.e. a homogeneous lighting over the fibre material within the detection area, e.g. arranged in the transport duct.

The use of a reflector in particular is of advantage in combination with the use of LED’s for building the light source. In comparison to other types of light sources, the LED light is of directional nature. However, LED light spreads widely in the light emission direction. The reflector now allows to direct the light targeted into the detection area.

In an embodiment the reflector is curved in cross-sectional view.

For converging the reflected light the reflector can have a concave shape. The reflector can be a concave mirror.

It is possible, that the focal points of a concave reflector are arranged between the reflecting surface of the reflector and the fibre material to be illuminated. As a result, the reflected light can diverge towards the fibre material to be illuminated after passing the focal point.

It is possible, that the light source and the reflector are designed and arranged such that the reflected light runs parallel towards the detection area. In particular, in such a case the scattered emittance of the light is reflected and bundled into parallel light. This can be the case, if the light source is positioned at about the focal point of the parabolic reflector.

According to an embodiment, the light source is a linear light source. The light source in particular extends along the width of the spatial extent of the detection area and thus of the fibre transport duct and perpendicular to the longitudinal axis of the fibre transport duct, which corresponds to the main transport direction. Such an arrangement ensures a uniform illumination of the transverse section of the detection area, in particular within the fibre transport duct.

In this embodiment, the reflector preferably also extends along the linear light source and in particular in parallel to the linear light source.

The reflector, can e.g. be designed as a parabolic trough.

The light source in particular comprises a plurality of light units. The light units in particular are LED's (Light Emitting Diodes). The light units in particular are arranged in a linear array.

In particular, the light source contains at least one light unit, e.g. with an LED, that emits visible light (visible spectral light, white light).

The visible (white) light e.g. ranges between 380 n to 680 nm.

The light source can comprise exclusively one or several light units, e.g. with an LED, that emits visible light (visible spectral light, white light).

In particular, the light source contains at least one light unit, e.g. with an LED, that emits infrared light, in particular short-wavelength infrared light (SWIR).

The short-wavelength infrared light (SWIR) e.g. ranges between 1200 nm to 2000 nm.

In an embodiment the light source contains a plurality of light units, wherein at least one light unit, in particular a plurality of light units for emitting visible light are arranged together with at least one light unit, in particular a plurality of light units for emitting infrared light. In particular the light units are arranged in a linear arrangement.

The light units for emitting visible light and the light units for emitting infrared light can be arranged in an alternating manner.

In an embodiment the lighting arrangement comprises at least one first light source, in particular with an allocated reflector, with at least one, in particular a plurality of light units, e.g. with an LED, that exclusively emits visible light (visible spectral light, white light).

Further, the lighting arrangement according to this embodiment comprises at least one second light source, in particular with an allocated reflector, with at least one, in particular a plurality of light units, e.g. with an LED, that exclusively emits infrared light, in particular short-wavelength infrared light (SWIR).

The at least two (different) light sources and their light units and reflectors can be designed and arranged as described above and further below.

The light units in each case can comprise a lens or a lens system for emitting directed, in particular focused light rays towards the reflector.

In particular, the light source and the reflector associated to the light source or the lighting module are arranged on one side of the fibre transport duct of a contamination detection device.

In an embodiment, on both sides of the fibre transport duct at least one light source with an associated reflector, in particular at least one lighting module, are arranged. In particular, the at least two light sources with associated reflector or lighting modules, respectively, are located opposite to each other. In particular, the least two light sources with associated reflector or lighting modules, respectively, can be located directly opposite to each other or opposite to each other with a lateral offset distance.

In case that a detector arrangement is arranged on a first side of the detection area, in particular of a transport duct, and a light source with an associated reflector is arranged on second side of the detection area, in particular transport duct, and opposite to the detector arrangement, then the light rays which are reflected from the reflector are directed towards the detection area at such an angle that said light is not directed to the detector arrangement, in particular to a lens of the detector arrangement.

In an embodiment, on at least one side of the fibre transport duct of the contamination detection device two light sources with an associated reflector in each case, in particular two lighting modules are arranged, in particular in a mirror symmetrical manner, such that the light reflected by the reflectors is directed towards a common detection area.

In an embodiment the two light sources with the associated reflector in each case can be distanced from each other (in the main transport direction of the fibre material) and fonn a light passing gap, in particular a light passing channel. In particular, the light passing gap, in particular channel, is running perpendicular to the main transport direction of the fibre material within the transport duct.

According to this embodiment a first light source can be designed for emitting exclusively visible light and the second light source can be designed for emitting exclusively infrared light

In particular, the detector is arranged to receive the light which is passing through the light passing gap, in particular channel between the two groupings of light source and reflector. In particular, the detector arrangement is arranged behind/after the two groupings of light source and reflector as viewed from the transport duct.

The above mentioned embodiments concerning the arrangement of the light source or lighting modules, respectively, can be combined with each other.

The presented lighting arrangement in particular is suited to illuminate the detection area over its entire width and depth. In other words, the lighting arrangement in particular illuminates the whole cross-section of the fibre transport duct.

The presented lighting arrangement in particular is suited to illuminate a detection area which defines a volume within the transport duct based on the width and the depth of the transport duct and a length section parallel to the transport direction or the longitudinal axis of the transport duct.

Of course, the above described first and second aspect of the invention and the associated features, respectively, can be combined with each other

Present invention also concerns a method for detecting contaminants in a raw fibre material by using a contamination detection device as disclosed above.

The method contains the following steps:

- directing light emitted by the light source towards a detection area containing raw fibre material;

- receiving the light reflected from the raw fibre material and from the contaminants contained therein by the detector arrangement;

- sensing the received light by the sensor module;

- processing and analysing of the sensed light signals and identifying of contaminants, in particular detecting the presence and the type of contaminants in the raw fibre material, by the signal-processing unit. The raw fibre material in particular is transported in a fibre flow or stream, in particular in a continuous fibre flow or stream, in the fibre transport duct through the detection area. Accordingly, the detector arrangement is continuously processing the continuously received light signals from the passing raw fibre material for detecting contaminants.

The method can also comprise the step of removing of the identified contaminants from the raw fibre material.

Accordingly, contaminants are removed, e.g. separated or ejected, from the (continuous) fibre flow. In particular, the removal of the contaminants is pneumatically by directed air blasts which are directed towards the contaminants and which deflect them out of the fibre flow.

If a contaminant is detected within the volume of fibre material being in or passing the detection area, respectively, then the mentioned volume of fibre material in particular is ejected together with the contaminant.

The directed air blasts for the targeted expulsion of the contaminants can be generated by means of valves.

A control unit synchronizes the detector arrangement with the ejection arrangement.

As already mentioned above, according to the second aspect of the invention, light, in particular visible and infrared light, is emitted by the light source. The emitted light is reflected by the reflector and thus directed into the detection area of the raw fibre material. The emitted and reflected light illuminates the raw fibre material in the detection area.

The light rays from the light source or the light units, respectively, can impinge the raw fibre material simultaneously or sequentially. In particular, emitted visible light and emitted infrared light can impinge the raw fibre material simultaneously or sequentially.

In case of more than one light source or lighting modules, respectively, the emitted, i.e. reflected light rays can illuminate the raw fibre material from the same angle or from different angles.

In particular, the emitted and reflected light rays are directed towards the detection area at an acute angle with respect to a plane which is perpendicular to the main flow direction of the fibre material within the transport duct. The acute angle e. g. can be 60° (angle degree) or less. Further, the acute angle can be 20° or more.

The intensity, frequency and sequencing of the emitted fight or fight rays, respectively, can be variable and controllable, e.g. by the control unit.

The information contained in the light reflected by the raw fibre material and contaminants and received by the detector arrangement by using the mentioned illumination system is used for detecting and, as the case may be, for classifying or identifying the contaminants.

The arrangement of at least one light source with an associated reflector, in particular at least one fighting module on both sides of the fibre transport duct of a contamination detection device in particular allows to cover its entire width and depth for scanning, i.e. detection.

Furthermore, the arrangement of at least one light source with an associated reflector, in particular at least one lighting module on both sides of the fibre transport duct of a contamination detection device in particular allows to illuminate the same plane and/or different planes of raw fibre material by either physically moving the fight sources or the fight source modules, respectively, and/or by changing the angle of illumination. Latter can be done by moving, e.g. tilting, the reflector. The moving and tilting of the light source or the reflector can be controlled by the control unit.

The detector arrangement in particular is such that it receives the light reflected from the fibre material and the contaminants having a light path perpendicular to the transport duct or the main transport direction of the fibre material within the transport duct.

Accordingly, the lens of the detector arrangement in particular is facing the transport duct.

In particular, the lighting arrangement, i.e. its components, are designed and arranged such that a substantial part of the emitted light is reflected by the fibre material and contaminants perpendicular to the transport duct or the main transport direction of the fibre material.

As already mentioned above, according to the first aspect of the invention the light signal separators in the detector arrangement separate parts of the electromagnetic spectrum of the received light.

In particular, light signal separators separate parts of the color spectrum of the visible part of the received light.

In particular, a light signal separator separates an infrared signal, such as short- wavelength infrared light (SWIR), from the received light.

The broken up electromagnetic bands of the received light are directed separately to the sensor module for sensing and for processing/analysis. According to an embodiment, the light signal separators separate a first, second and third primary colour from the visible part of the sensed light and the infra-red light from the sensed light. The broken up colour signals and infrared light signal are directed separately to the sensor module for sensing processing and analysis.

Each material has a specific reflectivity which varies across the electromagnetic spectrum in terms of the colour spectrum of visible light, each material reflects or absorbs different colours of this spectrum. The same also applies to infrared light.

Accordingly, also contaminants and raw fibre materials have a different reflectivity and moreover also different types of contaminants have a different reflectivity.

Thus, the colour signal gives an information about the reflectivity of the passing raw fibre material or contaminant in the visible light spectrum. The infrared signal gives a thermal infomiation from the raw fibre material or contaminant.

By analysing the presence or non-presence and the intensity of the color signals and the infrared light signals it can be determined whether the light signal is from the raw fibre material or from a contaminant. Furthermore, as the case may be, also the type of contaminant can be identified.

In particular, each separated colour is directed to a pixel field.

The sensor module, i.e. the at least one electronic image sensor, converts the received separated colour and infrared signals into pixel information. This step in particular is a digitization step. The pixel information are further processed (image processing) by means of the signal-processing unit.

The main information which is gained from the image sensor is the presence or non presence of a colour light signal. Further, also the intensity of the colour light signal may be sensed by the image sensor. This information may also contain information about the presence and/or type of the contaminant.

The signal-processing unit detects contaminants, and as the case can be, also the type of contaminants from the pixel information by means of at least one detection algorithm.

In particular, the at least one detection algorithm compares the pixel information, which are colour information, with stored surface colour data of the fibre material. A deviation between the pixel information and the stored surface colour data of the fibre material means the presence of a contaminant.

In particular, the at least one detection algorithm compares the pixel information with stored surface colour data of various known contaminants. If the pixel information corresponds to stored surface colour data of a contaminant, then the type of contaminant is identified.

The at least one detection algorithm can do the same procedure as described above with a infra-red information.

The at least one detection algorithm in particular is or comprises a machine learning algorithm comprising methods that leverage data to improve performance on detection of contaminants.

The signal-processing unit in particular is a vision processing unit (VPU), The vision processing unit (VPU) comprises a special type of microprocessor which is designed for running algorithm based on methods of Artificial Intelligence (AI), in particular based on machine learning methods. In particular it is a specific type of AI accelerator, designed to accelerate machine vision tasks. The vision processing unit is characterised by its suitability for running machine vision algorithms such as CNN (convolutional neural networks), SIFT (Scale-invariant feature transform) and similar.

Examples of vision processing units are e.g. the vision processing unit in the Myriad VPU line from Intel Corporation, such as Movidius Myriad X. Another example is Pixel Visual Core (PVC), which is a fully programmable Image, Vision and A1 processor.

It has to be noted that the colour signals and the infrared light signal broken up by the light signal separators originate from the same received light signal and thus from the same detection area and the same time of measurement and thus from the same raw fibre material or contaminant.

In other words, the reflected light received by the detector arrangement contains one common optical information from the raw fibre material within the detection area. If the raw fibre material is a fibre stream, e.g. within a transport duct, then the reflected light received by the detector arrangement at a specific point in time contains one common optical information of the raw fibre material moving through the detection area at the time of measurement. In other words, there is no space-resolved resolution of the received reflected light.

As mentioned above, the raw fibre material in particular are cotton fibres, e.g. in the form of cotton flocks. The cotton flocks are the product of a bale opener which tears flocks of cotton from a cotton bale and feeds them into the process line of the blowroom.

Accordingly, the contamination detection device or the contamination cleaning device, respectively, in particular is arranged in a blowroom of a spinning mill. In particular the contamination detection device or the contamination cleaning device is arranged between a bale opener and a carding machine. DESCRIPTION OF THE DRAWINGS

The invention and embodiments thereof are described in further detail in connection with the appended drawings that are all schematical. Same reference numbers refer to same or analogous elements. In the drawings:

Figure 1 illustrates, in a side view, a lighting arrangement with light sources arranged on both sides of a fibre material transport duct;

Figure 2 illustrates, in a perspective view, a lighting module with a light source and a reflector;

Figure 3 illustrates, in a side view, a lighting arrangement with light sources in combination with a detector arrangement arranged on a side of a fibre material transport duct.

Figure 1 and 2 concern the second aspect of the invention. Figure 1 shows the raw fibre material 1 passing or streaming, respectively, through a fibre material transport duct 22. The direction of passage (main transport direction) of raw fibre material 1 can be either from top to bottom or from bottom to top. In this case the transport duct is vertically orientated. The transport duct can also be horizontally oriented. In this case the main transport direction of raw fibre material is horizontally.

On both sides of the fibre material transport duct 2, lighting modules 8 are arranged, two lighting modules 8 on each side. The two lighting modules 8 on each side of the duct 22 are arranged in a mirror symmetrical maimer, such that the light rays 25b of the illumination are directed towards the same detection area A. Further, two opposing lighting modules 8 on each side of the duct 22 are arranged mirror symmetrical as well for the same reason. The lighting modules 3 form a lighting arrangement 23 for illuminating a detection area A within the fibre material duct 22. The two lighting modules 8 on each side of the transport duct 22 are distanced from each other in the main transport direction T and form a light passing channel 27. The light passing channel 27 is running perpendicular to the main transport direction T of the fibre material 1 within the transport duct 22.

The detector arrangement 2 is arranged to receive the reflected light 25b which is passing through the light passing channel 27 between the two lighting modules 8. Accordingly, the detector arrangement 2 is arranged behind/after the two lighting modules 8 as viewed from the transport duct 22.

Each lighting module 8 comprises a light source 26 and a reflector 24. The reflector 24 forms a concave surface for directing the light rays 25b towards the detection area A.

The shown light path of the emitted light 25a and the reflected light 25b is only schematical and does not represent a specific converging or diverging behaviour. The same applies to figure 3.

In the shown embodiment the reflector 24 is connected to a base plate on which the light units 26a, 26b are arranged and forms a concave wall towards the light units 26a, 26b. However, this does not automatically mean that the reflector surface, where the light rays 25a effectively impinge on the reflector 24 is concave.

The light source 26 emits light rays 25a which are reflected by the reflector 24. The reflected light rays 25b are directed into the detection area A and fall over the raw fibre material 1 which is passing the detection area A for the entire width and depth of the fibre material transport duct 22. Alternatively, no reflectors 24 are provided and the emitted light rays 25a fall directly over the raw fibre material 1.

Figure 2 shows the design of a lighting module 8 with a light source 26 and a reflector 24. The light source 26 contains a plurality of light units 26a which emit white (visible) light sources and a plurality of light units 26b which emit short wave infrared light. The light units 26a, 26b are arranged in a line. The length of the line of light units 26a, 26b corresponds to the width of the fibre material transport duct 22. Accordingly, the light source 26 with its light units 26a, 26b extends across the whole width of the fibre material transport duct 22. Here, the white (visible) light units 26a and the short wave infrared light units 26b are arranged alternately adjacent to each other. But this arrangement is not restricted to the manner as represented. Any combination and sequence of white light units 26a and short wave infrared light units 26b is possible.

Figure 3 shows a detector arrangement 2 according to the first aspect of the invention. The detector arrangement 2 contains an infrared light separator 3, a red light separator 4, a green light separator 5 and a blue light separator 6. The separated colour light signals correspond to the primary colours of the additive colour system.

The information, i.e. the light signal reflected by the raw fibre material 1 is received by the detector arrangement 2 through the lens 7.

A lighting arrangement 23 with two lighting modules 8, each with a light source 26 and a reflector 24, illuminates the raw fibre material 1 which passes the detection area A within the fibre material transport duct 22. Hereto, light rays 25a are emitted by the light source towards the associated reflector 24 and reflected by the reflector towards the raw fibre material 1 which passes the detection area A within the fibre material transport duct 22.

The light 25c reflected by the fibre material 1 and the contaminants 15 passes through a light passing gap which is established between the two lighting modules 8 on one side of the transport duct 22. The reflected light 25c passes the lens of the detector arrangement 2 as a light signal.

Once the received light signal 25c has passed the lens 7, the optical (visible light) and thermal (infrared light) information received from or reflected by the raw fibre material 1, respectively, is separated by the various separators 3, 4, 5 and 6 in the detector arrangement 2. The separated signals are then provided to the sensor module 10 for sensing the presence and strength of a light signal and subsequently processed by the signal processing unit 9 for the detection of presence and type of contaminants 15 in the raw fibre material 1. All the separators 3, 4, 5 and 6 in the detector arrangement 2 collect the information from the same location of the raw fibre material 1 or of the contaminant 15.