Abstract:
The invention relates to a method and a device for detecting impurities (F) in a fiber stream ( 1 ) of mainly textile fibers, wherein the fiber stream and at least one reference quantity ( 15 ) are artificially visually sensed. To enable even impurities which are difficult to detect to be removed with improved efficiency, the reference quantity is to be adapted at least periodically.

Description:
The invention relates to a method and a device for detecting impurities in a loosened fiber stream of mainly textile fibers, wherein the fiber stream and at least one reference quantity are artificially visually sensed. 
     BACKGROUND OF THE INVENTION 
     From DE-A-4340165 and DE-A-4340173 such methods are known, by means of which, for example, cotton or wool in the form of flocks polluted to a greater or lesser extent with impurities may be freed of said impurities. With said methods it is possible to distinguish between external impurities, which relate to different material, and internal impurities, which relate to the same material but in a different state or a different color. Internal impurities are, for example, cotton or woollen fibers which are partially rotten, agglutinated or contaminated. External impurities are stones, soil, glass, stalk residues, leaves, packaging material, hair, feathers etc. Whereas crude impurities are removed in the known spinning preparation devices, impurities which are more difficult to separate are, according to the known methods, to be detected and removed from the stream of loose material. To said end, the fibers or flocks are conveyed continuously past color sensors which are to detect impurities. Material containing constituents, to which the color sensors have responded, is then removed. 
     A perceived drawback of such known methods is that many impurities are not detected thereby. one reason is, for example, that impurities, in order to be detected, have to vary in color to a relatively great extent from the textile fibers or the background, which is not always the case. Such known methods do not operate very selectively. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method and apparatus which allow impurities, which are difficult to separate, to be detected in the fiber stream with greater efficiency. 
     The object is achieved in that the fiber stream is artificially visually sensed together with a reference quantity, which is adapted at least at intervals or from time to time. This may be effected on the one hand in that the fiber stream, which is to be opened into flocks or into individual fibers, is to be sensed against a background, which is likewise formed by the fiber stream and acts as a reference quantity. On the other hand, the reference quantity may be formed, for example, also by a background which is periodically or continuously adapted to the material to be measured. A possible construction comprises, for example, a channel for a loosened fiber stream and a channel, arranged parallel thereto, for a retained fiber stream. The channel for the loosened fiber stream is to be permeable to light and the channel for the retained fiber stream is to be permeable to exactly the same light at one side. The loosened fiber stream is then sensed or viewed against the background of the retained part of the same stream or of a further fiber stream. 
     The advantages achieved by the invention are in particular that the comparison process or processes, which precede a decision about the absence or presence of impurities, automatically adapt continuously to the true conditions of the fibers carried along in the fiber stream. The adaptability is to be regarded as stable and robust so long as the precondition is met that, from a statistical viewpoint, impurities are rare in comparison to good fiber material. The same advantages are achieved when a fiber stream, which has already been cleaned and freed of impurities, is used as a reference quantity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There follows a detailed description of the invention by way of example and with reference to the accompanying drawings. The drawings show: 
     FIG. 1 is a diagrammatic view of a device according to the invention; 
     FIG. 2 is a simplified view of basic structural features of the device; and 
     FIGS. 3 to  6  are simplified views of further embodiments of the device according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows, by way of example, part of a cleaning machine for flocks which produces a highly loosened fiber stream  1 . The machine comprises, for example, a retaining channel  2 , an exhaust air channel  3  and a channel  4  for cleaned flocks or fibers. Also shown are two small feed rollers  5  and  6 , a cleaning roller  7 , a cutter screen  8  and a drive  9  for the feed rollers  5 ,  6  and the cleaning roller  7 . To said extent, the machine is a known cleaning machine. In one region  10 , however, the retaining channel  2  and the channel  4  are each provided with a window  11 ,  12 ,  13  so that said channels are permeable to light in the direction of a double arrow  14 , i.e. are, for example, of a transparent design. Said arrangement is used to enable sensing of the fiber stream  1  in the channel  4  from the direction of the arrow  14 , e.g. by means of a sensor. For said purpose, the retained fibers  15  in the retaining channel  2  form a background or even a reference quantity for the flocks or fibers in the fiber stream  1 , which reference quantity is continuously adapted at least at intervals or, in the present case, by the slow, continuous forward motion of the fibers  15 . 
     FIG. 2 shows in a simplified manner a path of rays  16  such as arises during the detection of impurities in the device according to FIG.  1  and also in the devices to be described below. Disposed along an optical axis  17  are a line or point sensor  18 , an objective  19 , a foreground or object surface  20  and a background  21  or reference surface. Disposed as light sources on both sides of the optical axis  17  in front of the foreground  20  and in front of the background  21  are, for example, gaseous discharge tubes or tubular incandescent lamps with approximately elliptical reflectors  22 ,  23 ,  24  and  25 . One tubular light source  26  lies in each case at a focal point of the ellipse of the associated reflector  27 , while the other focal point is situated in such a way that the background  21  is uniformly lit. The light sources  22 ,  23  and  24 ,  25  are all of an identical design and are intended to illuminate the foreground  20  and the background  21  equally brightly. According to FIG. 1, the object surface  20  lies approximately in the center plane of the channel  4 , while the background  21  lies approximately in the window  13  of the side wall of the retaining channel  2 . The depth of focus is preferably so great that, instead of the object surface, it is possible to talk of an object zone  28  which corresponds approximately to the depth of a channel for the flock flow. By means of the illustrated path of rays  16 , the object zone  28  is imaged in a clearly defined manner and the background is imaged in a poorly defined, indistinct manner on the point or line sensor  18 . A diffusing screen  29  may optionally also be disposed in the path of rays  15  between the object zone  28  and the background  21 . The understanding is that, in the practical realization, a plurality of point sensors forming a line or a plurality of point or line sensors forming a field is provided. 
     FIG. 3 shows a further device for detecting impurities in a fiber stream. A loosened fiber stream  30 , which in the present case comprises fibers combined into flocks  33  and conveyed preferably pneumatically, e.g. in a laminar air flow, more or less loosely in the direction of an arrow  31 , is fed in a channel  32 . In said flow there are possibly also impurities F. The channel  32  has two windows  34 ,  35  lying opposite one another. Disposed next to or behind the channel  32  is a further channel  36  with a window  37 . The windows  34 ,  35  and  37  are positioned relative to one another in such a way as to afford a view through the channel  32  into the channel  36 . In the channel  36 , flocks or fibers are retained in front of the window  37 . Feed rollers  38 ,  39  are also used to control the flow of the retained fibers in the channel  36  in such a way that there are always fibers behind the window  37 . Disposed in front of the channels  32  and  36  are, in each case, two light sources  40 ,  41  and  42 ,  43  which may, for example, take the form of standard tubular light sources and are used to illuminate the fiber streams behind the transparent windows  34  and  37  in the channels  32  and  36  in a uniform, equally powerful, shadow-free manner. A sensor  44  which may be a camera, for example, has a view through the channel  32  into the channel  36 . Thus, the window  34  forms a first location for acquiring measured values and the window  37  forms a second location for acquiring mean values or reference quantities from a fiber stream. The sensor  44  is connected by a line  45  or a bus to an evaluation unit  46 , which in turn is connected to a data output unit  47  such as, for example, a visual display unit or printer and to a data input unit  48  such as, for example, a keyboard. The evaluation unit  46  may, for example, comprise an image processing system which, on the basis of statistical features, further improves the differentiation between impurities and flocks. A line sensor may be provided for sensing radiation which is reflected or diffused by the fiber stream in the channel  32 . The sensor  44 , the evaluation unit  46 , the data output unit  47  and the data input unit  48  are elements which are known as such and therefore not shown in greater detail here. 
     FIG. 4 shows a further construction of the device, in which however only one channel  50  is provided. Here, instead of the channel  36  (FIG.  3 ), a container  51  is provided which is filled with textile fibers corresponding to fibers in the channel  50 . Said container  51  is designed so as to be transparent or open by means of a window  52  in the direction of the channel  50  and serves as a background for viewing the flock stream in the channel  50 . The container  51  or its contents  53  may be periodically exchanged in order to adapt the background to variations in the flock stream in the channel  50  which are not to be detected as impurities. Also shown here is a sensor  54  for sensing the flock stream in the channel  50  using the contents  53  as a reference quantity. As contents  53 , fibers or flocks are conceivable, which contain impurities or from which the impurities have already been removed. 
     FIG. 5 shows a further construction of the device which, as in FIG.  4 ,. has only one channel  55  for a loosened flock stream. Here, instead of the channel  36  (FIG.  3 ), a surface  56  is provided which is illuminated by light sources  57 ,  58 . For controlling the intensity and color of the lighting of the surface  56 , said light sources  57 ,  58  are connected by lines  59 ,  60  and a controller  61  to one another so that flocks in the channel  55  disappear against said background. This applies particularly to the region of an image  62  which lies in the field of vision of a sensor  63 . Here, it is a matter of generating or simulating an image of a collection of textile fibers such as might be seen, for example, in the retaining channel  2 . For said purpose, the surface  56 ,  62  could also take further forms, e.g. it could also receive a projection of an image or be formed by a display screen. A line  64  moreover connects the controller  61  to the sensor  63 . 
     FIG. 6 shows a further construction and application of the invention in connection with a carding machine  65 . Provided next to the carding machine  65  there is once more a channel  66  for a loosened flock stream. Said channel  66  preferably lies upstream of the carding machine. A sensor  67  is disposed on one side and a picture tube  68  is disposed on the other side of the channel  66 . The sensor  67  and the picture tube  68  are connected by lines  69 ,  70  to a controller  71 , which in turn is connected by a line  72  to a further sensor  73 . The latter is disposed, in the present case, in the region of a stripping roller  74  in the carding machine. 
     There are however additional places where such a sensor might be disposed. They are occupied by sensors  75  and  76 . Sensor  75  is provided, for example, in the region of the outgoing fiber fleece, sensor  76  in the retaining chamber. 
     The mode of operation of the device is as follows: A fiber or flock stream containing impurities is loosened as far as possible so that the flocks are fed as separately as possible in an air stream such as arises in the channels  4 ,  32 ,  50 ,  55 ,  66 . The manner in which the flocks are separated out is known as such and therefore not shown in detail here, except for the cleaning roller  7  in FIG.  1 . The fiber or flock stream thus treated is conveyed parallel to, in front of or next to a background and visually inspected, e.g. by a sensor, the background being periodically or continuously adapted to variations of the flock or fiber stream. This is effected in particular to take account of gradually occurring changes in the color or brightness of the fiber or flock stream in that the color or the brightness of the background is adapted to the fiber or flock stream. To guarantee this, the fiber or flock stream is viewed against an adaptable background which preferably comprises the same fiber or flock material. Thus, in the fiber or flock stream there is a first location for measuring or sensing said stream and a second location where said stream acts as a reference quantity or as a background. In the device according to FIG. 1, the first location is to be found in the region  10  and the second location in the retaining channel  2  by the window  13 . Here, the two locations are placed in series along the fiber or flock stream. In the device according to FIG. 3, said locations (windows  34  and  37 ) are disposed next or parallel to one another and the fiber or flock stream is conveyed in two parallel streams. It is preferably to be ensured that the intensity of the lighting is equally high at both locations. For viewing the flock stream, said lighting is to be concentrated on a region around the axis  17  in the object zone  28  (FIG.  2 ). For the reference quantity or the background  21 , the region between light sources  24  and  25  is to be uniformly lit. 
     In the device according to FIG. 3, a fiber stream  30  consisting of more or less large flocks  33 , which for example substantially comprise cotton fibers possibly interspersed with impurities F, is fed in the channel  32 . In the channel  36 , the flocks or fibers are retained and moved only slowly in a downward direction. In the channel  32 , they are moved more quickly in as loose a formation as possible. The purpose of said arrangement is that the retained fibers in front of the window  37  in the channel  36  form a background, which is adapted as time passes, for visual sensing by the sensor  44  of the flocks moving separately through the channel  32 . 
     The same effect may be achieved by an arrangement of channels  2 ,  4  according to FIG.  1 . Unlike the construction according to FIG. 3 where the channel  36  serving as a background and the channel  32  in which the fiber stream is sensed are connected in parallel, here the retaining channel  2  serving as a background is connected in series to the channel  4  for sensing the fiber stream. Furthermore, in said construction, the compressed flocks or fibers  15  are conveyed out of the retaining channel  2  by the feed rollers  5 ,  6  of a cleaning roller  7 , which together with the cutter screen  8  opens the flocks in a known manner. The opened flocks are sucked into the channel  4  where they move in a very separated-out manner past the windows  11 ,  12  and so maybe viewed from direction  14 . 
     The reference quantity, i.e. the background for the viewed flock stream is therefore adoptively variable because it always corresponds to the color or the image of fibers provided on average. This may alternatively be simulated, in the manner possible with the devices according to FIGS. 4 and 5. According to FIG. 4, the adaptation is simulated in that it may be effected, not continuously, but in discrete steps by exchanging the contents  53  or the container  51 . According to FIG. 5, the material too is simulated in that, instead of real textile flocks or fibers with impurities, an image thereof is generated which preferably imitates only mean values of color or brightness of the fibers and flocks. The image preferably shows the same material, e.g. in that it is a picture of the same cotton bale or the same delivery taken by a single sensor or by a camera and projected onto the surface  56 . In the simplest case, the surface  56  is lit so brightly by the light sources  57 ,  58  that the individual flocks in the channel  55 , which contain no impurities, do not stand out visually from the surface  56 . The luminosity and color of the light sources  57 ,  58  may be controlled by the controller  61 , namely, for example, in such a way that flocks passing in front of the image  62  in the channel  55  do not stand out from the image  62  and that in the image  62  an average color or brightness is generated. A signal from the sensor  63 , which passes through the line  64  to the controller  61 , adjusts the lighting in such a way that only greater color variations stand out from the image  62  but the lighting is adapted to smaller gradual variations in the fiber stream. 
     In the construction according to FIG. 6, an—in terms of time and location—averaged color or brightness image of a fiber stream of the kind which may be generated at various points, for example, in a carding machine  65  by a single sensor or a camera is generated in the picture tube  68 . The signal from said recording passes through line  72  to the controller  71  and from there through line  70  to the picture tube  68 . The sensor  67  therefore detects impurities which stand out from the image in the picture tube  68 . Through the line  69  the sensor  67  supplies a signal, which is used for a continuous color or brightness adjustment in the controller  71  and hence corrects the color and luminosity. The basic color adjustment is set once at the sensor  73 . Through a line  77  the sensor  67  produces a signal for the removal of impurities. 
     In conclusion, it should be stated that the signal produced in a sensor by the fiber flocks moving past is evaluated in a manner, which is known as such and therefore not described in greater detail here, and may be used for control of a removal of impurities from the flock stream in the channels  4 ,  32  in the manner already described in the publications cited in the introduction. The method and the device according to the invention however considerably improve the mode of operation of known sensors.