Abstract:
An opto-electronic device (S) for detecting the movement of yarn (Y) (10) passing transversely through a detection zone (11) on the storage drum (3) of a yarn feeder (F), has at least one light source (L) directed on the detection zone (11), at least one reflector (B) fitted on the storage drum (3) a short distance away on the side of the detection zone (11) away from the light source (L) and at least one signal-generating receiver (R) directed towards the detection zone. The opto-electronic device also has a reflector which includes (B) at least one narrow and approximately flat reflection area (15, 15&#39;, 15&#34;) extending essentially parallel to the longitudinal direction of the yarn and in the circumferential direction of the storage drum (3). The reflection area is bounded at its longitudinal sides by either a strip diaphragm fitted between the reflector (B) and the yarn passage plane (13), or diaphragmed regions (17) arranged approximately in the reflector plane.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an opto-electronic device provided on a storage drum of a yarn feeder for detecting a yarn in a detection zone. 
     BACKGROUND OF THE RELATED ART 
     In a device of this kind known from EP-A-0 199 059, the light source and the receiver pointing into the detection zone at the storage drum are provided in a bracket of the housing of the yarn feeder and distant from the surface of the storage drum. Below the detection zone a glass plate is inserted into the surface of the storage drum. At the lower side of said glass plate a full plane reflective coating is provided. The yarn windings wound onto the storage drum in circumferential direction are pushed axially forwards so that each yarn winding passes the detection zone lateral to its longitudinal direction. The device serves as a sensor for the detection of the axial position of at least the first winding of the yarn supply on the storage drum and is responding to the movement, absence or presence of the yarn with a signal which, e.g., is used for the control of the rotational drive of the yarn feeder. The receiver exclusively registers the shade of the yarn or the variation of the light intensity as soon as the yarn is interrupting the light beams directed towards the reflector or coming from the reflector. Independent from the design, only a relatively weak modulation of the signal can be derived from the shadowing, particularly in case of thin yarns, such that in order to generate a useful and clear active signal relatively high efforts are necessary for the evaluation, amplification and discrimination. The device is vulnerable in case of dirt, disturbing light or unavoidable lint or lint bundles. In addition, the frequency of necessary cleaning--or maintenance--cycles is undesirably high. 
     It is, nevertheless, for similar devices known to provide a diaphragm and/or lenses for an opto-electronic yarn detection between the yarn and the receiver and/or between the light source and the yarn. However, that measure cannot significantly improve the response behavior of the device and does not have a considerable influence on the vulnerability against contamination. 
     It is an object of the invention to create a device of the kind as disclosed which is apt to derive strong and useful effective signals from the passage of the yarn through or the presence or absence of the yarn in the detection zone, which is relatively insensitive for contaminations, lint and disturbing light. 
     SUMMARY OF THE INVENTION 
     The object of the invention is achieved by providing the opto-electronic sensor device of the invention with a reflector having a narrow reflection area which extends in a circumferential direction of the storage drum. 
     As the yarn, even with its relatively slow forward motion on the storage drum, covers or clears at least one bar-code-shaped reflection-area extending in longitudinal direction of the yarn, relatively quickly, i.e. only very short time is expiring till maximum coverage or complete clearing, very strong and effective use-signals are generated. The narrow but long reflection zone is illuminated during absence of the yarn over its full length and width and is reflecting, due to its large longitudinal extension, much light to the receiver. When the yarn is present between the reflection-strip and the light source, it may happen that the entire reflection strip is covered. Due to the bar-code shape and the small width of the reflection-strip in moving direction of the yam, there is not only a strong difference in the light amount between the covered and the cleared conditions but also a strong and progressive or degressive transition from high light amount to low light amount and vice versa. The strong signal-modulation occurring therewith allows to avoid high electronic efforts for the signal evaluation. The response behavior is hardly changed by uniform and weak contamination. Lint or lint bundles can normally not shadow or clear the reflection zone in the same way as the yarn and for this reason, are almost uncritical for the derivation of correct effective signals. 
     Such advantageous properties also result, from a width of the long reflection area approximately corresponding to the dimensional order of the thickness of the strongest processed yarns. 
     Said advantageous response behavior either is achieved with a diaphragm-like operating strip-shaped reflection zone of the reflector, or with a strip diaphragm having at least one strip-shaped diaphragm aperture which optically defines the reflection area at the reflector and efficiently uses the distance between the detection zone and the reflector. At least one reflection area decisive for the receiver is, in other words, optically formed on a much bigger reflector surface by means of said diaphragm aperture of the strip diaphragm or without a diaphragm aperture only bounded by the length side, non-reflecting zones. Since with the optical limiting of the reflection strip by means of the strip diaphragm, adjacent areas of the reflector are not used for reflecting purposes already. By means of a strip diaphragm only at least one bar-code-shaped reflection area could be used. 
     In the embodiment wherein a distance is defined between the strip diaphragm and the reflection strip, a focal-depth adjustment can optionally be preset. For the diaphragm function, the distance between the light source and the diaphragm aperture or between the receiver and the diaphragm aperture is of secondary importance, since the diaphragm aperture is situated at the side of the yarn facing the reflector. 
     Another embodiment is advantageous, because it is provided with at least two parallel and separated diaphragm apertures in said strip diaphragm. The yarn passing through the detection zone is interrupting the light path two fold, and each time in almost exactly the same manner. 
     In the embodiment which is operating without a strip diaphragm, several, i.e. two, reflection areas with intermediate non-reflecting zones are provided so that the yarn during its passage is registered by the receiver so to speak, in steps and very clearly. The receiver is recognizing the passage across each reflection area at least once and forcefully, since the same yarn so to speak, twice approaches from infinity and vanishes into infinity as soon as it is above said zone. 
     In the embodiment wherein the reflection areas and zones have the same width and form regular strip pattern, a multiple-forceful signal modulation is achieved in steps. The strip pattern is designed so that it can be used for all available yarn qualities or yarn thicknesses. 
     For practical employment, a dimensioning is useful. 
     As the storage drum of a yarn feeder, particularly a stationary storage drum, is hindered by means of mutually cooperating magnets or a ballast weight against co-rotation with the rotating drive shaft supporting said storage drum during operation of said yarn feeder, rotational oscillations of the storage drum nevertheless cannot be avoided. A possibly weak curvature of at least the reflection area is apt to avoid a disturbing influence of such rotational oscillations, since then the reflection area is maintaining its reflecting-properties even under rotational oscillations of the storage drum (having a diameter of approximately 90 mm or more). 
     The embodiment wherein a light exiting direction of the light source is in a radial plane at an acute angle with a radius to the light source is of particular advantage. The yarn is passing the light path twice, i.e. across the diaphragm apertures of the strip diaphragm. The receiver is responding by forceful and effective use-signals, when firstly the light path into the reflection area is interrupted and then the light path from the reflection area to the receiver. The reflection area in this case is directed to the light source and the receiver. Both, accordingly, are positioned accordingly inclined. 
     In this alternative embodiment, a forceful signal modulation is generated, since the yam is covering and clearing each reflection area quickly and, what is important, with a sharp transition between the maximum covering and the maximum clearing. 
     The embodiment having a light permeable plate is structurally simple. The light permeable plate functions as carrier of the reflection area and of said zones and also limits by its surface the detection zone. 
     In the embodiment having the light permeable plate, the strip diaphragm having at least one diaphragm aperture is provided at the surface of the plate or closely below said surface, while the reflector or each reflection area is provided deeply inside the plate or even at the plate&#39;s lower surface. The spatial inter-relationship between the detection zone, the strip diaphragm and the reflector or the reflection area in this case, is optimized and predetermined. Of course, the adjustments and the distance to the light source and to the receiver have to be matched with these given prerequisites in order to guarantee an optimum response behavior of the receiver. 
     The embodiments wherein the plate thickness is between 3.0 and 10.0 mm, the plate width is about 10 to 30 mm, and a longitudinal extension of the plate is about 10 mm or more are of useful importance. 
     In the embodiment wherein the upper surface of the plate includes a plurality of diaphragm apertures, the thickness of the plate determines the distance between the strip diaphragm and the continuous reflector, only strip-shaped reflection areas of which are used according to the optical limitation by means of the diaphragm apertures of said strip diaphragm. The diaphragm apertures are kept clean by the yarn sliding across the strip diaphragm. The reflector there is protected against contamination. 
     The embodiment wherein the lower surface of the plate includes the reflection area is simply to manufacture. 
     Where the plate is movably positioned by a holder on the storage drum, a precise positioning and an easy replacement of the plate can be achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described with the help of the drawings. In the drawings is: 
     FIG. 1 is a schematic side view of a yarn feeder having a device for the detection of the movement, presence or absence of a yarn in a detection zone, 
     FIGS. 2A,B are two schematic views associated to each other of a first embodiment of the device, 
     FIGS. 3A,B are two associated schematic views of a further embodiment, 
     FIG. 4 is a further embodiment seen in a circumferential direction of the storage drum, 
     FIG. 5 is a further embodiment seen in the circumferential direction of the storage drum 
     FIGS. 6A,B are two associated schematic views of a further embodiment, 
     FIG. 7 is a further embodiment seen in the circumferential direction of the storage drum, 
     FIG. 8 is a perspective view of a detail of the device, 
     FIG. 9 is a section in plane IX--IX in FIG. 8, and 
     FIGS. 10A,B are detailed variants in a section according to the section of FIG. 9. 
    
    
     DETAILED DESCRIPTION 
     A yarn feeder F, as conventionally used for supplying a textile machine, e.g. a weaving machine with a left yarn, is provided with a stationary housing 1 and a housing bracket 2. At housing 1 a storage drum 3 is stationarily provided on a drive shaft indicated by its axis 5. The incoming yarn Y enters the housing 1 from the left side through a hollow section of said drive shaft in FIG. 1, and is wound by means of a rotatably driven winding element 4 in an adjacent, preferably separated, yarn windings 9 onto the surface 6 of said storage drum in order to form an intermediate yarn store or yarn supply. Said yarn then is withdrawn by said textile machine overhead of said storage drum 3 depending on consumption. In housing 1 a drive motor 7 for said winding element 4 is received which is controlled by a control device 8. Said control device 8 is receiving control signals from a device S (yarn sensor) provided in housing bracket 2. Drive motor 7 for example is controlled such that the yarn Y is wound onto the storage drum 3 until the first winding 10 in withdrawal direction is reaching a detection zone 11. Then the drive motor 7 is stopped or decelerated and will only then be accelerated again as soon as said detection zone has been cleared by said yarn again. 
     Said device S contains at least one light source L and at least one signal generating receiver R (light diode or photo transistor), both of which are integrated into a switching circuit 12. A reflector B is provided countersunk below the surface 6 of said storage drum 3 which reflects light emitted by said light source L towards receiver R. Advantageously, said reflector is situated at a light permeable plate P inserted into the surface 6 of said storage drum 3 such that its outer surface is flush with surface 6. The plate P or the reflector B, respectively, can be curved with the weak circumferential curvature of the storage drum 3. 
     In the first embodiment of device S according to FIGS. 2A and 2B, a yarn passage plane 13 exists in detection zone 11 which passage plane 13 may correspond to the surface 6 of storage drum 3. Within said yarn passage plane 13 or first below it, a strip diaphragm A is located having a strip-shaped diaphragm aperture 14 extending essentially in circumferential direction and having a longitudinal extension which is considerably bigger than i.e., is a multiple of its width seen in the direction of axis 5 of storage drum 3. With the distance h below said yarn passage plane 13, or below strip diaphragm A, respectively, said reflector B is situated of which only an optically defined bar-code-shaped reflection-area 15 is used as defined by said diaphragm aperture 14. The width of said diaphragm aperture 14 essentially corresponds to the biggest available yarn thickness, i.e. it may even be somewhat bigger or somewhat smaller. In the circumferential direction, said diaphragm aperture 14 or the reflection area 15, respectively, has a longitudinal extension between about 8 and 20 mm. The light exiting direction of the light source L is approximately radial to axis 5 and runs somewhat inclined in the radial plane containing axis 5 such that the reflected light from reflection area 15 can hit the receiving surface of receiver R which is positioned on the same plane and with an according inclination. The distance between the light source and the yarn passing plane 13 or the strip diaphragm A, respectively, as well as the distance h between strip diaphragm A and reflector B are selected so that during passage of the yarn, across diaphragm aperture 14, a sufficiently strong signal modulation is achieved in receiver R. 
     In the embodiment of FIGS. 3A and 3B, the receiver R and the light source L are aligned radially to the axis 5 of storage drum 3 but are located circumferentially offset to each other. The arrangement of strip diaphragm A and reflector B with its reflection area 15, correspond to the arrangement of FIGS. 2A and 2B. 
     In the embodiment of FIG. 4 the light source and the receiver are similarly provided as in FIGS. 2A and 2B. In order to carry out a differential-evaluation, two light sources and/or two receivers R could be provided as well. In this embodiment strip diaphragm A has two strip-shaped diaphragm apertures 14, 14&#39; separated from each other by means of a non-reflecting zone 16, wherein said diaphragm aperture 14 optically defines the reflection area 15 on reflector B. The light exit direction of light source L is directed such that the reflection light coming from reflection zone 15 may hit the receiver R. During its passage (in FIG. 4 e.g. from left to right), the yarn Y, 10 is blocking the beam path twice. 
     In the embodiment of FIG. 5, the strip diaphragm A has even more than two diaphragm apertures 14, 14&#39; separated by non-reflecting zones 16 from another. The reflector B extends continuously but is optically subdivided into several reflection areas 15&#39;. Said diaphragm apertures 14, 14&#39; are of the same width. Said zones 16 have a width which is adapted to the inclination of the light exit direction from the light source. Advantageously, said zones 16 are of the same width among another. 
     In the embodiment of FIGS. 6A and 6B the reflection area 15 of the reflector B is made as a bodily narrow strip essentially extending in circumferential direction. At both sides of reflection area 15, non-reflecting zones 17 are provided. A strip diaphragm is not used. 
     The non-reflecting zones as explained in connection with the above explained embodiments can be designed randomly, provided that they absorb incoming light or reflect incoming light in no case towards receiver R. 
     In the embodiment according to FIG. 7, in axial direction of said storage drum, several reflection areas 15, 15&#39; 15&#34; are provided in a parallel array with a distance below said yarn passage plane 13. Two adjacent reflection areas are separated from each other by a non-reflecting zone 17 having strip form. 
     FIGS. 8 and 9 show an embodiment in which the reflection areas 15, 15&#39;, 15&#34; are situated in a light permeable plate P, e.g. made from glass or plexi-glass. The upper surface of said plate, which according to FIG. 1 is countersunk in storage drum 3, defines said yarn passage plane 13. The reflection areas 15, 15&#39;, 15&#34; are situated at, or close to, the lower side 18 of plate P and extend in circumferential direction of storage drum 3, the axis of which is indicated by 5. In the section of FIG. 9 it can be seen that the reflection areas 15, 15&#39;, 15&#34; are bodily integrated into the plate P or its lower side 18, respectively, and are separated from each other by zones 17 in strip-shape. A preferably regular strip pattern of reflection area strips 15, 15&#39;, 15&#34; and diaphragmed zones 17 are formed which extend either over the entire length of plate P or at least over a limited axial portion of plate P. Plate P is received in a holder 20 mounted into storage drum 3 and can be replaced. In case that storage drum 3 is formed as a so-called rod cage comprising a plurality of rods 19, said holder 20 advantageously is situated in one of said rods 19. 
     Alternatively, said plate according to FIG. 10A (corresponding to the embodiment of FIG. 5) could be provided at its lower side with a continuous reflector B (a reflective coating), while at the upper side a strip diaphragm A with its diaphragm apertures 14 and the intermediate zones 16 is situated. Within strip diaphragm A at least two diaphragm apertures 14, 14&#39; are provided. 
     In the embodiment of FIG. 10B, which functionally corresponds to the embodiment of FIG. 10A, the strip diaphragm A is situated with its diaphragm apertures 14, 14&#39; and its zones 16 below the upper surface of plate P inside of it, and with a distance to the reflector B, which is provided inside the plate P as well. 
     Plate P of FIG. 9 can be made such that at its lower surface 18, a continuous reflective coating is firstly brought up, at least in the axial portion in which later the reflection areas 15, 15&#39;, 15&#34; will be needed. Then the zones 17 are formed by etching, grinding or cutting and may be filled by light absorbing material (black). It is also possible to first form the grooves or structures which will, at a later stage, define zones 17, and then to coat the remaining smooth lower surface portions with reflective coatings then forming said reflection areas 15, 15&#39;, 15&#34;. In this case, advantageously, first a ring of light permeable material is formed, the inner surface of which is finish treated with said reflection areas 15, 15&#39;, 15&#34; and the zones 17. Following this, the ring is subdivided in single sections, each of which is then forming one of the plates P of FIGS. 8 and 9.