In the yarn feeder known from WO 97/37247 the reflector surface is situated at a light transparent plate, which is inserted into the periphery of the storage drum such that the outer surface of the plate is flush with the periphery. The plate, conventionally, consists of an ordinary glass material or Plexiglas. During the feeding or transportation of the yarn windings axially on the storage drum surface the yarn windings slide over the surface of the plate and thus cause wear by friction and abrasion. Additionally, in most cases the yarn is treated with oil or other chemical substances ("avivage") which by time may chemically"attack"the plate surface. Increasing wear of the surface deteriorates the optical properties and the operational reliability of the yarn sensor. At least the plate, and in most cases also the reflector surface, may have to be replaced after a relatively short time.

In the yarn feeder known from US 4,865, 085 A a striped reflector of the yarn sensor is protected by a glass layer. The glass surface slightly projects beyond the periphery of the storage drum so that the yarn windings, while moving forward on the drum, skim the surface of the glass, preventing dust and yarn treatment substances from settling thereon. The surface of the protective glass layer is prone to wear by friction and chemical attacks.

Other types of conventional yarn feeders (WO 02/052081) comprise at least one optoelectronic yarn sensor provided with a reflective surface in the metallic periphery of the storage drum. The periphery of the storage drum per se is plasma coated. The well-polished reflective surface is arranged on a coin-shaped metal body inserted into the storage drum periphery. The polished surface fulfils both the reflecting and the protecting tasks. The lifetime of the polished surface is limited, mainly due to an unsatisfactory surface hardness. It is an object of the invention to provide a yarn feeder, the optoelectronic sensor of which has a theoretically unlimited operational life time in terms of wear resistance of the surface of the protective layer contacted by the yarn windings, and a reflector body for a yarn sensor.

This object can be achieved by a yarn feeder characterised by the feature combination of claim 1 or by a reflector body having the feature combination of claim 18.

The light transparent amorphous ceramic material, at least at the surface of the protective layer, performs with a wear resistance that is much better than the best surfaces used until now for the same purpose. The operational lifetime is theoretically unlimited, because neither the abrasive friction influence nor the yarn treatment substances are able to deteriorate the optical properties of the surface. Additionally, the surface of the protective layer consisting of transparent amorphous ceramic material is chemically resistant against practically all substances possible carried by the yarn windings or used to impregnate the yarn in question.

Basically, it would suffice to provide the ceramic material in the surface region of the protective layer only. However, it is found preferred to provide a solid protective layer of amorphous ceramic material. The amorphous ceramic material may be Sapphire glass, Zirconium glass, Hafnium glass, Quartz glass or crystalline Aluminoxide glass.

However, the listed group of useful materials must not to be limited to those just specified. Any other amorphous ceramic material which is or can be made light transparent and provides a hard surface may be used in accordance with the invention.

Preferably, at least the surface of the protective layer contacted by the yarn windings is optically polished.

Expediently, the hardness at least of the surface contacted by the yarn windings amount to more than 1000 Hv, preferably in a range of up to about 2000 Hv (Vicker's hardness).

In a preferred embodiment the protective layer is formed with a lower side extending at least substantially parallel to the surface. The lower side carries a metallic coating forming the reflective surface. This concept results in a quality of the reflective surface which is much better than the best reflective surfaces used until now for the same purpose. In the combination of the protective layer consisting of a transparent amorphous ceramic material and a metallic coating forming the reflector surface easily a wear resistance thickness up to 1.0 mm can be achieved, compared to the conventional solutions, where there is a maximum wear resistance thickness of just about 0.2 mm.

As a further protective measure for the reflector surface the reflector surface in turn may be covered by a protective coating, preferably a protective painted coating. In order to totally"seal" (avoid negative interaction with the yarn) the protective coating expediently extends around the edge of the reflector surface to the outer edge of the protective layer.

Expediently, the protective layer and the reflector surface, preferably including the protective coating, form a structural unit, namely a reflector body of rectangular, rectangular and rounded, oval or round shape. The reflector body, e. g. , may have a rounded shape with an outer diameter of about 6.0 mm and a thickness of about 1.0 mm.

The edge of the surface contacted by the yarn windings may expediently be rounded to avoid trouble with the yarn windings.

Expediently, the reflector body is fixed in a recess formed in the storage body periphery, preferably by means of a bonding agent or a pottant. The arrangement of the reflector body in the recess allows to exactly locate the surface in a height position in which the yarn windings permanently skim and clean the surface.

Expediently, the recess contains a foss-like groove defining the opening edge of the recess and encompassing at least one inner fixing boss, the top side of which is located below the height of the opening edge of the recess. The reflector body is fixed by the bonding agent or the pottant on the top side of the fixing boss. The bonding agent or the pottant fills the groove at least partially and such that it extends to the outer edge of the reflector body to seal the transition from the fixing boss to the reflector body and also the transition from the reflector surface to the protective layer.

Expediently, the top side of the fixing boss is smaller than the lower side of the reflector body. This dimensional relationship allows to easily fit the reflector body accurately in the recess.

The bonding agent or the pottant, expediently, fills the preferably foss-like groove up to the full height of the surface of the protective layer or almost up to this height. This measure results in the avoidance of any inappropriate depression where lint, avivage or contamination might otherwise collect.

Expediently, the reflector body, preferably at least the surface contacted by the yarn windings, is plane. Alternatively, the surface, or even the entire reflector body, may have a convex curvature at least substantially similar to the convex peripheral curvature of the storage drum.

A high quality reflector surface can be achieved by metal vacuum vapour deposition on a separate carrier or on the protective layer. Expediently, the metal is evaporated by electronic beam energy while it is deposited in an evacuated surrounding. The carrier or the protective layer may be well polished with an optically correct and even surface quality for the reflector surface.

Alternatively, the reflector surface may be provided on a separate carrier, e. g. on a metallic plastics or glass carrier, which either just abuts or is bonded to or is spaced apart from the protective layer, alternatively.

Embodiments of the invention will be explained with reference to the drawings. In the drawings is : Fig. 1 a schematic side view of a yarn feeder comprising an optoelectronic yarn sensor; Fig. 2 a part of a cross-section of a reflector body, and Fig. 3 a cross-section of a reflector body fitted in a storage drum of the yarn feeder.

A yarn feeder F in Fig. 1, as conventionally used e. g. for feeding a yarn Y to a textile machine, e. g. a weft yarn Y to a weaving machine or a knitting yarn Y to a knitting machine, is provided with a housing 1 and a housing sub-unit 2. A yarn storage drum 3 is stationary or rotatably provided on a central shaft. The storage drum 3 is provided to carry windings 9 of the yarn Y. The yarn windings 9 move forward in axial direction on the peripheral surface 6 of the storage drum 3. The yarn feeder is equipped with at least one optoelectronic yarn sensor S comprising components in the housing 1 and/or in the housing sub-unit 2 and in the storage drum 3.

The yarn feeder F shown as an example in Fig. 1 is a weft yarn feeder for a weaving machine. The storage drum 3 is kept stationary by means known per se, while the central shaft is driven to rotate a winding-on element 4 fixed to said shaft. The incoming yarn Y enters the housing 1 in Fig. 1 from the left side through a hollow section of the drive shaft and is wound by the winding-on element 4 in adjacent, preferably somewhat separated, yarn windings 9 on the peripheral surface 6 of the storage drum 3.

The textile machine withdraws the yarn Y overhead the storage drum 3 in a consumption-depending kind of manner. A drive motor 7 for the winding-on element 4 is comprised in the housing 1. The drive motor 7 is controlled by control device 8. In the shown embodiment the control device 8 is receiving control signals from the yarn sensor S. The drive motor 7 is e. g. controlled such that the yam Y is wound on the storage drum surface 6 until the first (leading) yarn winding 10 reaches a detection zone 11.

Then the yarn sensor S responds to the presence of said first yarn winding 10 and stops or decelerates the drive motor 7, which only starts or accelerates again as soon as the detection zone 11 again is"cleared"or free from yarn windings.

The yarn sensor S instead could alternatively e. g. be a so-called yarn withdrawal sensor responding and/or counting each yarn winding being withdrawn from the yarn feeder, or a so-called reference sensor, or a so-called input yarn sensor, or a so-called yarn break sensor. The structure of all yarn sensors just mentioned is principally similar. The yarn sensor S has at least one light source L, and at least one signal generating receiver R (a light diode or a phototransistor), both connected into a circuitry 12, and a reflector surface B. The reflector surface B is located below the peripheral surface 6 of the storage drum 3 in order to reflect light emitted by the light source L back towards the receiver R. The reflector surface B is located behind a protective layer 5, e. g. in the form of a light transparent plate inserted into the peripheral surface 6 of the storage drum 3 such that the outer surface 13 of the protective layer 5 is substantially flush with the peripheral surface 6 in the detection zone 11 and is skimmed by the forwardly (axially) moving yarn windings 9,10. The protective layer 5 and the reflector surface B, preferably, constitute a prefabricated reflector body P of the yarn sensor S.

The protective layer 5 (Fig. 2) consists at least at the surface 13 of a light transparent amorphous ceramic material C. The protective layer 5 may be solid amorphous ceramic material, or, alternatively, only may have an upper layer defining the surface 13 of amorphous ceramic material C and a lower layer (not shown) of another light transparent material.

The amorphous ceramic material may be chosen e. g. from the following group: Sapphire glass, Zirconium glass, Hafnium glass, Quartz glass or crystalline Al-Oxide glass (AL303) glass, or a similar light transparent amorphous ceramic material.

The reflector body P may have a rectangular, a rectangular and rounded, an oval or a round plate or disc shape and e. g. with substantially uniform thickness. As an example, a round reflector body P may have an outer diameter of about 6.0 mm and a thickness of about 1.0 mm. The surface 13 is plane, or, alternatively, in case of a circumferentially curved periphery surface 6 of the storage body 3 convexly curved in circumferential direction of the storage body 3 as well. In this case even the entire reflector body P may be curved.

The protective layer 5 has a lower side 14 which extends at least essentially parallel to the surface 13, and an outer edge 15. The reflector surface B, expediently, is constituted by a reflective metal coating 16 provided at the lower side 14 of the protective layer 5. The reflective metal coating may consist of Aluminoxide. The metal coating 16 may be made by metal vacuum vapour disposition, preferably electronic beam metal evaporation in an evacuated surrounding. The thickness of the metal coating is preferably smaller than the thickness of the protective layer 5. However, the dimensional relations in Fig. 2 and Fig. 3 are exaggerated for the purposes of illustration and do not necessarily correspond to the dimensional relationships used in practice.

In Fig. 2 the lower side of the reflector surface B is covered with a protective coating 17, e. g. a protective paint-coating extending around the edges of the reflector surface B up to the outer edge 15 of the protective layer 5.

Alternatively, the reflector surface B may be an optically well polished surface of a metallic carrier or a mirror surface of a plastics or glass carrier (not shown). The carrier may be arranged loosely below the protective layer 5, even with some distance, or may be attached in some way to the protective layer 5.

Fig. 3 illustrates one possibility to fit the reflector body P, e. g. the one in Fig. 2, in the storage drum 3 of the yarn feeder F.

In the peripheral surface 6 of the storage body 3 (the periphery 6'may have a circumferential curvature) a recess 20 is formed. The opening edge 19 of the recess 20 is defined by a preferably annular (endless, foss-like) groove 18 enclosing an inner fixing boss 21 (or several separate fixing bosses indicated by dotted lines at 22), the top side 23 of which is situated below the height of the opening edge 19 or the periphery surface 6 of the storage drum 3. The top side 23 is smaller than the lower side of the reflector body P. The reflector body P is fixed on the top side 23 by means of bonding agent or a pottant 24 (a glue or a resin material), filling the groove 18 at least partially so that the transition from the top side 21 to the reflector plate P as well as the transition from the mirror surface B to the protective layer 5 is"sealed". Expediently, the bonding agent or the pottant 24 fills the groove 18 up to close the full height of the opening edge 19 to avoid a"dead space"where lint, avivage or contamination might collect.

The surface 13 is essentially flush with the periphery 6. In case that the periphery 6 has the curvature (indicated in dotted lines as 6'), at least the surface 13 can have a similar curvature.

In the reflector plate P two contrary tasks, namely reflection and protection against wear and chemical influences, have been so to speak"divided". The reflector surface B has to have as good reflecting properties as possible. The wear protection and the protection against chemical attacks are obtained by the extra hard and chemically resistant protective layer 5.

In case of a protective layer 5 consisting of Sapphire glass, the surface 13 (even at the lower side 14) is optically polished, may show a hardness of up to 1900 Hv. The circumferential edge of the surface 13 may expediently be rounded to avoid trouble (negative interaction) with the yarn windings 9,10. The protective coating 17 is applied to secure the quality of the interface between the metal coating defining the reflector surface and the protective layer 5.

The mounting principle shown in Fig. 3 is particularly expedient for a storage body, the periphery of which is plasma coated. Forming the recess 20 as shown and described allows to form an area into which the bonding agent or the pottant can be filled such that it covers the thickness of the reflector body. On the other hand, the selected shape helps to minimise the problems that otherwise might easily occur with the plasma coating of the periphery 6, due to the known fact that plasma coating always tends to round sharp edges and thus does not allow a good positioning of components.

In a not shown embodiment the reflector body P may be fixed by a mechanical fastening arrangement. Furthermore, the reflector surface B on the lower side 14 of the protective layer 5 may be smaller than the lower side 14. In another, not shown embodiment, the reflector surface B is not continuous (uniform) as shown but consists of a stripe pattern of parallel and spaced apart reflective and non-reflective stripes (a solution known per se).