ELECTRO-OPTICAL YARN SENSOR

The invention relates to a yarn feeding device according to the preamble of claim 1 and to an electro-optical yarn sensor according to the preamble of claim 16.

The electro-optical yarn sensor of the yarn feeding device according to WO 00/48934 A has as light source either an LED or a laser diode, namely a so-called VCSEL (Vertical Cavity Surface Emitting Laser) capable of generating a narrow conical light beam directed on the reflective yarn scanning zone of the storage body. The light beam generates a substantially round, e.g. annular and small, light spot on the scanning zone. The scanning zone is retroreflective, i.e. reflects the light in the same direction as the light hits on the light scanning zone. The reflective yarn scanning zone is curved convexly in circumferential direction of the storage body such that the light spot is somewhat spread to a longitudinal or elliptical light strip while being reflected to the receiver. The light spot is spread in the direction of the axes of yarn windings carried by the storage body periphery. The publication mentions an embodiment with a lens or aperture in the light path e.g. in the case of a light emitting diode as the light source to achieve a light spot on the reflective yarn scanning zone as small and sharp as possible. Due to the fact that reflective light from the concentrated small light spot is only spread a little in circumferential direction of the storage body by the convex reflective yarn scanning zone, relatively high precision is needed for positioning and aligning the light source and the receiver properly. Unavoidable manufacturing and assembly tolerances deteriorate the reading quality of the receiver and cause severe scanning fluctuations within a series of yarn feeding devices equipped with theoretically identical yarn sensors.

It is a task of the invention to provide a yarn feeding device and an electro-optical yarn sensor as mentioned above, the reading quality of the receiver of which is improved, and which are less to prone to manufacturing and assembly tolerances than the prior art devices.

This object is achieved either by the features of claim 1 or by the features of the claim

The transparent spreading body provided in the light path surprisingly improves the reading quality of the receiver and compensates better for unavoidable manufacturing and assembly tolerances. Moreover, the yarn sensor operation is not at all sensitive to unavoidable relative movements occurring between the stationarily mounted light source/receiver combination and the reflective yarn scanning zone on the storage body.

It is assumed that this improvement results from the fact that the transparent spreading body already spreads the small light spot created by the light beam from the light source on the spreading body essentially linearly in circumferential direction of the storage body into a relatively long and sharp light strip on the reflective yam scanning zone, with the longitudinal axis of the light strip being oriented essentially parallel to the axes of the yarn windings carried on the storage body. The light concentration in the light strip is high and results in a high concentration in the light reflected to the receiver. The receiver then is subjected to concentrated light which the transparent spreading body retransmits to the receiver, and for this reason, reliably responds to the reflected light irrespective of manufacturing and assembly tolerances and also of the unavoidable relative movements of the storage body. As soon as a yarn winding reaches the location of the light strip of the reflective yarn scanning zone, any reflection from the light strip is interrupted so sharply that the receiver reliably responds to the resulting high degree of modulation between the full light and the shadowed conditions. The output signal from the receiver is strong and for this reason does not need significant amplification. The transparent and solid spreading body already spreads the small and concentrated light spot into the sharp light strip distant from the reflective yarn scanning zone such that the light strip will be relatively narrow but relatively long on the reflective yarn scanning zone. The reflected light is collected by the transparent spreading body and is converted again into a substantially round, e.g. annular, reflection light spot from which the light travels to the receiver. The longer the light strip on the scanning zone is, the better reflected light can be evaluated and processed by the receiver.

The provision of the markedly transparent spreading body allows to improve the yarn sensor performance for fair cost. The yarn sensor may not only be implemented in yarn feeding devices but also may be used for other yarn scanning applications operating with light reflection.

The transparent spreading body, preferably, is structured such that it operates similarly in both light directions along the optical axis of the yarn sensor. A majority of the light reflected from the longitudinal light strip on the scanning zone is collected by the transparent spreading body and is converted into a substantially round light beam directed to the location of the light source/receiver combination in order to actuate the receiver. Collected reflected light is emitted from a light spot which is essentially round or annular and has a size which assures that the receiver reliably is hit by the reflected light irrespective of manufacturing and assembly tolerances.

In an expedient embodiment the light source is a laser light source for emitting a slightly conical round and/or ring-shaped laser light beam, preferably of infrared light. A laser light source is of particular advantage because of a strong light beam and a relatively low power consumption.

Particularly expedient is to use a vertical cavity surface emitting laser-diode (VCSEL) as the laser light source. VCSELs are available for fair cost in different specifications, have a long service life, and withstand the coarse operating conditions in a yarn feeding device without problems.

Alternatively, the light source may be a light diode, preferably emitting a slightly conical infrared light beam.

It has been proven that so-called "reflective object sensors" available from OPTEK Technology Inc., Texas 75006, USA types OPB 609, OPB 609V are perfect for the implementation in yarn feeding devices, because the reflective object sensor contains the source (infrared emitting diode or VCSEL) and the receiver (NPN silicone phototransistor) side by side on parallel axes in a compact plastic housing which easily can be mounted, e.g. according to the surface mounting technology, on a printed circuit board. Combining these reflective object sensor types with the transparent spreading body results in an optimum performance of the yam sensor particularly in a yarn feeding device. The distance between the light source and the receiver is, preferably, less than 1.0 mm.

Expediently the transparent spreading body is arranged about halfway between the light source/receiver combination and the scanning zone. This arrangement assures similar optical conditions for both light directions. In particular the distance between the transparent spreading body and the reflective scanning zone results in a magnifying effect such that a sharp light line formed on the exit side of the transparent spreading body from the light spot created by the light source will form a relatively long and well defined light strip on the scanning zone.

Expediently, the transparent spreading body is injection moulded from plastic material having optimised optical properties. Instead, the transparent spreading body as well could be made from glass. Surface parts of the transparent spreading body which are not used for receiving or emitting light could be covered with light absorbing or other types of coatings.

In a simple embodiment the transparent spreading body is a solid cylinder with the cylinder axis oriented perpendicular to the storage body axis and parallel to a tangent on the storage body periphery. Already a simple solid cylinder converts a round light spot into a linear light line or light strip in one direction, and collects reflected light and converts the collected reflected light in a substantially round light spot and a well defined light beam to the receiver.

An even better performance of the yarn sensor can be achieved if the transparent spreading body is solid and has two diametrically opposed and spaced apart convex cylindrical surface regions with at least substantially the same radius of curvature and straight parallel generatrices. In this case the radius of curvature is either equal or longer than the largest distance between both surface regions along the optical axis of the yarn sensor. The "squeezed" cylinder shape with a radius of curvature of each cylindrical surface region being larger than the distance between the surface regions along the optical axis treats the light in both directions such that the light is well focused to a certain extent.

In another expedient embodiment the reflective scanning surface either is constituted by a reflector which is inserted into the storage body periphery, or by the storage body periphery itself, e.g., in the latter case by providing a mirror surface region on the storage body periphery. The inserted reflector, expediently, is positioned such that its outer surface is swept over by the yarn windings when the yarn windings are conveyed forward on the storage body periphery. This results in a desirable self-cleaning effect.

As unavoidably relative movements occur, mainly in circumferential direction of the storage body, between the light source/receiver combination and the reflective scanning zone which relative movements could cause oscillations in the light when reflected from a planar scanning zone, the scanning zone, preferably, is curved convexly in circumferential direction of the storage body and has a straight generatrice essentially parallel to the storage body axis. The convex curvature of the reflective scanning zone, preferably, is similar to the curvature of the storage body periphery.

In order to improve the reflection properties of the reflective scanning zone, in another embodiment the reflective scanning zone is retroreflective. Retroreflective means that the majority of the light is reflected in the same direction as it hits the scanning zone.

An embodiment of the invention will be described with the help of the drawings. In the drawings is:

Fig. 1 a schematic side view of a yarn feeding device being equipped with two electro- optical yarn sensors,

Fig. 2 a schematic side view, partially as a sectional view, of a yarn sensor, seen in circumferential direction of the storage body,

Fig. 3 a view of the yarn sensor in the direction of the storage body axis,

Fig. 4 a view similar to Fig. 2, illustrating a light path of light emitted from a light source,

Fig. 5 a view on a reflective scanning zone in the direction of the optical axis of the yarn sensor,

Fig. 6 a view of the yarn sensor in the direction of the storage body axis, illustrating the light path of Figs 4 and 5,

Fig. 7 a view of the yarn sensor in the direction of the storage body axis, illustrating the light path of reflected light, and

Fig. 8 a schematic plan view of a light source/receiver combination as used in the embodiments of Figs 1 to 7.

A yarn feeding device F in Fig. 1 , e.g. a weft yarn feeding device for a weaving machine or a knitting yarn feeding device for a knitting machine, comprises a housing 1 containing an electric motor 2 and a drum-shaped storage body 3. The storage body 3 rotatably supported on a not shown drive shaft, however, is hindered by co-acting magnets 3' to rotate with the drive shaft (stationary storage drum). In a not shown alternative, the feeding device could be equipped with a rotatable storage body instead. The drive shaft drives a winding element 4 which winds a yarn Y inserted from the left side into the yarn feeding device F into adjacent windings on the periphery of the storage body 3. The yarn then is withdrawn from the frontmost winding overhead of the storage body 3 and, optionally, through a withdrawal eyelet 6 axially. The housing has a housing bracket 5 in which, in the shown embodiment, two electro-optical yarn sensors S are mounted stationarily which are directed from the exterior into a reflective scanning zone 12, e.g. constituted by an inserted reflector M in the storage body 3. The yarn sensors S are in signal transmitting connection with a control unit C of the electric motor 2. The control unit C executes the control of the electric motor 2, e.g. depending on the signals from the yarn sensors S, in order to accelerate, decelerate, or stop the electric motor, i.e., to drive winding element 4 such that a predetermined number of windings will be present on the storage body periphery for consumption. The predetermined number of windings or the size of the yarn store on the storage body is scanned by the yarn sensors S in conventional fashion.

Each of the yarn sensors S includes at least one light source E and one receiver R. The light source E emits a slightly conical light beam to the reflector M; the receiver R receives reflective light from the reflector M. The emitted light beam e.g. generates a light strip on the reflector M which light strip is shadowed while a yarn winding is passing. The receiver R responds to the shadowing or the presence of the light strip and generates a control signal representing the presence or absence or passage of a yarn winding, respectively.

The yam sensor S, e.g. shown in Fig. 1 on the left side, may scan the position of the frontmost boundary of the yarn store on the storage body 3. The yarn sensor S on the right side in Fig. 1 may scan either a maximum size of the yarn store or the passage of each withdrawn yarn winding. The yarn feeding device could be equipped with a single yarn sensor only, or with more than two yarn sensors. An additional yarn sensor of the same type could be used to detect yarn breakages. Even in the region of the withdrawal eyelet 6 a yam sensor S could be installed.

The light source E either is a light emitting diode (preferably infrared light) or a laser light source L, preferably a VCSEL (Vertical Cavity Surface Emitting Laser). The receiver R is a photodiode or phototransistor. Particularly useful is a so-called "Reflective Object Sensor" as available from OPTEK Technology Inc., Texas 75006, USA, product types OPB 609, OPB 609V. Such a reflective object sensor is shown in Fig. 8 and is a light source/receiver combination 8 consisting of either an infrared emitting diode or a VCSEL as the IR emitter and an NPN silicone phototransistor 24 which are mounted side by side on parallel axes in a plastic housing 22. The outer dimensions of the housing 22 are f = about 3.2 mm and e = about 2.7 mm, meaning that the distance between the light source E and the receiver R is less than 1.0 mm.

Part of each yarn sensor S is a transparent spreading body B made from plastic material or glass having optimised optical properties. Expediently, the transparent spreading body is an injection moulded plastic part. The transparent spreading body B is mounted about halfway between the light source/receiver combination 8 and the reflector M in the light path or optical axis of the yarn sensor S, i.e. spaced apart from the light source/receiver combination 8 and also from the reflective scanning zone 12 of the storage body 3 (yarn passing gap). The light source/receiver combination 8 e.g. is mounted on a printed circuit board 7 in the housing bracket 5. The transparent spreading body B as well may be mounted on the circuit board 7, e.g. by means of fastening elements 10 and spacers 11. In order to facilitate mounting the transparent spreading body B the spreading body B is integrally shaped with mounting lugs 9.

In a not shown embodiment the transparent spreading body B may be a true solid cylinder and is mounted with the cylinder axis in the optical axis of the yarn sensor such that the cylinder axis is perpendicular to the storage body axis and parallel to a tangent on the storage body periphery.

In the embodiment shown in Figs 2 to 7, however, the transparent spreading body B has the shape of a "squeezed" cylinder with diametrically opposed convex cylindrical surface regions 13, 14 having essentially the same radius of curvature X and straight generatrices which extend perpendicular to the axis of the storage body and parallel to a tangent on the storage body periphery. The radius of curvature X is either equal or larger (as shown) than the biggest diametrical distance between both surface regions 13, 14. For this reason, the thickness of the transparent spreading body B in the direction of the optical axis of the yarn sensor S is about the same as the radius of the curvature X or even is less.

The reflective yarn scanning zone 12 is conventional, i.e. either is constituted by a mirror surface on the storage body periphery, or by the shown inserted reflector M. The outside surface in the scanning zone 12, preferably, is flush with the adjacent periphery of the storage body 3 such that the yarn windings sweep over the surface in order to keep it clean. Surface portions of the transparent spreading body B which are not used for passing light may be covered or coated like surface 15 that is shown in Fig. 3.

The light source E emits a slightly conical (about 20°) light beam 16 (Fig. 4) which hits the surface region 13 and produces a light spot 17 which is round or annular. The transparent spreading body B is structured, e.g. by its geometrical shape, such that it spreads the light spot 17 on the lower surface region 14 in the direction of the cylinder axis and such that (Fig. 6) an axial light line 17' is formed from which the light beam continues as indicated by 19 and hits the scanning zone 12. In the scanning zone 12 a longitudinal sharp light strip 18 is generated (Fig. 5), the longitudinal extension of which is by far larger than the dimension of the light spot 17. The longitudinal axis of the light strip 18 extends in circumferential direction, i.e. essentially parallel to the axis of each yarn winding which is conveyed during the operation of the yarn feeding device in the direction of an arrow 25 over the reflective yarn scanning zone 12. The longitudinal extension L of the light strip 18 e.g. may be as long as the length of the transparent spreading body B, or even longer.

Fig. 3 indicates that in the light source/receiver combination 8 the light source E and the receiver R are arranged in close proximity to each other. Both are facing transparent spreading body B.

The reflective yarn scanning zone 12, preferably, is convexly curved in circumferential direction of the storage body 3, preferably with the same radius X1 as the storage body periphery. The curvature of the scanning zone 12 is of advantage in order to suppress oscillations in the reflected light (Fig. 7) caused by unavoidable relative movements occurring in operation of the feed-up device between the storage body 3 and the housing bracket 5. The reflective scanning zone 12 may have a polished finish or a mirror or is even made retroreflective. Retroreflective means that the light is reflected in the same direction as it hits the reflective scanning zone 12.

Fig. 7 illustrates how light 20 is reflected from the light strip 18 back to the transparent spreading body B where it hits the lower cylindrical surface region 14. The transparent spreading body B is structured such that it collects the reflected light 20 and forms on the upper cylindrical surface region 13 a light spot (round or annular) which is similar to the light spot 17 but may be somewhat larger. From this light spot the reflected light 21 is directed to the location of the receiver R. In other words, the receiver R sees a clear round or annular light spot or light ring on the upper cylindrical surface region 13 of the transparent spreading body B.

The yarn sensor S is configured to respond to the reflective light 20, 21, i.e. to either output a signal when a yarn winding is absent at the location of the light strip 18 or when a yarn winding is present at the location of the light strip 18, or while the winding is passing.

The transparent spreading body B does not necessarily have to have the shape as shown in Figs 2 to 7. Instead any transparent spreading body B could be used which has the above-mentioned properties, e.g. a prismatic transparent body or the like.

Since the transparent spreading body B generates a well defined and relatively long light strip 18 on the reflective yarn scanning zone 12, and since reflected light is reliably brought back to the receiver R, unavoidable manufacturing and assembly tolerances in the geometric relation or optical chain between the light source/receiver combination 8, the transparent spreading body B and the reflective yarn scanning zone 12 do not deteriorate the scanning property or performance of the yarn sensor.

Moreover, due to the well defined and long light strip 18 on the reflective scanning zone 12 and the property of the transparent spreading body B to reliably retransmit reflected light precisely to the receiver, a high modulation is achieved between a full light condition and a shadowed condition (when a yarn winding shadows the light strip 18), meaning that a strong output signal will be obtained even if some contamination like lint should be present in the light path. The strong output signal does not need significant amplification measures. The transparent spreading body B is a fair cost component like the VCSEL ₁ meaning that the yarn sensor can be manufactured for fair cost, is reliable and has a long service life.

It is even possible to retrofit already implemented electro-optical yam sensors with the transparent spreading body B in order to improve the performance of the yarn sensor.

In another, not shown, assumed embodiment, more than one spreading body could be mounted in series along the light path, in order to achieve the same function, but to an even higher performance.