Abstract:
The weft break stop motion (1) detects without contact a potential displacement in the feeler (5a) effected by a weft thread moving past by means of a plate-like layered sensor element (2). With the feeler (5a) turned towards the weft thread insertion, the sensor element (2) can be introduced between the drop wires (23) of the reed (18). The weft break stop motion (1) and the sensor element (2) can be variably positioned along the reed (18), depending on the screen of the drop wires (23), and is normally placed directly outside the warp threads according to the loom width.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a weft stop motion, or detector, for looms in which the sensor element responds or is sensitive to an electric charging of the weft thread without contact and also to looms in which the weft break stop motion of the present invention is used. 
     A concept for thread detection is known from German Patent Specification 3,758,403, for example. Various embodiments of electrostatic transformers are disclosed therein. These sensors are mainly used in air-jet looms. The weft thread is electrically charged during its removal from the weft thread supply because of the resultant friction and also during the weft insertion because of friction with the air. The electrostatic detection registers the presence of a textile fiber which is moving past and is electrically charged in this way, and the passage of the tip of an inserted weft thread in particular can also be detected. Weft break stop motions are used in the weft channel of the loom. The known embodiments are relatively large and heavy and are frequently constructed in the form of a confusor drop wire. The high-speed air-jet looms having a correspondingly high beat-up speed of the reed which are commonly used nowadays produce high vibration and acceleration loads on the known weft break stop motions, so that the known embodiments are no longer suitable for use on air-jet looms or the resultant electrical signals are very noisy. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to produce a contact-free weft thread detector based on a capacitative type sensor, which is particularly suitable for use with high-speed air-jet looms. 
     The weft thread detector detects without contact a change in the potential effected by a passing weft thread by means of a sensor element layered like a plate. With the feeler turned towards the weft thread insertion, the sensor element can be inserted between the drop wires of the reed. The weft break stop motion and the sensor element can be positioned variably along the reed, independently of the screen of the drop wires, and is normally placed directly outside the warp wires according to the loom width. 
     The sensor element is constructed from plate-like layers having a low mass. The two most outer supported layers are electrically conductive and serve to screen electrical fields. Between them there is a plate-like layer of insulating material and in the middle there is the actual feeler, a plane electric conductor preferably formed as an open loop. The sensor element, especially the layers of the feeler, is preferably perpendicular to the weft insertion direction. The edge of the sensor element close to the weft channel preferably follows the contours of the weft channel in the reed, such as, for example, the contours of a profiled reed. The sensor element can be inserted between the drop wires of the reed, as a result of which there is support for the sensor element with respect to the forces, vibrations and acceleration load acting in the direction of the weft channel. The rigid, low-mass, laminated construction is dimensionally stable, prevents reciprocal relative movements of the plate-like conductive layers and thus reduces the noise of the electrical signal occurring in the event of high vibrational and acceleration loads, which is caused by changes in capacitance. 
     The entire weft stop motion is preferably constructed as a multi-layer plate, and it is also possible for the middle conductive layer together with the feeler to have further strip conductors for electronic components, especially a charge amplifier. The sensor element can be produced very cheaply. If an integrated switching circuit, such as, for example, a charge amplifier, is directly mounted on the middle layer, then it is possible to provide a very thin weft stop motion, which is electrically shielded by the two outer, overlapping plate-like conductive layers. If larger components are used as electronic components, the strip conductors can also be formed from a sub-region of the outermost electrically conductive layer of the weft stop motion and the electronic components can be mounted thereon. In addition a metal housing, which shields the electronic components and also the strip conductors from the outside, is also required. 
     The weft stop motion can be attached to the reed or loom sley by an attachment device. It is preferably inserted between the drop wires of the reed and can be variably positioned along the reed, independently from the screen of the drop wires, so that the sensor element comes to lie outside the loom width. The reed can therefore be kept at the original length for different loom widths and the sensor can be positioned so that it directly abuts the warp threads, for example outside the present loom width. The sensor can therefore be brought into an optimal position along the reed depending on the width of the woven goods. 
     The invention has the advantage that it is to a large extent possible to dispose the weft stop motion along the reed as desired without altering the functional design of the loom. 
     A further advantage of the sensor element of the present invention is that it is not sensitive to soiling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a weft break stop motion exploded in the direction of the weft channel; 
     FIG. 2 shows a diagrammatic detail of a reed in an air-jet loom to illustrate the position of the weft break stop motion in the profiled reed; 
     FIG. 3 shows a perspective detail of a sensor element according to FIG. 1; 
     FIG. 4 shows a diagrammatic cross section through the sensor element in FIG. 3 to illustrate the stratified construction; 
     FIG. 5 shows a diagrammatic view of the middle conductive layer of the sensor element; 
     FIG. 6 diagrammatically shows the perspective view of a weft break stop motion with an attachment device on the reed; 
     FIG. 7 diagrammatically shows the perspective view of a weft break stop motion with attachment to the loom sley; and 
     FIG. 8 shows a further perspective representation for a weft break stop motion with an attachment device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a perspective view of the weft stop motion or detector 1 with its components. The weft stop motion 1 contains a sensor element 2 and also a board 8 for electronic components 9. Electrically conductive housing lids 11, 12 protect the interior of the weft break stop motion 1 surrounded thereby from electrical fields and mechanical effects and, together with the attachment means 20 constructed as screws and also an attachment device 15, enable the weft stop motion 1 to be fixed to the loom sley 22 or to the reed 18. 
     FIG. 2 shows a reed 18 which is normally constructed from the drop wires 23 shown. The reed of an air-jet loom having an integrated weft channel 19 is shown as an example. 
     In FIG. 3 the feeler 5a of the sensor 2 detects the relatively small potential fluctuations which occur through the electrically charged thread as it passes the feeler 5a. A shielded electrically conductive connection 5b supplies the detected signal to a charge amplifier 10. The components following the charge amplifier 10 for the further preparation and processing of the signals are not shown. 
     In FIG. 4 the sensor element 2 is constructed from plate-like layers. A middle electrically conductive layer 5 is surrounded on both sides by an insulating layer 6, 7 respectively, on which in turn there is an electrically conductive layer 3 or 4. The three electrically conductive layers 3, 4 and 5 are thin metal layers with a thickness in the micrometer range, with the outer layers 3 and 4 being grounded so as to shield the electrical conductors and connections formed with the layer 5 from external electrical fields. The insulating layers 6 and 7 are preferably substantially thicker than the electrically conductive layers 3, 4 and 5 so as to achieve a rigid mechanical sandwich construction. 
     The sensor element shown in FIG. 3 is designed so that it can be inserted between the drop wires 23 of the reed 18 and has thicknesses of less than 1 mm. The edge of the sensor element 2 close to the weft channel 19 of the profiled reed 18 follows the contours of the reed 18. The laminated construction of the sensor element 2 is achieved with a multi-layer printed circuit board, for example. The middle electrically conductive layer 5 of the sensor element 2 is preferably made from a metal, such as copper, for example, and has a thickness of a few micrometers. The actual feeler 5a is constructed as an open loop in the present exemplified embodiment from this electrically conductive layer 5, with the feeler 5a surrounding the weft channel 19 inside the profiled reed 18 so that the cross section of the weft channel 19 is not reduced by the sensor element 2. Of course the feeler 5a can naturally be constructed with different shapes, thus, for example, only with the lower half of the shape shown in FIG. 3. Together with the feeler 5a, the middle layer 5 comprises a conductive connection 5b from the feeler 5a to a charge amplifier 10. Further conductive connections or shielding, grounded layers can be formed from the middle layer 5. In FIG. 3 the feeler 5a is disposed so that the side close to the weft channel 19 is electrically conductive with respect to the outside. The feeler 5a can also be integrated in the sensor element 2 so that on the side of the weft channel there is an electrically insulating layer between the weft channel 19 and the feeler 5a. As a result the feeler becomes less sensitive to soiling. To increase the sensitivity of the sensor, an electrical conductor 24, which is only connected to the feeler 5a in an electrically conductive manner, can be mounted on the edge close to the weft thread. The sensor element 2 and the support 8 can be combined as a cohesive unit if both parts have the same plate-like structure and consequently form a single part. 
     FIG. 5 shows a printed circuit board 13 from the middle conductive layer 5 of which the strip conductors 5c, the conductive connection 5b and also the sensor 5a were formed. The electronic components 9 are preferably mounted on the printed circuit board 13 using SMD technology so as to avoid holes for their connection. The integrated switching circuits are directly mounted on the insulating layer 7 and connected to the strip conductors 5c. For flat electronic components located inside the insulating layer 6, there is a flat weft stop motion 1, in which, the electronic components 9, 10 are electrically shielded by the outer conductive layers 3 and 4. The strip conductors 5c may also be formed from a sub-region of the outermost layer 4 of the support 8. The conductive connection 5b is through-plated to the strip conductors 5c. The electrical shielding of the electronic components 9, 10 is achieved by additional electrically conductive housing lids 11 and 12. An electrical connection 16 conveys the signal from the feeler 5a amplified at least with one charge amplifier towards the outside. 
     In FIG. 6 the weft stop motion 1 is detachably fixed with attachment means 20 to the reed 18 or to the loom sley 22 and with the sensor 5a penetrates the drop wires. It can be variably positioned along the reed 18, with the weft stop motion 1 and also the sensor element 2 lying outside the loom width and not touching any warp threads. 
     FIG. 7 shows a further embodiment of a weft stop motion 1 having an attachment device 15. By extending the conductive connection 5b between feeler 5a and the charge amplifier 10, the shape of the sensor element 2 is constructed so that the sensor element 2 can be inserted on the side of the weft channel between the drop wires 23 and so that the weft stop motion 1 can be attached on the side of the weft channel to the loom sley 22, also within the loom width so that its position can be varied. 
     FIG. 8 shows a further embodiment of a sensor element 2 with an attachment device 15, which can be attached on the side of the reed 18 remote from the weft channel 1 to the loom sley 23, also within the loom width, so that its position can be varied. 
     The attachment device 15 has the additional property that there are devices which enable the feeler 5a in the weft channel 19 of the reed 18 to be positioned so that the sensor element at least partially surrounds the weft channel 19, without protruding into the weft channel 19. The weft stop motion 1 described for air-jet looms is also suitable for other types of looms in which the thread has an electrostatic charge. Thus this weft stop motion is also suitable for projectile weaving machines, for example.