Thread brake

Abstract: Thread brake, characterized in that it mainly consists of a number of fixed thread guide elements (13,14,15,16); at least two movable thread guide elements (18,19) mounted on a rotatable body (17) which, through rotation, can be brought in an opposite direction through the trajectory of a thread (2) guided by the fixed thread guide elements (13,14,15,16), such that the thread (2) is bent in two places; means (20) which restrict the rotation of said body (17) during the braking; and drive means (21) to rotate said body (17).

Description: This invention concerns a thread brake, in particular a thread brake for weaving machines. In general the thread brake can be used for different applications in weaving machines, but it is meant in the first place for braking the weft threads between the feed spool and the means with which the weft thread is inserted in the shed. The thread brake hereby aims to brake the weft thread before it has reached the end of the shed, such that the risk that the weft thread breaks at the time its movement is blocked is small. Thread brakes are already known in many forms. For example FR 2.271.126 and US 2.326.714 disclose thread brakes comprising a number of fixed thread guide elements; at least two movable thread guide elements mounted on a rotatable body which, through rotation, can be brought in an opposite direction through the trajectory of a thread guided by the fixed thread guide elements, such that the thread is bent in two places; and means to rotate said body. During braking, the position of the rotatable body of these brakes is determined by the balance between the braking force and the tension in the thread, as a result of which this position permanently fluctuates. These known brakes are very slow and are not able to provide in braking forces at welldefined moments of time, and therefore are not apt for use as a insertion brake. In fact, the invention aims a thread brake which reacts very quickly, such that the weft thread is always braked at the right moment in each weaving cycle. The invention also aims a thread brake with a very long life. Another aim of the invention is to offer a thread brake with a very compact construction. To this end the invention relates to thread brake, comprising a number of fixed thread guide elements; at least two movable thread guide elements mounted on a rotatable body which, through rotation, can be brought in an opposite direction through the trajectory of a thread guided by the fixed thread guide elements, such that the thread is bent in two places; and drive means to rotate said body, characterized in that said brake further comprises means which, during braking, restrict the rotation of said body at a set position. Preferably said body can rotate along a rotary shaft and the movable thread guide elements consist of pins which are mounted on the body at equal distances along either side of said rotary shaft. The drive means preferably consist of an electromagnetic drive. The thread brake according to the invention offers the advantage that the bearing of said body and of the drive means only has to absorb a small force thanks to the symmetrical load, such that there is little wear. The thread brake also offers the advantage that even with a slight rotation a considerable braking force is offered, as two brake zones are provided. Moreover, between the two brake zones there is a zone available which is suited to integrate other functions. In order to better explain the characteristics according to the invention, by way of example only and without being limitative in any way, the following preferred embodiments are described with reference to the accompanying drawings, in which: figure 1 shows a thread brake according to the invention in an application; figure 2 shows a thread brake according to the invention in a front view and in a cross section; figure 3 shows a cross section according to line III-III in figure 2; figure 4 shows a cross section according to line IV-IV in figure 3; figure 5 shows the thread brake from figure 2, but for a different position; figure 6 shows a variant according to the invention; figure 7 shows a cross section according to line VII-VII in figure 6. Figure 1 shows an arrangement of a thread brake 1 for braking a thread 2, in this case a weft thread of a weaving machine. As is known the thread 2 is hereby unspooled from a feed spool 3, spooled in a prewinder 4 on a drum 5 by means of a winding tube 6, intermittently released from the drum 5 by means of an electromagnetically controlled blocking element 7 and inserted in the shed 9 of the weaving machine by insertion means 8. In the case of an airjet weaving machine, the insertion means 8 usually consist of a fixed auxiliary main nozzle 10 and a main nozzle 12 mounted on the sley 11 of the weaving machine. The thread brake 1 is preferably mounted at the entry of the auxiliary main nozzle 10 and aims to brake the thread 2 at the end of each insertion in the shed 9, such that the thread 2, as the blocking element 7 closes, is brought to a standstill in a less abrupt manner. According to the invention the thread brake 1 as represented in figures 2 to 5 mainly consists of a number of fixed thread guide elements 13, 14, 15 and 16; at least two movable thread guide elements 18 and 19 mounted on a rotatable body 17; means 20 which restrict the rotation of the body 17 during the braking; and drive means 21 to rotate said body 17. The fixed thread guide elements 13, 14, 15 and 16 are preferably placed according to one straight line. In the example shown the thread guide elements 13, 14 and 15 consist of thread eyes, whereas the thread guide element 16 is formed by the entry of the auxiliary main nozzle 10. Through rotation, the movable thread guide elements 18 and 19 can be brought in an opposite direction through the trajectory of a thread 2 guided by the fixed thread guide elements 13-16, such that the thread 2, during the braking, as shown in the position from figure 5, is bent in two directions. To this end the movable thread guide elements 18 and 19 respectively can be moved between the fixed thread guide elements 13-14 and 15-16. It is clear that the same effect is obtained when the thread guide elements 14 and 15 are replaced by a common element. Said body 17 is mounted on a shaft 22 which is mounted in a rotatable manner in the housing 24 by means of bearings 23. The movable thread guide elements 18 and 19 preferably consist of pins, formed of folded threads, which are situated on either side of the rotary shaft 25 at equal distances. Because of the symmetrical arrangement, the centre of gravity of the body 17 and the thread guide elements 18 and 19 mounted on it coincides with the rotary shaft 25, which is advantageous in that no forces are created in the bearings 23 of the shaft 22 which are due to the accelerations and decelerations which occur during the rotation of said body 17. The rotary shaft 25 is mounted horizontally in the example shown, such that the dust which is created in the thread brake 1 can drop down and does not come into contact with the drive means 21. The drive means 21 consist of an electrical drive, such as for example a metal or magnetic rotor 26 which is mounted on the shaft 22, and a solenoid 27 which forces the rotor 26 in a sense of rotation V as it is excited. Naturally, the drive means 21 can also consist of another electrical drive such as a stepping motor or a DC motor. The thread brake 1 is also provided with drawback means, such as a drawback spring 28 which makes the body 17 turn back after the excitation of the drive means 21 has stopped. The drawback spring 28 forces the body 17 against stopping means 29, such as for example two taps 30 which can cooperate with the respective thread guide elements 18 and 19. The above-mentioned means 20 which restrict the rotation of the body 17 during the braking may for example also consist of two taps 31 which can cooperate with the respective thread guide elements 18 and 19. Preferably the above-mentioned taps 30 and 31 are situated at equal distances from the rotary shaft 25 of the body 17, such that due to this arrangement no forces are created in the bearings 23 of the shaft 22 as the thread guide means 18 and 19 bump against said taps 30 and 31. It is clear that according to a variant the above-mentioned means 20 and 29 which restrict a rotation of the body can also be provided at the height of the shaft 22 on which the body 17 is mounted or at the height of the rotor 26. Preferably the thread brake 1 is provided with setting means 32 which allow to alter the braking force of the thread brake 1. To this end at least the means 20, and preferably also the stopping means 29 can be moved. To this end the taps 30 and 31 are mounted on a support 33 which can be rotated around the rotary shaft 25 and which is clamped in the required angle position by means of an adjusting screw 34. In the zone between the thread guide elements 14 and 15, as represented in figures 2 and 3, a nozzle 35 can be provided to blow the thread 2 in a duct 36 if required. The duct 36 may be connected to a waste can 37 so as to carry off the thread 2. It is known that a wrongly inserted weft thread 2 can be removed from the shed 9 by providing a connection for it to the feed spool 3 and by applying a procedure on it as described for example in US patent 4.898.214. According to this procedure the thread 2 is tightened at the height of the insertion means 8. However, as the thread 2 may not break, the blocking element 7 is put out of its blocking position such that a winding thread 2 is released. In order to prevent this extra thread end from entering in the shed 9, a reversing nozzle is provided to keep the thread 2 taught. According to the present invention the function of the reversing nozzle is performed by the nozzle 35 which blows the thread 2 in the duct 36. When weaving with several ducts and when switching over to one duct in case of break, it is known that the thread should be removed out of the main nozzle of the non-active duct after a while so as to prevent it from fraying and being blown in the shed. As is known from US patent 4.998.567 use can be made to this end of a thread removal device. The function of such a device can be carried out according to the present invention by the nozzle 35 which to this end blows the thread 2 in the duct 36. In the above-mentioned zone a detector 38 can also be integrated which allows to check the presence of the thread 2. At the height of the thread guide element 13 a threading nozzle 39 can be provided. Figures 2 and 5 further show how the auxiliary main nozzle 10, the nozzle 35 and the threading nozzle 39 can be provided with compressed air by means of valves 40, 41 and 42 which are driven by means of a drive and control unit 43. Also the solenoid 27 is controlled by the unit 43 by means of a control line 44. The working of the thread brake is described hereafter by means of figures 2 and 5. In a state of rest the rotatable body 17 takes up a position as represented in figure 2, whereby the thread guide elements 18 and 19 are forced against the taps 30 with their bottom end by means of the drawback spring 28. In this position the thread 2 can pass freely through the thread brake 1. At the end of each insertion the thread 2 is braked before being completely stopped by the blocking element 7. To this end the solenoid 27 is excited, as a result of which the body 17 rotates and takes up a position as represented in figure 5, whereby the bottom ends of the thread guide elements 18 and 19 make contact with the taps 31. Due to the bending around the thread guide elements 18 and 19 the thread 2 is braked. The braking force is determined by the set position of the taps 31, and not by the torque of the drive means 21. This torque is high so as to cause a very fast braking. In the embodiment from figures 2 to 5 the thread 2 is exclusively braked due to the bending along the thread guide elements 13, 18, 14, 15, 19 and 16. As shown in figures 6 and 7 the taps 31 can also be placed such that the thread 2, as the thread brake 1 is excited, is also braked because it is clamped between the thread guide elements 18 and 19 and the taps 31. In the embodiment of figures 6 and 7 the drive means 21 are integrated in the rotatable support 33. For clarity's sake, the adjusting screw 34 is represented in two different places in the views from figures 6 and 7. It is clear that the thread brake 1 can also be used in other than airjet weaving machines. It is clear that the above-mentioned element 17 can also be provided with several pairs of the above-mentioned thread guide elements 18 and 19 which can be moved respectively between fixed thread guide elements. Thus, use can be made for example of six fixed thread guide elements placed in line and four movable thread guide elements, whereby each movable thread guide element can move between each time two fixed thread guide elements. The present invention is in no way limited to the embodiments described by way of example and shown in the accompanying drawings; on the contrary, such a thread brake can be made in various forms and dimensions while still remaining within the scope of the invention.

Claims: Thread brake, comprising a number of fixed thread guide elements (13,14,15,16); at least two movable thread guide elements (18,19) mounted on a rotatable body (17) which, through rotation, can be brought in an opposite direction through the trajectory of a thread (2) guided by the fixed thread guide elements (13,14,15,16), such that the thread (2) is bent in two places; and drive means (21) to rotate said body (17), characterized in that said brake further comprises means (20) which, during braking, restrict the rotation of said body (17) at a set position. Thread brake according to claim 1, characterized in that it has at least three fixed thread guide elements (13;14,15;16), and in that the movable thread guide elements (18,19) consist of pins which can be moved between two fixed thread guide elements (13,14;15,16) respectively. Thread brake according to claim 1 or 2, characterized in that the movable thread guide elements (18,19) are situated on either side of the rotary shaft (25) of said body (17), at equal distances from this rotary shaft (25). Thread brake according to any of the above claims, characterized in that the above-mentioned means (20) consist of taps (31) which are situated at equal distances from the rotary shaft (25) of said body (17). Thread brake according to any of the above claims, characterized in that the above-mentioned drive means (21) consist of an electrical drive. Thread brake according to any of the above claims, characterized in that it is provided with drawback means (28) which force said body (17) to make contact with stopping means (29) when in a state of rest. Thread brake according to claim 6, characterized in that the above-mentioned stopping means (29) consist of taps (30) which are situated at equal distances from the rotary shaft (25) of said body (17). Thread brake according to any of the above claims, characterized in that it is provided with setting means (32) to set the braking force which allow to alter the position of the means (20) which restrict the rotation as the thread brake (1) is switched on. Thread brake according to any of the above claims, characterized in that between the movable thread guide elements (18,19) a nozzle (35) and a duct (36) for threads (2) have been applied. Thread brake according to any of the above claims, characterized in that it is provided with a threading nozzle (39). Thread brake according to any of the above claims, characterized in that the movable thread guide elements (18,19) cooperate with the means (20) which restrict the movement during the braking, such that the thread (2) is braked between these thread guide elements (18,19) and these means (20).

Inventors: DE RO IGNACE, MARKEY HUGO, DE RO, IGNACE, MARKEY, HUGO
Applicants: PICANOL NV, PICANOL N.V.
Application year: 1992
Main classification: B65H59
IPC codes: D03D47, B65H59