WO2017076600A1

WO2017076600A1 - Method for inserting a weft thread

Info

Publication number: WO2017076600A1
Application number: PCT/EP2016/074588
Authority: WO
Inventors: Patrick Puissant
Original assignee: Picanol
Priority date: 2015-11-06
Filing date: 2016-10-13
Publication date: 2017-05-11
Also published as: CN108350627B; EP3371359B1; BE1023583A1; CN108350627A; BE1023583B1; EP3371359A1

Abstract

A method for inserting a weft thread (4, 5), comprising the steps of activating the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) successively, with the advancement of the weft thread (4, 5) through the shed (1), detecting an average arrival instant (T_A, T_A1) at which a leading end of an average weft thread (4, 5) reaches an arrival detector (25) arranged at an arrival end of the shed (1), detecting an instant (T_LW) at which the last winding is unwound from the winding drum (53), determining as a reference value (DT) the time difference between an average arrival instant (T_A, T_A1) and an average instant (T_LW) at which the last winding is unwound from the winding drum (53), determining at least one point (P_i) of an estimated trajectory (49, 49A, 49B, 49C) of the leading end of the average weft thread (4, 5) transported through the shed (1) as a function of the reference value (DT), and adapting the start of the period of time (40, 41, 42, 43, 44, 45, 46, 47, 48) for supply of compressed air to at least one of the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) to this estimated trajectory (49, 49A, 49B, 49C). An airjet weaving machine with a device for applying this method.

Description

Method for inserting a weft thread

TECHNICAL FIELD AND PRIOR ART

[0001 ] The invention relates to a method for inserting a weft thread in an airjet weaving machine, and an airjet weaving machine adapted to apply this method.

[0002] Airjet weaving machines in which compressed air is supplied to a number of relay blowers in order to transport a weft thread via an air guide channel through a shed are known. Such airjet weaving machines comprise a supply device for supplying compressed air to the relay blowers. Supplying compressed air to a relay blower is effected, for example, by activating during a certain period of time a shut off valve which is disposed between the relay blower and a buffer reservoir comprising compressed air at a specific pressure.

[0003] It is known amongst other from US 3705608, US 4262707 and EP 1951941 B1 to supply compressed air successively to the successive relay blowers with an advancement of a leading end of an inserted weft thread. At each relay blower compressed air is supplied sufficiently long so that both a fast weft thread and a slow weft thread are sufficiently supported by compressed air coming from the successive relay blowers.

[0004] It is known amongst other from EP 164773 A1 and EP 1951941 B1 to provide at least one arrival detector for detecting the arrival of the leading end of an inserted weft thread at the arrival detector. It is also known amongst other from EP 229432 A2 and EP 1951941 B1 to provide at least one winding detector at the height of a prewinder for detecting a part of a weft thread arriving at or passing along the winding detector when a weft thread is drawn off from the winding drum of the prewinder.

SUMMARY OF THE INVENTION

[0005] It is an object of the invention to provide a method for inserting a weft thread in an airjet weaving machine which allows to reduce the amount of compressed air used for inserting weft threads into a shed.

[0006] This object is solved by a method for inserting weft thread with the features of claim 1 and an airjet weaving machine with the features of claim 10. Preferred embodiments are defined in the dependent claims. The invention is particularly suitable for being applied for inserting a weft thread in an airjet weaving machine with a prewinder which allows to release weft threads of different lengths.

[0007] According to a first aspect, a method for inserting a weft thread in an airjet weaving machine is provided, which weft thread is wound in a number of windings on a winding drum of a prewinder, is drawn off from the prewinder and is transported through a shed by means of compressed air blown by at least one main blower and by successive relay blowers, wherein the method comprises the steps of activating the relay blowers successively, with the advancement of the weft thread through the shed, over a period of time for supporting the weft thread, detecting an average arrival instant T_A at which a leading end of an average weft thread reaches an arrival detector arranged at an arrival end of the shed, detecting the instant T_Lw at which the last winding is unwound from the winding drum, and determining as a reference value DT the time difference between an average arrival instant and an average instant at which the last winding is unwound from the winding drum, and wherein at least one point of an estimated trajectory of the leading end of the average weft thread transported through the shed is determined as a function of the reference value, and the start of the period of time for the supply of compressed air to at least one of the relay blowers is adapted to this estimated trajectory.

[0008] As a result of the method according to the invention, in case a weft thread is estimated to arrive on average earlier in the weaving cycle at a relay blower, the instant at which the supply of compressed air to this relay blower with respect to the weaving cycle can be advanced, and in case a weft thread is estimated to arrive on average later in the weaving cycle at a relay blower, the instant at which the supply of compressed air to this relay blower with respect to the weaving cycle can be delayed. This method according to the invention has the advantage that the start of the supply of compressed air to a relay blower can take place as late as possible in the weaving cycle, which results in a reduction of the compressed air consumption.

[0009] When inserting weft threads having a slow speed and a late arrival instant and assuming unvaried instants at which the windings are unwound from the winding drum, the reference value is larger compared to weft threads having a high speed and an earlier arrival instant. This reference value is used to start the supply of compressed air later for weft threads having a slow speed than for weft threads having a high speed.

[0010] For weaving a fabric of a defined width, weft threads of different lengths can be inserted resulting in different waste lengths, this means different lengths of the weft thread extending past the woven fabric. For this purpose, a prewinder can be applied that allows a variation in the length of the weft thread to be inserted, such as a prewinder of the type as known from WO 92/01 102 wherein the circumferential length of the winding drum can be varied by means of a motor. It are the findings of the inventor, that the different length and the resulting different circumferential length of each winding influences the trajectory of the leading end of the weft thread without significant changes in the arrival instant, wherein this effect is also taken account of by the reference value. It should be noted that depending on the waste length, the difference A - T|_w can also be a negative value in case the instant at which the last winding is unwound from the winding drum is later than the arrival instant due to a comparatively long waste length.

[001 1 ] In one embodiment, the estimated trajectory is constructed using one point determined as a function of the reference value. In preferred embodiments, several successive points of the estimated trajectory of the leading end of an average weft thread transported through the shed are determined as a function of the reference value.

[0012] In one embodiment, the trajectory of the leading end of the weft thread up to the arrival detector is split into a number of equal intervals and the points of the estimated trajectory are determined in function of endpoints of each interval and the reference value. In preferred embodiments, the instants at which the windings are unwound from the winding drum are detected, and at least one point of the estimated trajectory of the leading end of the average weft thread transported through the shed is determined as a function of the reference value and a detected instant, at which an associated winding is unwound from the winding drum. This allows an adjustment of the active period of time of blowing to actual measurements on an inserted weft thread. In case the reference value has a positive sign or a negative sign, the average instants at which the windings are unwound from the winding drum are used for calculating the points of the trajectory.

[0013] In preferred embodiments, the at least one point is determined using the formula i = T_iW + k^*DT, with index i, detected instant T_iW at which i-th winding is unwound, reference value DT = T_A - T_Lw, and constant fraction k,, wherein 0 < k, < 1 .

[0014] The constant fraction k, is determined by the person skilled in the art considering the knowledge of weft thread flight characteristics, unwinding effects such as ballooning etc.

[0015] When weaving from a thread supply, the average speed of the weft threads may increase or decrease with the thread supply becoming smaller. In order to compensate for trends of the average speed of the weft threads, in preferred embodiments the average arrival instant and/or the average instant at which the last winding is unwound from the winding drum are continuously updated based on the last N number measurements, in particular the last ten to fifty measurements, more particular the last twenty measurements. It is obvious to the person skilled in the art that for determining the average values, known methods of statistical evaluation can be applied.

[0016] In one embodiment, a diameter of the winding drum of the prewinder is variable, wherein after a variation of the diameter, the average arrival instant and/or the average instant at which the last winding is unwound from the winding drum are determined again. In other words, in case the boundary conditions are varied, the method will be "calibrated".

[0017] In one embodiment, the start of the period of time for supply of compressed air to at least one of the relay blowers is adapted to said estimated trajectory so that said relay blower blows at least almost at full pressure immediately after the leading end of an average weft thread as determined by the estimated trajectory has passed said relay blower.

[0018] At each average speed, slow weft threads and fast weft threads are inserted. It is assumed that starting the period of time for the activation of the blowers as late as possible results in fast weft threads being slowed down so that both fast weft threads and slow weft threads are sufficiently supported by airjets from the relay blowers. By starting the blowing of the relay blowers as late as possible the supplied amount of compressed air and the air consumption are reduced.

[0019] In addition, according to one embodiment the end of the period of time for supply of compressed air to at least one of the relay blowers is adapted to measurements on the inserted weft threads, wherein the period of time for supply of compressed air to at least one of the relay blowers is ended earlier in case of fast weft threads than in case of slow weft threads. This allows for a further reduction of the air consumption as the blowing is stopped in case the airjet from said relay blower no longer or at least no longer significantly contributes to the transportation of the weft thread.

[0020] In one embodiment, all relay blowers are activated and/or deactivated separately. In preferred embodiments, the relay blowers are grouped in sets, wherein the relay blowers of one set are activated and deactivated conjointly.

[0021 ] According to a second aspect, an airjet weaving machine with a prewinder, at least one main blower and successive relay blowers is provided, wherein a weft thread is wound in a number of windings on a winding drum of the prewinder, drawn off from the prewinder and transported through a shed by means of compressed air blown by the at least one main blower and by the successive relay blowers, and wherein a device for applying a method as described above is provided. In preferred embodiments, a prewinder is provided with at least one winding detector for detecting the instants at which the windings are unwound from the winding drum. In preferred embodiments, the prewinder allows to release weft threads of different lengths, in particular the prewinder is provided with a winding drum of which the circumferential length can be varied by means of a motor.

[0022] Further characteristics and advantages of the invention will emerge from the following description of the exemplary embodiments shown in the drawings and from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematically a part of an airjet weaving machine that is particularly suitable for applying the method according to the invention;

Figure 2 shows schematically a prewinder that is particularly suitable to be applied in the method according to the invention;

Figure 3 shows a trajectory and a line for an average weft thread;

Figure 4 shows a flowchart for the supply of compressed air to successive relay blowers for the estimated trajectory of Fig. 3;

Figure 5 shows a variant of Fig. 3, wherein the arrival at the arrival detector is varied with respect to the weaving cycle;

Figure 6 shows a variant of Fig. 3, wherein per weaving cycle a larger length of weft thread is released at the prewinder;

Figure 7 shows a variant of Fig. 3, wherein per weaving cycle a substantially larger length of weft thread is released at the prewinder.

Figure 8 shows another flowchart for the supply of compressed air to successive relay blowers.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0023] Figure 1 shows a device for transporting a weft thread through a diagrammatically indicated shed 1 of an airjet weaving machine. This device has two supply channels 2, 3 for the supply of weft threads 4, 5. Each supply channel comprises a thread supply 6, a prewinder 7, a first main blower 8 and a second main blower 9. Furthermore, the airjet weaving machine has a reed 10 in which a guide channel 1 1 is provided which allows a weft thread to be transported through the shed 1 via this guide channel 1 1 with the aid of compressed air. Near this guide channel 1 1 , successive sets of relay blowers 12, 13, 14, 15, 16, 17, 18, 19 and 20 are provided in order to successively support a weft thread with compressed air. In addition, an arrival detector 25 is provided for detecting the arrival of the leading end of an inserted weft thread at the arrival detector 25. The arrival detector 25 is arranged at the arrival end of the guide channel 1 1 which is situated opposite the end of the guide channel 1 1 where the main blowers 9 are arranged. The instant relative to a reference instant in the weaving cycle at which a leading end of the weft thread 4, 5 reaches the arrival detector 25 is referred to as arrival instant T_A.

[0024] Fig. 1 also shows a winding detector 26 near each prewinder 7, which winding detector 26 transmits a signal to a control unit 35 each time a winding 28 is drawn off from a winding drum of a prewinder 7, more particularly each time a part of a weft thread arrives at or passes along the winding detector 26. Such a winding detector 26 is also referred to as a winding sensor. The signals from the winding detectors 26 are in this case transmitted to the control unit 35 by means of a wired or wireless connecting line 34. In this case, the instant at which a winding 28 arrives at a winding detector 26 is determined relative to the reference instant in the weaving cycle, also named winding time Tw, wherein the index i indicates the successive windings 1 , 2, 3, .... The instant at which a last winding 28 arrives at the winding detector 26 is referred to as last winding time T_Lw- Between each prewinder 7 and an associated main blower 8 there is arranged a balloon limiter 27 for limiting the diameter of the weft thread balloon when weft thread is drawn off from the prewinder 7. Between the balloon limiter 27 and the main blower 8 there is also arranged a thread brake 29 in order to brake a weft thread at the end of the insertion of it.

[0025] The main blowers 8 and 9 are connected to a compressed-air source 23 via associated shut-off valves 21 and throttle valves 22. Each set of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 is analogously connected via a shut-off valve 24 and an associated throttle valve 30 to the compressed-air source 23. According to a variant (not shown), a separate compressed-air source may be provided for both the main blowers and the relay blowers. In addition, a stretching blower 31 is shown which serves to keep a weft thread stretched after the insertion of it. The stretching blower 31 is connected to a compressed-air source 23 via a shut-off valve 32 and a throttle valve 33. According to a variant (not shown), a separate compressed-air source may be provided for both the main blowers, the relay blowers and/or the stretching blower. In the embodiment shown, the relay blowers are grouped in sets of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20, each set comprising at least two relay blowers. [0026] The shut-off valves 21 , 24, 32 and the throttle valves 22, 30, 33 are controlled by the control unit 35 of the airjet weaving machine, as shown in Fig. 1 . The arrival detector 25 and the winding detectors 26 in this case also cooperate with the control unit 35. The shut-off valves for example consist of electromagnetic valves which can be controlled by the control unit 35. The throttle valves can in this case also be designed such that they can be driven by a motor and controlled by the control unit 35.

[0027] A weft thread 4, 5 is blown into the guide channel 1 1 by the main blowers 8, 9 and is then transported further along the guide channel 1 1 by jets of air from the relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20. The guide channel 1 1 is, for example, arranged in a reed 10 and is disposed in a known way in a shed during the insertion of a weft thread 4, 5. The main blowers 9, the relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20, the reed 10 and the arrival detector 25 are mounted in a known way on a sley (not shown) moving in a reciprocating fashion. The thread supply 6, the prewinders 7, the main blowers 8 and the stretching blower 31 , for example, are mounted on a frame of the airjet weaving machine.

[0028] The arrival detector 25 is, for example, connected to the control unit 35 by means of a wired connecting line 36. The shut-off valves 21 , 24, 32 and the throttle valves 22, 30, 33 are connected to the control unit 35 by means of a common wired connecting line 37. Each prewinder 7 comprises a magnet pin 38 in order to release a desired length of weft thread 4 or 5 at a suitable instant in the weaving cycle. The magnet pins 38 and the thread brakes 29 are connected to the control unit 35 via a common wired connecting line 39. The weaving machine also comprises an input unit 50 in order to input parameters into the control unit 35 and a display unit 51 that is connected to the control unit 35 in order to display data. In other embodiments, some or all of the wired connecting lines are replaced by a wireless connecting line, in other words a wireless communication link.

[0029] In Fig. 2 a part of a prewinder 7 is shown wherein the circumferential length of the winding drum 53 can be varied by means of a motor 52 (shown schematically). The motor 52 is arranged in the frame 61 of the prewinder 7. The winding drum 53 is formed by four fingers 54, 55, 56, 57. The finger 54 that is situated opposite to the magnet pin 38 is fixed to the frame 61 of the prewinder 7 by means of a fixation 58. The winding detector 26 is arranged near the magnet pin 38. The fingers 55, 56, 57 can be displaced radially with respect to the center 62 and each are guided by rods 59, 60, respectively in direction R55, R56, R57. The rods 59 can be driven by the motor 52 in order to vary the circumferential length of the winding drum 53. A weft thread 4 is wound on the winding drum 53 by means of a winding arm 63. Another embodiment of a prewinder with a winding drum and a motor in order to vary the circumferential length of the winding drum is described in WO 92/01 102.

[0030] The windings 28 are drawn off in the direction R indicated by an arrow in Fig. 2, wherein when the weft thread 4 is being drawn off a part of the weft thread 4 passes along the winding detector 26 so that the winding detector 26 detects the instant T_iW at which the i-th winding is drawn off. In case the weft thread is wound, for example, in five windings on the prewinder 7 (see Fig. 1 ), five instants T_1W, T2W, T_3W, T_4W and T_Lw at which the windings are unwound from the winding drum of the prewinder 7 are detected.

[0031 ] Fig. 3 shows schematically an estimated trajectory 49 of a leading end of an average weft thread 4 transported through the guide channel 1 1 reaching at an average arrival instant T_A the arrival detector 25 (see Fig. 1 ), wherein at least one point P, of the estimated trajectory 49 of the leading end of the average weft thread 4, 5 transported through the guide channel 1 1 is determined as a function of a reference value DT.

[0032] The abscissa of the diagram shown in Fig. 3 is expressed units of time t and the ordinate is expressed in a distance p along the guide channel 1 1 , wherein the distance L almost corresponds to the length of the guide channel 1 1 up to the arrival detector 25. If the speed of the weaving machine is known, the units of time can easily be converted to crank degrees of the main shaft of the weaving machine. In this case, one crank degree of the weaving machine corresponds, for example, to a number of milliseconds or one millisecond corresponds to a number of crank degrees. However, the use of crank degrees is preferred, as in this case the control of the supply of compressed air to the sets of relay blowers can take place independently of the speed of the weaving machine. This is particularly advantageous if successive insertions of weft threads take place at a different speed of the weaving machine, in other words if the speed of the weaving machine is not constant.

[0033] According to an embodiment of the invention, in case the weft thread is wound in five windings to the prewinder 7 (see Fig. 1 ), as explained above five instants T_1W, T₂w, T_3W, T_4W, T|_w at which the windings are unwound from the winding drum of the prewinder 7 are detected. Also the length L is divided in five length parts and a line 64 is shown based on these five instants T_1W, T₂w, T_3W, T_4W, T_Lw and these five length parts. In addition, the time difference between the average arrival instant T_A and an average instant T_Lw at which the last winding is unwound from the winding drum is determined as a reference value DT, this means the reference value DT = T_A - T_Lw- In function of these values, at least one point P, of an estimated trajectory of a leading end of an average weft thread 4 transported through the guide channel 1 1 is calculated.

[0034] In the embodiment shown, four points P-i, P₂, P3, P₄ of the estimated trajectory 49 of the leading end of an average weft thread are determined as a function of the first four instants T_1W, 2w, T_3W, T_4W, and the reference value DT, using the formula P, = Τ,νν + k *DT, with Τ,νν being the detected instant at which the i-th winding is unwound from the winding drum, DT being the determined reference value, and k, being a constant fraction, wherein 0 < k, < 1 , which is established for each of the instants Tw. The fraction k, can be determined considering the knowledge about a formation of a balloon in the beginning of the insertion and braking effects at the end of the insertion.

[0035] In the embodiment shown, the points P, are calculated as follows: Pi = T_1W + 1/3 DT, P₂ = T_2W + 2/3 DT, P₃ = T_3W + 2/3 DT, P₄ = T_4W + 3/3 DT, P₅ =T_LW + 3/3 DT. Subsequently the estimated trajectory 49 of the leading end of an average weft thread transported through the guide channel 1 1 is determined based on the points P1 , P2, P3, P4 and P5 as indicated in Fig. 3.

[0036] Further, according to the invention, the instant at which the supply of compressed air to a set of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 (see Fig. 1 ) starts, is determined based on the estimated trajectory 49. In preferred embodiments, the instant to start the supply of compressed air is optimized such that each set of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 blows almost at full pressure a short time after the leading end of the weft thread as determined by the estimated trajectory 49 has passed by the respective set of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20. When setting the start time, the person skilled in the art will have little trouble to consider the fact that delay times for example due to reaction times of the valves and/or for build-up of pressure have to be considered.

[0037] Fig. 4 shows a flowchart with blocks 40, 41 , 42, 43, 44, 45, 46, 47, 48 indicating in each case a period of time in which one of the sets of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 respectively, are supplied with compressed air, in other words, a period when the associated shut-off valves 24 (see Fig. 1 ) are opened in order to supply compressed air to an associated set of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20. These blocks are adjoining the line 49. The flowchart as shown in Fig. 4 is, for example, displayed on the display unit 51 that is connected to the control unit 35. As known to the person skilled in the art, for each average weft thread speed, slow weft threads as well fast weft threads may take place, which are arriving later or earlier than the average weft thread 4 at the arrival detector. Hence, the periods of time have to be chosen for allowing the correct insertion of slow weft threads and fast weft threads.

[0038] As shown in Fig. 5, during the weaving process the average arrival instant T_A can vary, for example being delayed to a later average arrival instant T_Ai . This variation may be caused for example if the weft thread is inserted less stretched through the shed. Assuming that the average unwinding instants T_1W, T2W, T_3W, T_4W, T_Lw remain at least sufficiently the same, this delay of the average arrival instant will result in a larger reference value DT, that in Fig. 5 is determined as DT = T_Ai - T_Lw- In this case the estimated trajectory 49 is calculated again and an updated estimated trajectory 49A as shown in Fig. 5 is determined. In order to allow for a sufficient support of the weft threads and minimizing the compressed air consumption, the activation of the sets of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 is adapted to said updated estimated trajectory resulting in a later activation of the sets of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 in the embodiment shown.

[0039] The method is particularly suitable to be applied in weaving machines wherein the circumferential length of the windings can be varied. By varying the circumferential length of the windings, the length of the inserted weft thread is also varied, so that fabrics are woven with more or less waste length. When varying the weft thread length, even if the weft thread is inserted with almost constant speed into the shed and an arrival instant remains at least substantially unvaried, the instants at which windings are unwound will be effected. More particular, the instants at which the windings are unwound will be delayed with an increasing winding circumference of the winding drum of the prewinder. Similarly, the instants at which the windings are unwound will be advanced with a decreasing winding circumference of the winding drum of the prewinder. This because the length of a winding is determined by the circumferential length of the winding drum. Further, according to the findings of the inventor, the winding circumference will also influence a balloon forming near the prewinder. These effects are compensated by the method of the invention as will be explained with reference to Figs. 6 and 7.

[0040] Fig. 6 shows a variant of Fig. 3, wherein, per weaving cycle a slightly longer weft thread is drawn off from the prewinder. The arrival instant T_A remains unchanged. However, the five instants T_1W, T₂w, T_3W, T_4W, T_Lw and the reference value DT = T_A - T_Lw change. When using the method according to the invention, a line 64B based on the five instants T_1W, T_2W, T_3W, T_4W, T_Lw is determined and an estimated trajectory 49B is determined using the reference value DT and the instants T _W, T_2W, T_3W, T_4W. [0041 ] Fig. 7 shows a variant of Fig. 3, wherein, per weaving cycle a substantially longer weft thread is drawn off from the prewinder. This results in an instant T_Lw at which the last winding is unwound from the winding drum taking place later than the arrival instant T_A. Therefore, the reference value DT = T_A - T_Lw has a negative sign. When using the method according to the invention, a line 64C based on the five instants T_1W, T₂w, T_3W, T_4W, T_Lw is determined and an estimated trajectory 49C is determined using the reference value DT and the instants T_1W, T_2W,

[0042] As will be understood by comparing Figs. 3, 6 and 7, in case a weft thread having a greater length is released by the prewinder, the instants T_1W, T_2W, T_3W, T_4W, T_Lw at which the windings are unwound from the winding drum are delayed with the increased length, and the reference value DT is varied or even has a negative sign (see Fig. 7). According to the invention, the estimated trajectory 49 is adapted to an estimated trajectory 49B or 49C. This results in the instant at which the supply of compressed air to a set of relay blowers starts with respect to the weaving cycle being advanced for longer weft threads. Similarly, in case a weft thread with a smaller length is released by the prewinder, the instant at which the supply of compressed air to a set of relay blowers starts with respect to the weaving cycle is delayed.

[0043] In case the reference value DT has a negative sign as shown in Fig. 7, the points of the estimated trajectory are assumed to take place before the instants T_1W, T^, T_3W, T_4W. Therefore, the points of the estimated trajectory are determined using the formula P, = T_iW + k ^*DT, with index i, an average instant Τ,νν at which i-th winding is unwound, reference value DT, and constant fraction k,, wherein 0 < k, < 1 .

[0044] As shown in Fig. 8, the instant at which the supply of compressed air to a set of relay blowers 12, 13, 14, 15, 16, 17, 18, 19, 20 is interrupted, can be further determined based on measurements on the inserted weft thread, wherein the period of time indicated by the blocks 40, 41 , 42, 43, 44, 45, 46, 47, 48 for the supply of compressed air to at least one set of relay blowers 14, 15, 16, 17, 18 is ended earlier in case of fast weft threads than in case of slow weft threads, as indicated by the shorter blocks 42, 43, 44, 45, 46 than in Fig. 4.

[0045] Similarly as shown in Figs. 4 and 8 wherein blocks 40, 41 , 42, 43, 44, 45, 46, 47, 48 adjoining the line 49, blocks can adjoin the lines 49A, 49B, 49C as shown respectively in Figs. 5, 6 and 7.

[0046] If the windings 28 are drawn off opposite to the direction R indicated by an arrow in Fig. 2, a winding detector 65 can be applied that is arranged at the opposite side of the magnet pin 38 close to the magnet pin 38, as shown in Fig. 2. It is preferred to arrange a winding detector 26, 65 close to the magnet pin 38, so that a part of the last winding passes along the winding detector 26, 65 a short time before the weft thread is blocked by the magnet pin 38. According to a variant a winding detector 66 can be applied that can generate a signal that is little influenced by the direction at which the windings 28 are drawn off, in other words a winding detector 66 that is arranged opposite to the magnet pin 38, as shown in Fig. 2.

[0047] It is also clear that an individual flowchart for the supply of compressed air to successive relay blowers may be provided for each type of weft thread 4, 5. The latter is particularly applicable if various weft threads are woven at a different weaving speed or transporting speed, more particularly when the speed of the weaving machine is adjusted to the weft thread to be inserted. In addition, an individual function may be provided for each type of weft thread 4, 5.

[0048] It is clear that a set of relay blowers may consist of at least one single relay blower or a number of relay blowers, for example two relay blowers, which are connected to a compressed- air source via a specific shut-off valve. The supply devices for compressed air to the main blowers, relay blowers and stretching blowers are, of course, not limited to the shut-off valves, throttle valves and compressed-air source shown, but may be replaced by any supply device which can set, control or adjust the supply of compressed air. It is clear that a method for regulating the supply of compressed air to the main blowers may be carried out independently of the method according to the invention and that both methods almost do not affect one another.

[0049] It is clear that notwithstanding in the drawings an embodiment is shown with nine sets of relay blowers, it is also possible to choose another number of sets of relay blowers depending on the width of the weaving machine. The method according to the invention can be applied advantageous, for example, in a relatively wide weaving machine.

[0050] The method according to the invention offers the advantage that, independently of the type of weft thread and of a variation in the measurements on a plurality of transported weft threads during transport of these weft threads, it is possible to achieve the activation of the supply of compressed air to at least one set of relay blowers in an optimum manner, so that the air consumption is suitably reduced.

[0051 ] In case two weft threads are transported together through a shed, the relay nozzles may be activated so that the fastest weft thread is supported sufficiently early, and then also the slowest weft thread is supported sufficiently early. [0052] It is clear that the airjet weaving machine is not limited to an airjet weaving machine wherein a weft thread is blown into a guide channel 1 1 by means of compressed air. The sets of relay blowers of the airjet weaving machine can also blow onto a holder for a weft thread which transports a weft thread through the shed. In addition, instead of standard compressed air, any fluid, such as standard compressed air mixed with a gas, a liquid or a vapor, can be used for inserting a weft thread in a shed of an airjet weaving machine. The method according to the invention claimed in the claims is not limited to the exemplary embodiments which have been shown and described, but may also comprise variants and combinations thereof which fall under the claims.

Claims

1 . Method for inserting a weft thread (4, 5) in an airjet weaving machine, which weft thread (4, 5) is wound in a number of windings on a winding drum (53) of a prewinder (7), is drawn off from the prewinder (7) and is transported through a shed (1 ) by means of compressed air blown by at least one main blower (8, 9) and by successive relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20), the method comprising the steps of activating the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) successively, with the advancement of the weft thread (4, 5) through the shed (1 ), over a period of time (40, 41 , 42, 43, 44, 45, 46, 47, 48) for supporting the weft thread (4, 5), detecting an average arrival instant (T_A, T_Ai) at which a leading end of an average weft thread (4, 5) reaches an arrival detector (25) arranged at an arrival end of the shed (1 ), detecting an instant (Ti_w) at which the last winding is unwound from the winding drum (53), and determining as a reference value (DT) the time difference between an average arrival instant (T_A, T_Ai) and an average instant (T_Lw) at which the last winding is unwound from the winding drum (53), characterized in that at least one point (P,) of an estimated trajectory (49, 49A, 49B, 49C) of the leading end of the average weft thread (4, 5) transported through the shed (1 ) is determined as a function of the reference value (DT), and the start of the period of time (40, 41 , 42, 43, 44, 45, 46, 47, 48) for the supply of compressed air to at least one of the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) is adapted to this estimated trajectory (49, 49A, 49B, 49C).

2. Method according to claim 1 , characterized in that successive points (P-i, P₂, P₃, P₄) of the estimated trajectory (49, 49A, 49B, 49C) of the leading end of the average weft thread (4, 5) transported through the shed (1 ) are determined as a function of the reference value (DT).

3. Method according to claim 1 or 2, characterized in that the instants (T_iW; T_1W, T₂w, T_3W, T₄w, T|_w) at which the windings are unwound from the winding drum (53) are detected, and at least one point (P,) of the estimated trajectory (49, 49A, 49B, 49C) of the leading end of the average weft thread (4, 5) transported through the shed (1 ) is determined as a function of the reference value (DT) and a detected instant (T_iW), at which an associated winding is unwound from the winding drum (53).

4. Method according to claim 3, characterized in that the at least one point (P,) is determined using the formula P, = Τ,νν + k *DT, with index i, detected instant Τ,νν at which i-th winding is unwound, reference value DT, and constant fraction k,, wherein 0 < k, < 1 .

5. Method according to any one of claims 1 to 4, characterized in that the average arrival instant (T_A) and/or the average instant (T_Lw) at which the last winding is unwound from the winding drum (53) are continuously updated based on the last N number measurements, in particular the last ten to fifty measurements, more particular the last twenty measurements.

6. Method according to any one of claims 1 to 5, characterized in that a diameter of the winding drum (53) of the prewinder (7) is variable, wherein after a variation of the diameter, the average arrival instant (T_A) and/or the average instant (T_Lw) at which the last winding is unwound from the winding drum (53) are determined again.

7. Method according to any one of claims 1 to 6, characterized in that the start of the period of time (40, 41 , 42, 43, 44, 45, 46, 47, 48) for supply of compressed air to at least one of the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) is adapted to an estimated trajectory (49, 49A, 49B, 49C), so that said relay blower (12, 13, 14, 15, 16, 17, 18, 19, 20) blows at least almost at full pressure immediately after the leading end of an average weft thread (4, 5) as determined by the estimated trajectory (49, 49A, 49B, 49C) has passed said relay blower (12, 13, 14, 15, 16, 17, 18, 19, 20).

8. Method according to any one of claims 1 to 7, characterized in that the end of the period of time (40, 41 , 42, 43, 44, 45, 46, 47, 48) for supply of compressed air to at least one of the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) is adapted to measurements on the inserted weft threads, wherein the period of time (40, 41 , 42, 43, 44, 45, 46, 47, 48) for supply of compressed air to at least one of the relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) is ended earlier in case of fast weft threads than in case of slow weft threads.

9. Method according to any one of claims 1 to 8, characterized in that the successive relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20) are grouped in sets, wherein the relay blowers of one set are activated and deactivated conjointly.

10. An airjet weaving machine with a prewinder (7), at least one main blower (8, 9) and successive relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20), wherein a weft thread (4, 5) is wound in a number of windings on a winding drum (53) of the prewinder (7), drawn off from the prewinder (7) and transported through a shed (1 ) by means of compressed air blown by the at least one main blower (8, 9) and by the successive relay blowers (12, 13, 14, 15, 16, 17, 18, 19, 20), characterized in that a device for applying a method according to any one of claims 1 to 9 is provided. The airjet weaving machine according to claim 10, characterized in that the prewinder (7) is provided with a winding detector (26, 65, 66) for detecting the instants (T_M; T_1W, T₂w, T3w, T_4W, T|_w) at which the windings are unwound from the winding drum (53).

The airjet weaving machine according to claim 10 or 1 1 , characterized in that the prewinder (7) allows to release weft threads of different lengths, in particular the prewinder (7) is provided with a winding drum (53) of which the circumferential length can be varied by means of a motor (52).