US3805850A

US3805850A - Control device for repairing weaving defects in a pneumatic weaving machine

Info

Publication number: US3805850A
Application number: US00395430A
Authority: US
Inventors: Duynhoven A Van; G Vermeulen
Original assignee: MASCHF TE STRAKE L NV
Current assignee: Machinefab Te Strake L Nv nl; MASCHF TE STRAKE L NV
Priority date: 1972-06-09
Filing date: 1973-09-10
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

Weft threads are presented in measured lengths by a weft preparing device, comprising a continuously operating drawing off device and an intermittently operating storage device. Said lengths are presented to a main blowing nozzle positioned at one end of the weaving shed. A thread detector is provided at a weaving shed end remote from the main blowing nozzle, said detector comprising a pick up which in absence of a weft thread stops the main shaft of the machine. Said pick up controls, apart from the drive of the main shaft of the machine, also the supply of air to the main blowing nozzle, in such a manner that a defect signal delivered by said pick up immediately causes the main blowing nozzle to be shut off. The main machine shaft is connected to a signal transmitter which issues a signal when the main shaft is stationary, said signal effecting the immediate throwing out of a coupling provided between said main shaft and the weft preparing device. The throwing out movement causes the throwing in of a reverse rotation device and of a coupling between said reverse rotation device and the main shaft, which coupling is normally thrown out. Means are provided to throw out again the reverse rotation device and the corresponding coupling after the main shaft has been reversed through an angle corresponding to a complete weaving cycle and to couple again the weft preparing device with the main shaft. Further means are provided to remove the defect causing weaving thread, which has been freed by the reverse rotation, from the weaving shed by means of auxiliary blowing nozzles, to signal said removal and to initiate thereby the postponed launching of the next weft length and to restart the machine.

Description

United States Patent 1 Van Duynhoven et al.

[451 Apr. 23, 1974 CONTROL DEVICE FOR REPAIRING WEAVING DEFECTS IN A PNEUMATIC WEAVING MACHINE [75] Inventors: Adrainus Henricus Van Duynhoven;

Geert Jan Vermeulen', both of Deurme, Netherlands [73] Assignee: N.V. Machinefabrik L. Te Strake,

Deurne, Netherlands [22] Filed: Sept. 10, 1973 [21] Appl. No.: 395,430

Related US. Application Data [63] Continuation of Ser. No. 261,408, June 9, 1972,

abandoned.

[52] US. Cl. 139/1 E, 139/ 127 P [51] Int. Cl D03d 51/08 [58] Field of Search..... 139/1 R, l E, 127 R, 127 P,

[56] References Cited UNITED STATES PATENTS 2,962,056 11/1960 Paul et al 139/1 3,661,185 5/1972 Zamat 139/1 Primary Examiner-Henry S. Jaudon Attorney, Agent, or Firm-Marshall & Yeasting 57 ABSTRACT Weft threads are presented in measured lengths by a weft preparing device, comprising a continuously op erating drawing off device and an intermittently operating storage device. Said lengths are presented'to a weaving shed end remote from the main blowing noz-.

zle, said detector comprising a pick up which in absence of a weft thread stops the main shaft of the machine. Said pick up controls, apart from the drive of the main shaft of the machine, also the supply of air to the main blowing nozzle, in such a manner that a defect signal delivered by said pick up immediately causes the main blowing nozzle to be shut off. The main machine shaft is connected to a signal transmitter which issues a signal when the main shaft is-stationary, said signal effecting the immediate throwing out of a coupling provided between said main shaft and the weft preparing device. The throwing out movement causes the throwing in of a reverse rotation device and of a coupling between said reverse rotation device and the main shaft, which coupling is normally thrown out. Means are provided to throw out again the reverse rotation device and the corresponding coupling after the main shaft has been reversed through an angle corresponding to a complete weaving cycle and to couple again the'weft preparing device with the main shaft. Further means are provided to remove thedefect causing weaving thread, which has been freed by the reverse rotation, from the weaving shed by means of auxiliary blowing nozzles, to signal said removal and to initiate thereby the postponed launching of the next weft length and to'restart'the machine;

5 Claims, 8 Drawing Figures CONTROL DEVICE FOR REPAIRING WEAVING DEFECTS .IN A PNEUMATIC WEAVING MACHINE This is a continuation of US. Pat. application Ser. No. 261,408 filed June 9, 1972.

BACKGROUND OF THE INVENTION lengths :by a weft preparing device, comprising a continuously operating drawing off device and an intermittently operating storage device, which is coupled with the main shaft of the machine as are the weaving healds and the .reed. Said lengths are presented to a main blowing nozzle, positioned at one end of the weaving shed, which is intermittently supplied with air to transport sa id lengths in cooperation with a plurality of auxiliary blowing nozzles positioned between the weaving shed ends through the weaving shed in successive weaving cycles. A weft detector provided at the weaving shed end remote from the main blowing nozzle, said detector comprising means which in the absenceof a weft threadstops the main shaft ofthe machine.

Weaving machines of this type are generally known and operateyusingthe possibilities offered by the handling of the weft threads by means of a flowing fluid such as air, at .high speeds and therefore with a large number of picks per time unit.

By the term weaving defectit is meant that a weft thread launched by the main blowing nozzle does not reach the opposite weaving shed end within a predetermined time interval. German Offenlegungsschrift Pat. No. 1,904,584 teaches to stop the machine in case of a weaving defect before the weft thread causing the weaving defect can be beaten up by the reed, in order to permit easy removal of said weft thread from the weaving shed after said thread has been cut off.

Withthe relatively high weaving speeds prevailing for the weaving machines of the type considered, it is practically impossible tostop the main shaft and the relatively heavy mass of the reed and the weaving healds coupled therewith prior to the completion of the beating up movement by the reed and prior to the weaving shed having been changed.

SUMMARY OF THE INVENTION The invention aims at providing a control device for automatically repairing weaving defects in a weaving machine of the above mentioned type, on the basis that the weft thread which caused the weaving defect has already beenbeaten up by the reed and has been bound into thecloth prior to the moment at which the main machine shaft and theparts coupled therewith come to a standstill after the defect has been detected.

According to theinvention, in a control device of the type :above referred to the said detector means con trols, apart from the drive of the main shaft of the machine, alsothe supply of air to the main, blowing nozzle, in such a manner that an *error" signal delivered by said means immediately causes the main blowing nozzle to be shut off. The main machine shaft is connected toa signal transmitter which issues a signal when the main shaft is stationary, said signal effecting the immediate throwingout of a coupling provided between said main shaft and the weft preparing device: The throwing out movement causes the throwing inof a reverse rotation device and of acouplingbetween said reverse rotation device and the main shaft, the latter coupling being normally thrown out. Means are provided to throw out again the reverse rotation device and the correspond ing coupling after the main shaft has been rotated back through an angle corresponding to a complete weaving cycle and to couple again the weft preparing device with the main shaft. Further means are provided to remove the defect causing weaving thread, which has been released by the reverse rotation, from the weaving shed by means of the auxiliary blowing nozzles, to signal said removal and to initiate thereby the postponed launching of the next weft length and to restart the machine.

Therefore with a weaving cycle of 360 (e.g. corresponding to a complete revolution of the main shaft of the weaving machine) during the first 180 of which the weft insertion occurs and in the second 180 of which the reed movement and the change of weaving shed take place, if a weft defect is signalled by the thread detector at the end of the weft insertion phase, the order to stop the main shaft of the machine is given, for example to a brake. Then themain shaft will notimmediately be at a standstill but will still permit the reed to beat up the incorrectly inserted weft length into the cloth and permit the shed to close(at the 270 position) andthen to re-open (at the 360 position). In the last mentioned position with normal operation the launching of the next weft length would start, but as a consequence of thesaid order the supply signal forithe transport air, required for said launching, isnot given or in any case remains without results. For signalling the removal of the faulty weft length use may be made of a separate, e.g. photo-electric device, the signal of which immediately cancels the blocking of the air supply to the main blowing nozzle, so that the next weft length is signalled and the correct signalof the normal thread detection effects the restarting of the machine.

However, preferably for signalling the removal of the faulty weft length and therefore the removal of the defect use is made of the. normal thread detector. Thereby, however, a correct signal given by the pick up of the thread detector when the faulty weft length is removed could occur, when the main shaft has come to a standstill ata position which is relatively far. beyond the 360 position and therefore a longway in to the weft phase of the next weaving cycle, and too late to have the transport air supply to the main blowing nozzle, necessary for the postponed launching of the next weft length, take place. However, ithas to be noted in this respect that normallyin a weaving machine of the type considered a weft length, after it has been beaten up into the cloth, is cut withthe intermediary of a cutting means prior tothe next launching at the position between the mainblowing nozzle and the adjacent cloth edge. Thereby the launching of the next weft iength would not be carried out in spite of the cob rect" signal, while themachine drive would nevertheless be started by the same correct signal. Said last mentioned problem is obviated in a simple and effective manner in a preferred embodiment of the. inven tion, in that the pick up of the thread detector at the same time controls the cutting means so that the cutting means is immediately switched off by the defect signal delivered by the pick up and is switched on again by the correct signal delivered by the pick up when the defective weft length is removed.

In this manner the weft thread which has caused the weaving defect remains connected with the next weft length and said last mentioned weft length is drawn into the weaving shed when the faulty weft length "is removed. Thereby for launching the next weft length one is not dependent on whether or not the normal transport air supply to the main blowing nozzle has been restored, while the moment at which the main shaft comes to a standstill after the signalling of a weaving defect is not critical but may be anywhere within the next weft phase, e.g. 270 after the moment of detectron.

According to a further feature of the invention a gripping device is positioned at the launching side of the machine adjacent the beating up line, said gripping device being adapted to be operated during a short interval by a signal delivered at the end of a reverse rotation movement in order to move a faulty weft length from its beating up position into the path of the transport jet of the main and auxiliary blowing nozzles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of a pneumatic weaving machine provided with the control device according to the present invention.

FIG. 1A is a perspective view of the weaving machine.

FIG. 1B is another perspective view of the weaving machine.

FIG. 2 is a diagrammatic view of the weft preparing device with the main blowing nozzle and its supply.

FIG. 3 is a diagrammatic perspective view of the discharge end of the main blowing nozzle and of the adjacent parts of the cutting means and the gripping device.

FIG. 4 is a block diagram showing the pick up of the detector connected with the electro-magnetic main coupling, the electro-magnetic device for shutting off the supply of air to the main blowing nozzle and the device for switching off the cutting means.

FIG. 5 is a block diagram of a signal transmitter coupled with the main shaft of the machine, a pulse emitter and the electro-magnetic device for throwing out the coupling between the main shaft and the weft preparing device, and

FIG. 6 is a block diagram of a switch, an electropneumatic device for starting the reverse rotating device, the device for switching on the coupling between said lastmentioned device and the main shaft, and the control device for the gripping device With reference to FIG. 1 the weaving machine has been indicated at 1. The main shaft 2 of said machine is normally driven through the electro-magnetically controlled coupling 3 by the main drive motor 4 as shown in FIGS. 1 and 1B, and imparts in a well-known manner (not further shown) during the relative phase of the weaving cycle a reciprocal movement to the reed 5 and an up and down movement tothe weaving healds (5A). The main shaft 2 further drives through an intermediate shaft 2a and a coupling 6 which may be electro-magnetically thrown out, the input shaft 7 of the weft preparing device 8 as shown in FIGS. 1 and At one side of themachine 1, i.e., the right side as seen in FIG. 1, in front of the opening of the weaving shed the main blowing nozzle 9 is positioned, by means of which during normal operation a weft length 10 prepared by the weft preparing device 8 is transported through the weaving shed in cooperation with a plurality of auxiliary blowing nozzles 11 carried by the reed 5. The launching of a prepared weft length is effected in a well-known manner (see FIG. 2) each time when; due to the diaphragm 12a of the so-called quick air release means 12 being switched over into the position indicated with broken lines), a sudden and brief connection is effected between the main blowing nozzle 9 and the reservoir 13. In the latter reservoir a measured quantity of air has been accumulated during the preceding period, supplied via a valve 15, controlled by a cam 14 associated with the weft preparing device, and via the quick air releasemeans 12. FIG. 2 shows the weft preparing device in that phase of a normal weaving cycle in which the quick air release means 12 is connected through the valve 15 and the conduit 16 with the air supply conduit 17, the reservoir 13 is being filled through the quick air release means, and the connection between the main blowing nozzle 9 and the reservoir 13 is closed by the diaphragm 12a, while the buffer device 18 is preparing a fresh weft length 10 in loop shape from the weft yarn continuously supplied from the drawing off rollers 19. The launching of said last mentioned weft length is effected as soon as the thread clamp 21 is opened and the valve 15 is placed by the cam 14 against the pressure of the spring 20 in a position in which the conduit 16 is connected with the air release conduit 22 whereby the diaphragm l2a is switched in the above described manner and as a result thereof air from the reservoir 13 is supplied to the main blowing nozzle 9. The

shafts

7a and 7b of the cam 14 and the drawing off rollers respectively, as well as the actuating shaft (not further shown) of the thread clamp 21 receive their motion from the input shaft 7 of the weft preparing device 8.

Adjacent the discharge opening of the main blowing nozzle 9 there is the usual cutting means 23 (see FIG. 3) which in the embodiment shown comprises a fixed cutting blade 23a, rigidly mounted to the machine frame 25 through a sleeve 24, and a movable cutting blade 23b which is secured to a shaft 26 rotatably jour-.

nalled in the sleeve 24, the movable blade being axially pulled towards the fixed blade by a spring (not shown) received in the sleeve 24. An arm 27 is fixed to the shaft 26 and is pivotally connected-to an actuating rod 28 in which is reciprocable the direction of the arrow to actuate the movable knife 23b. Normally a weft length after being inserted and beaten up by the reed into the cloth is cut by said cutting means 23. The cutting means 23 may, however, be made inoperative by moving the movable cutting blade 23b with the intermediary of a push rod or plunger 29, coaxial units the. shaft 26, against the action of the spring in the sleeve 24, so that it is moved away from the fixed blade23a and the turning movement (which continues normally) is no longer effective. For this purpose the push rod 29 is connected with an electro-magnetically energizable actuating device which may be of the electropneumatic or electro-mechanical type and has been indicated at 30 rather diagrammatically.

At a short distance from the discharge opening of the main blowing nozzle 9 there is a guiding means 31 which is reciprocable in a plane perpendicular to the axis of the main blowing nozzle 9 (in the direction of the arrow) together with the reed and is adapted to guide, after the launching of a weft length by the main blowing nozzle 9, the tail end of said weft length and the head end" 10" of the next weft length, connected therewith, between the cooperating blades 23a and 23b of the cutting means 23 (see the thread portion indicated in FIG. 3 with the dash lines 10', 10"). It appears from FIG. 3 that the next weft length is thereby drawn into the slit shaped space of a lateral wing 9a of the main blowing nozzle 9.

A thread clamp 32 is mounted in the lateral wing 9a and comprises a clamping rod 33 movable in the direction of the arrow, said rod being connected with one end of a double armed lever 35 pivotable around a fixed point 34, said lever being engaged at its other end by a spring 36 which tends to keep the clamping rod 33 in its inoperative position. The spring loaded end of the lever 35 is also connected to an electro-pneumatic or electro-mechanical actuating device diagrammatically indicated at 37, which upon energization puts the clamping rod 33 against the action of the spring 36 in its operative position, in which the head end 10" may be clamped in the position indicated in FIG. 3 with broken lines. The thread clamp 32 constitutes one part of a special gripping device, the purpose of which will be further elucidated hereinafter, a second part of which is constituted by an ejector means 38, which is reciprocable along the selvage and is located with its operative end adjacent the beating up line x. A reciprocal movement may be imparted to the ejector means 38 by means of an electro-pneumatic or electromechanical actuating device, diagrammatically shown at 39.

At the side opposite to the main blowing nozzle 9 a thread detector 41 is provided in the launching path, within the suction nozzle 40 (FIG. 1), e.g. constituted by a photo-electrical pick up with light emitter and light receiver according to U.S.Pat. No. 3,658,098. During normal operation said thread detector delivers for each weft within a predetermined time interval, e.g. determined by a so-called vane switched oscillator (with which the oscillation is determined by the position of a vane coupled to the main shaft of the machine) within the considered weaving cycle a signal which constitutes an indication for a non-faulty weft, which signal keeps the machine in its normal operating condition.

However, as soon as the pick up 41 does not observe the presence of a weft length within thepredetermined time interval the said signal is not issued, so that in fact the pick up delivers an error" signal f (see the diagram in FIG. 4). As soon as said error" signal f occurs and therefore a weaving defect is'presentfthe coupling 3 is thrown off through the energization of the correspond, ing coil s1.- Thereby the main shaft 2-is disconnected from the main motor 4 but keeps on moving'forsome time together with the reed 5 and the weaving healds connected therewith and is brought to a standstill by a brake (not shown)-in a position between 360 and 540, e.g. 270 after the moment of detection.

At the same moment at which the coil s1 is energized a second coil s2 is energized which is associated with the electro-pneumatic valve 42 (see FIG. 2) which has been provided in the release conduct 22 and by which said release conduct is then closed so'that the quick release means 12 cannot release and the connection between the main blowing nozzle 9 and the transport air reservoir 13 remains interrupted so that the launching of the fresh weft length, which has been prepared already and which should be launched after the beating up by the reed, does not take place. At the same time also the coil s3 of the device 30 is energized by which the cutting means 23 becomes inoperative and the incorrectly inserted weft length is not cut at the time of the beating up by the reed or after that time.

The further course of the repair process is as follows:

As soon as the main shaft (at about 270 after the detection) has come to a standstill, e. g. at a position with open weaving shed and retracted reed, a signal transmitter 43 suitable therefor and coupled with the main shaft (see FIG. 1 and 5) emits a signal 44. Said signal controls a pulse emitter 45, e.g. a monostable multivibrator, which delivers at its output end a brief pulse 46 for the energization of the coil 54 of the electro magnet 47 whereby the coupling 6 is uncoupled against the force of the spring 48 (FIG. 1), so that the weft preparing device 8 is disconnected from the main shaft of the machine.

The uncoupling of the coupling 6 is attended with the closing of a pair of contacts 49 (e.g. of a reed switch) whereby the energization occurs of a coil s5 of the electro'pneumatic switching on valve 50 of a pneumatic reverse rotation cylinder 51 and of the switching on coil s6 of the electro-magnetic auxiliary coupling 52 which is provided between the main shaft 2 and the reverse rotation cylinder 51.

Therefore the main shaft 2 is reversed directly after it has come to a standstill, by the reverse rotation cylinder 51 through a complete revolution. The end of the reverse rotation movement is governed by the special construction of the coupling 6 between the intermediate shaft 2a and the weft preparing device 8. As indicated in FIG. 1 the coupling 6 comprises a first disc 6a having a peripheral cam 53 projecting in the axial direction, and a second disc 6b having a peripheral notch 54 corresponding with the cam 53. Due to the fact that the signal which energizes the coil s4 of the electromagnetic device 47 for uncoupling said coupling only operates briefly, the coupling 6 tends to couple again under the influence of the spring 48 shortly after the main shaft 2 has come to a standstill. However, said coupling is prevented up to the moment at which the cam 53 and the notch 54 have re-arrived directly opposite to each other and this is exactly the moment at which the main shaft 2 has been reversed by the reverse rotation cylinder 51 through 360. At the same time when at that moment the coupling 6 is recoupled, the

contacts 49 are moved apart and therewith the auxili-j ary coupling 52 is uncoupled while the electropneumatic switching on valveSOis.again switched off and the reverse rotationcylinder 51 may return to'its initial position under the influence of the return spring 55. i i

Herewith the machine has arrived ina position in which the main shaft and thereby the reed, the weaving healds and the weaving shed are again in the same positions as when the launching of the faulty'weft length took place. However,'the main drive and the coupling 3 remain uncoupledup to the moment at which the faulty weft length has been removed from the weaving shed. By the reverse rotation of the main shaft 2 the bindingof the faulty weft length in the cloth has been cancelled and therefore said length lies freely in the opened shed. In order now to further the removal of the thus freed weft length from the weaving shed the above mentioned ejector means 38 is energized so that it grips the freed weft length at the beating up line and brings it in line with the axis of the main blowing nozzle and the auxiliary blowing nozzles cooperating therewith. For the energization of said ejector means use is made in the embodiment shown of the re-opening of the contacts 49. The signal corresponding with said opening is supplied e.g. by an inverting amplifier 56 (see FIG. 6) to a pulse emitter such as the monostable multi-vibrator 57 which issues a brief signal 58 to the energization coils s7 and s8 of the

devices

37 and 39 respectively. Thereby the clamping rod 33 is brought in its operative position so that the tail end of the faulty weft length and the head end 10" of the next weft length still connected thereto are fixed during a short time in the position indicated in FIG. 3 near the lateral wing 9a of the main blowing nozzle 9, while the ejecting means 38 grips the tail end 10' of the faulty weft length and returns it from the beating up position into the launching path and immediately thereafter withdraws. The faulty weft length has thereby arrived under the influence of the auxiliary blowing nozzles 1 1, which are in the retracted position of the reed fully energized, and is carried out of the weaving shed by transport jets issued by said auxiliary blowing nozzles 11. The faulty weft length takes along with it the already completely prepared fresh weft length (which has been released by the clamping rod 33 which in the meantime has been retracted to its inoperative position). Thereby the pick up 41 of the thread detector is passed which therefore observes a correct weft and delivers the signal necessary for the restarting of the normal operation of the machine. Said signal causes the reconnection of the coupling 3 with the main motor 4 and from this moment the normal operation of the machine is restored. The fresh weft length has been launched at this moment and is cut after the beating up of the reed by the cutting means 23 which has been returned to its normal operative position. The faulty weft length is sucked in by the sucking nozzle 40 and afterwards it is cut off in a known manner as is done with the normally woven weft lengths, as a superfluous piece of thread.

We claim:

1. A control device for repairing weaving defects in a weaving machine of the type in which the weft threads are presented in measured lengths by a weft preparing device comprising a continuously operating drawing off device and an intermittently operating storage device which is coupled with the main shaft of the machine as are the weaving healds and the reed, said lengths being presented to a main blowing nozzle positioned at one end of the weaving shed, said nozzle being intermittently supplied with air to transport said lengths in cooperation with a plurality of auxiliary blowing nozzles positioned between the weaving shed ends in subsequent weaving cycles through the weaving shed, a thread detector being provided at the weaving shed end remote from the main blowing nozzle, said detector comprising a pick up which in absence of a weft thread stops the main shaft of the machine, characterized in that said pick up controls, apart from the drive of the main shaft of the machine, also the supply of air to the main blowing nozzle such that a defect signal delivered by said means immediately causes the main blowing nozzle to be shut off, whereas the main machine shaft is connected to a signal transmitter which issues a signal when the main shaft is stationary, said signal effecting the immediate throwing out of a coupling provided between said main shaft and the weft preparing device, the throwing out movement causing the throwing in of a reverse rotation device and of a coupling between said reverse rotation device and the main shaft, which coupling is normally thrown out, means being provided to throw out again the reverse rotation device and the corresponding coupling after the main shaft has been reversed through an angle corresponding to a complete weaving cycle and to couple again the weft preparing device with the main shaft, further means being provided to remove the defect causing weaving thread which has been freed by the reverse-rotation, from the weaving shed by means of the auxiliary blowing nozzles, to signal said removal and to initiate thereby the postponed launching of the next weft length and to restart the machine.

2. A control device according to claim 1 for a weaving machine provided with a cutting means which is adapted to cut the weft lengths after their launching, in a point between the main blowing nozzle and the adjacent edge of the fabric, characterized in that the pick up of the detector at the same time controls the cutting means such that the cutting means is immediately made inoperative by the defect signal delivered by the pick up and is made operative again by the correct signal delivered by the pick up when the faulty weft length is removed. I

3. A control device according to claim 1, characterized in that at the launching side of the machine, adjacent the beating up line a gripping device has been arranged, which is adapted to be made operative for a brief time by a signal delivered at the end of a reverse rotation movement in order .to place a faulty weft length from its weft position into the transport jet path of the main and auxiliary blowing nozzles.

4. A control device according to claim 3, characterized in that the gripper device comprises a thread clamp provided at the discharge opening of the auxiliary blowing nozzle and an ejector means mounted reciprocally movable along the cloth edge and situated with its fork shaped gripper end adjacent the beating up line.

5. A control device according to claim 4, characterized in that the thread clamp comprises a clamping rod movable up and down in a slit shaped chamber of the lateral wing of the main blowing nozzle.

Claims

1. A control device for repairing weaving defects in a weaving machine of the type in which the weft threads are presented in measured lengths by a weft preparing device comprising a continuously operating drawing off device and an intermittently operating storage device which is coupled with the main shaft of the machine as are the weaving healds and the reed, said lengths being presented to a main blowing nozzle positioned at one end of the weaving shed, said nozzle being intermittently supplied with air to transport said lengths - in cooperation with a plurality of auxiliary blowing nozzles positioned between the weaving shed ends - in subsequent weaving cycles through the weaving shed, a thread detector being provided at the weaving shed end remote from the main blowing nozzle, said detector comprising a pick up which in absence of a weft thread stops the main shaft of the machine, characterized in that said pick up controls, apart from the drive of the main shaft of the machine, also the supply of air to the main blowing nozzle such that a defect signal delivered by said means immediately causes the main blowing nozzle to be shut off, whereas the main machine shaft is connected to a signal transmitter which issues a signal when the main shaft is stationary, said signal effecting the immediate throwing out of a coupling provided between said main shaft and the weft preparing device, the throwing out movement causing the throwing in of a reverse rotation device and of a coupling between said reverse rotation device and the main shaft, which coupling is normally thrown out, means being provided to throw out again the reverse rotation device and the corresponding coupling after the main shaft has been reversed through an angle corresponding to a complete weaving cycle and to couple again the weft preparing device with the main shaft, further means being provided to remove the defect causing weaving thread which has been freed by the reverse rotation, from the weaving shed by means of the auxiliary blowing nozzles, to signal said removal and to initiate thereby the postponed launching of the next weft length and to restart the machine.

2. A control device according to claim 1 for a weaving machine provided with a cutting means which is adapted to cut the weft lengths after their launching, in a point between the main blowing nozzle and the adjacent edge of the fabric, characterized in that the pick up of the detector at the same time Controls the cutting means such that the cutting means is immediately made inoperative by the defect signal delivered by the pick up and is made operative again by the ''''correct'''' signal delivered by the pick up when the faulty weft length is removed.

3. A control device according to claim 1, characterized in that at the launching side of the machine, adjacent the beating up line a gripping device has been arranged, which is adapted to be made operative for a brief time by a signal delivered at the end of a reverse rotation movement in order to place a faulty weft length from its weft position into the transport jet path of the main and auxiliary blowing nozzles.