The present invention relates to a woof preparation device for pneumatic looms.

Woof preparation devices are already known, which mainly con¬ sist of a stationary stock-drum on which the woof thread is wound and of mechanical means which, for every shot, separate the necessary number of windings from the following ones and release same for delivery to the main blower of the loom.

It is also known to provide a movable thrust piece or blocking component at the delivery end of the aforesaid drum, whereby the deliver ^*-7 of woof thread is prevented during a part of the weaving cycle.

Under normal circumstances such arrangements work in a sa¬ tisfactory way. They have, however, the drawback of a possi¬ ble inaccuracy concerning the number of windings effectively delivered each time. This inaccuracy may result from one or more of the following facts : - the aforesaid mechanical separating means work in a rather static manner; - these separating means cannot be adjusted according to the thickness of the thread, when one shifts from a thinner to a thicker woof thread or inversely; - the aforesaid blocking component is, directly or indirectly, exclusively controlled as depending from the angular posi-

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tion of the main shaft of the loom. On the other hand, the introduction speed of the woof on a pneumatic loom is sub¬ ject to variations from shot to shot and from one kind of thread to another.

The object of the invention is now to eliminate the problems mentioned hereinabove.

For this, there is proposed a woof preparation device of the type described hereinabove, wherein, according to the inven¬ tion, at this delivery end of the stock-drum there is provi¬ ded a winding counter, whereby the shifting of the aforesaid blocking component, from the retracted position to the block¬ ing position is controlled.

The invention is more clearly explained hereinafter with the help of an example of execution illustrated by means of the attached schematic drawings. In these drawings,

Figure 1 shows a schematic side view of a device accor¬ ding to claim 1,

Figure 2 shows a block diagram of the circuit of the sender-receiver located adjacent to the winding end, Figure 3 shows a block diagram of the circuit of the other sender-receiver.

In a support 1 mounted on the frame of a pneumatic loom a shaft 2_ is rotatably mounted. This shaft is made so as to be partially hollow and carries a thread winder 3_. On the shaft 2 a stock-drum 4 is rotatably mounted. The shaft 2_ can be driven by means of an electric motor 5, the feeding of which is controlled by two optic detectors 6 _^ and 1_.

A magnet 8_ carried by the support 1_ cooperates with a little iron block 9 _^ provided in the drum 4 to prevent any rotation of the drum.

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The woof thread 10, coming from a spool 11_ passes through shaft 2_ and winder 3_ in order to be wound by the latter around the drum 4 and reaches further, through a clamp L2, the main blower 13_ of the loom. 5

At the delivery end of the drum 4, there is provided a blocking component 14_, which can be shifted from the active to the pas¬ sive position and inversely by means of an electro-magnet 15.

10 The motor 5_ is fed with current as long as detector 6 _^ does not detect thread and this feeding stops as soon as detector 1_ de¬ tects thread.

Means not shown, known themselves in principle, may be provi- 15 ded to ensure the displacement of the windings from one end of the drum to the other.

The electro-magnet 15_ is being controlled either through a determined angular position of the main shaft or by means of

20 the programmation of the loom, whereby the component 14_ of the drum 4 becomes retracted (passive position) . The returning of this component of the active position is controlled, accor¬ ding to the invention, by means of a counter 1_6 which is pro¬ vided at the delivery end of the drum 4. In this case this

25 is an optic detector which cooperates with a little mirror 17 carried by the drum 4. The detection signals are counted in a counter ]3 properly speaking. As soon as a desired number of

. signals is reached, the feeding of electro-magnet 15_ becomes interrupted until it is put again on the programmation at the

<_*_ 30 intervention of the main shaft.

The drum 4 is preferably of a known type with a continuously adjustable diameter, so that the number of windings that are required per shot may remain constant, whatever the selected 35 weaving breadth. This, however, does not exclude the possibi¬ lity for the counter 18 to be adjustable.

The controlling device according to the invention is descri¬ bed hereinafter.

An oscillator 19_ (figure 2 ) controls an infrared diode of sen- der-receiver 6^ The rays that are reflected on a reflecting plane 20 of the stock-drum 4 are received by a photo-transis¬ tor, which is amplified in 21_ and further rectified in 2_2 to be sent to the switch 2_3_. When the plane 20 is covered by thread, the reflected signal is weak and the rectified signal is non-existent. Switch 23 _^ then remains open.

If the stock of thread disappears, the rectified signal beco¬ mes high, so that the switch 23 _^ becomes closed. At this moment, a regulating circuit 24 controls a thyriεtor 2_5 _^ so that the motor 5_ starts rotating. A tachometer with impulse giver 26 delivers a signal which is compared by the regulation circuit 24 with a value set by means of 2_7. Via the thyriεtor 2 , the circuit 24 regulates the speed of the motor 5_ so that it be¬ comes equal to the set value.

One may set 2J7, independently of the quantity of woof to be delivered, in such a way that the motor 5 _^ must start and stop a minimum number of times.

The fixing of the length of woof that is unwound each time takes place through counting a determined number of windings of the drum 4 with a known circumference during the pulling off of the thread and, when this number is reached, control¬ ling the magnet 1 of the blocking component 14. The change of the aforesaid number of windings may be seen as a rough adjustement, whilst the fine adjustment is preferably carried out through modifying the circumference of the drum.

The sender-receiver 16 _^ (figure 3) is a part of a regulating circuit 28_ which tries to adjust always in the same working area the signals received by 16^ this in order to eliminate the influence of dust deposition on the thread, undesired

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light and aging.

From the control box 29_ of the loom comes a signal which is produced by a time burst given by a clock.

This signal is used as a "set" for a flip-flop 30 which via a power stage 3_1 controls the little magnet L5 either to clamp or to release the thread.

In 3_2 there is formed a control area as well of the signals coming from the time control as of the ones of the receiver 16, this in order to avoid incorrect countings due for instance to dust, between two thread passages.

The detected signal is transmitted to the counter 3_3 only when both the signal of the control 32_ and of the detection 16 are high.

This counter 33_ is adjustable and will, for instance, send a reset signal to the flip-flop only at the third thread.

At that moment, the magnet L5_ becomes energized and the thread is braked. The adjustment of the detector 16_ and magnet 15 is such that the magnet, after a count of three, has just the time of a winding left to attract.

An additional blower 3_4 is also controlled via a valve 3_5 by the time burst 2_9 and is used for increasing the speed of the thread when unwinding; (this blower is in fact an auxiliary blower of the main blower).

A second valve 3_6 ensures that in the stopped position there still remains a slight pressure on the main blower 13_, so that the thread remains taut. In the case of the net falling out, the valve will be ruled out, whereby an unnecessary unwinding of the woof will be prevented.

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It is clear that the woof preparation device and circuits des¬ cribed hereinabove can be executed in various shapes.