This invention relates to the field of weaving, and in particular refers to an electro-pneumatic selvedge machine.

A fabric is an article obtained with a weaving machine (loom) from the interweaving between warp (row of yarns placed in longitudinal direction) and weft (yarn placed in transversal direction).

The weft is inserted by a vector (grippers, shell, air jet, water jet) into a compartment (shed or mouth) which is created by dividing the warp yarns into two high and low rows (as shown in more detail in Figure 1).

In modern weaving machines, whose insertion principles are mentioned above, each weft yarn is cut at the two ends (left and right of the fabric) at a length a little longer than the width of the fabric; in this way, a 10- 15 mm stretch of yarn protrudes on the two sides of the fabric, which in some good quality fabrics is not desired.

This is why special auxiliary machines, called selvedge machines, have been designed to be mounted on the edges of the fabric.

A selvedge machine is a device designed to insert the protruding weft sections into the fabric during weaving, in order to create a finished, stable and elegant edging (selvedge), as shown in detail in Figures 2 and 3. Selvedge machines are generally mechanical and involve the operations, generated by a cam system, of cutting the yarn by means of a shear, gripping the yarn by means of a special gripper and return of the projecting end by means of a crochet needle. Such a device is known for example from patent document EP2800829A1. There are also pneumatic selvedge machines, in which the shear is driven by a pneumatic cylinder and the return of the end is entrusted to a jet of air coming from the outside of the edge.

If the mechanical selvedge machines are applicable to any type of weft yarn, the pneumatic selvedge machines are limited to yarns which are flexible and compliant enough to be bent by an air flow (wool, cotton, composite fibres, etc.). Moreover, the traditional mechanical selvedge machines are extremely complex, require careful adjustments and are suitable for working on looms with a limited number of revolutions per minute.

For example, in the production of terry towelling fabrics there are two types of terry curl formation: in one, the comb brings two wefts together at a certain distance from the contact line, and then makes the third make contact together with the other two on the yarn of the fabric, changing the position of the comb; in the second, it is the yarn which is moved backwards, then forwards so that the three wefts make contact together. In both cases, the selvedge machine, which must thus return three ends at once, must be operated intermittently every three contacts, which is quite complex if it is to be made by mechanical transmission. With the proposed selvedge machine, the problem is overcome by programming the intermittence of the needle motion through the relative motor driver. Lastly, as already mentioned, the selvedge machines of the pneumatic or mixed mechanical-pneumatic type employ unsatisfactory and unreliable technical solutions, with specific limitations for each of the systems.

The main aim of the invention is, therefore, to overcome the above-mentioned drawbacks of the prior art, making an electro-pneumatic selvedge machine which is fully adaptable to the recent types of modern looms.

Another aim of the invention is to make an electro-pneumatic selvedge machine, which guarantees precision and operational reliability, both mechanical and, above all, technological, during the return phase of the weft tails in the warp mouth.

Another aim of the invention is to make an electro-pneumatic selvedge machine which is able to carry out rapid and repeatable movements of the components designed for processing the yarn. A further aim of the invention is to make an electro-pneumatic selvedge machine with a simple and compact structure in order to achieve the stiffness and lightness characteristics necessary for the higher working speeds of the looms. These and other aims, which will appear more clearly below, are achieved by an electro-pneumatic selvedge machine, according to the attached claim 1 ; further technical characteristics are contained in the subsequent dependent claims.

Further features and advantages of the electro-pneumatic selvedge machine, according to the invention, will be more evident from the following description, referring to a preferred, but not limiting, example embodiment, and from the accompanying drawings, in which:

- Figure 1 shows a diagram of a traditional weaving loom with gripper weft insertion;

- Figure 2 schematically shows the principle of formation of a selvedge;

- Figure 3 shows an enlarged view of the L detail in Figure 2;

- Figures 4 and 5 show respective perspective views of an electro pneumatic selvedge machine and its support, according to the invention;

- Figures 6 and 7 show the main components of the electro-pneumatic selvedge machine in Figures 4 and 5, according to the invention;

- Figures 8A, 8B and 8C show the various cutting steps of the electro pneumatic selvedge machine, according to the invention.

With particular reference to the attached Figures 4 and 5, which show a preferred embodiment of the electro-pneumatic selvedge machine according to the invention, the above-mentioned selvedge machine has a support 10, which can be realized in different ways according to the type of weaving machine to which the selvedge machine is coupled, and uses a pair of motors 1 , 2 (stepper, brushless or similar), which are used in the formation of the selvedge, respectively, for the gripping and cutting of the weft yarn 9 and for the return of the protruding end of the above-mentioned weft yarn 9.

In this case, no mechanical transmission is required, as the motion is supplied by two motors, controlled by two electronic drivers (not illustrated in the figures), one for each motor, synchronized with each other and synchronized with the weaving machine by means of a suitable encoder (not illustrated). The weft yarn 9 is captured by a hollow suction needle 3 inserted at the end of a hollow arm 4, in which a suction flow is created by means of a pneumatic ejector 5; the pneumatic ejector 5, by introducing a flow of compressed air into a hole 6, creates a negative pressure at the hole 7 orthogonal to the hole 6 (due to the Venturi effect, based on Bernoulli's three-dimensional theorem).

In this way, compared to traditional selvedge machines, all the set of movement cams contained in an oil bath box and the mechanical connection with the weaving machine (usually made with pulleys, belts and/or gears) are eliminated.

The operation of the electro-pneumatic selvedge machine, according to this invention, is basically as follows.

The attached Figure 1 shows the diagram of a weaving machine (loom) with yarn insertion by means of a traction gripper 11 ; the yarn 12 and, after the comb 15, the fabric 13 are tensioned and pulled by a cylinder 14.

When comb 15 is in position A, the shed is open and allows the gripper 11 to pass through for the insertion of the weft yarn 9.

When the traction gripper 11 leaves the fabric edge, the end of the weft yarn 9 is blocked and cut by a special shear 16 of the selvedge machine, which actuates both the blocking (gripper) and yarn cutting functions and which is driven by the same motor 1.

In particular, the shear 16 has a fixed part 17 with a projection having on one side a supporting surface 18, which constitutes the upper striker of a first mobile claw 20, and on the other side a cutting edge 19, which constitutes the fixed part of the shear 16. The mobile claw 20 is connected to the fixed part 17 and to a mobile blade 21 in an elastic manner and, in particular, by means of a needle spring 22 (as shown in detail in Figures 6 and 7 attached).

Figures 8A, 8B and 8C show the different steps of operation of the shear 16; when the motor 1 rotates at a predetermined angle (for example, 10 °, Figure 8B) the mobile claw 20 blocks the end of the weft yarn 9 on the fixed supporting surface 18 and holds it until the next contact, when the hollow needle 3 is about to suck it; a further rotation of the motor (for example, equal to 10°, Figure 8C) makes the blade 21 close, loading the spring 22, so as to cut the weft yarn 9 and allow the hollow needle 3 to suck the end. The spring 22 will unload in the next return stroke of the motor 1 , in a single movement (in the case considered -20°), dragging along also the mobile claw 20, until reaching the initial configuration of Figure 8A.

Simultaneously, the comb 15 moves towards the weaving line and the inserted weft (comb position 15 indicated with B in figure 1 ) is moved towards it at speed; during the movement of the comb 15 from position A to position B, the shed closes and blocks the inserted weft in its final position. A new shed is opened, exchanging the positions of the two rows of yarns, high and low, whilst the comb 15 moves away from the contact line (from position B to position A).

When opening the shed, the motor 2 of the selvedge machine rotates the hollow arm 4 from position C to position D (Figures 4 and 5) at an angle necessary to bring the end of the hollow needle 3 close to the end of the weft yarn 9, through the row of high yarns (Figure 1).

By introducing compressed air into the hole 6 of the ejector 5 of the selvedge machine, a sufficient negative pressure is created in the hollow needle 3 to capture the end of the weft yarn 9, which is kept in the return stroke, thus making the end retract into the warp shed, before releasing it and allowing it to approach the contact line together with the new inserted weft yarn 9 (Figures 2 and 3); in particular, Figure 3 shows in detail the two extreme positions of the hollow needle 3, respectively at the beginning of the suction of the protruding end (position indicated with 3A) and at the moment of release (position indicated with 3B).

The cycle repeats itself with every contact.

The ejector 5 of the selvedge machine according to the invention is a three-way ejector and is controlled by two inlet valves (not illustrated).

In a first step, a first valve opens to introduce compressed air into hole 6 and create the necessary negative pressure for the hollow needle 3 to capture the head of the weft yarn 9, whilst the second valve is closed; in a second step, the second valve opens to introduce compressed air into hole 8, whilst the first valve is closed. The air flow reversed in this second step, through the hole 7, allows the cleaning of the arm 4 and the hollow needle 3 with a programmable frequency (for example, after a certain number of contacts, which can vary from 1 to 60 contacts). The characteristics of the electro-pneumatic selvedge machine, according to the invention, clearly emerge from the description, as do the advantages thereof.

The invention thus conceived is in any case susceptible to numerous modifications and variations, all falling within the scope of the inventive concept of the attached claims; moreover, all the details may be replaced by other technically equivalent elements.

Where the characteristics and the techniques mentioned in the following claims are followed by reference signs, the reference signs have been used only with the aim of increasing the intelligibility of the claims themselves and, consequently, the reference signs do not constitute in any way a limitation to the interpretation of each element identified, purely by way of example, by the signs numbers.