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Field of the invention

The invention relates to an air flow control unit for a relay nozzle in air-jet looms, in particular a control and air pressure adjustment unit for a relay nozzle in a multi-weft yarn weaving loom .

BACKG ROU N D

As known, mu lticolour weaving looms employ weft threads of d iffer- ent nature in the weaving of the same fabric. The inserted weft threads may d iffer, between a beating cycle and the next, in terms of colour, nature and count.

In the case of air jet looms, the weft thread is inserted by means of air jet nozzles, provided both for the launch of the thread (launching noz- zle), and for supporting and causing the weft thread to fly into the shed (re ^¬ lay nozzles) until it reaches the exit side of the weaving loom .

The variability of the weft threads which are woven between one cycle and the next req uires the air pressure both of the launching nozzle and especial ly of the relay nozzles in the shed (i .e. in the reed channel ) to be continuously varied to adapt it to the type of yarn ; as a matter of fact, the air jet must not be so intense as to damage the yarn, but at the same time the driving force must be sufficient to transport the thread into the shed and to cause it to fly accord ing to a req uired constant arrival time across the ful l working width of the loom .

Moreover, it is known that for large weaving widths it is advantageous to d rive the relay nozzles more than once d uring a sing le weft inser ^¬ tion cycle, in order to improve the fl ig ht characteristics and to reduce the stop rate . Al l this by careful ly adjusting the pressure, to prevent the weft threads from becoming damaged or arriving at irregular times at the exit side, which may lead to flaws or poor fabric q uality.

In order to suitably adjust the pressure in the relay nozzles, various techniques have already been suggested . In one case, d ifferent fl ig ht condi ^¬ tions in the reed channel are achieved by arranging the valves, wh ich sup ^¬ ply the nozzles, in series along the weaving loom width and by d riving them to open/close d ifferently according to their position along the weaving loom width, so as to establish a pressure profile which varies along the weaving loom width . The d isadvantage of this method is the hig h, continuous pres ^¬ sure found at the exit of the relay nozzles, leading to yarn damage and to considerable air consumption ; a further d isadvantage is connected to the slow operating speed and minimum switch-on time of the valves.

Accord ing to another known approach, the different pressure cond itions are achieved by using a pl urality (typical ly two or more) of air tan ks and valves arranged in paral lel , upstream of the nozzles. The d isadvantage of this method is the increased cost of materials, since all units such as valves, power electronics and air tanks must be multiplied in number sev ^¬ eral times.

The disadvantage of the first as well as of the second mentioned ap ^¬ proach is the inefficient use of energy or material . Moreover, by the known systems it is not possible to set an optimal , freely prog rammable pressure field along the weaving loom width (better, along the reed channel ) or to set d ifferent pressure levels inside the same weft insertion cycle, because the reaction speed of the valves is not sufficient.

The object of the present invention is hence that of provid ing a relay nozzle control and adjustment system in an air jet weaving loom, which is cost-effective in al l respects, in particular which does not require component d upl ications, and wh ich has a prompt reaction at high speed , so as to open/close the flow and adapt the pressure level to the one desired within a short delay, even shorter than the ones typical of a weaving loom cycle . SU M MARY OF TH E INVENTION

Such object is achieved by a system wh ich has the innovative fea ^¬ tures set forth in their specific aspects in the accompanying claims.

In particular, according to the invention a relay nozzle control and adjustment system is provided, which consists of a sing le unit wherein a pres- sure adjusting element and an open-and-close element are combined , each element being shaped as a two-way valve which can be switched independ ^¬ ently from the other and at a high operation freq uency, at least the second one at a g reater frequency than the operation freq uency of the weaving loom . Preferably, the pressure adjusting and open-and-close elements con ^¬ sist of piezoelectric bending elements. An alternative sol ution can be ob ^¬ tained by using more conventional electromag netic systems.

More preferably, the system can also be implemented in such a way that both the pressure adjusting and the open-and-close elements are two open-and-close (switching ) elements, the latter being used to open and close the flow from the unit and the former to open and close various air in let cond uits in the unit and having d ifferent flow rates.

According to a preferred aspect of the invention, the first pressure control element is designed as a controlled throttle with d ifferent diameter apertures which are selectively closed/opened by at least one piezoelectric bending element.

In order to achieve a responsive and cost-effective construction of the unit, the pressure adjustment fu nction is preferably implemented in the form of flow openings with different d iameter and selected accord ing to d ifferent (for example three) switch positions of a piezoelectric bend ing ele ^¬ ment. For the hig hest pressure level (flow rate eq ual to the sum of the two flow rates of the two apertures) the bend ing transducer element is in a neu ^¬ tral central position, for med ium and low pressure levels the bend ing trans- d ucer is deflected into the two extreme positions and covers - depend ing on the selected pressure level - the smal ler or the larger aperture, respec ^¬ tively. Due to the substantial ly static conditions of the closed system, the opening or the closing of flow holes having d ifferent diameter translates correspond ingly into a pressure increase or decrease in a del ivery d uct of the unit and in turn on the relay nozzles.

It is not ruled out that the pressure adjustment function may be obtained through a piezoelectric bend ing transd ucer element wh ich is prog ressive, i .e . having work (bend ing ) positions proportional to a feed back sig nal, which allows to set any desired pressure level depend ing on the d istance from an outlet hole (red uction or enhancement of flow rate and hence of pressu re being obtained , for example, by d isplacement of a metering need le in a hole) ; in such a case, the bending piezoelectric transd ucer element acts as a progressive shutter.

The opening/closing function of the valve unit is preferably performed by another piezoelectric bending transducer, which in one extreme position closes the flow, in the other one it releases the full flow. This function can be alternatively performed by an electromagnetic fast switching valve.

If the valve is built in the version with at least two open-and-close elements, in the closed position all holes are closed. Depending on the desired pressure level, one or more holes are open at any one time, until all the holes are open at the same time, which leads to reach the maximum pressure.

Additionally, according to an other aspect of the inventions, it is pro- vided an air delivery system for air relay nozzles in a weaving looms, comprising a plurality of consecutive control valve units as above described, each of said units being independently operated so as to cause a programmable pressure level along the reed channel of the loom. Additional aspects of the invention are disclosed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the system according to the invention will in any case be more evident from the following detailed description of some preferred embodiments of the same, given by way of example and illustrated in the accompanying drawings, wherein :

fig. 1 is a perspective, exploded view showing all the components of the unit according to a first embodiment of the invention;

fig. 2 is a longitudinal section view of the assembled unit of fig . 1; fig. 3 is a section view taken along the line III-III of fig. 2;

fig . 4 is a section view taken along the line IV-IV of fig . 2;

fig. 5 is a transparent perspective view, with separated parts, of the unit of fig. 1 whereon the air flows and the movements of the piezoelectric shutters are shown by arrows; and

figs. 6-10 are views similar to the ones of figs. 1-5, respectively, concerning a second embodiment of the invention.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS

In the following the unit intended to control and adjust the pressurised air flow immediately upstream of each relay nozzle will be described in detail . Said relay nozzle will not be described nor shown in the drawings, since it represents a component well-known per se to any person skilled in the field . The unit with which the present invention deals hence ends with an outlet which can be connected to one or more relay nozzles of a weaving loom, the outlet typically being in the form of a conduit which branches preferably into two to four sub-conduits (one for each connected nozzle) having a mutually equal diameter, mutually slightly converging, in a delivery head which the actual nozzles is intended to be connected with.

Fig . 1 shows such control and adjustment valve unit, which consists of a basic body 1 which a cover 2 is coupled with, which cover carries delivery head 3. The airtight coupling between cover 2 and basic body 1 is ac- complished by detachable means, such as four stud bolts, possibly arranging a seal (not shown) between body 1 and cover 2.

On basic body 1 there is provided an inlet hole 4 through which compressed air (for example at a substantially constant pressure of 2-7 bar) is introduced in the unit, which air flows towards an inner conveying chamber which will be described in detail further on. The inlet hole 4 can be connected to a standard air supply, comprising air tank and valves according to any conventional technique.

According to the invention, between the inner conveying chamber for compressed air and the delivery head there are arranged a pressure adjust- ing element and - preferably downstream of the same - a shut on/off or open/close element. The former of the two elements has the function of determining the desired pressure level, while the latter element determines the closing/opening of the valve unit, i.e. of the air delivery towards the air jet nozzle. According to an embodiment, the two functions are taken by two different elements within the same unit, which allows to make air pressure adjustment and control more efficient, in compliance with the requirements desired for a relay nozzle: in particular, it allows to reduce as far as possible the internal air volume in the unit between the pressure regulator element and the shut on/off element. This feature lead to minimize the pressure peak after opening of the second shutter element, due to the system pressure (up to 7 bar) being inside the switching volume.

Additionally, the switching speed of the adjusting pressure element can be even lower (in the order of the weaving loom operation frequency) than the switching speed of the shut on/off element which must be higher than the weaving loom frequency, so as to be able to switch even multiple times within the same weft insertion cycle.

In the present context, by the term operation frequency of the weaving loom the number of operation cycles of the weaving loom (i.e. the num- ber of weft yarn insertions) per time unit is intended.

In order to achieve the best result in terms of reaction time as well as of economics and construction reliability, the pressure adjusting element is preferably formed as a shutter suited to alternately close internal calibration conduits having mutually different diameters.

In particular, as shown in the drawing, inlet hole/conduit 4 opens inward into a hoof-shaped internal conveying chamber 5. From the opposite ends of chamber 5, calibration conduits 5a and 5b depart, having different diameter, which open into a same switching area 6. Switching area 6 is furthermore in communication with a delivery conduit 7 of head 3, where the shut on/off element is instead arranged . In the embodiment shown in the drawings, such a delivery conduit 7 is provided in the cover 2, with a main axis perpendicular to the axis of calibration conduits 5a and 5b.

In the switching area 6 an adjusting element is movably arranged as a shutter capable - suitably driven from the outside - of alternately shutting calibration conduit 5a or 5b, or neither of the two.

When both calibration conduits are unobstructed, pressure inside switching chamber 6 - and hence available for the delivery head 3 - is set on the maximum available level. When the shutter closes the smaller- diameter calibration conduit 5a, the pressure is set on the intermediate level (of the three available ones). When the shutter closes the larger- diameter calibration conduit 5b, the pressure is set on the lowest level.

The diameter of entry hole 4 is in the order of 5-15 mm. The diameter of the calibrated holes or controlled throttles is ideally between 0.5-6 mm. The size of these holes depending also on the number of relay nozzles connected to the same valve unit.

It is understood that, by providing a greater number of calibration conduits, between the inlet hole 4 and the switching chamber 6, and by suitably configuring the shutter element, the available pressure levels could become even more than three. Although the shutter can be of various types, according to a preferred embodiment of the invention it is shaped as a piezoelectric actuator. In particular, as shown in figs. 1-5, the pressure adjusting element is shaped as a flexible piezoelectric lamina designed so that it can bend on either side based on the applied electric voltage. The actuator comprises a root base 10 wherefrom a flexible lamina 11 departs, which can be driven piezoelec- trically. At the distal end of the lamina, i.e. the end opposite to base 10, a shutter button 12 can be provided, for example of rubber or elastomeric material better suited to seal the exit of calibration conduits 5a and 5b.

The piezoelectric shutter is mounted in the base body 1 so that root base 10 is flush with the external wall of body 1 (fixed in a respective seat by an adhesive or by soldering), so as to be able to easily connect the electric supply cables which come from outside the unit. The lamina 11 is mounted cantilevered within a cavity of body 1, so as to be free to oscillate, with shutting button 12 arranged in the middle of switching chamber 6 in correspondence of calibration conduits 5a and 5b. The driven oscillation of flexible lamina 10 brings shutting button 12 to alternately obstruct one calibration conduit or the other.

Experimental tests have shown that such a shutter has a very prompt reaction and is highly reliable, hence ensuring an efficient operation of the unit and construction economy.

Again preferably also the shut on/off element intended to open /close delivery conduit 7, downstream of the pressure adjustment area, is built with a similar piezoelectric actuator.

Advantageously, for space optimisation, this second flexible-lamina actuator is arranged so that the oscillation axis is orthogonal to the one of the first pressure adjusting actuator.

As can be clearly seen in the drawings, the second actuator hence consists of a root base 10' which is mounted again flush with the external surface of the unit, adjacent to root base 10 of the first actuator but twisted by 90°. Base 10' is tightened between base body 1 and cover 2 and has a flexible lamina 11' whose main surface lies parallel and in the proximity of the separation plane between base 1 and cover 2. At the distal end of lamina 11' there is similarly provided a shutting button 12' intended to obstruct the entry port of delivery conduit 7. Since this shutter is intended to open/close a single port (and not two opposite ports, as in the case of the pressure adjusting shutter), the distance which button 12' must travel and hence the oscillation width of the lamina, can be smaller (typically half of those required by the pressure adjusting element). The control of this piezoelectric actuator can also be provided to cause a deflection of the lamina in a single direction, the oscillation in the opposite direction being ensured by the elastic return force of the lamina. For example, it can be provided that the lamina is mounted to keep closed, in the home position, delivery conduit 7 (hence relay nozzle off), while it is deflected only upon electric energisation, opening upon control delivery conduit 8 (hence relay nozzle on). Or viceversa.

The short travel required to make the shut on/off element operational, combined with the very small mass of the shutter and the opportu- nity to exploit the elastic return force of lamina 11', allow to define an extremely fast actuator with a very high resonance frequency, which makes it suitable to operate at higher frequencies than the typical one of the weaving loom. The shut on/off element can hence drive the opening and closing of the relay nozzle also several times within the same weft insertion cycle, as desired .

Fig. 5 - wherein base body 1 and cover 2 are separated merely for ease of representation's sake - shows the development of air flows as well as the (mutually perpendicular) oscillation directions of the laminae of the two shutters.

Figs. 6-9 show another embodiment of the unit according to the invention, further employing two piezoelectric actuators. In this case, base body 100 is configured in a way substantially identical to the previous embodiment, but both shutter elements are flexible along the same axis and both act as pressure adjuster and as shut on/off element at the same time. As a matter of fact, as clearly visible in fig. 8, two flexible laminae 111 and 111' are arranged within the same switching chamber of the base body 100, side by side and parallel to each other; the respective shutting buttons 112 and 112' are arranged in the proximity of two different calibration conduits having different diameter, arranged opposite to each other as in the previously described embodiment.

The control of each actuator, through a short travel, causes the respective shutting button 112 or 112' to alternatively obstruct either one of the calibration conduits, or both simultaneously, or neither one. Thereby, with both calibration conduits shut, the closed condition of the valve unit is obtained (an additional closing/opening element acting on the delivery conduit is not required), while in all other three conditions the opening of the valve unit is accomplished according to three different pressure levels.

The short run required to obstruct or open calibration conduits 105a and 105b allows to obtain fast operation : hence both a pressure adjustment function and a shut on/off function can be performed at a greater frequency than the weaving loom operation one.

Fig. 10 - wherein base body 100 and cover 102 are separated merely for ease of representation's sake - shows with arrows the development of air flows, as well as the oscillation directions (in this case, in the same plane) of the laminae of the two shutter elements.

Although not explicitly illustrated, it is possible to increase the number of shutter elements inside the switching compartment/chamber of base body 1 and accordingly the number of calibration conduits to be shut, in or- der to thus be able to obtain a greater number than three pressure levels to use for the adjustment of the relay nozzle.

As already highlighted above, by the unit according to the invention it is possible to obtain a particularly effective air pressure adjustment and an opening/closing of the relay nozzle with limited construction costs.

Due to the programming flexibility and to the fast reaction time of this combined pressure adjusting and switching valve unity, it is now possible to advantageously create a freely programmable dynamic pressure profile within the reed channel along the entire weaving width, as well as several open-and-close switching cycles of the nozzle within a single weft inser- tion cycle. In particular, a single combined pressure adjusting and switching valve unit is able, within a few milliseconds - namely 3 to 5 ms - to switch from a 3-bar pressure level to 5 bars or to perform several open-and-close switching cycles within the same cycle time.