EP0299553B1 - Thread clip - Google Patents

Description

The present invention relates to a wire clamp, and more particularly to a wire clamp for use on weaving machines or other machines processing spun yarn. By wire clamp or clamp, we mean here any device whose operation ensures the clamping of a wire between two faces, either to brake a moving wire, that is to say to slow the movement or for the '' bring to a halt, either to simply grab a stationary wire presented between the two faces of the clamp. In particular, the present invention relates to wire clamps whose movement is ensured by the reverse piezoelectric effect.

To ensure the driving or the control of a clamp intended, for example, for braking a weft thread on a pneumatic weaving machine, use is conventionally made of mechanical systems whose mechanism relies mainly on the use of cams and / or springs. These mechanical systems have several drawbacks. Indeed, the modification of the opening and closing times, or even the modification of the force of pressure of the clamp, requires a long and difficult adjustment of the mechanical part of the control of the clamp. Likewise, the modification of the pressure force and / or that of the opening and closing speed generally requires the installation of another spring and / or of a cam having a different profile.

Another major disadvantage of mechanical systems is that their reliability leaves something to be desired at very high machine speeds. In addition, weaving involving several colors or several types of thread requires complex mechanisms. As with multi-color weaving, the control of the different pliers can be subordinated to the weaving cycle, it is easily understood that after an interruption of the operation of the weaving machine, for example following the action of a device such as a step finder, it is necessary to ensure each time the good synchronization between control of the pliers and weaving cycle.

We also know that the control of a weft thread clamp can be ensured by electromagnetic devices. These electromagnetic clamps, however, have the disadvantage of requiring a high electrical power to offer appropriate reaction times during weaving at high speed. In most cases, this results in overexcitation of the control electromagnets.

Another disadvantage of the devices which we have just mentioned resides in the fact that the opening and closing moments, as well as the opening and closing speeds, are characterized by a very great dispersion, so that It is not always possible to obtain correct operation at high weaving rates.

The present invention relates to a wire clamp which does not have the disadvantages mentioned. To this end, the invention provides a clamp having the characteristic of comprising a drive mechanism consisting essentially of at least one piezoelectric element with reverse action. Such a reverse action piezoelectric element consists of one or more piezoelectric crystals provided with the required electrical connections, the application of an appropriate electrical voltage conventionally making it possible to obtain a deformation of the expanding piezoelectric crystal. or in contraction. This deformation is used to close or open the clamp.

The advantages of the pliers for piezoelectric wire according to the invention consist in the small amount of electrical energy required for its operation, in its extremely rapid reaction time, in the fact that its clamping force is completely controllable, in the relatively inexpensive nature of its production and, finally, in its small size when mounted in a weaving machine.

It is clear that the use of such pliers on a weaving machine makes it possible to use a fully electronic control for the adjustments necessary after a machine stop, eliminating the tedious mechanical adjustments such as a carefully measured reverse of a system of cams, for example.

It is also clear that a thread clamp according to the invention, in addition to its use as a weft clamp, can be used at other points of a weaving machine and in particular at all points requiring clamps, operation requires very precise control.

• la figure 1 représente une pince pour fil selon l'invention;
• la figure 2 représente la pince illustrée à la figure 1 en position fermée;
• la figure 3 représente une variante selon l'invention;
• la figure 4 représente la pince illustrée à la figure 3 en position fermée;
• les figures 5 et 6 représentent des graphiques illustrant le rapport entre la tension appliquée et la force de serrage obtenue;
• les figures 7 à 9 représentent une autre variante selon l'invention, ainsi que son utilisation;
• la figure 10 représente une application de pinces selon l'invention.

In order to better highlight the characteristics of the invention, the description below, given by way of example only and without any limiting nature, of a few preferred embodiments, with reference to the accompanying drawings, in which :

• Figure 1 shows a wire clamp according to the invention;
• Figure 2 shows the clamp illustrated in Figure 1 in the closed position;
• FIG. 3 represents a variant according to the invention;
• FIG. 4 represents the clamp illustrated in FIG. 3 in the closed position;
• Figures 5 and 6 show graphs illustrating the relationship between the applied voltage and the clamping force obtained;
• Figures 7 to 9 show another variant according to the invention, as well as its use;
• FIG. 10 represents an application of pliers according to the invention.

In the embodiment illustrated in Figures 1 and 2, the piezoelectric element with reverse action is formed by a piezoelectric crystal 1 fixed permanently on a support 3 at one of its ends 2, and whose l other end 4, free, forms a clamping element or clamping face which can interact with another element or clamping face 5, fixed permanently to the support 3. In order to avoid wear of the piezoelectric crystal, the clamping face 4 can be provided with a wear-resistant jaw 6 made for example from a ceramic material. Of course, the clamping face 5 can also be provided with a ceramic or other coating.

Optionally, the assembly of this device may include layers of elastic material 7 intended to absorb shocks or vibrations and interposed for example, as illustrated in FIGS. 1 and 2, between the crystal 1 and the wear-resistant jaw 6 and / or between the clamping face 5 and the part of the support 3 on which it rests.

Furthermore, the piezoelectric crystal 1 is provided with electrical connections 8 to which an appropriate electrical voltage V can be applied, for example using an electrical supply 9 as illustrated diagrammatically in FIG. 1.

The operation of the wire clamp is illustrated in FIGS. 1 and 2. In the diagram in FIG. 1, the applied voltage V has a given value V1 and the clamp does not exert any clamping or braking force, so that the wire 10 passes freely between the clamping faces. In the diagram of FIG. 2, the applied voltage has a value V2 lower than V1, causing an expansion of the crystal proportional to the drop in voltage, so that the wire 10 is wedged between the jaw 6 and the clamping face 5. However, the clamping force will increase in proportion to any greater drop in voltage V.

Figures 3 and 4 show another alternative embodiment, using a curved piezoelectric crystal 11 whose magnitude of the curvature is a function of the magnitude of the voltage V applied. The piezoelectric crystal 11 is fixed permanently to one of its ends 12 and provided, at the other end 13, with a clamping face 4 formed by a jaw 6 similar to that of the variant embodiment illustrated in FIGS. 1 and 2. This jaw can interact with a clamping element or fixed clamping face 5.

The end 12, fixed permanently, is provided with the required electrical connections 8.

The operation of the clamp according to the embodiment illustrated in Figures 3 and 4 can easily be deduced from the diagrams of the illustrations. In the state where a voltage V = V3 is applied, the piezoelectric crystal 11 takes the shape illustrated in FIG. 3. When a lower voltage V = V4 is applied, the shape of the piezoelectric crystal 11 will change as illustrated in Figure 4, so that the clamping faces 4 and 5 interact. The clamping force will be determined, as before, by the voltage V applied.

Figures 5 and 6 illustrate, for an exemplary embodiment, the relationship between the speed of the voltage V applied to the electrical connections 8 and the corresponding clamping force F. In the first phase A, the voltage V has a high value such that the clamp is completely open, the clamping force being F = 0 in this case. During phase B, the voltage V is reduced so that the clamp begins to exert a certain clamping force F1 on the wire placed in the clamp. A higher clamping force F2 can be achieved by further reducing the applied voltage, as illustrated in phase C.

Figures 7 to 9 illustrate another embodiment which uses two piezoelectric crystals 14 and 15 arranged so as to face each other. Their distant ends 16 and 17 are fixed permanently, while their close ends 18 and 19, provided with wear-resistant jaws, are placed opposite.

The operation of this clamp is easily deduced from the diagrams represented in FIGS. 7 to 9. The expansion of the piezoelectric crystal 14 only, as illustrated in FIG. 8, makes it possible to obtain a small clamping force, while the expansion of the two piezoelectric crystals 14 and 15 at the same time, as illustrated in FIG. 9, generates a large clamping force.

This last variant offers the advantage of providing, on the one hand, an adjustable clamping force _ two values it is true _ when only one tension is applied, and on the other hand, a relatively large passage for the wire 10 when the two crystals 14 and 15 are energized at the same time.

It is clear that such a double action clamp may also be produced by using two curved piezoelectric crystals 11 of the type mentioned above. In such an alternative embodiment, the piezoelectric elements 11 or 14-15 do not necessarily have to be mounted opposite. They can, for example, be placed one on the other in a series arrangement, so to speak, in which case they will interact with a clamping face permanently fixed. Such a series connection could also consist of several piezoelectric crystals, the application of a single voltage value V then making it possible to obtain a clamping force adjustable in several steps. It goes without saying that these variant embodiments may also include a layer of damping material 7.

FIG. 10 shows an assembly of a weft thread driving mechanism for weaving machines, using four thread clamps 20 to 23. Furthermore, this weft driving mechanism essentially provides a reel holder 24, a supply device 25 formed by reel rollers 26 and a cylindrical tube 27 in which the weft thread 10 is stored in spiral form, preferably a main blower 28 and a comb 29 in a U shape.

The first clamp 20, placed at the outlet of the cylindrical tube 25, has the function of blocking at the required moments the wire taken in the tube. It should be noted that such a piezoelectric clamp 20 proves to be particularly advantageous on weft yarn supply devices of the type in which the weft yarn 10, as illustrated in FIG. 20, is stored in spiral form in a cylindrical tube 27 and more generally on any supply device in which the length of the pick is not directly determined by the shape of the supplier. On such devices in Indeed, the exact determination of the pick to be inserted requires precise adjustment of the clamp 20 acting as a weft insertion clamp. This precision concerns both the opening and closing times, the opening and closing speeds and the dosage of the clamping force. It is clear that a clamp for piezoelectric wire according to the invention makes it possible to meet these requirements in a much more rigorous manner than conventional clamps.

The operation of the clamp 20 largely determines the operation of the entire weft insertion mechanism. When the clamp 20 is closed, a certain amount of wire is blown into the cylindrical tube 25 where it accumulates by depositing in a spiral along the inner wall of the tube. At the opening of the clamp 20, the weft thread is released; at the end of the insertion, the complete closure of the clamp 20, with the application of a high clamping force, causes the weft thread 10 to be blocked when its free end reaches the end of the crowd. As the clamp 20 is caused to abruptly close, it will preferably be provided with a layer of damping material 7.

The second clamp 21 is placed at the end of the crowd. It is known that when a weft thread is braked by the clamp 20 when this thread reaches the end of the crowd, its force of inertia imposes an elastic elongation followed by a contraction, resulting in a recoil effect of the end of the wire 10. To avoid this recoil and, consequently, to prevent the formation of loops in the fabric, the wire 10 is conventionally straightened using a pneumatic weft guide which intercepts the front end of the wire weft. Interception and straightening of the wire could however also be carried out by pliers offering a sufficiently short reaction time to grasp the wire within an adequate time on receipt of a command signal. If the clip closes too quickly, the thread will tie; if it closes too slowly, the wire will form a loop in the crowd when it is removed, as mentioned above. Due to its reduced reaction time, a piezoelectric clamp 21 according to the invention is particularly suitable for the application which has just been described. Since the clamp 21 must be capable, in the open position, of intercepting the weft thread inserted in the crowd, it should preferably have a relatively wide passage in the open position. It is therefore advisable to use for this application a wire clamp of the type illustrated in Figure 7 or, a clamp incorporating one or more piezoelectric crystals connected in series. The presence of the wire 10 will preferably be detected by the piezoelectric crystals of the clamp 21 itself, so as to generate the control signal mentioned above.

Similarly, a piezoelectric clamp can be used to hold the weft thread on the insertion side. Here again, a high clamping force and a relatively large passage for the wire 10 are two very important factors.

The third clamp 22 straightens the wire 10 in front of the unwinding rollers 26. In the illustrated embodiment, the clamp 22 is formed by two curved crystals 11 which can work in interaction and capable of clamping the wire 10 between the jaws 6.

The fourth clamp 23, mounted just in front of the main blower 28, can exert an adjustable pressing force on a wire, so that the wire 10 can be braked gradually when it reaches the end of the crowd, so as to avoid overvoltages and reduce the risk of breakage of the weft thread.

It should be noted that the assembly given in FIG. 10 illustrates a whole series of possible applications of the clamp for piezoelectric wire according to the invention. Thus, the first clamp 20 has the function of blocking a moving wire. The second clamp 21 is used only to grip a wire. The third and fourth clamps, 22 and 23 respectively, have a braking function and exert only a reduced clamping force on the moving wire 10.

It is obvious that the control of the different clamps can be carried out in a large number of variants and that the present invention is in no way limited to the execution versions given by way of example and illustrated in the figures; on the contrary, the wire clamps according to the invention can be produced in different shapes and dimensions without leaving the scope of the invention.

Claims (10)

1. Thread clip characterized in that its movement is primarily guaranteed by at least one piezoelectric element acting inversely (1; 11; 14; 15).

2. Thread clip according to claim 1, characterized in that it is essentially composed of at least one piezoelectric crystal (1), one of the ends of which is fixed, and the other end of which is free, forming a first clamping surface (4) which can work upon a second fixed clamping surface (5) as a result of the deformation of the crystal (1).

3. Thread clip according to claim 1, characterized in that it is essentially composed of two piezoelectric crystals (14, 15) arranged such that they face each other, and whose far ends (16, 17) are fixed, whereas the nearby ends (18, 19) are mounted opposite each other and can work upon each other as a result of the deformation of the crystals (14, 15).

4. Thread clip according to claim 1, characterized in that the piezoelectric element is composed of a curvable crystal (11), one of the ends of which (12) is fixed, whereas the other end (13) is provided with a laterally positioned clamping surface (4).

5. Thread clip according to claim 1, characterized in that it is essentially composed of two curvable piezoelectric crystals (11) whose free ends can work upon each other.

6. Thread clip according to any of the above claims, characterized in that either one or both the piezoelectric crystals are connected to an adjustable power supply (9).

7. Thread clip according to claims 3 or 5, characterized in that the two piezoelectric crystals (11; 14-15) are controlled by one and the same electric current (V), the relative position of the two crystals being such that the expansion of either one of them exerts a reduced clamping pressure on a yarn (10), whereas the expansion of both crystals exerts an increased clamping pressure on the yarn (10).

8. Thread clip according to any of the above claims, characterized in that at least the clamping surface (4) formed by the end of the element or the piezoelectric crystal is provided with a hard-wearing clip piece (6).

9. Thread clip according to claim 8, characterized in that a layer of elastic damping material (7) is placed between the element or the piezoelectric crystal and the hard-wearing clip piece (6).

10. Thread clip according to any of the above claims, characterized in that a layer of elastic damping material (7) is placed between the clamping surface (5) and the support (3) upon which it rests.

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