A. Field
This invention relates to a thread clamp, in particular for a weaving machine, as well as to a weaving machine using such thread clamp.
B. Related Art
More particularly, the invention relates to a thread clamp which at least consists of an actual clamp with at least two clamping parts between which a thread can be clamped, as well as of actuation means for moving said clamping parts in mutual respect between a closed position, whereby the clamping parts are pushed towards each other, and an open position whereby the clamping parts are situated located at a distance from each other.
It is known that such thread clamps can be used at different locations in a weaving machine. In particular, they are used for gripping weft threads, either for holding them at their place, or for braking and/or stopping them in their movement.
It is also known that such thread clamps can be actuated in different manners.
So, for example, electric actuating means can be used, whereby use is made of an electromagnet or a piezo-actuator for controlling the clamp, for which of course an electric wiring must be provided up to the thread clamp concerned, which often is viewed as disadvantageous, especially if such thread clamp is provided on a moving part, such as the sley of the weaving machine.
It is also known to apply pneumatic actuation means, whereby such thread clamp then is provided with a movable part which can be actuated by means of fluid (air) pressure.
With the known electric as well as the pneumatic embodiments, that is the electric drive and the pneumatic drive, respectively, the clamp is forced into one well-defined position, whereas the clamp, when switching off the actuation means, automatically is brought into the other position, by means of a return spring. The use of such return spring has various disadvantages. A first disadvantage consists in that it is rather difficult to mount a return spring which has a relatively large stroke and which does not vary too much in pre-tension, into a small built-in space, which return spring moreover, notwithstanding the relatively large displacement, does not buckle and also still has a long service life. A second disadvantage consists in that in certain applications, for example, when the thread clamp is mounted on a sley which is moving rapidly to and fro, it may occur that such return spring is excited automatically, for example, due to inertia forces, at moments when this is not desired. A third disadvantage consists in that mutual friction between the windings of the spring may occur, as well as between the spring and the surrounding housing, as a result of which the proper spring functioning can be disturbed. A fourth disadvantage consists in that, with high speeds, undesired effects can be created in such return spring, for example, as windings, so to speak, beat against each other and create undesired effects. A fifth disadvantage consists in that such return springs, due to their manifold movements, are subjected to intense wear and tear.
It is known to apply actuation means which are double-acting, for example, electromagnetic or pneumatic drives with which the thread clamp, by means of a controlled actuation, is forced into opened condition as well as into closed condition, without using passive readjustment means. This, however, has the disadvantage that a higher number of cables and compressed air conduits, respectively, have to be brought up to the thread clamps concerned, which in particular is a disadvantage with thread clamps which are mounted on a moving part.
The invention provides a thread clamp for a weaving machine which allows new constructional possibilities, control possibilities and combinations of controls, and is very efficient in its use and with which, depending on its form of embodiment, one or more of said disadvantages can be excluded or at least minimized.
To this aim, the invention in the first instance relates to a thread clamp for a weaving machine, which at least consists of an actual clamp with at least two clamping parts between which a thread can be clamped, as well as of actuation means for moving said clamping parts in mutual respect between at least two positions, a closed position, whereby the clamping parts are pushed towards each other, and an open position whereby the clamping parts are situated at a distance from each other, respectively, with as a characteristic that said actuation means comprise at least a pneumatically actuatable part for bringing the clamp into at least one of said two positions, which part also can be actuated by means of a negative pressure, more particularly vacuum.
By using a part which can be actuated by means of negative pressure, the advantage is obtained that new forms of constructions, as well as mounting possibilities are created. Another advantage consists in that a new actuation method is provided for, which, on one hand, enables an efficient control and, on the other hand, allows various new combinations with existing techniques.
Preferably, the thread clamp according to the invention comprises a pneumatically actuatable part which enables the actual clamp, on one hand, to be brought into at least one position by means of at least a negative pressure, and on the other hand, enables the clamp to be forced into the other position by means of at least another manner of actuation. Thereby, a control is offered which has the advantage that two control possibilities are obtained, to wit a control by means of negative pressure, more particularly vacuum, and a control by means of another manner of actuation.
Preferably, the pneumatically actuatable part is configurated such that the clamp is forced into opened condition by means of feeding the negative pressure, whereas the closed condition is brought about by means of the other manner of actuation. The pressure difference which can be created by means of a negative pressure, more particularly a vacuum, even if it should be possible to create an absolute vacuum, in different application thus is too small to provide for a good clamping force, and preferably the negative pressure, thus, as aforementioned, is used for performing the opening of the clamp, whereas for closing the clamp, an actuation then can be provided for in another manner.
For the aforementioned other manner of actuation, preferably use will be made of a medium which is at overpressure, for example, compressed air, such that, depending on the pressure of the available medium, thus larger forces can be generated.
In the most preferred form of embodiment, the actuatable part has a common actuation surface to which the negative pressure can be fed, and the overpressure can be exerted upon, respectively. By using a negative pressure as well as an overpressure, it is thus possible to create, with one of the same actuation surface, forces in two opposed directions and to effect movements of the actuatable part in two opposed directions.
In the aforementioned case, the thread clamp may have a single conduit for pneumatically actuating said actuatable part, which conduit is used in is common for actuating the clamp towards the closed condition as well as for actuating the clamp towards the open condition. An important advantage then consists in that only one operation conduit is necessary, in other words, only one pneumatic conduit, as a consequence of which the pneumatic circuit is considerably simplified, in particular at the location of the thread clamp itself. This advantage is particularly relevant when different thread clamps must be mounted next to each other or if such thread clamps must be mounted next to other parts, as then the small space available often poses a problem and imposes a limitation on the number pneumatic conduits locatable in the direct proximity of the thread clamp.
This is also particularly useful with thread clamps which are mounted on moving parts of a weaving machine, for example, on the sley, as then, thanks to the invention, the number of connecting conduits between the moving parts and the fixed control may remain limited.
In the most preferred form of embodiment, said actuation means are designed such that the movement of the actuatable part is performed exclusively pneumatical, with which it is meant that the movement of this part exclusively takes place under the influence of negative pressure and/or overpressure, realized by means of fluid, possibly, however, assisted by the gravity of certain parts, but surely not assisted by additional means for exerting a displacement force, such as return springs, electromagnetic drive means or the like.
Thanks to the fact that negative pressure is applied, as well as by combining this preferably with a control by means of overpressure, such additional means for exerting a displacement force in fact can completely be excluded, with the advantage that such thread clamp constructively can be realized in a particularly simple manner.
In a practical form of embodiment, said actuatable part consists of at least one small movable piston, the displacement of which controls the opening or closing of the clamp.
Preferably, this small movable piston has a piston surface which opens to a chamber in which an overpressure and negative pressure, respectively, can be created, which permits the small piston to be actuated from one side for performing the displacement thereof in one direction, as well as in the opposite direction, by creating either an overpressure or a negative pressure, more particularly vacuum, in the aforementioned chamber.
In the most preferred form of embodiment, the small piston substantially will consist of a small plunger, one extremity of which forms one of the aforementioned two parts of the actual clamp, whereas the other extremity functions as a piston surface. Hereby, a particularly compact construction of the thread clamp is enabled.
Of course, the invention also relates to weaving machines using at least one thread clamp as described in the aforegoing.
Important applications of such thread clamp on a weaving machine are as follows:                as a thread clamp at the inlet of the shed of the weaving machine;        as a thread clamp which cooperates with a main blower or auxiliary main blower;        as a thread clamp which cooperates with a main blower or auxiliary main blower which is attached on the sley of the weaving machine;        as a thread clamp at the end of the shed for holding the end of an inserted weft thread;        as a thread clamp on a moving part of the weaving machine, more particularly on the shed;        as a thread clamp which cooperates with a thread-preparing system.        