Modulated weft thread braking device for textile machines

Abstract

 A device (10) for the modulated braking of a weft thread, comprising a set of three fixed thread guiding eyelets (13,14,15) which trace a straight path of the thread through the device and at least one actuated braking element (27) adapted to engage the thread in the spaces between the thread guiding eyelets in order to deflect its path for braking. The braking element is actuated by a movable yoke (19) which is subjected to the interacting actions of a magnetic field (Φ) and of a current (I) which circulates in at least one excitation coil (21), and the movable yoke actuates a first oscillating lever (24) to which the braking element is rigidly coupled, the braking element being constituted by a second oscillating lever (27) which is U-shaped and is suitable to straddle the central thread guiding eyelet (14) in order to engage the thread (F) that slides within the eyelets, deflecting its path in the free portions that lie between the central eyelet (14) and the end eyelets (13,15).

Description

[0001] The present invention relates to a modulated weft thread braking device for textile machines.

[0002] More specifically, the invention relates to a conventional braking device comprising two or more fixed and mutually spaced thread guiding eyelets, which trace a straight path for the thread through the braking device, and at least one braking element, which is actuated electrically and is adapted to engage the thread in the spaces between the thread guiding eyelets in order to deflect the thread from its straight path and produce the modulated braking thereof according to the breadth of the angles of deflection imparted to said thread.

[0003] These devices are typically interposed between the loom (or other textile machine) and the weft feeder, which is usually provided with a braking means of its own of the friction type, and are meant to eliminate the peaks of mechanical tension that the loom discharges onto the thread during its operation.

[0004] In weaving looms, and more generally in weft-insertion textile machines, during the execution of the beat the thread advancement speed undergoes an approximately sinusoidal variation and the action of the braking means of the weft feeder (which depends on the friction coefficient between the thread and said braking means) varies correspondingly; accordingly, the mechanical tension of the thread undergoes considerable and undesirable increases which cause frequent breakages.

[0005] In order to avoid this drawback, it is known to interpose, between the loom and the feeder, the modulated braking device in which the braking element is actuated with an excitation current variable according to the same criterion as the advancement speed or mechanical tension of the thread, so as to constantly adapt the braking action and maintain the mechanical tension of the thread substantially constant.

[0006] Conventional modulating braking devices of this type are described for example in European Patent no. 527,510 and in Italian Patent Application MI 96A001316. Both these devices, provided with a braking element actuated by the rotor of an electric motor, have failed to yield entirely satisfactory results.

[0007] Due to the high inertia of the rotor, and due to the modest torque generated by the motor, the response of the braking element to variations in the mechanical tension of the thread is generally inadequate, bearing in mind the high operating speeds of current weaving looms, which require the braking element to react within a few milliseconds.

[0008] Another device, described in European Patent no. 326,784, actuates the braking element by means of an electromagnet provided with a movable keeper which, in addition to having a considerable mass, has a high mutual inductance coefficient. Both of these factors considerably delay the response of the device, eliminating the benefit of the greater electrodynamic force applied by the electromagnet to the braking element.

[0009] The aim of the present invention is accordingly to solve said drawbacks.

[0010] Within the scope of this general aim, an important object of the present invention is to provide a modulated thread braking device of the specified type, with actuation means which are adapted to ensure the maximum response speed of the braking element, which in practice reacts without appreciable delay to variations in the advancement speed of the thread and accordingly in its mechanical tension.

[0011] Another object of the invention is to provide a modulated thread braking device of the specified type, with actuation means which are adapted to actuate the braking element with high intensity and accordingly to accelerate the braking element adequately in order to follow, without appreciable delays, variations in the speed and mechanical tension of the thread.

[0012] Another object of the invention is to provide a modulated thread braking device which has a simple structure and is reliable in operation.

[0013] According to the present invention, this aim, these objects and others which will become apparent from the following detailed description are achieved by a modulated thread braking device which has the specific characteristics stated in the appended claims.

[0014] Substantially, the invention is based on the concept of providing a braking device with an actuation system which is extremely lightweight but at the same time capable of providing a substantial working force. The system uses, for this purpose, a movable yoke which is subjected to the interacting actions of a magnetic field and of a current which circulates in an excitation coil. The movable yoke has an actuation rod rigidly coupled thereto which actuates a first oscillating lever, whereto the braking element is rigidly coupled; said braking element is constituted by a second oscillating lever which is U-shaped and is adapted to straddle a central thread guiding eyelet which is interposed between two end thread guiding elements in order to engage the thread that slides within said eyelets, deflecting its path in the free portions that lie between the central eyelet and the end ones.

[0015] According to an embodiment of the invention, the movable yoke supports said excitation yoke, which is wound on a hollow cylindrical support and is placed in the field of a permanent magnet which generates a flux which circulates in a cylindrical jacket which surrounds the coil and is closed across an annular air gap on a cylindrical pivot which is slidingly contained in the cavity of the cylindrical support of said coil.

[0016] According to a constructive embodiment, the movable yoke is constituted by at least one movable permanent magnet which replaces said actuation rod and moves in the cylindrical seat of the jacket of an electromagnet which is excited by at least one coil through which the corresponding excitation current flows.

[0017] Further characteristics and advantages of the modulated braking device according to the invention will become apparent from the following detailed description and with reference to the accompanying drawings, which are given by way of non-limitative example and wherein:

Figure 1 is a front elevation view of the braking device according to a preferred embodiment of the invention, shown with the braking element in the active position;

Figure 2 is a view, similar to Figure 1, of the device with the braking element in the inactive position;

Figure 3 is a sectional view, taken along the plane III-III of Figure 2;

Figure 4 is a perspective view of the hollow cylindrical support which supports the excitation coil and constitutes the movable yoke of the braking device of Figure 1;

Figures 5 and 6 are respectively an elevation view and a plan view of the support of Figure 4;

Figure 7 is a sectional view, similar to Figure 3, of a different embodiment of the braking device according to the invention.

[0018] Initially with reference to Figures 1 to 6, the reference numeral 10 generally designates a braking device, which comprises a box-like body 11 with a cover 12, to the side of which there is a set of three thread guiding elements 13, 14 and 15 which are aligned, are mutually spaced by an extent t which has a convenient length, and trace a straight path of the thread F through the braking device 10. Inside the box-like body 11 there is a permanent magnet 16 (Figure 3) which generates a magnetic flux which circulates in a cylindrical jacket 17 made of a material with very high magnetic permeance and closes across a cylindrical pivot 18 which is separated from the jacket 17 by an annular air gap TA.

[0019] A movable yoke 19 is fitted on the cylindrical pivot 18 so as to slide freely and comprises a hollow cylindrical support 20 made of electrically insulating material with a low relative density, for example cardboard, a mat of resin-impregnated fibers and the like, whereon an excitation coil 21 is wound. A current I flows through the coil and can vary with a criterion which is equal to, and the inverse of, the criterion with which the advancement speed of the thread F varies. The current I is generated in a known manner by a microprocessor (not shown) which receives in input a signal modulated by a movable element of the loom or, as an alternative, by a sensor for detecting the mechanical tension of the thread.

[0020] As clearly shown in the figures, the electrical connection between the coil 21 and the conductors for supplying the excitation current I (not shown) is provided by means of a highly flexible connection system, which on the one hand does not introduce mechanical resistance in the movement of the yoke 19 and on the other hand does not subject the connection conductors to fatigue stress. This connection system uses a pair of strips 22 made of elastic material, for example the material known commercially as Kapton, on which a copper lamina a few hundredths of a millimeter thick is applied by electrolytic methods. The strips have a substantial free length which significantly reduces stresses, which are mainly torsional, increasing the fatigue strength of the connection.

[0021] By way of the interaction between the magnetic field Φ produced by the magnet 16 and the excitation current I, the movable yoke 19 is subjected to an electrodynamic force

, where L is the number of turns of the coil 21, which tends to move the yoke in an axial direction along the cylindrical pivot 18. By means of a rod 23 guided in a bush of the cover 12, the movement of the yoke 19 is transmitted to a first oscillating lever 24 which is pivoted to a support 25 of the cover and is provided with a slot 26 in which a transverse pivot of the rod 23 engages. The actual braking element is rigidly coupled to the lever 24 and is constituted by a second U-shaped oscillating lever 27 which is adapted to straddle the central thread guiding element 14 in order to engage the thread F and deflect its path in the free portions that lie between the central eyelet and the end ones 13-15, as clearly shown in Figure 2.

[0022] The above-described system is extremely lightweight and follows without appreciable delay the variations in the excitation current I, modulating the braking action on the thread with corresponding larger or smaller deflections of the path of the thread applied by the oscillating lever 27.

[0023] In the embodiment of Figure 7, the movable yoke is constituted by at least one permanent magnet, preferably two permanent magnets 190-191 shaped like cylindrical bars, for example made of neodymium, which are arranged end to end, replace the rod 23 and move in the cylindrical seat of the jacket 170 of an electromagnet which is excited by at least one coil, preferably two coils 210-211 arranged electrically in parallel and crossed by the excitation current I.

[0024] As clearly shown in the Figure, the magnet bar 191 has an end portion which passes through the cover 12 in order to be articulated to the lever 24 so as to move said lever.

[0025] Without altering the concept of the invention, the details of execution and the embodiments may of course vary extensively with respect to what has been described and and illustrated by way of non-limitative example without thereby abandoning the scope of the invention.

[0026] The disclosures in Italian Patent Application No. TO98A000207 from which this application claims priority are incorporated herein by reference.

[0027] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A device (10) for the modulated braking of a weft thread (F) for textile machines, comprising a set of three fixed thread guiding eyelets (13,14,15) which trace a straight path of the thread through the device and at least one actuated braking element which is adapted to engage the thread in spaces defined between said thread guiding eyelets in order to deflect its path for braking, characterized in that it comprises a movable yoke (19;190) which is subjected to the interacting actions of a magnetic field (Φ) and of a current (I) which circulates in at least one excitation coil (21;210), and in that said movable yoke actuates a first oscillating lever (24) whereto the braking element is rigidly coupled, said braking element being constituted by a second oscillating lever (27) which is U-shaped and is adapted to straddle the central thread guiding eyelet (14) in order to engage the thread (F) that slides within the eyelets, deflecting its path in the free portions that lie between the central eyelet (14) and the end eyelets (13,15).

2. The device (10) according to claim 1, characterized in that the movable yoke (19) is formed by a hollow cylindrical support (20) whereon said excitation coil (21) is wound, said coil being placed in the magnetic field (Φ) of a permanent magnet (16) which generates a flux which circulates in a cylindrical jacket (17) which surrounds the coil and is closed across an annular air gap (TA) on a cylindrical pivot (18) which is slidingly contained in the cavity of said hollow cylindrical support (20).

3. The device (10) according to claim 2, characterized in that said hollow cylindrical support (20) is made of electrically insulating material with a low relative density.

4. The device (10) according to claims 1 to 3, characterized in that the electrical connection between said excitation coil (21) and conductors that supply said excitation current (I) is provided by means of a pair of strips (22) made of elastic material, whereon a copper lamina is applied by electrolytic methods and constitutes the electrically conducting element.

5. The device (10) according to claim 1, characterized in that it comprises a box-like body (11) with a cover (12) on which said first lever (24) is pivoted and to the side of which the set of three thread guiding eyelets (13,14,15) is arranged, said thread guiding eyelets being mutually aligned and spaced by a suitable length (t).

6. The device (10) according to claim 1, characterized in that said hollow cylindrical support (20) of the movable yoke (19) is provided with a rigid rod (23) which passes through said cover (12) and transmits the straight motion of the yoke to said first lever (24), the rigid rod (23) being provided with a transverse end pivot which is articulated in a slot (26) of said first lever.

7. The device (10) according to claim 1, characterized in that said movable yoke is constituted by at least one movable permanent magnet (190) which moves in the cylindrical seat of a jacket (170) of an electromagnet which is excited by said one coil (210) through which said excitation current (I) flows.

8. The device (10) according to claim 7, characterized in that said movable yoke comprises two permanent magnets which are constituted by cylindrical bars (190,191) which are arranged end to end, and in that one of said cylindrical bars (191) has an end portion which is articulated to said first oscillating lever (24) for actuation.

Drawing