Device for modulated braking of a weft yarn for textile machines

Abstract: Device for modulated braking of a weft yarn for textile machines, comprising a set of three yarn guiding eyes (13, 14, 15), which form a straight path for the yarn, and an oscillating lever (24), which is connected to a U-shaped braking element (27) which straddles a central eye (14) of said eyes and engages the yarn (F) in free portions that lie between said central eye and the end eyes (14, 15) of said eyes in order to divert its straight path for braking, characterized in that the oscillating lever (24) is controlled by an electromagnetic actuation means which comprises at least one permanent magnet which is constituted by a cylindrical body (20) having a N-S polar axis arranged radially; the body is associated with a stem (19) which is articulated to the oscillating lever (24) and can move in a linear fashion inside a cylindrical shroud (22) with high magnetic permeance, on which at least one coil (220) is wound, an excitation current (I) flowing through the coil; the axis of the cylindrical shroud (22), which coincides with the axis of the movable stem (19), being perpendicular to the polar axis (N-S) of the cylindrical permanent-magnet body (20).

Description: The present invention relates to a device for modulated braking of a weft yarn for textile machines. More specifically, the invention relates to a device of the type disclosed in the prior EP 942 083 A (published on 1999-09-15) by same Applicant, which comprises a set of three fixed yarn guiding eyes, which determine a straight path of the weft yarn through the device, and at least one controlled braking element, which is adapted to engage the yarn in the spaces between said yarn guiding eyes in order to divert its straight path for braking. In such conventional device, a movable electromagnetic yoke, subjected to the interacting actions of a constant magnetic field and of a current which circulates in an excitation coil, actuates a first oscillating lever with which the braking element proper is rigidly coupled. Said braking element is constituted by a second U-shaped oscillating lever which arranges itself so as to straddle the central yarn guiding eye and engages the yarn in the free portions that lie between the central eye and the end eyes. The movable yoke is formed by a hollow cylindrical support on which the excitation coil is wound; the coil is immersed in the field of a permanent magnet which generates a flux which circulates in a cylindrical shroud of a material having high magnetic permeance. Although this conventional device has a response which is generally adequate in terms of reaction to the extremely rapid variations in the mechanical tension of the yarn that occur in modern weaving processes, it is not entirely satisfactory from the constructive point of view, because of a certain mechanical fragility of the movable yoke, whose mass is intentionally very modest, and from the functional point of view, due to some uncertainty in the operation of the movable yoke, which sometimes, especially in the processing of higher-count yarns, can be subject to an electromotive force which is insufficient to produce an adequate response to the device in the above specified terms. Document WO 97 49630 A, which represents the most relevant state of the art, discloses a Device for modulated braking of a weft yarn in which the U. shaped braking element is controlled by a rotation drive. The aim of the present invention is to provide a braking device according to the preamble of in dependent claim 1 having an adequate response by extremely rapid variations in the tension of the yarn. Within the scope of this aim, a particular object of the present invention is to provide a device for modulated braking of a weft yarn for textile machines, comprising a set of three yarn guiding eyes, which form a straight path for the yarn, and an oscillating lever, which is connected to a U-shaped braking element which straddles a central eye of said eyes and engages the yarn in free portions that lie between said central eye and the end eyes of said eyes in order to divert its straight path for braking, characterized in that said oscillating lever is controlled by an electromagnetic actuation means which comprises at least one permanent magnet which is constituted by a cylindrical body having a N-S polar axis arranged radially, said body being associated with a stem which is articulated to said oscillating lever and can move in a linear fashion inside a cylindrical shroud with high magnetic permeance, on which at least one coil is wound, an excitation current flowing through said coil; the axis of said cylindrical shroud, which coincides with the axis of the movable stem, being perpendicular to the polar axis of said cylindrical permanent-magnet body. Advantageously, according to the present invention, said cylindrical permanent-magnet body is made of one of the magnetic materials neodymium, samarium-cobalt and alloys thereof, and is connected on a support of nonmagnetic material, typically polymeric material, which is stably rigidly coupled to said movable stem. According to a different embodiment of the present invention, a linear motion sensor is associated with the movable stem of the electromagnetic actuation means and is capable of providing a feedback signal which allows to control the current supplied to the excitation coil and accordingly control the speed and/or method of motion of said stem. Further characteristics and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a front elevation view of a first embodiment of the braking device according to the present invention; Figure 2 is a transverse sectional view of the device, taken along the plane II-II of Figure 1; Figure 3 is a highly enlarged-scale view of a detail of Figure 2; Figure 3a is highly enlarged-scale view, similar to Figure 3, of a second embodiment of the device according to the present invention; Figure 4 is a sectional view, similar to Figure 2, of a third embodiment of the device according to the present invention; Figure 5 is an electrical diagram of the means for generating and controlling the current supplied to the excitation coil. With reference to Figures 1 to 3, the reference numeral 10 designates a braking device, which comprises a box-like body 11 with a cover 12 to one side of which a set of three aligned yarn guiding eyes 13, 14 15 is arranged; the eyes are mutually spaced by a convenient extent "t" and form a straight path for a yarn F through the braking device 10. A first oscillating lever 24 is articulated to the cover 12 and is pivoted to a support 25 of the cover; the braking element proper is rigidly coupled to the lever. The braking element is constituted by a second oscillating lever 27, which is U-shaped and is adapted to arrange itself so as to straddle the central eye 14 in order to engage the yarn F and divert its path in the free portions that lie between said central eye and the end eyes 13-15 (Figure 1). According to the present invention, the braking element 27 is actuated by an actuator which has a movable stem 19, with a transverse pivot which engages a slot 26 of the oscillating lever 24 and is provided with at least one permanent magnet which is constituted by a cylindrical body 20 made of a material having an extremely high magnetic hysteresis, typically neodymium or samarium-cobalt. The N-S polar axis of the cylindrical permanent-magnet body 20 is arranged radially and is preferably orientated so that the N polarity faces outward (Figure 3). Said body is fitted on a support 21 made of nonmagnetic material, typically thermoplastic polymeric material, which is in turn rigidly coupled to the stem 19. Preferably, a cylindrical sleeve 20a made of ferromagnetic material (Figure 3a) is interposed between the cylindrical body 20 and the support 21. The stem 19 moves in a linear fashion inside a cylindrical shroud 22 made of a material having high magnetic permeance which is arranged inside the box-like body 11 formed in two portions 22'-22" which are juxtaposed due to assembly requirements; each portion delimits a corresponding stator pole which is separated from the cylindrical magnet body 20 by a gap TR. Each portion of the shroud 22 is provided with a corresponding bush 23 for the guiding and retention of the stem 19. The bushes have respective circular abutment surfaces 230 provided with annular seats for corresponding elastomeric rings 231 of the O-ring type which are suitable to cushion the stroke limit impact of the support 21 against said circular abutment surfaces. An excitation coil 220 is wound on the shroud 22 and is supplied in a conventional way by an excitation current I which varies with a rule which is equal to, and the inverse of, the rule with which the advancement speed of the yarn F varies. With the above-described arrangement, the magnet 20 generates a field Φ whose lines of force, by concatenating with the lines of force of the field generated by the coil 220, produce an intense force F which is directed along the axis of the stem 19 and is expressed by the relation F=K.Br.Dm.n.I, where n is the number of turns of the coil 220, I is the excitation current, K is a constant whose value depends on the overall geometry of the system and on the type of permanent magnet 20, Br is the residual induction of said permanent magnet and Dm is its average diameter. In the embodiment of Figure 3a, which is suitable to generate a significantly higher magnetomotive force F for an equal power absorption, the cylindrical shroud 22 comprises a third cylindrical shroud portion 22"' which is interposed between the two juxtaposed portions 22'-22" and forms a corresponding third stator pole. In this case, two superimposed cylindrical permanent-magnet bodies 20'-20" are provided and rigidly coupled to the stem 19; those bodies have opposite radial polarities, as shown in the figure, and both are fitted on the support 21 with the cylindrical sleeve of ferromagnetic material 20a interposed. Likewise, the excitation coil 220 is split into two windings 220'-220" which are separated by the third shroud portion and are preferably electrically series-connected. According to the different embodiment of Figure 4, a linear motion sensor, generally designated by the reference numeral 30, is associated with the movable stem 19 of the device. The sensor is capable of providing an analog feedback signal SR, for example in terms of voltage, which can be used to control the movement of the stem 19. For this purpose, and as shown in Figure 5, the feedback signal SR, after analog/digital conversion performed by a converter Cad, is applied to a microprocessor µP and is used to vary the excitation current I produced by a power transducer AM which is driven by the microprocessor with the interposition of a further digital/analog converter, designated by Cda. In this way, the feedback signal SR can be used, for example, to reduce the travel speed of the stem 19 at the stroke limit points in order to avoid rebounding or in order to apply to the stem a preset rule of motion which is suitable to optimize the modulated braking of the yarn. Without altering the concept of the present invention, the details of execution and the embodiments may of course be altered extensively with respect to what has been described and illustrated by way of nonlimitative example without thereby abandoning the invention. 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 each element identified by way of example by such reference signs.

Claims: Device for modulated braking of a weft yarn for textile machines, comprising a set of three yarn guiding eyes (13, 14, 15), which form a straight path for the yarn, and an oscillating lever (24), which is connected to a U-shaped braking element (27) which straddles a central eye (14) of said eyes and engages the yarn (F) in free portions that lie between said central eye and the end eyes (14, 15) of said eyes in order to divert its straight path for braking, characterized in that said oscillating lever (24) is controlled by an electromagnetic actuation means which comprises at least one permanent magnet which is constituted by a cylindrical body (20) having a N-S polar axis arranged radially, said body being associated with a stem (19) which is articulated to said oscillating lever (24) and can move in a linear fashion inside a cylindrical shroud (22) with high magnetic permeance, on which at least one coil (220) is wound, an excitation current (I) flowing through said coil; the axis of said cylindrical shroud (22), which coincides with the axis of the movable stem (19), being perpendicular to the polar axis (N-S) of said cylindrical permanent-magnet body (20). The device according to claim 1, characterized in that said cylindrical permanent-magnet body (20) is made of one of the following magnetic materials: neodymium, samarium-cobalt. The device according to claim 1, characterized in that said cylindrical permanent-magnet body (20) is fitted on a support (21) made of polymeric material which is stably coupled to said movable stem (19). The device according to claim 3, characterized in that said cylindrical permanent-magnet body is rigidly coupled to the support (21) made of polymeric material with a cylindrical sleeve (20a) made of ferromagnetic material interposed. The device according to claim 1, characterized in that said cylindrical shroud (22) is provided in at least two juxtaposed portions (22'-22"), each of which delimits a corresponding stator pole which is separated from the cylindrical permanent-magnet body (20) by a gap (TR). The device according to claim 5, characterized in that said juxtaposed portions of the cylindrical shroud (22) are provided with respective bushes (23) for the guiding and retention of the movable stem (19). The device according to claim 6, characterized in that said bushes (23) are provided with respective circular abutment surfaces (230) which have annular seats for corresponding elastomeric rings (231) which are suitable to cushion the stroke limit impact of said support (21) against said circular abutment surfaces. The device according to claim 5, characterized in that said cylindrical shroud (22) comprises a third cylinder portion (22"') which is interposed between said juxtaposed portions (22'-22") and forms a corresponding third stator pole; said movable stem (19) being provided with two cylindrical permanent-magnet bodies (20'-20") which have opposite radial polarities (N-S) and are fitted and superimposed on said nonmagnetic support (21); the at least one coil (220) being split into two windings (220'-220") which are separated by said third shroud portion (22"') and are electrically series-connected. The device according to claim 1, characterized in that the movable stem (19) of the electromagnetic actuation means has a linear motion sensor (30) associated therewith, said sensor being capable of providing a feedback signal (SR) which allows to control the excitation current (I) which is supplied to the excitation coil (220) and accordingly to control the speed and/or the criteria of the motion of said stem (19).

Inventors: ZENONI PIETRO, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 1999
Main classification: B65H59
IPC codes: D03D47, B65H59