Device for the positive modulated braking of the thread for weft feeders

Abstract: The device comprises a braking means (12), typically a frustum-shaped braking body, that is supported frontally and coaxially to the drum (T) of the feeder (10) in order to directly or indirectly engage the thread (F) that unwinds from the drum (T). The braking means (12) is subjected to the action of an electromechanical actuation means, supplied by an excitation current (I m ) that is modulated so as to match the variation in the mechanical tension of the thread during the weaving process; the braking means is rigidly coupled to a support (13) that is movable in the axial direction of the drum (T) of the feeder (10) and is supported and guided by a fixed support (14). The movable support is subjected to the action of a reversible motor (M) that is supported by the fixed support (14), is supplied with the modulated current (I m ), and is connected to the movable support (13) with the interposition of a mechanical coupling (19) capable of converting the angular movements of the shaft of the motor (M) into corresponding translatory motions of the movable support (13) with respect to the fixed support (14).

Description: The present invention relates to a device for the positive modulated braking of the thread for weft feeders of shuttle-less looms, particularly gripper looms, projectile looms, and air-jet looms. In the present description, the term "positive" relates to the modulated braking of the thread produced by the action applied to the braking means by an electric excitation or pick-up current that is modulated so as to match the variations in the mechanical tension of the thread during the weaving process. More specifically, the present invention relates to a device for the positive modulated braking of the thread, that comprises a braking means having a continuous circular shape, typically a frustum-shaped body, which is supported frontally and coaxially to the drum of the feeder in order to engage, either directly or with the interposition of resilient elements, the thread that unwinds from said drum, and in which the frustum-shaped braking body is subjected to the action of an electromechanical actuation means capable of varying the pressure with which said body makes contact with the drum of the feeder, said actuation means being supplied with said modulated excitation current. In conventional devices for positive modulated braking the braking body is subjected to the electrodynamic action produced by the interaction of the excitation current that flows in a moving coil associated with the braking body and the magnetic field of a permanent magnet that is fixed with respect to said braking body. Devices according to the preamble of claim 1 are disclosed in EP-A-536 088 and EP-A-652 312 (not prepublished), and hereinafter they will be briefly referenced to as "conventional devices". Although both of these conventional devices achieve effective modulated braking, they have structural and functional drawbacks. From a structural point of view, they are relatively complicated and bulky and require accurate manufacture of the moving coils and of the fixed permanent magnet, between which a minimal air gap must be provided in order to achieve a significant electrodynamic action with low excitation currents. On the other hand, the conductor of the moving coils must be small in size and the coils must be formed by a minimal number of turns in order to avoid excessive increases in the mass and therefore in the inertia of the frustum-shaped body that supports said coil; this is the main structural drawback, since it in any case limits the maximum allowable value of the excitation current; accordingly, the electrodynamic action affecting the frustum-shaped body, which depends on the ampere-turns, is in any case limited to small values that are sufficient to produce the modulated thread braking action if the frustum-shaped body acts by direct contact on the drum of the device but are substantially insufficient if said body acts on the thread with the interposition of flexible elements, such as rows of flexible laminae or rings of bristles. A principal aim of the present invention is to eliminate the above-mentioned drawbacks and, within the scope of this aim, it has the following important particular objects: to provide a device for the positive modulated braking of the thread having an extremely simplified structure, in which the positive braking body, which is typically frustum-shaped, is subjected to the action of an actuation means capable of applying, under the control of said excitation current, a mechanical force of substantially significant intensity that is in any case adapted to actuate said body even if it applies the action not directly but with the interposition of flexible elements; to provide a modulated braking device in which the braking body has minimal mass and therefore minimal inertia by virtue of the elimination of the electrodynamic interaction coils associated therewith, said body being therefore capable of following, without appreciable delays, the modulation of the excitation current that supplies the positive actuation means of said frustum-shaped body; to provide a modulated braking device that has minimum bulk, is extremely sensitive and highly reliable in operation. According to the present invention, this aim and other important objects are achieved with a positive modulated braking device having the specific features disclosed in the appended claims. Substantially, the invention is based on the concept of rigidly coupling the braking body, which is typically a frustum-shaped body, to a movable support that is supported and guided by a fixed support, and of subjecting the movable support to the action of a reversible motor, preferably a step motor. The motor is supplied with an excitation current that is modulated in proportion to the variations in the mechanical tension of the thread, and acts on said movable support of the braking body with the interposition of a mechanical coupling system capable of converting the angular movements of the motor shaft into corresponding translatory motions of the movable support with respect to the fixed support. The fixed support is in turn supported by a movable slider, which is slideable on a supporting structure parallel to the axis of the drum of the feeder, and is controlled by an adjustment knob allowing to vary the tension applied by the braking body to the thread in static conditions. Preferably, the shaft of the step motor is coupled to the movable support of the braking body by means of a coupling comprising a screw and a ball bearing nut. The characteristics, purposes, and advantages of the modulated braking device according to the present invention will become apparent from the following detailed description and with reference to the accompanying drawings, given by way of non-limitative example, wherein: figure 1 is a schematic partially sectional lateral elevation view of a weft feeder with the modulated braking device according to the invention, in the embodiment comprising a modulated braking body that acts directly on the thread; figure 2 is an enlarged-scale view of a detail of figure 1; figure 3 is a partial front view of the device, taken along the direction of the arrows II-II of figure 1; figure 4 is a view of a further embodiment of the device of figure 1; figure 5 is a partial view, similar to figure 1, of another embodiment of the device, in which the braking body acts on rows of braking laminae; figure 6 is a partial view, similar to figure 1, of a further embodiment of the device, in which the braking body acts on a braking ring of the type with bristles. With reference to figures 1 to 3, the reference numeral 10 designates a conventional weft feeder comprising a fixed drum T on which a hollow rotating arm 11, or windmilling arm, winds a plurality of turns SF that constitute a reserve of weft. The hollow arm is rigidly coupled to an equally hollow driving shaft, and the thread F coming from the spool, not shown, runs in the cavities of the shaft and of the arm. At each beat, the loom TE draws a certain number of turns from the reserve SF, and the thread that unwinds from the drum T of the feeder 10 is affected by a positive modulated braking means that allows to control the mechanical tension of the thread, keeping it substantially constant when variations occur in the sliding acceleration that the loom TE applies to said thread in performing each individual beat. The braking means is constituted by a braking body 12, typically a frustum-shaped body having a continuous circular shape, is made of high-strength synthetic material, and is supported by a movable support 13 formed by three arms arranged at 120° frontally and coaxially to the drum T of the feeder 10, against which said body 12 is pushed into contact to engage the thread F. According to the present invention, the movable support 13 is supported, so as to be axially movable, by a fixed support 14, also having three arms; for this purpose, the support 13 is slideable on two guiding and retention pivots 14a that are preferably cylindrical and are rigidly coupled to the fixed support 14 or vice-versa. Said fixed support, in turn, is supported by a slider 15 that is slideable on guides of a fixed structure 16 running parallel to the drum T of the feeder 10. A screw system, which is per se known and not shown, allows to move, by means of a knob 18, the slider 15 and the support 14 therewith, in order to set the force with which the body 12 presses on the drum T in static conditions, that is to say, when the thread is not running. A motor M of the reversible type, preferably a step motor, is arranged on the fixed support 14 and is adapted to act on the movable support 13 in order to modulate, proportionally to the variation in the mechanical tension of the thread during the beat of the loom, said pressure applied by the body 12 to the drum T. For this purpose, a mechanical coupling, designated by the reference numeral 19, is interposed between the motor M and the movable support 13 and is capable of converting the angular movements of the shaft of the motor M into corresponding axial movements of the movable support 13 with respect to the fixed support 14. Preferably, the coupling 19 is constituted by a screw 20 associated with the shaft of the motor M and meshes with a threaded ball bearing nut 21 rigidly coupled to the movable support 13. The motor M is powered so as to move in very small steps and in opposite directions with an excitation current I m that is modulated in intensity and direction and is produced for example by a microprocessor µP, which receives from the loom TE, or as an alternative from a sensor S, a signal "st" for modulation of the current I m that is proportional to the momentary value of the tension of the thread F. In the further embodiment of figure 4, the frustum-shaped body 12 is rigidly coupled to the movable support 13 with the interposition of springs 22 that provide an elastic suspension capable of damping the braking action but most of all of ensuring perfect centering of the frustum-shaped body 12 with respect to the drum of the feeder 10. The embodiment of figure 5 instead differs from the embodiment of figure 1 in that the frustum-shaped body 12, instead of acting directly on the drum T of the feeder 10, acts on the front ends of a paraboloidal row 30 of elastic metallic laminae 31 which, in a per se known manner, adhere elastically to the cylindrical surface of the drum in order to brake the unwinding of the thread F. The modulated movement of the body 12 on the front ends of said paraboloidal row 30 changes the end circumference of the paraboloid and accordingly varies the contact pressure of the laminae 31 on the drum T, correspondingly modulating the braking action applied by said laminae on the thread F. In the embodiment of figure 6, the frustum-shaped body 12 is used to modulate the braking action of a ring of bristles 40 that frontally engage, in a per se known manner, the drum T of the feeder 10. For this purpose, the wider end of the frustum-shaped body 12 ends with a ring 41 internally provided with said ring of bristles 40. Of course, without altering the concept of the invention, the details of the execution and the embodiments may be varied extensively with respect to what has been described and illustrated by way of non limitative example, without thereby abandoning the scope of the invention defined by the appended claims. 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: Device for the positive modulated braking of the thread for weft feeders (10), comprising a braking means (12), typically a frustum-shaped braking body, that is supported frontally and coaxially to the drum (T) of the feeder (10) in order to directly or indirectly engage the thread (F) that unwinds from said drum (T), and wherein said braking means (12) is subjected to the action of an electromechanical actuation means, supplied by a modulated excitation current (I m ) that is modulated so as to match the variation in the mechanical tension of the thread during the weaving process; characterized in that the frustum-shaped body that constitutes the braking means (12) is rigidly coupled to a movable support (13) that is movable in the axial direction of the drum (T) of the feeder (10) and is supported and guided by a fixed support (14), and in that said movable support is subjected to the action of a reversible motor (M) supported by the fixed support (14), is supplied with said modulated current (I m ), and is connected to the movable support (13) with the interposition of a mechanical coupling (19) capable of converting the angular movements of the shaft of the motor (M) into corresponding translatory motions of the movable support (13) with respect to the fixed support (14). Device according to claim 1, characterized in that the motor (M) that acts on the movable support (13) is a step motor. Device according to claim 1, characterized in that said movable support (13) and said fixed support (14) are each formed by three arms arranged at 120°, and in that the movable support is slideable on two cylindrical guiding and retention pivots (13a) rigidly coupled to the fixed support (14) or vice versa. Device according to one or more of the preceding claims, characterized in that said mechanical coupling (19) interposed between the motor (M) and the movable support (13) is constituted by a screw (20) that is associated with the motor shaft and meshes with a threaded ball bearing nut (21) rigidly coupled to the movable support. Device according to one or more of the preceding claims, characterized in that said modulated current (I m ) that supplies the motor (M) is produced by a microprocessor (µP) that receives from the loom (TE), or as an alternative from a sensor (S), a signal (st) adapted to modulate the intensity and direction of the current (I m ) proportionally to the momentary value of the tension of the thread (F). Device according to one or more of the preceding claims, characterized in that said braking means (12) is constituted by a frustum-shaped body having a continuous circular shape and made of high-strength synthetic material. Device according to one or more of the preceding claims, characterized in that said frustum-shaped body having a continuous circular shape that constitutes the braking means (12) acts by direct contact engagement with the drum (T) of the feeder (10). Device according to one or more of the preceding claims, characterized in that the frustum-shaped body that constitutes the braking means (12) is rigidly coupled to the movable support (13). Device according to one or more of the preceding claims, characterized in that the frustum-shaped body that constitutes the braking means (12) is rigidly coupled to the movable support (13) with the interposition of springs (22) that provide an elastic suspension for said frustum-shaped body. Device according to one or more of the preceding claims, characterized in that said frustum-shaped body that constitutes the braking means (12) acts on the front ends of a paraboloidal row (30) of elastic metallic laminae (31) that adhere elastically to the drum (T) of the feeder (10), and in that the modulated movement of the braking body (12) varies the end circumference of said paraboloid (30) and accordingly varies the contact pressure of the laminae (31) against the drum (T), correspondingly modulating the braking action of said laminae on the thread (F). Device according to one or more of the preceding claims, characterized in that the frustum-shaped body that constitutes the braking means (12) ends, at its wider end, with a ring (41) internally provided with a ring of bristles (40) that frontally engage the drum (T) of the feeder (10) to provide modulated braking of the thread (F). Device according to one or more of the preceding claims, characterized in that the fixed support (14) for the frustum-shaped body that constitutes the braking means (12) is supported by a slider (15) slideable on guides of a fixed structure (16) that runs parallel to the drum (T) of the feeder (10), and in that the slider (15) is controlled by a screw-operated movement system that allows, by means of a knob (18), to move the support (14), and the braking means (12) together with said support, in order to set the tension with which said braking means (12) act on said drum (T) in static conditions, that is to say, when the thread (F) is not running.

Inventors: ZENONI PIETRO, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 1995
Main classification: D03D47
IPC codes: D03D47, B65H51