ELECTROMAGNETIC DEVICE FOR STOPPING THE WEFT THREAD IN A WEFT FEEDER FOR WEAVING MACHINES AND SLIDER FOR SUCH DEVICE

Abstract

 Electromagnetic device for stopping the weft thread in a weft feeder for weaving machines, of the type comprising a slider (C), apt to be moved along an alternate rectilinear path between two end-stop positions responsive to the activation of electromagnetic coils (B) housed in a case (6), consisting of a bush-shaped ferromagnetic core (3), of a cylindrical end-piece (1) for stopping the weft thread projecting from one side of said ferromagnetic core (3) and of an intermediate element (2) forming the mechanical connection between said ferromagnetic core (3) and said end-piece (1). Said intermediate element (2) is a cylindrical aluminium element which is fastened, through a mechanical coupling with interference, within the cylindrical inner cavity of said bush-shaped ferromagnetic core (3), and which further has an axial cylindrical inner cavity (2c) in which said end-piece (1) is fastened, through a mechanical coupling with interference.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an electromagnetic device for stopping the weft thread in a weft feeder for weaving machines and to a slider for such device. In particular, the stopping device of the present invention has been specifically designed for weft feeders used in air and water looms, and in particularly harsh environmental working conditions, both for the high frequency of insertion of the weft thread and for dust pollution, dust being always present at high rates in textile environments.

PRIOR STATE OF THE ART

[0002] As it is well known, weft feeders are weft thread feeding devices which continuously accumulate the weft thread in successive turns on a drum, to create a weft thread reserve which is readily available, by extraction in the axial direction, during the operation of weft thread insertion. The electromagnetic weft thread stopping devices of the present invention are positioned on the exit side of said weft feeders to block the unwinding of the weft thread from the drum as soon as the desired amount of weft thread (measured by the number of turns exiting from the drum) has been drawn by the weft feeder, and to keep it permanently blocked while the operations of weft thread insertion along the shed and the subsequent closure of the shed are completed.

[0003] The above said stopping devices usually comprise electromagnetic coils which control the movement of a slider, the free end of which- when it penetrates the surface of the drum on which the thread is wound, by inserting itself into a corresponding hole - prevents the unwinding of other turns from the drum itself. The electromagnetic coils used in this type of device are therefore apt to provide a bistable condition of the slider, i.e. the slider is controllable between a retracted condition, during which the weft thread is fed, and a forward position, during which the weft thread remains locked on the weft feeder drum.

[0004] To ensure adequate wear resistance and, at the same time, avoid deterioration of the weft thread, providing the free end of the slider, also indicated hereinafter as an end-piece, in a suitable ceramic material, is known. Naturally, the slider must also comprise a core of ferromagnetic material, sensitive to the magnetic fields formed by the coils, and the coupling between these two different materials is now carried out by means of a matrix of thermosetting plastic material; specifically, the slider of the presently known devices is obtained by a moulding process of said thermosetting plastic material at the molten state, in which the ceramic material end-piece and the ferromagnetic core are previously positioned into the mould as inserts and then mutually made integral by the solidified plastic matrix.

[0005] A standard configuration of a known slider Cn of this type is shown in fig. 2, where it is possible to clearly identify: the ferromagnetic core F, in the shape of a cylindrical bush, in the central peripheral portion of the slider Cn; the ceramic material end-piece P, which is a first end portion of the slider Cn, having a generally cylindrical shape and extending axially within the aforementioned central portion of the slider, inside the core F, where it is provided with a series of annular grooves or depressions which favour the adhesion of the plastic material matrix M; the plastic material matrix M extending axially from the central portion of the slider Cn - where it takes up the intermediate annular space between the ferromagnetic core F and the end-piece P - in the direction opposite to the end-piece P, so forming a second end portion of the slider. The use of the plastic material for the matrix M also has the purpose to lighten the slider Cn as much as possible, to reduce its inertia and thus allow its use also in looms with high frequencies of weft thread insertion.

[0006] The above described slider is housed inside a cylindrical guide bush made of plastic material, axially positioned inside the coils case, with the minimum clearance between the ferromagnetic core F of the slider Cn and the cylindrical guide bush, necessary to allow said movement.

[0007] The known weft thread stopping devices utilizing the sliders Cn of the type just described above have some typical drawbacks, closely related to their construction and use features, which drawbacks will now be briefly illustrated.

[0008] A first drawback is related to the wear to which the cylindrical guide bush of the slider is subjected. In this regard, it should be noted that the slider, when running in its alternating path controlled by the coils, is only subjected to the attraction/repulsion forces exerted by the magnetic field formed by the coils, these forces having a central symmetry with respect to the slider's axis and therefore, in themselves, keeping the slider perfectly centred within its guide bush. However, when the end-piece P of the slider exerts its function of stopping the weft thread, it is also subjected to the transverse force that the suddenly blocked weft thread exerts on the same when the weft thread becomes completely stretched throughout the shed. Although this force is relatively low, the high arm existing between the action point - i.e. the free end of the end-piece - and the reaction point - i.e. the contact areas between the core F and the respective guide bush - causes the force discharged onto said guide bush to be high enough, in the weft thread stop position, to cause progressive wear of the guide bush wall over time. This entails both a progressive misalignment of the movement of the slider with respect to the theoretical axial operating line and, above all, the formation of plastic material dust which progressively contaminates the end-piece and is finally transferred to the weft thread, causing it to become dirty and causing therefore possible defects in the fabric.

[0009] A second drawback of the traditional stopping devices is then given by the useful life which, in particularly heavy applications, is rather short. The progressive misalignment of the slider Cn, also due to the inherent fragility of the ceramic material of the end-piece with respect to bending stresses, can cause the end-piece to break with a certain frequency when, during the weft thread stopping, the end-piece undergoes the effect of forces with non-axial components having a non-negligible entity.

[0010] A third drawback which reduces the useful life of the device is finally linked to the special assembly system of the known slider through the plastic material matrix M which, obviously, has mechanical resistance characteristics which are much lower than the two ferromagnetic and ceramic materials which the matrix M makes integral to each other. It therefore happens that following the repeated impacts that the end-piece P undergoes at each end-stop of its alternating movement, the plastic material volume comprised between the end-piece P and the ferromagnetic core F is subjected to high shear stresses and therefore progressively shows structural failures, losing its resilience properties up to cause the complete separation and the subsequent slipping of the end-piece P from the surrounding plastic material matrix M, thus making the device unusable.

[0011] The problem underlying the present invention is therefore that of providing an electromagnetic device for stopping a weft thread, of the type described above, which has a useful service life which is considerably extended. Preferably, the useful service life should moreover be easily determinable beforehand based on the normal wear criteria, because it is no longer determined by phenomena - as the misalignment of the slider Cn and the structural failure of the plastic material matrix M - whose speed of evolution towards final collapse is quite difficult to predict.

[0012] To achieve the solution of this problem, a first object of the present invention is to improve the composite structure of the slider, particularly in relation to the space of the plastic material matrix M comprised between the end-piece P and the ferromagnetic core F.

[0013] A second object of the present invention is also that of improving the slider guide system, to counteract more effectively the transverse forces imposed by the stretched weft thread which cause the progressive misalignment of the slider due to wear of its sliding guides.

[0014] Further additional objects of the present invention are finally those of reducing the negative impact of the end-stop collisions on the structural integrity of the slider and to reduce dust formation to safeguard the space where the slider guides are positioned and further reduce the effect of the wear on the slider guides themselves.

BRIEF DESCRIPTION OF THE INVENTION

[0015] This problem is solved, and these objects are achieved by means of an electromagnetic device for stopping the weft thread in a weft feeder of weaving machines having the features defined in claim 1 and by means of a slider having the features defined in claim 12. Other preferred features of the electromagnetic device of the present invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Further features and advantages of the electromagnetic device for stopping the weft thread in a weft feeder according to the present invention will anyhow become more evident from the following detailed description of a preferred embodiment of the same, given by mere way of non-limiting example and illustrated in the appended drawings, wherein:

fig. 1 is an axial sectional view of the electromagnetic stopping device according to the present invention, with the slider in a forward position for stopping the weft thread;

fig. 2 is a side elevational and partly sectional view of a known-type slider (PRIOR ART);

fig. 3 is side elevational and partly sectional view of a slider according to the present invention; and

fig. 4 is a perspective view of the electromagnetic stopping device of fig. 1, with exploded parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] According to the present invention, in order to solve the problem highlighted above with a compact and particularly effective solution, the composite structure of the slider of the electromagnetic stopping device has been radically modified, abandoning the use of the thermosetting plastic material matrix as a connecting element between the end-piece of ceramic material and the ferromagnetic core and modifying the same guide system of the slider.

[0018] As clearly shown in figs. 1 and 3, the slider C of the weft thread stopping device according to the present invention consists of a ceramic material end-piece 1 having a cylindrical shape throughout its extension. A suitable ceramic material for this application must have high-hardness mechanical characteristics, to adequately withstand the wear caused by rubbing during the weft thread stopping phase, and a high surface smoothness, to reduce friction with the guides during movement of the slider and to avoid damaging the weft thread in the stopping operation of the same.

[0019] The end-piece 1 is coupled in the corresponding axial cylindrical cavity 2c of an aluminium cylindrical intermediate element 2 which has an appendix 2a, opposed to the end-piece 1 and preferably having a cylindrical shape. Externally to the aluminium intermediate element 2 there is a bush-shaped ferromagnetic core 3; as it is clear from fig. 3, the ferromagnetic core 3 is provided with a cylindrical inner wall and an outer wall having a shape generally similar to a one-sheeted hyperboloid, so that the wall thickness of the ferromagnetic core varies from a minimum at its median area to a maximum at its two opposing ends.

[0020] The coupling between the ceramic material end-piece 1 and the cavity 2c of the aluminium intermediate element 2 is preferably a mechanical coupling with interference performed through a press, which offers an absolute coupling stability even after a long service life. To avoid increases in air pressure inside the cavity 2c, which could hinder a complete coupling during the coupling step, a transverse hole is provided at the bottom of the cavity 2c, for connecting the latter to the exterior.

[0021] Similarly, also the coupling between the aluminium intermediate element 2 and the bush-shaped core 3 is preferably a mechanical coupling with interference carried out with any known method, for example through a press, in cold conditions or with a hot core 3. Other types of couplings, for example by means of adhesives or resins, are obviously possible even if they are not preferred in view of their lower resistance over time compared to the repeated impact loads occurring at each end-stop of the slider C.

[0022] The greater weight of the aluminium intermediate element 2 in the slider C of the present invention, with respect to the plastic material matrix F of the sliders Cn of the known type, is compensated by the hyperboloid shape of the outer surface of the ferromagnetic core 3 which reduces the weight of this element at such ban extent to compensate for the greater weight of the intermediate element 2. This reduction in weight of the ferromagnetic core 3 does not significantly reduce the magnetic efficiency of the system since the curvature of the outer surface of the core 3 still allows to have enough ferrous material in the portions of the core 3 where it is important to have adequate interaction with the electromagnetic field.

[0023] The particular outer hyperboloid shape of the ferromagnetic core 3 is made possible thanks to the fact that, according to the present invention, the guide of the alternate axial movement of the slider C is no longer obtained by using a sliding contact between the outer surface of the ferromagnetic core 3 and a corresponding cylindrical bush housed inside the coil case, as for the known slider Cn. As a matter of fact, in view to guide the reciprocating movement of the slider C, in the present invention two opposing bushes 4 are provided, apt to cooperate in a sliding contact respectively with the end-piece 1 and with the cylindrical appendix 2a of the intermediate element 2. The bushes 4 are housed in corresponding seats 5 formed in the opposite flat walls of a case 6 in which coils B are housed, which coils B control the alternate movement of the slider C, in a manner well known per se as above described. The bushes 4 are preferably made of a material having low friction and high wear resistance characteristics such as a ceramic material. Alternatively, a plastic material may be used which exhibits the same mechanical characteristics indicated above, for example a member of the polyether-ether-ketone (PEEK) family which has the advantage of a lower cost compared to ceramic materials traditionally used in such applications. In a preferred embodiment, the bush 4 in contact with the end-piece 1, intended to support at a higher extent the transverse forces imposed by the weft thread during the stopping phase, is made of ceramic material, whereas the bush 4 in contact with the appendix 2a of the aluminium intermediate element 2 is made of a plastic material having mechanical characteristics similar to those of a member of the PEEK family.

[0024] During the use of the device, the slider C moves alternately inside the channel 7, axially provided between the coils B and inside the case 6 containing the same, between end-stop positions determined by the beating of the central body of the slider C against the outer wall of the seats 5 of the bushes 4 described above. To cushion the alternating impacts of the slider C in said end-stop positions, inside the channel 7 and over the seats 5 dampening washers 8 made of a suitable shock-absorbing material which is not subjected to pulverization due to repeated impacts are provided.

[0025] At the free end of the appendix 2a, in a per se known manner, a conical wire spring M is provided, whose vertex is fitted to a final tapered portion of the appendix 2a and whose base rests on a wear bowl 9 positioned in a special seat formed in the cover 10 of the external container 11 of the device (in the drawing, for greater clarity, the spring M is only partially shown). The function of the spring M is to keep the end-piece 1 pressed in a forward position, i.e. the weft thread stopping position, in the event of a power shortage, to prevent uncontrolled weft outflow from the weft feeder in this case. During the normal movement of the slider C, the spring base rests with a varying force on the wear bowl 9, the surface of which is thus gradually and uniformly worn due to the fact that the unpredictable actions of the weft thread and of the electromagnetic field can, and in fact do, continuously rotate the entire slider C, which in fact is not in any way restrained from this type of movement. A preferred material for the construction of the bowl 9 is the PEEK plastic material already described above in relation to the bushes 4, or a plastic material having similar mechanical characteristics.

[0026] As an alternative to the coupling between the spring M and the bowl 9 - which has the disadvantage of requiring the periodic replacement of the bowl 9 and the formation of wear material inside the device - according to the present invention a permanent magnet is provided in an appropriate position to keep the slider C in the forward position, i.e. the weft thread stopping position, when the coils B are not energized due to a power shortage. In a preferred embodiment, said permanent magnet is housed on the free end of the appendix 2a of the intermediate element 2 so that an attraction force on the same is provided by the fixed case 6, made of ferrous material, maintaining the slider C in the forward position shown in fig. 1 in the event of a power shortage.

[0027] In order to contain the entry of dust inside the device, the outer envelope of the same is formed by a cup container 11 having a generally cylindrical shape and by a cover 10 which closes the mouth of the cup container 11, a first O-ring sealing gasket 12, opposite the cover 10, being housed in a special peripheral circular seat of the cup container 11. Advantageously, and as clearly shown in the exploded view of fig. 4, a second inner gasket 12c is joined to the gasket 12, whose function is to keep the case 6 of the coils B in the correct position, recovering assembly slacks. The second inner gasket 12c has a C-shape to allow the exit of the power cable of the electronic device and a greater thickness in respect of the gasket 12; it is worth to note that, thanks to their mutual joining, the inner gasket 12c is automatically and readily placed in its correct working position as soon as the firs O-ring sealing gasket 12 is positioned in its circular seat.

[0028] The cup container 11 is obviously provided with a central opening to allow passage of the end-piece 1 and this opening is internally protected by an anti-dust washer 13 which provides a seal against the outer surface of the end-piece 1.

[0029] It is understood, however, that the invention is not to be considered as limited by the particular arrangements illustrated above, which represent only an exemplary embodiment of the same, but different variants are possible, all within the reach of a person skilled in the art, without departing from the scope of the invention itself, which is exclusively defined by the following claims.

Claims

1. Electromagnetic device for stopping the weft thread in a weft feeder of a weaving machine, of the type comprising a slider (C), apt to be moved along an alternate rectilinear path between two end-stop positions responsive to the activation of electromagnetic coils (B) housed in a case (6), and consisting of a bush-shaped ferromagnetic core (3), of a cylindrical end-piece (1) for stopping the weft thread projecting from one side of said ferromagnetic core (3) and of an intermediate element (2) forming the mechanical connection between said ferromagnetic core (3) and said end-piece (1), characterised in that said intermediate element (2) is a cylindrical aluminium element which is fastened, through a mechanical coupling with interference, within the cylindrical inner cavity of said bush-shaped ferromagnetic core (3), and which further is provided with an axial cylindrical inner cavity (2c) within which said end-piece (1) is fastened, through a mechanical coupling with interference.

2. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 1, wherein said slider (C) is guided in its alternate rectilinear movement by two opposite bushes (4) within which said end-piece (1) and, respectively, a cylindrical appendix (2a), projecting from said cylindrical aluminium element (2) in a direction opposite to the end-piece (1), slide.

3. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 2, wherein said bushes (4) are housed in corresponding seats (5) formed in said case (6).

4. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 3, wherein said bushes (4) are made of a ceramic material or of a high-performance plastic material, like PEEK family material.

5. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 1, wherein the outer surface of said bush-shaped ferromagnetic core (3) has the shape of a one-sheeted hyperboloid, the wall thickness of the ferromagnetic core (3) varying from a minimum at its median area to a maximum at the two opposite ends thereof.

6. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 1, wherein the end-stop positions of said slider (C) are determined by the beating of said ferromagnetic core (3) against the outer wall of the seats (5) of said bushes (4), wherein dampening washers (8) positioned above said beating outer walls of the seats (5), are further provided.

7. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 1, wherein said device is housed into a cup container (11) having a generally cylindrical shape, the mouth of said cup container is closed by a cover (10), and a first O-ring sealing gasket (12), opposite said cover (10), is housed in a suitable peripheral circular seat of the cup container (11).

8. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 7, wherein a conical wire spring (M) is further provided, which acts on the free end of the appendix (2a) of the cylindrical aluminium element (2) for maintaining the slider (C) pushed in a forward position stopping the weft thread in case of power shortage, and wherein the base of said spring (M) rests onto a wear bowl made of high-performance plastic material, like PEEK family material, said wear bowl being housed in a respective seat formed in said cover (10).

9. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 7, wherein a permanent magnet is further provided, which permanent magnet is housed into the end of the appendix (2a) of the cylindrical aluminium element (2) for maintaining said slider (C) in a forward position stopping the weft thread in case of power shortage.

10. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 7, wherein a second inner gasket (12c) is joined to said first O-ring sealing gasket (12), said second inner gasket (12) being apt to maintain in a correct position said case (6) while compensating for assembly slacks thereof.

11. Electromagnetic device for stopping the weft thread in a weft feeder as in claim 7, wherein said cup container (11) has a central opening for letting the end-piece (1) go through outside, the inside of said central opening being protected by an anti-dust washer (13) providing a seal against the outer surface of the end-piece (1).

12. Slider for an electromagnetic device for stopping the weft thread in a weft feeder as defined in any one of the preceding claims, of the type consisting of a ferromagnetic bush-shaped core (3), of a cylindrical end-piece (1) for stopping the weft thread projecting from one side of said ferromagnetic core (3), and of an intermediate element (2) forming the mechanical connection between said ferromagnetic core (3) and said end-piece (1), characterised in that said intermediate element (2) is a cylindrical aluminium element which is fastened, through a mechanical coupling with interference, within a cylindrical inner cavity of said bush-shaped ferromagnetic core (3), and which further has an axial cylindrical inner cavity (2c) in which said end-piece (1) is fastened, through a mechanical coupling with interference.

13. Slider for an electromagnetic device for stopping the weft thread in a weft feeder as in claim 12, wherein the outer surface of said bush-shaped ferromagnetic core (3) has the shape of a one-sheeted hyperboloid, the wall thickness of the ferromagnetic core (3) varying from a minimum at its median area to a maximum at the two opposite ends thereof.

14. Slider for an electromagnetic device for stopping the weft thread in a weft feeder as in claim 13, wherein a permanent magnet is further provided, which permanent magnet is housed into the end of the appendix (2a) of the cylindrical aluminium element (2) for maintaining said slider (C) in a forward position stopping the weft thread in case of power shortage.

Drawing