Controlled thread brake

Abstract

A controlled thread brake for braking a weft thread (10) in a weaving machine is presented which comprises a brake band (3) and a brake body (2), with the thread brake (1) additionally comprising an electromagnet (6) and a rotatable or rocking lever (4) which can be moved by means of the electromagnet. The lever (4) is connected to the brake band (3) so that a pulling force can be exerted in the longitudinal direction of the brake band by means of the electromagnet (6) in order to be able to press the latter against the brake body (2) for braking the weft thread.

Description

This application claims the priority of European patent application No. 06405031.3, dated Jan. 24, 2006, the disclosure of which is incorporated herein by reference.

The invention relates to a controlled thread brake for braking a weft thread in a weaving machine in accordance with the preamble of claim 1 and to a weaving machine with a thread brake of this kind.

In weaving machines a thread brake is usually provided between the supply bobbins for the weft thread and the shed in order to brake the weft thread at the end of the weft insertion. More recent weaving machines are provided with controlled thread brakes which permit the weft thread to be braked during any desired phase of the weft insertion. The document EP 0 475 892 A1 discloses a thread brake of this kind with a brake band and a movable brake body which is connected to a setting motor in such a manner that the rotational movement of the setting motor is converted to a stroke movement of the brake body. In this manner it is possible to control both the time point of the application of the brake and the braking force which is exerted on the weft thread via the setting motor. A disadvantage of the thread brake which is disclosed in EP 0 475 892 A1 is that it is slow in comparison with the duration of the individual phases of the weft insertion, i.e. that the braking action takes place only with a delay of typically 30 ms or more when a control signal is applied to the setting motor. A regulation of the braking as a result of the current weft data is thus not possible or is at least made considerably more difficult at higher weft insertion rates. A further disadvantage is represented by the comparatively high manufacturing costs of this thread brake.

The object of the invention is to make available a controlled thread brake for braking a weft thread in a weaving machine and a weaving machine with a thread brake of this kind which has a shorter reaction time than the above described state of the art and which can be manufactured comparatively economically.

This object is satisfied in accordance with the invention by the thread brake which is defined in claim 1 and by the weaving machine which is defined in claim 10.

The controlled thread brake in accordance with the present invention for braking a weft thread in a weaving machine includes a brake band, for example a yielding or flexible brake band, and a brake body which can for example be stationary and/or arranged in a fixed position. In addition the thread brake comprises an electromagnet and a rotatable or rocking lever which can be moved by means of the electromagnet and which is operationally connected to the brake band in order to be able to exert a pulling force in the longitudinal direction of the brake band and in order to place the latter or press the latter against the brake body for braking the weft thread. In an advantageous variant the thread brake comprises two or more brake bodies, and in a further advantageous variant the brake body or bodies are provided with a rounded off form and/or are formed as passive braking members.

The brake band can be connected firmly or elastically to a holder at a first securing point, for example on one side of the brake band and, with a spacing from it in the longitudinal direction, for example on other side, be firmly or elastically connected to the lever. In an advantageous embodiment the thread brake comprises a spring element for releasing the thread brake, for example a tension or compression spring, which acts on the lever and/or a leg spring at the point of rotation of the lever. The brake band can optionally also be provided with a bias tension so that it acts as a spring element for releasing the thread brake.

The lever is optionally straight or angled. The point of rotation of the lever can, for example, be arranged between the brake band and the electromagnet or to one side on the side of the brake band or of the electromagnet. In an advantageous variant the lever is arranged substantially at right angles to the brake band.

In an advantageous embodiment an armature is provided at the lever of the electromagnet, said armature containing a ferromagnetic or permanent magnetic material, for example in that the lever or a part of it is formed as an armature. If required, the thread brake can comprise at least one second electromagnet, by means of which the lever and/or the brake band can be moved and which for example can be used as a release magnet and/or to assist the first electromagnet. In a further advantageous embodiment the electromagnet has a U-shaped core or the electromagnet is formed as a pot magnet, with the magnetic field passing through the armature.

In a further advantageous embodiment an air gap is provided between the armature and the electromagnet or electromagnets during the braking. In this way it is possible to set the braking force during the braking via the current which flows through the electromagnet.

Furthermore, the invention comprises a weaving machine with at least one thread brake in accordance with any one of the above described embodiments.

The thread brake in accordance with the invention is a rapid reaction thread brake which is particularly suited for rapidly running weaving machines with weft insertion speeds of for example 500 insertions/min. and higher. The paths which are travelled by the moving parts can be kept short, for example 1 mm or less, so that the reaction time that can be achieved is less than 10 ms. Furthermore, it is possible to control the braking force during the braking via the current flowing through the electromagnet, with the braking force being nearly proportional to the current. This means that the thread brake in accordance with the invention enables a regulation of the braking as a result of the currently determined weft data, in particular also in rapidly running weaving machines. Also advantageous is its large adjustable braking force range, which permits its use in practically the entire yarn spectrum, from fine to coarse yarns. Moreover, the thread brake in accordance with the invention has a useful self cleaning effect if the brake band is vented by 1 to 2 mm so that the brake band slaps against the brake body when the brake is applied. A further advantage is represented by the comparatively favorable manufacturing costs of the described thread brake and the simple and economical control.

The above description of embodiments serves merely as an example. Further advantageous embodiments result from the independent claims and the drawings. Moreover, in the context of the present invention, individual features from the described or illustrated embodiments and variants can also be combined with one another in order to form new embodiments.

The invention will be explained in the following in more detail with reference to the exemplary embodiment and with reference to the drawings. Shown are:

FIG. 1 a perspective view of an exemplary embodiment of a thread brake in accordance with the present invention,

FIG. 2 a side view of the same exemplary embodiment,

FIG. 3A a side view of a second exemplary embodiment of a thread brake in accordance with the present invention during the braking, and

FIG. 3B a side view of the exemplary embodiment which is shown in FIG. 3A with released thread brake.

FIG. 1 shows a perspective view and FIG. 2 a side view of an exemplary embodiment of a thread brake in accordance with the present invention. The illustrated thread brake 1 for braking a weft thread 10 in a weaving machine comprises a brake band 3, which can for example be designed as a flexible and/or resilient band, e.g. as a steel band, and a brake body 2, which is preferably provided with an abrasion resistant surface, for example with a ceramic plate on the upper side or a coating of a ceramic material or of hard chromium. In addition the thread brake 1 of the exemplary embodiment comprises an electromagnet 6 and a rotatable or rocking lever 4 which can be moved by means of the electromagnet and which is actively connected to the brake band 3 in order to be able to exert a pulling force in the longitudinal direction of the brake band and to place the latter against the brake body 2 for braking the weft thread 10. Of course two or more brake bodies can also be provided. The brake body or bodies are advantageously formed as passive brake elements.

The brake band can be firmly or elastically connected to a holder 8 at a first securing point, for example at one end of the brake band and, spaced in the longitudinal direction, firmly or elastically connected to the lever 4 at a second securing point, in particular at the other end. In an advantageous embodiment the thread brake comprises a spring element in order to be able to release the thread brake when the current is switched off, for example a tension or compression spring which acts on the lever and/or a leg spring at the point of rotation of the lever. The brake band can optionally also be provided with a bias tension so that it is effective as a spring element to release the thread brake. In the exemplary embodiment which is shown in FIGS. 1 and 2 the brake band is deflected slightly by the brake body 2, so that it is placed against the brake body 2 if the electromagnet 6 exerts a force via the lever 4 in the longitudinal direction of the brake band and a weft thread 10 which is inserted between the brake band and the brake body is clamped.

The lever 4 can, as is shown in FIGS. 1 and 2, be straight and the point of rotation of the lever can be arranged between the brake band and the electromagnet. It is however also possible to provide angled levers and/or to arrange the point of rotation to one side on the side of the brake band or of the electromagnet. In the illustrated exemplary embodiment the lever 4 is arranged substantially at right angles to the brake band 3 and the latter is secured to the lever.

In an advantageous embodiment an armature 5 of the electromagnet 6 is provided at the lever 4, for example in that the lever or a part of it is formed as an armature. The armature or the part 5 of the lever which is formed as an armature expediently contains a magnetically active region of a ferromagnetic or permanent magnetic material, for example a soft magnetic steel or, in the case of a permanent magnetic material, e.g. of ALNICO. If a permanent magnetic material is provided in the armature the electromagnet can also be used for the release of the brake band through reversal of the current flow. The electromagnet advantageously has a U-shaped core or the electromagnet is advantageously formed as a pot magnet, with the magnetic circuit being closed by the armature on excitation of the electromagnet with the exception of an air gap.

FIGS. 1 and 2 show the thread brake 1 during the braking; i.e. the electromagnet stretches the brake band 3 via the lever 4 so that it lies in contact with the brake body 2, and the weft thread 10 is clamped between the brake band and the brake body. In the illustrated exemplary embodiment an air gap is present between the armature 5 and the electromagnet 6 during the braking. In this way it is possible to set the braking force during the braking via the current flowing through the electromagnet, with the braking force being approximately proportional to the current.

FIG. 3A shows a side view of a second exemplary embodiment of a thread brake in accordance with the present invention during the braking. The thread brake which is shown in FIG. 3A differs from that shown in FIGS. 1 and 2 only through a second electromagnet 6′. As has been explained in more detail in the context of the description of FIGS. 1 and 2, the thread brake 1 comprises a brake band 3 and a brake body 2 as well as additionally a first electromagnet 6 and a rotatable or rocking lever 4 which is in operationally connected to the brake band 3 in order to be able to exert a pulling force or a pressure in the longitudinal direction of the brake band. In the second exemplary embodiment the lever 4 can be moved by means of the two electromagnets 6, 6′, with it being possible for example for the first one, e.g. as described above, to be used for the braking and the second one for the release of the brake band, for example.

In FIG. 3A the thread brake 1 is shown during the braking; i.e. the first electromagnet 6 stretches the brake band 3 via the lever 4 so that it lies in contact with the brake body 2, and the weft thread 10 is clamped between the brake band and the brake body. In the exemplary embodiment which is shown in FIG. 3A, in contrast, the second electromagnet 6′ is switched off during the braking. The significance of the air gap between the first electromagnet 6 and the armature 5 was already discussed in the context of the description of the first exemplary embodiment.

In an advantageous variant a part of the lever 4 is formed as an armature 5, with it being possible for the two electromagnets to be arranged e.g. on oppositely disposed sides of the armature, with an air gap in each case between the electromagnet and the armature. Instead of U-shaped cores or pot cores a magnetically conducting yoke can, for example, also be provided on which two electromagnets are arranged, so that the yoke forms a closed magnetic circuit with the electromagnets 6, 6′ and the armature 5 with the exception of the air gaps.

FIG. 3B shows a side view of the exemplary embodiment which is shown in FIG. 3A with a released thread brake. The thread brake which is shown in FIG. 3B differs from that shown in FIG. 3A only through the excitation of the second electromagnet 6′ and the position of the lever 4 as well as the state of the brake band 3. In FIG. 3B the second electromagnet 6′ ventilates the brake band 3 via the lever 4, so that the brake band is lifted off from the brake body 2 and the weft thread 10 can be led through the gap between the brake band and the brake body without hindrance, with the gap typically amounting to 1 to 2 mm. In contrast, the first electromagnet 6 is switched off in the exemplary embodiment which is shown in FIG. 3B during the release or venting of the thread brake. An air gap can be provided between the second electromagnet 6′ and the armature 5 during the release, but is not required in most cases since a regulation of the force during release can be dispensed with.

It is advantageous that the controlled thread brake for braking a weft thread in accordance with the present invention can be used on different weaving machine types such as for example projectile and rapier weaving machines and is in particular also suitable for rapidly running weaving machines, since the paths travelled by the lever and the brake band can be kept short and the thread brake reacts correspondingly quickly. It is furthermore advantageous that the thread brake is also suitable for very coarse yarns thanks to its large braking force range.

Claims

1. Controlled thread brake for braking a weft thread (10) in a weaving machine with a brake band (3) and a brake body (2), characterized in that the thread brake (1) includes an electromagnet (6, 6′) and a rotatable or rocking lever (4) which can be moved by means of the electromagnet and which is operationally connected to the brake band (3) in order to exert a pulling force in the longitudinal direction of the brake band and to place the latter against the brake body (2) for braking the weft thread.

2. Thread brake in accordance with claim 1, with the thread brake comprising two or more brake bodies (2) and/or with the brake body or bodies (2) being formed as a passive brake element.

3. Thread brake in accordance with claim 1, with the brake band (3) being firmly or elastically connected to a holder (8) at a first securing point, in particular at one end, and, spaced in the longitudinal direction, being firmly or elastically connected to the lever (4) at a second securing point, in particular at the other end.

4. Thread brake in accordance with claims 1, comprising a spring element for the release of the thread brake, in particular a tension or compression spring, which acts on the lever (4) and/or a leg spring at the point of rotation of the lever and/or a prestressed brake band (3).

5. Thread brake in accordance with claims 1, with the lever (4) being straight or angled, and/or with the lever (4) being arranged substantially at right angles to the brake band (3).

6. Thread brake in accordance with claims 1, with the point of rotation of the lever (4) being arranged between the brake band (3) and the electromagnet (6) and/or one-sidedly on the side of the brake band or of the electromagnet.

7. Thread brake in accordance with claims 1, with an armature (5) of the electromagnet (6, 6′) being provided at the lever (4), said armature containing a ferromagnetic or permanent magnetic material, and/or with the lever (4) or a part thereof being formed as an armature (5), and/or with the electromagnet (6, 6′) having a U-shaped core or being formed as a pot magnet and with the magnetic field passing through the armature (5).

8. Thread brake in accordance with claims 1, comprising at least one second electromagnet (6′) by means of which the lever (4) and/or the brake band (3) can be moved and which is provided as a release magnet and/or to assist the first electromagnet (6).

9. Thread brake in accordance with claims 1, with an air gap being provided between the armature (5) and the electromagnet or electromagnets (6, 6′) during the braking.

10. Weaving machine comprising at least one thread brake in accordance with claims 1.