EP0597239B1 - Yarn brake - Google Patents

Abstract

The invention relates to a device for the variable braking of running threads, wires or the like, especially for use during weft insertion on weaving machines, the thread (F) running through between two brake parts which can be brought into resilient bearing contact with one another and of which one forms a spring element and the other an abutment, and one of the brake parts being movable for the purpose of changing the braking. To improve the efficiency, provision is made for the abutment to be designed as an essentially cylindrical body (2) loaded rotatably by the spring element (1), with a first portion (4, 5) of essentially circular cross-section and with a second portion (8) having at least one circumferential region (6, 7) of reduced cross-section, the abutment being seated on the shaft (1) of an electric motor designed as a stepping motor (9). <IMAGE>

Description

The invention relates to a device for variable braking of running threads, wires or the like, in particular for use in weft insertion on weaving machines. And a method for operating such a thread brake.

A thread brake is known from French patent application FR-A-23 75 366. There, the thread is passed between two brake parts that can be brought together in a resilient manner. One of the two brake parts is fixed and not resilient and the other brake part is cushioned and movable relative to the fixed brake part, so that the thread braking can be varied in its strength by a change in the spring tension achieved as a result of the movement. The resilient brake part can also be spaced apart from the fixed brake part via a push rod via a push rod, so that an unbraked thread run can be achieved. The problem with such a thread brake is that the spring force has to be relatively strong in order to brake the thread effectively. On the other hand, in order to achieve a free running of the thread, the resilient braking part must be completely lifted off the fixed braking part. The spring of the resilient brake part must be at least partially relaxed. This results in relatively high displacement paths of the push rod driving the resilient element. There are also limits to such an arrangement with regard to the cycle times between braking and releasing the thread, since the relaxation of the spring can no longer follow high cycle frequencies.

From the European patent application EP-A-0 384 502 a thread brake is also known in which a rotationally movable non-resilient brake part acts on a prestressed resilient tab. With this arrangement, however, no cyclical changing of the thread braking is provided. The rotating cylinder body, which forms the seam of the brake element, merely serves to remove dust particles lying on the thread by means of friction.

The model for the invention was also the device for the different braking of running threads, which is not part of the prior art and was proposed in the non-prepublished utility model DE-U-91 13 430. Such a device was also disclosed in document EP-A-0 524 429 belonging to the prior art according to Article 54 (3) EPC. The device shown there already shows a fixed leaf spring which is acted upon by a cylindrical brake part. This brake part is driven by an electric motor and has a cylindrical first section, the circumferential surface of which holds the spring in a pretension in the release position of the thread run. A second section of the body has a peripheral section that is reduced in cross section. The thread runs between this second section and the leaf spring. If the cylindrical body is aligned with the window towards the leaf spring, the thread is unbraked. After a further angular amount of further rotation of the rotatable body, the thread is acted upon by the non-reduced cross-sectional circumferential section of the second section, so that the thread-braking position is achieved, the thread being clamped between the leaf spring and the cylinder surface. This device works in cyclical operation, with the drive motor running back and forth between two stops. In order to achieve a high clock frequency, the motor must both be driven at high acceleration and braked strongly. The use of mechanical stops for braking the motor, for example, is not optimal.

Starting from the device known in the aforementioned European patent EP-A-0 384 502, the object of the invention is to improve the performance of such a thread brake.

To achieve the object, the device specified in claim 1 and the method specified in claim 6 are proposed. The subclaims represent advantageous developments of the invention. As a result of the configuration of the invention, the resilient braking part no longer needs to be moved during operation to vary the braking. Due to the essentially cylindrical first section of circular cross-section, the spring element is constantly held in a prestress, which can be varied by adjusting means. The second section, which can also be brought into contact with the spring element, has in the circumferential direction at least one reduced cross-sectional circumferential section, which is reduced in cross-section to the extent that a window remains between the circumferential section and the spring element when it is opposite the spring element, through which the thread can be pulled off without braking. After a further rotation of an essentially cylindrical counter bearing, a non-cross-sectionally reduced peripheral section then faces the spring element, so that the thread is clamped between the spring element and the essentially cylindrical body forming the counter bearing, which results in braking. It can be provided that the leaf spring is displaced by the thickness of the thread. As a result of the pre-brake, there is a certain, separately adjustable braking force even when the thread brake is open. Is the first section of the substantially cylindrical counter bearing is exactly circular, and if the circumferential section of the second section, which is not reduced in cross-section, merges into this first section, the spring element is deflected by a thread thickness when the device enters the braking position. As a result of the design of the counter-bearing drive part as an electrical stepping motor, the shaft of the electric motor can be gradually rotated further without mechanical stops having to be provided. Starting from a thread release position in which the reduced cross-sectional circumferential section is opposite the spring element, the stepper motor then only needs to be rotated by a corresponding number of steps, which is done by a corresponding number of switching impulses until the reduced cross-sectional reduced circumferential area is opposite the spring element and the thread brake position is reached. Here, a preferably curved leaf spring can serve as a spring element and at the same time as a thread guide. Another preferred embodiment is one in which a plurality of circumferentially reduced circumferential surfaces are provided in the circumferential direction. Circumferential areas not reduced in cross section are provided between these reduced-area circumferential surfaces. Here, too, a thread-free position occurs when a circumferentially reduced cross-sectional area is placed opposite the spring element, while when a circumferential area that is not reduced in cross-section is placed opposite, the thread is clamped between the counter-bearing and the spring element. The embodiment of the invention in which the number of steps of the stepping motor corresponds to at least twice the number of circumferentially reduced cross-sectional sections is considered to be particularly advantageous. As a result of this configuration, the stepper motor needs Transition from a braking position to a release position can only be switched by a single step. If, for example, two circumferentially reduced cross-sectional areas are provided, which are advantageously arranged opposite one another, between which there are corresponding opposing, non-reduced cross-sectional circumferential areas, the number of steps of the motor is four. That means with every step the shaft of the stepper motor is turned through 90 °. In total, four steps are necessary to make one revolution of the shaft of the stepper motor. In order to design the circumferential sections with reduced cross-sections, the invention proposes in a further development that these circumferential sections are designed as flattenings arranged transversely to the radial. The transitions to the circumferential sections which are adjacent in the circumferential direction and are not reduced in cross-section could be rounded in order to protect the thread. The stepper motor preferably has a magnetically polarized armature. In the simplest embodiment, this armature can be formed from a permanent magnet. The orientation of the magnet is oriented radially to the axis. Around the armature, this preferred stepper motor has an excitation coil running in the circumferential direction, which is subdivided into a number of partial windings which corresponds to the number of steps of the electric motor. Associated with the individual step positions of the electric motor, the annular coil core of the excitation coil has opposite pole pairs. The armature of the electric motor is oriented between these pole pairs in accordance with the polarization of the excitation coil. For example, the excitation coil consists of an annular coil core with a total of four poles, each offset by 90 °, between which poles a partial winding is provided and if the armature is to be held between two of these poles by magnetic forces, the partial windings arranged between these two opposite poles are polarized in the same direction, so that a magnetization parallel to the armature magnetic field is built up. If the armature is now to be rotated one step, in this case by 90 °, the second pole pair lying transverse to the first pole pair is magnetized accordingly. Now the partial windings lying between these two poles are traversed by current in the same direction, so that a magnetic field aligned between these two magnetic poles is created. As soon as this new current has been applied, the armature orients itself into its new position in accordance with the rotated magnetic field. A further rotation of the armature accelerated from the old position into the new position is prevented by magnetic holding forces. There is therefore a magnetic stop that prevents the armature from rotating further. The larger the magnetic field, the greater this stop.

The method for operating a thread brake in accordance with a device according to the invention includes that with each step of the stepping motor, the thread brake alternates from a braking position into a release position, starting from a braking position corresponding to a step position of the electric motor, in which a non-reduced circumferential area is opposite to the spring element, in the subsequent step of the electric motor a cross-section-reduced area is brought opposite to the spring element. As a result of these method steps, the direction of rotation of the electric motor need not change after the transition from the braking position to the release position. The electric motor, however, can always turn in the same direction operate. This enables the armature to be magnetically bonded in any step position. The body forming the counter bearing is rotated clockwise, step by step.

Fig. 1

eine perspektivische Darstellung einer erfindungsgemäßen Fadenbremse;

Fig. 2

eine Draufsicht auf eine Vorrichtung nach Fig. 1 in Bremsstellung;

Fig. 3

eine Seitenansicht einer Vorrichtung gemäß Fig. 1 in Bremsstellung;

Fig. 4

eine Darstellung gemäß Fig. 2 in Freigabestellung;

Fig. 5

eine Darstellung gemäß Fig. 3 in Freigabestellung;

Fig. 6

eine schematische Darstellung eines vierpoligen Schrittmotors.

An exemplary embodiment of the invention is explained below with reference to the accompanying drawings. It shows:

Fig. 1

a perspective view of a thread brake according to the invention;

Fig. 2

a plan view of a device of Figure 1 in the braking position.

Fig. 3

a side view of a device according to Figure 1 in the braking position.

Fig. 4

a representation of Figure 2 in the release position.

Fig. 5

a representation of Figure 3 in the release position.

Fig. 6

is a schematic representation of a four-pole stepper motor.

The device shown in FIGS. 1 to 5 has an engine block 24 which is formed on the outside with cooling fins 23. The engine block is made of aluminum. A motor shaft (not shown in FIGS. 1 to 5) emerges on one side of the engine block and carries an essentially cylindrical body 2. The cylindrically shaped body 2 forms the counter bearing to a resilient tab 1, which thread F in the braking position between itself and the counter bearing 2 (Fig. 2) jammed. The tab 1 is carried by a substantially U-shaped carrier plate 13 which is screwed onto the motor housing 24 with its bottom surface. The bottom surface of the carrier 13 is penetrated by the shaft of the motor.

On one of the U-legs 13 'of the carrier 13 there is a thread withdrawal eyelet 12 through which the thread F entering through the thread opening 21 of the opposite U-leg is drawn off after it has been formed by the pre-brake formed by the two opposite tabs 19 and 20 and the actual thread brake, formed by the tab 1 and the body 2, is pulled.

Thread take-off opening 12, thread brake and thread inlet opening 21 lie almost on a straight line.

The above-mentioned pre-brake consists of two brackets 19, 20 which are spring-loaded against one another and which are each screwed onto square axes 18, 14. The square axis 18, which is approximately opposite to the square axis 14 by means of an adjusting wheel 22, is pivotally adjustable. The square bracket 14, which is also pivotably adjustable via the adjusting disk 50 and the worm gear 16, 17, carries the tab 1 in addition to the tab 19. The two tabs are screwed onto opposite surfaces of the square 14. By adjusting the setting wheel 15, the strength of the support of the spring tab 1 on the counter bearing 2 can thus be adjusted. With the setting wheel 22, the strength of the pre-brake can be adjusted by tensioning the spring leaf 20.

All three spring elements 1, 19, 20 have essentially the same rigidity and the same width, which cover the sections 4, 5, 8 of the body 2. The section 8 is located between the sections 4, 5 of the body 2 which have a circular cross section. The section 8 has two opposite circumferential sections 6, 7 with reduced cross sections in the circumferential direction. These circumferential sections are formed by flats which are arranged essentially transversely to the radial and which, in the transition region to the sections 10, 11 of the body 2 which are not reduced in cross section, have roundings 6 ', not shown in the drawings. The cross-section-reducing circumferential sections 6, 7 form windows through which the thread can be drawn off without friction in the release position (cf. FIGS. 4 and 5).

The pre-brake consisting of the leaf springs 20 and 19 can be deactivated by appropriately adjusting the setting wheel 22 and pivoting the spring tabs 19, 10, namely by spacing the resilient tab 20 from the resilient tab 19.

According to the exemplary embodiment shown, the first section of the substantially cylindrical body forming the counterbearing consists of two circular sections 4, 5. These circular sections 4, 5 have the effect that, even in a position according to FIGS. 4 and 5, the leaf spring 1 is in a prestressed manner Location remains. The sections 4 and 5 run horizontally to the axis of rotation of the body 2. A minimal change in the position of the spring 1 takes place in the braking position (see FIGS. 2 and 3), namely when the thread between one of the circumferential sections 10 or 11 not reduced in cross section and the Tab 1 is pinched. The tab can be deflected by the thickness of the thread F. This is accompanied by a lifting of the tab 1 from the two Observe circular sections 4 and 5 in cross section.

The operation of the device is as follows: The thread runs from the inlet eyelet 21 through the brake and is drawn off by the draw-off eyelet 12 and fed to a loom or the like, not shown. In the position of the body 2 shown in FIGS. 2 and 3, the resilient tab 1 is acted upon by the circumferential section 11 of the second section 8, which section is not reduced in cross-section, with the thread F being clamped in. The thread is braked in this position. In this position, the thread is not drawn off, but is held at a certain thread tension only on the part of the thread insertion eyelet 21. If, on the other hand, the thread is withdrawn from the thread take-off eye 12, the body 2 is displaced by 90 °, as a result of which the thread's release position shown in FIGS. 4 and 5 is reached. Apart from the effect of the pre-brake, the thread can now be pulled out without braking. In the position shown in FIGS. 4 and 5, the reduced-cross-sectional circumferential section 6 now has an opposite position to the leaf spring 1. Since the reduction in cross-section is many times larger than the diameter of the thread, it can be pulled off almost frictionlessly in the window formed by the reduction in cross-section. Because of the circular sections 4 and 5 which act on the tab 1 in this position, the tab 1 remains essentially in the same position.

By continuously shifting the body 2, maintaining the same direction of rotation, in each case by a 90 ° rotation, a braking and a releasing position of the thread are then assumed alternately. The direction of rotation can be parallel to or against the thread The staggered advancement of the body 2 is effected by a stepper motor which is arranged in the motor housing 23 and is designated by the reference number 9. This stepper motor has a step number of four. This means that the shaft is rotated 90 ° with each step. Each step of the stepper motor thus corresponds to a transition from a braking position to a release position or vice versa.

The structure of the stepping motor 9 is shown schematically in FIG. 6. The armature 44, which is designed as a permanent magnet oriented transversely to the axis of rotation, sits on the shaft 43, which is rotatably mounted in the motor housing. The armature is surrounded by an annular core 30 of an excitation coil. The excitation coil consists of a total of four partial areas each comprising an angle of 90 °. Each sub-area has a sub-coil 31, 32, 33, 34 and an inwardly projecting pole 39, 40, 41, 42. The partial coils 31, 32, 33, 34 are arranged between the four poles 39, 40, 41, 42, each offset by 90 °. The ends of adjacent coils - for example those of the coils 31 and 32 - are connected to one another, the respective ends 31 "being connected to the ends 32 '. The connecting position of the coils 31, 32, 33, 34 form electrical connection contacts 35, 36, 37, 38 out.

If, for example, the state shown in FIG. 6 is to be fixed, ie the armature 44 points with its north pole to the pole 39 or with its south pole to the pole 41, the corresponding electrical connections 35 and 37 are to be subjected to voltage current in such a way that a magnetic field aligned parallel to the magnetic field of the armature 44 is built up by the excitation coil.

If a position shown in FIG. 6 is to be carried out clockwise with the stepper motor 9, then the electrical connections 36 and 38 must accordingly be supplied with voltage current, so that a magnetic field builds up between the poles 40 and 42. If a corresponding magnetic field is then built up between the opposing poles 40 and 42, the armature 44 endeavors to orient itself in this magnetic field in accordance with its magnetization. As a result, the armature 44 makes a 90 ° clockwise rotation. The north pole and south pole of the armature are thereby shifted out of the orientation to the likewise opposite poles 39 and 41.

Because the armature is bound in the magnetic field built up by the excitation coil, the armature is prevented from rotating due to its angular momentum. As soon as the armature rotates beyond the equilibrium position parallel to the excitation magnetic field, the angle of the two magnetic fields causes the armature to return to its equilibrium position. This restoring force quasi forms an electromagnetic stop.

By clocked changing of the voltage applied to the electrical connections 35, 36, 37, 38, a clocked rotating field is accordingly generated, which the armature follows accordingly.

Claims (6)

1. Device for variably braking moving threads, wires or the like, in particular for use during weft insertion on looms, wherein the thread (F) passes through between two braking members which can be brought into spring contact with each other and of which one forms a spring element and the other an abutment and one of the braking members is movable to vary the braking, wherein the abutment is constructed as an essentially cylindrical body (2) which is acted upon by the spring element (1) rotatably, wherein a section (8) of the cylindrical body (2) comprises at least one circumferential region of reduced cross-section (6, 7) and wherein a preliminary brake comprising two plates pivotably adjustable about their bearing spindles (18, 11) is provided.
2. Device for variably braking moving threads, wires or the like according to claim 1, characterised in that in the circumferential direction of the body (2) are provided a plurality of circumferential sections of reduced cross-section (6, 7) between which is provided in each case an unreduced circumferential cross-section (10, 11).
3. Device for variably braking moving threads, wires or the like according to claim 1 or 2, characterised in that the abutment is mounted on the shaft (1) of an electric motor designed as a stepping motor (9), and in that the number of steps of the electric motor (9) corresponds to a multiple, preferably twice the number of circumferential sections of reduced cross-section (6, 7).
4. Device for variably braking moving threads, wires or the like according to any of the preceding claims, characterised in that the circumferential section of reduced cross-section is constructed as a flattened portion (6, 7) arranged transversely to the radial.
5. Device for variably braking moving threads, wires or the like according to claim 3 or 4, characterised in that the stepping motor (9) comprises an armature (44) which is magnetically polarised, preferably formed by a permanent magnet, and which is surrounded by an annular exciting coil which consists of a number of partial windings (31, 32, 33, 34) corresponding to the number of steps of the electric motor and of which the core forms pairs of magnetic poles (39, 41, 40, 42) associated with the step positions of the armature.
6. Method for the operation of a thread brake for variably braking moving threads, wires or the like, in particular for use during weft insertion on looms, wherein the thread (F) passes through between two braking members which can be brought into spring contact with each other and of which one forms a spring element and the other an abutment and one of the braking members is movable to vary the braking, wherein the abutment is constructed as an essentially cylindrical body (2) which is acted upon by the spring element (1) rotatably, with a first partial section (4, 5) of essentially circular cross-section and a second partial section (8) comprising at least one circumferential region of reduced cross-section (6, 7), wherein the abutment is mounted on the shaft (1) of an electric motor designed as a stepping motor (9), according to any of claims 1 to 5, characterised in that, while retaining the direction of rotation of the motor, at each step the thread brake changes alternately from a braking position to a thread release position, wherein, starting from a braking position which corresponds to a step position of the electric motor and in which a circumferential region of unreduced cross-section (10, 11) is located opposite the spring element (1), at the next step of the electric motor a region of reduced cross-section (6, 7) is brought opposite the plate (1).

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