Device and method for severing a thread

Abstract

The invention relates to a device (1) for severing a thread that comprises two blades (2, 3). An electric drive (4) enables said blades to be moved counter to the action of leaf springs (6, 7; 9, 10) and into a ready position, from which the blades can be moved back by means of the force of the leaf springs in order to execute a severing process.

Description

The invention relates to a device for severing a thread that has two blades, at least one of which is movable relative to the other by means of an electric drive, and to a method for severing a thread.

A device for severing a weft thread for a weaving loom is known (German Patent Disclosure DE 2230099), which has two blades that are movable relative to one another. This device is located in the vicinity of the fabric edge, in order to cut off a weft thread that is picked up by a gripper and transported into the shed. To improve the cutting operation, the blades are pressed against one another by spring force. One of the blades is driven via a cam system, which in turn is driven by the weaving loom. Such a device has the disadvantage that the speed of motion of the blades in cutting off the thread is determined by the speed of the drive means, whose speed is determined by the speed of the weaving loom.

A device of the type defined at the outset is also known (European Patent Disclosure EP 0284766 A1), which as its drive includes an electric drive motor. In this known device, one problem is that the relative speed of the blades upon severing a thread is determined by the activating and properties of the electric drive means.

The object of the invention is to create a device of the type defined at the outset in which the speed of motion of the blades during the severing operation is independent of the speed of the weaving loom or of properties of an electric drive.

This object is attained in that the at least one movable blade is movable by the drive counter to the action of at least one spring element into a ready position from which, by means of the force of the at least one spring element, it can be moved back again for executing a severing operation.

The invention offers the advantage that the speed of motion of the blades is independent of the drive means and can thus be selected as a function of the thread to be severed, in particular a weft thread of a weaving loom. The speed of the relative motion between the blades is determined essentially by the natural frequency of the means that retain the movable blade and that move with the blade.

The application of the device according to the invention to weaving looms leads to the advantage that the speed of severing is independent of the weaving speed of the weaving loom and independent of the response times and reaction times of the electric drive means. The speed for the cutting can be set adequately high in all cases to enable satisfactory severing of a weft thread. This is advantageous above all whenever the power loom is operated at slow speed, and a weft thread has to be severed or cut.

According to an embodiment of the invention, it is provided that both blades can be moved into a ready position with contrary motion by means of electric drives and can be moved back again by means of spring elements. Thus substantially higher cutting speeds can be attained than with one stationary blade and only one moving blade. In a further embodiment of the invention, it is provided that the blade or blades are each retained by respective pairs of leaf springs, which are oriented transversely to the direction of motion of the associated blade and are disposed spaced apart from and parallel to one another. Since the blades need not execute excessively great motions, and since the leaf springs in turn can have a relatively great length, it is possible in this way to move the blades substantially rectilinearly, without having to provide guides for the purpose.

In an embodiment of the invention, it is provided that the blade or blades are connected to an armature which contains at least one permanent magnet and with which an electromagnet is associated. In further embodiment both blades are provided with armatures in which the permanent magnets are arranged such that like poles face each other in the ready position and unlike poles face each other in the severing position. In this arrangement, the armatures and thus the blades attract one another while they are in the region in which the severing operation takes place. The cutting operation is thus improved. The armatures and hence also the blades repel one another, however, while they are in the region of the ready position, and as a result wear to the blades moving relative to one another is reduced.

As an embodiment of the invention, one common electromagnet is provided for the armatures of both blades; and the permanent magnets of the armatures are oriented in opposite directions. The common electromagnet has the effect that upon its excitation, the two armatures are moved with their blades in opposite directions.

In a preferred embodiment, it is provided that the two units comprising a blade, an armature, and leaf springs are designed for different natural frequencies. By the choice of the mass of the unit comprising the leaf springs, armature and blade, and the choice of the spring characteristic curve for the leaf spring, the natural frequency can be defined. It is advantageous if the speeds of motion, selected by means of the natural frequency, are set so differently that the position in which the cutting is done differs from the position of repose when the electromagnet is not excited. It can thus be attained that in gripper looms, in a position of repose assumed when the electric drive means are not excited, the device is located above the fabric, so that upon beating up, the weft threads can pass underneath the device. Nevertheless, the weft threads can be severed at the level of the plane of the fabric. This mode of operation is made possible whenever the blade that is moving downward is faster than the blade that is moving upward. The different speed and hence a different course of motion can be attained by providing that leaf springs of different stiffness or with a different spring characteristic curve, and/or armatures of different mass, and/or blades of different mass are used. Each of these provisions contributes alone or in combination with other provisions to a change in the natural frequency.

In a preferred embodiment, for a control unit of the electric drive or drives, a CAN bus system is provided.

The object is attained by a method in which the electric drive moves the at least one blade into a ready position counter to spring force, and for executing a severing operation, this blade is moved back again from the ready position at least by means of the spring force.

In a refinement, the electric drive is activated while the associated blade is being moved back from the ready position by means of spring force. Thus the speed and the course of motion during the severing can both be varied. In particular, it is provided that the electric drive brakes the associated blade during the motion back from the ready position, particularly after the severing operation has been performed.

In a further embodiment of the invention, a signal dependent on the motion of an armature of the electric drive is formed, by means of which the course of motion of the associated blade is monitored. This signal, which comprises a voltage, for instance, serves as feedback for controlling the device of the invention.

Further characteristics and advantages of the invention will become apparent from the ensuing description of the exemplary embodiments shown in the drawings.

FIG. 1 shows a device according to the invention in a position of repose;

FIG. 2 shows the device of FIG. 1, with a few components having been left out to increase the clarity;

FIG. 3 is a vertical section through FIG. 2;

FIG. 4 shows the device of FIG. 1 (leaving out additional components) in a ready position;

FIG. 5 shows the device of FIG. 1 in a severing position; and

FIG. 6 is a fragmentary view in the direction of the arrow F6 of FIG. 1.

The device according to the invention shown in FIG. 1 has two blades 2 and 3, movable relative to one another, and electric drive means for moving these blades 2, 3 relative to one another. The blade 2 is connected to an armature 5, which is retained movably by means of leaf springs 6, 7. The blade 3 is connected to an armature 8, which is retained movably by means of leaf springs 9, 10. The leaf springs 6, 7 and 9, 10 are oriented transversely to the direction of motion of the blades 2, 3 and are disposed parallel to and spaced apart from one another. Each of two leaf springs 6, 7; 9, 10 are located directly one above the other, so that thin leaf springs, which are advantageous with respect to the service life, can be used. The armatures 5, 8 are each retained on both ends by relatively long leaf springs 6, 7; 9, 10, so that the armatures 5, 8 move essentially linearly. The ends of the leaf springs 6, 7; 9, 10 remote from the armatures 5, 8 are retained by means of a holder 11 in which they are fastened. The leaf springs 6, 7 and 9, 10 are embodied in one piece in the region of the holder 11, in this exemplary embodiment. The holder 11 has a shaft 12, which is mounted for instance by means of an arm 13 on a frame of a textile machine. The shaft 12 is fastened between the arm 13 and a clamping element 14 and as a result can be disposed at an arbitrary axial or radial point. As a result, the device according to the invention can be positioned relative to a textile machine in such a way that a thread can be severed or cut off. In this way, the device according to the invention can be disposed in a gripper weaving loom in the direction of the weft thread in a predetermined position relative to the fabric. In addition, holder elements 15 are secured to the holder 11; they carry an electromagnet 16, cooperating with the armatures 5 and 8, and a control unit 17. The control unit 17 is connected to a control unit of the textile machine via a cable 18. The control unit of the textile machine sends signals to the control unit 17 for actuating the device 1 according to the invention synchronously with the textile machine.

As can be seen from FIGS. 1 through 3, each electromagnet 16, cooperating with a respective armature 5 or 8, has two mirror-symmetrically disposed iron cores for the armatures 5 and 8; that is, two iron cores 19 for the armature 5, and two iron cores 20 for the armature 8. The iron cores 19, 20 are formed from plates. In the exemplary embodiment shown, a pair of coils 21 for the iron cores 19, 20 is provided, so that both electromagnets 16 can be controlled by the same pair of coils 21. The coils 21 are each disposed around a middle part 22 of the iron cores 19, 20 in the region of the armatures 5, 8. The iron cores 19, 20 are secured to the holder elements 15 by means of screws. In a modified embodiment, the iron cores 19, 20 are embodied in one piece; that is, they comprise only one set of plates fastened together. As shown in FIG. 1, a housing 23 of nonmagnetizable material is disposed around the electromagnets 16.

In a modified embodiment, only one coil 21 is provided, which performs the function of the two coils 21 that are connected in series. Instead of two mirror-symmetrically disposed iron cores 19, 20 for the armature 5 and for the armature 8, it is also possible for a single iron core to be used, while the other is replaced by a beam that is either disposed in stationary fashion or is connected to the associated armature. In another modified embodiment, each electromagnet 16 that cooperates with one of the armatures 5 or 8 is controlled by its own coil.

As can be seen in FIG. 2, two permanent magnets 24, 25 are accommodated in the armature 5 and two permanent magnets 26, 27 are accommodated in the armature 8. These permanent magnets 24 through 27 have a rodlike shape and have two poles. The north-south direction of the permanent magnets 24 through 27 extend vertically to the direction of motion of the armatures 5 and 8. The permanent magnets 24, 25 on the one hand and the permanent magnets 26, 27 on the other are each disposed such that the unlike poles border one another. Each of the permanent magnets 24 through 27 has a length equivalent to approximately the magnitude of the motion of the associated armature 5 or 8 between a position of repose, with the coil not excited, and a position with the coil 21 excited. The permanent magnets 24, 25 are oriented with their poles oppositely to the poles of the permanent magnets 26, 27, so that upon excitation of the coil 21, the armatures 5, 8 are each moved in opposite directions. Because of this embodiment, it is possible for both armatures 5, 8 to be actuated with either the same coil 21 or with one coil set 21.

In FIG. 2, the blades 2, 3 are in a position of repose, in which the coil 21 is not excited. When the coil 21 of the electric drive means 4 is excited, the armatures 5, 8 move in opposite directions as far as a position that is shown in FIG. 4. This position is called the open position or ready position. In this position, the armatures 5, 8 and thus also the blades 2, 3 are moved counter to the force of the leaf springs 6, 7; 9, 10. The electromagnets 16 and the exciter current for the electromagnets 16 are understood to be adapted to the strength of the leaf springs 6, 7; 9, 10, or else the leaf springs 6, 7; 9, 10 are adapted to the electromagnets 16 and to the exciter current. Since the like poles of the permanent magnets 24, 26 on the one hand and the permanent magnets 25, 27 on the other rest side by side in the ready position, the armatures 5, 8 are pressed apart somewhat, so that the blades 2, 3 are pressed against one another with only slight force. In this position, a thread A to be severed or to be cut, for instance a weft thread in the case of a gripper weaving loom, is placed between the blades 2 and 3. This can be done for instance in the way described in DE 2230099. Once the excitation of the coil 21 is ended, the armatures 5, 8 are moved back again out of the ready position by the force of the prestressed leaf springs 6, 7; 9, 10, so that they sever the thread A located between the blades 2, 3, in a cutting position that is shown in FIG. 5. In this cutting position, the unlike poles of the permanent magnets 24 through 27 face one another, so that the armatures 5, 8 attract one another, which reinforces the cutting operation.

As can be seen from FIG. 5, the cutting position is located somewhat lower than the position of repose shown in FIG. 2. This is due to the fact that the blade 3 moves downward at a higher speed than the speed at which the blade 2 moves upward. This difference in speed is due, in the embodiment shown, to a difference in the natural frequency between the unit comprising the blade 2, armature 5 and leaf springs 6, 7 and the unit comprising the blade 3, armature 8 and leaf springs 9, 10. In the embodiment shown, the difference in the speed of motion is caused for instance by the fact that the unit having the blade 2 is heavier and thus moves more sluggishly than the unit having the blade 3. It is understood also to be possible to attain a different speed of motion by means of varying the natural frequency of the applicable unit in some other way, in particular by varying the mass of the unit or the spring stiffness of the leaf springs 6, 7; 9, 10.

In order to vary the speed of motion of the blades 2 and 3, the coil 21 may also be activated. To reduce the speed of motion, it can be provided that the excitation of the coil 21 not be interrupted, but instead that a relatively low current be made to flow through the coil. As a rule, however, the latter is unwanted, since in most cases as high a speed as possible is advantageous for cutting. Therefore, to increase the speed of the motion, a current is passed through the coil 21 that is opposite the current that flows through the coil 21 for putting the blades 2 and 3 into the ready position shown in FIG. 4. In that case, the blades 2, 3, during their motion out of the ready position, are likewise controlled by the electric drive means 4. However, since the acceleration and the speed reached by the leaf springs 6, 7; 9, 10 are relatively high, in most cases activated the coil 21 with an oppositely oriented current affects the speed of the motion during cutting only slightly. To limit the speed of the blades 2, 3, it is advantageous to activated the electric drive means 4 briefly, directly after the cutting, in such a way that the blades 2, 3 are forced back into the direction to the position shown in FIG. 4, or in other words are braked after the cutting.

If the device of the invention is used in a gripper weaving loom, the coil 21 is briefly excited after the cutting—for instance as described above—in other to brake the blades 2, 3. After that, the unit can settle freely until the position of repose of FIG. 2 has been resumed. The settling process is damped since the blades 2, 3 rest on one another and rub against one another. In a modified version, damping is accomplished by the drive means 4. To that end, the coils 21 can be short-circuited after the severing operation. The motion of the permanent magnets 24 through 27 generates a voltage which, with short-circuited coils 21, generates a current through the coils 21. As a result, some of the energy of motion into the coils 21 is converted into heat. Because of this, moreover, the frequency of the operation can be increased further. In the position of repose of FIG. 2, a beaten-up weft thread can travel beneath the blade 2. In gripper weaving looms, it is also important for the instant at which the drive means are no longer activated and the severing operation takes place to be synchronized with the weaving cycle.

The control unit 17 of the device of the invention is connected via a cable 18 to a CAN bus system, so that the electric drive means, and in particular the coil 21, can be activated via this CAN bus system. As a result, it is possible to use the device according to the invention in any already-existing textile machine that is equipped with a CAN bus system.

In a modified embodiment, the control unit 17 is provided with means for detecting the course of motion of the blades 2, 3 during the motion and in particular the cutting motion. This can be done for instance by measuring an electrical signal that occurs in the coil 21 as a result of the permanent magnets 24 through 27, moving relative to the coil 21, of the armatures 5, 8. On the basis of this signal, the instant of cutting can be determined. The determination of the instant of cutting can also be done in some other way, such as with the aid of optical sensors, or as known from International Patent Disclosure WO 99/29946.

In gripper weaving looms, this method can for instance be employed to compare the correct instant of cutting with the instant when the coil 21 is no longer excited. The instant when the drive means 4 are no longer excited is synchronized with the weaving cycle by setting or adjusting the instant of the end of excitation within the weaving cycle such that cutting is done at the correct instant within the weaving cycle. Hence a correct setting of the instant of the end of excitation can be defined for every device for cutting, without there being any influence by the properties of the leaf springs, armatures or blades on the synchronization of the instant of cutting with the weaving cycle. Such a setting can be achieved for instance by providing that the instant of the end of excitation of the coils 21 is set relative to the position of the drive shaft of the gripper weaving loom such that the armatures 5 and 8, which are restrained firmly in their ready position, are released at that instant. The relative instant of thread cutting relatively to the instant of the end of excitation can then be used as a feedback value for setting or adjusting the instant of the end of excitation relative to the position of the drive shaft of the gripper weaving loom. By shifting the instant of the end of excitation of the coil set 21 to a greater or lesser extent relative to a previously determined position of the drive shaft, the instant of cutting can be set precisely or changed by the control of the end of excitation as a function of the aforementioned, previously determined position relative to the position of the drive shaft and thus relative to the weaving cycle.

In FIGS. 1, 3 and 6, details are also shown for how the blades 2 and 3 are connected to the armatures 5 and 8. On the underside of the armature 5, the leaf springs 7 are secured to the armature by means of a clamping element 28. A T-element 30 is secured to this clamping element 28 by means of a screw. The blade 2 is secured to this T-element 30 by fastening means 31. The leaf springs 10 are secured to the underside of the armature 8 by means of a clamping element 29. By means of a screw, a T-element 32 is secured to this clamping element 29. A leaf spring 33 is secured to this T-element 32 by a fastening means 34. The blade 3 is secured to this leaf spring 33 by adhesive bonding, soldering, or welding, or the like, for instance. By means of the fastening of the T-elements 30 and 32 relative to one another and the deformation of the leaf spring 33, the force with which the blades 2, 3 are pressed against one another can be adjusted. By the fastening means 31 and 34, the relative height of the blades 2 and 3 with respect to one another can also be adjusted. The blades 2 and 3 are ground in a known manner so that they will cut optimally.

In a modified embodiment, the armatures 5 and 8 each have only one permanent magnet, for instance the permanent magnets 25 and 26, respectively. For cutting and to avoid wear of the blades 2, 3, however, it is more advantageous to use two permanent magnets 24, 25; 26, 27 each, respectively.

Different speeds for the motion of the blades 2 and 3 can also be attained by providing that in the motion toward the cutting position, the blades 2, 3 are controlled differently by the electric drive means 4, by using permanent magnets of different strengths for the two armatures 5, 8, by activating the electromagnets 21 differently, by activating each armature 5, 8 by a different electromagnet, or by a combination of these provisions. Moreover, an auxiliary coil may be provided for each armature 5, 8, in order to speed up or slow down the motion of the armature 5, 8 during cutting.

In the embodiment shown, the ready position is determined essentially by the longitudinal dimensions of the permanent magnets 24 through 27. In a modified embodiment, this position can be determined with the aid of sensors, for instance optical sensors, that cooperate with the control unit 17. The control unit 17 may for instance control the current delivered to the coil 21 such that the armatures 5, 8 assume a previously defined ready position.

It is understood that the device of the invention is not limited to use in a gripper weaving loom. It can readily be employed in any other textile machine in which threads must be severed, such as air jet looms, gripper shuttle looms, water jet looms, projectile looms, other types of weaving looms, knitting machines, sewing machines, and other textile machines. The device of the invention offers the advantage that it can be built into any existing textile machine without problems. A particular advantage is that a thread can be severed at a relatively high cutting speed, which can be adjusted independently of the speed of the textile machine and independently or at least largely independently of the electric drive means. Because the two blades 2, 3 move relative to one another upon cutting, a higher cutting speed is obtained compared to the case in which one of the blades is stationary.

The device according to the invention and the method according to the invention are not limited to the embodiments described here as examples and shown in the drawings. On the contrary, they may be realized in various variants.

Claims

1. A device (1) for severing a thread (A), which has two blades (2, 3) at least one of which is movable relative to the other by means of an electric drive (4), characterized in that the at least one movable blade (2, 3) is movable by the drive (4) counter to the action of at least one spring element (6, 7; 9, 10) into a ready position from which, by means of the force of the at least one spring element, it can be moved back again for executing a severing operation.

2. The device of claim 1, characterized in that both blades (2, 3) can be moved into a ready position with contrary motion by means of electric drives (4) and can be moved back again by means of spring elements (6, 7; 9, 10).

3. The device of claim 1, characterized in that the blade or blades (2, 3) are each retained by respective pairs of leaf springs (6, 7; 9, 10), which are oriented transversely to the direction of motion of the associated blade (2, 3) and are disposed spaced apart from and parallel to one another.

4. The device of claim 1, characterized in that the blade or blades (2, 3) are connected to an armature (5, 8) which contains at least one permanent magnet (24, 25; 26, 27) and with which an electromagnet (19, 20, 21) is associated.

5. The device of claim 4, characterized in that the armature (5, 8) includes two permanent magnets (24, 25; 26, 27), which contact one another with unlike poles.

6. The device of claim 4, characterized in that both blades (2, 3) are provided with armatures (5, 8), whose permanent magnets (24, 25; 26, 27) are disposed such that they face one another with like poles in the ready position and with unlike poles in the severing position.

7. The device of claim 1, characterized in that the length of the permanent magnets (24, 25; 26, 27) of the armatures (5, 8) in the direction of motion of the blades (2, 3) approximately equals to the magnitude of the relative motion between the blades.

8. The device of claim 1, characterized in that one common electromagnet (19, 20, 21) is provided for the armatures (5, 8) of both blades (2, 3); and that the permanent magnets (24, 25; 26, 27) of the two armatures (5, 8) are oriented in opposite directions.

9. The device of claim 1, characterized in that the two units comprising a blade (2, 3), an armature (5, 8), and leaf springs (6, 7; 9, 10) are designed for different natural frequencies.

10. The device of claim 1, characterized in that for a control unit (17) of the electric drive or drives (4), a CAN bus system is provided.

11. A method for severing a thread (A) by means of two blades (2, 3), at least one of which is moved relative to the other by means of an electric drive (4), characterized in that the electric drive (4) moves the at least one blade (2, 3) into a ready position counter to spring force; and that this blade (2, 3), for executing a severing operation, is moved back again from the ready position at least by means of the spring force.

12. The method of claim 11, characterized in that the electric drive (4) is activated while the associated blade (2, 3) is being moved back from the ready position by means of spring force.

13. The method of claim 11, characterized in that the electric drive (4) brakes the associated blade (2, 3) during the motion back from the ready position, particularly after the severing operation has been performed.

14. The method of claim 11, characterized in that a signal dependent on the motion of an armature (5, 8) of the electric drive (4) is formed, by means of which the course of motion of the associated blade (2, 3) is monitored.