Wire-tensioning device for a coil-winding machine

Abstract

 A wire-tensioning device for a coil-winding machine can be arranged between a supply reel and a core or jig on which the wire is to be wound. The wire-tensioning device comprises a rotatable tensioning wheel (15) which is coupled to a drive unit (19). The wheel (15) has a circumferential surface (29) for supporting the winding wire and is equipped with a wire guide (31) for guiding the wire towards a specific location on the wire-supporting surface (29) of the wheel (15).

Description

[0001] The invention relates to a wire-tensioning device for a coil-winding machine in which a winding wire is fed from a supply reel to a core or jig on which the wire is to be wound, which wire-tensioning device can be arranged between the supply reel and the core or jig.

[0002] Such a wire-tensioning device is described in German Offenlegungsschrift 2,318,884. The known device comprises a pivotally mounted lever-mechanism which cooperates with a spring and has a pulley for the winding wire.

[0003] It is common practice to employ wire-tensioning devices in coil-winding machines for providing windings on cores of non- circular cross-section. Such winding machines are employed, for example, in the production of toroidal deflection coils for cathode-ray tubes or rectangular rotors of electric motors. Further, wire-tensioning devices are employed in coil-winding machines in which saddle-shaped deflection coils are wound on an irregularly shaped jig.

[0004] Due to the asymmetrical shape of the core or jig the wire consumption per unit of time will vary during winding, i.e. the speed at which the wire is wound onto the core or jig is subject to variations. This also gives rise to variations in wire tension, which may result in slack in the wire or wire breakage at higher winding speeds. Moreover, the varying wire tension results in a non-uniform distribution of the windings, which is undesirable in particular in the case of deflection coils for cathode-ray tubes.

[0005] In order to reduce the variations in wire tension in coil-winding machines a wire-tensioning device may be arranged between the supply reel and the core or jig. Such a wire-tensioning device should meet al least two requirements: first, it must be capable of taking up as rapidly as possible any slack formed in the wire during winding, so that the winding wire remains constantly taut; secondly, the wire tension should be maintained as constant as possible in order to avoid excessive tension.

[0006] When a wire-tensioning device of the type described in the above mentioned DE 2,318,884 is employed in a coil-winding machine the wire which runs over the pulley forms a wire loop which becomes smaller or larger as the wire accelerates or decelerates. In order to ensure that variations in wire tension are minimal and the wire loop does not become too large or too small, the knom wire-tensioning device nust be provided with a separate wire-braking device. Such a braking device is known per se and may comprise a rotatable cylinderical roller on which an adjustable braking force is exerted and which guides the winding wire is.

[0007] A disadvantage of the known wire-tensioning device is that owing to its relatively large mass and dimensions the lever mechanism responds comparatively slowly to accelerations and decelerations of the wire, so that significant variations in tension may occur. Another disadvantage is that the wire-tensioning device must be used in junction with a separate wire braking device, which obviously renders the coil-winding machine more expensive. A further disadvantage is that the lever mechanism has only a limited capacity for taking-up slack in the wire.

[0008] The invention aims at providing a rapidly responding wire-tensioning device with a large capacity for taking-up slack and which does not require the use of a separate wire-braking device.

[0009] To this end the wire-tensioning device in accordance with the invention is characterized in that it comprises a rotatable tensioning wheel which is coupled to a drive unit and which has a peripheral surface for supposing the wire, and wire guide rotatable with the wheel for guiding the wire towards a specific location on the wire-supporting surface of the wheel.

[0010] When the wire-tensioning device in accordance with the invention is in use in a coil-winding machine, the winding wire runs from the supply reel to the tensioning wheel, the wire reaching the wire-supporting contact surface of the wheel via the wire guide. After passing around at least part of the wire-supporting surface the wire runs on to the core or jig on which it is to be wound. The drive unit exerts a moment on the tensioning wheel in a direction opposite to that in which the wire runs onto the wire-supporting surface of the wheel. By means of the friction which occurs between the wire and the wheel, the drive unit then exerts a specific tensile force on that part of the winding wire which is situated between the wheel and the core or jig, which force produce a specific tension in the wire. In the case of a uniform wire take-off the wheel is stationary and the wire slides over the wire-supporting surface of the wheel, which surface always supports a constant length of wire. However, in the case of a varying wire take-off the wheel immediately responds to accelerations or decelerations in the movement of the wire by rotating, so that the length of wire in contact with the wire-supporting surface changes and more wire is supplied or wire is taken up. In both cases the device in accordance with the invention is capable of maintaining a highly constant wire tension in the winding wire supplied to the core or jig.

[0011] Preferably, the drive unit is controllable so as to permit a rapid and effective adjustment of the moment exerted on the tensioning wheel and hence of the desired wire tension. The drive unit may be a spring motor or a pneumatic motor. However, preferably a d.c. electric motor is employed because such a motor can be controlled more conveniently.

[0012] An advantage of the wire-tensioning device in accordance with the invention is that the device is of small dimensions and has a low mass, so that it can respond rapidly to a varying wire .take-off. In this way fluctuations in wire tension can be reduced to an acceptable level. Suitably, the tensioning wheel is made of a material with a low specific mass, such as aluminium or a plastics, for example polycarbonate. Very satisfactory results are achieved if the wheel comprises a plurality of spokes between the hub and the wire-supporting surface.

[0013] Another advantage of the wire-tensioning device in accordance with the invention is that a separate braking device is not needed, because the friction exerted on the winding wire by the tensioning wheel depends on the length of wire in contact with the wire-supporting surface of the wheel and thus constitutes a suitable braking force for the wire. In the present device variations in the coefficient of friction between the wire and the wire-supporting surface do not affect the wire tension. Moreover, a device in accordance with the invention can handle wires of different cross-section without any modifications being necessary.

[0014] In order to preclude premature wear of the wire-supporting surface of the tensioning wheel, this surface may be provided with a wear-resistant or hardened layer.

[0015] A preferred embodiment of the invention is characterized in that the wire guide extends from the axis of the tensioning wheel up to the wire-supporting surface of the wheel.

[0016] This has the advantage that a smooth movement of the wire is also guaranteed in the case of high speeds of the tensioning wheel, because uncontrollable movements, such as oscillatory movements, of the lenghts of wire between the supply reel and the wheel cannot occur.

[0017] For the wire guide different constructions may be employed, for example two pulleys arranged transversely of each other. A surprisingly simple, cheap and effective wire guide is obtained by the use of a tube which is curved towards its ends and terminates in two open end portions of which one extends along the axis of the tensioning wheel and the other extends along a line tangential to the wire-supporting surface of the wheel. This wire guide has the additional advantage that its mass can be very lew with a suitable choice of the material of which it is made. The material may be,for example, a plastics, such as polyvinyl chloride.

[0018] The invention also provides to a coil-winding machine in which the winding wire is fed from a supply reel to a core or jig on which the wire is to be wound, and in which a wire-tensioning device in accordance with the invention is arranged between the supply reel and the core or jig.

[0019] The invention will now be described in more detail, by way of example, with reference to the drawings, in which

Figure 1 shows schematically and not to scale a coil-winding machine comprising a wire-tensioning device in accordance with the invention, and

Figure 2 is a side view of the tensioning wheel of this device, taken on the line II-II in Figure 1.

[0020] The coil-winding machine shown in Figure 1 comprises a winding jig 3 arranged on a rotatable shaft 1 which can be driven by an electric motor 5. A winding wire 9, which is taken off a supply reel 7, is fed to the jig 3. Between the supply reel 7 and the winding jig 3 the wire 9 passes through a wire-tensioning device 11 contsructed in accordance with the invention. In order to preclude soiling of the device 11 the wire 9 is first passed through a cleaning element 13, which comprises, for example, two feltpads which are spring loaded towards one another. The felt pads give the wire 9 a certain pretension, which has a favourable effect on the operations of the wire-tensioning device 11.

[0021] The wire-tensioning device 11 comprises a tensioning wheel 15 which is mainted on a rotatable shaft 17 of a controllable d.c. rotor 19. The wheel 15 comprises a hub 21 which is locked on the shaft 17 for rotation therewith and a rim 23 which is connected to the hub 21 by spokes 25 (see also Figure 2). At its outer circumference the rim 23 has two redially projecting flanges 27 between which is formed a cylindrical surface 29 for supporting a turn or turns, or part of a turn, of the wire 9. On the side of the wheel 15 which is remote from the motor 19 a nylon tube 31 is mounted, which tube functions as a wire guide. The tube 31 is curved towards its ends and terminates in two open end portions 31A and 31B constituting the wire inlet and the wire outlet, respectively. The end portion 31A is coaxial with the wheel 15 and the end portion 31B is arranged at a fixed location relative to the wire-supporting surface 29 and extends along a line tangential to the surface 29 at this location. This shape of the tube 31 ensures that the wire is quided onto the wire-supporting surface 29 without being kinked or otherwise unacceptably deformed.

[0022] The coil-winding machine operates as follows. When the winding jig 3 is rotated it takes up wire 9. The jig 3 has an irregular, non- circular shape, with the result that the speed of the wire 9 periodically varies significantly as a function of the angle of rotation. Unless special provisions are made, the tension with which the wire 9 runs onto the jig 3 is consequently subject to substantial fluctuations, which will result in a poorly wound coil. It is to preclude this that the wire-tensioning device 11 in accordance with the invention is provided, the wire 9 being wrapped around the tensioning wheel 15 and being guided over the wire-supporting surface 29 of this wheel.

[0023] The motor 19 exerts a constant moment M on the tensioning wheel 15 in a direction opposite to that in which the wire 9 runs onto the wire-supporting surface 29 of the wheel 15 from the wire guide 31. As a result of the friction between the wire 9 and the surface 29 the moment M exerts a tensile force on the wire which is being fed onto the jig 3, which force in turn produces a specific tension in the wire.

[0024] If the wire take-off is uniform a situation arises in which the tensioning wheel 15 is stationary as a result of the moment M exerted on it. The wire 9 than slides over the wire-supporting surface 15 and the wire which is being fed onto the jig 3 then has a constant tension The wrapping angle α of the wire 9 on the wheel 15 depends on the coefficient of friction µ between the wire 9 and the wire-supporting surface 29 and on the tension √v in the wire which is being fed onto the surface 29. The relationship between the said parameters

,

v, u and α may be epressed by the equation

=

v. e/^uα which is known from mechanical engineering.

[0025] The tension √v depends on inter alia the frictional force experienced by the wire 9 in the wire guide 31 and in the cleaning element 13. This tension √v is usually very small relative to the desired wire tension √. The coefficient of friction µ will generally be selected so that the wire 9 is wrapped a few times around the tensioning wheel 15 in the case of a uniform take-off.

[0026] However, as already stated in the foregoing, the jig 3 unwinds the wire 9 at varying speed. If this speed decreases, the tensioning- wheel 15 initially rotates in the direction of the moment M and the wrapping angle α increases. The factor e/^uα then increases, as a result of which the force exerted on the wire 9 which is being taken off the supply reel 7 decreases, causing the speed at which the wire 9 is pulled off the supply reel 7 to decrease. The opposite happens when the speed at which the wire 9 is taken off by the jig 3 increases. Initially, the length of wire wrapped on the tensioning wheel then decreases, so that more wire is pulled off the reel per unit of time. In both cases the tensions in the wire 9 which is being fed onto the jig 3 will be subject to very small variations.

[0027] In this suprising manner it is achieved that the length of the wire supported on the tensioning wheel remains approximately equal to a preselected average value. Further, it will be appreciated that the substantially constant wire tension in the winding wire which is being fed onto the jig is independent of variations in the cross-section of the wire and the coefficient of friction.

Claims

1. A wire-tensioning device for a coil winding machine in which a winding wire is fed from a supply reel to a core or jig on which the wire to be wound , which wire-tensioning device can be arranged between the supply reel and the core or jig, characterized in that the wire-tensioning device comprises a rotatable tensioning wheel which is coupled to a drive unit and which has a peripheral surface for supporting the wire, and a wire guide rotatable with the wheel for guiding the wire towards a specific location on the wire-supporting surface of the wheel.

2. A wire-tensioning device as claimed in Claim 1, characterized in that the wire guide extends from the axis of the tensioning wheel to the wire-supporting surface of the wheel.

3. A wire-tensioning device as claimed in Claim 2, characterized in that the wire guide comprises a tube which is curved towards its end and terminates ir two open end portions of which one extends along the axis of the tensioning wheel and the other extends along a line tangential to the wire-supporting surface of the wheel.

4. A coil-winding machine in which the winding wire is fed from a supply reel to a core or jig on which the wire is to be wound, characterized in that a wire-tensioning device as claimed in any one of the preceding Claims is arranged between the supply reel and the core or jig.

Drawing