GB2125072A

GB2125072A - Self-adjusting filament tensioner

Info

Publication number: GB2125072A
Application number: GB08321292A
Authority: GB
Inventors: Geoffrey Edmund Whellams
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-07
Filing date: 1983-08-08
Publication date: 1984-02-29
Also published as: GB2125072B; GB8321292D0

Abstract

A filament tensioner is controlled by a tension monitor to maintain tension. A tensioner, particularly for fine copper wire, comprises two discs (53a, 53b). An electromagnet assembly (50, 51) may vary the force with which the discs are urged together to vary the imparted tension. Wire tension is sensed by a pivotal arm (40). An eddy-current drive from a motor (44) biases the arm with a constant force and the angle of the arm is determined by an optical sensor arrangement (45, 47). A control unit (56) receives the output signal from the sensor, and supplies a drive current to both the motor and electromagnet assembly, whereby the tension in the wire 35 may be maintained substantially constant. The tensioner may alternatively comprise movable guides interleaved with fixed guides to provide a variable zig-zag filament path (Fig. 1). <IMAGE>

Description

SPECIFICATION Self-adjusting filament tensioner This invention relates to a self-adjusting filament tensioner, particularly-but not exclusively-suitable for the tensioning of relatively fine copper wire, for example having a diameter of down to 0.025 mm.

During the handling of various kinds of filaments, either during the manufacture thereof or subsequently when the filament is being employed in the manufacture of an article, it is generally necessary for the filament to be handled under conditions of some tension. The filament is tensioned by imparting a drag to the movement of the filament as it is transferred from one point to another-for example, after the filament has been despooled from a reel thereof, on route to a coil winding machine.

Particularly when handling fine copper wires, the tension imparted thereto is critical, for too much tension will at least stretch the wire, so reducing its current-handling capacity, but very frequently actually breaks the wire. On the other hand, too little tension will normally adversely affect the proper operation of the machine using the wire-for instance a coil-winding machine.

Thus, too little tension equally can cause breakages, or other snags.

Experience has shown that it is very difficult to maintain a constant and uniform tension on a filament, even if the filament passes at a constant speed through the tensioner. Minor variations in the filament thickness or diameter can have a significant effect on the tension imparted thereto, as can local surface finish variations. Moreover, if the speed of the filament is varying to an extent, then large variations in the tension can occur. In the case of enamelled copper wire, variations in the thickness of the enamel coating often occur, and this can increase the problems of handling very fine--and hence fragile-wire.

It is a principal aim of this invention to provide a filament tensioner which is able automatically to adjust to varying conditions, so as to impart a substantially uniform tension on a filament passing therethrough.

Accordingly, this invention provides a selfadjusting filament tensioner comprising adjustable filament tensioning means through which the filament is to pass for tensioning thereby, adjusting means to effect adjustment of the tensioning means, means to monitor the tension in the filament and to condition an electrical signal dependent thereon, and electronic control means acting on the conditioned electrical signal and arranged to effect operation of the adjustable filament tensioning means dependent thereon.

It will be appreciated that the filament tensioner of this invention operates on a closed loop feedback principle, in that the instantaneous tensoin in the filament constantly is monitored, and the drag imparted to the filament (so changing the tension therein) is continuously adjusted to compensate for variations in the detected tension. It is therefore preferred for the tensioner to be sensitive to minor variations in tension and to have a rapid response time to such variations.To enhance the operation of the tensioner, the adjustable tensioning means should therefore have a relatively low inertia and the preferred form of such tensioning means comprises a pair of concentric discs between which the filament is to pass, and an electric actuator-such as an electromagnetic device or a Piezo-electric device-arranged to urge the two discs together with a force suitable to impart the required tension to a filament passing between the discs. Preferably, the two discs are slidably mounted on a spindle, one of the discs being adapted for driving by the electric actuator, and the other disc being adjustable, so as to permit pre-setting of the required tension and to accommodate filaments of different basic diameters.

The tension monitoring means advantageously comprises two filament guides which are generally aligned and a third guide mounted at the end of a pivoted arm biased to move the third guide out of alignment with the other two guides, whereby a filament passing in sequence through the three guides is constrained to follow a generally V-shaped path, the angle the arm makes with respect to a reference position being used to assess the tension in the filament.

Though the bias applied to the pivoted arm could be provided by means of a mechanical spring, it is preferred for the biasing force to be constant irrespective of the angular position of the arm with respect to the reference position.

Advantageously therefore the bias is provided by means of an eddy-current drive from a constantly rotating shaft, the speed of rotation of which may be varied to change the biasing force.

Conveniently, the angular position of the arm is determined by means of an optical sensor arrangement, which may provide an analog or digital signal to the electronic control means which effects the operation of the adjustable filament tensioning means.

By way of example only certain specific embodiments of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a diagram showing a first embodiment of an automatic filament tensioner constructed in accordance with this invention; Figure 2 is a detailed view of a part of the tensioner shown in Figure 1; Figure 3 is a detailed view of an alternative form of detector to that shown in Figure 2; and Figure 4 is a part-schematic diagram of a second embodiment of automatic filament tensioner constructed in accordance with this invention.

Figures 1 and 2 illustrate the first embodiment of automatic tensioner device which may be used to control the tension of fine wire following the de-spooling thereof, prior to the wire being wound for example, into a coil. The tensioner comprises a first series of fixed wire guides 1 0 aligned axially, and a second series of movable guides 11, again aligned axially and disposed alternately with the guides 10. Each guide of the second series has an arm associated therewith by means of which the guide is connected to a spindle 12 driven by a direct current electric motor 13. A coil spring 14 is coupled to the spindle 12 such that the spring tends to align the guides 10 with the guides 11.

A second direct current electric motor 1 5 has an arm 1 6 mounted on its driving shaft 17, the arm having an eyelet 1 8 at its free end, through which wire 1 9 to be tensioned may pass after leaving the iast first guide 10 but before passing through an outlet guide 20. An optical detector 21 for the position of the motor shaft 1 7 feeds an output to an amplifier and servo control 22, the output of which drives the motor 1 3.

The'second electric motor 1 5 operates in a generally stalled condition and is provided with an input voltage which tends to move the eyelet 1 8 away from the outlet guide 20. The optical detector 21 has a quadrant 23 mounted on the shaft 1 7 eccentric with the centre of curvature of the arcuate edge 24 of the quadrant, the edge 24 operating in association with a slotted optical transmitter/receiver pair 25 such that the quadrant 23 attenuates to a greater or lesser extent the radiation emitted by the transmitter to the receiver, depending upon the instantaneous position of the motor shaft 1 7. The output from the receiver is then amplified and used to control the voltage applied to the motor 13, so as to set.

the guides of the second series at the required position to impart an appropriate tension (or drag) to the filament being drawn through the device.

By varying the voltage applied to the motor 15, the force imparted to the arm 1 6 can be varied, thus varying the drag which must be imparted by the two series of guides in order to allow the arm 1 6 to rest at a datum position. Clearly, the voltage applied to the motor 1 5 can be varied from a location remote from the tensioner itself, allowing the tensioner to find applications in a wide variety filament-but particularly fine copper wirehandling installations. The tensioner may, for example, be used in conjunction with a coil winding machine associated with skeining apparatus, such as is directed in my co-pending Patent Application No. 82-22852 [Serial No. ]- Figure 3 shows an alternative form of optical detector, to replace that shown in Figures 1 and 2.In this arrangement, a quadrant 27 made of transparent material is affixed to the motor shaft 17, the quadrant carrying radial opaque lines. The spacing between the radial lines is very close in the region 28, but is relatively wide in an angularly separated region 29. Consequently, the attenuation of the radiation emitted by the transmitter and received by the receiver of the optical transmitter/receiver pair 25 will depend upon the instantaneous angular position of the disc 27.

The quadrant 27 could be replaced by other types of sensor for the shaft position. For example, the quadrant may be formed as a neutral extent of the quadrant. Another possibility is to mount a polarising filter in front of the transmitter of the transmitter/receiver pair 25, the quadrant also being a polarising filter, such that the amount of light reaching the receiver depends upon the relative planes of polarisation of the fixed filter and the quadrant. Yet another possibility is for the quadrant to be formed as an optical encoder operating with more than transmitter/receiver pairs, thereby to yield a digital output indicative of the shaft position.

Figure 12 shows the second embodiment of automatic tensioner, which may be used in a similar manner to that of Figure 1. Wire 35 is drawn from a spool (not shown) through a disc tensioner 36 (though in practice a series of such disc tensioners typically would be provided to impart sufficient drag), and then through a tension detecting arrangement 37, including an inlet guide 38, an outlet guide 39 and an arm 40 with an eyelet 41 at its free end, the arm being mounted on a shaft 42. A spring (not shown) such as a torsion hair spring or other spring may be provided to apply a torque to the shaft 42 in the direction of arrow D. The shaft 42 is coupled to the shaft 43 of an electric motor 44 by means of an eddy-current coupling, comprising an aluminium disc 45 affixed to shaft 42 and closely associated with a permanent magnet 46 affixed to the motor shaft 43.The edge of the disc 45 is given a ramp profile for cooperation with a slotted optical transmitter/receiver pair 47, such that an output can be obtained from device 47 indicative of the instananeous angular position of the arm 40.

The disc tensioner 36 comprises a soft iron bobbin 50 (or pot-core) defining an annular channel-shaped coil-receiving section, in which is provided an electromagnet coil 51. The bobbin supports a non-magnetic spindle 52 co-axial therewith, on which is slidably mounted a pair of hard tensioner discs 53a and 53b, the lower disc 53a having affixed thereto a permanent magnet 54 magnetised so that its central region is one pole and its peripheral region is the other pole.

Alternatively, the magnet 54 could be magnetised with one face one pole and the other face the other pole, the energisation of the electromagnet taking this into account. The free end portion of the spindle 52 is screw-threaded and carries a threaded adjuster 55 associated with the upper disc 53b.

An electronic control unit 56 receives the output from the optical device 47 and also provides the drive for the coil 51 of the disc tensioner 36. An adjustable drive unit is provided for the motor 44, allowing selection of a particular rotational rate, and hence of a desired tension.

In use the required tension is set by adjusting the speed of the motor 44, so as to apply an appropriate force through the eddy-current coupling to the arm 40. Dependent upon the speed at which the wire is drawn through the device, the arm takes up a particular attitude which is detected by the optical transmitter/ receiver pair 47 and the output therefrom is fed to the control unit 56. This provides a drive to the coil 51 so as to repel the permanent magnet 54 with a force appropriate to set the required tension. It will be appreciated that when no drive is given to the coil 51, the permanent magnet 54 is attracted to the bobbin 50, thus releasing the tension, and the greater the drive to the coil, the greater is the applied tension-that is, the drag imparted to the wire being pulled therethrough.

The adjuster 55 is used to set the initial tension, for example to accommodate wires of different diameters or of different insulative coatings or coverings. However, in view of the fact that the device operates on a closed feedback loop, the apparatus is to some extent selfadjusting, in that the drive current to the electromagnet coil is increased or decreased until the tension sensor determines that the wire is being correctiy tensioned.

The electromagnetic coil arrangement operating in conjunction with the disc 53a and 53b may be replaced by other forms of electric actuator able to urge the discs together with the required force. For example, the coil and magnet assembly may be replaced by a Piezo-electric element operating directly on one of the discs, the tension being adjusted by varying the voltage impressed across the Piezo-electric element.

Such an arrangement may have a relatively rapid response time, so assisting the minimising of breakages especially when handling fine copper wires, maybe of only 0.025 mm diameter.

Claims

1. Self-adjusting filament tensioner comprising adjustable filament tensioning means through which the filament is to pass for tensioning thereby, adjusting means to effect adjustment of the tensioning means, means to monitor the tension in the filament and to condition an electrical signal dependent thereon, and electronic control means acting on the conditioned electrical signal and arranged to effect operation of the adjustable filament tensioning means dependent thereon.

2. Self-adjusting filament tensioner according to claim 1, wherein the adjustable tensioning means comprises a pair of concentric discs between which the filament is to pass and an electric actuator arranged to urge the two discs together with a force suitable to impart the required tension to a filament passing between the discs.

3. Self-adjusting filament tensioner according to claim 2, wherein the electric actuator comprises an electro-magnetic device driving coupled to one of the discs mounted for axial adjustment thereby with respect to the other disc.

4. Self-adjusting filament tensioner according to claim 3, wherein the electromagnetic device comprises a soft iron pot core containing a solenoid coil, a spindle extending axially of the core and a permanent magnet slidably mounted on the spindle at the open end of the pot core for repulsion by the solenoid when energised, the two discs also being slidably mounted on the spindle with one disc juxtaposed to the magnet and the other disc being next to the one disc and restrained against movement away from the core.

5. Self-adjusting filament tensioner according to claim 3, wherein the electric actuator comprises a Piezo-electric device drivingly coupled to one of the discs to effect adjustment of that disc with respect to the other disc.

6. Self-adjusting filament tensioner according to any of claims 2 to 5 wherein the surface of each disc facing the other disc is of generally convex form.

7. Self-adjusting filament tensioner according to the claim 1, wherein the adjustable tensioning means comprises a fixed first series of aligned filament guides through which the filament is to pass, and a second series of guides through which the filament also is to pass, the guides of the second series being arranged alternately with the guides of the first series and all of the guides of the second series being arranged for movement either in unison or individually away from or towards the common axis of the first series of guides.

8. A self-adjusting filament tensioner according to claim 7, wherein each guide of the second series is mounted on a respective arm extending generally radially from a shaft which may be turned by means of an electric actuator to adjust the tension imparted to a filament.

9. A self-adjusting filament tensioner according to any of the preceding claims, wherein the monitoring means comprises two filament guides which are generally aligned and a third guide mounted at the end of a pivoted arm biased to move the third guide out of alignment with the other two guides, whereby a filament passing in sequence through the three guides is constrained to follow a generally V-shaped path, the angle the arm makes with respect to a reference position being used to assess the tension in the filament.

1 0. A self-adjusting filament tensioner according to claim 9, wherein the angle of the arm with respect to the reference position is determined by means of an optical sensor which conditions an electrical signal.

11. A self-adjusting filament tensioner according to claim 10, wherein the optical sensor comprises a transmitter/receiver pair, and attenuator means coupled to the arm and arranged to attenuate the light falling on the receiver from the transmitter.

12. A self-adjusting filament tensioner according to any of claims 9 to 11, wherein the bias on the arm is provided by means of a torsion spring.

1 3. A self-adjusting filament tensioner according to any of claims 9 to 11, wherein the bias on the arm is provided by means of an eddycurrent drive from a constantly rotating shaft, the bias being adjustable by varying the speed of rotation of the shaft.

14. A self-adjusting filament tensioner substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or in Figures 4 of the accompanying drawings.