The present invention relates to the fabrication of fri ction elements and, in particular, to the winding of a fi lament, or a tape, into a generally disc-shaped preform suitable to be cured to form a friction element,

Disc-shaped friction elements, for example, are employed as the facings for clutches, the facing being secured to a backing plate, for example, by rivets. For convenience, hereinafter in this specifi¬ cation, reference is made only to a friction element corriDrising a facing for a clutch, but it wi ll be understood that, where appropriate, such references to a facing for a clutch refer also to any friction element made by a simi lar process.

Many di ferent compositions of the fi laments, and tapes, have been used in winding such preforms, for example, a composition as disclosed in British patent specificat on No. 2,096,654.

In present methods of winding a fi lament, or a tape, into a generally disc-shaped preform, the fi lament, or tape, is guided on to a rotating face plate by a guide which is moved in a displacement plane around a path. The shape of the path is deter¬ mined by a rotating cam. The winding pattern of the fi lament, or tape, on to the face plate can only be varied by changing the cam for one with a different profi le and only relatively simple winding patterns are possible.

It is an object of the present invention to provide a method of winding a fi lament, or a tape, into a generally disc-shaped oreform suitable to

be cured to form a friction element which allows the preform to be wound without relying on the shape of a cam to determine the movement of the guide thereby enabling more complex and consistent winding patterns to be used.

The invention provides a method of winding a filament, or a tape, into a generally disc-shaped preform suitable to be cured to form a friction element, the method comprising rotating a face plate about an axis, the face plate having a substantially planar surface extending radially of said axis, and guiding said f lament, or taoe, on to said planar surface by means of a guide which is movable in a displacement plane to determine the pattern in which the filament, or tape is wound on to the planar surface, characterised in that the method also comprises producing a plate position signal representative of the angular position of the face plate about said axis, producing a demand signal representati e of a demanded position of the guide in the displacement plane, the demand signal being produced in response to the plate position signal and varying therewith to provide a predeterm ned winding pattern, producing a feedback signal representative of the position of the guide in the displacement plane, and moving the guide in the displacement plane as a function of the demand signal and the feedback signal by means of a closed loop control.

In a method in accordance with the invention, the winding pattern is controlled in accordance with a demand signal which allows greater complexity and

consistency than present cam-based methods. For example, the pattern can be different for different parts of a preform and it can be ensured that both ends of the fi lament, or tape, are at an inside edge of the preform which cannot be achieved with present methods. Problems of cam wear and delays whi le cams are changed are also avoided.

In a method in accordance with the invention, a speed signal may be produced representing the speed of displacement of the guide in the displacement plane, and the speed signal may be uti lised to limit the speed or acceleration applied to the guide. This provision can be used to reduce the possibi lities of whip- like effects occurring in the fi lament, or tape, and the possibi lity of breakage.

The invention also provides apparatus for winding a fi lament, or a tape, into a generally disc¬ shaped preform suitable to be cured to form a friction element, the apparatus comprising a face plate having a substantially planar surface, rotating means operable to rotate the face plate about an axis extending normally of the planar surface of the face plate, a guide for said fi lament, or tape, arranged to guide the fi lament, or tape, on to the planar surface of the face plate, and moving means operable to move the guide in a displacement plane to determine the pattern in which the fi lament, or tape, is wound on to the planar surface, characterised in that the apparatus also comprises angular position determining means operable to produce a plate position signal representative of the angular position of the face plate about said axis,

producing means ooerable in response to the plate position signal to produce a demand signal representati e of a demanded position of the guide in the displacement plane, the demand signal varying with the plate position signal to provide a predeter¬ mined winding pattern, guide position determining means operable to produce a feedback signal representative of the Dosition of the guide in the displacement plane, and closed loop control means operable to control the operation of the moving means so that the guide is moved in the disDlace ent Diane as a function of the demand signal and the feedback signal.

The moving means may be operable to move the guide arcuately in the displacement plane. In this case, the demand signal represents an angular position of the guide about the centre of curvature of the arc. The moving means may also be operable to move the guide linearly towards or away from the axis of the face plate, thereby enabling the position of the arc to be adjusted for a particular size of preform. The filament, or tape, in passing through the guide may pass through the centre of curvature of the arc along which the guide moves, thereby reducing the inertia of the guide.

The present invention will now be described by way of example with reference to the accompanying drawi ngs in wh ch:

Figure 1 is a perspective view of one embodiment of an apparatus, in accordance with the present invent¬ ion, for winding a filament, or tape, to provide a generally disc-shaped preform;

Figure 2 i llustrates in greater detai l a guide for the fi lament, or tape, included in the apparatus of Figure 1, the guide being shown mounted on moving means arranged to move the guide along a restricted arc by energisation of a motor of the moving means;

Figure 3 is a block diagram representative of the closed loop control means of the apparatus of Figures 1 and 2;

Figures 4 and 5 each i llustrate alternative combinations of a guide and moving means; and

Figure 6 shows di agrammat i ca I ly constituent layers of different patterns for the deposited filament, or tape, capable of being obtained by employing the apparatus of Figure 1.

The apparatus shown in F gures 1 to 3 is for winding a fi lament, or tape, 34 into a generally disc-shaped preform suitable to be cured to form a friction element in the form of a clutch facing. The apparatus comprises a dri lled face plate 12 which has a substantially planar vertically-extending annular surface 36. The plate 12 is mounted to rotate about a horizontal axis by being secured to the spindle 14 of a motor 16, the motor having an associated gear box 18. The motor 16 provides rotating means operable to rotate the face plate 12 about the horizont¬ al axis which extends normally of the planar surface of the face plate. The face plate 12 is included in a headstock of the apparatus. A co-operating tai lstock 20 of the apparatus is mounted on a spindle 22, coaxial with the motor spindle 14, and the spindle 22 is supported in a bearing 24. The motor 16 and the bearing 24 are mounted on a base, indicated general¬ ly at 26.

The face plate 12 has the diameter greater than that of the generally cylindricaLly-shaped motor 16, and partially resides in a transverse channel formed in the base 26 extending between the motor and the beari ng 24.

The tailstock 20 comprises an annular-shaped plate 28, of the same diameter as the face plate 26. The spindle 22 mounting the tailstock 20 is capable of reciprocating within the bearing 24, under the control of a displacing unit indicated generally at 30. The tailstock 20 is held against rotating with the face plate in any convenient manner, by means such as a second, anti-rotation, bearing (not shown) .

A radially extending rectangular aperture 32 is provided in the plate 28, through which aperture the filament, or tape, 34 is fed to be deposited on the opposing plane annular surface 36 of the face plate 12. The arrangement is such that the aperture 32 extends vertically. A plurality of smaller, radial¬ ly extending apertures 38 also are provided in the plate 28, these apertures being equi-angular ly separa¬ ted from each other over the part of the plate not containing the vertical aperture 32 for the filament, or tape, 34. Mounted for rotation about a radially extending axis within each of the smaller apertures 38 is a roller 40, the arrangement being such that each roller protrudes from its associated aperture at least on the side of the plate 28 opposite to the rotating face plate 12.

When the tailstock 20 is displaced by the unit 30 to one extremity of the stroke of its reciprocat¬ ing movement, the rollers 40 engage the surface 36

of the rotating face plate 12 or any filament, or tape, 34 deposited on the surface 36. Thus, the rollers 40 are caused to rotate with the surface 36, as the surface 36 rotates relative to the tailstock 20. The arrangement is such that the displacing unit 30 causes the rollers 40 to apply pressure to the deposited filament, or tape, 34, causing it to compact, and to form a required preform (not shown) of sufficient strength to be capable of being handled, before the preform is cured to form the required clutch facing. When a required preform has been produced on the surface 36 of the face plate 12, and the supply of the f lament, or tape, 34 to the face plate 12 has ceased, the displacing unit 30 is energised to cause the tai lstock 20 to move away from the face plate 12.

The completed preform is removed from the face plate 12 by actuation of a cut-off blade 42. One end of the blade 42 is pivotably mounted at 44 on a supporting arm 46, and is disolaced by an actuator indicated at 48. The arrangement is such that during the production of a preform the blade 42 is held at a home position spaced from the face plate 12. However, when the preform has been completed, and the tai lstock 20 has been moved away from the face plate 12, the blade is moved to be brought between the surface 36 of the face plate and the preform, to cause the release of the preform from the surface. Hence, the preform falls away from the surface 36, and is directed by a chute 50 away from the machine.

The supply of the filament, or tape, 34 to the face plate is then re-commenced, the tai lstock 20 is moved back into engagement with the face plate

12, and the production of the next preform is begun.

The approDriate amount of the filament, or taoe, 34 to form a required preform is supplied to the machine discretely in a bin (not shown). One extremity of the filament, or tape, is arranged to protrude from the bin; and when the bin is in its required location, this extremity is engaged by a Dair of feed rollers (not shown), and is fed, through a tube (not shown), and via a guide 52 arranged to guide the filament, or tape, on to the surface 36 of the face plate 12, to be secured thereto. Sub¬ sequently, the feed rollers are disengaged from the filament, or tape, and the filament, or taσe, is oulled from the bin by rotation of the face plate.

The guide 52 is inclined at any appropriate angle to the plane of the surface 36, but for the sake of simplicity is shown as extending at right angles thereto. The guide 52 may have any convenient form, but the illustrated embodiment is trumpet-shaped, the flared end of the guide facilitating the feeding of a Leading end of a discrete length of the filament, or taoe, through the guide. When leaving the other end of the guide, the filament, or taoe, is directed on to the surface 36 of the face plate 12, through the vertical aperture 32 in the plate 28 of the tail¬ stock, this end of the guide being opposite to the aperture 32.

Because, as the filament, or tape, 34 is wound on the face plate 12, it is required to be directed by the guide 52 on to positions of the surface 36 of the face plate at different radial distances from the spindle 14, the guide has to be displaced bi- directionally in an appropriate manner in a displace-

merit plane in which the guide extends. To this end, the apparatus comprises moving means operable to move the guide 52 in the disDlacement plane to deter¬ mine the pattern in which the filament, or tape, is wound on to the surface 36. In t is case, the moving means is a motor 56 which is operable to move the guide arcuately in the disolacement plane as indicated by the arrows 54 in Figure 2. The motor 56 is adjustably mounted within an aperature 57 through a rectangular-shaped bracket 58. A vertically extend¬ ing taper collet device, indicated generally at 60, is mounted on the horizontal axle 62 of the motor, with the guide 52 supported by this device.

The motor 56 extends horizontally on the opposite side of the bracket 58 to the guide 52. The taper collet device 60, and the guide 52, are displaced upon energisation of the motor 56. Over an extended period of use, wear on the motor 56 can be evened out by rotating the motor relative to the bracket 58, and the arrangement re-datumed via a location hole 64.

In order that the filament, or tape, 34 is deposited in a precise manner the arrangement of the moving means is required to be such that the guide 52 is displaced precisely to a position rep¬ resented by an instantaneous demand signal, as shown in Figure 3, the demand signal is supplied from a processor which provides producing means 66 to a closed loop control means 68. The producing means 66 also receives input data, so that there is obtained a sequence of electrical signals to drive the motor 56, causing the filament, or tape, to be deposited on the face plate 12 with a selected one of a plurality of obtainable winding actions.

The apparatus of Figures 1 and 2 also comprises angular Dosition determining means in the form of a shaft encoder 70 which is mounted on the spindle 14 of the motor 16. The shaft encoder 70 is operable to produce a plate position signal, in the form of a train of pulses, which is representative of the instantaneous position of the face plate 12 about the axis about which it rotates. These signals are suDplied to the producing means 66 which is operable n response to the plate position signal, a demand signal representative of the demanded, or desired, corresponding instantaneous position of the guide 52 in the displacement plane. The demand signal varies with the plate position signal to provide a predetermined winding pattern. Thus, the position of the guide 52 varies throughout the winding of a preform in correspondence to determined changes in the angular position of the face plate 12, so that a required winding action is obtained.

The apparatus also comprises guide position determining means in the form of a shaft encoder 80 mounted on the motor 56. The shaft encoder 80 is operable to produce a feedback signal reoresentati ve of the position of the guide 52 in the displacement p lane .

As is shown in Figure 3, the closed loop control means 68 is operable to control the operation of the motor 56 so that the guide 52 is moved in the displacement plane as a function of the demand signal and the feedback signal. The processor 66 receives the position feedback electrical signals from a shaft encoder 80 and energises the motor 56 through a servo- amplifier 84. The processor 66 controls the motor 56 essentially in accordance wi h the difference

between the demand signal and the feedback signal. However, the processor 66 also limits the speed or acceleration of the guide 52 by uti lising a speed signal. The speed signal is produced by speed detect¬ ing means in the form of a tachometer 84 mounted on the motor 56. The speed signal is representative of the speed of displacement of the guide 52 in the displacement plane. The speed signal could alternative¬ ly be produced by differentiation of the signals from the shaft encoder 80. In response to the receipt of simultaneous demand and feedback signals being supplied to the processor 66, there is determined any instantaneously requi red displacement of the guide 52, and there is provided to the motor 56 an electrical control signal to cause the required dis¬ placement of the guide to be obtained.

In an uni llustrated modification of the moving means of Figure 2, the taper collet device is omitted, and the guide 52 is mounted directly on the axle 62 of the motor 56 so that, the fi lament, or tape, in passing through the guide passes through the centre of curvature of the arc along which the guide moves.

An alternative moving means for displacing the guide 52 is shown in Figure 4. In this arrange¬ ment, the guide 52 is mounted on an arm 90 pivotted at a point 92 spaced from the guide. Mounted on the axle 62 of the motor 56 is a cam 94. The arm 90 bears directly on the profi led surface of the cam 94 under the action of a spring 96 held in com¬ pression between the arm and an anchorage 98. The cam 94 is in contact with a part of the arm 90 inter¬ mediate between the guide 52 and the pivot point 92, the arrangement being such that rotation of the

cam by the motor causes the arm, and hence, also the guide 52, to rotate over a restricted range, as indicated by the arrows 54.

A different moving means for displacing the guide 52 is shown in Figure 5. In this arrangement, the guide 52 is mounted directly on the moving member 100 of a linear motor 102, the linear motor having an integral position sensor (not shown), in response to energisation of the linear motor the guide is displaced as indicated by the arrows 104.

Shown in Figure 6 are constituent Layers of different patterns for the deposited filament, or tape, capable of being obtained by employing the machine described above.

Figure 6a is of a constituent Layer of a known pattern, in which the filament, or tape, 34 undulates in a regular manner over the whole of the annular- shaped planar surface 36 of the face plate 12, with the filament, or tape, being adjacent to a plurality of equi -angu lar Ly separated locations of each of the radially inner, and outer, peripheries of the surface. For convenience, all the Locations referred to above are shown as being uniformly distributed along the peripheries of the surface. Usually, however, the preform has a plurality of such layers, and the locations are not as shown in Figure 6a, but such that all the locations of the constituent Layers of the preform are equi-anguLar ly separated, the deposited pattern having the form of a rosette as shown in Figure 6b. In Figure 6b only three constit¬ uent layers of the pattern are illustrated, but the complete rosette may have more Layers.

Shown in Figure 6c is one layer of a known pattern comprising a spiral of the deposited fi lament, or tape 34, the spiral form extending over the whole of the annular-shaped planar surface of the face plate.

The apparatus described above is used in a method, according to the invention, of winding the fi lament, or tape, 34 into a generally disc-shaped preform. In the method, the face olate 12 is rotated at constant speed by operation of the motor 16. The fi lament, or tape, 34 is guided on to the planar surface 36 of the plate 12 by the guide 52 and the guide 52 is moved in the displacement plane by operation of the motor 56 to determine the pattern which is wound. In the method, a plate position signal is produced by the shaft encoder 76, and a demand signal is produced by processor 66 in response to the plate position signal. The demand signal may be calculated according to an equation or drawn from a memory in which it is stored in tabulated form. The demand signal varies with the plate position signal to give the predetermined winding pattern.

Also in the method, a feedback signal is produced, by the shaft encoder 80, representative of the position of the guide 52 in the displacement plane. The processor 66 operates the servo-amplifier 84 according to a function representing the difference between the demand signal and the feedback signal but subject to Limits on speed and acceleration derived from a speed signal produced by the tachometer 82.