FILAMENT WINDING MACHINE

Abstract: A machine for winding a tow of resin-wetted fibres (44) onto a laminar winding card (24) is arranged to rotate the card about an axis (B) lying in its own plane in a manner so as to describe a cardioid locus having a cusp (31) through which every point on the surface of the card processes, thereby enabling a tow laying-on head (32) to be located at a fixed position adjacent the cusp. The machine has the advantage of minimal wetted-tow length between the laying-on head and its feed means (33) which, together with its simple mechanical synchronisation, ensures reliable and consistent winding characteristics.

Description: FILAMENT WINDING MACHINE This invention relates to a winding machine for use in the manufacture of hoop-wound fibre-reinforced resin structures of substantially laminar form. It is well known to lay fibre reinforcements in selected directions in the manufacture of resin articles in order to secure specifically orientated qualities in the resultant article. In particular, it is known to engender hoop stresses in a cylindrical article by the inclusion of hoop-wound fibres. The manufacture of a hoop-wound cylinder is fairly simply achieved by machines which rotate a cylindrical former about its own axis so as to cause a tow of resin-wetted fibres to be drawn onto its circumference from a feed means having a laying-on head main¬ tained continguous with the circumference at the laying-on location so as to consolidate the fibres. These machines rely upon the axial symmetry of the cylinder to ensure that the laying-on location remains at a constant radial distance from the axis of rotation. Obviously, a more complex system is required for the fabrica¬ tion of hoop-wound articles which are not axi-symmetric, in order to maintain the laying-on head constantly in contact with the periphery of the article. Machines are known for fabricating flat panels, in which a resin-wetted fibre tow is wound onto a substantially laminar former, hereinafter referred to as a winding card. These normally operate on the principle of moving the laying-on head with respect to a fixed winding card, the laying-on head being mounted, together with a tow wetting means, on a carriage which runs on tracks surrounding the periphery of the card at a constant separation therefrom. Such machines require computer control to ensure consistency of the various feed parameters which include, for example, tow tension, tow velocity (upon which depends the resin volume picked up by the tow as it is drawn through the wetting means), and consolidation of the laid-on tow. It is also known to rotate a winding card about an axis lying in its own plane whilst applying the fibre tow from a laying-on head located on an articulated robot arm having complex computer control for following the periphery of the card, the wetting means being located at the fixed end of the arm. A disadvantage of this system is the long linkage length necessary between the moving and fixed ends of the arm, particularly when the length of the card, ie the diameter of the rotation locus, is great. The correspondingly long length of wetted tow that must therefore be drawn through the various rollers of the arm increases the risk of fouling. The present invention seeks to provide a machine for rotating a winding card about an axis in the plane of the card in a manner permitting the laying-on head to be located at a fixed position with a minimal wetted tow length. Accordingly, a filament winding machine for winding a resin- wetted fibre tow onto a substantially laminar winding card includes: a framework; a prime mover attached to the framework; a drive shaft journalled in the framework and driveable by the prime mover about a drive axis; a crank arm attached to the drive shaft so as to rotate therewith; a driven shaft journalled in the crank arm so as to be rotatable about a driven axis parallel with the drive axis and spaced therefrom by a crank length; a transmission mechanism coupled between the two said shafts, geared for rotating the driven shaft at half the speed of the drive shaft; a winding card securing means attached to the driven shaft and orientated so as to locate a median of the axial plane of the winding card in alignment with the driven axis, the winding card being selected to have a card length perpen¬ dicular to the said median which is four times greater than the crank length, thereby to provide that rotation of the drive shaft will cause the card length to describe a cardioid locus in a plane perpendicular to the drive axis, the cardiod having a cusp located at the orthogonally occurring intersection of the crank length with the card length; which machine further includes a resin-wetted tow feed means located outwardly of the cardiod locus adjacent the cusp. Preferably the transmission mechanism comprises: a drive sprocket centred on the drive axis and fixed to the framework; a driven sprocket centred on the driven axis and attached to the driven shaft, the driven sprocket being selected to have twice the diameter of the drive sprocket; and a continuous toothed drive belt or drive chain engaged between the drive sprocket and the driven sprocket. An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings of which Figures 1 and 2 are side and front elevations respectively of a filament winding machine fitted with a winding-card, Figure 3 is an enlarged part-section taken on line III-III of Figure 1 , Figure 4 is a diagrammatic representation of Figure 2 showing two distinct positions of the winding card, and Figure 5 is a plot of the locus of the winding card through 180° of revolution, as seen from the same viewpoint as Figure 4 and indicating the location of the feed means. The winding machine illustrated in Figures 1 and 2 comprises a framework 1 supporting a prime mover 2 and a pair of bearings 3 disposed in alignment on a drive axis A. A hollow drive shaft 4, externally journalled in the bearings 3, carries a crank plate 5 and a toothed drive ring 6 which is engaged with the prime mover 2 by a drive chain 7 (Figure 2). The drive shaft 4 and the crank plate 5 are depicted in section i n Figure 3 > revealing a fixed shaft 10 extending co-axially through the hollow drive shaft 4, which shaft 10 is secured at one end to the framework 1 by a clamp 11. The shaft 10 is maintained co-axial with the shaft 4 by a bearing sleeve 12 and extends through a clearance hole 13 in the crank plate 5 to support a drive sprocket 14 rigidly attached to the emergent end. The crank plate 5 extends through equal radii on either side of the drive axis A, one radius bearing a counterweight 15 and the opposing radius being provided with a drive belt cover plate 16, which plate together with the confronting portion of the crank plate 5 comprises the crank arm 17. A driven shaft 20 is journalled in a pair of bushes 19 located in the crank arm 17 and centred on a driven axis B parallel with and separated from the axis A by a crank length L. Attached to the shaft 20 interjacent the plates 5 and 16 is a driven sprocket 21 having a 2:1 relationship with the drive sprocket 14, with which it is coupled by a toothed drive belt 22. The driven shaft 20 supports a socket 23 comprising the winding card securing means, a winding card 24 of card length 4L being provided with a centrally disposed mandrel 25 which is located in the socket 23 and held therein by a transverse locking pin 26. In use, rotation of the drive shaft 4 causes the crank arm 17 to rotate about the drive axis, thereby tracking the drive belt 22 around the fixed drive sprocket 14. This movement of the belt 22 consequently causes the driven sprocket 21 to rotate the driven shaft 20 at half the speed of the drive shaft 4. Figure 4 illustrates two positions ϋf the winding card 24 and 24', one (24) being that shown in Figure 2 and the other (24') occurring when the crank length L has rotated counter-clockwise (as drawn) through an angle 2a. At this second position, the axial plane 30 of the winding card has been rotated through an angle a. Consequently the winding card will be rotated through 180° for every complete revolution of the drive ring 6. A fuller plot of the winding card positions obtained for one complete revolution of the crank arm 17 about the axis A appears in Figure 5, from which it will be readily seen that the perimetric curve of the locus of the card is equivalent to that followed by a point on the circumference of a circle having a diameter 2 L when rolled around another circle of equal diameter, ie a cardioid. The cardiod has a cusp 31 situated at the axis B where the crank length L Is perpendicular to the axial plane 30 of the card. The particular advantage of this locus Is that all points on the surface of the winding card must process through the cusp 31 , which cusp thus defines a fixed location adjacent which a laying-on head 32 of a resin-wetted fibre feed means 33 can be sited. With an infinitely thin winding card this procession would occur through a single spatial point, which spreads into a circle of increasing diameter as card thickness is increased. When the ratio of card length to card thickness is great, as in the case of a beam-like structure, the spread of the point is of no great significance. A suitable feed means 33 includes the laying-on head 32 com¬ prised in this embodiment by a leaf spring adjacent the winding card at the cusp 31, a feed eye 41, wetting-out rollers 42 supplied with resin from a resin pump 43, and a tow of fibres 44 which is drawn from a fibre creel 45 through the rollers 42, the eye 41 and the leaf spring 32 by the rotation of the winding card 24. Compensation for any significant spread of the cusp point which occurs when thick winding cards are wound may be achieved by mount¬ ing the head 32 on a cam-follower (not shown). The feed means 33 may be extended to comprise a multiple array perpendicular to the plane of Figure 5 so as to lay parallel tows simultaneously over the full width of the winding card. Alter¬ natively, the single head 32 and the eye 41 may be traversed perpen¬ dicularly to the said plane by appropriate drive means (not shown). The manner in which the winding card always presents itself to the laying-on head is advantageous not only in permitting a fixed location of the head, but also in reducing to a minimum the feed length of wetted tow, ie the distance of the wetting-out rollers from the winding card. Further advantage lies in the simple mechanical synchronization of the card and the crank, ensuring reliability and consistency throughout the winding process. The cardioid rotation of the winding card causes sinusoidal variation of the tow velocity. The amplitude of this variation is however 50% less than would be obtained by simple circular rotation of the card about its own axis. If desired, these sinusoidal variations can be reduced still further to provide a constant tow velocity by appropriate control of the speed of the prime mover.

Claims: CLAIMS 1. A filament winding machine for winding a resin-wetted fibre tow (44) onto a substantially laminar winding card (24) including: a framework (1) ; a prime mover (2) attached to the framework; a drive shaft (4) journalled in the framework and driveable by the prime mover about a drive axis (A);&crank arm (17) attached to the drive shaft (4) so as to rotate therewith; characterised by a driven shaft (20) journalled in the crank arm (17) so as to be rotatable about a driven axis (B) parallel with the drive axis (A) and spaced therefrom by a crank length (L) ; a transmission mechanism (14, 21, 22) coupled between the two said shafts, geared for rotating the driven shaft at half the speed of the drive shaft; a winding card securing means (23) attached to the driven shaft (20) and orientated so as to locate a median of the axial plane of the winding card in alignment with the driven axis (B) , the winding card being selected to have a card length perpendicular to the said median which is four times greater than the crank length (L) , thereby to provide that rotation of the drive shaft will cause the card length to describe a cardioid locus in a plane perpendicular to the drive axis, the cardioid having a cusp (31) located at the orthogonally occurring intersection of the crank length with the card length; said machine further including a resin-wetted tow feed means (33) located outwardly of the cardioid locus adjacent the cusp (31). 2. A filament winding machine as claimed in Claim 1 wherein the transmission mechanism is characterised by a drive sprocket (14) centred on the drive axis (A) and fixed to the framework (1); a driven sprocket (14) centred on the driven axis (B) and attached to the driven shaft (20) , the driven sprocket being selected to have twice the diameter of the drive sprocket; and a continuous toothed drive belt (22) or chain engaged between the drive sprocket and the driven sprocket.

Inventors: FOOT PETER, FOOT, PETER
Applicants: SECR DEFENCE BRIT, THE SECRETARY OF STATE FOR DEFENCE IN HER MAJESTY'
Application year: 1987
Main classification: B29C53
IPC codes: B29C53, B29C70, F16H37