Fibre laying machine, presser assembly therefor, and method of laying and compacting fibre tows

Abstract: A segmented presser assembly (100) for laying fibre tows (14) and producing composite plastic articles has a plurality of presser element disks (113, 114, 115). The disks, stacked side-by-side, are independently movable and biased against a work surface (104) such as a mandrel or mold. An elastic band (121) is provided on the rotary outer periphery of each disk. Each band is unconnected to elastic bands on adjacent disks. Some at least of the disks (114, 115) and their respective bands (121) are radially movable during the laydown and compaction of the fibre tows over the changing contour of the workpiece surface. The elastic band has a low friction face, such as, for example, a "Teflon" film, for engaging the fibre tows.

Description: This invention relates to fibre laying machines. More particularly this invention relates to segmented presser assemblies employed in placing and compacting fibre tows onto a work surface or form and a method of laying and compacting fibre tows onto a workpiece. Fibre tow laying machines and fibre tape laying machines are well known in the art and enjoy increasing usage to produce composite plastic parts, especially in aerospace applications, to replace comparable metallic parts. These composite plastic parts advantageously have a high strength to weight ratio, are producible in complex shapes that eliminate the need for several individual metallic parts, exhibit corrosion resistance and have other desirable physical properties (e.g. low electrical and heat conductivity). Various fibre tow laying machines and improvements thereto have been described in the literature of the art and the distinctions and advantages of these machines over filament winding and tape laying machines has been well documented (see for example US Patent 4,699,683 to McCowin and US Patent 5,022,952 to Vaniglia). Fibre tow laying machines can individually feed and cut separate fibre bundles or tows forming a fibre band being laid down on a work surface or form. This selective cutting and feeding of tows advantageously allows the fibre placement head to put down the tows in an arcuate path on the work surface that prevents buckling, wrinkling or misalignment of fibres. The fibre tows, also known as tow pregs, are generally a bundle of continuous fibres impregnated with a resin (i.e. a polymeric material that may be in a cured, uncured or partially cured state). Many improvements have been made to fibre tow laying machines and fibre tape laying machines, and these improvements have been described in the literature of the composite plastics art, especially the patent literature. One of these improvements has been the segmented presser assembly. The segmented presser assembly generally has a series of side-by-side parallel arranged individual linearly movable presser elements that engage fibre tows to lay and compact the tows onto a work surface or form. The presser elements, which may be non-rotating or rotating elements, usually travel above and below a datum line. This improvement permits the presser assembly of the fibre tow laying and compacting head of a fibre tow laying machine to more easily and readily conform to changes in the contour of the work surface or form during the lay up procedure. Such segmented presser assemblies are described, for example, in US-A-4,292,108, US-A-4,601,775, US-A-4,867,834, US-A-4,869,774, US-A-5,015,326, US-A-5,045,147 and US-A-5,110,395. The prior art segmented presser assemblies commonly employ a resiliently deformable sleeve to cover and stretch across the fibre tow engaging faces of all the presser elements to form a continuous elastic or resilient fibre tow engaging surface for laying and compacting the fibre tows onto a work surface. This elastic sleeve is usually made of an elastomeric material such as elastomeric polyurethane. As the contour of the work surface changes during the lay up procedure the elastic sleeve deforms in response to the changing contour. This deformation of the sleeve is mirrored by linear movement of individual presser elements contacting the sleeve so that the presser assembly maintains contact with the work surface during changes in the surface contour. The segmented presser assembly and elastic sleeve combination improves the lay down and compaction of fibre tows onto a work surface because of the improved conformation of the presser assembly to changes in the work surface contour and improved contact of the presser elements with the work surface. Notwithstanding this combination produces other problems. One of the problems is the added spring force that the common sleeve induces on the presser elements as they are forced to move against the sleeve especially during compaction of the tows. This force varies in a spring-rate-like manner and increases as the presser elements move further away from the mid-travel datum line as in the case when laying down and compacting over a convex surface. Since the common sleeve induces a sleeve resistance on the presser elements as they move it is difficult to maintain a uniform pressure gradient across the compaction line as the presser assembly lays and compacts the fibre tows over a varying contour. The common sleeve effectively decreases the compaction force output capability of the presser elements thus causing the compaction line force to be nonlinear with presser element position. In the case of a presser assembly having compaction rollers moving with respect to a datum centerline, the sleeve resistance is unsymmetrical about the centre line and increases with each presser element location moving away from the centre line in either direction. A second problem is caused by the stretching or bulging of the common sleeve. As the presser elements move to conform to the changing contour of the work surface they induce a shearing-like force into the sleeve. This shear-like force causes the sleeve to bulge out and not maintain a tight fit to the presser element. The sleeve distortion or bulging may affect the incoming fibre tow feed path and tend to produce degraded lap/gap within the tow band, tow wander at end cuts and degraded end cut accuracy that may, in turn, lead to imperfections or defects in the composite plastic article and thus to unreliable and scrap articles, as well as increased costs and lower production. A presser assembly in accordance with the preamble of claim 1 and a method of laying and compacting of a fibre tape are disclosed in US patent: US-A-4 915 771. It is an object of this invention to provide a segmented presser assembly in accordance with claim 1 for a fibre tow laying machine having a fibre tow laying and compacting head which is compliant to adapt to changing contours across a lay up work surface while maintaining a substantially uniform compaction force across the entire compaction face when compacting fibre tows onto a work surface and a method of laying and compacting fibre tows in accordance with claim 11. Preferred embodiments are described in the dependent claims. There will now be given a detailed description, to be read with reference to the accompanying drawings, of a fibre tow laying machine having a segmented presser assembly which has been selected to illustrate this invention by way of example. In the accompanying drawings:- Figure 1 is a schematic perspective view of a fibre placement machine employing a fibre placement head having a presser assembly in accordance with this invention; Figure 2 is a side elevational view of the fibre placement head of Figure 1; Figure 3 is a view taken generally along line 3-3 of Figure 2, in partial cross section, of the presser assembly of this invention; Figure 3a is a view similar to Figure 3, showing the screw arrangement for assembling the presser assembly; Figure 3b is an enlarged view of a portion of two adjacent presser elements showing a gap between the elastic bands of the elements; Figure 4 is a view taken generally along line 4-4 of Figure 3 of the centre presser element of the presser assembly of this invention; Figure 4a is a sectional view, taken along the line 4a-4a of Figure 4, showing typical facial reliefs formed into the cores of the presser element disks; Figure 5 is a view taken generally along line 5-5 of Figure 3 of an intermediate presser element of the presser assembly of this invention; Figure 6 is a view taken generally along line 6-6 of Figure 3 of an end presser element of the presser assembly of this invention; Figure 7 is a view of the presser assembly of Figure 3 with the presser elements displaced according to the contour of the work surface; Figure 8 is a view in partial section of an alternative embodiment of the presser assembly of this invention; Figure 9 is a view taken generally along line 9-9 of Figure 8 of the centre presser element; Figure 10 is a view taken generally along line 10-10 of Figure 8; Figure 11 is a view taken generally along line 11-11 of Figure 8. Referring to Figure 1, a perspective view of a fibre tow laying machine 10 is illustrated which mounts a fibre tow placement head 12, having a segmented presser assembly according to this invention, in a position to apply fibre tows 14 onto a mandrel 16 rotatably carried on a pair of mandrel supports 18, 20. As used herein, the term "tow" is meant to refer to a composite strand consisting of a number of continuous fibres preferably impregnated with a binder or matrix material such as epoxy resin. The detailed construction and operation of the fibre tow laying machine 10 and mandrel supports 18 and 20 form no part of this invention. Reference should be made to US-A-5,022,952, assigned to the assignee of this application, for a detailed discussion of the fibre tow laying machine. The fibre tow laying machine 10 includes a base support 22 having substantially horizontally extending side rails 24, 26 which are interconnected by longitudinally spaced support beams 28. The side rails 24, 26 are connected at opposite ends to end panels 30, 32, each of which is supported by relatively short vertical legs 34. The base support 22 mounts a carriage 36 which comprises a pair of spaced beams 38, 40 interconnected by rods (not shown). Each of the beams 38, 40 has bearing blocks 50, 51 at opposite ends which slidably engage ways 52, 53 respectively mounted on the side rails 24, 26 of base support 22. Movement of the carriage 36 with respect to the base support 22 is effected by a rack and pinion drive. An elongated gear rack 54 is mounted to the underside of side rail 24 of base support 22 which is drivenly connected to a pinion (not shown) mounted to a gear box 55 and motor 56 connected by a support 57 to the carriage 36. Rotation of the pinion by operation of the motor 56 and gear box 55 causes the carriage 36 to move along the gear rack 54 parallel to the longitudinal axis of the base support 22, i.e. along the X axis as depicted in Figure 1. A cross slide 58 is pivotally mounted on opposite sides to a pair of bearings 60 each carried on a vertical column 66, one of which is shown in Figure 1. The vertical columns 66 in turn, are mounted on the beams 38, 40. A pair of ways 67 are mounted to cross slide 58, one of which is shown in Figure 1, which are carried by forward bushings 71 mounted to a tilt saddle having laterally spaced support plates 68, 70. The rearward end of each way 67 is carried by a bushing 73 connected to each bearing 60. The forward end of each support plate 68, 70 of the tilt saddle mounts an arcuate rack 72, one of which is shown in Figure 1. Each arcuate rack 72 is drivenly connected to a pinion (not shown) connected to the output of a gear box 74 driven by a motor 76. A first gear box 74 and motor 76 pair is mounted to a side wall 77 connected to a beam 40, and a second gear box and motor pair (not shown) is mounted to a side wall 78 connected to beam 38. In response to operation of the motors 76 and gear boxes 74, the pinions drive arcuate racks 72 to pivot cross slide 58 on the bearings 60 in a substantially vertical direction, i.e. along a Y axis as depicted in Figure 1. A separate drive (not shown) is also provided to move the cross slide 58 along a Z axis wherein the ways 67 are movable along the bushings 71, 73. Additionally, motor 75 fixed to the rear of the cross slide 58 is drivenly connected by means (not shown) to rotate the fibre laying head 12 about the Z axis. One end of the cross slide 58 mounts a roll-bend-roll type robotics wrist 80 which carries the fibre laying head 12. The robotics wrist 80 is commercially available and is effective to move the fibre tow laying head 12 along a number of axes. Such motion provided by the robotics wrist 80 is in addition to the movement of cross slide 58 along the X axis with carriage 36, the pivotal and tilting movement of cross slide 58 along the Y axis and the cross feed movement of the cross slide 58 along the Z axis as described above. The fibre tow laying machine 10 is, therefore, capable of manipulating the position of the fibre tow laying head 12 along a number of axes with respect to the mandrel 16, and such motions are coordinated with the movement of the mandrel supports 18,20 by a controller (not shown) as discussed in detail in US-A-5,022,952. The operation of fibre tow laying machine 10 will now be further described with reference to Figures 1 and 2. The illustrated embodiment of the fibre tow laying machine 10 in Figure 1 is effective to supply a total of sixteen individual fibre tows 14 to a fibre tow laying head 12 for application onto the surface of mandrel 16. The fibre tows 14 are supplied from a creel assembly 82 carried on the cross slide 58 which includes eight individual spools 84 on one side and another eight spools (not shown) on the opposite side, each of which supplies a single fibre tow 14. These tows 14 are drawn from spools 84 over a fixed roller 86 and a redirect roller 88, both mounted on the creel assembly 82, and a second redirect roller 90 mounted to the housing 13 of the fibre tow laying head 12. The purpose of the redirect rollers 88 and 90 is to maintain the same relative spatial orientation of the fibre tows 14 passing between the fibre laying head 12 and the creel assembly 82 as the fibre tow laying head 12 is manipulated with respect to the mandrel 16 and creel assembly 82. The structure and operation of redirect rollers 88,90 forms no part of this invention per se. Eight fibre tows 14 are fed from the redirect roller 90 to an upper idler roller 92 (Figure 2) rotatably mounted to the fibre tow laying head 12 and the other eight fibre tows 14 are directed from redirect roller 90 to a lower idler roller 94 mounted beneath the upper idler roller 92. The fixed roller 86, redirect rollers 88, 90 and the upper and lower idler rollers 92, 94 all include an individual roller for each tow 14; the individual rollers are mounted side-by-side and are rotatable relative to one another so that each tow 14 can be fed to the fibre tow laying head 12 at independent rates from the creel 82. Fibre tows 14 are guided from the upper and lower idler rollers 92, 94 through a cooling assembly, a cut, clamp and restart mechanism and a guide chute to beneath segmented presser assembly 100 and hence onto the surface of mandrel 16 under segmented presser assembly 100. The eight fibre tows from the upper roller 92 are parallel and laterally spaced from one another forming upper tows 14a and the eight fibre tows from lower idler roller 94 are parallel and laterally spaced from one another forming lower tows 14b. The upper and lower tows 14a and 14b are staggered or offset from one another so that upon exiting the guide chute the upper and lower tows 14a and 14b are laid down side by side onto the surface of the mandrel 16 forming an essentially continuous-width fibre band 101 which is pressed against the mandrel 16 by segmented presser assembly 100. The cooling assembly, cut, clamp and restart mechanism and guide chute forming part of fibre tow laying head 12 form not part of this invention and their structure and operation are discussed and described in detail in US-A-5,110,395. Referring now to Figure 2 there is shown the fibre tow laying head 12 having a segmented presser assembly 100, for laying and compacting fibre tow 14 onto surface 104 of mandrel 16. The segmented presser assembly 100 is joined with a presser mount 102 and two side plates 105 (see Figure 3) by screws 106a, 106b, and carried by an attached slider 103 for moving segmented presser assembly 100 into and from engagement with surface 104 of mandrel 16. A compaction fluid cylinder 107, preferably a double-acting pneumatic cylinder, is mounted on bracket 108 attached to housing 13 and has a piston 109 passing through bracket 108 and joined to bracket assembly 110 mounted on slider 103 that moves slider 103 linearly on a linear slide table 103a to bring segmented presser assembly 100 into and out of compaction engagement with surface 104 of mandrel 16 for compacting fibre tow 14. Cylinder 107 provides controlled compaction force on the fibre tow and sets the level of compaction force on the fibre tow applied to mandrel 16. A null fluid cylinder 111, preferably a pneumatic cylinder, mounted on bracket 108 has a piston 112 that engages bracket assembly 110 to hold segmented presser assembly 100, carried on slider 103 in a null position and zero compaction force engagement with surface 104 at the initiation of a fibre tow laying and compaction operation. The segmented presser assembly 100 will now be described with reference to Figure 3, a partial section taken along line 3-3 of Figure 2. A plurality of presser element disks having a centre disk 113, a pair of end disks 114, 114a and several identical intermediate disks 115 located between the centre disk 113 and the end disks 114, 114a are mounted on a housing afforded by a support block 116 between side plates 105 in a side-by-side stacked parallel array. Support block 116 is in two identical halves 116a, 116b joined together by screws 106a, 106b passing through the centre disk 113, each half 116a, 116b of support block 116, the side plates 105, and the presser mount 102 (see Figure 3a). The presser mount 102 is, in turn, carried on the slider 103 (see Figure 2). The centre disk 113, secured to support block 116 with two pins 117 (see Figure 4), remains stationary with respect to linear movement along a path coincident with the centre line W of the stacked array of disks. Intermediate disks 115 and end disks 114 are independently linearly movable on support block 116 in a path parallel to centre line W with changes in the contour of the surface of mandrel 16. Each of the disks has a low friction ball bearing 118 mounted on the periphery of the respective core 119, 119a, 119b, to provide rolling contact of the presser element disk with the surface 104 of mandrel 16 for laying and compacting fibre tows onto mandrel 16. The ball bearing 118 may be press-mounted onto the cores. The cores 119 of end disks 114 have a shoulder 120 that engages the ball bearing 118. A band 121 is attached to the outer periphery of ball bearing 118 on each presser element disk 113, 114, 115 that rotates with the bearing 118 and moves linearly with the linear movement of the presser element disk, independent of the rotary and linear movements of bands on adjacent presser element disks. Attached to and covering the outer periphery of each band 121 is a low friction film ring 122 that forms the fibre tow engaging surface or face of each presser element disk 113, 114, 115 and which has the same rotary and linear movements as the band 121 to which it is attached independent of the rotary and linear movement the low-friction film rings 122 attached to adjacent bands 121 on adjacent presser element disks. The band 121 is of a material that deforms and regains its original shape and size upon removing the force that produces deformation of the band 121. Any suitable resilient material may be used for the band 121 including, but not limited to, elastomeric polymers; for example, elastomeric polyurethane. The low friction film ring 122 is of a material that exhibits low friction against the fibre tow. For example, the low friction film ring 122 may be made of "Teflon" (Teflon is a registered trademark). There is provided in the segmented presser assembly 100 (shown in Figure 3) two fluid pressure bladder springs 123a, 123b extending through the intermediate presser element disks 115 and the end presser element disks 114. These bladder springs 123a, 123b apply fluid pressure to the movable presser element disks (i.e. the intermediate presser element disks 115 and end presser element disks 114) during the compaction of the fibre tows onto the mandrel 16. Each of the bladder springs 123a, 123b has an elastic membrane 124 enclosing a chamber 125 and is confined by the centre presser element disk 113, the respective side plate 105, intermediate presser element disks 115, end presser element disks 114, and the support block 116. Clamping plates 126, retained by socket head cap screws 126a, clamp and seal the membranes 124 to the support block 116. Ports 127 through the cap screws 126a provide fluid communication between passageways 128a,b, and the respective chambers 125. Fluid passageways 128a,b in turn, connect to fluid supply inlets 129a,b. Preferably the fluid used to pressurize the bladder springs 123a, 123b is compressed air. The clamping plates 126 have a lip 130 for engaging and holding elastic membrane 124 in place against support block 116. In operation, pressurised fluid (i.e. compressed air) is fed to the inlets 129a,b, through passageways 128a,b and ports 127 into chambers 125. As chamber 125 is pressurised, membrane 124 is forced against intermediate disks 115 and end disks 114 to move these disks toward the mandrel 16 and maintain contact of these presser element disks with the surface 104 of mandrel 16. The pressure of the compressed air is adjusted and maintained by a means (not shown) to provide constant contact of the presser element disks 114, 115 with surface 104 of mandrel 16. Centre disk 113, intermediate disks 115 and end disks 114 are spaced side-by-side so as to be close enough together to permit easy independent linear movement relative to each other. A gap 132 is provided between adjacent roller bearings 118, elastic bands 121 and low friction film rings 122, typically 0.005 inches (0.13mm) (see Figure 3b), sufficient to permit rotation and linear movement of the assembly of roller bearing 118, elastic band 121 and low friction ring 122 during the laying and compacting of fibre tows 14 onto mandrel 16. The structure and operation of individual presser element disks of segmented presser assembly 100 will now be further described with reference to Figures 4, 5, and 6 taken along lines 4-4, 5-5 and 6-6 respectively in Figure 3. In the preferred embodiment the centre presser element disk 113 (shown in Figure 4 in side elevation with partial section, taken along line 4-4 of Figure 3) is held stationary with respect to linear movement along a path coincident with centre line W (Figure 3) and perpendicular to a datum axis 131 by screws 106a, 106b and a pair of pins 117 passing through core 119a of centre disk 113 into both halves 116a, 116b of support block 116. Ball bearing 118, having on its outer periphery elastic band 121 to which is attached low-friction film ring 122, provides rolling contact of centre presser element disk 113 with fibre tow 14 during the laying and compaction of the tow 14 onto mandrel 16. Figure 4a illustrates shallow facial reliefs, R, which are formed into the sides of the cores of the presser element disks to reduce the sliding area. Intermediate presser element disk 115, shown in Figure 5 in side elevation with partial section, taken along line 5-5 of Figure 3, is mounted on the support block 116, for linear movement along a path parallel to centre line W (Figure 3) and perpendicular to a datum axis 131 (Figure 3), through a substantially rectangular opening 133 formed by side guide surfaces 134a,b in core 119b of intermediate presser element disk 115. The bladder spring 123a passes through the lower end of opening 133 so as to place the elastic membrane 124 of bladder spring 123a in contact with core 119b of intermediate disk 115, whereby the bladder spring 123a, upon being pressurised, can exert a force on intermediate disk 115 in a direction toward mandrel 16 causing intermediate disk 115 to apply compaction pressure or force on fibre tow 14 on surface 104 of mandrel 16. Free space is provided at the upper end of opening 133 to permit the linear movement of intermediate disk 115 with changes in the contour of surface 104 during the laying and compaction of fibre tow 14. Rolling contact of intermediate presser element disk 115 occurs with fibre tow 14 during the laying and compaction of fibre tow 14 by roller bearing 118 having elastic band 121 on its outer periphery and low friction film ring 122 on elastic band 121 engaging fibre tow 14. End presser element disk 114, shown in Figure 6 in side elevation with partial section, taken along line 6-6 of Figure 3, is mounted on the support block 116, for linear movement along a path parallel to centre line W (Figure 3) and perpendicular to the datum axis 131 (Figure 3), through a substantially rectangular opening 135 formed by side guide surfaces 136a,b in core 119 of end presser element disk 114. The bladder spring 123a passes through the lower end of opening 135 so as to place elastic membrane 124 of bladder spring 123a in contact with core 119 of end presser element disk 114 whereby bladder spring 123a, upon being pressurised, can exert a force on end disk 114 in a direction toward mandrel 16 thereby causing end presser element disk 114 to apply a compaction force on fibre tow 14 on surface 104 of mandrel 16. Free space is provided at the upper end of opening 135 to allow linear movement of end disk 114 in response to changes in the contour of surface 104 of mandrel 16. The ball bearing 118, on the outer periphery of core 119 and resting against flange 120 of core 119, and the band 121 and low friction film ring 122 carried thereby provide rolling contact between end presser element disk 114 and fibre tow 14 during the layup and compaction of tow 14. A change in the configuration of segmented presser assembly 100 with respect to the position of the presser element disks in response to a change in the contour of surface 104 of mandrel 16 from a flat contour shown in Figure 3 to V-groove or valley contour is depicted in Figure 7. The centre presser element disk 113 is stationary with respect to linear movement along a path that is coincident with centre line W and perpendicular to datum axis 131 and thus any adjustment of the spatial position of centre disk 113 with a change in the contour of the surface 104 of mandrel 16 requires that the entire segmented presser assembly 100 move accordingly. Such movement was discussed earlier in conjunction with Figure 2 for the movement of segmented presser assembly 100. In a situation where the centre presser element disk 113 would move into a valley contour of surface 104 during layup and compaction of fibre tow 14, the linearly movable intermediate presser element disks 115 and end presser element disks 114 would move in response to that change in contour so that they would maintain contact with and constant compaction force against the walls of the valley as is shown in Figure 7. To adjust to the change in contour of surface 104 so as to maintain such contact with and compaction force against the walls of the valley the elastic membrane 124 of bladder springs 123a, 123b deforms with the movement of the disks in a direction and amount consistent with the linear movement of the movable presser element disks. Pressurised fluid in chamber 125 of bladder springs 123a, 123b, pressing against elastic membrane 124 that, in turn, presses against intermediate disks 115 and end disks 114, and maintains these disks in contact with the walls of the valley under a constant compaction force. As discussed earlier in connection with Figure 2 compaction force or pressure is applied by the centre presser element disk 113 to tow 14 on mandrel 16 by the fluid cylinder 107 moving the segmented presser assembly 100 into engagement with surface 104 of mandrel 16. To maintain the compaction force applied by the centre disk 113, the pressure of the fluid in chamber 125 of bladder springs 123a, 123b is adjusted to a value which would prevent disengaging centre disk 113 from contact with surface 104 and/or reduce the compaction force being applied by centre disk 113. Further the fluid pressure in chamber 125 of bladder springs 123a and 123b would be kept at a value to provide compaction force being applied by the intermediate disks 115 and end disks 114 equal to the compaction force being applied by centre disk 113. This can be done by means for dumping pressurised fluid from or adding pressurised fluid to chamber 125. Such means for adjusting the pressure of the fluid in chamber 125 are well known in the art. In accordance with one embodiment of this invention each elastic band 121 and associated low friction film ring 122 on each linearly movable disk (i.e. intermediate presser element disks 115 and end presser element disks 114) moves independently of adjacent elastic bands 121 and associated low friction film ring 122 on adjacent linearly movable disks. Thus the elastic bands 121 and associated low friction film rings 122 are not connected together between adjacent disks. This is shown by the configuration of the upper end of the disks 113, 114, 115 of segmented presser assembly 100 shown in Figure 7. The independent movement of elastic bands 121 eliminates the spring or rubber band effect produced by a prior art continuous elastic sleeve or cover spanning adjacent linearly movable presser disks of a segmented presser assembly. Thus in accordance with this invention there is achieved a uniform compaction force applied, to the fibre tow, along the compaction line of contact between segmented presser assembly 100 and the fibre tows on the surface 104 of mandrel 16. An alternative embodiment of a segmented presser assembly in accordance with this invention is shown in Figure 8, in which there are fewer presser element disks than in the segmented presser assembly 100 of Figure 3. In this alternative embodiment, the low friction film rings 122 of Figure 3 are absent. The low friction film ring 122, that engages fibre tow 14 during laydown and compaction of the tow, is chosen so as to prevent sticking and/or high friction between the fibre tow engaging surface of the presser element disk and the fibre tow during the layup and compaction of the tow. Such prevention of sticking and/or high friction reduces or eliminates damage to the fibre tow, as well as poor tracking and misalignment of the tow on the surface of a mandrel or other work surface. Similar prevention of sticking and/or high friction between the fibre tow engaging face of a presser element (e.g. presser element disk) of a segmented presser assembly 138 can be achieved by having the elastic band 142 made of a material that has low friction and anti-sticking properties against the fibre tow. In Figure 8, the segmented presser assembly 138 has a centre presser element disk 139, with intermediate and end presser element disks 140, 141 at each side. Each of the presser element disks 139,140,141 has, on the outer periphery, an elastic band 142 of a resilient low friction material that provides the fibre tow engaging face of the disk for laying and compacting the tow. The centre presser element disk 139 does not have linear radial movement capability with respect to its central datum axis 143, whereas the intermediate and end presser element disks 140,141 are free to move with independent linear motion perpendicular with respect to the central datum axis 143 with changes in the contour of the surface of a mandrel or other work surface during layup and compaction of the fibre tow. A ball bearing 144 is provided on the outer periphery of the core 145 of each of the movable presser element disks 140, 141, and the core 145a of the centre disk 139, to give rolling engagement of each disk with the fibre tows during layup and compaction of the tows. The segmented presser assembly 138 has a bladder spring 146, extending through all of the presser element disks 139, 140,141, having a flexible membrane 147 forming a chamber 148 and engaging each of the disks of the segmented presser assembly 138. The membrane 147 extends through a small, close-fitting opening 139a in the centre disk 139 in order to span all of the disks. Pressurised fluid (e.g. compressed air) is supplied to inlet 149, and flows through passageway 150 in block 151; the fluid enters chamber 148 through ports 152 extending through flat head screws 153 used to mount a membrane clamping plate 154 to block 151. The plate 154 has a lip 155 that engages and holds the flexible membrane 147 against the block 151 to keep the membrane 147 in place. Block 151 has two halves 151a and 151b, held together by screws 156 and a pin 157 (see Figure 9), that capture the centre disk 139 and hold it stationary, with respect to linear movement normal the central datum axis 143. The halves 151a,b are piloted into the core 145a of the centre disk 139. The halves 151a are also fixed with the side plates 158 and mounting brackets 159a,b by pins 157. With reference also to Figures 10 and 11, block 151 passes through an opening 160 which runs through the movable presser element disks 140, 141 to carry and guide the disks 140, 141 for independent linear movement normal to the central datum axis 143. Pressurised fluid (e.g. compressed air) entering chamber 148 pressurizes bladder spring 146 causing flexible membrane 147 to apply a force (i.e. compaction force) on the movable presser element disks 140, 141 that, in turn, apply the compaction force on fibre tows on the surface of a mandrel or other work surface (e.g. mold). As in the case in Figure 3 the elastic bands 142 on adjacent presser element disks are separated from each other by a small gap that permits independent linear movement of the elastic bands 142, on adjacent disks, along with their associated presser element disks. The practice of this invention has been described with respect to a segmented presser assembly having a centre presser element that is stationary with respect to linear movement along a path parallel to or coincident with an imaginary line through the centre of the presser element and passing through the area of contact between the presser element and the work surface (e.g. mold surface or surface of a mandrel). It is recognized that this invention includes and may be practised with a segmented presser assembly wherein all presser elements are free to independently move linearly along a path parallel to or coincident with an imaginary line through the centre of the presser element and passing through the area of contact between the presser element and the work surface. Thus, the segmented presser assembly in accordance with this invention may comprise a plurality of presser elements wherein at least one of the presser elements is independently, linearly movable as previously described herein. Preferably the segmented presser assembly in accordance with this invention comprises a plurality of presser elements that are independently, linearly movable as previously described therein. The rotary motion of the presser elements in accordance with this invention may be achieved by various means well known in the art. One such means, namely an antifriction ball bearing, has been identified herein. In the embodiments of this invention described herein wherein an antifriction bearing is employed to produce rotary movement to the presser element (e.g. presser element disk) the bearing may be attached by a press fit onto the presser element. Various other methods, well known in the art, may be used to attach means for producing rotary motion to the presser element. In the practice of this invention the elastic band or elastic material layer may be adhesively attached to the presser element or may be attached to the presser element by other methods well known in the art which permit the deformation and recovery from deformation of the elastic band during layup and compaction of the fibre tows. The low-friction film may be attached to the elastic band with adhesive or other suitable means. Presser elements of the segmented presser assembly in accordance with this invention may be made of suitable rigid materials well known in the art, including but not limited to rigid plastic and metals such as steel and aluminum. The terms presser element and presser segment are interchangeably used herein and shall have the same meaning in respect to this description and the appended claims.

Claims: A presser assembly (100) for a fibre laying and compacting device for making a composite fibre article, comprising a plurality of independently, linearly movable individual presser elements (113, 114, 115) in a stacked side-by-side parallel array supported in a housing (105, 116), each presser element comprising an outer portion (119) extendable from the housing toward a workpiece surface (104) and being mounted for movement along an axis extending through the centre of the presser element and intersecting the area of contact between the presser element and the workpiece surface, there being provided on each outer portion an elastic material layer (121) which is independent of adjacent elastic material layers on adjacent presser elements, characterised in that each said presser element further comprises a means (118) for allowing rotary motion of the element. A presser assembly according to claim 1 wherein the outer portion of the presser element upon which said layer (121) of elastic material is provided is an outer periphery thereof. A presser assembly according to any one of the preceding claims comprising at least one presser element (113) that is stationary relative to adjacent linearly movable presser elements (115) in respect to movement along an axis extending through the centre of the presser element and intersecting the area of contact between the presser element and the workpiece surface (104). A presser assembly according to any one of the preceding claims wherein the elastic material layer (121) is an elastomeric polyurethane. A presser assembly according to any one of the preceding claims wherein the elastic material layer is provided on its outer face with a low friction material (122). A presser assembly according to any one of the preceding claims wherein a gap (132) is provided between adjacent presser elements. A presser element according to claim 6 wherein said gap is in the order of 0.13mm. A presser assembly according to any one of the preceding claims further comprising a bladder spring means (123, 124, 125). A fibre laying and compacting machine (10) comprising a machine base (22, 70), an arm (58) on the base, a robotics wrist (80) carried by the arm, and a presser assembly mounted on the wrist (80) for movement thereby about plural axes, the presser assembly being in accordance with any one of Claims 1 to 8. A machine according to Claim 9 comprising a creel assembly (82) for fibre tows mounted on the arm (58). A method of laying and compacting fibre tows onto a workpiece surface to produce a composite fibre article involving the steps: a) providing a segmented presser assembly (100) according to any one of Claims 1 to 8; b) supplying fibre tows (14) to the presser elements of said presser member; and c) laying and compacting the fibres tows onto a workpiece surface (104) by the presser elements of said presser member whilst substantially excluding fibre penetration between the presser elements of the presser member.

Inventors: VANIGLIA MILO M, VANIGLIA, MILO M.
Applicants: CINCINNATI MILACRON INC, CINCINNATI MILACRON INC.
Application year: 1995
Main classification: B29C70
IPC codes: B29C70