Patent Application
20080272221
The technology described here may be manufactured, used, or licensed by or for the United States government.
The technology described here generally relates to tensioning of fibers.
Filament winding processes have been used to produce a variety of products, such as pressure vessels, pipes, rocket motor casings, tanks, and gun barrels, by winding a continuous fiber or filament onto a rotating mandrel in a pre-determined pattern. These wound structures are often formed from advanced composites, including a combination of fibers, such as carbon, graphite, and/or Kevlar™, and a matrix, such as polyester, epoxy, or vinyl ester.
A conventional “wet-winding” process is schematically illustrated in
Various tensioning techniques are available for providing tension in the fiber 2 in order to promote alignment and compaction in the filament-wound article 10. For example,
Such static bars 20 are often used in conjunction with creel racks for holding bobbins or spools of “outside-pull” fibers which are unwound from the outside of a bobbin, spool, or other packaging. During filament winding, the package is mounted on the creel, and the fiber is pulled from the outside diameter of the package. Such creel frames typically incorporate either a mechanical, or electro-mechanical, system for applying controlled levels of torque to the spool and, consequently; of tension to the fiber as it is unwound from the spool.
U.S. Pat. No. 4,545,548 to Kato et al., is incorporated by reference here in its entirety and discloses an equal tension wire winding device. The device pays out thin wires from a plurality of wire reels and then winds them on a take-up bobbin. The Kato et al. device includes a plurality of revolving shafts, which are juxtaposed next to one another on a base, and support reels upon which the wires are coiled. Two pulleys are mounted on opposite ends of the revolving shafts, and a plurality of braking belts are trained between the neighboring pulleys for producing sliding friction. Rollers engage with the braking belts to adjust the tension in the belts. If some of the revolving shafts rotate at a higher or lower velocity, the associated braking belts will move so that variations in the rotation are suppressed by the neighboring shafts and the tension in the wires paid out from the wire reels is consistently maintained.
These and other tensioning devices may suffer from a variety of drawbacks. For example, as the fiber or other filament is pulled from the spool under high tension, the fiber can be damaged as the outermost fiber abrades against the underlying fiber upon which it is wound. This abrasive damage upon is compounded as the tension increases and the normal force acting on the wrapped fiber increases. Even at relatively low levels of tension, compared with the tensile strength of the fiber, this damage can quickly accumulate until the fiber breaks.
The technology described below generally relates to a fiber tensioning device which includes a frame, a plurality of axles rotatably supported by the frame, each axle having a drum that engages the fiber, each axle also having a wheel, a belt for coupling each of the wheels, and a brake for controlling the belt. For example, the wheel may include a gear and the belt may include a chain. At least some of the axles may be arranged substantially parallel to each other in a plane and/or may be supported on the frame by a friction-reducing bearing. Furthermore, each drum may include at least one groove for receiving the fiber
The technology described below also generally relates to a fiber tensioning device including a first drum arranged substantially parallel to a second drum, at least one fiber guide arranged between the first and second drums for maintaining a spacing between passes of the fiber extending between the drums, and a brake for controlling a rotation of at least one of the drums. For example, the fiber guide may include a plurality of axially-aligned sheaves arranged substantially parallel to the first and second drums, and each sheave may have a groove for receiving a pass of the fiber between the first and second drums. One or more pairs of fiber guides may be arranged substantially parallel to each other for maintaining a spacing between passes of the fiber extending between each side of the drum.
The technology described below also generally relates to a fiber tensioning device including a first drum, a second drum arranged substantially parallel to the first drum, the fiber being wrapped around and extending between the first and second drums, a brake for controlling a rotation of at least one of the drums, and means, arranged between the first and second drums, for maintaining a spacing between passes of the fiber extending between the drums. For example, the spacing means may further include a pair of fiber guides arranged near each of the first and second drums for maintaining a spacing between passes of the fiber extending between each side of the drum. Each of the fiber guides may include a plurality of axially-aligned sheaves arranged substantially parallel to the first and second drums, where each sheave may have a groove for receiving a pass of the fiber between the first and second drums.
These and other aspects of this technology will be described with reference to the following figures which are not necessarily drawn to scale, but use the same reference numerals to designate similar components throughout each of the several views.
As best shown in
As best illustrated in
The illustrated axles 34 are arranged on flange-mounted friction-reducing bearings 46 which may include any suitable bearing, including, but not limited to ball bearings and journal bearings. Also supported by the frame 32 is a brake 42 for controlling the belt 40 and providing the appropriate level of torque to the wheels 36. For example, the brake 42 may be supported on the frame 32 by a bracket or other mounting device 50. Friction-enhancing bearings may also be used to increase the torsion resistance of the axles 34.
As best illustrated in
For a given material in the fiber 2 (including, but not limited to carbon, fiberglass, cotton, nylon, and etc.), the number and arrangement of the drums 36 around which the fiber 2 is threaded can be chosen so as to balance between minimizing the length of the fiber that interacts with the drums 36, (i.e., using the lowest number of drums) while also maintaining sufficient contact between the fiber 2 and the drums 36 so that slip between the fiber and drums is eliminated. Thus, some or all of the drums 36 may make contact with fiber 2. The sizes, configuration, and/or number of rolling drums 36 around which the fiber 2 passes may be optimized in order to minimize the length of the fiber 2 upon which the tensioning device 30 acts while maintaining a condition of no-slip. For example, in a typical configuration for the illustrated fiber tensioning device 30, the fiber 2 may make contact with between four and eight of the disk-shaped drums 36 illustrated in
After passing over the drums 36, the tensioned fiber may be arranged to pass through exit guide elements 48 that direct the fiber 2 to be properly deposited on the mandrel 10 or other structure which may be arranged on a winding device 12 (not shown in
Turning now to
The spacing elements 52 include several axially-aligned sheaves or pulleys arranged substantially parallel to the drums 36 on friction reducing bearings 46. For example, each sheave may have a groove for receiving a single pass of the fiber 2 between the drums. In this configuration, the drums 36 and/or spacing elements 52 are arranged on the frame 32 substantially parallel to each other and secured on friction reducing bearings 46.
Although the frame 32 shown in
In addition to, or instead of the illustrated spacing elements 52, some or all of the drums 36 may be provided with slots or grooves 54 or other surface texturing to perform the same or similar functions as the spacing elements 52. When provided on the drums 36 from the embodiment illustrated in
Each of the drums 36 in
After the fiber passes around the first drum 36, it is directed back toward the second drum 36. The guide elements 52 may be arranged to shift or index the fiber 2 along the length of the rolling drums 36 during passes between drums 36. For example, as shown in the schematic top view of
As shown in the schematic cross-sections of
It should be emphasized that the embodiments described above, and particularly any “preferred” embodiments, are merely examples of various implementations that have been set forth here in order to provide a basic understanding of various aspects of the invention. One of ordinary skill will be able to alter many of these embodiments without substantially departing from the scope of the invention defined solely by a proper construction of the following claims.
