The present invention relates generally to polishing fibers. More particularly, the present invention relates to polishing the side surfaces of thin fibers such as ceramic fibers.
Ceramic fibers are small-dimensional filaments or threads composed of a ceramic material, typically alumina, silicon carbide, and silica, often used in composite reinforcements, optical devices, and other high temperature applications. For example, transparent single crystal and polycrystalline ceramic fibers are currently being developed for optical and laser applications. Based on factors such as the fabrication processes used for producing the fibers, particular materials of the fibers, etc., side surfaces of the fibers are often rough or otherwise suffer from small surface defects. In particular, the side surfaces of polycrystalline ceramic fibers tend to be relatively rough because of grain boundary grooving during the fabrication process. Similarly, faceting and/or stepwise pullout for production of single crystal fibers results in relatively rough side surfaces of these fibers.
Though the side surfaces of ceramic fibers for structural applications are not as smooth as glass fibers, their tensile strength is typically between about 2-3 GPa. As a result of their high strength, surface roughness has not been a significant issue for structural applications (e.g., composite reinforcements) of ceramic fibers. On the other hand, a high surface roughness has been found to often impact performance of the fibers for optical applications. For example, a high surface roughness for transparent polycrystalline ceramic fibers results in high scattering coefficients for the fibers, which is detrimental for optical applications of the fibers.
Additionally, it may also be desired to reduce, provide consistency, or otherwise control the diameter of small-diameter fibers such as ceramic fibers after fiber production. However, there is no current system for altering the diameter of fibers post-production.
What is needed therefore is a system for efficiently and effectively polishing side surfaces of small-diameter fibers such as ceramic fibers. In addition to removing surface imperfections, a system for controlling/reducing the diameter of ceramic fibers after fiber production is desired.
According to one embodiment of the invention, the above and other needs are met by an apparatus for polishing a side surface of a fiber that includes a fiber loading mechanism, a polishing mechanism, and a linear motion mechanism. The fiber loading mechanism positions the fiber with respect to the apparatus. The polishing mechanism includes at least a first polishing pad having a first polishing surface and a second polishing pad having a second polishing surface. The polishing mechanism is configured to clamp the first polishing pad and the second polishing pad together such that the first polishing surface contacts the second polishing surface with a portion of the fiber disposed between the first and second polishing surfaces. The linear motion mechanism linearly translates one of the polishing mechanism and the fiber for polishing a side surface of the fiber after the first polishing pad and the second polishing pad are clamped together with the portion of the fiber disposed between the first and second polishing surfaces.
According to certain embodiments, the fiber loading mechanism is configured to axially rotate to thereby axially rotate the fiber secured to the fiber loading mechanism.
According to certain embodiments, the linear motion mechanism is configured to linearly translate the polishing mechanism while the fiber loading mechanism is stationary. According to other embodiments, the linear motion mechanism is configured to linearly translate the fiber while the polishing mechanism is stationary.
According to certain embodiments, the fiber loading mechanism includes a plurality of rollers and the linear motion mechanism is configured to linearly translate the fiber between the plurality of rollers.
According to certain embodiments, the polishing mechanism is configured to clamp the first polishing pad to the second polishing pad according to a plurality of clamping pressures.
According to certain embodiments, the apparatus further includes a tensioning mechanism to provide a desired tension to the fiber.
According to another embodiment of the invention, a method of polishing side surfaces of a fiber includes providing a polishing apparatus having a fiber loading mechanism, a polishing mechanism, and a linear motion mechanism for linearly translating one of the polishing mechanism and the fiber. The polishing mechanism includes at least a first polishing pad having a first polishing surface and a second polishing pad having a second polishing surface. The polishing mechanism is configured to clamp the first polishing pad and the second polishing pad together. The method further includes positioning the fiber in the fiber loading mechanism such that a portion of the fiber is disposed between the first polishing pad and second polishing pad of the polishing mechanism; clamping the first polishing pad and the second polishing pad together such that the first polishing surface contacts the second polishing surface with the portion of the fiber disposed between the first and second polishing surfaces; and linearly translating one of the polishing mechanism and the fiber for polishing at least a first side surface of the fiber.
According to certain embodiments, the linearly translating step includes linearly translating the polishing mechanism for polishing the first side surface of the fiber, and the method further includes unclamping the first polishing pad and the second polishing pad; axially rotating the fiber loading mechanism to thereby axially rotate the fiber secured to the fiber loading mechanism; re-clamping the first polishing pad and the second polishing pad together with the axially rotated fiber disposed between the first and second polishing surfaces; and linearly translating the polishing mechanism for polishing at least a second side surface of the fiber.
According to certain embodiments, the method further includes selecting a clamping pressure for application of the polishing mechanism against the fiber based on the strength of the fiber being polished.
According to certain embodiments, the linearly translating step includes linearly translating the polishing mechanism while the fiber loading mechanism is stationary. In other embodiments, the linearly translating step includes linearly translating the fiber while the polishing mechanism is stationary.
According to certain embodiments, the apparatus further includes a tensioning mechanism, and the method further includes adjusting a tension of the fiber by modifying the tensioning mechanism.
According to certain embodiments, the fiber includes a maximum diameter of one millimeter or less. In certain embodiments, the fiber is one of a monocrystalline, polycrystalline, and amorphous ceramic fiber having a maximum diameter of one millimeter or less.
According to certain embodiments, the fiber loading mechanism includes a plurality of rollers and the linearly translating step includes linearly translating the fiber between the plurality of rollers while the polishing mechanism is stationary. In some embodiments, the plurality of rollers includes at least a first spool and a second spool, and the linearly translating step includes unwinding the fiber from the first spool while re-winding the fiber with the second spool.
According to yet another embodiment of the invention, an apparatus for polishing a side surface of a fiber includes a fiber loading mechanism having a plurality of rollers for positioning the fiber with respect to the apparatus, a polishing mechanism, and a drive mechanism for linearly translating the fiber between the plurality of rollers such that the fiber transverses the polishing mechanism for polishing a side surface of the fiber.
According to certain embodiments, the plurality of rollers includes one or more spools for unwinding the fiber prior to polishing or winding the polished portion of fiber after polishing is completed.
According to certain embodiments, one or more of the rollers include an abrasive surface for forming the polishing mechanism.
Other embodiments of the invention will become apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
Referring to
While apparatus 10 may be used for polishing a side surface of virtually any type of fiber 12 (including polymer and metal fibers), the apparatus 10 described below is more specifically intended to be utilized in connection with single, polycrystalline, and amorphous ceramic fibers having a diameter of about one millimeter or less and a strength between about 300 MPa and about 5 GPa. According to certain embodiments, the apparatus 10 may be used to polish the side surfaces of ceramic fibers 12 having a diameter as small as about eight microns. While any polishing of the fibers 12 using apparatus 10 should reduce the surface roughness of the side surfaces of the fibers 12 and make the cross-sectional shape of the fibers more evenly rounded for improved performance, surface roughness of fibers 12 (as measured by root mean square or “RMS”) have been found to be minimized to as low as about 0.03 microns using apparatus 10 with a 0.5 micron diamond slurry for the polishing surfaces 33, 35 of the polishing mechanism 30. Lower surface roughness of fibers 12 are possible using a polishing slurry with smaller abrasive particles.
Referring specifically to
In certain embodiments, the opposing ends 22 of the fiber loading mechanism 20 are able to be manually moved between the fiber loaded position and the fiber loading position. For example, the opposing ends 22 may be biased (e.g., spring-loaded) to the fiber loaded position. To move the opposing ends 22 from the fiber loaded position to the fiber loading position, the opposing ends 22 are operatively connected to respective handle portions 24. Pushing in on the handle portions 24 separates the opposing ends 22. Releasing the handle portions 24 would then allow the natural bias of the fiber loading mechanism 20 to bring the opposing ends 22 back together for engaging the first end 14 of the fiber 12.
It should be understood that many other fiber loading mechanisms 20 may be used within the teachings of the present disclosure so long as the fiber loading mechanism 20 is able to sufficiently position the fiber 12 as desired. Further, the fiber loading mechanism 20 may be operated manually as described above or automatically using a CNC machining system. For example, fiber loading mechanism 20 may be in the form of a collet having a plurality of fiber loading segments (i.e., opposing ends) that are able to be tightened around the fiber 12 based on instructions from the CNC machining system. Other forms of the fiber loading mechanism 20 include, but are not limited to, adhesives, wedge grips, weave pulling grips, alligator grips, and one or more rollers or spools (as depicted in
According to certain embodiments, the fiber loading mechanism 20 is able to adjust its clamping pressure against the fiber 12 as desired. For example, different clamping settings may be provided and selected based on the strength of the fiber being polished. For example, strength of the commercially available alumina and silicon carbide fibers ranges between 2-3 GPa, so clamping pressure should be lower than 2 GPa of these fibers. While the fiber loading pressure may vary based on different factors including the strength of the fiber, the fiber loading pressure should typically be lower than the strength of the fiber.
As shown in
With continued reference to
According to certain embodiments, both the first polishing surface 33 and second polishing surface 35 will have an abrasive surface with an average abrasive particle size of less than about fifteen microns. In certain embodiments, the polishing surfaces 33, 35 of each polishing pad 32, 34 are easily removed and replaced. Thus, polishing surfaces having abrasive surfaces of varying average abrasive particle size may be utilized as desired. For example, according to certain embodiments, the abrasive particle sizes of the polishing surfaces 33, 35 could get successively smaller by replacing polishing pads 32, 34. In this regard, if the polishing surfaces 33, 35 with the smallest abrasive particle sizes are employed from the beginning, it may take a longer time to polish the fiber 12 as desired. Thus, if the fiber 12 is strong enough, pads 32, 34 with coarser polishing surfaces 33, 35 may be used at the beginning of the polishing and then replaced with pads 32, 34 having smaller abrasive particle sizes to reduce the polishing time. Similarly, when it is desired to reduce the diameter of fiber 12 while polishing, pads 32, 34 with coarse polishing surfaces 33, 35 can be utilized first to reduce the diameter and then replaced with pads 32, 34 having finer polishing surfaces 33, 35 to complete the polishing.
According to other embodiments of the invention, the first polishing surface 33 and second polishing surface 35 may be provided without embedded abrasive particles. According to this embodiment, the abrasive particles may be provided by pumping polishing slurries through flexible tubing to first polishing pad 32 and second polishing pad 34 in the clamped position as known in the art. According to this embodiment, various abrasive sizes can be used by changing the particular polishing slurry being pumped to the polishing surfaces 33, 35.
With reference to
In certain embodiments, the linear motion mechanism 40 includes a connecting arm 42 that fixedly connects the polishing mechanism 30 to the linear motion mechanism 40. According to this embodiment, the connecting arm 42 moves the polishing mechanism 30 when the linear motion mechanism 40 is linearly moved. One or more stabilizing tracks 44 may be provided to assist in holding the connecting arm 42 and polishing mechanism 30 steady while being moved between the first polishing position and the second polishing position.
According to certain embodiments, the linear motion mechanism 40 is a pneumatic linear actuator for providing precise and consistent linear movement of the polishing mechanism 30 based on instructions from the CNC machining system. In typical embodiments, the velocity of the linear motion mechanism 40 is between about 0.2 in/sec to about 20 in/sec, and most preferably about 3 in/sec to about 4 in/sec.
Referring to
It should be understood that fiber 12 may be axially rotated as many times as desired. The more times the fiber 12 is axially rotated, generally the more consistent the polishing of the finished fiber 12, though each additional axial rotation increases polishing time with increasing less effect on the end fiber. In typical embodiments, the fiber 12 will be axially rotated at least once (i.e., 45°), which will provide at least four immediate contact areas of the fiber 12 during as few as two movements of the linear motion mechanism between the first polishing position and the second polishing position.
While the linear motion mechanism 40 is shown in
Similarly, referring to apparatus 100 of the embodiment of
In other embodiments, one or more of rollers 120A, 120B, and/or 120C may include an abrasive surface for polishing the fibers 112. Rollers with abrasive surfaces may be a replacement for polishing pads 132, 134, or they may be in addition to the polishing pads. In certain embodiments, particularly when a roller includes an abrasive surface for polishing, one or more of the rollers may be stationary while the fiber translates/rolls across the roller. For example, roller 120A could be rotated by linear motion mechanism 140A while rollers 120B and 120C have an abrasive surface and are held stationary for polishing fiber 112 that is being linearly translated via the linear motion mechanism 140 rotating roller 120A.
According to certain embodiments, one or more of the rollers may be in the form of spools from which the fiber 112 can be wound and unwound. For example, referring to apparatus 200 of
It is noted that the embodiments exemplified in
Further, according to the embodiments of
The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 62/736,490, entitled “Apparatus for Polishing Side Surfaces of Fibers,” filed on Sep. 26, 2018, the entirety of which is incorporated by reference herein.
The invention described herein may be manufactured and used by or for the Government of the United States for all government purposes without the payment of any royalty.
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Number | Date | Country | |
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20200094367 A1 | Mar 2020 | US |
Number | Date | Country | |
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62736490 | Sep 2018 | US |