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Investigation of Spherical Bearings for Use in the Ultraform Finishing Polishing Process

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Investigation of Spherical Bearings for Use in the Ultraform Finishing Polishing Process Rochester Institute of Technology RIT Scholar Works Theses 11-24-2014 Investigation of Spherical Bearings for Use in the UltraForm Finishing Polishing Process Randall Scott DeFisher II Follow this and additional works at: https://scholarworks.rit.edu/theses Recommended Citation DeFisher, Randall Scott II, "Investigation of Spherical Bearings for Use in the UltraForm Finishing Polishing Process" (2014). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. R·I·T Investigation of Spherical Bearings for Use in the UltraForm Finishing Polishing Process by Randall Scott DeFisher II A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Engineering Kate Gleason College of Engineering Department of Mechanical Engineering Rochester Institute of Technology November 24, 2014 Committee Approval Investigation of Spherical Bearings for Use in the UltraForm Finishing Polishing Process by Randall Scott DeFisher II Dr. Stephen Boedo Signature: ____________________________ Professor, Thesis Advisor Date: ____________________________ Department of Mechanical Engineering Dr. Agamemnon Crassidis Signature: ____________________________ Associate Professor Date: ____________________________ Department of Mechanical Engineering Dr. Mario Gomes Signature: ____________________________ Assistant Professor Date: ____________________________ Department of Mechanical Engineering Dr. Steven Weinstein Signature: ____________________________ Professor Date: ____________________________ Department of Chemical Engineering Abstract UltraForm Finishing (UFF) is a production-level optical polishing process consisting of a moving belt that is pressed into an optical surface by a carrier wheel. The current configuration is comprised of a cylindrical carrier wheel attached to cylindrical roller bearings. As the optics market is moving towards aspheric geometry with smaller radii of curvature, geometric limitations associated with roller bearings requires the development of a modified approach to the UFF process. This thesis explores the feasibility of incorporating spherical fluid bearing elements in the UFF process as a replacement for roller bearings. Self-acting (or wedge film) and externally pressurized hydrostatic spherical fluid-film bearings were investigated for the UFF process. The self-acting bearing was modeled and analyzed using a previously developed hydrodynamic finite element computer program. The hydrostatic bearing was modeled using an analytical formulation of the Reynolds equation coupled with empirical data to account for entrance flow effects at the feed hole and to account for pressure drops in the bearing fluid supply system. Both bearing configurations predicted adequate fluid film thickness under steady load and speed. Performance tests on the UFF were completed with both bearing configurations under steady load and speed. Ball to cup seizure was observed with the self-acting configuration nearly immediately after initial load and speed application, with seizure presumably due to inadequate squeeze film resistance during the transient startup period. The hydrostatic bearing operated successfully over a wide range of applied loads and speeds employed in the current UFF process with minimal cup and ball wear. The feasibility of the hydrostatic spherical bearing element in the UFF process was subsequently demonstrated through the generation of repeatable and acceptable removal function maps which were then employed in the polishing of a planar optical surface. i Acknowledgements I would like to recognize my advisor Dr. Stephen Boedo for the support and guidance over the last several years. I learned a great deal from his professional insight and expectations of excellence. To the committee, and the faculty of the Mechanical Engineering department at the Rochester Institute of Technology for sharing their time and knowledge. The technical and financial support of OptiPro Systems and its president Mike Bechtold has made this thesis possible. My colleagues at OptiPro were instrumental with the experimental portion of this thesis, and I am very thankful for their help and creativity. I am grateful for my parents Lynda and Randy, and my sister Amanda for encouraging higher education and demonstrating lifelong learning. Finally, I’d like to thank my loving wife Meghan. I will forever appreciate your patience and support throughout the entirety of my graduate studies. ii Table of Contents Chapter 1: Introduction ....................................................................................................... 1 1.1 UltraForm Finishing .............................................................................................. 1 1.2 Current System Design and Limitations ............................................................... 3 1.3 Thesis Goals .......................................................................................................... 4 Chapter 2: UltraForm Finishing with Spherical Bearings .................................................. 5 2.1 Machine Description ............................................................................................. 5 2.1.1 Bearing configurations .................................................................................... 6 2.2 Machine Operation ................................................................................................ 7 2.2.1 Belts, Coolants, and Slurries ........................................................................... 7 2.2.2 Applied Loads ................................................................................................. 8 2.3 Metrology ............................................................................................................ 10 Chapter 3: Spherical Bearing Design ................................................................................ 11 3.1 Fluid Film Lubrication ........................................................................................ 11 3.1.1 Hydrostatic .................................................................................................... 11 3.1.2 Squeeze.......................................................................................................... 12 3.1.3 Wedge............................................................................................................ 12 3.2 Self-Acting Bearing Analysis.............................................................................. 13 3.2.1 Meshing ......................................................................................................... 13 3.2.2 Solving .......................................................................................................... 14 3.3 Comparison of Self-Acting Bearing with Known Literature .............................. 14 3.3.1 Dimensional Design Constraints ................................................................... 18 3.3.2 Dimensional Design Charts ........................................................................... 19 3.4 Hydrostatic Bearing Analysis.............................................................................. 21 iii 3.4.1 Reynolds Equation ........................................................................................ 23 3.4.2 Pressure Distribution ..................................................................................... 24 3.4.3 Flow ............................................................................................................... 26 3.4.4 Entrance Effects ............................................................................................ 27 3.4.5 Supply pressure ............................................................................................. 27 3.4.6 Load ............................................................................................................... 27 3.4.7 Design Strategy ............................................................................................. 28 Chapter 4: Experimental Results ...................................................................................... 29 4.1 Bearing Manufacturing ....................................................................................... 29 4.2 Tensioner Load .................................................................................................... 32 4.3 Belt Compression Load ....................................................................................... 33 4.4 Calibration of Fluid Delivery Pressure Loss ....................................................... 35 4.5 Self-Acting Bearing Results ................................................................................ 37 4.6 Hydrostatic Bearing............................................................................................. 39 4.6.1 Dimensional Results with Hydrostatic Analysis ........................................... 40 4.7 Removal Functions .............................................................................................. 46 4.7.1 Multiple Removal Function Creation ............................................................ 47 4.7.2 Removal Function Topography and Load ..................................................... 49 4.8 Polishing a Flat Optic with the Hydrostatic Bearing..........................................
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