107 Ball Bearing Analysis with the ORBIS Tool  

Jacob D. Halpin* 

Abstract    Ball bearing design  is critical to the success of aerospace mechanisms.  Key bearing performance  parameters, such as load capability, stiffness, torque, and life all depend on accurate determination of the internal load distribution. Hence, a good analytical bearing tool that provides both comprehensive  capabilities and reliabl e results becomes a significant asset to the engineer . This paper introduces the   ORBIS bearing tool.  A discussion  of key modeling assumptions  and a technical overview  is provided .  Numerous validation studies and case studies using the ORBIS tool are presented. All results suggest the  ORBIS code closely correlates to predictions on bearing internal load distributions , stiffness, deflection and  stresses.   

Introduction    ORBIS was first released to the public  in 2008 and has been actively maintained and enhanced since. The  program  was devel oped to modernize the state- of-the-art for bearing codes. Most prior industry stan dard  tools came from  the MS -DOS era and required a flat -file type input deck for operation. While these codes  pioneered the analytical be aring industry they r equire d a fairly steep learning curve to operate proficiently.  With the advent  of 64- bit processors in  modern computer technology , support for MS -DOS  has declined  rapidly  leaving software programmers with the burden to update their co des. Unfortunately, many   developers of the early  bearing tools are no longer around to maintain their codes .    The development approach for  ORBIS began with selection of the Java programming language for its  foundation. Java was initially selected because it runs on a virtual machine that is supported by  most   computer platform s (i.e., Windows, Mac OS, Unix) . Also,  the widespread popularity of Java over the internet  gave confidence that  it would  be actively supported for m any years to come. Some additional fringe benefits  of the Java  language that proved particularly  useful during the development stages  were its object -oriented  programming environment and support of  multi- threaded processing.  

The core bearing model used w ithin ORBIS is based on A. B. Jones’ mathematical theory of roll ing element  bearings  [1]; herein referred to as the Jones model.  This model provides  a nonlinear solution to an entire  system  of bearings  and has been the industry  standard for many decades. The primary handicap to the  Jones model is its inherent fixed ring  assumption. This assumption is generally  not tolerable for modern  aerospace bearing designs , particularly those that utilize thin section bearings. ORBIS addresses this by  including ring compliance algorithms into the core solver . These algorithms determine ring strain  during the  mounting,  preloading, and thermal expansion stages of the solver, thereby g reatly improving model  accuracy . A more thorough discussion on key bearing modeling assumptions is provided herein .   To validate the ORBIS code a multi -tiered approach is taken. First, the core solver  is compared against the  A. B. Jones High Speed Ball and Roller Bearin g Analysis Program . This comparison study includes  twenty - nine different configurations and results such as maximum mean Hertzian contact stresses, bearing row  displacements, row reaction forces, and row stiffness components are evaluated.  Since these cases must  use a fixed ring assumption t o match the A. B. Jones program , the next validation step focuses on the ring  compliance  algorithms. In this study , Alan Leveille’s codes  BRGS10 and BRGS14 are compared in a case  study that was jointly  run by Brian Gore from Aerospace Corporation and Steve Koss from Naval Research                                                         * Halpin Engineering LLC, Torrance, CA  

Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames Research Center, May 4-6, 2016