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Models for Steady and Nonsteady Coulomb Torque in Ball Bearings.

N8821208

Publication Date	1987
Personal Author	Todd, M. J.
Page Count	12
Abstract	For steady state torque estimation in ball bearings (equilibrium rolling and spinning of the ball), two alternative models are assessed against experimental data from typical space mechanism bearings. The calculation of steady torque requires a measured value of sliding friction coefficient between ball and race. In small-angle oscillations, where the rolling/spinning motion of the ball does not reach an equilibrium value, the torque describes hysteresis loops whose size and shape depend upon the amplitude of oscillation. A method of loop estimation based upon the Dahl fit and with a quantitative estimate of the initial stiffness, i.e., the torque per unit angle is discussed. Predictions are compared with experiment. It is concluded that in a bearing with many balls or with thin-section, easily distortable rings, it is necessary to allow for nonuniform loading at the points of contact.
Keywords	Ball bearings Spacecraft components Torque Tribology Kinematics Prediction analysis techniques Sliding friction Foreign technology
Source Agency	NASA Foreign Exchange Program
NTIS Subject Category	41L - Tribology 94 - Industrial & Mechanical Engineering 84G - Unmanned Spacecraft 84C - Manned Spacecraft
Corporate Authors	National Centre of Tribology, Risley (England). European Space Tribology Lab.; National Aeronautics and Space Administration, Washington, DC.
Supplemental Notes	In Esa, Proceedings of the 3rd European Space Mechanisms and Tribology Symposium p 137-148. Sponsored by Esa/Estec, Noordwijk, the Netherlands.
Document Type	Analytic Daughter
NTIS Issue Number	198817

Models for Steady and Nonsteady Coulomb Torque in Ball Bearings.

Models for Steady and Nonsteady Coulomb Torque in Ball Bearings.
N8821208

Publication Date	1987
Personal Author	Todd, M. J.
Page Count	12
Abstract	For steady state torque estimation in ball bearings (equilibrium rolling and spinning of the ball), two alternative models are assessed against experimental data from typical space mechanism bearings. The calculation of steady torque requires a measured value of sliding friction coefficient between ball and race. In small-angle oscillations, where the rolling/spinning motion of the ball does not reach an equilibrium value, the torque describes hysteresis loops whose size and shape depend upon the amplitude of oscillation. A method of loop estimation based upon the Dahl fit and with a quantitative estimate of the initial stiffness, i.e., the torque per unit angle is discussed. Predictions are compared with experiment. It is concluded that in a bearing with many balls or with thin-section, easily distortable rings, it is necessary to allow for nonuniform loading at the points of contact.
Keywords	Ball bearings Spacecraft components Torque Tribology Kinematics Prediction analysis techniques Sliding friction Foreign technology
Source Agency	NASA Foreign Exchange Program
NTIS Subject Category	41L - Tribology 94 - Industrial & Mechanical Engineering 84G - Unmanned Spacecraft 84C - Manned Spacecraft
Corporate Authors	National Centre of Tribology, Risley (England). European Space Tribology Lab.; National Aeronautics and Space Administration, Washington, DC.
Supplemental Notes	In Esa, Proceedings of the 3rd European Space Mechanisms and Tribology Symposium p 137-148. Sponsored by Esa/Estec, Noordwijk, the Netherlands.
Document Type	Analytic Daughter
NTIS Issue Number	198817