Dynamic Model Development and Characterization of Gear Bearing Transmission Systems: Theory and Experiments

The Gear Bearing Drive (GBD) is a newly developed actuator concept based on NASA's high-reduction gear bearing technology and brushless outrunner motor technology. Compared to conventional precision drive systems such as harmonic drives, the GBD offers similar advantages such as high torque in a compact assembly but with the potential of better stiffness characteristics and lower transmission friction and more predictable output speed response. In this paper, the open-loop behavior of a GBD prototype is experimentally characterized to obtain a dynamic model for its velocity/position response. Two analytical models for the transmission stiffness are developed using the bending flexure of gear-teeth and transmission geometry that accurately capture the stiffness characteristics. Finally, a sensitivity study is presented that reproduces the response of this transmission under various input and output loads. Analysis of the system dynamics suggests that the GBD behavior is dominated by linear dynamics that are characterized by finite friction dissipation and geometric errors in its gear mesh resulting from imperfect manufacturing. In addition, the transmission shows no unpredictable open-loop dynamics or transmission resonance within its speed range, making its closed-loop control problem a simple task.