Modeling of geared positioning systems: An object-oriented gear contact model with validation

Abstract

In aerospace positioning actuators, gear efficiencies of 85% as well as breakout forces as high as 50% of the stall load of the actuator are observed at very low temperature conditions. Due to the low efficiency and high loading, stiction in these actuators is common which can lead to limit cycles or problems with controlling the actuators. To be able to correctly predict and assess these effects using simulations, a complete actuator, including motor, inverter, load and controller is needed. This article presents an object based, numerically efficient gear contact in a planar environment with user-defined friction- and stiffness laws. The emphasis of the modeling is not a fully detailed contact model, but the description of a gear contact model which can be used for system simulations like complete aircraft electro-mechanical actuators including control surfaces. The presented model is suitable for complex gearing configurations (e.g. compound planetary gears). This is enabled by breaking down the transmission into the basic gear contacts. By adding masses and constraints from an existing component library, a complete transmission can be modeled. The generated model can be used for standalone simulations or can be used in multi-domain simulations like actuator modeling, in order to analyze the complete actuator model including parts such as drives, controllers and mechanical systems. The presented models have been validated using a gear test rig for a single stage spur gear.