Direct electromagnetic actuation on high ratio gears

This document demonstrates a conceptual study, design and development of unconventional electromagnetic actuators for applications where a high torque over a limited part of a rotational turn is required. The unconventionality of the actuators is that the electromagnetic actuation is applied directly on a high ratio transmission gear such as a cycloid disc in a cycloid drive or a flex-spline in a harmonic drive. Furthermore, normal forces are intentionally used to displace and rotate a cycloid disc or deform a flex-spline instead of tangential forces, which are typically used when integrating conventional rotating machine driving a high ratio gear transmission. The conceptual study is based on a number of finite element models where the idea is first presented and followed by field and force analysis. A finite element static model is used to calculate the expected excitation versus the gear location. The gear location of the cycloid disc is defined by an eccentric origin and rotation angle while the flex-spline is defined by a deformation and rotation angle. The analysis of the integrated normal force actuator inside the harmonic drive demonstrates the challenging strain gearing action in terms of elasticity and magnetic saturation. The challenge with the cycloid drive is the electromagnetic action force direction compared to the desired mechanic reaction force direction that causes unnecessary inner load or even locks the gear mechanisms. A prototype machine with the maximized rotor eccentricity is used to characterize four different rolling and geared cycloid transmissions.