Optimization of an Axial Flux Motor-Cycloid Gear Actuator for Sizing Wearable Robots

Actuators for wearable robots are difficult to design due to the competing requirements of minimizing weight and form factor while achieving desired performance requirements. Current solutions often rely on a “one-size-fits-all” approach utilizing classical motors and gears. Here, we present a thin, high torque density wearable actuator consisting of a cycloid gear and PCB axial flux motor, along with a modeling and design optimization framework to minimize actuator and battery mass while maintaining target performance. The model predicts motor mass with 95.9% accuracy and battery power with 75.9-87.9% accuracy. We then apply this design and optimization framework to quantify the benefits of creating optimized sizes of wearable actuators for gait assistance for stroke survivors, which was found to reduce average actuator and battery mass by 384 g with just 5 sizes. Furthermore, sizing the actuator and battery together resulted in an average of 28.9% to 48.3% more weight savings than sizing only the motor or only the battery, respectively, for individually optimized actuators. This paradigm of sizing actuators like clothing, along with new actuator architectures, may yield weight savings that could improve adoption of daily-wear assistive devices.