Gear Ratio Optimization of a Multifunctional Walker Robot Using Dual-Motor Actuation

Optimization of gear ratios for dual-motor actuators is presented for the development of a walker-type assist robot. The robot is reconfigurable to provide an elderly user with multiple physical support functions; one is to assist sitto-stand transitions and the other is to serve as a walker to aid the user in walking. To avoid falling while walking, the robot must react quickly and reconfigure its footprint for supporting the user. This requires high speed actuators. In contrast, for assisting sit-to-stand transitions, high torque actuators are required. To meet the bimodal, conflicting load conditions, i.e. high-torque, low-speed v.s. high-speed, low-torque, this paper presents a dual-motor actuation solution, where two motors with diverse gear ratios are combined. The system is characterized with two key parameters: an internal gear ratio between a high-speed motor and a torque-booster, and an external gear ratio for connecting the dual motor actuator to the load. The internal and external gear ratios are optimized for performing both sit-to-stand assist and rapid foot reconfiguration.