Exploiting Physical Human-Robot Interaction to Provide a Unique Rolling Experience with a Riding Ballbot

This study introduces the development of hands-free control schemes for a riding ballbot that was previously developed to allow riders, including manual wheelchair users, to control its movement through torso motion. The hardware platform, Personal Unique Rolling Experience (PURE), utilizes a ballbot drivetrain, a dynamically stable robot that uses a ball as its wheel to provide omnidirectional movement. To accommodate users with varying torso motion functions, the control scheme should be adjustable based on the rider’s torso function and personal preferences. Therefore, concepts of impedance and admittance control were integrated into the existing control scheme. A duo-agent optimization-based simulation framework was utilized to assess the efficiency of this rider-ballbot system for a critical task: braking from 1.4 m/s. The candidate control schemes were further implemented in the physical robot hardware and validated with two experienced users, demonstrating the efficiency and robustness of the hands-free admittance control scheme. This interface, which utilized physical human-robot interaction as the input, resulted in lower braking effort and shorter braking distance and time. Twelve novice participants, six able-bodied individuals (ABI) and six manual wheelchair users (mWCU), with different levels of torso functions, were then recruited to benchmark the braking performance with HACS. They successfully finished the braking task and achieved similar performance compared with experienced users. By exploiting pHRI, the proposed admittance-style control scheme provided effective control of the ballbot via torso motions. This interface enables PURE to provide a personal unique rolling experience to ABI and mWCU for safe and agile indoor navigation.