Balance and velocity control of a novel spherical robot with structural asymmetry

This paper proposes a novel spherical robot design. The pendulum of this robot is actuated by the step motor with cable being the transmission mechanism. Compared to the existing spherical robots, this design concept can reduce the influence of the gear backlash and pendulum vibrations. Until now, few published results have presented rigorous analysis for the asymmetry of the spherical robot system. In order to solve this issue, asymmetry is considered when the dynamic model of the spherical robot is established in our paper and then the system is decoupled into two underactuated subsystems. The relationship between the two subsystems is explored by projection method. Finally, we proposed adaptive hierarchical sliding mode controller (AHSMC), which is a combination of hierarchical sliding mode (HSMC) and adaptive laws for the eccentric moment/resistance torque estimation. The simulated and experimental results were provided to verify the proposed method for balance and velocity control.