Motion control of an underactuated planar 3-DOF biped robot using time-scale method

In this paper, we propose motion control of a planar biped robot without ankle with its center of mass (COM) located at the hip using a novel model. Using the properties of this novel model, necessary conditions for periodic motion without sliding are derived. Applying these conditions and using optimized problem, desired joints trajectories, which are periodic, are determined as a function of a time-scale parameter. Designing a PD controller, these trajectories are tracked. To compensate for underactuation, second derivative of the time-scale parameter is used as an input. Simulation results are finally presented to show the stability of the motion.

Keywords:

Biped robot , underactuation , optimization problem , periodic motion , limit cycle , control , time scale