Energy-Based Feed-Forward and Extended Feedback Linearization Control Strategies for Realistic Series Elastic Actuated Hopping Robots

In this paper, we describe modeling and control techniques for a real-world series-elastic actuated 1D hopping robot. There is an abundance of work regarding the implementation of highly simplified hopper models, with the hopes of extracting fundamental control ideas for running and hopping robots. However, real-world systems unfortunately cannot be accurately described by such simple models, as real actuators have their own dynamics including additional inertia and nonlinear frictional losses. Therefore, an important step towards demonstrating high controllability and robustness to real-world, uneven terrain is in providing accurate higher-order hybrid models of real-world hopper dynamics. Implementing feedback based control for series-elastic actuators is difficult when the actuator has real dynamics, as the input variable does not instantaneously change the leg length acceleration. In addition to providing analytically exact feed-forward based control, we also provide an interesting method for regulating apex heights by extending the method of feedback linearization to a higher order. Motivated by actual hardware, our work here addresses 1D modeling and control of the real-world dynamics of a hopper designed for energy efficiency, with the eventual goal of developing robust and agile control for 2D and 3D hoppers.