Robustness to Joint-Torque-Tracking Errors in Task-Space Inverse Dynamics

Simulation of 30 HRP-2 robots walking in the presence of uncertainties, the goal being to compare the classic TSID controller (left line, gray heads) to the proposed robust TSID controllers: stochastic (central line, green heads) and worst-case (right line, red heads). Some of the simulation results can be seen in the accompanying video.

Abstract

Task-Space Inverse Dynamics (TSID) is a well-known optimization-based technique for the control of highly-redundant mechanical systems, such as humanoid robots. One of its main flaws is that it does not take into account any of the uncertainties affecting these systems: poor torque tracking, sensor noises, delays and model uncertainties. As a consequence, the resulting control-state trajectories may be feasible for the ideal system, but not for the real one. We propose to improve the robustness of TSID by modeling uncertainties in the joint torques, either as Gaussian random variables or as bounded deterministic variables. Then we try to immunize the constraints of the system to any—or at least most—of the realizations of these uncertainties. When the resulting optimization problem is too computationally expensive for online control, we propose ways to approximate it that lead to computation times below 1 ms. Extensive simulations in a realistic environment show that the proposed robust controllers greatly outperform the classic one, even when other unmodeled uncertainties affect the system (e.g. errors in the inertial parameters, delays in the velocity estimates).

Publication
IEEE Transactions on Robotics
Date
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