Partial Force Control of Constrained Floating-Base Robots

TL;DR

This paper introduces a novel control method for floating-base robots that efficiently manages motion and partial contact forces, reducing computational load while maintaining flexibility, validated through simulations on a humanoid robot.

Contribution

A new formulation of the multitask optimization problem enables sparse analytical solutions for partial force control, improving efficiency over traditional methods.

Findings

Reduced computational complexity similar to inverse-dynamics approaches

Ability to eliminate force/torque discontinuities

Validated on a 23-DOF humanoid robot in simulations

Abstract

Legged robots are typically in rigid contact with the environment at multiple locations, which add a degree of complexity to their control. We present a method to control the motion and a subset of the contact forces of a floating-base robot. We derive a new formulation of the lexicographic optimization problem typically arising in multitask motion/force control frameworks. The structure of the constraints of the problem (i.e. the dynamics of the robot) allows us to find a sparse analytical solution. This leads to an equivalent optimization with reduced computational complexity, comparable to inverse-dynamics based approaches. At the same time, our method preserves the flexibility of optimization based control frameworks. Simulations were carried out to achieve different multi-contact behaviors on a 23-degree-offreedom humanoid robot, validating the presented approach. A comparison with another state-of-the-art control technique with similar computational complexity shows the benefits of our controller, which can eliminate force/torque discontinuities.