Study of Human Push Recovery

TL;DR

This study investigates human push recovery control laws by collecting and analyzing motion data, revealing that proportional-derivative control models effectively describe human responses and vary across different phases of push recovery.

Contribution

The paper presents a comprehensive experimental design and data analysis showing that PD control can model human push recovery, with insights into strategy switching based on center of mass properties.

Findings

PD control accurately models human push recovery with low RMS error.

Different PD gains are used in different recovery phases.

Strategy switching correlates with initial center of mass position and velocity.

Abstract

Walking and push recovery controllers for humanoid robots have advanced throughout the years while unsolved gaps leading to undesirable behaviours still exist. Because previous studies are mainly pure engineering methods, while the use of data-driven methods has made impressive achievements in the field of control, we set motivation for exploration of control laws applied by human beings. Successful findings may help fill the gaps in current engineering-based controllers and can potentially improve the performance. In this thesis, we show our complete design and implementation of a set of experiments to collect and process human data, as well as data analysis for model fitting. Using the processed motion data and force data collected, we export the position, velocity and acceleration of our participants' centres of mass to form a one-dimensional point mass model defined by the direction of pushes. As a result, we find that proportional-derivative (PD) control can describe the underlying control law that people used and different PD gains are set for different phases of a push recovery trial within the scope of our study. Our final PD control fittings have an average root mean square error below 0.1m with above 90% of a trial's data points are taken into account on average. We also explore how different error metrics that the PD control model uses influence its performance but neither of the two metrics we proposed can help improve the performance. Finally, we have statistics on how people switch push recovery strategies based on their centre of mass properties at the start of the push. We find that the further the centre of mass is from the steady-state point and the higher the velocity it has, a person is more likely to make a step for push force compensation.