Joint-Space Control of a Structurally Elastic Humanoid Robot

TL;DR

This paper introduces a joint control strategy for a structurally elastic humanoid robot, PANDORA, using a disturbance observer to handle model variations and enable flexible additive manufacturing of compliant components.

Contribution

The proposed control method allows robust joint control of a structurally elastic humanoid without system identification, facilitating design iteration of 3D printed linkages.

Findings

DOB effectively manages model variations in elastic components.

The control strategy maintains balance under external pushes.

Hardware tests validate robustness and effectiveness.

Abstract

In this work, the joint-control strategy is presented for the humanoid robot, PANDORA, whose structural components are designed to be compliant. As opposed to contemporary approaches which design the elasticity internal to the actuator housing, PANDORA's structural components are designed to be compliant under load or, in other words, structurally elastic. To maintain the rapid design benefit of additive manufacturing, this joint control strategy employs a disturbance observer (DOB) modeled from an ideal elastic actuator. This robust controller treats the model variation from the structurally elastic components as a disturbance and eliminates the need for system identification of the 3D printed parts. This enables mechanical design engineers to iterate on the 3D printed linkages without requiring consistent tuning from the joint controller. Two sets of hardware results are presented for validating the controller. The first set of results are conducted on an ideal elastic actuator testbed that drives an unmodeled, 1 DoF weighted pendulum with a 10 kg mass. The results support the claim that the DOB can handle significant model variation. The second set of results is from a robust balancing experiment conducted on the 12 DoF lower body of PANDORA. The robot maintains balance while an operator applies 50 N pushes to the pelvis, where the actuator tracking results are presented for the left leg.