Robust Control of a Multi-Axis Shape Memory Alloy-Driven Soft Manipulator

TL;DR

This paper presents a robust feedback control scheme for a multi-axis shape-memory-alloy soft robotic manipulator, addressing actuator dynamics and multi-dimensional motion, with proven stability and verified hardware performance.

Contribution

It introduces a novel control approach combining a static beam model, SVD-based decoupling, and anti-windup for SMA-driven soft robots, enhancing robustness and stability.

Findings

Low tracking error in hardware tests

Robustness against unmodeled dynamics demonstrated

Effective multi-axis motion control achieved

Abstract

Control of soft robotic manipulators remains a challenge for designs with advanced capabilities and novel actuation. Two significant limitations are multi-axis, three-dimensional motion of soft bodies alongside actuator dynamics and constraints, both of which are present in shape-memory-alloy (SMA)-powered soft robots. This article addresses both concerns with a robust feedback control scheme, demonstrating state tracking control for a soft robot manipulator of this type. Our controller uses a static beam bending model to approximate the soft limb as an LTI system, alongside a singular-value-decomposition compensator approach to decouple the multi-axial motion and an anti-windup element for the actuator saturation. We prove stability and verify robustness of our controller, with robustness intended to account for the unmodeled dynamics. Our implementation is verified in hardware tests of a soft SMA-powered limb, showing low tracking error, with promising results for future multi-limbed robots.