Safe Balancing Control of a Soft Legged Robot

TL;DR

This paper introduces Horton, a soft legged robot with a safety-verified feedback control system that ensures safe operation of thermal actuators during balancing, marking the first such demonstration in soft robotics.

Contribution

It presents a novel safety-verified control framework for soft legged robots, integrating thermal SMA actuators and supervisory control for safe operation.

Findings

Horton successfully maintains balance using the proposed control system.

The supervisory control keeps SMA wire temperatures below safety thresholds.

First demonstration of safety-verified feedback control in soft legged robots.

Abstract

Legged robots constructed from soft materials are commonly claimed to demonstrate safer, more robust environmental interactions than their rigid counterparts. However, this motivating feature of soft robots requires more rigorous development for comparison to rigid locomotion. This article presents a soft legged robot platform, Horton, and a feedback control system with safety guarantees on some aspects of its operation. The robot is constructed using a series of soft limbs, actuated by thermal shape memory alloy (SMA) wire muscles, with sensors for its position and its actuator temperatures. A supervisory control scheme maintains safe actuator states during the operation of a separate controller for the robot's pose. Experiments demonstrate that Horton can lift its leg and maintain a balancing stance, a precursor to locomotion. The supervisor is verified in hardware via a human interaction test during balancing, keeping all SMA muscles below a temperature threshold. This work represents the first demonstration of a safety-verified feedback system on any soft legged robot.