SiMPLeR: A Series-Elastic Manipulator with Passive Variable Stiffness for Legged Robots

TL;DR

SiMPLeR introduces a mechanically simple, cost-effective series elastic actuator with passive variable stiffness, enabling more animal-like capabilities in legged robots through a novel torsional spring design.

Contribution

The paper presents a new passive variable stiffness actuator design using torsional springs on timing belts, simplifying and reducing costs compared to existing solutions.

Findings

Prototype matches theoretical behavior.

Demonstrated application in robotic hopping.

Achieved controllable stiffness with simple mechanism.

Abstract

We propose a mechanically simple and cheap design for a series elastic actuator with controllable stiffness. Such characteristics are necessary for animals for running, jumping, throwing, and manipulation, yet in robots, variable stiffness actuators are either complicated or mimicked at low bandwidth through feedback controllers. A robust and simple design is needed to build reliable and cheap robots with animal capabilities. The key insight of our design is attaching torsional springs to timing belts to create a variable stiffness linear spring. In an antagonistic pair, varying the distance between motor and joint then varies the actuator stiffness. We build a prototype of our proposed actuator, show the theoretical behavior matches the experimental characterization, and demonstrate an application to robotic one-legged hopping.