Combining Performance and Passivity in Linear Control of Series Elastic Actuators

2025-09-21

AI Summary

To address the challenge of simultaneously ensuring safety and motion performance in series elastic actuators (SEAs) during human–robot physical interaction, this paper proposes a novel co-design architecture integrating end-effector PD control with elastic transmission damping—thereby overcoming conventional passivity- and stability-imposed gain limitations inherent in load-side control. Leveraging linear systems theory, we analytically derive stability boundaries across diverse mechanical configurations. Both simulation and hardware experiments demonstrate that the approach achieves high-precision trajectory tracking even under low-stiffness hardware conditions, while actively dissipating energy upon collision to ensure user safety. The core contribution is a unified “control–damping–configuration” coupled design paradigm, which significantly expands the feasible domain for stable, high-gain control. This work provides both theoretical foundations and practical implementation guidelines for safe, high-performance SEA control.

Technology Category

• Intelligent Robots: Behavior Learning & Control
• Humans and AI: Human-Aware Planning and Behavior Prediction
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Security and Privacy: Browser and end-point security
• Search and Retrieval-Augmented AI: Assisted, interactive, and conversational search

Abstract

When humans physically interact with robots, we need the robots to be both safe and performant. Series elastic actuators (SEAs) fundamentally advance safety by introducing compliant actuation. On the one hand, adding a spring mitigates the impact of accidental collisions between human and robot; but on the other hand, this spring introduces oscillations and fundamentally decreases the robot's ability to perform precise, accurate motions. So how should we trade off between physical safety and performance? In this paper, we enumerate the different linear control and mechanical configurations for series elastic actuators, and explore how each choice affects the rendered compliance, passivity, and tracking performance. While prior works focus on load side control, we find that actuator side control has significant benefits. Indeed, simple PD controllers on the actuator side allow for a much wider range of control gains that maintain safety, and combining these with a damper in the elastic transmission yields high performance. Our simulations and real world experiments suggest that, by designing a system with low physical stiffness and high controller gains, this solution enables accurate performance while also ensuring user safety during collisions.

Problem

• Balancing safety and performance in series elastic actuators
• Analyzing linear control configurations for compliance and tracking
• Achieving accurate motion while ensuring human-robot collision safety

Innovation

• Actuator side PD control for safety
• Damper in elastic transmission for performance
• Low stiffness with high controller gains