Investigating the Effect of a Series Elastic Actuation Retrofit to Black-Box Actuators

2026-05-22

AI Summary

This study addresses the limited compliance of conventional rigid actuators in uncertain environments, which often results in poor force control accuracy and potential damage. To overcome this, the authors propose a low-cost series elastic module that imparts compliance to off-the-shelf black-box actuators, thereby enhancing force control performance. The module features a torsional elastic element optimized via finite element analysis and leverages Hooke’s law to enable high-fidelity force sensing. Experimental results demonstrate that the system’s force control bandwidth increases from 10.32 Hz to 30.32 Hz (a 2.93-fold improvement), while achieving 7.63% higher force control accuracy than commercial sensors. With a hardware cost of only £25, the solution offers a compelling balance between performance and affordability.

Abstract

In robotic applications, actuators are typically designed to be stiff with minimal backlash to ensure precision and repeatability. However, this limits compliance, leading to potential damage and poor force control in uncertain environments. Series Elastic Actuation (SEA) introduces compliance to enhance disturbance rejection and enable force measurement via Hooke's Law but reduces system bandwidth. A custom Series Elastic (SE) element was retrofitted to a black-box actuator to mitigate non-linearities like backlash and static friction. Integrating the SE element enabled high-fidelity force measurements, improving force control bandwidth and performance. A torsional SE element was designed through Finite Element (FE) analysis, yielding a stiffness of 2155.4 Nm/rad. Open-loop force control bandwidth was measured for the original motor and the SEA-integrated configuration, while closed-loop bandwidth was assessed using feedback from the SEA and a commercial force sensor. The SEA module increased bandwidth from 10.32 Hz to 30.32 Hz, a 2.93X improvement. Additionally, it outperformed the commercial sensor by 7.63% despite costing 25 GBP, a fraction of the price.

Problem

• Series Elastic Actuation
• force control
• backlash
• compliance
• actuator nonlinearity

Innovation

• Series Elastic Actuation
• Black-box Actuator Retrofit
• Force Control Bandwidth
• Compliance
• Torsional Spring Design