SEA Retrofit Boosts Actuator Bandwidth 2.93x at Fraction of Cost

A team led by Ivan Tregear at Imperial College London has developed a simple, low-cost retrofit that turns rigid black-box actuators into compliant, force-sensing units. By adding a custom Series Elastic Actuation (SEA) element—a torsional spring with a measured stiffness of 2155.4 Nm/rad—they enabled high-fidelity force measurement via Hooke's Law. The SEA module was designed using finite element analysis and attached between the motor output and the load. This approach directly addresses the trade-off between stiffness (needed for precision) and compliance (needed for safe human-robot interaction and disturbance rejection).

In lab tests, the retrofit more than tripled the open-loop force control bandwidth—from 10.32 Hz to 30.32 Hz—while closed-loop control using the SEA's internal feedback outperformed a commercial force sensor by 7.63%. Crucially, the entire module costs just 25 GBP, making it an accessible upgrade for research and industrial robots. The team has open-sourced the design on GitHub. This work shows that high-performance force control can be achieved without expensive new actuators, potentially accelerating the adoption of compliant robotics in manufacturing, healthcare, and service applications.