Amplifying Human Strength Through a Virtual Sprung Inertia (Under Review)

While better known for their ability to work autonomously in structured tasks, robots have the potential to aid human workers in unstructured tasks via force control. More specifically, cobots and exoskeletons that physically interact with human operators can amplify human strength by feeding back measurements of their interaction forces, agnostic to the task the operator is performing. However, due to limited control bandwidth and coupled human–robot dynamics, naive force-feedback can easily result in instability similar to pilot-induced oscillation in planes.

Controllers that amplify strength while also guaranteeing some stability properties have become the standard approach in the space, often at the cost of the user’s perception of a transparent system. This paper:

1. Extends a previously theorized virtual-mass-based exoskeleton controller to a strength-amplifying robot arm.
2. Theoretically and experimentally demonstrates its stability compared to naive force-feedback.
3. Identifies the robot dynamics using a spring-box apparatus as a human surrogate.
4. Determines the extent to which the robot can reliably measure the stiffnesses of the apparatus to better understand its ability to identify human mechanical impedance.

Recommended citation: A. Petrakian, Z. Bucknor-Smartt, C. Scott, G. C Thomas, “Amplifying Human Strength Through a Virtual Sprung Inertia”, IEEE International Conference on Rehabilitation Robotics, May 12th, 2025 (Under Review) [Conference Paper]