Phantom limb with Variable Stiffness Actuator

Abstract

Technology and healthcare are improving faster than ever, and with it comes an increased demand to be able to test new innovations before they get approved for use. However, with strict guidelines on how these tests are allowed to be performed, it is not always that easy. One of the areas affected by these guidelines is the continued development of better exoskeletal arms for people with impaired movement. Due to the risk of potential injury when testing these products in a patient who does not have full control over their arm, and who might experience rapid and spasmodic movement in it, testing on people is highly limited [1].

Therefore, this thesis presents the design and development of a robotic phantom limb with a VSA (Variable Stiffness Actuator), intended as a test platform for exoskeletal devices used in rehabilitation. The motivation comes from the need to test exoskeletons safely without relying on human subjects, particularly for conditions involving involuntary or spasmodic movements. The project combines mechanical, electrical and control system engineering to create an anthropomorphic arm capable of replicating realistic joint dynamics and variable stiffness behaviors.

Key objectives included designing the VSA using nonlinear springs to mimic human muscle behavior, implementing a control system using an STM32 microcontroller and ROS2 architecture, and integrating sensors such as IMUs, hall sensors, and force-torque sensors to monitor system performance. The system was modeled and simulated in Simulink to validate control strategies and mechanical performance prior to physical implementation. The experimental results demonstrated that the prototype could achieve the target stiffness levels, torque outputs, and angular positions necessary to simulate human arm movement under various conditions. This work contributes a valuable tool to the advancement of rehabilitation robotics by enabling more efficient and safer testing of assistive devices, ultimately aiming to accelerate the development and clinical deployment of user-centered robotic systems.