Robotic Phantom Knee and Digital Twin Platform for Early-Stage Exoskeleton Validation: Nonlinear Stiffness and Tuneable Soft-Tissue Compliance

Sammanfattning

Testing wearable exoskeletons and rehabilitation devices directly on human subjectsis often expensive, time-consuming, and ethically challenging, especially duringearly-stage development when designs and control strategies are frequently updated.In addition, human trials introduce variability that complicates systematic benchmarkingand controller verification. This thesis presents the design and developmentof a robotic phantom knee (RPK) testbed and a real-time Unity-based digital twin(DT) intended to provide a controlled bench-top platform for evaluating exoskeletoncontrollers.The developed system combines a single-degree-of-freedom knee hinge with antagonisticactuation using two Koala BEAR linear actuators coupled through an elasticlinkage to shape the joint’s passive resistance. To emulate tuneable soft-tissue andinterface compliance, the platform integrates inflatable chambers whose stiffness isadjusted via closed-loop pressure regulation using solenoid valves, a pump and reservoir,and pressure sensing. A modular ROS 2 (Jazzy) software stack on a RaspberryPi 5 handles hardware communication, pressure control, and safety functions (includingE-STOP and release-air). A Unity-based DT connects via ROS–TCP tovisualize system state in real time and support interactive parameter tuning andexperiment execution.Subsystem validation demonstrated stable ROS–TCP streaming, safety handling (ESTOPand release-air), and closed-loop pressure tracking suitable for bench-top trials.The platform supports systematic controller development and validation beforehuman testing by enabling controlled experiments under configurable complianceconditions.