Wearable dummy to simulate joint impairment: Model for the discontinuous friction resistance due to arthritis

Physical therapists master manual examination techniques for testing impaired motor functions. We developed a wearable robotic dummy joint to simulate disordered joint resistances for supporting physical therapists to learn such techniques. A model to simulate discontinuous joint friction resistances due to diseases such as osteoarthritis was developed. Because such resistance originates from abnormal frictions of bones and cartilages, we used a stick-slip model to simulate the resistances. The model was validated based on the introspection of physical therapists. This study concludes that a discontinuous friction model presents forces that are perceptually similar to those typically caused by damaged or roughened joint cartilages.