Mechatronic Design of a 2-DoF Wearable Robot for Wrist Stiffness Assessment

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by a variety of motor symptoms including joint rigidity, typically assessed through semi-quantitative clinical scales, which are subjective and low-reliable. To address the limitations of current methods, we introduce in this paper the PDMeter2, a portable, wearable device for objective, quantitative assessment of wrist rigidity along two coupled Degrees of Freedom (DoFs): Flexion-Extension (FE) and Radio-Ulnar Deviation (RUD). The system includes two actuators to deliver controlled and repeatable perturbations to the wrist, and simultaneously measures provided torques and joint motions necessary for estimating the stiffness, which is closely related to clinical rigidity. Its lightweight aluminum structure and 3D-printed interfaces prioritize wearability and comfort, facilitating assessments in non-clinical environments without clinicians' supervision. In this work we present the mechatronic design of the PDMeter2 and its functional characterization in terms of restrictions to the wrist Range Of Motion (ROM). Results suggest that wrist ROM is primarily reduced along the FE DoF; however, the available ROM remains suitable for effective stiffness assessment and ADLs performance. The PDMeter2 represents a significant step toward more accessible, objective, and cost-effective diagnostic and treatment management tools for Parkinson's Disease.