Self-Aligning Finger Exoskeleton for the Mobilization of the Metacarpophalangeal Joint

In the context of hand and finger rehabilitation, kinematic compatibility is key for the acceptability and clinical exploitation of robotic devices. Different kinematic chain solutions have been proposed in the state of the art, with different trade-offs between characteristics of kinematic compatibility, adaptability to different anthropometries, and the ability to compute relevant clinical information. This study presents the design of a novel kinematic chain for the mobilization of the metacarpophalangeal (MCP) joint of the long fingers and a mathematical model for the real-time computation of the joint angle and transferred torque. The proposed mechanism can self-align with the human joint without hindering force transfer or inducing parasitic torque. The chain has been designed for integration into an exoskeletal device aimed at rehabilitating traumatic-hand patients. The exoskeleton actuation the unit has a series-elastic architecture for compliant human-robot interaction and has been assembled and preliminarily tested in experiments with eight human subjects. Performance has been investigated in terms of (i) the accuracy of the MCP joint angle estimation through comparison with a video-based motion tracking system, (ii) residual MCP torque when the exoskeleton is controlled to provide null output impedance and (iii) torque-tracking performance. Results showed a root-mean-square error (RMSE) below 5 degrees in the estimated MCP angle. The estimated residual MCP torque resulted below 7 mNm. Torque tracking performance shows an RMSE lower than 8 mNm in following sinusoidal reference profiles. The results encourage further investigations of the device in a clinical scenario

Development and Experimental Characterization of a Low and Middle Level Control Strategy for a Robotic Hand Exoskeleton

In this work, a state-of-the-art exoskeleton has been used as an initial framework to implement low-level control strategies and a proof of concept for a middle-level control strategy, to evaluate the applicability and safety of the control architecture for further implementation in clinical scenarios. The low-level control has been synthesized starting from a system identification phase, where first an ideal transfer function has been derived by mathematical modelling. Through a black box input-output based estimation, the real values of the plant’s coefficients have been defined, taking into account the non-linearities of the system. The controller synthesis has been addressed, using a pole-placement strategy to better cope with the dynamical requirements and with the configuration of poles and zeros detected. The obtained controller has been tested against a gold standard fine-tuned PID controller. The characterization of the performances has been addressed and a middle-level control strategy able to implement three different types of exercises based on the low-level torque control has been designed. Finally, the results obtained and a brief discussion has been provided, demonstrating the safety and feasibility of the control strategy during exercises and establishing a good setup for further investigation with clinical patients in future pilot studies