Robotics in Rehabilitation - Part II: Design of Devices and Mechanisms

Robotics in rehabilitation presents many aspects of physical human-robot interaction. In the companion paper (Part I, this issue) some general requirements derived from rehabilitation scenarios have been introduced. In that context, issues in the domain of robot control have been detailed, leaving for this part the discussion about the design process of manipulators or machines for rehabilitation. In particular, the design of upper limb solutions is particularly challenging from structural and mechanical points of view because of the complex kinematic topology and anatomy of the human arm. End-effector devices-sometimes anthropomorphic manipulators or, more often, machines with a limited number of degrees of freedom-do not constrain all the segments of a limb and therefore do not allow a complete control of the joints trajectories. Exoskeletons, on the contrary, completely wrap the arm and are therefore suitable for controlling all the limb joints along the kinematic chain, exchanging forces all along the limb. For this reason, the topology and the kinetostatic validation of exoskeletal robotic devices assume a very significant importance in order to prevent unwanted articular motions or damages due to exceeding torques. In particular, the analysis of singularities in robot kinematics is directly used for evaluating the behavior of a machine closely coupled with the human arm and is also preliminary for any robust implementation of control strategies. A case study of an exoskeleton design is presented along with singularity and kinetostatical analysis in order to display the effects of topological choices onto the actual dynamical behavior of the robot in interaction with living, yet impaired, limb.