Flexibility in upper limb rehabilitation with the use of 1-DOF fourbar linkages

In robotic rehabilitation the interaction is usually implemented by means of robots based on multi-Degree of Freedom (DOF) open kinematic chains. Despite their inherent flexibility these machines are expensive, complex and require routine maintenance and IT support. In contrast, mechanisms based on closed kinematic chains and especially 1-DOF four- and six bar linkages are simple, yet capable of generating paths with complex kinematic characteristics. These mechanisms are preferable when simplicity and cost are the major criteria, for example in the case of community-based rehabilitation in developing countries. On the other hand, rehabilitation using 1-DOF limits flexibility and potentially impairs the exercise effectiveness, since the patient does not have access to a variety of kinematic challenges. Nevertheless, by careful ergonomic design and by considering varying time constraints, link rotation ranges and varying link lengths this limitation can be overcome. This work aims to demonstrate the potential of 1-DOF four-bar linkages to provide flexibility in therapy by considering a Hoeken's straight line four-bar linkage. After the mechanism is dimensioned, a previonsly developed method is employed for establishing a final prototype design which accounts for significant neurophysiological models such as Minimum Jerk Model, Fitts's Law and Just Noticeable Differences. Given the mechanism characteristics, its potential for generation of exercises that vary with respect to temporal and spatial characteristics is demonstrated.