I. INTRODUCTION
In recent years, electro-mechanical systems for rehabilitation have become ubiquitous, thanks to recent advances on human machine interaction research. Using robotic devices to assist repetitive and labor intensive rehabilitation exercises help decrease physical burden of the therapists and application related costs. Robot assisted rehabilitation devices can be applied to patients with all levels of impairment, can quantitatively measure patient progress, allow for easy tuning of duration and intensity of therapies and make customized, interactive treatment protocols feasible. Moreover, rehabilitation robots not only increase the reliability, accuracy, and effectiveness of physical therapy sessions, but also enable active participation of patients by assisting patients only as-needed. Clinical trials on robot assisted rehabilitation provide evidence that this form of therapy is effective for motor recovery and possesses high potential for improving functional independence of patients [1]–[4].