Exoskeletons for Rehabilitation and Motor Control A. F. Ruiz, A. Forner-Cordero, E. Rocon and J. L. Pons, Member, IEEE Grupo de Bioingenieria Instituto de Automatica Industrial - CSIC Ctra. Campo Real km 0.200, 28500 Madrid, Spain afruiz@iai.csic.es Abstract – Exoskeletons are mechatronic systems worn by a person in such a way that the physical interface permits a direct transfer of mechanical power and exchange of information. These robotic mechanisms have been applied in telemanipulation, man-amplifier, rehabilitation and to assist impaired human motor control. In addition, the neuromotor control research can benefit from a exoskeleton in order to manipulate human arm movements within its natural workspace, which is not possible with traditional robotic manipulandum because of its constraints. The aim of this paper is to describe a set of experiments in motor control and the application of powered upper limb exoskeleton in which the mechanical requirements of the movement will be modified, e.g. removal of the interaction torques in order to identify their impact on the production of complex coordination patterns in healthy subjects with the possibility for a future application to neurologically impaired subjects. As preliminary results, are shown responses to changes in viscosity and inertia when external perturbations (viscous load and inertia) are applied during execution of elbow angular cyclical movements using a robotic exoskeleton. Index Terms – Exoskeletons, rehabilitation robotics, motor control, orthotics. I. INTRODUCTION The scientific and medical community is becoming more and more interested in the so-called Rehabilitation Robotics. Rehabilitation Robotics has been envisioned as technology for the restoration and functional compensation of people suffering from physical disability or disorders, either for the rehabilitation therapy or assistance of people. In robotic field, exoskeletons are mechatronic devices of which segments and joints correspond to some extend to these of the human body and the system is externally coupled to the person (“wearable” robot). The primary applications of exoskeletons were teleoperation and power amplification. Later, exoskeletons have been considered as devices for rehabilitation and assistance of disabled or elderly people by means of upper and/or lower limb orthosis. Lastly, taking into account that robotic exoskeletons are able to apply independent dynamic forces on human joints and segments, these devices permits to realize experiments and studies on motor control, adaptation and neuro-motor research. In rehabilitation applications, the exoskeleton should be able to replicate with a patient the movements performed with a therapist during the treatment. In addition, the sensors attached to the exoskeleton can assess forces and movements of the patient. This would give to the therapist quantitative feedback on the recovery of the patients and would imply a more efficient rehabilitation process. Therefore, the exoskeleton could act as tool for the measurement of the performance and the evolution of the treatment. For instance, in Reference [1] was presented a robotic device based on impedance control to guide patient's movements in specified trajectories and was demonstrated the beneficial effects of the treatment. In the case of exoskeletons for human performance amplification or functional compensation, the patient provides control signals to the device, while the exoskeleton provides most of the mechanical power required to carry out the task. The human becomes a part of the system and feels a scaled-down version of the external load carried by the device due to the force reflection [2]. Most of the developments have focused on the upper and lower limb. In general, rehabilitation robots can be classified, see [3], under three categories: 1) Posture support mechanisms. 2) Rehabilitation mechanisms. 3) Robots to assist or replace body functions. One important and specific aspect in Rehabilitation Robotics is the intrinsic interaction between human and robot. This interaction is twofold. First, cognitive, because the human controls the robot while it provides feedback to the human; second, a biomechanical interaction leading to the application of controlled forces between both actors. In Reference [2] it was discussed mechanism and control for power assist robotic arms defined as “extenders” and it was analysed the dynamics of human-machine interaction in sense of the transfer of power and information signals. There is a physical interface between person and device to provide the mechanical power. Concerns of this physical interface are safety, robustness and reliability of the robotic mechanism taking into account the characteristics of the human neuromuscular-skeletal system. A relevant aspect in the interface to assist impaired human motor control is the information (control signal) required of voluntary motor control which may be provided using several channels and methods, for instance: measurement of movement, interface forces with the device, muscles activation, brain activity. The channel used will depend on the specific application and availability.