This paper presents the first design results of an upper extremity exoskeleton mounted on a wheel chair. This new device is dedicated to a regular and efficient rehabilitation training as well as arm tasks motion assistance for weak and injured people without the continuous presence of a therapist. The exoskeleton being a wearable robotic device attached to the human arm, the user provides information signals to the controller In order to generate the appropriate control signals for different training strategies and paradigms. This upper extremity exoskeleton covers four basic degrees of freedom of the shoulder and the elbow joints, with a mobile center of rotation mechanism for the shoulder abduction / adduction motion in order to match the human shoulder anatomy.