State of the art

In this chapter we wrap up our literature investigation, pointing out the key focuses and requirements to be considered. We will go through our evaluations upon actuators, sensors, control systems and we will present some designs examples. Although literature is rich in studies on limbs exoskeletons aimed to several target applications, (such as rehabilitation, function restoring and virtual reality), the stringent requisites of EVA make most of the actuation and sensing solutions unsuitable for our device. Safety reasons and pressurization of the space suit force to avoid modern actuation technologies (i.e. air muscles), and focus on traditional motors such as piezoelectric ones. For what concerns sensors and control systems, most of the currently developed exoskeletons use physiological signals and are based on Electroencefalography (EEG) and on Electromyograpy (EMG). In the latter case, a big advantage is due to the fact that input signals are picked up directly from the motor units involved in the hand control. In the next pages we also present several examples of exoskeletons, including a pinching device for rehabilitation based on a cable mechanism, one finger device based on pulleys-lever structure, the four bar mechanism, a tendon system glove for function restoring and the EVA K-Glove from NASA. Finally, a couple of examples of feedback devices for medical applications are presented, integrating a variety of sensors, such as accelerometers, ultrasound, flow, pressure and vibration sensors, heat infrared camera, gyroscopes.