A low-cost wearable hand exoskeleton for hand opening disabilities B. Allotta, R. Conti, L. Governi, E. Meli, A. Ridolfi Abstract—This research activity is focused on the development of a low-cost wearable hand exoskeleton for supporting daily gestures, in particular for patiences affected by hand opening disabilities. The hand exoskeleton system, developed at the MDM Lab during this initial project phase, is based on a single-phalanx architecture and consists of a mechanical part (mechanism) and an electronic one (actuators, control unit and battery pack). The design of the mechanism has been performed in parallel with the development of its complete 3D multibody model: this model- based approach allows the authors to optimize the wearability of the system. The preliminary prototype of the system is currently being tested to verify the system performance. Keywords—Wearable Robotics, Hand Exoskeleton, Hand dis- abilities In the last years, the increase of the population mean age has led to a growing of hand disabilities, mainly due to injuries or diseases, the so called Acquired Brain Injuries; most of these cases result in a loss of hand perception capabilities and/or mobility. These disabilities deeply influence patient common life, introducing difficulties in many daily operations such as grasping objects, writing, driving, etc. and reducing the self-sufficiency of the person [1]. A possible solution to this problem is the use of a Functional Electrical Stimulation (FES) system to stimulate muscles that are no longer receiving signals from the central nervous system. The main drawbacks related to this first approach are the limited usability of these devices, the fast fatigue affecting the patients and the reduced appli- cability to patient with limited muscular recruitment abilities. More effective solutions may be provided by robotic devices such as different hand exoskeletons, especially designed to assist and improve the performance of the patient hands. Particularly, the use of robotic exoskeletons of the human hands allows the achievement of different manipulation tasks (dexterous manipulation and power grasping) and the solution of many medical rehabilitative issues (diseases involving finger opening and closing, perception and fatigue) [2],[3]. The authors fully endorse this second approach, aiming at the development of a low-cost hand exoskeleton focused on strict wearability requirements: the goal is to realize a light wearable solution that can support daily life activities for several hours in a day, not a tool tailored to rehabilitation sessions but a real daily living activity support, addressed to people who suffer of hand opening disability. In this work, the authors devel- oped a hand-exoskeleton system, based on a single-phalanx architecture (Fig. 1). The hand exoskeleton is cable driven to improve its reliability and robustness. The development of the mechanical part started from the analysis of the human hand kinematics obtained through a simplified 3D multibody All the authors belong to the Department of Industrial Engineering, Uni- versity of Florence, Florence, 50139, Italy. Mail: roberto.conti@unifi.it Fig. 1. The low-cost hand exoskeleton developed by MDM Lab model. A novel exoskeleton kinematic chain, based on a 1 DOF mechanism, is studied to reproduce the desired trajectories of the fingers. Thus, a complete 3D multibody model involving both the hand and the exoskeleton models is built up: through this model a calibration phase of the mechanism geometrical parameters and a preliminary evaluation of the forces necessary to the hand opening gestures are performed. The numerical simulations helped to design the hardware part of the sys- tem (e.g. servomotors and electronics). The hand exoskeleton mechanism is then optimized to reduce both the lateral and the height encumbrances and, finally, all the parts are built (Fused Deposition Modelling machine) and assembled. The electronic part consists of servomotors, a control unit and a battery pack. The results of the numerical simulations determine the characteristics of the most suitable servomotors in terms of torque, size and weight. The control unit is carried out through a low cost device (MicroMaestro) using only two buttons to permit the opening phase. The preliminary prototype has a reduced weight, less than 500 g. The numerical results obtained through the whole 3D multibody model are compared with the experimental results measured on the hand exoskeleton prototype: the results confirm the proper modelling of the system. The hand exoskeleton is now involved in the testing phase on a patient. REFERENCES [1] W. S. Harwin, J. L. Patton, V. R. Edgerton, Challenges and Opportunities for Robot-Mediated Neurorehabilitation, Proceedings of the IEEE, vol. 94(9), pp.1717-1726, 2006. [2] B. Siciliano, O. Khatib, Handbook of Robotics, Springer Handbooks, Napoli and Stanford, 2008. [3] P. Dario, E. Guglielmelli, B. Allotta, M.C. Carrozza, Robotics for medical applications, IEEE Robotics and Automation Magazine, 3 (3), pp. 44-56, 1996.