Soft Wearable Robotic Hand for People with Hand Paralysis

Abstract

Soft wearable robots are good alternatives to rigid-frame exoskeletons because they are compact and lightweight. Especially, the hand is very complicated and dense structure so that the pre-researched wearable exoskeleton robots have limitation in terms of compactness. However, in order to achieve both soft and wearable features, the soft wearable robot has several issues that have to be solved. Firstly, soft wearable robot, consists of soft structure, is operated being worn by the user. Because of the soft features, the force applied to the body can be larger and more concentrated than that of the rigid exoskeleton. Therefore, the safety issues have to be carefully considered. Moreover, the characteristics of wearers hands which have various properties have to be considered while determining design parameters that affects the posture and resultant grasping force. The second is that the proposed system consists with soft structure driven by tendons. In order to comprise the whole system with minimum use of the rigid structure, the conventional element should be replaced with soft structure. However, the soft structure is easily deformed while the tendon is tensed. The deformation of the structure totally changes the fixation position and the path of the tendon. Therefore, the structural deformation should be significantly considered during the development of soft wearable robot. The main contributions of the dissertation are as following. Proper mechanical elements are proposed which are suitable for the soft wearable robot. An issue related with the pretension in soft wearable robot is raised and the issues are solved by developing the slack enabling mechanism. The proper design parameter for pinch are searched with considering deformation of the soft structure. All of the concept and element are verified by the experiment on the subject with spinal cord injury. The proposed concepts can be used to develop other types of soft wearable robots. By combining all elements mentioned above, Exo-Glove is developed, which is the soft wearable robotic hand for the people with hand paralysis. The wearing part of the system is compact and weighs 194 g. The clinical experiments and results show the sufficient performance for the execution of daily life activities, namely, a pinch force of 20 N, a wrap grasp force of 40 N, and a maximum grasped object size of 76 mm. Use of an under-actuation mechanism enabled the grasping of objects of various shapes without active control. Consequently, Exo-Glove is expected to increase independency and quality of life of the people with hand paralysis.