Mechanism and kinematic analysis of a robotic gadget for assisting hand movements of persons with severe disabilities to promote their community participation

Hand movements such as those necessary to use smart devices or credit cards are vital to modern-day daily life, both for able-bodied people and those with disabilities. Therefore, we have developed a robotic gadget for assisting people with severe disabilities by supporting the hand movements needed for everyday life and social activities, and thus promote those persons' participation in the community. To select the optimal services to be provided, we implemented focus-group interviews, targeting people with spinal cord injuries above the C4 vertebrae. Based on the extracted optimal services, we developed a robotic gadget to assist with a wide range of hand movements. The robotic gadget consists of a complex work module (offering three degrees of freedom) to assist with a range of hand movements, and a robotic arm (also with three degrees of freedom) to move the complex work module. The robotic arm incorporates a “tendon mechanism” whereby wires are used to minimize the size of the robotic arm joint. A parallel link mechanism automatically controls the position of the complex work module so that the smart device always faces the user regardless of the rotation of the robotic arm. The use of the parallel link mechanism also reduces the number of actuators required to keep the complex work module facing the user. The complex work module incorporates a card holder, which can load and eject up to four cards, and uses micro piezo motors to minimize its size. By implementing kinematic analysis, we calculated the position and orientation of an end-effector that can determine the space in which the complex work module operates. In this study, we verified the performance of the robotic gadget by building a prototype. The robotic gadget for supporting hand movements can be installed on a wheelchair or within the user's range of activity, and is expected to help severely disabled people as it improves their access to smart devices, assists them with the hand movements needed to partake in social activities, increases their interactions with able-bodied people, and promotes their participation in the community.