Functional movement modeling for robot-assisted upper limb rehabilitation: The case of a simulated reduced-freedom anthropomorphic manipulator

This paper presents the results of an on-going investigation into the use of an anthropomorphic robotic manipulator with three degrees of freedom (two DOF shoulder joint and one DOF elbow joint) for rehabilitation of a human upper arm. The reduction to three DOF for this manipulator allows for a simpler project, leading to a lower cost of production and maintenance: important factors for its intended wide-spread use in financially restricted areas, e.g., the state of Goiás, Brazil. The project focuses on determining the variations observed for a class of trajectories known as functional movements. These functional movements are trajectories realized when a limb is used for a given function, e.g., combing the hair. In this present paper we use three functional movements: hair combing, bringing a cup to one's mouth and a waving movement. We describe how these functional movements are acquired from test subjects and compared in computer simulations to the equivalent functional movements of our proposed reduced-order anthropomorphic manipulator. Our research indicates that the errors incurred in using a reduced-order shoulder joint are well within the observed variation in the functional movements of human subjects, when compared among different subjects and also between similar functional movements of any one given human subject. Despite the limitations, the proposed manipulator would be viable for rehabilitation of patients in early phases of a stroke, at lower cost of production.