Development of a robotic ortho-prosthesis for trans-humeral amputees

Abstract

Over the years trans-humeral prostheses have been developed as a remedy for trans-humeral amputation: the amputation occurs between shoulder and elbow. For thebest usage of the trans-humeral prostheses, amputee should have a strong residual arm(stump arm) after the amputation. Furthermore, the ranges of motions and also thefull functionality of the prosthesis will be limited if the amputee has a weak stump arm.Moreover, prolonged applying of the loads on the stump arm can cause musculo-skeletaldisorders.In order to improve the dexterity of the prosthesis, they are developed with more jointsand actuators. Hence, the weight of the prosthesis increases. There is a need forpower assisting the weak stump arm while the prosthesis is at work. Trans-humeralortho-prosthesis is a device which assists the power of stump arm from an orthosis whilereplacing the missing upper limb with trans-humeral prosthesis. This research is carriedto develop a 9 Degrees of Freedom trans-humeral ortho-prosthesis. It consists of 4 DoFmotions: shoulder horizontal flexion/extension, shoulder vertical flexion/extension,shoulder abduction/adduction and shoulder internal/external rotation, at the ortho-sis and 5 DoF motions: elbow flexion/extension, forearm supination/pronation, wristulnar/radial deviation, wrist flexion/extension and compound motion of thumb andindex finger, at the prosthesis. Moreover, shoulder abduction/adduction is supportedas a passive DoF in order to compensate the misalignments of the joints caused bythe motions of clavicle and the scapula in the sagittal plane while enabling shoulderabduction/adduction . Even though the orthosis is designed to achieve 4 DoF motions,it contains 6 DoF motions. Therefore, the whole ortho-prosthesis becomes a redundantmanipulator.Simulation experiments have been carried out to determine the workspace of the handof the ortho-prosthesis and to determine the manipulability of the ortho-prosthesis.Workspace plots show that it can reach the workspace of a human hand. Manipu-lability measures: manipulability index, minimum singular values, condition numberand manipulability ellipsoids verify that the trans-humeral ortho-prosthesis would notreach singular configurations. Furthermore, it is confirmed that the ortho-prosthesis iscapable of performing dexterous motions due to its high manipulability after carryingout experiments with the fabricated prototype of the trans-humeral ortho-prosthesis.