Connecting a Human Limb to an Exoskeleton

• Published in: IEEE transactions on robotics Vol. 28; no. 3; pp. 697 - 709
• Main Authors: Jarrasse, N., Morel, G.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.06.2012; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Automatic; Biological and medical sciences; Biomechanics; Biomechanics. Biorheology; Computer science; control theory; systems; Control theory. Systems; Drives; Engineering Sciences; Exact sciences and technology; exoskeleton; Exoskeletons; fixations; Force; Fundamental and applied biological sciences. Psychology; Humans; hyperstaticity; isostaticity condition; Joints; Kinematics; Legs; Linkage mechanisms, cams; Mechanical engineering. Machine design; Mechanics; Robotics; Robots; Tin; Tissues, organs and organisms biophysics; Vertebrates: osteoarticular system, musculoskeletal system; wearable robotic structures; Human; Freedom degree; Passive system; Experimental study; Modeling; Robotics; hyperstaticity; Biomechanics; isostaticity condition; Fixation; Limb; fixations; Kinematics; exoskeleton; Kinematic chain; Skeleton; Arm; Robot; wearable robotic structures; kinematics; Wearable robotic structures; biomechanics
• ISSN: 1552-3098; 1941-0468
• DOI: 10.1109/TRO.2011.2178151

When developing robotic exoskeletons, the design of physical connections between the device and the human limb to which it is connected is a crucial problem. Indeed, using an embedment at each connection point leads to uncontrollable forces at the interaction port, induced by hyperstaticity. In practice, these forces may be large because in general the human limb kinematics and the exoskeleton kinematics differ. To cope with hyperstaticity, the literature suggests the addition of passive mechanisms inside the mechanism loops. However, empirical solutions that are proposed so far lack proper analysis and generality. In this paper, we study the general problem of connecting two similar kinematic chains through multiple passive mechanisms. We derive a constructive method that allows the determination of all the possible distributions of freed degrees of freedom across different fixation mechanisms. It also provides formal proofs of global isostaticity. Practical usefulness is illustrated through two examples with conclusive experimental results: a preliminary study made on a manikin with an arm exoskeleton controlling the movement (passive mode) and a larger campaign on ten healthy subjects performing pointing tasks with a transparent robot (active mode).