A crucial problem in developing robotic exoskeletons lies in the design of physical connexions between the device and the human limb it is connected to. Indeed, because in general the human limb kinematics and the exoskeleton kinematics differ, using an embedment at each connection point leads to hyperstaticity. Therefore, uncontrollable forces can appear at the interaction port. To cope with this problem, literature suggests to add passive mechanisms at the fixation points. However, empirical solutions proposed so far suffer from a lack of proper analysis and generality. In this paper, the general problem of connecting two similar kinematic chains through multiple passive mechanisms is studied. A constructive method that allows to determine all the possible repartitions of freed DoFs across the different fixation mechanisms is derived. It includes formal proofs of global isostaticity. Practical usefulness is illustrated through an example with conclusive experimental results.

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Some of the work presented in this thesis expands on two earlier publications documenting this research. The first is a conference paper “Programmable Springs: Developing Compliant Actuators for Autonomous Robots” and was presented at the “Towards Autonomous Robotic Sys-tems» (TAROS) conference in 2006, where it received the Springer books best paper award. The second publication is an extended version of this first paper, published in the Journal of Robotics and Autono-mous Systems in 2007, and entitled “Programmable springs: Developing actuators with programmable comp-liance for autonomous robots”. The term ‘Programmable Spring’ is not entirely appropriate for the system I have developed during the course of this thesis, but it has established itself as catchy term for refer-ring to my research. More appropriate descriptions might be ‘Mechanical Systems Emulator’, ‘Programmable Compliance Actuator’ or ‘Programmable Spring Damper’, but these are less catchy and I suspect the original term will persist.

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Background: Manual body weight supported treadmill training and robot-aided treadmill training are frequently used techniques for the gait rehabilitation of individuals after stroke and spinal cord injury. Current evidence suggests that robot-aided gait trai-ning may be improved by making robotic behavior more patient-cooperative. In this study, we have investigated the immediate effects of patient-cooperative versus non-cooperative robot-aided gait training on individuals with incomplete spinal cord injury (iSCI).
Methods: Eleven patients with iSCI participated in a single training session with the gait rehabilitation robot Lokomat. The pati-ents were exposed to four different training modes in random order: During both noncooperative position control and compliant im-pedance control, fixed timing of movements was provided. During two variants of the patient-cooperative path control approach, free timing of movements was enabled and the robot provided only spatial guidance. The two variants of the path control approach diffe-red in the amount of additional support, which was either individually adjusted or exaggerated. Joint angles and torques of the ro-bot as well as muscle activity and heart rate of the patients were recorded. Kinematic variability, interaction torques, heart rate and muscle activity were compared between the different conditions. Results: Patients showed more spatial and temporal kinematic va-riability, reduced interaction torques, a higher increase of heart rate and more muscle activity in the patient-cooperative path control mode with individually adjusted support than in the non-cooperative position control mode. In the compliant impedance con-trol mode, spatial kinematic variability was increased and interaction torques were reduced, but temporal kinematic variability,
heart rate and muscle activity were not significantly higher than in the position control mode. Conclusions: Patient-cooperative robot-aided gait training with free timing of movements made individuals with iSCI participate more actively and with larger kine-matic variability than non-cooperative, position-controlled robotaided gait training.

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We provide a general approach for learning robotic motor skills from human demonstration. To represent an observed movement, a non-linear differential equation is learned such that it reproduces this movement. Based on this representation, we build a library of movements by labeling each recorded movement according to task and context (e.g., grasping, placing, and releasing). Our differential equation is formulated such that generalization can be achieved simply by adapting a start and a goal parameter in the equation to the desired position values of a movement. For object manipulation, we present how our framework extends to the control of gripper orientation and finger posi-tion. The feasibility of our approach is demonstrated in simulation as well as on the Sarcos dextrous robot arm. The robot learned a pick-and-place operation and a water-serving task and could generalize these tasks to novel situations.

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Background: In many stroke patients arm func-tion is limited, which can be related to an abnormal coupling between shoulder and elbow joints. The extent to which this can be translated to activities of daily life (ADL), in terms of muscle activation during ADL-like movements, is rather unknown. There-fore, the present study examined the occurrence of abnormal coupling on functional, ADL-like reaching movements of chronic stroke patients by comparison with healthy persons. Methods: Upward multi-joint reaching movements (20 repetitions at a self-selected spe-ed to resemble ADL) were compared in two conditions: once facilitated by arm weight compensation and once resisted to provoke a potential abnormal coupling. Changes in movement performance (joint angles) and muscle activation (amplitude of activity and co-activation) between conditions were compared between healthy persons and stroke patients using a repeated measures ANOVA. Results: The present study showed slight changes in joint excursion and muscle activation of stroke patients due to shoulder elevation re-sistance during functional reach. Remarkably, in healthy persons similar changes were observed. Even the results of a sub-group of the more impaired stroke patients did not point to an abnormal coupling between shoulder elevation and elbow flexion during func-tional reach. Conclusions: The present findings suggest that in mildly and moderately affected chronic stroke patients ADL-like arm movements are not substantially affected by abnormal synergistic coupling. In this case, it is implied that other major contri-butors to limitations in functional use of the arm should be identified and targeted individually in rehabilitation, to improve use of the arm in activities of daily living.

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