Series Elastic Actuation decouples actuator inertia from the interaction ports and is thus advantageous for force-controlled devices. Parallel or even passive compliance can fulfill a complementary role by compensating for gravitational or periodic inertial forces or by providing passive guidance. Here, these concepts are combined in an underactuated six degree of freedom (DoF) compliant manipulator with one actuated DoF. The mechanism comprises a spring assembly in which each spring serves as an actuation element and simultaneously provides passive compliance in the unactuated DoF. The device is designed to assist weight shifting via controlled lateral forces on a human pelvis during treadmill walking and its eigenfrequencies are tuned to align with normal gait. Six-DoF force and torque sensing are realized via a model of the spring deformation characteristics in combination with low-cost inertial and optical sensors. Experimental evaluation demonstrates that the system can effectively follow physiological weight shifting with low interaction forces and also has little impact on remaining pelvis motions.

One key question in motor learning is how the complex tasks in daily life - those that require coordinated movements of multiple joints - should be trained. Often, complex tasks are directly taught as a whole, even though training of simple movement components before training the entire movement has been shown to be more effective for particularly complex tasks ('part-whole transfer paradigm'). The important implication of the part-whole transfer paradigm, e.g. on the field of rehabilitation robotics, is that training of most complex tasks could be simplified and, subsequently, devices used to train can become simpler and more affordable. In this way, robot-assisted rehabilitation could become more accessible. However, often the last step in the training process is forgotten: the recomposition of several simple movement components to a complete complex movement. Therefore, at least for the last training step, a complex rehabilitation device may be required.In a pilot study, we wanted to investigate if a complex robotic device (e.g. an exoskeleton robot with many degrees of freedom), such as the ARMin rehabilitation robot, is really beneficial for training the coordination between several simpler movement components or if training using visual feedback would lead to equal benefits. In a study, involving 16 healthy participants, who were instructed in a complex rugby motion, we could show first trends on the following two aspects: i) the part-whole transfer paradigm seems to hold true and therefore, simple robots might be used for training movement primitives. ii) Visual feedback does not seem to have the same potential, at least in healthy humans, to replace visuo-haptic guidance for movement recomposition of complex tasks. Therefore, complex rehabilitation robots seem to be beneficial for training complex real-life tasks.

On the quest to bring function of prosthetic legs closer to their biological counterparts, intuitive interplay of their control with the user’s impedance modulation is key. We present two control features to enable more physiological and more user-adaptive control of prosthetic legs: a neuromusculoskeletal impedance model (NeurImp) including a reflexive component, and a human model reference adaptive controller (HuMRAC), which can be combined with the former. In stance-phase simulations, the NeurImp allowed to control a prosthetic leg with physiological knee joint angle and moment. When perturbations were applied, the HuMRAC reduced the resulting root mean square error (RMSE) between simulated and physiological reference angle by 96%. In a pilot experiment with two unimpaired and one amputee subject, gait with the NeurImp deviated more from a physiological reference than with a conventional visco-elastic impedance controller. Subjects, however, preferred the NeurImp. When adding the HuMRAC to either of the two impedance controllers, the RMSE between the actual and the physiological reference angle was reduced by up to 54%. Subjects confirmed this finding and reported an easier stance-toswing transition. Simulation and pilot experiment suggest that a reflex-based impedance controller combined with an adaptive controller may improve user-cooperative behavior of active knee exoprostheses.