Technical session talks from ICRA 2012
TechTalks from event: Technical session talks from ICRA 2012
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A Comparison of Parallel and Series Elastic Elements in an Actuator for Mimicking Human Ankle Joint in Walking and RunningElastic elements in prosthetic devices can help to reduce peak power (PP) and energy requirements (ER) for the actuators. Calculations showed that it is impossible with current commercial motor technology to mimic human ankle behavior in detail for higher walking and running speeds with single motor solutions using a Serial Elastic Actuator (SEA). Concerning this result we checked the requirements of a parallel elastic actuator (PEA) and a combination of serial and parallel (SE+PEA) springs. We found that a PEA can reduce PP additionally in comparison to the SEA by preloading the spring in the flight phase. This reduces also peak torque. But this loading needs additional energy so that the ER increase in comparison to the SEA. The SE+PEA concept can further decrease PP. With that, the ER are less than the PEA but higher than for the SEA. The results show less benefit for the PEA and the SE+PEA when a constant stiffness and a fixed parallel spring slack length is used for both gaits and all speeds. All concepts show that mimicking human ankle joint behavior in running and walking at higher speeds is still challenging for single motor devices.
Measuring End-Point Stiffness by Means of a Modular Mechatronic Systemhuman arm muscular stiffness measurement is often a complex procedure which is of great interest for many disciplines from biomechanics to medicine and robotics. Modulation of impedance represents the principal mechanism underlying control of movements and interaction with external environment. Past literature proposed several methods to estimate multijoint hand stiffness while postural maintaining and dynamic tasks, mainly performed by means of planar robotic manipulanda. Despite these approaches are still considered robust and accurate, the computational burden of the robotic controller and hardware limitations make them not easy to implement. In the present paper a novel mechanism conceived for measuring multijoint planar stiffness by in single trial and in a reduced execution time is described and tested in different configurations. The device consisted in a mechanical rotary mechanism which applies cyclic radial perturbation to human arm of a known displacement and the force is acquired by means of a 6-axes commercial load cell. The outcomes suggest that the system is not only reliable in standalone mode but allows obtaining a reliable bi-dimensional estimation of arm stiffness even plugged in a planar manipulandum, dramatically reducing the amount of time for measurement and allowing to decouple the two controllers of the planar manipulator on which is mounted and the device itself.
AssistOn-SE: A Self-Aligning Shoulder-Elbow ExoskeletonWe present AssistOn-SE, a novel powered exoskeleton for robot-assisted rehabilitation that allows for movements of the shoulder girdle as well as shoulder rotations. Automatically adjusting its joint axes, AssistOn-SE can enable a perfect match between human joint axes and the device axes, not only guaranteeing ergonomy and comfort throughout the therapy, but also extending the usable range of motion for the shoulder joint. Moreover, the adjustability feature significantly shortens the setup time required to attach the patient to the exoskeleton, allowing more effective time be spend on exercises instead of wasting this valuable resource for adjustments. Back-driveable design of AssistOn-SE supports both passive translational movements of the center of glenohumeral joint and independent active control of these degrees of freedom. Thanks to this property, glenohumeral mobilization and scapular stabilization exercises can also be delivered with AssistOn-SE, extending the type of therapies that can be administered using upper-arm exoskeletons. We introduce the design of the exoskeleton and present the kinematic analysis of its self-aligning joint. We also provide implementation details for an early prototype as well as some experimental results detailing range of motion of the device and its ability to track movements of the shoulder girdle.