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Biomechanical effects of passive hip springs during walking

Authors: Haufe, Florian L; Wolf, Peter; Riener, Robert; Grimmer, Martin

 

Passive spring-like structures can store and return energy during cyclic movements and thereby reduce the energetic cost of locomotion. That makes them important components of the human body and wearable assistive devices alike. This study investigates how springs placed anteriorly across the hip joint affect leg joint angles and powers, and leg muscle activities during level walking at 0.5 to 2.1 m/s.

We hypothesized that the anterior hip springs (I) load hip extension, (II) support hip flexion and (III) affect ankle muscle activity and dynamics during walking. Effects at the ankle were expected because hip and ankle redistribute segmental power in concert to achieve forward progression.

We observed that the participants’ contribution to hip power did not increase during hip extension as the spring stored energy. Simultaneously, the activities of plantarflexor muscles that modulate energy storage in the Achilles tendon were reduced by 28% (gastrocnemius medialis) and 9% (soleus). As the spring returned energy with the onset of hip flexion, the participants’ contribution to hip power was reduced by as much as 23%. Soleus activity before push-off increased by up to 9%.

Instead of loading hip extension, anterior hip springs seem to store and return parts of the energy normally exchanged with the Achilles tendon. Thereby, the springs support hip flexion but may reduce elastic energy storage in and hence recoil from the Achilles tendon. This interaction should be considered during the design and simulation of wearable assistive devices as it might – depending on user characteristics – enhance or diminish their overall functionality.

Reference

Posted on: November 7, 2019

An Omnidirectional Aerial Manipulation Platform for Contact-Based Inspection

Authors: Bodie, Karen; Brunner, Maximilian; Pantic, Michael; Walser, Stefan; Pfändler, Patrick; Angst, Ueli; Siegwart, Roland; Nieto, Juan

This paper presents an omnidirectional aerial manipulation platform for robust and responsive interaction with unstructured environments, toward the goal of contact-based inspection. The fully actuated tilt-rotor aerial system is equipped with a rigidly mounted end-effector, and is able to exert a 6 degree of freedom force and torque, decoupling the system’s translational and rotational dynamics, and enabling precise interaction with the environment while maintaining stability. An impedance controller with selective apparent inertia is formulated to permit compliance in certain degrees of freedom while achieving precise trajectory tracking and disturbance rejection in others. Experiments demonstrate disturbance rejection, push-and-slide interaction, and on- board state estimation with depth servoing to interact with local surfaces. The system is also validated as a tool for contact-based non-destructive testing of concrete infrastructure.

Reference

  • Detailed record: arXiv
  • DOI:
  • Date: 2019
Posted on: October 22, 2019

Multiple Hypothesis Semantic Mapping for Robust Data Association

Authors: Bernreiter, Lukas; Gawel, Abel; Sommer, Hannes; Nieto, Juan; Siegwart, Roland; Cadena Lerma, Cesar

In this letter, we present a semantic mapping approach with multiple hypothesis tracking for data association. As semantic information has the potential to overcome ambiguity in measurements and place recognition, it forms an eminent modality for autonomous systems. This is particularly evident in urban scenarios with several similar-looking surroundings. Nevertheless, it requires the handling of a non-Gaussian and discrete random variable coming from object detectors. Previous methods facilitate semantic information for global localization and data association to reduce the instance ambiguity between the landmarks. However, many of these approaches do not deal with the creation of completely globally consistent representations of the environment and typically do not scale well. We utilize multiple hypothesis trees to derive a probabilistic data association for semantic measurements by means of position, instance, and class to create a semantic representation. We propose an optimized mapping method and make use of a pose graph to derive a novel semantic SLAM solution. Furthermore, we show that semantic covisibility graphs allow for a precise place recognition in urban environments. We verify our approach using real-world outdoor dataset and demonstrate an average drift reduction of 33% w.r.t. the raw odometry source. Moreover, our approach produces 55% less hypotheses on average than a regular multiple hypothesis approach.

Reference

Posted on: October 22, 2019

CVI-SLAM—Collaborative Visual-Inertial SLAM

Authors: Karrer, Marco; Schmuck, Patrik; Chli, Margarita

With robotic perception constituting the biggest impediment before robots are ready for employment in real missions, the promise of more efficient and robust robotic perception in multiagent, collaborative missions can have a great impact on many robotic applications. Employing an ubiquitous and well-established visual-inertial setup onboard each agent, in this letter, we propose CVI-SLAM, a novel visual-inertial framework for centralized collaborative simultaneous localization and mapping (SLAM). Sharing all information with a central server, each agent outsources computationally expensive tasks, such as global map optimization to relieve onboard resources and passes on measurements to other participating agents, while running visual-inertial odometry onboard to ensure autonomy throughout the mission. Thoroughly analyzing CVI-SLAM, we attest to its accuracy and the improvements arising from the collaboration, and evaluate its scalability in the number of participating agents and applicability in terms of network requirements.

Reference

Posted on: October 22, 2019

Cortico–reticulo–spinal circuit reorganization enables functional recovery after severe spinal cord contusion

Authors: Asboth, Leonie; Friedli, Lucia; Beauparlant, Janine; Martinez-Gonzalez, Cristina; Anil, Selin; Rey, Elodie; Baud, Laetitia; Pidpruzhnykova, Galyna; Anderson, Mark A.; Shkorbatova, Polina; Batti, Laura; Pagès, Stephane; Kreider, Julie; Schneider, Bernard L.; Barraud, Quentin; Courtine, Grégoire

Severe spinal cord contusions interrupt nearly all brain projections to lumbar circuits producing leg movement. Failure of these projections to reorganize leads to permanent paralysis. Here we modeled these injuries in rodents. A severe contusion abolished all motor cortex projections below injury. However, the motor cortex immediately regained adaptive control over the paralyzed legs during electrochemical neuromodulation of lumbar circuits. Glutamatergic reticulospinal neurons with residual projections below the injury relayed the cortical command downstream. Gravity-assisted rehabilitation enabled by the neuromodulation therapy reinforced these reticulospinal projections, rerouting cortical information through this pathway. This circuit reorganization mediated a motor cortex–dependent recovery of natural walking and swimming without requiring neuromodulation. Cortico–reticulo–spinal circuit reorganization may also improve recovery in humans.

Reference

Posted on: October 22, 2019

Vision-based Control of a Quadrotor in User Proximity: Mediated vs End-to-End Learning Approaches

Authors:  Mantegazza, Dario; Guzzi, Jérôme, Gambardella, Luca M.; Giusti, Alessandro

We consider the task of controlling a quadrotor to hover in front of a freely moving user, using input data from an onboard camera. On this specific task we compare two widespread learning paradigms: a mediated approach, which learns an high-level state from the input and then uses it for deriving control signals; and an end-to-end approach, which skips high-level state estimation altogether. We show that despite their fundamental difference, both approaches yield equivalent performance on this task. We finally qualitatively analyze the behavior of a quadrotor implementing such approaches.

Reference

  • Detailed record: arXiv
  • DOI: 
  • Date: 2019
Posted on: October 21, 2019

Video: Pointing Gestures for Proximity Interaction

Authors: Gromov, Boris; Guzzi, Jérôme; Abbate, Gabriele; Gambardella, Luca; Giusti, Alessandro

We propose a system to control robots in the users proximity with pointing gestures-a natural device that people use all the time to communicate with each other. Our system has two requirements: first, the robot must be able to reconstruct its own motion, e.g. by means of visual odometry; second, the user must wear a wristband or smartwatch with an inertial measurement unit. Crucially, the robot does not need to perceive the user in any way. The resulting system is widely applicable, robust, and intuitive to use.

Reference

Posted on: October 21, 2019

User-driven walking assistance: first experimental results using the MyoSuit

Authors: Haufe, Florian L.; Kober, Alessia M.; Schmidt, Kai; Sancho-Puchades, Alejandro; Duarte, Jaime E.; Wolf, Peter; Rieber, Robert

Wearable robots for the legs have been developed for gait rehabilitation training and as assistive devices. Most devices have been rigid exoskeletons designed to substitute the function of users who are completely paralyzed. While effective for this target group, exoskeletons limit their users’ contributions to movements. Soft wearable robots have been suggested as an alternative that allows, and requires, active contributions from users with residual mobility. In this work, we first tested if the MyoSuit, a lightweight, lower-limb soft wearable robot, affected the walking kinematics of unimpaired users. Secondly, we evaluated the assistance delivered to a patient with a gait impairment. In our first study, 10 unimpaired participants walked on a treadmill at speeds between 0.5 and 1.3 m/s. We found that wearing the MyoSuit in its transparency mode did not affect the participants’ walking kinematics (RMS difference of joint angles <; 1.6°). Step length and the ratio of stance-to-stride duration were not affected when wearing the MyoSuit. In our case study with one spinal cord injured participant, the MyoSuit supported the participant to increase his 10 MWT walking speed from 0.36 to 0.52 m/s, a substantial clinically meaningful improvement. Our results show that the MyoSuit allows user-driven, kinematically unaltered walking and provides effective assistance. Systems like the MyoSuit are a promising technology to bridge the gap between rigid exoskeletons and unassisted ambulation.

Reference

Posted on: October 21, 2019

User-centered Design and Evaluation of Physical Interfaces for an Exoskeleton for Paraplegic Users

Authors: Meyer, Jan T.; Schrade, Stefan O.; Lambercy, Olivier; Gassert, Roger

Over the last decade, the use of wearable exoskeletons for human locomotion assistance has become more feasible. The VariLeg powered lower limb robotic exoskeleton is an example of such systems, potentially enabling paraplegic users to perform upright activities of daily living. The acceptance of this type of robotic assistive technologies is often still affected by limited usability, in particular regarding the physical interface between the exoskeleton and the user (here referred to as pilot). In this study, we proposed and evaluated a novel pilot attachment system (PAS), which was designed based on user-centered design with experienced paraplegic exoskeleton users. Subjective assessments to compare usability aspects of the initial and the redesigned physical interfaces were conducted with two paraplegic and five healthy pilots. The redesigned PAS showed a 45% increase in the system usability scale (SUS), normalized to the PAS of a commercial exoskeleton assessed in the same manner. Pain rating scales assessed with healthy pilots indicated an increased comfort using the redesigned PAS while performing several activities of daily living. Overall, an improvement in usability relative to the initial PAS was achieved through intensified user evaluation and individual needs assessments. Hence, a user-centered design of physical body-machine interfaces has the potential to positively influence the usability and acceptance of lower limb exoskeletons for paraplegic users.

Reference

Posted on: October 21, 2019