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Trajectory Optimization for Wheeled-Legged Quadrupedal Robots Driving in Challenging Terrain

Authors: Suzano Medeiros,V.; Jelavic, E.; Bjelonic, M.; Siegwart, R.; Meggiolaro, M. A.; Hutter, M.

Abstract

Wheeled-legged robots are an attractive solution for versatile locomotion in challenging terrain. They combine the speed and efficiency of wheels with the ability of legs to traverse challenging terrain. In this paper, we present a trajectory optimization formulation for wheeled-legged robots that optimizes over the base and wheels’ positions and forces and takes into account the terrain information while computing the plans. This enables us to find optimal driving motions over challenging terrain. The robot is modeled as a single rigid-body, which allows us to plan complex motions and still keep a low computational complexity to solve the optimization quickly. The terrain map, together with the use of a stability constraint, allows the optimizer to generate feasible motions that cannot be discovered without taking the terrain information into account. The optimization is formulated as a Nonlinear Programming (NLP) problem and the reference motions are tracked by a hierarchical whole-body controller that computes the torque actuation commands for the robot. The trajectories have been experimentally verified on quadrupedal robot ANYmal equipped with non-steerable torque-controlled wheels. Our trajectory optimization framework enables wheeled quadrupedal robots to drive over challenging terrain, e.g., steps, slopes, stairs, while negotiating these obstacles with dynamic motions.

Reference

  • Published in: EEE Robotics and Automation Letters
  • Detailed record: yy
  • DOI: 10.1109/LRA.2020.2990720
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  • Date: 2020
Posted on: May 10, 2020

Minimalist Design of a 3-Axis Passive Compliant Foot for Sprawling Posture Robots

Authors: Melo, K. ; Horvat, T. ; Ijspeert, A. J.

Abstract

A sprawled posture amphibious biorobot resembling a salamander had helped us in conquering scientific questions of the locomotion of these animals and offer us with technological possibilities for applications in disaster response. However, so far the foot structure of these robots is simplified in a ball foot that occludes many interesting aspects of the rich dynamics of interaction with the ground that these animals/robots have. In this paper, we present a minimalist design of a three degree of freedom foot that uses passive mechanics, soft materials and simple fabrication techniques to achieve features observed in sprawling posture animals walking gaits. The parameters of our design can be adjusted for specific visco-elastic properties (stiffness, damping) and easily adapted to different sizes and forms. We presented the fabrication technique used to achieve several configurations of the foot structure. Stress analysis of the design helped us to verify the right selection of materials and configurations to achieve desired behaviors. We expect to use these feet for better understanding the limb-ground interaction in sprawled animals as well as improving the locomotion capabilities of biorobots in general.

Reference

  • Published in: 2019 2nd IEEE International Conference on Soft Robotics (Robosoft 2019), 788-794
  • DOI: 10.1109/ROBOSOFT.2019.8722792
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  • Date: 2019
Posted on: May 10, 2020

Biomechanical effects of passive hip springs during walking

Authors: Haufe, F. L. ; Wolf, P. ; Riener, R. ; Grimmer, M.

Abstract

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

  • Published in: Journal of Biomechanics (Volume 98, 2. January 2020, 109432)
  • DOI: 10.1016/j.jbiomech.2019.109432
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  • Date: 2020
Posted on: May 10, 2020

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

Authors: Mantegazza, D. ; Guzzi, J.; Gambardella, L. M.; Giusti, A.

Abstract

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 a 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

  • Published in: 2019 International Conference on Robotics and Automation (ICRA), Montreal, QC, Canada, 2019, pp. 6489-6495
  • DOI: doi: 10.1109/ICRA.2019.8794377
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  • Date: 2019
Posted on: May 10, 2020

Matching Features without Descriptors:Implicitly Matched Interest Points

Authors: Cieslewski, T. ; Bloesch, M. ; Scaramuzza, D.

Abstract

The extraction and matching of interest points is a prerequisite for many geomet-ric computer vision problems. Traditionally, matching has been achieved by assigningdescriptors to interest points and matching points that have similar descriptors. In this pa-per, we propose a method by which interest points are instead already implicitly matchedat detection time. With this, descriptors do not need to be calculated, stored, commu-nicated, or matched any more. This is achieved by a convolutional neural network withmultiple output channels and can be thought of as a collection of a variety of detec-tors, each specialised to specific visual features. This paper describes how to design andtrain such a network in a way that results in successful relative pose estimation perfor-mance despite the limitation on interest point count. While the overall matching score isslightly lower than with traditional methods, the approach is descriptor free and thus en-ables localization systems with a significantly smaller memory footprint and multi-agentlocalization systems with lower bandwidth requirements. The network also outputs theconfidence for a specific interest point resulting in a valid match. We evaluate perfor-mance relative to state-of-the-art alternatives.

Reference

  • Presented at: British Machine Vision Conference (BMVC), Cardiff, UK, 2019
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  • Date: 2019
Posted on: May 10, 2020

Trajectory features estimation for legged robots

Authors: Chavez-Garcia, R. O. ; Guzzi, J. ; Giusti, A. ; Gambardella, L. M.

Reference

  • Presented at: IEEE International Conference on Robotics and Automation (ICRA) 2019, Montreal, QC, Canada, May 20-24, 2019
  • Date: 2019
Posted on: May 10, 2020

Biomechanical effects of passive hip springs during walking

Authors:Haufe, F. L. ; Wolf, P. ; Riener, R. ; Grimmer, M.

Abstract

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

  • Published in: Journal of Biomechanics, 109432
  • DOI: 10.1016/j.jbiomech.2019.109432
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  • Date: 2019
Posted on: May 10, 2020

Focus Is All You Need: Loss Functions For Event-based Vision

Authors: Gallego, G.; Gehrig, M.; Scaramuzza, D.

Abstract

Event cameras are novel vision sensors that output pixel-level brightness changes (“events”) instead of traditional video frames. These asynchronous sensors offer several advantages over traditional cameras, such as, high temporal resolution, very high dynamic range, and no motion blur. To unlock the potential of such sensors, motion compensation methods have been recently proposed. We present a collection and taxonomy of twenty two objective functions to analyze event alignment in motion compensation approaches (Fig.1). We call them focus loss functions since they have strong connections with functions used in traditional shape-from-focus applications. The proposed loss functions allow bringing mature computer vision tools to the realm of event cameras. We compare the accuracy and runtime performance of all loss functions on a publicly available dataset,and conclude that the variance, the gradient and the Laplacian magnitudes are among the best loss functions. The applicability of the loss functions is shown on multiple tasks:rotational motion, depth and optical flow estimation. The proposed focus loss functions allow to unlock the outstanding properties of event cameras.

Reference

  • Presented at: IEEE Conference on Computer Vision and Pattern Recognition (CVPR), Long Beach, USA. 2019
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  • Date: 2019
Posted on: May 10, 2020

Iterative Design and Evaluation of a Tangible Robot-Assisted Handwriting Activity for Special Education

Authors: Guneysu Ozgur, A.; Özgür, A.; Asselborn, T.; Johal, W.; Yadollahi, E.; Bruno, B.; Skweres, M.; Dillenbourg, P.

Abstract

In this article we investigate the role of interactive haptic-enabled tangible robots in supporting the learning of cursive letter writing for children with attention and visuomotor coordination issues. We focus on the two principal aspects of handwriting that are linked to these issues: Visual perception and visuomotor coordination. These aspects, respectively, enhance two features of letter representation in the learner’s mind in particular, namely the shape (grapheme) and the dynamics (ductus) of the letter, which constitute the central learning goals in our activity. Building upon an initial design tested with 17 healthy children in a preliminary school, we iteratively ported the activity to an occupational therapy context in 2 different therapy centers, in the context of 3 different summer school camps involving a total of 12 children having writing difficulties. The various iterations allowed us to uncover insights about the design of robot-enhanced writing activities for special education, specifically highlighting the importance of ease of modification of the duration of an activity as well as of adaptable frequency, content, flow and game-play and of providing a range of evaluation test alternatives. Results show that the use of robot-assisted handwriting activities could have a positive impact on the learning of the representation of letters in the context of occupational therapy (V = 1, 449, p < 0.001, r = 0.42). Results also highlight how the design changes made across the iterations affected the outcomes of the handwriting sessions, such as the evaluation of the performances, monitoring of the performances, and the connectedness of the handwriting.

Reference

  • Published in: Frontiers in Robotics and AI (Volume: 7 Issue: 29, 2020)
  • DOI: 10.3389/frobt.2020.00029
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  • https://www.frontiersin.org/articles/10.3389/frobt.2020.00029/full

  • Date: 2020
Posted on: May 10, 2020

Robogami: A Fully Integrated Low-Profile Robotic Origami

Authors: Firouzeh, A.; Paik, J.;

 

Abstract

Intelligent robotic systems that can react to unprogrammed tasks and unforeseen environmental changes require augmented “softness.” Robogami, a low-profile origami robot, addresses intrinsic (material-wise) and extrinsic (mechanism-wise) softness with its multi-degree-of-freedom (DOF) body driven by soft actuators. The unique hardware of the Robogami and its submillimeter thick construction enable diverse transformations as those achievable by the paper origami. The presented Robogami shows the first fully integrated version that has all the essential components including its controller within a thin sheet. Construction of this robot is possible via precise, repeatable, and low cost planar fabrication methods often reserved for microscale fabrications. In this research, we aim at expanding the capabilities of Robogamis by embedding bidirectional actuation, sensing, and control circuit. To assess the performance of the proposed sensors and actuators, we report on the performance of these components in a single module and in the four-legged crawler robot.

Reference

    • Published in: Journal Of Mechanisms And Robotics-Transactions Of The Asme (Volume: 7, Issue: 2, 2015)
    • DOI: 10.1115/1.4029491
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    • Posted on: May 10, 2020