5,592 research outputs found
A Passivity-Based Distributed Reference Governor for Constrained Robotic Networks
This paper focuses on a passivity-based distributed reference governor (RG)
applied to a pre-stabilized mobile robotic network. The novelty of this paper
lies in the method used to solve the RG problem, where a passivity-based
distributed optimization scheme is proposed. In particular, the gradient
descent method minimizes the global objective function while the dual ascent
method maximizes the Hamiltonian. To make the agents converge to the agreed
optimal solution, a proportional-integral consensus estimator is used. This
paper proves the convergence of the state estimates of the RG to the optimal
solution through passivity arguments, considering the physical system static.
Then, the effectiveness of the scheme considering the dynamics of the physical
system is demonstrated through simulations and experiments.Comment: 8 pages, International Federation of Automatic Conference 2017, 8
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A Minimal Developmental Model Can Increase Evolvability in Soft Robots
Different subsystems of organisms adapt over many time scales, such as rapid
changes in the nervous system (learning), slower morphological and neurological
change over the lifetime of the organism (postnatal development), and change
over many generations (evolution). Much work has focused on instantiating
learning or evolution in robots, but relatively little on development. Although
many theories have been forwarded as to how development can aid evolution, it
is difficult to isolate each such proposed mechanism. Thus, here we introduce a
minimal yet embodied model of development: the body of the robot changes over
its lifetime, yet growth is not influenced by the environment. We show that
even this simple developmental model confers evolvability because it allows
evolution to sweep over a larger range of body plans than an equivalent
non-developmental system, and subsequent heterochronic mutations 'lock in' this
body plan in more morphologically-static descendants. Future work will involve
gradually complexifying the developmental model to determine when and how such
added complexity increases evolvability
Cable Robot Performance Evaluation by Wrench Exertion Capability
Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided
Probabilistic RGB-D Odometry based on Points, Lines and Planes Under Depth Uncertainty
This work proposes a robust visual odometry method for structured
environments that combines point features with line and plane segments,
extracted through an RGB-D camera. Noisy depth maps are processed by a
probabilistic depth fusion framework based on Mixtures of Gaussians to denoise
and derive the depth uncertainty, which is then propagated throughout the
visual odometry pipeline. Probabilistic 3D plane and line fitting solutions are
used to model the uncertainties of the feature parameters and pose is estimated
by combining the three types of primitives based on their uncertainties.
Performance evaluation on RGB-D sequences collected in this work and two public
RGB-D datasets: TUM and ICL-NUIM show the benefit of using the proposed depth
fusion framework and combining the three feature-types, particularly in scenes
with low-textured surfaces, dynamic objects and missing depth measurements.Comment: Major update: more results, depth filter released as opensource, 34
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Bearing-based formation control with second-order agent dynamics
We consider the distributed formation control problem for a network of agents using visual measurements. We propose solutions that are based on bearing (and optionally distance) measurements, and agents with double integrator dynamics. We assume that a subset of the agents can track, in addition to their neighbors, a set of static features in the environment. These features are not considered to be part of the formation, but they are used to asymptotically control the velocity of the agents. We analyze the convergence properties of the proposed protocols analytically and through simulations.Published versionSupporting documentatio
A Dynamics and Stability Framework for Avian Jumping Take-off
Jumping take-off in birds is an explosive behaviour with the goal of
providing a rapid transition from ground to airborne locomotion. An effective
jump is predicated on the need to maintain dynamic stability through the
acceleration phase. The present study concerns understanding how birds retain
control of body attitude and trajectory during take-off. Cursory observation
suggests that stability is achieved with relatively little cost. However,
analysis of the problem shows that the stability margins during jumping are
actually very small and that stability considerations play a significant role
in selection of appropriate jumping kinematics. We use theoretical models to
understand stability in prehensile take-off (from a perch) and also in
non-prehensile take-off (from the ground). The primary instability is tipping,
defined as rotation of the centre of gravity about the ground contact point.
Tipping occurs when the centre of pressure falls outside the functional foot. A
contribution of the paper is the development of graphical tipping stability
margins for both centre of gravity location and acceleration angle. We show
that the nose-up angular acceleration extends stability bounds forward and is
hence helpful in achieving shallow take-offs. The stability margins are used to
interrogate simulated take-offs of real birds using published experimental
kinematic data from a guinea fowl (ground take-off) and a diamond dove (perch
take-off). For the guinea fowl the initial part of the jump is stable, however
simulations exhibit a stuttering instability not observed experimentally that
is probably due to absence of compliance in the idealised joints. The diamond
dove model confirms that the foot provides an active torque reaction during
take-off, extending the range of stable jump angles by around 45{\deg}.Comment: 21 pages, 11 figures; supplementary material:
https://figshare.com/s/86b12868d64828db0d5d; DOI: 10.6084/m9.figshare.721056
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