1,320 research outputs found
Critically fast pick-and-place with suction cups
Fast robotics pick-and-place with suction cups is a crucial component in the
current development of automation in logistics (factory lines, e-commerce,
etc.). By "critically fast" we mean the fastest possible movement for
transporting an object such that it does not slip or fall from the suction cup.
The main difficulties are: (i) handling the contact between the suction cup and
the object, which fundamentally involves kinodynamic constraints; and (ii)
doing so at a low computational cost, typically a few hundreds of milliseconds.
To address these difficulties, we propose (a) a model for suction cup contacts,
(b) a procedure to identify the contact stability constraint based on that
model, and (c) a pipeline to parameterize, in a time-optimal manner, arbitrary
geometric paths under the identified contact stability constraint. We
experimentally validate the proposed pipeline on a physical robot system: the
cycle time for a typical pick-and-place task was less than 5 seconds, planning
and execution times included. The full pipeline is released as open-source for
the robotics community.Comment: 7 pages, 5 figure
Robotic manipulation of a rotating chain
This paper considers the problem of manipulating a uniformly rotating chain:
the chain is rotated at a constant angular speed around a fixed axis using a
robotic manipulator. Manipulation is quasi-static in the sense that transitions
are slow enough for the chain to be always in "rotational" equilibrium. The
curve traced by the chain in a rotating plane -- its shape function -- can be
determined by a simple force analysis, yet it possesses complex multi-solutions
behavior typical of non-linear systems. We prove that the configuration space
of the uniformly rotating chain is homeomorphic to a two-dimensional surface
embedded in . Using that representation, we devise a manipulation
strategy for transiting between different rotation modes in a stable and
controlled manner. We demonstrate the strategy on a physical robotic arm
manipulating a rotating chain. Finally, we discuss how the ideas developed here
might find fruitful applications in the study of other flexible objects, such
as elastic rods or concentric tubes.Comment: 12 pages, 9 figure
Time-Optimal Path Tracking via Reachability Analysis
Given a geometric path, the Time-Optimal Path Tracking problem consists in
finding the control strategy to traverse the path time-optimally while
regulating tracking errors. A simple yet effective approach to this problem is
to decompose the controller into two components: (i)~a path controller, which
modulates the parameterization of the desired path in an online manner,
yielding a reference trajectory; and (ii)~a tracking controller, which takes
the reference trajectory and outputs joint torques for tracking. However, there
is one major difficulty: the path controller might not find any feasible
reference trajectory that can be tracked by the tracking controller because of
torque bounds. In turn, this results in degraded tracking performances. Here,
we propose a new path controller that is guaranteed to find feasible reference
trajectories by accounting for possible future perturbations. The main
technical tool underlying the proposed controller is Reachability Analysis, a
new method for analyzing path parameterization problems. Simulations show that
the proposed controller outperforms existing methods.Comment: 6 pages, 3 figures, ICRA 201
A New Approach to Time-Optimal Path Parameterization based on Reachability Analysis
Time-Optimal Path Parameterization (TOPP) is a well-studied problem in
robotics and has a wide range of applications. There are two main families of
methods to address TOPP: Numerical Integration (NI) and Convex Optimization
(CO). NI-based methods are fast but difficult to implement and suffer from
robustness issues, while CO-based approaches are more robust but at the same
time significantly slower. Here we propose a new approach to TOPP based on
Reachability Analysis (RA). The key insight is to recursively compute reachable
and controllable sets at discretized positions on the path by solving small
Linear Programs (LPs). The resulting algorithm is faster than NI-based methods
and as robust as CO-based ones (100% success rate), as confirmed by extensive
numerical evaluations. Moreover, the proposed approach offers unique additional
benefits: Admissible Velocity Propagation and robustness to parametric
uncertainty can be derived from it in a simple and natural way.Comment: 15 pages, 9 figure
An ecological perspective on the motivational trajectories of high school students learning English in rural areas in Vietnam : A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Applied Linguistics at Massey University, Palmerston North, New Zealand.
This study explores the motivational trajectories of four students learning English at a rural high school in Southern Vietnam. It draws on a person-in-context relational view of motivation (Ushioda, 2009) as the overarching theoretical framework and uses ecological systems theory (Bronfenbrenner, 1993) as an analytical tool to develop insights into the ways motivation is implicated in a multiplicity of settings and social relationships. Specifically, it aims to identify motivational affordances for these students, the synergistic effects across settings on their language learning motivation, and their motivational trajectories within and across settings and relationships.
The study utilises a qualitative case study design, relying primarily on interviews from social practice perspectives and observations. The data collection, spanning approximately one and a half years, comprised two main phases, one on-site and one off-site. In the first phase, data were gathered in different settings, including the school, the participants’ homes as a site for private tuition, and other more informal public spaces such as food stores. In the second phase, Skype interviews and Facebook exchanges were the main means of data collection.
The findings suggest that while language affordances were evident in both formal and informal learning settings, students developed diverse individual motivational trajectories. Their motivational constructions resulted from a synergy of environmental and idiosyncratic elements pertinent to their own language learning conditions, social relationships, and personal appraisals of such affordances and learning opportunities. These relationships and students’ agentive use of resources were shaped and reshaped by their interactions with significant others within and across settings. Sociocultural features related to the school systems, local and national education policies, family traditions, cultural values, and future prospects also have synergistic impacts on their L2 motivation.
The present study illustrates the value of interpreting the situated and dynamic nature of L2 motivation using an ecological paradigm. It also points to the need to adopt a set of data collection methods, tools, and data sources that diverge from more conventional means to explore L2 motivation. The study offers a fresh theoretical and methodological approach for future research geared towards lifewide adaptive perspectives on English language teaching and learning
Homotopy groups of
Let be any spectrum in a class of finite spectra whose mod
cohomology is isomorphic to a free module of rank one over the subalgebra
of the Steenrod algebra. Let be the second Morava-
theory associated to a universal deformation of the formal completion of the
supersingular elliptic curve defined over
and a maximal finite subgroup of automorphism group
of the formal completion of . In this paper, we compute the
homotopy groups of by means of the homotopy fixed
point spectral sequence.Comment: 82 pages, 29 figure
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