3,340 research outputs found
Realtime State Estimation with Tactile and Visual sensing. Application to Planar Manipulation
Accurate and robust object state estimation enables successful object
manipulation. Visual sensing is widely used to estimate object poses. However,
in a cluttered scene or in a tight workspace, the robot's end-effector often
occludes the object from the visual sensor. The robot then loses visual
feedback and must fall back on open-loop execution.
In this paper, we integrate both tactile and visual input using a framework
for solving the SLAM problem, incremental smoothing and mapping (iSAM), to
provide a fast and flexible solution. Visual sensing provides global pose
information but is noisy in general, whereas contact sensing is local, but its
measurements are more accurate relative to the end-effector. By combining them,
we aim to exploit their advantages and overcome their limitations. We explore
the technique in the context of a pusher-slider system. We adapt iSAM's
measurement cost and motion cost to the pushing scenario, and use an
instrumented setup to evaluate the estimation quality with different object
shapes, on different surface materials, and under different contact modes
Learning and adaptation in physical agents
Learning and adaptation is fundamental for autonomous agents that operate in a physical world and not a computer network. The paper is providing a general framework of skills learning within behaviour logic framework of agents that communicate, sense and act in the physical world. It is advocated that playfulness can be important in learning and to improving skills of agents
Autonomous Robotic System using Non-Destructive Evaluation methods for Bridge Deck Inspection
Bridge condition assessment is important to maintain the quality of highway
roads for public transport. Bridge deterioration with time is inevitable due to
aging material, environmental wear and in some cases, inadequate maintenance.
Non-destructive evaluation (NDE) methods are preferred for condition assessment
for bridges, concrete buildings, and other civil structures. Some examples of
NDE methods are ground penetrating radar (GPR), acoustic emission, and
electrical resistivity (ER). NDE methods provide the ability to inspect a
structure without causing any damage to the structure in the process. In
addition, NDE methods typically cost less than other methods, since they do not
require inspection sites to be evacuated prior to inspection, which greatly
reduces the cost of safety related issues during the inspection process. In
this paper, an autonomous robotic system equipped with three different NDE
sensors is presented. The system employs GPR, ER, and a camera for data
collection. The system is capable of performing real-time, cost-effective
bridge deck inspection, and is comprised of a mechanical robot design and
machine learning and pattern recognition methods for automated steel rebar
picking to provide realtime condition maps of the corrosive deck environments
Feature discovery and visualization of robot mission data using convolutional autoencoders and Bayesian nonparametric topic models
The gap between our ability to collect interesting data and our ability to
analyze these data is growing at an unprecedented rate. Recent algorithmic
attempts to fill this gap have employed unsupervised tools to discover
structure in data. Some of the most successful approaches have used
probabilistic models to uncover latent thematic structure in discrete data.
Despite the success of these models on textual data, they have not generalized
as well to image data, in part because of the spatial and temporal structure
that may exist in an image stream.
We introduce a novel unsupervised machine learning framework that
incorporates the ability of convolutional autoencoders to discover features
from images that directly encode spatial information, within a Bayesian
nonparametric topic model that discovers meaningful latent patterns within
discrete data. By using this hybrid framework, we overcome the fundamental
dependency of traditional topic models on rigidly hand-coded data
representations, while simultaneously encoding spatial dependency in our topics
without adding model complexity. We apply this model to the motivating
application of high-level scene understanding and mission summarization for
exploratory marine robots. Our experiments on a seafloor dataset collected by a
marine robot show that the proposed hybrid framework outperforms current
state-of-the-art approaches on the task of unsupervised seafloor terrain
characterization.Comment: 8 page
Enforcing Constraints over Learned Policies via Nonlinear MPC: Application to the Pendubot
In recent years Reinforcement Learning (RL) has achieved remarkable results. Nonetheless RL algorithms prove to be unsuccessful in robotics applications where constraints satisfaction is involved, e.g. for safety. In this work we propose a control algorithm that allows to enforce constraints over a learned control policy. Hence we combine Nonlinear Model Predictive Control (NMPC) with control-state trajectories generated from the learned policy at each time step. We prove the effectiveness of our method on the Pendubot, a challenging underactuated robot
Optimal Navigation Functions for Nonlinear Stochastic Systems
This paper presents a new methodology to craft navigation functions for
nonlinear systems with stochastic uncertainty. The method relies on the
transformation of the Hamilton-Jacobi-Bellman (HJB) equation into a linear
partial differential equation. This approach allows for optimality criteria to
be incorporated into the navigation function, and generalizes several existing
results in navigation functions. It is shown that the HJB and that existing
navigation functions in the literature sit on ends of a spectrum of
optimization problems, upon which tradeoffs may be made in problem complexity.
In particular, it is shown that under certain criteria the optimal navigation
function is related to Laplace's equation, previously used in the literature,
through an exponential transform. Further, analytical solutions to the HJB are
available in simplified domains, yielding guidance towards optimality for
approximation schemes. Examples are used to illustrate the role that noise, and
optimality can potentially play in navigation system design.Comment: Accepted to IROS 2014. 8 Page
Scheduling Dimension Reduction of LPV Models -- A Deep Neural Network Approach
In this paper, the existing Scheduling Dimension Reduction (SDR) methods for
Linear Parameter-Varying (LPV) models are reviewed and a Deep Neural Network
(DNN) approach is developed that achieves higher model accuracy under
scheduling dimension reduction. The proposed DNN method and existing SDR
methods are compared on a two-link robotic manipulator, both in terms of model
accuracy and performance of controllers synthesized with the reduced models.
The methods compared include SDR for state-space models using Principal
Component Analysis (PCA), Kernel PCA (KPCA) and Autoencoders (AE). On the
robotic manipulator example, the DNN method achieves improved representation of
the matrix variations of the original LPV model in terms of the Frobenius norm
compared to the current methods. Moreover, when the resulting model is used to
accommodate synthesis, improved closed-loop performance is obtained compared to
the current methods.Comment: Accepted to American Control Conference (ACC) 2020, Denve
Learning Contact-Rich Manipulation Skills with Guided Policy Search
Autonomous learning of object manipulation skills can enable robots to
acquire rich behavioral repertoires that scale to the variety of objects found
in the real world. However, current motion skill learning methods typically
restrict the behavior to a compact, low-dimensional representation, limiting
its expressiveness and generality. In this paper, we extend a recently
developed policy search method \cite{la-lnnpg-14} and use it to learn a range
of dynamic manipulation behaviors with highly general policy representations,
without using known models or example demonstrations. Our approach learns a set
of trajectories for the desired motion skill by using iteratively refitted
time-varying linear models, and then unifies these trajectories into a single
control policy that can generalize to new situations. To enable this method to
run on a real robot, we introduce several improvements that reduce the sample
count and automate parameter selection. We show that our method can acquire
fast, fluent behaviors after only minutes of interaction time, and can learn
robust controllers for complex tasks, including putting together a toy
airplane, stacking tight-fitting lego blocks, placing wooden rings onto
tight-fitting pegs, inserting a shoe tree into a shoe, and screwing bottle caps
onto bottles
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