25 research outputs found
Efficient Supervision for Robot Learning via Imitation, Simulation, and Adaptation
Recent successes in machine learning have led to a shift in the design of
autonomous systems, improving performance on existing tasks and rendering new
applications possible. Data-focused approaches gain relevance across diverse,
intricate applications when developing data collection and curation pipelines
becomes more effective than manual behaviour design. The following work aims at
increasing the efficiency of this pipeline in two principal ways: by utilising
more powerful sources of informative data and by extracting additional
information from existing data. In particular, we target three orthogonal
fronts: imitation learning, domain adaptation, and transfer from simulation.Comment: Dissertation Summar
Incremental Adversarial Domain Adaptation for Continually Changing Environments
Continuous appearance shifts such as changes in weather and lighting
conditions can impact the performance of deployed machine learning models.
While unsupervised domain adaptation aims to address this challenge, current
approaches do not utilise the continuity of the occurring shifts. In
particular, many robotics applications exhibit these conditions and thus
facilitate the potential to incrementally adapt a learnt model over minor
shifts which integrate to massive differences over time. Our work presents an
adversarial approach for lifelong, incremental domain adaptation which benefits
from unsupervised alignment to a series of intermediate domains which
successively diverge from the labelled source domain. We empirically
demonstrate that our incremental approach improves handling of large appearance
changes, e.g. day to night, on a traversable-path segmentation task compared
with a direct, single alignment step approach. Furthermore, by approximating
the feature distribution for the source domain with a generative adversarial
network, the deployment module can be rendered fully independent of retaining
potentially large amounts of the related source training data for only a minor
reduction in performance.Comment: International Conference on Robotics and Automation 201
Addressing Appearance Change in Outdoor Robotics with Adversarial Domain Adaptation
Appearance changes due to weather and seasonal conditions represent a strong
impediment to the robust implementation of machine learning systems in outdoor
robotics. While supervised learning optimises a model for the training domain,
it will deliver degraded performance in application domains that underlie
distributional shifts caused by these changes. Traditionally, this problem has
been addressed via the collection of labelled data in multiple domains or by
imposing priors on the type of shift between both domains. We frame the problem
in the context of unsupervised domain adaptation and develop a framework for
applying adversarial techniques to adapt popular, state-of-the-art network
architectures with the additional objective to align features across domains.
Moreover, as adversarial training is notoriously unstable, we first perform an
extensive ablation study, adapting many techniques known to stabilise
generative adversarial networks, and evaluate on a surrogate classification
task with the same appearance change. The distilled insights are applied to the
problem of free-space segmentation for motion planning in autonomous driving.Comment: In Proceedings of the 2017 IEEE/RSJ International Conference on
Intelligent Robots and Systems (IROS 2017
Mutual Alignment Transfer Learning
Training robots for operation in the real world is a complex, time consuming
and potentially expensive task. Despite significant success of reinforcement
learning in games and simulations, research in real robot applications has not
been able to match similar progress. While sample complexity can be reduced by
training policies in simulation, such policies can perform sub-optimally on the
real platform given imperfect calibration of model dynamics. We present an
approach -- supplemental to fine tuning on the real robot -- to further benefit
from parallel access to a simulator during training and reduce sample
requirements on the real robot. The developed approach harnesses auxiliary
rewards to guide the exploration for the real world agent based on the
proficiency of the agent in simulation and vice versa. In this context, we
demonstrate empirically that the reciprocal alignment for both agents provides
further benefit as the agent in simulation can adjust to optimize its behaviour
for states commonly visited by the real-world agent
Scrutinizing and De-Biasing Intuitive Physics with Neural Stethoscopes
Visually predicting the stability of block towers is a popular task in the
domain of intuitive physics. While previous work focusses on prediction
accuracy, a one-dimensional performance measure, we provide a broader analysis
of the learned physical understanding of the final model and how the learning
process can be guided. To this end, we introduce neural stethoscopes as a
general purpose framework for quantifying the degree of importance of specific
factors of influence in deep neural networks as well as for actively promoting
and suppressing information as appropriate. In doing so, we unify concepts from
multitask learning as well as training with auxiliary and adversarial losses.
We apply neural stethoscopes to analyse the state-of-the-art neural network for
stability prediction. We show that the baseline model is susceptible to being
misled by incorrect visual cues. This leads to a performance breakdown to the
level of random guessing when training on scenarios where visual cues are
inversely correlated with stability. Using stethoscopes to promote meaningful
feature extraction increases performance from 51% to 90% prediction accuracy.
Conversely, training on an easy dataset where visual cues are positively
correlated with stability, the baseline model learns a bias leading to poor
performance on a harder dataset. Using an adversarial stethoscope, the network
is successfully de-biased, leading to a performance increase from 66% to 88%
Attention-Privileged Reinforcement Learning
Image-based Reinforcement Learning is known to suffer from poor sample
efficiency and generalisation to unseen visuals such as distractors
(task-independent aspects of the observation space). Visual domain
randomisation encourages transfer by training over visual factors of variation
that may be encountered in the target domain. This increases learning
complexity, can negatively impact learning rate and performance, and requires
knowledge of potential variations during deployment. In this paper, we
introduce Attention-Privileged Reinforcement Learning (APRiL) which uses a
self-supervised attention mechanism to significantly alleviate these drawbacks:
by focusing on task-relevant aspects of the observations, attention provides
robustness to distractors as well as significantly increased learning
efficiency. APRiL trains two attention-augmented actor-critic agents: one
purely based on image observations, available across training and transfer
domains; and one with access to privileged information (such as environment
states) available only during training. Experience is shared between both
agents and their attention mechanisms are aligned. The image-based policy can
then be deployed without access to privileged information. We experimentally
demonstrate accelerated and more robust learning on a diverse set of domains,
leading to improved final performance for environments both within and outside
the training distribution.Comment: Published at Conference on Robot Learning (CoRL) 202
TACO: Learning Task Decomposition via Temporal Alignment for Control
Many advanced Learning from Demonstration (LfD) methods consider the
decomposition of complex, real-world tasks into simpler sub-tasks. By reusing
the corresponding sub-policies within and between tasks, they provide training
data for each policy from different high-level tasks and compose them to
perform novel ones. Existing approaches to modular LfD focus either on learning
a single high-level task or depend on domain knowledge and temporal
segmentation. In contrast, we propose a weakly supervised, domain-agnostic
approach based on task sketches, which include only the sequence of sub-tasks
performed in each demonstration. Our approach simultaneously aligns the
sketches with the observed demonstrations and learns the required sub-policies.
This improves generalisation in comparison to separate optimisation procedures.
We evaluate the approach on multiple domains, including a simulated 3D robot
arm control task using purely image-based observations. The results show that
our approach performs commensurately with fully supervised approaches, while
requiring significantly less annotation effort.Comment: 12 Pages. Published at ICML 201
Electronic structure of fully epitaxial Co2TiSn thin films
In this article we report on the properties of thin films of the full Heusler
compound Co2TiSn prepared by DC magnetron co-sputtering. Fully epitaxial,
stoichiometric films were obtained by deposition on MgO (001) substrates at
substrate temperatures above 600{\deg}C. The films are well ordered in the L21
structure, and the Curie temperature exceeds slightly the bulk value. They show
a significant, isotropic magnetoresistance and the resistivity becomes strongly
anomalous in the paramagnetic state. The films are weakly ferrimagnetic, with
nearly 1 \mu_B on the Co atoms, and a small antiparallel Ti moment, in
agreement with theoretical expectations. From comparison of x-ray absorption
spectra on the Co L3/L2 edges, including circular and linear magnetic
dichroism, with ab initio calculations of the x-ray absorption and circular
dichroism spectra we infer that the electronic structure of Co2TiSn has
essentially non-localized character. Spectral features that have not been
explained in detail before, are explained here in terms of the final state band
structure.Comment: 11 pages, 8 figure
Equivariant Data Augmentation for Generalization in Offline Reinforcement Learning
We present a novel approach to address the challenge of generalization in
offline reinforcement learning (RL), where the agent learns from a fixed
dataset without any additional interaction with the environment. Specifically,
we aim to improve the agent's ability to generalize to out-of-distribution
goals. To achieve this, we propose to learn a dynamics model and check if it is
equivariant with respect to a fixed type of transformation, namely translations
in the state space. We then use an entropy regularizer to increase the
equivariant set and augment the dataset with the resulting transformed samples.
Finally, we learn a new policy offline based on the augmented dataset, with an
off-the-shelf offline RL algorithm. Our experimental results demonstrate that
our approach can greatly improve the test performance of the policy on the
considered environments