827 research outputs found
Enhancing the performance of a safe controller via supervised learning for truck lateral control
Correct-by-construction techniques, such as control barrier functions (CBFs),
can be used to guarantee closed-loop safety by acting as a supervisor of an
existing or legacy controller. However, supervisory-control intervention
typically compromises the performance of the closed-loop system. On the other
hand, machine learning has been used to synthesize controllers that inherit
good properties from a training dataset, though safety is typically not
guaranteed due to the difficulty of analyzing the associated neural network. In
this paper, supervised learning is combined with CBFs to synthesize controllers
that enjoy good performance with provable safety. A training set is generated
by trajectory optimization that incorporates the CBF constraint for an
interesting range of initial conditions of the truck model. A control policy is
obtained via supervised learning that maps a feature representing the initial
conditions to a parameterized desired trajectory. The learning-based controller
is used as the performance controller and a CBF-based supervisory controller
guarantees safety. A case study of lane keeping for articulated trucks shows
that the controller trained by supervised learning inherits the good
performance of the training set and rarely requires intervention by the CBF
supervisorComment: submitted to IEEE Transaction of Control System Technolog
Correct-By-Construction Control Synthesis for Systems with Disturbance and Uncertainty
This dissertation focuses on correct-by-construction control synthesis for Cyber-Physical Systems (CPS) under model uncertainty and disturbance. CPSs are systems that interact with the physical world and perform complicated dynamic tasks where safety is often the overriding factor. Correct-by-construction control synthesis is a concept that provides formal performance guarantees to closed-loop systems by rigorous mathematic reasoning. Since CPSs interact with the environment, disturbance and modeling uncertainty are critical to the success of the control synthesis. Disturbance and uncertainty may come from a variety of sources, such as exogenous disturbance, the disturbance caused by co-existing controllers and modeling uncertainty. To better accommodate the different types of disturbance and uncertainty, the verification and control synthesis methods must be chosen accordingly. Four approaches are included in this dissertation. First, to deal with exogenous disturbance, a polar algorithm is developed to compute an avoidable set for obstacle avoidance. Second, a supervised learning based method is proposed to design a good student controller that has safety built-in and rarely triggers the intervention of the supervisory controller, thus targeting the design of the student controller. Third, to deal with the disturbance caused by co-existing controllers, a Lyapunov verification method is proposed to formally verify the safety of coexisting controllers while respecting the confidentiality requirement. Finally, a data-driven approach is proposed to deal with model uncertainty. A minimal robust control invariant set is computed for an uncertain dynamic system without a given model by first identifying the set of admissible models and then simultaneously computing the invariant set while selecting the optimal model. The proposed methods are applicable to many real-world applications and reflect the notion of using the structure of the system to achieve performance guarantees without being overly conservative.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145933/1/chenyx_1.pd
Robust Autonomous Vehicle Pursuit without Expert Steering Labels
In this work, we present a learning method for lateral and longitudinal
motion control of an ego-vehicle for vehicle pursuit. The car being controlled
does not have a pre-defined route, rather it reactively adapts to follow a
target vehicle while maintaining a safety distance. To train our model, we do
not rely on steering labels recorded from an expert driver but effectively
leverage a classical controller as an offline label generation tool. In
addition, we account for the errors in the predicted control values, which can
lead to a loss of tracking and catastrophic crashes of the controlled vehicle.
To this end, we propose an effective data augmentation approach, which allows
to train a network capable of handling different views of the target vehicle.
During the pursuit, the target vehicle is firstly localized using a
Convolutional Neural Network. The network takes a single RGB image along with
cars' velocities and estimates the target vehicle's pose with respect to the
ego-vehicle. This information is then fed to a Multi-Layer Perceptron, which
regresses the control commands for the ego-vehicle, namely throttle and
steering angle. We extensively validate our approach using the CARLA simulator
on a wide range of terrains. Our method demonstrates real-time performance and
robustness to different scenarios including unseen trajectories and high route
completion. The project page containing code and multimedia can be publicly
accessed here: https://changyaozhou.github.io/Autonomous-Vehicle-Pursuit/.Comment: 9 pages, 4 figures, 3 table
Safe Policy Synthesis in Multi-Agent POMDPs via Discrete-Time Barrier Functions
A multi-agent partially observable Markov decision process (MPOMDP) is a
modeling paradigm used for high-level planning of heterogeneous autonomous
agents subject to uncertainty and partial observation. Despite their modeling
efficiency, MPOMDPs have not received significant attention in safety-critical
settings. In this paper, we use barrier functions to design policies for
MPOMDPs that ensure safety. Notably, our method does not rely on discretization
of the belief space, or finite memory. To this end, we formulate sufficient and
necessary conditions for the safety of a given set based on discrete-time
barrier functions (DTBFs) and we demonstrate that our formulation also allows
for Boolean compositions of DTBFs for representing more complicated safe sets.
We show that the proposed method can be implemented online by a sequence of
one-step greedy algorithms as a standalone safe controller or as a
safety-filter given a nominal planning policy. We illustrate the efficiency of
the proposed methodology based on DTBFs using a high-fidelity simulation of
heterogeneous robots.Comment: 8 pages and 4 figure
Risk-Sensitive Path Planning via CVaR Barrier Functions: Application to Bipedal Locomotion
Enforcing safety of robotic systems in the presence of stochastic uncertainty is a challenging problem. Traditionally,researchers have proposed safety in the statistical mean as a safety measure in this case. However, ensuring safety in the statistical mean is only reasonable if robot safe behavior in the large number of runs is of interest, which precludes the use of mean safety in practical scenarios. In this paper, we propose a risk sensitive notion of safety called conditional-value-at-risk (CVaR) safety, which is concerned with safe performance in the worst case realizations. We introduce CVaR barrier functions asa tool to enforce CVaR safety and propose conditions for their Boolean compositions. Given a legacy controller, we show that we can design a minimally interfering CVaR safe controller via solving difference convex programs. We elucidate the proposed method by applying it to a bipedal locomotion case study
Measurable Safety of Automated Driving Functions in Commercial Motor Vehicles
With the further development of automated driving, the functional performance increases resulting in the need for new and comprehensive testing concepts. This doctoral work aims to enable the transition from quantitative mileage to qualitative test coverage by aggregating the results of both knowledge-based and data-driven test platforms. The validity of the test domain can be extended cost-effectively throughout the software development process to achieve meaningful test termination criteria
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