arXiv subjects

Andrew J. Taylor

Publications and source records attributed to Andrew J. Taylor.

22 records · Page 2Linked to original sources

arXiv2019

Adaptive Safety with Control Barrier Functions

Adaptive Control Lyapunov Functions (aCLFs) were introduced 20 years ago, and provided a Lyapunov-based methodology for stabilizing systems with parameter uncertainty. The goal of this paper is to revisit this classic formulation in the context of safety-critical control. This will motivate a variant of aCLFs in the context of safety: adaptive Control Barrier Functions (aCBFs). Our proposed approach adaptively achieves safety by keeping the systems state within a safe set even in the presence of parametric model uncertainty. We unify aCLFs and aCBFs into a single control methodology for systems with uncertain parameters in the context of a Quadratic Program (QP) based framework. We validate the ability of this unified framework to achieve stability and safety in an adaptive cruise control (ACC) simulation.

eess.SY↗

arXiv2019

A Control Lyapunov Perspective on Episodic Learning via Projection to State Stability

The goal of this paper is to understand the impact of learning on control synthesis from a Lyapunov function perspective. In particular, rather than consider uncertainties in the full system dynamics, we employ Control Lyapunov Functions (CLFs) as low-dimensional projections. To understand and characterize the uncertainty that these projected dynamics introduce in the system, we introduce a new notion: Projection to State Stability (PSS). PSS can be viewed as a variant of Input to State Stability defined on projected dynamics, and enables characterizing robustness of a CLF with respect to the data used to learn system uncertainties. We use PSS to bound uncertainty in affine control, and demonstrate that a practical episodic learning approach can use PSS to characterize uncertainty in the CLF for robust control synthesis.

eess.SY↗

arXiv2019

Episodic Learning with Control Lyapunov Functions for Uncertain Robotic Systems

Many modern nonlinear control methods aim to endow systems with guaranteed properties, such as stability or safety, and have been successfully applied to the domain of robotics. However, model uncertainty remains a persistent challenge, weakening theoretical guarantees and causing implementation failures on physical systems. This paper develops a machine learning framework centered around Control Lyapunov Functions (CLFs) to adapt to parametric uncertainty and unmodeled dynamics in general robotic systems. Our proposed method proceeds by iteratively updating estimates of Lyapunov function derivatives and improving controllers, ultimately yielding a stabilizing quadratic program model-based controller. We validate our approach on a planar Segway simulation, demonstrating substantial performance improvements by iteratively refining on a base model-free controller.

cs.RO↗

arXiv2012

Luminescence of Nanodiamond Driven by Atomic Functionalization: Towards Novel Biomolecular Detection Principles

High biocompatibility, variable size ranging from ~ 5 nm, stable luminescence from its color centers and simple carbon chemistry for biomolecule grafting make nanodiamond (ND) particles an attractive alternative to molecular dyes for drug-delivery. Here we present a novel method for remote monitoring of chemical processes in biological environment based on color changes from photo-luminescent NV centers in ND. We propose to drive the NV luminescence chemically, by alternating the surface electric field developed by interacting atoms and molecules with the diamond surface. Due to the small ND size, the developed electric field penetrates into the bulk of the nanoparticle and intermingles with the electronic NV states. This allows construction of optical chemo-biosensors operating in cells, visible in classical confocal microscopes. We demonstrate this phenomenon on oxidized and hydrogenated ND as well as single crystal diamond containing engineered NV centers. Hydrogenation of NDs leads to quenching of luminescence related to negatively charged (NV-) centers and by this way produces color shifts from NV- (636 nm) to neutral NV0 (575nm) luminescence. We model how the reduction of diamond size increases the magnitude of NV color shift phenomena.

cond-mat.mtrl-sci↗