Assuring Safety of Vision-Based Swarm Formation Control

Vision-based formation control systems are attractive because they can use inexpensive sensors and can work in GPS-denied environments. The safety assurance for such systems is challenging: the vision component's accuracy depends on the environment in complicated ways, these errors propagate through the system and lead to incorrect control actions, and there exists no formal specification for end-to-end reasoning. We address this problem and propose a technique for safety assurance of vision-based formation control: First, we propose a scheme for constructing quantizers that are consistent with vision-based perception. Next, we show how the convergence analysis of a standard quantized consensus algorithm can be adapted for the constructed quantizers. We use the recently defined notion of perception contracts to create error bounds on the actual vision-based perception pipeline using sampled data from different ground truth states, environments, and weather conditions. Specifically, we use a quantizer in logarithmic polar coordinates, and we show that this quantizer is suitable for the constructed perception contracts for the vision-based position estimation, where the error worsens with respect to the absolute distance between agents. We build our formation control algorithm with this nonuniform quantizer, and we prove its convergence employing an existing result for quantized consensus.Comment: 8 pages, 7 figures, submitted to the 2024 American Control Conference (ACC 2024

Verse: A Python library for reasoning about multi-agent hybrid system scenarios

We present the Verse library with the aim of making hybrid system verification more usable for multi-agent scenarios. In Verse, decision making agents move in a map and interact with each other through sensors. The decision logic for each agent is written in a subset of Python and the continuous dynamics is given by a black-box simulator. Multiple agents can be instantiated and they can be ported to different maps for creating scenarios. Verse provides functions for simulating and verifying such scenarios using existing reachability analysis algorithms. We illustrate several capabilities and use cases of the library with heterogeneous agents, incremental verification, different sensor models, and the flexibility of plugging in different subroutines for post computations.Comment: 26 pages, 16 figure

Refining Perception Contracts: Case Studies in Vision-based Safe Auto-landing

Perception contracts provide a method for evaluating safety of control systems that use machine learning for perception. A perception contract is a specification for testing the ML components, and it gives a method for proving end-to-end system-level safety requirements. The feasibility of contract-based testing and assurance was established earlier in the context of straight lane keeping: a 3-dimensional system with relatively simple dynamics. This paper presents the analysis of two 6 and 12-dimensional flight control systems that use multi-stage, heterogeneous, ML-enabled perception. The paper advances methodology by introducing an algorithm for constructing data and requirement guided refinement of perception contracts (DaRePC). The resulting analysis provides testable contracts which establish the state and environment conditions under which an aircraft can safety touchdown on the runway and a drone can safely pass through a sequence of gates. It can also discover conditions (e.g., low-horizon sun) that can possibly violate the safety of the vision-based control system

Software tools for scenario verification of autonomous systems exploiting dynamical symmetries

In this thesis, we discuss using formal verification techniques to ensure the safety of autonomous systems. We present a particular type of verification problem called scenario verification, which involves vehicles executing complex plans in large cluttered workspaces. To solve the scenario verification problem, we present the tool SceneChecker. SceneChecker converts the scenario verification problem to a standard hybrid system verification problem and solves it effectively by exploiting structural properties in the plan and the vehicle dynamics. SceneChecker implements symmetry abstractions, a novel refinement algorithm, and is built to enhance the performance of existing reachability analysis tools as a plug-in subroutine. We evaluated SceneChecker on several complicated scenarios with different types of agents. Compared to two leading tools, DryVR and Flow*, SceneChecker shows 20x speedup in verification time, even while using those tools as reachability subroutines. We further look into a variation of the scenario verification problem, with multiple agents running independently in the shared workspace. In addition, the plan is generated as the agent executing the scenario, which requires safety checking to be performed during runtime. To solve this problem, we present Swerve, an open-source cloud computing toolkit for efficient runtime collision checking for multi-agent autonomous systems. Swerve implements a remote server to check safety for different agents by using boundedtime reachability analysis. In addition, Swerve implements a cache to store already computed reachable sets and reuses them to avoid repeated computations. We evaluate Swerve on several scenarios and are able to show that Swerve is able to properly detect potential collisions between agents and static obstacles. In addition, we show that with symmetry and caching, Swerve is able to obtain 16x average speedup in service response time.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

Mechanistic study on the depression of calcite by sodium hexametaphosphate in sodium oleate system

Sodium hexametaphosphate (NaHMP), a common depressant for calcium-containing minerals, is widely used in flotation practice. In this work, the depression mechanism of NaHMP on calcite was thoroughly investigated by using experiments and DFT calculations. Accordingly, the micro-flotation results revealed that NaHMP possessed noticeable depression effect on calcite, with the calcite recovery decreasing from 94.21% without NaHMP to 17.29% with NaHMP concentration of 1 mg/L at pH 8. The surface Zeta potential suggested that NaHMP could be strongly adsorbed on calcite, while no absorption band of hexametaphosphate was detected in the FTIR spectra of calcite treated by NaHMP, but a remarkable weakening of the absorption peak of sodium oleate (NaOL) was detected in the presence of NaHMP, which was also reflected in the XPS spectra. In addition, the significant chemical shifts in the binding energies of Ca 2p and P 2p electrons observed from the XPS high-resolution spectra suggested that the hexametaphosphate groups (HMP) were chemisorbed on calcite. DFT calculations further revealed that the sorption of HMP on calcite was more preferable than that of oleate ion (OL) in thermodynamics, which explained the beneficiation practice that NaOL was difficult to float calcite in the presence of NaHMP

ARCH-COMP23 category report: Continuous and hybrid systems with linear continuous dynamics

We present the results of the ARCH 2023 friendly competition for formal verification of continuous and hybrid systems with linear continuous dynamics. In its seventh edition, three tools participated to solve nine different benchmark problems in the category for linear continuous dynamics (in alphabetical order): CORA, JuliaReach, and Verse. This report is a snapshot of the current landscape of tools and the types of benchmarks they are particularly suited for. Due to the diversity of problems, we are not ranking tools, yet the presented results provide one of the most complete assessments of tools for the safety verification of continuous and hybrid systems with linear continuous dynamics up to this date

ARCH-COMP20 Category Report: Continuous and hybrid systems with linear dynamics

We present the results of the ARCH 2020 friendly competition for formal verification of continuous and hybrid systems with linear continuous dynamics. In its fourth edition, eight tools have been applied to solve eight different benchmark problems in the category for linear continuous dynamics (in alphabetical order): CORA, C2E2, HyDRA, Hylaa, Hylaa-Continuous, JuliaReach, SpaceEx, and XSpeed. This report is a snapshot of the current landscape of tools and the types of benchmarks they are particularly suited for. Due to the diversity of problems, we are not ranking tools, yet the presented results provide one of the most complete assessments of tools for the safety verification of continuous and hybrid systems with linear continuous dynamics up to this date

Engineering <i>Yarrowia lipolytica</i> for Sustainable Production of Fatty Acid Methyl Esters Using in Situ Self-Cycled Glycerol as a Carbon Source

On the basis of <i>Thermomyces lanuginosus</i> lipase functionally displayed on the cell surface of <i>Yarrowia lipolytica</i> yeast, a new green, integrated, and sustainable bioprocess for fatty acid methyl esters (FAMEs) production was developed. It couples surface-displayed enzyme generation to enzymatic FAMEs production, in combination with simultaneous regeneration of in situ carbon source for yeast utilization. During FAMEs synthesis, in a one-pot fermentation flask containing growing cells displaying lipase, waste cooking oil, and methanol, the in situ formed byproduct glycerol was used as an alternative carbon source to support further cell growth and lipase generation. The partial consumption of glycerol pushed the reversible reactions (transesterification, esterification, hydrolysis) toward formation of FAMEs. In the growing cells integrated system, the production of FAMEs via hydrolysis–esterification or transesterification–esterification reactions was dependent on the time when methanol was added to the culture medium. Compared to the resting cells system with an 81% FAMEs yield after 16 h, the self-cycling of glycerol for cell consumption (allowing cell growth and lipase displaying for further FAMEs forming) in the growing cells system significantly increased FAMEs synthesis with a more than 91% yield obtained in less time (6–10 h). The cells recovered from growing cell systems still exhibited satisfactory reusability, showing more than 80% FAMEs yield during 12 successive batches