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Quantifying the Safety of Trajectories by Minimizing the Peak Control Effort Required to Crash into an Unsafe Set


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The core message of this article is that the safety of trajectories of a dynamical system can be quantified by the minimum control effort (perturbation intensity) required to render the system unsafe and cause it to crash into an unsafe set.
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The article presents a framework for quantifying the safety of trajectories of a dynamical system by formulating an optimal control problem (OCP) that minimizes the peak control effort (perturbation intensity) required to steer the system into an unsafe set.

The key highlights and insights are:

  1. The safety of a trajectory is quantified by the maximum control effort (OCP cost) needed to crash the agent into the unsafe set. This can be interpreted as the minimal data corruption required for a data-consistent model to crash.

  2. The crash-safety problem is formulated as a peak-minimizing free-terminal-time OCP, where the variables are the stopping time, the initial condition, and the input process.

  3. The peak-minimizing OCP is transformed into an equivalent Mayer-form OCP, which is then relaxed into an infinite-dimensional linear program (LP) that produces the same optimal value under certain assumptions.

  4. The infinite-dimensional LP is further approximated using a moment-Sum-of-Squares (SOS) hierarchy of semidefinite programs (SDPs) to compute convergent lower bounds on the minimal peak value of the control effort.

  5. The crash-safety framework is applied to a data-driven setting, where the data-consistent model parameters are treated as the uncertain input, and the minimal data corruption required to crash the system is quantified.

  6. SOS programs are formulated to compute the crash-safety bounds, and their computational complexity is analyzed.

  7. A subvalue function is developed to assess the safety of arbitrary initial conditions, and it is shown to converge almost uniformly to the true crash-safety value as the SOS degree is increased.

The article provides a comprehensive framework for quantifying the safety of trajectories by minimizing the peak control effort required to crash the system into an unsafe set, with applications in both the known dynamics and data-driven settings.

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by Jared Miller... om arxiv.org 10-02-2024

https://arxiv.org/pdf/2303.11896.pdf
Quantifying the Safety of Trajectories using Peak-Minimizing Control

Diepere vragen

How can the crash-safety framework be extended to handle more general uncertainty models beyond the L∞-bounded polytopic case considered in the article?

The crash-safety framework can be extended to accommodate more general uncertainty models by leveraging the robust counterpart methods and the moment-Sum-of-Squares (SOS) hierarchy. Instead of restricting the uncertainty to L∞-bounded polytopic forms, one can consider other types of uncertainty representations, such as L2-bounded uncertainties or semidefinite bounded uncertainties. For instance, when dealing with L2-bounded uncertainties, the framework can incorporate ellipsoidal constraints, which can be represented as intersections of quadratic forms. This would involve reformulating the crash-safety problem to include these new constraints while ensuring that the underlying dynamics remain Lipschitz continuous. Moreover, the robustification of the Lie derivative constraints can be adapted to these new uncertainty models, allowing for the inclusion of more complex dynamics that may not fit neatly into the polytopic framework. By employing techniques such as the robust counterpart method, one can derive conditions that ensure the feasibility of the crash-safety program under these broader uncertainty models. This flexibility enhances the applicability of the crash-safety framework to a wider range of real-world scenarios where uncertainties are often more complex than simple bounded polytopes.

How can the crash-safety analysis be used to guide the design of safe control systems or the selection of safe initial conditions?

Crash-safety analysis provides a quantitative measure of the safety of trajectories within a dynamical system, which can be instrumental in guiding the design of safe control systems and the selection of safe initial conditions. By computing the peak-minimizing control cost, which quantifies the perturbation intensity required to render a trajectory unsafe, designers can identify critical thresholds for control inputs that maintain safety. In practice, this analysis can inform the design of control algorithms that actively avoid unsafe regions by incorporating safety margins derived from the crash-safety quantification. For instance, control systems can be designed to operate within a defined safe set, ensuring that the maximum control effort required to reach the unsafe set remains below a certain threshold. Additionally, crash-safety analysis can be utilized to evaluate and select initial conditions that minimize the risk of unsafe trajectories. By analyzing the crash-safety cost associated with various initial conditions, designers can prioritize those that exhibit lower crash-bound values, thereby enhancing the overall safety of the system. This proactive approach to safety can lead to more robust and reliable control systems, particularly in applications such as autonomous vehicles, robotics, and aerospace systems, where safety is paramount.

What are the potential applications of the crash-safety quantification beyond the data-driven safety analysis discussed in the article?

The crash-safety quantification framework has a wide array of potential applications beyond the data-driven safety analysis presented in the article. Some notable applications include: Autonomous Systems: In the development of autonomous vehicles and drones, crash-safety quantification can be employed to ensure that trajectories remain within safe operational limits, even in the presence of uncertainties in sensor data or environmental conditions. Robotics: In robotic motion planning, crash-safety analysis can help in designing paths that avoid collisions with obstacles while considering dynamic changes in the environment. This is particularly useful in collaborative robotics, where multiple robots operate in close proximity. Aerospace Engineering: The framework can be applied to flight trajectory optimization, ensuring that aircraft maintain safe distances from restricted airspaces or other aircraft, even under varying atmospheric conditions. Manufacturing Systems: In automated manufacturing processes, crash-safety quantification can guide the design of robotic arms and automated guided vehicles to prevent accidents and ensure safe interactions with human workers. Healthcare Robotics: In medical robotics, such as surgical robots, crash-safety analysis can ensure that the robotic systems operate safely around patients, minimizing the risk of unintended movements that could lead to harm. Game Development and Simulation: In virtual environments, crash-safety quantification can enhance the realism of simulations by ensuring that virtual agents behave safely and predictably, adhering to safety constraints similar to those in real-world scenarios. By extending the application of crash-safety quantification to these diverse fields, researchers and engineers can enhance safety protocols, improve system reliability, and foster innovation in the design of complex dynamical systems.
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