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Safe Returning FaSTrack with Robust Control Lyapunov-Value Functions for Handling Unexpected Disturbances in Autonomous Navigation


Core Concepts
The core message of this paper is to propose the Safe Returning FaSTrack (SR-F) framework, which merges concepts from Robust Control Lyapunov-Value Functions (R-CLVF) and the Fast and Safe Tracking (FaSTrack) framework, to handle unexpected disturbances during autonomous navigation while also accelerating navigation speed in open environments.
Abstract
The paper presents the SR-F framework, which aims to address two main limitations of the original FaSTrack framework: The error bound used to augment obstacles in FaSTrack is based on worst-case assumptions, leading to conservative trajectories. FaSTrack is unable to deal with unexpected sudden disturbances, which may be common in uncertain and unstructured environments. The key components of the SR-F framework are: Offline computation of a Robust Control Lyapunov-Value Function (R-CLVF) in the relative state space between the tracker (true robot) and planner (simplified model). This R-CLVF is used to guarantee exponential stabilization of the relative state back to the Tracking Error Bound (TEB) after an unexpected disturbance. Online, the SR-F algorithm senses the environment, computes a "safe resetting region" (sTEB) based on the R-CLVF, and augments obstacles with this sTEB. The planning block in SR-F can intentionally "jump" the planner model towards the goal when safe to do so, forcing the tracker to converge back to the planner at the exponential rate specified by the R-CLVF. This allows for faster navigation in open environments while maintaining safety. The authors validate the SR-F framework using a 10D quadrotor system and show that it is empirically 20% faster than the original FaSTrack while maintaining safety, even in the presence of unexpected disturbances.
Stats
The paper provides the following key figures and metrics: The SR-F algorithm is empirically 20% faster than the original FaSTrack framework while maintaining safety. When no disturbance occurs, all three frameworks (FaSTrack, Meta-FaSTrack, and SR-F) are able to reach the goal 100% of the time. When unexpected disturbances are introduced, the FaSTrack and Meta-FaSTrack frameworks collide with obstacles more than 80% of the time, while the SR-F framework maintains 100% safety.
Quotes
"The SR-F computes an R-CLVF offline between a model of the true system and a simplified planning model. Online, a planning algorithm is used to generate a trajectory in the simplified planning space, and the R-CLVF is used to provide a tracking controller that exponentially stabilizes to the planning model." "When an unexpected disturbance occurs, the proposed SR-F algorithm provides a means for the true system to recover to the planning model. We take advantage of this mechanism to induce an artificial disturbance by "jumping" the planning model in open environments, forcing faster navigation."

Deeper Inquiries

How can the SR-F framework be extended to handle more complex environments with dynamic obstacles or adversarial agents

To extend the SR-F framework to handle more complex environments with dynamic obstacles or adversarial agents, several modifications and enhancements can be implemented. One approach is to integrate real-time sensing and perception capabilities into the system to detect and react to dynamic obstacles or adversarial agents. This would involve updating the sensed obstacle information and adjusting the planning and tracking algorithms accordingly. Additionally, incorporating machine learning or reinforcement learning techniques can enable the system to adapt and learn from interactions with dynamic elements in the environment. By training the system to anticipate and respond to changing obstacles or adversarial agents, the SR-F framework can enhance its robustness and safety in complex environments.

What are the computational trade-offs and limitations of the R-CLVF computation compared to other reachability analysis techniques used in motion planning

The computational trade-offs and limitations of R-CLVF computation compared to other reachability analysis techniques in motion planning primarily revolve around the complexity and efficiency of the computation process. While R-CLVF offers robust control Lyapunov-value functions that provide stability guarantees in the presence of disturbances, the computation of these functions can be computationally intensive, especially for high-dimensional systems. The iterative nature of solving the R-CLVF value function and optimal controller can lead to increased computational complexity, potentially impacting real-time performance. In contrast, other reachability analysis techniques may offer faster computation times but might lack the robustness and stability guarantees provided by R-CLVF. Balancing the computational cost with the desired level of safety and robustness is crucial when choosing between different reachability analysis techniques in motion planning.

Can the idea of "jumping" the planner model be generalized to other motion planning frameworks beyond FaSTrack to achieve faster navigation while maintaining safety guarantees

The concept of "jumping" the planner model can be generalized to other motion planning frameworks beyond FaSTrack to achieve faster navigation while maintaining safety guarantees. By introducing controlled disruptions or advancements in the planner's trajectory, the system can expedite its path towards the goal while ensuring safety constraints are met. This approach can be applied in various motion planning algorithms by incorporating mechanisms to strategically adjust the planned path based on real-time feedback and environmental conditions. By dynamically optimizing the trajectory to take advantage of safe opportunities for acceleration, the system can achieve faster navigation speeds without compromising safety. This adaptive and proactive approach to planning can be integrated into different motion planning frameworks to enhance efficiency and performance in various robotic applications.
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