Input-to-State Safety With Control Barrier Functions

TL;DR

This paper introduces input-to-state safe control barrier functions (ISSf-CBFs) to ensure nonlinear system safety under disturbances, providing a methodology for their construction and a unified control approach combining safety and stability.

Contribution

It proposes a novel ISSf-CBF framework, a method to derive ISSf-CBFs from existing CBFs, and a unified quadratic program for safety and stability under disturbances.

Findings

ISSf-CBFs guarantee safety despite input disturbances.

A systematic method to construct ISSf-CBFs from CBFs.

Unified control law ensures safety and stability simultaneously.

Abstract

This letter presents a new notion of input-to-state safe control barrier functions (ISSf-CBFs), which ensure safety of nonlinear dynamical systems under input disturbances. Similar to how safety conditions are specified in terms of forward invariance of a set, input-to-state safety (ISSf) conditions are specified in terms of forward invariance of a slightly larger set. In this context, invariance of the larger set implies that the states stay either inside or very close to the smaller safe set; and this closeness is bounded by the magnitude of the disturbances. The main contribution of the letter is the methodology used for obtaining a valid ISSf-CBF, given a control barrier function (CBF). The associated universal control law will also be provided. Towards the end, we will study unified quadratic programs (QPs) that combine control Lyapunov functions (CLFs) and ISSf-CBFs in order to obtain a single control law that ensures both safety and stability in systems with input disturbances.