Safety Assist Control for Nonautonomous Control-affine Systems via Time-varying Control Barrier Function

Abstract

The recent research on nonlinear control systems tends to prioritize safety beyond stability, and control barrier functions (CBFs) have been gaining popularity as a CBF-based controller can theoretically ensure safety of control systems with the notion of set invariance. In this paper, we define a time-varying CBF (Tv-CBF) for a nonautonomous control-affine system with a human operator input to address a time-dependent safety constraint problem. Then, we propose a human assist control law using a Tv-CBF that satisfies time-dependent safety constraints. We also prove that solutions to an ordinary differential equation denoting control systems are forward complete by employing the proposed human assist controller. Lastly, the effectiveness of the proposed method is confirmed through computer simulation.