A Novel Safety-Aware Energy Tank Formulation Based on Control Barrier Functions

Abstract

In this work, we propose a novel formulation for energy tanks based on Control Barrier Functions (CBF). Our approach is able to handle simultaneously energy constraints to ensure passivity, as well as enforce power limits in the system to enhance safety. Furthermore, our approach overcomes the discrete switching nature of classical energy tanks, ensuring smooth control commands. To achieve our desiderata, we formulate our tank as a second order dynamical system, where we exploit CBF and Higher-Order CBF to obtain theoretical guarantees on fulfilling the energy and power constraints in the system. Furthermore, we derive conditions related to our tank design in order to ensure the passivity of the controlled robot. Our proposed approach is tested in a series of robot experiments where we validate our approach on tasks such variable stiffness and force control, and in a scenario where it is desired to constrain the kinetic energy in the system.