Augmented Invariance Control for Impedance-controlled Robots with Safety Margins

Abstract

Various robotic applications require enforcing constraints, to achieve task performance or to hinder the robot from causing danger. Especially in human-robot-interaction, collision avoidance and velocity limits are crucial for safety. A promising approach to enforce adherence to safety margins is invariance control. Considering the system dynamics, it corrects a nominal control based on a switching policy. To overcome the resulting lack of smoothness in terms of control inputs and states, a control scheme is developed that adds dynamics to the input and thereby augments the system. In previous work it is shown that the closed loop system is stable in combination with an exponentially stabilizing nominal control. However, this could not be shown for impedance controlled robots. Therefore, in this paper, an augmented invariance control for robotic applications is developed and proven to be uniformly asymptotically stable with an impedance-type nominal control. The proposed control law is validated in experiments on a KUKA LWR4+ in a collision avoidance scenario demonstrating stable behaviour with improved smoothness and chattering characteristics while enforcing the imposed hard constraints.

Shared invariance control for constraint satisfaction in multi-robot systems

“…This assumption is imposed for convenience of notation and poses no additional restrictions on the systems, because the relative degree may be increased, if necessary, by augmented invariance control as introduced for general systems by Kimmel et al (2016) and for robotic systems by Jähne and Hirche (2017). Note that for robotic systems with position constraints, for example, the assumption is naturally fulfilled as the relative degree equals two for all agents.…”

Collision detection and force control based on the impedance approach and dynamic modelling

“…In Davliakos and Papadopoulos (2009), with electro-hydraulic servo control, the impedance controller based on model filter is proposed and achieved better control effect than PI control strategy during the trajectory tracking process. In Jähne and Hirche (2017), considering the collision and speed limit in the process of interaction between robot and human, the research and new impedance control are realized. Finally, an effective research strategy of impedance collision avoidance control is verified on the KUKA robot.…”