Compliant Explicit Reference Governor for Contact Friendly Robotic Manipulators

TL;DR

The paper addresses safe robotic manipulation during environmental contact by extending the Explicit Reference Governor to a Compliant ERG (C-ERG). By introducing an OR-based safety mechanism and a Compliant Dynamic Safety Margin that combines hard constraints, soft contact boundaries, and energy limits, the C-ERG enables seamless transitions between free motion and contact without altering the underlying controller. The approach is validated across a 2D double integrator, a two-link planar arm, and a 7-DoF Franka Emika Panda in Drake simulations, showing reduced contact forces and stable, energy-bounded interaction with the environment. The work offers a practical safety layer that can be integrated with high-level planners to enable efficient, contact-rich manipulation while guaranteeing safety and real-time feasibility.

Abstract

This paper introduces the Compliant Explicit Reference Governor (C-ERG), an extension of the Explicit Reference Governor that allows the robot to operate safely while in contact with the environment. The C-ERG is an intermediate layer that can be placed between a high-level planner and a low-level controller: its role is to enforce operational constraints and to enable the smooth transition between free-motion and contact operations. The C-ERG ensures safety by limiting the total energy available to the robotic arm at the time of contact. In the absence of contact, however, the C-ERG does not penalize the system performance. Numerical examples showcase the behavior of the C-ERG for increasingly complex systems.

Figures (8)

• Figure 1: The ERG Architecture. The applied reference is the integral of the product of navigation field and Dynamic Safety Margin.
• Figure 2: C-ERG applied to a double integrator. When $r$ (red star) is inadmissible, $v$ penetrates the constraint, causing the controller to push against the wall.
• Figure 3: Energy of the double integrator. The constraint $V(x,v)\leq E_{\max}$ is not enforced during free motion, but is enforced in preparation of contact at time $t= 7.9$.
• Figure 4: Forces exchanged between the double integrator and the wall. In the absence of the C-ERG, impact happens sooner and with a higher force. The C-ERG successfully reduces the contact forces by upper bounding the energy of the prestabilized system at the time of contact $t=7.9$.
• Figure 5: C-ERG applied to the RR arm with joint space control and end effector space control. The final configuration of the robot minimizes the joint space error for the former and the end effector error for the latter. The path of the auxiliary references, however, are identical.

Theorems & Definitions (7)

• Lemma 1
• proof
• Definition 1
• Proposition 1
• proof
• Theorem 1
• proof