Easing Reliance on Collision-free Planning with Contact-aware Control

TL;DR

This paper introduces a contact-aware control method for robots that allows them to execute smooth trajectories despite unexpected contacts, reducing reliance on collision avoidance and improving robustness.

Contribution

It presents a novel quadratic programming controller that manages contact forces and enables stable contact handling during motion execution.

Findings

Effective contact force regulation demonstrated on KUKA iiwa arm.

Controller maintains trajectory tracking despite collisions.

Allows operation without precise dynamic models or torque control.

Abstract

We believe that the future of robot motion planning will look very different than how it looks today: instead of complex collision avoidance trajectories with a brittle dependence on sensing and estimation of the environment, motion plans should consist of smooth, simple trajectories and be executed by robots that are not afraid of making contact. Here we present a "contact-aware" controller which continues to execute a given trajectory despite unexpected collisions while keeping the contact force stable and small. We introduce a quadratic programming (QP) formulation, which minimizes a trajectory-tracking error subject to quasistatic dynamics and contact-force constraints. Compared with the classical null-space projection technique, the inequality constraint on contact forces in the proposed QP controller allows for more gentle release when the robot comes out of contact. In the quasistatic dynamics model, control actions consist only of commanded joint positions, allowing the QP controller to run on stiffness-controlled robots which do not have a straightforward torque-control interface nor accurate dynamic models. The effectiveness of the proposed QP controller is demonstrated on a KUKA iiwa arm.