An online trajectory generator on SE(3) with magnitude constraints

Abstract

With the increasing demand of humans and robots collaborating in a confined workspace, it is essential that robots can react instantaneously to unforeseen events while respecting comfort of human co-workers. As the human pays especial attention to the end-effector movement rather than individual joints in such tasks, we argue that it is necessary to limit exactly these end-effector dynamics directly on SE(3), regardless of any specific coordinate system. Only then it is possible to constrain the robot end-effector in its absolute dynamic values, to enhance human comfort. Common online trajectory generators (OTGs) are either limited to single degrees of freedom (DOFs) or consider decoupled multi-DOF mainly in joint space. While these strategies can be directly applied to Cartesian coordinate systems by using Euler angles for orientation, constraining the change in Euler angles does not lead to the correct angular velocities. In this work we present a novel OTG with constraints on translational and rotational magnitudes on SE(3). Simulations as well as experiments on a KUKA LWR4+ show the potential contribution towards improved Human-Robot-Collaboration.