Compliant Manipulation of Free-Floating Objects

TL;DR

This paper introduces a direct force control method for compliant manipulation of free-floating objects, effectively minimizing interaction forces and maintaining contact without pushing objects away, demonstrated through simulations and experiments.

Contribution

The paper presents a novel direct force control approach specifically designed for free-floating objects, outperforming impedance control in maintaining contact and controlling forces.

Findings

The proposed control law effectively manages interaction forces.

Experimental results show successful object alignment without pushing away.

Simulation highlights the importance of relative inertia in control performance.

Abstract

Compliant motions allow alignment of workpieces using naturally occurring interaction forces. However, free-floating objects do not have a fixed base to absorb the reaction forces caused by the interactions. Consequently, if the interaction forces are too high, objects can gain momentum and move away after contact. This paper proposes an approach based on direct force control for compliant manipulation of free-floating objects. The objective of the controller is to minimize the interaction forces while maintaining the contact. The proposed approach achieves this by maintaining small constant force along the motion direction and an apparent reduction of manipulator inertia along remaining Degrees of Freedom (DOF). Simulation results emphasize the importance of relative inertia of the robotic manipulator with respect to the free-floating object. The experiments were performed with KUKA LWR4+ manipulator arm and a two-dimensional micro-gravity emulator (object floating on an air bed), which was developed in-house. It was verified that the proposed control law is capable of controlling the interaction forces and aligning the tools without pushing the object away. We conclude that direct force control works better with a free-floating object than implicit force control algorithms, such as impedance control.