Compliant Manipulation of Free-Floating Objects
This addresses the challenge of compliant manipulation in space or micro-gravity environments for robotics, though it is incremental as it builds on existing force control methods.
The paper tackled the problem of manipulating free-floating objects without pushing them away by proposing a direct force control approach that minimizes interaction forces while maintaining contact, achieving successful alignment in experiments with a KUKA LWR4+ manipulator and a micro-gravity emulator.
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.