Three Degrees of Freedom Compliant Motion Control for Robotic Aircraft Refueling

Abstract

The Air Force Institute of Technology (AFIT) supports on-going research in application of robotic technology to enhance assembly tasks. As a testbed, AFIT supports the ground-based aerial refueling project, with an emphasis on visual servoing techniques and compliant motion control. This thesis focuses on compliant motion control. Previous research developed the testing environment, which includes a PUMA-560 industrial manipulator, and a half scale mock-up of an aerial refueling system. This effort corrected and expanded the existing two degree of freedom (DOF) compliant controller to three DOF. Three DOF compliance was demonstrated by inserting the refueling nozzle into the receiver port. Tuning, carried out by adjusting desired model variables, characterized the impedance controller to function over a wide range of desired dynamics. In addition, irregular force and velocity torque profiles were attenuated through basic filtering schemes, providing an environment in which friction compensation was tested. Finally, preliminary studies into faster trajectories provide impetus for further study in the area of high speed compliant assembly. The three DOF compliant controller combined with the visual servoing techniques, provides a strong environment to test and evaluate robotic technologies for constrained motion assembly tasks.