We present the design, motion planning, and control of an aerial manipulator for non-trivial physical interaction tasks, such as pushing while sliding on curved surfaces—a task which is motivated by the increasing interest in autonomous non-destructive tests for industrial plants. The proposed aerial manipulator consists of a multidirectional-thrust aerial vehicle—to enhance physical interaction capabilities—endowed with a 2-DoFs lightweight arm—to enlarge its workspace. This combination makes it a truly-redundant manipulator going beyond standard aerial manipulators based on collinear multirotor platforms. The controller is based on a PID method with a “displaced” positional part that ensures asymptotic stability despite the arm elasticity. A kinodynamic task-constrained and control-aware global motion planner is used. Experiments show that the proposed aerial manipulator system, equipped with an Eddy current probe, is able to scan a metallic pipe sliding the sensor over its surface and preserving the contact. From the measures, a weld on the pipe is successfully detected and mapped.

/pdf/a-truly-redundant-aerial-manipulator-system-with-application-5fxp5kduky.pdf

A Truly-Redundant Aerial Manipulator System With Application to Push-and-Slide Inspection in Industrial Plants

This article analyzes the evolution and current trends in aerial robotic manipulation, comprising helicopters, conventional underactuated multirotors, and multidirectional thrust platforms equipped with a wide variety of robotic manipulators capable of physically interacting with the environment. It also covers cooperative aerial manipulation and interconnected actuated multibody designs. The review is completed with developments in teleoperation, perception, and planning. Finally, a new generation of aerial robotic manipulators is presented with our vision of the future. 

Past, Present, and Future of Aerial Robotic Manipulators

This paper presents an omnidirectional aerial manipulation platform for robust and responsive interaction with unstructured environments, toward the goal of contact-based inspection. The fully actuated tilt-rotor aerial system is equipped with a rigidly mounted end-effector, and is able to exert a 6 degree of freedom force and torque, decoupling the system's translational and rotational dynamics, and enabling precise interaction with the environment while maintaining stability. An impedance controller with selective apparent inertia is formulated to permit compliance in certain degrees of freedom while achieving precise trajectory tracking and disturbance rejection in others. Experiments demonstrate disturbance rejection, push-and-slide interaction, and on-board state estimation with depth servoing to interact with local surfaces. The system is also validated as a tool for contact-based non-destructive testing of concrete infrastructure.

An Omnidirectional Aerial Manipulation Platform for Contact-Based Inspection

In this letter we present an optimization-based method for controlling aerial manipulators in physical contact with the environment. The multi-task control problem, which includes hybrid force-motion tasks, energetic tasks, and position/postural tasks, is recast as a quadratic programming problem with equality and inequality constraints, which is solved online. Thanks to this method, the aerial platform can be exploited at its best to perform the multi-objective tasks, with tunable priorities, while hard constraints such as contact maintenance, friction cones, joint limits, maximum and minimum propeller speeds are all respected. An on-board force/torque sensor mounted at the end effector is used in the feedback loop in order to cope with model inaccuracies and reject external disturbances. Real experiments with a multi-rotor platform and a multi-DoF lightweight manipulator demonstrate the applicability and effectiveness of the proposed approach in the real world.

/pdf/direct-force-feedback-control-and-online-multi-task-rsi3mf2g16.pdf

Direct Force Feedback Control and Online Multi-Task Optimization for Aerial Manipulators

This article presents and validates active interaction force control and planning for fully actuated and omnidirectional aerial manipulation platforms, with the goal of aerial contact inspection in unstructured environments. We present a variable axis-selective impedance control which integrates direct force control for intentional interaction, using feedback from an on-board force sensor. The control approach aims to reject disturbances in free flight, while handling unintentional interaction and actively controlling desired interaction forces. A fully actuated and omnidirectional tilt-rotor aerial system is used to show capabilities of the control and planning methods. Experiments demonstrate disturbance rejection, push-and-slide interaction, and force-controlled interaction in different flight orientations. The system is validated as a tool for nondestructive testing of concrete infrastructure, and statistical results of interaction control performance are presented and discussed.

Active Interaction Force Control for Contact-Based Inspection With a Fully Actuated Aerial Vehicle

In this work, it is presented an innovative sensor for the monitoring of existing cracks on metallic structures. Compared to existing solutions, the proposed device is able to provide the direct information of the crack length. The principle of measurement is based on the Eddy current non-destructive testing. The technique dos not require special surface preparation and is largely employed in industry and aerospace.

Gilles Santi

Papers

A Truly-Redundant Aerial Manipulator System With Application to Push-and-Slide Inspection in Industrial Plants

Eddy Current Crack Monitoring System for Structural Health Monitoring (SHM) Applications