An Omnidirectional Aerial Manipulation Platform for Contact-Based Inspection

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.Comment: Accepted submission to Robotics: Science and Systems conference 2019. 9 pages, 12 figure

Omnidirectional Tilt-Rotor Flying Robots for Aerial Physical Interaction: Modelling, Control, Design and Experiments

This doctoral thesis addresses the study of omnidirectional tilt-rotor aerial robots, and their application to aerial physical interaction tasks. Through modelling, control, prototype design, and experimental evaluation, this work carves a new direction in aerial robotics research, and seeks to inspire a future of versatile and autonomous aerial manipulators. Recent developments in the field of fully actuated aerial robots have demonstrated the exceptional advantages of these systems for physical interaction. Characterised by their decoupled translational and rotational system dynamics, these systems not only outperform their underactuated counterparts, but extend their capabilities. Through the dynamic re-orientation of actuated thrust vectors, we now have access to a great expanse of possible morphologies, dynamic system capabilities, and new applications. Extending these novel tilt-rotor systems with an active manipulator further demonstrates enhanced end effector performance for manipulation tasks. The concept of macro-micro manipulation -- using a highly dynamic end effector mounted to a powerful base -- overcomes dynamic limitations that currently restrict the efficacy of aerial manipulators. In pursuit of versatile and high performance systems for aerial physical interaction, the present work combines these concepts to advance the state-of-the-art in aerial manipulation. The design space of a tilt-rotor aerial robot is selected by optimizing a general model around desired performance metrics and system parameters. The resulting system, chosen for a balance of omnidirectional and efficient flight capabilities, is compared against other state-of-the-art fully actuated systems. Aerial interaction models are developed for fixed and active manipulators, and a geometric optimization is performed to determine the design of a parallel manipulator in the context of an omnidirectional flying base. The control problem divides the system conceptually into tracking control of a pure wrench generating base, and a subsequent actuator allocation problem to achieve a six degrees of freedom wrench with 18 individual actuator commands. The nonlinear and highly dimensional actuator space is addressed with instantaneous and differential allocation methods, the latter of which incorporates secondary tasks, such as the unwinding of tilt-arm cables, in the actuation null space. Inverse-dynamics based controllers are introduced for control of the flying base, treating the whole tilt-rotor system as a single rigid body. Interaction controllers including axis-selective impedance and direct force control are developed for the system equipped with a fixed manipulator arm. A redundant control strategy is developed for the omnidirectional system with an attached translational parallel manipulator, where predicted reaction forces are fed to an independent base controller to compensate the manipulator dynamics. Several iterations of omnidirectional tilt-rotor aerial robots are designed and constructed, considering the requirements of aerial interaction tasks. Actuator selection, tilt-rotor mechanisms, and complete system assembly are presented, as well as design details for a parallel manipulator. Experimental trials evaluate the capabilities of the physical system and its control implementation to track omnidirectional trajectories. Aerial physical interaction tasks are demonstrated, involving point force application with the environment, push-and-slide tasks, and applications to non-destructive contact inspection of concrete. Fast end effector tracking and disturbance rejection experiments are performed to validate the macro-micro concept of an omnidirectional tilt-rotor parallel manipulator. Ranging from general modelling to control, design choices and complete system prototypes, the content of this work acts as a guide for envisioning and building innovative systems that will push the frontier of aerial manipulation

Dynamic End Effector Tracking with an Omnidirectional Parallel Aerial Manipulator

ISSN:2377-376

Flying corrosion inspection robot for corrosion monitoring of civil structures – First results

Potential mapping permits an early detection of corrosion and has major advantages over a purely visual condition assessment. The current manner of assessing the corrosion state of reinforced concrete structures with potential mapping is limited due to the lack of accessibility, leading to high involvement of manpower and finally to high inspection costs. A main challenge in the coming decades will be the assessment of our ageing infrastructure and their repair. Automating corrosion assessments of structures by an inspection robot will increase the use of non-destructive test methods and the quality of assessments and consequently lead to a more profound basis for the decision making and planning of the maintenance of the ageing infrastructure and lower inspection costs. At ETH Zurich, the development of an omnidirectional flying inspection robot is currently being tackled as a collaborative effort between two research groups. The flying robot will collect the following data from the structure: (1) images of the surface, (2) potential of the steel and (3) electrical resistance between the sensor to the reinforcement. These measurements require the sensor to make physical contact with the concrete surface. As this contact task requires high stability and full 6 degree of freedom force and torque tracking to be robust in the field, no commercially available robot can be used. Preliminary flight tests with the electrochemical sensor mounted on the inspection robot on a laboratory sample demonstrate that potentials and resistances can be successfully measured, with results similar to measurements taken by hand

Towards Efficient Full Pose Omnidirectionality with Overactuated MAVs

Omnidirectional MAVs are a growing field, with demonstrated advantages for aerial interaction and uninhibited observation. While systems with complete pose omnidirectionality and high hover efficiency have been developed independently, a robust system that combines the two has not been demonstrated to date. This paper presents VoliroX: a novel omnidirectional vehicle that can exert a wrench in any orientation while maintaining efficient flight configurations. The system design is presented, and a 6 DOF geometric control that is robust to singularities. Flight experiments further demonstrate and verify its capabilities

Direct Force and Pose NMPC with Multiple Interaction Modes for Aerial Push-and-Slide Operations

In this paper, we present a model predictive controller for a fully actuated aerial manipulator to track a hybrid force and pose trajectory at the end-effector in an aerial interaction task. A force sensor at the end-effector is used to detect contact and to directly control the interaction force. We propose an approach for automatic transition between three operation modes which reflect the state of contact constraints, including free flight and two modes for force control based on static or dynamic friction at the end-effector. This division into three modes allows for different mode-specific controller tunings to optimize the desired performance throughout an interaction task. Results from flight experiments which combine force, position, and attitude tracking, show the performance of the controller in terms of accuracy and precision. The performance is further benchmarked against a hybrid force/impedance controller