Agile Flight and Physical Interaction Control

Contact-based Navigation Path Planning for Aerial Robots​

In this work, we present a path planning method for exploiting contact by aerial robots to enable the traversal of highly anomalous surfaces. Apart from sliding in contact, the proposed strategy introduces a new locomotion modality of azimuth rotations perpendicular to the surface, dubbed the flying cartwheel mode. The developed planner is based on the mechanics of optimal sampling-based methods and exploits a surface traversability metric to decide when to switch from sliding to flying cartwheel mode and vice versa.

Haptic Feedback-based Reactive Navigation for Aerial Robots with failed Localization​

This video presents preliminary results on Haptic Feedback-based Reactive Navigation for Aerial Robots subject to Pose and Map Estimation Failure. THe goal is to develop a fall-back solution for aerial robots operating in very narrow environments and for which the localization and mapping solution might - temporarily - fail. A system of bending force sensors is integrated onboard the robot and facilitates safe touching and force sensing to enable reactive collision-resilient navigation.

Full Attitude Control of a VTOL Tailsitter UAV 

This work is conducted in collaboration with ETH Zurich and refers to the design, modeling and control contribution of a convertible tailsitter aerial robot that is able to transition from vertical take off and landing to fixed-wing navigation. You can find more information in our publication:
S. Verling, B. Weibel, M. Boosfeld, K. Alexis, M. Burri, R. Siegwart, "Full Attitude Control of a VTOL Tailsitter UAV", IEEE International Conference on Robotics and Automation 2016 (ICRA 2016), Stockholm, Sweden
Although agile and physical interaction flight control research is at its early stages at our lab, Dr. Kostas Alexis has conducted previous work in the field. A set of indicative results is shown below. 

Planning and Control for Inspection through Contact

A complete path-planning and control framework that allows the automated execution of inspection through contact operations was proposed and described in our publication:
K. Alexis, G. Darivianakis, M. Burri, and R. Siegwart, "Aerial robotic contact-based inspection: planning and control", Autonomous Robots, Springer US, DOI: 10.1007/s10514-015-9485-5, ISSN: 0929-5593, http://dx.doi.org/10.1007/s10514-015-9485-5

Aerial Physical Interaction Control towards Inspection Operations

Using the Hybrid Model Predictive Controller we described in our paper: 
G. Darivianakis, K. Alexis, M. Burri, R. Siegwart, "Hybrid Predictive Control for Aerial Robotic Physical Interaction towards Inspection Operations", IEEE International Conference on Robotics and Automation, ICRA 2014, Hong Kong, China, May 31-June 7, 2014, p. 53-58 (Best Automation Paper Finalist)

We demonstrated "Aerial-Writing"! The motivation is to conduct inspection-through contact paths on infrastructure using Non Destructive Testing (probes). 

Physical Interaction Control for Object Manipulation and Transfer

Ever flew an aerial robot and something there stopped its way? Ever wondered what if we just have to push a door to continue our aerial search? Model Predictive Control combined with a tilt-rotor provides the answer. Watch the video and check our publication:
C. Papachristos, K. Alexis, A. Tzes, "Efficient Force Exertion for Physical Manipulation with UAVs: Exploiting the Direct Thrust-Vectoring Capabilities of a Tri-TiltRotor", IEEE International Conference on Robotics and Automation, ICRA 2014, Hong Kong, China, May 31-June 7, 2014, p. 4500-4505

Nonlinear MPC with a propeller failure!

We recorded this interesting control performance during a propeller failure using an AscTec Firefly multicopter Micro Aerial Vehicle. The work is mostly done by Mina Kamel, one of our outstanding PhDs at the ASL. The proposed fast nonlinear model predictive attitude controller in combination with an optimal outer loop retain position tracking while yaw is left unregulated due to the asymmetries of the hexacopter with one motor failure. ​

Aerial Grinding

It is often that grinding is required at high altitudes. To remove corrossion, to refurbish our infrastructure. This simple process becomes tedius exactly because it has to happen above the ground. Why not using an aerial robot? In our work: 
C. Papachristos, K. Alexis, A. Tzes, "Technical Activities Execution with a TiltRotor UAS employing Explicit Model Predictive Control", 19th World Congress The International Federation of Automatic Control, August 24-29, 2014, Cape Town, South Africa, p. 11036-11042

we demonstrated exactly that!

AIRobots integration week

We developed a Robust Model Predictive Control Framework for aerial robots of different configurations. Check the video and our relevant paper: 
K. Alexis, C. Papachristos, R. Siegwart, A. Tzes, "Robust Model Predictive Flight Control of Unmanned Rotorcrafts", Journal of Intelligent and Robotic Systems, Springer (DOI: 10.1007/s10846-015-0238-7)

​AIRobots integration week

This video presents activities of the AIRobots last integration week. We demonstrate the capabilities of our coaxial helicopter for physical interaction and teleoperation control. ​

Aerial Physical Interaction Control

This video presents first results in the topic of aerial physical interaction. It accompanies our paper: 
K. Alexis, C. Huerzeler, R. Siegwart, “Hybrid Modeling and Control of a Coaxial Unmanned Rotorcraft Interacting with its Environment through Contact”, IEEE International Conference on Robotics and Automation (ICRA), May, 2013 (ICRA 2013), p. 5417-5424, Karlsruhe, Germany

Resonance!

Sometimes a design poses some extra challenges for the controller. This coaxial helicopter has a resonance that appears due to coupling of the blade dynamics with the body. We worked on the compensator and we demonstrate the problem and the effect after applying the corresponding filter. Check our publication: 
C. Huerzeler, K. Alexis, R. Siegwart, “Configurable Real-Time Simulation Suite for Coaxial Rotor UAVs”, IEEE International Conference on Robotics and Automation (ICRA), May, 2013 (ICRA 2013), p. 309-316, Karlsruhe, Germany
My work in the problems related with aerial robots control can be found in multiple publications. These include: 
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Autonomous Quadrotor Position and Attitude PID/PIDD Control in GPS-denied Environments”, in The International Review of Automatic Control, May 2011, Vol. 4, N.3, Praise Worthy Prize
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Switching Model Predictive Attitude Control for a Quadrotor Helicopter subject to Atmospheric Disturbances”, in the Control Engineering Practice Journal, Elsevier, DOI (10.1016/j.conengprac.2011.06.010) (almost constantly being ranked in the 25 Hottest Articles in Journal of Control Engineering Practice from December 2012 to May 2014))
  • K. Alexis, G. Nikolakopoulos, A. Tzes “Model Predictive Quadrotor Control: Attitude, Altitude and Position Experimental Studies”, IET Control Theory and Applications, DOI (10.1049/iet-cta.2011.0348), awarded with the IET 2014 Premium Award for Best Paper in Control Theory & Applications. 
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “On Trajectory Tracking Model Predictive Control of an Unmanned Quadrotor Helicopter subject to aerodynamic disturbances”, Asian Journal of Control, Wiley, DOI: 10.1002/asjc.587
  • G. Nikolakopoulos, K. Alexis, “Switching Networked Attitude Control of an Unmanned Quadrotor”, International Journal of Control, Automation and Systems, Springer-Verlag, DOI: 10.1007/s12555-011-0132-4, ISSN: 1598-6446
  • K. Alexis, G. Nikolakopoulos, A. Tzes “Experimental Constrained Attitude Control of a Quadrotor subject to Wind Disturbances”, International Journal of Control, Automation and Systems, December 2014, Volume 12, Issue 6, pp 1289-1302 ( ISSN: 0020-7179, DOI: 10.1007/s12555-013-0290-7)
  • K. Alexis, C. Huerzeler, R. Siegwart, “Hybrid Modeling and Control of a Coaxial Unmanned Rotorcraft Physically Interacting with its Environment through Contact”, Control Engineering Practice, Vol. 32, November 2014, Pages 96-112 (DOI: 10.1016/j.conengprac.2014.07.006)
  • K. Alexis, C. Papachristos, R. Siegwart, A. Tzes, "Robust Model Predictive Flight Control of Unmanned Rotorcrafts", Journal of Intelligent and Robotic Systems, Springer (DOI: 10.1007/s10846-015-0238-7)
  • C. Papachristos, K. Alexis, A. Tzes, “Dual-Authority Control of an Unmanned Tri-TiltRotor employing Model Predictive Control", Journal of Intelligent and Robotic Systems, Springer (DOI: 10.1007/s10846-015-0231-1)
  • K. Alexis, G. Darivianakis, M. Burri, and R. Siegwart, "Aerial robotic contact-based inspection: planning and control", Autonomous Robots, Springer US, DOI: 10.1007/s10514-015-9485-5, ISSN: 0929-5593, http://dx.doi.org/10.1007/s10514-015-9485-5
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Design and Experimental Verification of a Constrained Finite Time Optimal Control Scheme for the Attitude Control of a Quadrotor Helicopter Subject to Wind Gusts”, IEEE International Conference on Robotics and Automation, p.1636-1641, May 3-8, 2010 Anchorage, Alaska.
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Constrained Optimal Attitude Control of a Quadrotor Helicopter subject to Wind-Gusts: Experimental Studies”, IEEE American Control Conference, p.4451-4455, June 30-July 2, 2010, Baltimore Marriot Waterfront.
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Constrained-Control of a Quadrotor Helicopter for Trajectory Tracking under Wind-Gust Disturbances”, 15th IEEE Mediterranean Electromechanical Conference, Valletta, Malta, p.1411-1416, 26-28 April 2010
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Model Predictive  Attitude Control of an Unmanned Quadrotor Helicopter subject to atmospheric disturbances”, IEEE International Symposium on Industrial Electronics, Bari, Italy, 4-7 July, 2010
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Experimental Model Predictive Control of a Quadrotor Helicopter subject to Wind-Gusts”, 18th IEEE Mediterranean Conference on Control and Automation, p.1461-1466, June 23-25, 2010, Congress Palace, Marrakesh, Morocco
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Model Predictive Control for a Miniature Coaxial Helicopter”, 7th IFAC Symposium on Intelligent Autonomous Vehicles, p.139-144, September 6-8, Lecce, Italy (DOI: 10.3182/20100906-3-IT-2019.00026)
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Experimental Application of a Model Predictive Controller to an Unmanned Quadrotor Helicopter”, 2nd Hellenic Robotic Conference, 9-10 December, 2010, Patras, Greece
  • C. Papachristos, K. Alexis, G. Nikolakopoulos, A. Tzes, “Modeling and Control of an Unmanned Tilt-Rotor flying in Helicopter Mode”, 2nd Hellenic Robotics Conference, 9-10 December, 2010,Patras, Greece
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Switching Model Predictive Control for a Quadrotor Helicopter under Severe Environmental Flight Conditions”, 18th IFAC World Congress, p.11913-11918, August 28 – September 2 2011, Milan, Italy (DOI: 10.3182/20110828-6-IT-1002.03010)
  • C. Papachristos, K. Alexis, G. Nikolakopoulos, A. Tzes, “Model Predictive Attitude Control of an unmanned Tilt-Rotor aircraft”, 20th International Symposium on Industrial Electronics, p.922-927, June 27-30 2011, Gdansk, Poland
  • K. Alexis, G. Nikolakopoulos, A. Tzes, “Model Predictive Control Scheme for the Autonomous Flight of an Unmanned Quadrotor”, 20th International Symposium on Industrial Electronics, p.2243-2248, June 27-30 2011, Gdansk, Poland
  • K. Alexis,  C. Papachristos, G. Nikolakopoulos, A. Tzes, “Model Predictive Quadrotor Indoor Position Control”, 19th Mediterranean Conference on Control and Automation, p.1247-1252, June 20-23 2011, Aquis Corfu Holiday Palace, Corfu, Greece
  • C. Papachristos, K. Alexis, G. Nikolakopoulos, A. Tzes, “Design and Experimental Attitude Control of a Unmanned Tilt-Rotor Aerial Vehicle”, 15th International Conference on Advanced Robotics, Tallin, p.465-470, June 20-23 2011
  • K. Alexis, A. Tzes, “Revisited Dos Samara UAV: Design and Control”, International Conference on Robotics and Automation, p.465-470, May 14-18 2012, Minessota, USA
  • C. Papachristos, K. Alexis, A. Tzes, “Towards a High–End Unmanned Tri–TiltRotor:Design, Modeling and Hover Control”, Mediterranean Conference on Control and Automation, p.1579-1584, 3-6 July, 2012 
  • K. Alexis, C. Huerzeler, R. Siegwart, “Hybrid Modeling and Control of a Coaxial Unmanned Rotorcraft Interacting with its Environment through Contact”,  IEEE International Conference on Robotics and Automation (ICRA), May, 2013 (ICRA 2013), p. 5417-5424, Karlsruhe, Germany
  • C. Huerzeler, K. Alexis, R. Siegwart, “Configurable Real-Time Simulation Suite for Coaxial Rotor UAVs”, IEEE International Conference on Robotics and Automation (ICRA), May, 2013 (ICRA 2013), p. 309-316, Karlsruhe, Germany
  • C. Papachristos, K. Alexis, A. Tzes “Model Predictive Hovering-Translation Control of an Unmanned Tri-TiltRotor”,  IEEE International Conference on Robotics and Automation (ICRA), May, 2013 (ICRA 2013), p. 5425-5432, Karlsruhe, Germany
  • C. Papachristos, K. Alexis, A. Tzes, “Hybrid Model Predictive Flight Mode Conversion Control for Unmanned Quad-TiltRotors", European Control Conference, July, 2013, p. 1793-1798, Zurich, Switzerland
  • C. Huerzeler, K. Alexis, R. Siegwart, “Explicit Constrained Optimal Trajectory Control of an Unmanned Coaxial Rotorcraft”, Mediterranean Conference on Control and Automation, June, 2013, p. 363-368, Chania, Crete, Greece
  • C. Papachristos, K. Alexis, A. Tzes, “Trajectory control of an unmanned Tri-TiltRotor in hover flight via direct longitudinal actuation”, Mediterranean Conference on Control and Automation, June, 2013, p. 369-374, Chania, Crete, Greece
  • K. Alexis, C. Huerzeler, R. Siegwart, “Unmanned Coaxial Rotorcraft Force and Position Control for Physical Interaction through Contact”, Invited Session, Mediterranean Conference on Control and Automation, 2013, June, 2013, Chania, Crete, Greece 
  • C. Papachristos, K. Alexis, A. Tzes, “Linear Quadratic Optimal Trajectory–Tracking Control of a Longitudinal Thrust Vectoring–Enabled Unmanned Tri–TiltRotor”, International Conference on Informatics in Control, Automation and Robotics, November, 2013, p. 4174-4179, Vienna, Austria 
  • Christoph Huerzeler, roberto naldi, Vincenzo Lippiello, Raffaella Carloni, Janosch Nikolic, Kostas Alexis, Lorenzo Marconi, Roland Siegwart, "AIRobots: Innovative Aerial Service Robots for Remote Inspection by Contact", Video Submission, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2013, p. 4174 - 4179, Tokyo, Japan
  • G. Darivianakis, K. Alexis, M. Burri, R. Siegwart, "Hybrid Predictive Control for Aerial Robotic Physical Interaction towards Inspection Operations", IEEE International Conference on Robotics and Automation, ICRA 2014, Hong Kong, China, May 31-June 7, 2014, p. 53-58 (Best Automation Paper Finalist)
  • C. Papachristos, K. Alexis, A. Tzes, "Efficient Force Exertion for Physical Manipulation with UAVs: Exploiting the Direct Thrust-Vectoring Capabilities of a Tri-TiltRotor", IEEE International Conference on Robotics and Automation, ICRA 2014, Hong Kong, China, May 31-June 7, 2014, p. 4500-4505
  • C. Papachristos, K. Alexis, A. Tzes, "Technical Activities Execution with a TiltRotor UAS employing Explicit Model Predictive Control", 19th World Congress The International Federation of Automatic Control, August 24-29, 2014, Cape Town, South Africa, p. 11036-11042
  • K. Alexis, C. Papachristos, R. Siegwart, A. Tzes "Robust Explicit Model Predictive Flight Control ofUnmanned Rotorcrafts: Design and Experimental Evaluation", European Control Conference, 2014, Strasburg, France, June 24-June 27, 2014, p. 498-503
  • Philipp Oettershagen, Amir Melzer, Stefan Leutenegger, Kostas Alexis, Roland Y. Siegwart, "Explicit Model Predictive Control and L1-Navigation Strategies for Fixed–Wing UAV Path Tracking", Mediterranean Control Conference, 2014, Palermo, Italy, June 16-June 19, 2014, p. 1159-1165
  • S. Leutenegger, A. Melzer, K. Alexis, R. Siegwart, "Robust State Estimation for Small Unmanned Airplanes", IEEE Multiconference on Systems and Control (MSC), 2014, Antibes, France
  • Mina Kamel, Kostas Alexis, Markus Wilhelm Achtelik, Roland Siegwart, "Fast Nonlinear Model Predictive Control for Multicopter Attitude Tracking on SO(3)", Multiconference on Systems and Control (MSC), 2015, Novotel Sydney Manly Pacific, Sydney Australia. 21-23 September, 2015
  • S. Verling, B. Weibel, M. Boosfeld, K. Alexis, M. Burri, R. Siegwart, "Full Attitude Control of a VTOL Tailsitter UAV", IEEE International Conference on Robotics and Automation 2016 (ICRA 2016), Stockholm, Sweden (Accepted - to be presented)
  • Mina Kamel, Thomas Stastny, Kostas Alexis, Roland Siegwart, "Model Predictive Control for Trajectory Tracking of Unmanned Aerial Vehicles Using ROS", Springer Book on Robot Operating System (ROS) – The Complete Reference (Volume 2)
  • Sebastian Verling, Thomas Stastny, Gregory Bättig, Kostas Alexis, Roland Siegwart, "Model-based Transition Optimization for a VTOL Tailsitter", IEEE International Conference on Robotics and Automation (ICRA), May 29-June 3, 2017, Singapore
  • C. Papachristos, S. Khattak, K. Alexis, "Haptic Feedback-based Reactive Navigation for Aerial Robots Subject to Localization Failure", IEEE Aerospace Conference (AeroConf) 2019, Yellowstone Conference, Big Sky, Montana, Mar 2-9, 2019 
  • N. V. Khedekar, F. Mascarich, C. Papachristos, T. Dang, K. Alexis, "Contact-based Navigation Path Planning for Aerial Robots", IEEE International Conference on Robotics and Automation (ICRA), 2019, May 20-24, 2019 Montreal, Canada