Home News About Research Challenges Publications Software Personal

Marko Bjelonic

Logo

Marko Bjelonic is a PhD researcher at the Robotic Systems Lab of ETH Zurich focusing on motion control and planning for wheeled-legged robots in rough terrain.

               

Research

January, 2019  ·  IEEE Robotic and Automation Letters (RA-L)

Keep Rollin’ – Whole-Body Motion Control and Planning for Wheeled Quadrupedal Robots (RA-L2019.pdf) (Poster.pdf)

We show dynamic locomotion strategies for wheeled quadrupedal robots which combine the advantages of walking and driving. The developed optimization framework tightly integrates the additional degrees of freedom introduced by the wheels. Our approach relies on a zero-moment point based motion optimization which continuously updates reference trajectories. The reference motions are tracked by a hierarchical whole-body controller which optimizes the generalized accelerations and contact forces by solving a sequence of prioritized tasks including the nonholonomic rolling constraints. Our approach has been tested on the torque-controlled robot ANYmal equipped with non-steerable, torque-controlled wheels. We conducted experiments on flat, inclined and rough terrain, whereby we show that integrating the wheels into the motion control and planning framework results in intuitive motion trajectories, which enable more robust and dynamic locomotion compared to other wheeled-legged robots. Moreover, with a speed of 4 m/s and a reduction of the cost of transport by 83 % we prove the superiority of wheeled-legged robots compared to their legged counterparts.

January, 2019  ·  IEEE Robotic and Automation Letters (RA-L)

Trajectory Optimization for Wheeled-Legged Quadrupedal Robots using Linearized ZMP Constraints (RA-L2019.pdf)

We present a trajectory optimizer for quadrupedal robots with actuated wheels. By solving for angular, vertical, and planar components of the base and feet trajectories in a cascaded fashion and by introducing a novel linear formulation of the zero- moment point (ZMP) balance criterion, we rely on quadratic programming only, thereby eliminating the need for nonlinear optimization routines. Yet, even for gaits containing full flight phases, we are able to generate trajectories for executing complex motions that involve simultaneous driving, walking, and turning. We verified our approach in simulations of the quadrupedal robot ANYmal equipped with wheels, where we are able to run the proposed trajectory optimizer at 50 Hz. To the best of our knowledge, this is the first time that such dynamic motions are demonstrated for wheeled-legged quadrupedal robots using an online motion planner.

March, 2018  ·  IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

Skating with a force controlled quadrupedal robot (IROS2018.pdf)

Traditional legged robots are capable of traversing challenging terrain, but lack of energy efficiency when compared to wheeled systems operating on flat environments. The combination of both locomotion domains overcomes the trade-off between mobility and efficiency. Therefore, this paper presents a novel motion planner and controller which together enable a legged robot equipped with skates to perform skating maneuvers. These are achieved by an appropriate combination of planned reaction forces and gliding motions. Our novel motion controller formulates a Virtual Model Controller and an optimal contact force distribution which takes into account the nonholonomic constraints introduced by the skates. This approach has been tested on the torque-controllable robot ANYmal equipped with passive wheels and ice skates as end-effectors. We conducted experiments on flat and inclined terrain, whereby we show that skating motions reduces the cost of transport by up to 80 % with respect to traditional walking gaits.

November, 2015 - September, 2016  ·  Master thesis

Weaver: Hexapod robot for autonomous navigation on unstructured terrain (RA-L2019.pdf) (JFR2018.pdf) (ICRA2017.pdf) (ISER2016.pdf) (IROS2016.pdf)

Legged robots are an efficient alternative for navigation in challenging terrain. In this paper we describe Weaver, a six‐legged robot that is designed to perform autonomous navigation in unstructured terrain. It uses stereo vision and proprioceptive sensing based terrain perception for adaptive control while using visual‐inertial odometry for autonomous waypoint‐based navigation. Terrain perception generates a minimal representation of the traversed environment in terms of roughness and step height. This reduces the complexity of the terrain model significantly, enabling the robot to feed back information about the environment into its controller. Furthermore, we combine exteroceptive and proprioceptive sensing to enhance the terrain perception capabilities, especially in situations in which the stereo camera is not able to generate an accurate representation of the environment. The adaptation approach described also exploits the unique properties of legged robots by adapting the virtual stiffness, stride frequency, and stride height. Weaver's unique leg design with five joints per leg improves locomotion on high gradient slopes, and this novel configuration is further analyzed. Using these approaches, we present an experimental evaluation of this fully self‐contained hexapod performing autonomous navigation on a multiterrain testbed and in outdoor terrain.


Made by Marko Bjelonic