Torsten Kroeger

Stanford Artificial Intelligence Laboratory

On-Line Trajectory Generation and Reflexxes Motion Libraries

These works are funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Assosiation).


Motivation: Sensor Integration

This research focuses on sensor integration in robotics, in particular in robotic manipulation control systems. We consider a mechanical system with multiple degrees of freedom equipped with one or more sensors delivering digital and/or analog sensor signals. There is no question that sensor integration and sensor-based control belong to the dominating domains for the future advancement of robotic systems. Although there has been much research on this objective, there is still one important question that has not been answered yet: If we consider a robot in an arbitrary state of motion, how can we calculate a trajectory, if we want the robot to react instantaneously to unforeseen sensor events?

Reflex Motions for Robots

We investigate a new class of algorithms that generate motion trajectories for robotics systems on-line, that is, within one control cycle (typically one millisecond or less). Such an algorithm is executed in parallel to low-level
motion controllers, and systems using it are able to react instantaneously to unforeseen (sensor) events. In order to answer the above question, the algorithm enables switchings from sensor-guided robot motion control (e.g., force/torque or visual servo control) to trajectory-following motion control and vice versa, which is an important feature for the practical realization of sensor-based robot motion control systems. The proposed on-line trajectory generation algorithm acts as an open-loop pose controller at an intermediate control layer that functions as one element of the important bridge between low-level robot motion control and higher-level (sensor-based) motion planning. Furthermore, it enables robotic systems to perform a kind of robotic reflex.


The objective of this research plainly illustrated.

 

The generated trajectories are time-optimal and synchronized for all degrees of freedom, such that all degrees of freedom reach their target at the same time instant. Using the proposed on-line trajectory generation algorithm as one control submodule in a hybrid switched-control system simplifies the execution of sensor-guided and sensor-guarded motions. As the algorithm is able to take over control at any time instant and in any state of motion, safe and continuous motions can be guaranteed — even if sensors fail. An additional benefit is that unforeseen (sensor-dependent) switchings of reference frames and/or control spaces become possible.

The proposed concept is of a very basic nature and, thus, addresses various fields of robotics, in which sensor integration plays a fundamental role, for example, in service robotics, manipulation control systems, mobile robotics and manipulation, and robotic surgery. Samples and use-cases accompany the book in order to provide a comprehensible insight into this interesting and relevant field of robotics.

Software and documentation can also be found on the Reflexxes website.

 

Please refer to the following publications:

  • Virtual Whiskers - Highly Responsive Robot Collision Avoidance.
    In Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems, Tokyo, Japan, November 2013. BibTeX

    @inproceedings{Schlegl:13,
    	author = {T.~Schlegl and T.~Kr{\"o}ger and A.~Gaschler and O.~Khatib and H.~Zangl},
    	title = {Virtual Whiskers - Highly Responsive Robot Collision Avoidance},
    	booktitle = {Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems},
    	month = {November},
    	address = {Tokyo, Japan},
    	year = {2013}
    }
    			
  • Towards Online Trajectory Generation Considering Robot Dynamics and Torque Limits.
    In Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems, Tokyo, Japan, November 2013. BibTeX

    @inproceedings{Katzschmann:13,
    	author = {R.~Katzschmann and T.~Kr{\"o}ger and T.~Asfour and O.~Khatib},
    	title = {Towards Online Trajectory Generation Considering Robot Dynamics and Torque Limits},
    	booktitle = {Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems},
    	month = {November},
    	address = {Tokyo, Japan},
    	year = {2013}
    }
    			
  • On-Line Trajectory Generation: Nonconstant Motion Constraints.
    In Proc. of the IEEE International Conference on Robotics and Automation, pp. 2048-2054, Saint Paul, MN, USA, May 2012. BibTeX

    @inproceedings{Kroeger:12,
    	author = {T.~Kr{\"o}ger},
    	title = {On-Line Trajectory Generation: {N}onconstant Motion Constraints},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	month = {May},
    	pages = {2048--2054},
    	address = {Saint Paul, MN, USA},
    	year = {2012}
    }
    			
  • Simple and Robust Visual Servo Control of Robot Arms Using an On-Line Trajectory Generator.
    In Proc. of the IEEE International Conference on Robotics and Automation, pp. 4862-4869, Saint Paul, MN, USA, May 2012. BibTeX

    @inproceedings{Kroeger:12a,
    	author = {T.~Kr{\"o}ger and J.~Padial},
    	title = {Simple and Robust Visual Servo Control of Robot Arms Using an On-Line Trajectory Generator},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	month = {May},
    	pages = {4862--4869},
    	address = {Saint Paul, MN, USA},
    	year = {2012}
    }
    			
  • JediBot - Experiments in Human-Robot Sword-Fighting.
    In Proc. of the International Symposium on Experimental Robotics, , June 2012. BibTeX

    @inproceedings{Kroeger:12b,
    	author = {{T.~Kr{\"o}ger} and K.~Oslund and T.~Jenkins and D.~Torczynski and N.~Hippenmeyer and R.~B.~Rusu and O.~Khatib},
    	title = {JediBot\,---\,Experiments in Human-Robot Sword-Fighting},
    	booktitle = {Proc. of the International Symposium on Experimental Robotics},
    	month = {June},
    	address = {Qu\'{e}bec City, Canada},
    	year = {2012}
    }
    			
  • A Depth Space Approach to Human-Robot Collision Avoidance.
    In Proc. of the IEEE International Conference on Robotics and Automation, pp. 338-345, Saint Paul, MN, USA, May 2012. BibTeX

    @inproceedings{Flacco:12,
    	author = {F.~Flacco and T.~Kr{\"o}ger and A.~De~Luca and O.~Khatib},
    	title = {A Depth Space Approach to Human-Robot Collision Avoidance},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	month = {May},
    	pages = {338--345},
    	address = {Saint Paul, MN, USA},
    	year = {2012}
    }
    			
  • On-Line Trajectory Generation: Straight-Line Trajectories.
    IEEE Trans. on Robotics. Vol. 27, No. 5, pp. 1010-1016, October 2011. BibTeX

    @article{Kroeger:11c,
    	author = {T.~Kr{\"o}ger},
    	title = {On-Line Trajectory Generation: Straight-Line Trajectories},
    	journal = {IEEE Trans. on Robotics},
    	month = {October},
    	volume = {27},
    	number = {5},
    	pages = {1010--1016},
    	year = {2011}
    }
    			
  • A Depth Space Approach to Human-Robot Collision Avoidance.
    In Workshop on Human-Friendly Robotics, Twente, The Netherlands, November 2011. BibTeX

    @inproceedings{Flacco:11a,
    	author = {F.~Flacco and T.~Kr{\"o}ger and A.~De~Luca and O.~Khatib},
    	title = {A Depth Space Approach to Human-Robot Collision Avoidance},
    	month = {November},
    	booktitle = {Workshop on Human-Friendly Robotics},
    	address = {Twente, The Netherlands},
    	year = {2011}
    }
    			
  • Opening the Door to New Sensor-Based Robot Applications - The Reflexxes Motion Libraries.
    In Proc. of the IEEE International Conference on Robotics and Automation, Shanghai, China, May 2011. BibTeX

    @inproceedings{Kroeger:11,
    	author = {T.~Kr{\"o}ger},
    	title = {Opening the Door to New Sensor-Based Robot Applications\,---\,The Reflexxes Motion Libraries},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	month = {May},
    	address = {Shanghai, China},
    	year = {2011}
    }
    			
  • Robot Motion Control During Abrupt Switchings Between Manipulation Primitives.
    In Workshop on Mobile Manipulation at the IEEE International Conference on Robotics and Automation, Shanghai, China, May 2011. BibTeX

    @inproceedings{Kroeger:11a,
    	author = {T.~Kr{\"o}ger and B.~Finkemeyer},
    	title = {Robot Motion Control During Abrupt Switchings Between Manipulation Primitives},
    	month = {May},
    	booktitle = {Workshop on Mobile Manipulation at the {I}{E}{E}{E} International Conference on Robotics and Automation},
    	address = {Shanghai, China},
    	year = {2011}
    }
    			
  • On-Line Trajectory Generation: Basic Concepts for Instantaneous Reactions to Unforeseen Events.
    IEEE Trans. on Robotics. Vol. 26, No. 1, pp. 94-111, February 2010. BibTeX

    @article{Kroeger:10,
    	author = {T.~Kr{\"o}ger and F.~M.~Wahl},
    	title = {On-Line Trajectory Generation: {B}asic Concepts for Instantaneous Reactions to Unforeseen Events},
    	journal = {IEEE Trans. on Robotics},
    	month = {February},
    	volume = {26},
    	number = {1},
    	pages = {94--111},
    	year = {2010}
    }
    			
  • On-Line Trajectory Generation in Robotic Systems.
    First edition, Springer Tracts in Advanced Robotics, Vol. 58, Springer, January 2010. BibTeX

    @book{Kroeger:10a,
    	author = {T.~Kr{\"o}ger},
    	title = {On-Line Trajectory Generation in Robotic Systems},
    	address = {Berlin, Heidelberg, Germany},
    	series = {Springer Tracts in Advanced Robotics},
    	publisher = {Springer},
    	volume = {58},
    	edition = {first},
    	month = {January},
    	year = {2010}
    }
    			
  • Stabilizing Hybrid Switched Motion Control Systems with an On-Line Trajectory Generator.
    In Proc. of the IEEE International Conference on Robotics and Automation, pp. 4009-4015, Anchorage, AK, USA, May 2010. BibTeX

    @inproceedings{Kroeger:10c,
    	author = {T.~Kr{\"o}ger and F.~M.~Wahl},
    	title = {Stabilizing Hybrid Switched Motion Control Systems with an On-Line Trajectory Generator},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	month = {May},
    	pages = {4009--4015},
    	address = {Anchorage, AK, USA},
    	year = {2010}
    }
    			
  • Low-Level Control of Robot Manipulators: Sensor-Guided Control and On-Line Trajectory Generation.
    In Workshop on Innovative Robot Control Architectures for Demanding (Research) Applications - How to Modify and Enhance Commercial Controllers at the IEEE International Conference on Robotics and Automation, pp. 46-53, Anchorage, AK, USA, May 2010. BibTeX

    @inproceedings{Kroeger:10d,
    	author = {T.~Kr{\"o}ger and F.~M.~Wahl},
    	title = {Low-Level Control of Robot Manipulators: Sensor-Guided Control and On-Line Trajectory Generation},
    	month = {May},
    	booktitle = {Workshop on Innovative Robot Control Architectures for Demanding (Research) Applications - How to Modify and Enhance Commercial Controllers at the {I}{E}{E}{E} International Conference on Robotics and Automation},
    	address = {Anchorage, AK, USA},
    	pages = {46--53},
    	year = {2010}
    }
    			
  • Multi-Sensor Integration and Sensor Fusion in Industrial Manipulation: Hybrid Switched Control, Trajectory Generation, and Software Development.
    In Proc. of the IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems, pp. 411-418, Seoul, South Korea, August 2008. BibTeX

    @inproceedings{Kroeger:08e,
    	author = {T.~Kr{\"o}ger and F.~M.~Wahl},
    	title = {Multi-Sensor Integration and Sensor Fusion in Industrial Manipulation: {H}ybrid Switched Control, Trajectory Generation, and Software Development},
    	booktitle = {Proc. of the IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems},
    	month = {August},
    	pages = {411--418},
    	address = {Seoul, South Korea},
    	year = {2008}
    }
    			
  • Towards On-Line Trajectory Computation.
    In Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems, pp. 736-741, Beijing, China, October 2006. BibTeX

    @inproceedings{Kroeger:06d,
    	author = {T.~Kr{\"o}ger and A.~Tomiczek and F.~M.~Wahl},
    	title = {Towards On-Line Trajectory Computation},
    	booktitle = {Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems},
    	address = {Beijing, China},
    	month = {October},
    	pages = {736--741},
    	year = {2006}
    }