Torsten Kroeger

Stanford Artificial Intelligence Laboratory

Force Control

This research has been conducted at the Institut für Robotik und Prozessinformatik at the Technische Universität Braunschweig, Germany.

Motivation: Compliant Robot Motions

Robotic applications such as grinding, assembly, or deburring involve an extensive contact between the robot and its environment. In order to establish this contact, force/torque control is applied, that is, force (and/or toruqe) sensors are part of the feedback control loops. Force/torque control enables compliant motion of robot manipulators when the manipulator motion is constrained by environmental objects. Force control concepts can be distinguished in active and passive methods. Passive ones do not consider a force/torque sensor in the feedback control loop and are addressed here. The research field addressed here focusses on the usage of wrist-mounted force/torque sensors.

Advanced Control Structures

New classes of control structures are investigated:

  • adaptive implicit force/torque control and
  • multi-loop model-following control structures.

The control algorithms run in control submodules in a hybrid switch-system, such that all compliant direction of motion may be force/torque controlled and all other directions may be guided by an on-line or off-line generated trajectory or by any other control submodule (e.g., a computer vision system for visual servo control).

Block diagram of the MFC-p structure

The figure exemplarily shows a simple two-loop model-following structure with plant feedback (MFC-p). Both PID controllers in the structure simple classic and easy-to-configure: one controller (Rm) control the model but it is driven by the process error, and the corrective controller (Rc) uses the difference signal of the plant and the model outputs to "correct" model errors. Besides the analysis of control structures to improve the control behavior (in particular during impacts, that is, during transitions from free space to contact), this research is closely related to field of robot motion control architectures. The concepts proposed in the area of force and acceleration sensor data fusion are also used here in order to improve force/torque control quality.


Please refer to the following publications:

  • 3D Stiffness Actuators for Efficient Force Control Applications.
    In Robot Systems for Handling and Assembly. Springer Tracts in Advanced Robotics, Vol. 67, Springer, pp. 275-291, 2010. BibTeX

    @incollection{Osypiuk:10a,
    	author = {R.~Osypiuk and T.~Kr{\"o}ger},
    	title = {3D Stiffness Actuators for Efficient Force Control Applications},
    	booktitle = {Robot Systems for Handling and Assembly},
    	editor = {D.~Sch{\"u}tz and F.~M.~Wahl},
    	series = {Springer Tracts in Advanced Robotics},
    	address = {Berlin, Heidelberg, Germany},
    	publisher = {Springer},
    	volume = {67},
    	pages = {275--291},
    	edition = {first},
    	year = {2010}
    }
    			
  • A Three-Loop Model-Following Control Structure: Theory and Implementation.
    International Journal of Control. Vol. 83, No. 1, pp. 97-104, January 2010. BibTeX

    @article{Osypiuk:10,
    	author = {R.~Osypiuk and T.~Kr{\"o}ger},
    	title = {A Three-Loop Model-Following Control Structure: {T}heory and Implementation},
    	journal = {International Journal of Control},
    	publisher = {Taylor and Francis},
    	month = {January},
    	volume = {83},
    	number = {1},
    	pages = {97--104},
    	year = {2010}
    }
    			
  • Improving Force Control Performance by Computational Elimination of Non-Contact Forces/Torques.
    In Proc. of the IEEE International Conference on Robotics and Automation, pp. 2617-2622, Pasadena, CA, USA, May 2008. BibTeX

    @inproceedings{Kroeger:08,
    	author = {D.~Kubus and T.~Kr{\"o}ger and F.~M.~Wahl},
    	title = {Improving Force Control Performance by Computational Elimination of Non-Contact Forces/Torques},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	month = {May},
    	pages = {2617--2622},
    	address = {Pasadena, CA, USA},
    	year = {2008}
    }
    			
  • Force and Acceleration Sensor Fusion for Compliant Manipulation Control in Six Degrees of Freedom.
    Advanced Robotics. Vol. 21, No. 14, pp. 1603-1616, November 2007. BibTeX

    @article{Kroeger:07,
    	author = {T.~Kr{\"o}ger and D.~Kubus and F.~M.~Wahl},
    	title = {Force and Acceleration Sensor Fusion for Compliant Manipulation Control in Six Degrees of Freedom},
    	journal = {Advanced Robotics},
    	volume = {21},
    	number = {14},
    	month = {November},
    	pages = {1603--1616},
    	year = {2007}
    }
    			
  • A Two-Loop Implicit Force/Position Control Structure, Based on a Simple Linear Model: Theory and Experiment.
    In Proc. of the IEEE International Conference on Robotics and Automation, pp. 2232-2237, Orlando, FL, USA, May 2006. BibTeX

    @inproceedings{Kroeger:06b,
    	author = {R.~Osypiuk and T.~Kr{\"o}ger and B.~Finkemeyer and F.~M.~Wahl},
    	title = {A Two-Loop Implicit Force/Position Control Structure, Based on a Simple Linear Model: {T}heory and Experiment},
    	booktitle = {Proc. of the IEEE International Conference on Robotics and Automation},
    	address = {Orlando, FL, USA},
    	month = {May},
    	pages = {2232--2237},
    	year = {2006}
    }
    			
  • 6D Force and Acceleration Sensor Fusion for Compliant Manipulation Control.
    In Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems, pp. 2626-2631, Beijing, China, October 2006. BibTeX

    @inproceedings{Kroeger:06c,
    	author = {T.~Kr{\"o}ger and D.~Kubus and F.~M.~Wahl},
    	title = {{6}{D} Force and Acceleration Sensor Fusion for Compliant Manipulation Control},
    	booktitle = {Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems},
    	address = {Beijing, China},
    	month = {October},
    	pages = {2626--2631},
    	year = {2006}
    }
    			
  • Adaptive Implicit Hybrid Force/Pose Control of Industrial Manipulators: Compliant Motion Experiments.
    In Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems, pp. 816-821, Sendai, Japan, September 2004. BibTeX

    @inproceedings{Kroeger:04b,
    	author = {T.~Kr{\"o}ger and B.~Finkemeyer and M.~Heuck and F.~M.~Wahl},
    	title = {Adaptive Implicit Hybrid Force/Pose Control of Industrial Manipulators: {C}ompliant Motion Experiments},
    	booktitle = {Proc. of the IEEE/RSJ International Conference on Intelligent Robots and Systems},
    	address = {Sendai, Japan},
    	month = {September},
    	pages = {816--821},
    	year = {2004}
    }
    			
  • Placing of Objects in Unknown Environments.
    In Proc. of the IEEE International Conference on Methods and Models in Automation and Robotics, pp. 975-980, Miedzyzdroje, Poland, August 2003. BibTeX

    @inproceedings{Finkemeyer:03,
    	author = {B.~Finkemeyer and T.~Kr{\"o}ger and F.~M.~Wahl},
    	title = {Placing of Objects in Unknown Environments},
    	booktitle = {Proc. of the IEEE International Conference on Methods and Models in Automation and Robotics},
    	month = {August},
    	address = {Mi\c{e}dzyzdroje, Poland},
    	year = {2003},
    	pages = {975--980}
    }