title: Robust real-time robot-world calibration for robotized transcranial magnetic stimulation.
abstract: BACKGROUND
  For robotized transcranial magnetic stimulation (TMS), the magnetic coil is placed on the patient's head by a robot. As the robotized TMS system requires tracking of head movements, robot and tracking camera need to be calibrated. However, for robotized TMS in a clinical setting, such calibration is required frequently. Mounting/unmounting a marker to the end effector and moving the robot into different poses is impractical. Moreover, if either system is moved during treatment, recalibration is required.
  
  
  METHODS
  To overcome this limitation, we propose to directly track a marker at link three of the articulated arm. Using forward kinematics and a constant marker transform to link three, the calibration can be performed instantly.
  
  
  RESULTS
  Our experimental results indicate an accuracy similar to standard hand-eye calibration approaches. It also outperforms classical hand-held navigated TMS systems.
  
  
  CONCLUSIONS
  This robust online calibration greatly enhances the system's user-friendliness and safety.
authors.affiliation: Institute for Robotics and Cognitive Systems, University of Lübeck, Germany. richter@rob.uni-luebeck.de
authors.forename: Lars
authors.initials: L
authors.lastname: Richter
authors.forename: Floris
authors.initials: F
authors.lastname: Ernst
authors.forename: Alexander
authors.initials: A
authors.lastname: Schlaefer
authors.forename: Achim
authors.initials: A
authors.lastname: Schweikard
mesh_terms: D000465:Algorithms; D002138:Calibration; D003199:Computer Systems; D019544:Equipment Failure Analysis; D057918:Fiducial Markers; D005858:Germany; D010781:Photography / Q000295:instrumentation* / Q000592:standards*; D015203:Reproducibility of Results; D012371:Robotics / Q000295:instrumentation* / Q000592:standards*; D012680:Sensitivity and Specificity; D013813:Therapy, Computer-Assisted / Q000295:instrumentation / Q000592:standards; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation* / Q000592:standards*