FT-Control - Robotized Transcranial Magnetic Stimulation - page 97

system. Without hand-assisted positioning, this is hardly possible. Additionally, the
hand-assisted positioning method speeds up the positioning time for experienced
users. Thus, hand-assisted positioning greatly enhances the system's usability.
Furthermore, we have proven that the presented force-torque control reaches a
control frequency of 40 Hz to even detect short-lasting impacts. Our tests have
shown that this update frequency is sufficient for a smooth coil movement and
placement. During our experiments, we have found that the latency of the contact
pressure control is approximately 200 ms. This latency is acceptable to compen-
sate for coil-to-head distance changes. It is in the same range as pure motion
compensation (see Sect. 1.3.2.3 ).
Even though the FT-control continuously monitors the forces and torques,
system safety is still not achieved. On the one hand, the monitoring cycle is
depending on the software and on the current robot positions. On the other hand,
and this is the most critical aspect, the reaction time is far from real-time. A
latency of 200 ms is too large in an emergency situation to stop the robot. To
overcome that and to maximize system safety, we introduce an independent safety
layer in the next chapter.

References

1. ATI Industrial Automation: Multi-Axis Force/Torque Sensor. Tech. Rep. (2012)
2. Matthäus, L.: A robotic assistance system for transcranial magnetic stimulation and its
application to motor cortex mapping. Ph.D. thesis, Universität zu Lübeck (2008)
3. Matthäus, L., Giese, A., Wertheimer, D., Schweikard, A.: Planning and analyzing robotized
TMS using virtual reality. Stud. Health Technol. Inform. 119, 373-378 (2006)
4. Richter, L., Bruder, R., Schlaefer, A.: Proper force-torque sensor system for robotized TMS:
Automatic coil calibration. Int. J. Comput. Assist. Radiol. Surg. 5, S422-S423 (2010)
(Proceedings of the 24th International Conference and Exhibition on Computer Assisted
Radiology and Surgery (CARS' 10))
5. Richter, L., Bruder, R., Schlaefer, A., Schweikard, A.: Realisierung einer schnellen und
wiederholbaren hot-spot-bestimmung für die robotergestützte transkranielle magnet-stimula-
tion mittels kraft-momenten-steuerung. In: 10. Jahrestagung der Deutschen Gesellschaft für
Computer- und Roboterassistierte Chirugie (CURAC), pp. 31-34. CURAC (2011)
6. Richter, L., Bruder, R., Schweikard, A.: Hand-assisted positioning and contact pressure control
for motion compensated robotized transcranial magnetic stimulation. Int. J. Comput. Assist.
Radiol. Surg. 7(6), 845-852 (2012). doi: 10.1007/s11548-012-0677-6
7. Richter, L., Bruder, R., Schweikard, A.: Hand-assisted positioning and contact pressure control
for motion compensated robotized transcranial magnetic stimulation. Int. J. Comput. Assist.
Radiol.

Surg. 7, 123-124 (2012) (Proceedings of the 26th International Congress and

Exhibition on Computer Assisted Radiology and Surgery (CARS' 12))
8. Richter, L., Ernst, F., Martens, V., Matthäus, L., Schweikard, A.: Client/server framework for
robot control in medical assistance systems. Int. J. Comput. Assist. Radiol. Surg. 5, 306-307
(2010) (Proceedings of the 24th International Congress and Exhibition on Computer Assisted
Radiology and Surgery (CARS' 10))
9. Wassermann, E.M., Epstein, C.M., Ziemann, U., Walsh, V., Paus, T., Lisanby, S.H. (eds.): The
Oxford Handbook of Transcranial Magnetic Stimulation. Oxford University Press, Oxford
(2008)