FTA-Sensor: Combination of Force/Torque and Acceleration - Robotized Transcranial Magnetic Stimulation - page 114

Fig. 6.14 Robot latency of the robot emergency stop as a Boxplot. In this case the latency is the
time needed from the emergency stop signal until stop of robot
the estimated robot latencies as a boxplot. On average the latency is 66.15 ms with
a standard deviation of 19.44 ms. The maximum robot latency estimated is 98 ms.
Figure 6.15 shows the maximum forces (when the robot stopps) with respect to
the robot speed. Without the FTA sensor, the forces reach up to 530 N until the
robot stops due to hardware limitations. With the FTA sensor, the maximum force
stays below 30 N in the speed range of robotized TMS (gray area). At the max-
imum robot speed, the maximum force stays below 100 N.
6.3 FTA Sensor for Safe Robotized TMS
We have presented the application of acceleration measurements in combination
with an FT sensor to perform gravity compensation independent from the robot.
Therefore, the FTA sensor is independent from robot input. The required com-
putations are performed with an embedded system in real-time. The average
maximum latency of the FTA sensor is 1 ms. Thus, the FTA sensor immediately
stops the robot in case of an error, collision or unexpected behavior by continu-
ously checking the force, torque and acceleration readings. Hence, system safety is
achieved with the FTA sensor as it protects patient and/or operator from serious
harm.