Biomedical Engineering Reference
In-Depth Information
Chapter 7
Optimized FT-Control with FTA Sensor
In the previous chapters, we have shown how contact pressure control and hand-
assisted positioning have been integrated into the robotized Transcranial Magnetic
Stimulation (TMS) system. Furthermore, we have introduced the FTA sensor as an
additional independent safety layer to the system. In this chapter, we show the
integration of the Force-Torque-Acceleration (FTA) sensor into the robotized
TMS system and its application.
7.1 Advanced Hand-Assisted Positioning
We already introduced the idea of hand-assisted positioning for robotized TMS and
its implementation with an off-the-shelf FT sensor (
Sect. 5.2.2
). In principle, we
could substitute the Force-Torque (FT) sensor with our developed FTA sensor and
use the same software routines for the new sensor. However, this would be
somehow counterproductive. A key feature of the FTA sensor is that it performs the
gravity compensation in real-time (see Sect.
6.2.3
). When connecting the FTA
sensor to the TMS software, performing the necessary computations for hand-
assisted positioning and then sending the movement commands to the robot would
bring additional latencies. Thus, we would not gain any significant speed-up with
the FTA sensor. Therefore, we connect the FTA sensor directly to the robot con-
troller and implement the hand-assisted positioning method on the robot controller.
In this way, we reduce the latency to a minimum and gain a maximum speed-up.
As the gravity compensation is always affected by an error mainly due to the
TMS coil with the supply cable (cf. Sect.
5.3.1
), the hand-assisted positioning
method uses minimum thresholds in its implementation. Only forces and torques,
respectively, larger than the threshold will result in a robot motion. This leads to an
inflexible robot behavior. To overcome this consequence, we use a small button
that we attach directly to the coil holder. Figure
7.1
shows the mounted FTA
sensor with TMS coil and button attached to the holder. We connect this button to
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