Biomedical Engineering Reference
In-Depth Information
Note that
F and M are both initialized with zero. We now let the robot move
incrementally with respect to the current position. F is transferred into a transla-
tional movement and M into a rotational robot movement. The FTA sensor's
emergency control is active during complete operation. In case of an error or
extreme forces, torques or accelerations it will stop the robot immediately for
patient and operator safety.
7.2 Integration into the Robot Server
For robotized TMS the communication with the robot is done via a robot server
using an ethernet connection (see Sect. 1.3.2 )[ 3 ]. On the robot controller a cor-
responding program is running which converts the client commands into robot
commands and moves the robot. It also provides the client with the robot position
and status [ 6 ]. As the advanced hand-assisted positioning method (see above) must
run on the robot controller, the robot server is extended to the FTA sensor com-
munication. The most critical part is that either the robot server or the hand-assisted
positioning method have an active control of the robot. We must invariably avoid
that both programs can move the robot because this could lead to dangerous situ-
ations. Nevertheless, the robot server should still have access to the current robot
position and status, and should still be able to communicate with the client while the
hand-assisted positioning method is running. In addition, we must ensure that the
robot server is downwardly compatible in case no FTA sensor is connected.
Therefore, we implement two different tasks on the robot controller as illus-
trated in Fig. 7.4 . The first and main task is the robot server. It provides the
communication with the client. Initially, the robot server has the active robot
control. If an FTA sensor is connected to the robot controller and should be used,
the client must send a connection command first to initialize the sensor. When the
client sends the command to start the hand-assisted positioning, the robot server
detaches the active robot control and starts the hand-assisted positioning program
in a new task. This program now runs continuously (as described above) until
externally terminated. The robot server is still listening to requests from the client.
However, active commands from the client are not processed. Status information
from robot or FTA sensor are still executed in the usual manner. In this way, the
TMS software, for instance, can update the current coil position in relation to the
patient's head while the operator is moving the hand with the hand-assisted
positioning method. Once the command to stop the hand-assisted positioning is
received by the server, the server terminates the hand-assisted positioning program
running on the parallel task and attaches the active robot control again. Via the
robot server the client can also adjust the robot speed for hand-assisted positioning
by setting an additional factor. The calculated damped forces F and torques M are
now multiplied with this factor before using them as incremental robot movements.
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