Proper Force-Torque Sensor System for robotized TMS: Automatic Coil Calibration

Purpose: With a robotized system based on an Adept Viper s850 robot (Adept Technology, Inc., Livermore, CA, USA) a Transcranial Magnetic Stimulation (TMS) coil can be placed precisely at a given target position [1, 2]. When using a robotic TMS system we have to find a balance between safe placement of the coil and a minimized distance to the skull. The latter is important to improve treatment efficacy. However, the induced forces could cause discomfort or injuries to the patient. Hence, we have integrated a force-torque sensor in our system. Moreover, the force torque sensor can be used to manually position the coil close to the target region. While this generally improves the clinical workflow, it is particularly helpful if the robot is used solely for motion compensation e.g. in the treatment of depression [3]. A key prerequisite for force-torque based control of the robot is a calibration of the sensor to the world coordinate frame. We present and evaluate a calibration approach and illustrate the clinical approach to motion compensated TMS.