Calibration of force/torque and acceleration for an independent safety layer in medical robotic systems

Background: Most medical robotic systems require direct interaction with the robot. Force-Torque (FT) sensors can easily be mounted to the robot. However, an accurate FT control requires the current robot position to compute the spatial orientation of the sensor for gravity compensation.

Methods: We developed an independent safety system, named FTA sensor, which is based on an FT sensor and an accelerometer. With a calibration of accelerations to the FT coordinate frame, the current spatial orientation of the sensor is computed.

Results: We found that the calibration of accelerations into the FT coordinate frame can be performed with a median rotational error of 3.5°. The median error for gravity compensation based on accelerations was 0.3N and 0.04Nm for forces and torques, respectively.

Conclusion: By combining accelerations with force-torque readings, the FTA sensor works independently from robot input. Furthermore, the accuracy of the FTA sensor is sufficient for the purpose of medical robotic systems.